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I
\
r
A TEXT-BOOK
OF
ORGANIC CHEMISTRY
»^
A. F. HOLLEMAN, Ph.D., F.R.A.Amst.,
Professor Ordinarius in the University of Amsterdam
EDITED BT
A. JAMIESON WALKER, Ph.D., B.A., F.I.C.
ASftlRTED BY
OWEN E. MOTT, O.B.E., Ph.D., F.I.C.
WITH THE CO-OPERATION OF THE AUTHOB
FIFTH ENGLISH EDITION, COMPLETELY REVISED
TOTAL ISSUE, TWENTY-TWO THOUSAND
NEW YORK
JOHN WILEY & SONS, Inc. London: CHAPMAN & HALL, Limttbd
1920
Copyright, 1903, 1907, 1910, 1918, 109Q}
BT
A. JAMIEBON WALKER. {Entered at Stationer*' Hall.)
CHRONOLOGICAL SUMMARY.
Emoush Editioms. Piret Edition: 1903. Second Edition: 1907. Third Edition: 1910. Fourth Edition: 1913. Fifth Edition: 1920.
Editions in Otbek Lanouagbs.
Orioinal Dutch: Eight Editioni. Oerman: Fifteen Editions. Italian: Three Editions. French: Two Editions. Rueeian: Two •Editions. Poliah: One Edition. Japaneee: One Edition. flpofifM: One Edition.
TV
>
AUTHOR'S PREFACE TO THE FIFTH EDITION,
A NOVEL can be reprinted unchanged so long as there is a public to buy it; but even with an interval of only a few years between successive issues, each new edition of a text-book of chemistry needs not only a careful revision, but also the rewriting of some of its chapters.
It has, therefore, been impossible to avoid making many alterations for this new edition. One of the chief features is the additional space allotted to the applications in organic chemistry of physico-chemical methods such as refraction, absorption, viscosity, and so on. The importance of these properties in organic chemical research is steadily increasing, and I think it necessary to mention them even in a short text- book of this description.
When this book is read for the first time, the matter printed from small type should be omitted, as it contains numerous refer- ences to subsequent portions of the text. Such references are in great measure avoided in the part printed from large type.
I am again indebted to Dr. Jamieson Walker for the care bestowed by him on the revision, a task made difficult by the numerous alterations and extensive rearrangement.
A. F. HOLLEMAN.
Amstebdam, July, 1920.
Jii
3u4795
AUTHOR'S PREFACE TO THE FIRST EDITION.
Most of the short text-books of Organic Chemistry contain a great number of isolated facts; the number of compounds described in them is so considerable as to confuse the beginner, iloreover, the theoretical grounds on which this division of the science is based are often kept in the background; for example, the proofs given of the constitutional formulae frequently leave much to be desired. However useful these books may be for reference, they are often ill-suited for text-books, as many students have learned from their own experience.
In this book I have endeavoured to keep the number of uncon- nected facts within as narrow limits as possible, and to give promi- nence to the theory underlying the subject. For this reason, a proof of the structure of most of the compounds is given. This was not possible for the higher substitution-products of the aromatic series, so that the methods of orientation employed in it are de- scribed in a special chapter.
Physico-chenucal theories, such as the laws of equilibrium, ionization, and others, are becoming more and more prominent in organic chemistry. I have attempted in many instances to show how useful they are in this branch of the science. Such important technical processes as the manufacture of alcohol, cane-sugar, etc., are also included. The book is essentially a text-book, and makes no claim to be a "Beilstein " in a very compressed form.
I am deeply indebted to Dr. A. Jamieson Walker for the excel- lent way in which he has carried out the difficult task of translating this book from the original second Dutch edition into English. Lastly, it may be mentioned that it has also been translated into German, the second edition having just appeared, and that an Italian edition is in preparation.
A. F. HOLLEMAN.
It
EDITOR'S PREFACE TO THE FIFTH EDITION.
The issue of the fifth edition has been retarded by difficulties of communication incidental to the great European War. In the mean time, the unprecedented demand has had to be met by re- printing the f oiurth edition. The text has now been subjected to the usual complete revision, and a considerable proportion of new matter has been incorporated. Many minor alterations have also been made. I have again to thank Professor Holleman for devot- ing much time and energy to this work.
References in the text to "Inorganic Chemistry'' allude to Professor Holleman's "Text-Book of Inorganic Chemistry," edited by Dr. Hepjion C. Cooper, and published by Messrs. John Wiley & Sons, Inc. The "Laboratory Manual" referred to is Professor Holleman's "Liaboratory Manual of Organic Chemistry for Beginners," published under my editorship by Messrs. John Wiley & Sons, Inc. This work constitutes an appendix to the text-book, and should be employed as a guide to laboratory work prior to the systematic course of preparations essential to progress in the study of organic chemistry.
I have pleasure in acknowledging my indebtedness to corre- spondents who have drawn my attention to errors in the text and to other points needing revision, and thus materially assisted me in preparing the manuscript for the press; and my obliga- tion to Messrs. John Wiley & Sons, Inc., for the care bestowed by them on the preparation of the book for publication.
A. Jamieson Walker. August, 1020.
v
I
CONTENTS.
ligkt figures refer to pages, old-style figures to psragrapht.
INTRODUCTION (i-ar) 1
QwMUxtwe and quantUaiwe analyna (3-9) 8
Detection of the elements, 3. Estimation of carbon and hydrogen, 5. Estimation of nitrogen, 7. Estimation of halogens, sulphur, phosphorus, and other elements, 8. Calculation of formulse, 10.
Determination of molecular tveight (10-15) 11
Victor Mbyer'b method, 12. Cryosoopic methods, 14. Ebullio- soopic methods, 14.
The dement carbon (z6) 19
Laboratory-methods (17-26) 19
Heating substances together, 19. Distillation, 21. Vacuum- distillation, 21. Fractional distillation, 22. Steam-distillation, 26. Separation of two immiscible liquids, 28. Separation of solids and liquids, 30. Separation of solids from one another, 30. Determination of melting-points, 31. Determination of boiling-points, 32. Determination of specific gravity, 32. Polar- imetry, 33. Determination of refraction^ 34.
Ckueification of organic compounde (27) 35
FIRST ?ART.
ALIPHATIC COMPOUNDS (28-273) 36
Saturated Hydrocarbons (28-38) 36
Occurrence, 36. Preparation, 36. Physical and chemical properties, 37. Nomenclature, 38. Petroleum, 39. Homologous series, 41. Isomerism and structure, 43. Carbon chains, 47. Law of the even number of atoms, 47. Number of possible isomerides, 48. Physi- cal properties of isomeric compounds, 49.
Alooholb, CnHan+aO (39-50) 61
Methods of formation and constitution, 51. Nomenclature and iso- merism, 53. General properties of the alcohols, 54. Methyl alco- hol, 56. Ethyl alcohol, 56. Propyl alcohols, 61. Butyl alcohols, 63. Amyl alcohols, 64. Van 't Hoff's theory of stereoisomerism,
66. Higher alcohols, 69. Alkoxides, 69.
..
YU
• ••
viii CONTENTS.
P40B
Alktl Halidbs, Estbbs, and Ethers (51-56) 71
Alkyl halides, 72. Esters of other mineral acids, 75. Ethers, 77.
Alktl-radicals Linked to Sulphub (57-60) 80
Mercaptans, 81. Thioethers, 82. Sulphonic acids, 83.
ALKTI/-RADICAL8 Linked to Nitrogen (6i--7o) 85
Amines (61-67) 85
Nomenclature and isomerism, 86. Methods of formation, 86. Properties, 89. Individual members, 90.
NUro-compaunds (68-70) 92
Preparation, 92. Properties, 93. Derivatives, 94.
Alktl-radicals Linked to other Elements (71-75) 96
Alkyl-^radiccds linked to elements ofthenitrogen group (71--73) 96
Phosphines, 96. Arsines, 97.
Alkyl-^adicals linked to the elements of the carbon group (74) 98
Metallic aUcides (75) 99
NmULES AND i80NlTRILE8 (76-78) 101
Carbylamines, 102. Nitriles, 103.
Acids, CnHinOi (79-88) 104
Constitution, 104. Syntheses, 104. General properties, 106. Formic acid, 108. Acetic acid, 109. Butyric acids, 112. Higher fatty acids, 113. Soaps, 114. Electrolytic dissociation, 116. Derivatives of the Fattt Acids Obtained bt Modiftinq thb
Carboxtl-group (89-97) 119
Acid chlorides, 119. Acid anhydrides, 120. Esters, 120. Acid amides, 127. Other derivatives, 128.
Aldehydes and Ketones (98-111) 130
General properties (98-103) 130
Constitution, 130. Nomenclature, 132. Methods of forma- tion, 132. Properties common to both classes, 133.
Aldehydes (104-109) 137
Special properties, 137. Aldehyde-resin, 139. Aldol-condensa- tion, 139. Oxidation, 141. Tests, 141. Formaldehyde, 142. Aoetaldehyde, 144. Paracetaldehyde, 144. Metacetaldehyde, 144.
Ketones (no, in) 145
Special properties, 145. Acetone, 146.
Unsaturated Hydrocarbons (1x2-127) ^^
Alkylenes or defines^ CnHm (112-120) 148
Methods of formation, 148. Properties, 149. Ethylene, 151. Amylenes, 152. The structure of unsaturated compounds, 152.
Alicydic compounds (121) 158
Hydrocarbons with triple hands, CnH* (122-126) 169
Nomenclature, 159. Methods 7 /orDtt^^^ion, 159. Properties, 160. Acetylene, 162. ^' ^
Hydrocarbons tnih£wo double bond% p ^ (W7) 1^
iBoprene, 163. Dijjjetbylali^^^\\ ^ "^ Conjugated system, 164.
CONTENTS. ix
PAOB
SUBfinrCTION-PBODUCTB OF THB UNSATURATED HYDROCARBONS (Z28-
133) 165
Unsaturated halogen compounds (128-130) 165
Preparation, 165. Properties, 166. Allyl chloride, 166. Vinyl chloride and bromide, 166. Allyl bromide and iodide, 167. Propargyl compounds, 176. Bromaoetylidene, 167.
Unsaturated alcohols (131-133) 167
Vinyl alcohol, 168. Neurine, 168. Allyl alcohol, 168. Prop- argyl alcohol, 169.
Monobasic Unsaturated Acids (134-140) 170
Adds of the deic series (134-138) 170
Preparation, 170. Nomenclature, 170. Properties, 171. Acrylic ' acid, 171. Acids of the JOTmula C^HcOi, 172. Oleic acid, 173.
Acids of the propiolic series (i3^^o) 175
Preparation, 175. Properties, 175.
Unsaturated Ai.dehtdes and Ketones (X4X-X43) 177
Acraldehyde, 177. Crotonaldehyde, 178. Propiolaldehyde, 178. Geranial, 178. Derivatives of geranial, 179.
Compounds Containing more than one Substituent (144-160) 181
Halogen derioatwes of methane (144-146) 181
Chloroform, 181. Methylene chloride, 183. Tetrachloro- methane, 183. Bromoform, 183. Iodoform, 183. Methyl- ene iodide, 184.
Halogen derivatives of the homologues of methane (147-148) 184
Preparation, 184. Nomenclature, 185. Tetrachloroethane, 186. Ethylene chloride, 186. Hexachloroethane, 186. Ethylene bromide, 186. Trimethylene bromide, 186.
Polyhydric alcohols (149-157) 187
Glycols, 187. Trihydric alcohols, 190. Tetrahydric and hig;her alcohols, 193. Derivatives containing halogen atoms, hydroxyUgroupSf nUro-qrowps,
oramino^oups (158-160) 194
Chloroethers, 194. Halogen-hydrins, 195. Dinitro-compounds, 195. Diamines, 196. Choline, 196. Lecithin, 197.
PoLTBAsic Acids (161-174) 198
Saturated diabasic acids (x6z-z68) 198
Physical and chemical properties, 198. Oxalic acid, 200. Malonic acid, 203. Carbon suboxide, 206. Succinic acid, 206. Formation of anhydrides, 208. Saponification of esters of polyhydric alcohols and of polybasic acids, 210.
Unsaturated dibasic adds (169-173) 211
Fumaric acid and maleic acid, 211. Affinity-constants of the unsaturated acids, 217. Dibasic acids with more than one triple bond, 218.
Higher polybasic acids (174) 218
Tricarballylic acid, 219. Aconitic add, 220.
X CONTENTS.
FAOB
SxTBSTiTcmD AdDB (X75-X97) 221
HalogmsubsHMed acids (175-178) 221
Fonnation, 221. Properties^ 222. Ghloroaoetic acids, 223. Acids with more than one halogen atom in the molecule, 223.
Monobasic hydroxy-adda (x79-z36) 226
Formation, 226. Properties, 227. Glyoollic acid, 228. Hy- drozypropionic acids, 229. Lactones, 232.
DQkuic kydroxy-acids (187-196) 234
Tartronic acid, 234. Malic acid, 234. Tartaric adds, 235. d-Tartaric acid, 240. {-Tartaric acid, 242. r-Tartaric acid, 242. Mesotartaric add, 243. Raoemic substances, and their resolution into optically active constituents, 246. Op- tically active compounds with asynmietric atoms other than carbon, 260. ^^
Pdybanc hydroxy-adda (197) 252
Citric add, 252.
D1ALDEHTDB8 AND DiKETONBs: Halogbn-Subotituted Aldbhtdes
AND Kbtones (198-201) 254
DUddehydes (198) 254
Glyoxal, 254. Succindialdehyde, 255.
Dikeiones (199, 200) 255,
Diaoetyl, 256. Aoetylaoetone, 257. Aoetonylacetone, 258.
Halogenrnd>stituUd aldehydes (201) 258
Chloral, 258. Chloral hydrate, 258.
ALDEHTDO^ALOOBOLa AND EeTO-ALCOHOLS OB CaRBOHTDRATBS (202-
228) 261
NomendaJbvre and ffeneral properties of the monoses and their derivatives
(202, 203) 261
Constitution of the monoses (204, 205) 263
Methods of formation of the monoses (206) 266
Monoses (207-2x2) 268
Pentoses, 268. Hexoses, 270. Synthesis, 277. Stereochem- istry, 278.
Dioses (2x3-223) 281
Constitution, 281. Maltose, 282. Lactose, 283. Sucrose, 284. Manufacture of sucrose from sugar-beet, 287. Quantitative estimation of sucrose, 288. Velocity of inversion of sucrose, 289. Fermentation and the action of enzymes, 290. Asym- metric synthesis, 293.
Polyoses (224-228) 294
BaflSnose, 294. Manneotetrose, 295. Starch, 296. Glycogen, 299. Manufacture of starch 29^* Cellulose, 299. Techni- cal applications of cellulose; NitroceU^^^^^' Artificial silk, 300.
Amino-aldehtdes and Amino-ketonibb / ) 303
Aminoacetaidehyde, 303. M ,, ^^t9 ' 303. Chitin, 303.
CONTENTS. xi
PAGE
AlDBHTDO-ACTOB AND KSTONIC ACIDB (23O-339) 304
Aldehydo-acids (230) 304
Glyozylic acid, 304. KeUmic acids (231-334) 306
Pyroraoemic add, 305. Acetoacetic acid, 306. Acetoaoetio- ester synthesis, 307. Lcevulic add, 309. Meaoxalic add, 310. Tautameritm (235-237) 310
Ethyl acetoaoetate, 310. Oximes, 315. Pynme derwatives (238-239) 316
Dimethylpyrone, 316. Oxonium salts, 318.
Amino-acids (240-245) 320
Pormatian (240) 320
General properties (240, 241) 320
Inditridtud members (242, 243) 322
Glycine, 322. Betaine, 323. Alanine, 323. Leucine, 324. iwLeucine, 324. Asparagine, 324. Glutaznine, 325. Lysine, 325. Ornithine, 325.
The Walden inversion (244) 326
Examples, 326. Stark's hypothesis, 328.
Ethyl diazoaceUxte (245) 329
Formation, 329. Properties, 329.
Protbinb (246-254) 831
Composition, 331. Properties, 832. Tests, 333. Nomenclature, 333. Classification, 334. Structure of the molecule, 339. Syn- thesis, 342. Molecular weight 345.
Cyanogen Debiyatives (255-262) 847
Cyanogen, 347. Hydrocyanic acid, 348. (I)yanides, 349. Cyanic add, 351. Thiocyanic acid, 354. Fulminic acid, 356. Cyanuric acid and isocyanuric acid, 357.
Deriyativeb op Carbonic Actd (263-270) 359
Carbonyl chloride, 359. Carbon disulphide, 360. Carbon oxysul- phide, 361. Urea, 361. Derivatives of carbamic add, 366. Thiourea, 367. Guanidine, 368.
Urio-acid Group (271-273) 371
P&rabanic acid, 371. Oxaluric acid, 371. Alloxan, 371. Alloxantine, 372. Allantolne, 372. Uric acid, 373. Purine, 374. Xanthine, 875. Theobromine, 375. Caffeine, 375. Electro-reduction of purine derivatives, 377.
zii CONTENTS.
SECOND PART.
FAGB
CYCLIC COMPOUNDS (274-416) 881
iNTBODucnoN (274) 381
Classification of cyclic compounds 381
A. CARBOCTCLIC COMPOUNDS (275-386) 383
1. ALICYCLIC COMPOUNDS (275-280) 383
C2^c2oPropane derivativesi 383. cj^cloButane derivatives, 383. cj^c^oPentane derivatives, 384. Higher aiicyclic derivatives, 386.
2. AROMATIC COMPOUNDS (281-386) 389
Constitution of Benzene (281-284) 389
Relation to the aromatic compounds, 389. Structure of the molecule, Formulse of Kekul£ and Thiele, 392. Centric formula, 394. Nomenclature and isomerism of the benzene derivatives, 396.
Properties Characteristic of the Aromatic Compounds: Syn- theses FROM Aliphatic Compounds (285) 397
Benzene and the Aromatic Hydrocarbons with Saturated Side- chains (286-288) 399
Gas-manufacture and its by-products: Tar, 399. Benzene and its homologues, 400.
MONOSUBSTITUTION-PRODUCTS OF THE ArOMATIC HYDROCARBONS
(28^320) 404
Monohdogen compounds (289) 404
MononUTO-derioaiwes (290) 406
Preparation, 406. Nitrobenzene, 406. Nitrotoluenes, 407.
Monosidphonic adds (291) 408
Formation, 408. Properties, 408. Sulphonyl chlorides, 408. Sulphonamides, 409.
' Monohydric phenols (292-295) 409
Formation, 409. Properties, 410. Phenol, 411. Cresols, 411. Thymol, 411. Ethers, 412.
Monoatnino-compounds (296-299) 412
Formation, 412. Properties, 413. Aniline, 415. Homologues of aniline, 416. Secondary amines, 416. Tertiary amines, 417. Quaternary bases, 420. Intermediate producta in the rediiciian of aromatic nitro-compounde
(300-304) 420
Azoxybenzene, 420. P-Azoxto' '*ie*^^®» ^^* A«ob«ii*«'ie, 421. Hyd/a^obenzene, 421. ^ vliP®» ^^* El«ctn>-reduction o/nitno-oompounds, 422 ^^^^
J
CONTENTS. jdii
Diaeo-compounds (305-309) 425
Classification, 425. Constitution of the diazonium salts, 427. Reactions of the diazonium compounds, 428. Diazoamino- compounds, 431. Aminoazo-compounds, 432. Hydroxyazo- compounds, 433.
Hydrazines (310) 433
Phenylhydrazine, 433. Methylphenylhydrazine, 434. Ammabic monobasic adds: Benzoic acid and iU homdogues (31 1-3x3) . 434 Formation, 434. Benzoic acid, 436. Benzoyl chloride, 437. Benzoic anhydride, 437. Ethyl benzoate, 437. Benzamide, 437. Benzonitrile, 438. Toluic acids, 438. Xylic acids, 438.
Aromatic aldehydes and ketones (314-318) 438
Aldehydes, 438. Autoxidation, 440. Ketones, 441. Oximes, 443.
Aromaiic phosphonts and arsenic derivatives (319) 445
Phosphinobenzene, 445. Phenylphosphinic acid, 445. Phenyl- phosphine, 445. Phosphenyl chloride, 445. Phosphobenzene, 446. Phosphenylous acid, 446. Arsinobenzene, 446. Phenyl- arsinic acid, 446. Arsenobenzene, 446. Phenylarsine oxide, 446. Aromaiic metallic compounds (320) 446
BSNZENE HOMOLOGUES WITH SuBSTFrUTED SiDE-OHAINB (331-326) .... 448
Compounds triih halogen in the side^hain (331) 448
Formation, 448. Benzyl chloride, 449. Benzyl bromide, 449. Benzyl iodide, 450. Benzal chloride, 450. Bensotrichloride, 450.
Phenylnitromethane and the peevidoacids (322, 323) 450
Adds with carboxyl in the sido<hain (324) 452
Phenylacetic acid, 452. Mandelic acid, 452. AromoHc alcohols (325) 453
Benzyl alcohol, 453. Compounds with the amino-group in the side^hain (326) 454
Benzylamine, 554. Dibenzylamine, 454. Tribenzylamine, 454.
COHPOTTNDB CONTAININQ AN UnSATUBATED SlOE-CHAIN (327-328) 455
Hydrocarbons (327) 455
Styren, 455. Phenylacetylene, 455. Alcohoils and aldehydes (327) 455
Cinnamyl alcohol, 455. Cinnamaldehyde, 456. Adds (328) 456
Cinnamic acid, 456. AZ^cinnamic acid, 457. tsoCinnamic acids, 457
POLTSUBtrjL'iTUTED BeNZENE DERIVATIVES (329-353) 458
Pclyhologen derivatives (329) 458
Halogen^nitro-compounds (330) 459
Pdynitro-derioatvves (331) 460
Dinitrobenzenes, 460. Trinitrobenzenes, 460. Trinitrotoluene, 460. Trintrobutykylene, 461.
xiv CONTENTS.
SubtiiMedhentenestdphonieaeida (332) 461
SiibsHMedphenoUimdpolyhydnc phenoU (333-338) 462
Halogenphenoby 462. Nitrophenols, 462. Phenolmilphonic acids, 464. Nitrosophenol, 465. Dihydrio phenols, 465. Trihydric phenols, 467. Higher phenols, 472. Quinones, 473.
SvbMUutionr^products of aniline (339-341) 474
NitroanilineB, 475. p-Aminobensenesulphonic 'd, 476. Aminophenob, 476. Polyamino-oompounds, 478. Aso-dyes, 479. SubstUuted benzol aeid9;Polyba»icacidaa^ 484
Halogenbenjsolc adds, 484. Nitrobenzolc acids, 484. Sulpho- benjsolc adds, 485. Monohydroxy-acids, 486. Dihydioiy- adds, 487. Trihydrozy-adds, 488. Vegetable dyes and Tannins, 489. Aminobenzolc adds, 493. Phthalic add, 494. ifloPhthalic and Terephthalic adds, 498. Higher poly- badc adds, 499.
, SvbstUvied aldehydes (351) 490
Nitrobenzaldehydes, 499. Hydroiyaldehydes, 499. PdysybstUuled benzene derivoHvee toith eybslituenta in the side-chain
(35a, 353) 501
]>-Hydroxyphenylpropionic add, 501. o-Hydrozycinnamic acid, 501. Coumarin, 501. Piperic add, 502. Piperonal, 902. Adrenaline, 503. Hordenine, 503. p-Hydrozyphenylethjl- amine, 503.
Jbiemtateon of Aboicatig CoiiPOUNDe (354-362) 604
General prindples, 504. Absolute determination of podtion for oitAo-compounds, 505. Absolute determination of podtion for meto-compounds, 507. Absolute determination of podtion for pora-compounds, 509. Determination of podtion for the trisub- stituted and higher-substituted derivatives, 510. Equivalence of the six hydrogen atoms in benzene, 512. Influence of the sub- stituents on each other, 513.
Htdboctglb OB Hydroaboiiatic Compounds (363-370) 520
Hydroeydic compounds (363, 364) 520
Preparation', 520. cycZoHexane, 522. p-Diketocydohexane, 623. Quinitols, 523. Inodtol, 523. cycIoHexanone, 524. Hydro- cydic adds, 525.
Terpenes (365-369) 626
Isolation, 525. Nomenclature, 525. Menthol, 526. Terpin, 526. Cineol, 529. Terpineol, 529. Pulegone, 530. Terpin- olene, 530. Limonenes, 531. Carvone, 532. CSarvacrol, 532. Polycydic terpene derivatives, 533.
Camphors (370) 586
Camphor, 535. Bomeol, 535 pl^ipboric add, 536. Cam- •.k — ^;^ ^^:a fiOA fl,«., • V/^^ — ^u^, 537, Camphane,
phoronic acid, 536. Synthesis r i^Bfi^V^^^* 537. Thiyoiie, 638. ^^of*''^
r
CONTENTS. XV
PAOB
PolyUrpenes (370) 538
Caoutchouc, 638.
BSNZBNl>-NUCIiBI LiNKSD TOQETHBB DiBBCTLT OB InDIBBCTLT BT
Carbon (371-376) 640
Diphenyl (371) 640
Dij^ienylmethane (372) 641
TriphenylmeUtane and iU derwaiives (373-375) 642
Triphenylmethane, 642. Leuoomalachite-green, 643. Mala- chite-green, 643, Quinonoid reaction, 642. Halochromy, 644. Stages in the formation of the triphenyhnethane dyes,
646. CrjTstal-violet, 646. Pararoeaniline, 646. Paraleucan- iline, 646. Rosaniline, 646. Magenta, 647. Methyl-violet,
647. Aniline-blue, 647. Roeolic acid, 647. Triphenyl- methyl, 648.
DSbengyl and its derwaiives (376) 660
Dibenxyl, 660. Stilbene, 660. Benxoln, 661. Hydrobensebi, 661. Benzil, 661. Bencilic add, 661.
CoNDBNBBD Benzeme-nttclei (377-386) 662
Naphthalene (377-381) 662
Preparation from coal-tar, 662. Properties, 662. Constitution, 663. Number of substitution-products, 664. Orientation, 666. Substitution-products, 666. Addition-products, 660.
Anthracene (382-385) 662
Preparation from coal-tar, 662. Properties, 662. Constitu- tion, 662. Number of substitution-products, 463. Orienta- tion, 663. Anthraquinone, 663, Anthraquinol, 666. Oxan- throne, 666. Anthrone, 666. Anthranol, 666. Alixarin, 666. Lakes, 668. Purpurin, 668. Indanthren-group, 669.
Phenanthrene (386) 669
Preparation from anthracene-oil, 669. Properties, 669. Con- stitution, 669. Phenanthraquinone, 670. Dimethylmorphol, 671.
B. HETEBOCTCUC COMPOUNDS (387-4x6) 672
NtTCLEi Containing Nitbooen, Oxygen, and Sulphub (387-399) 672
Pyridine (387-391) 672
Preparation from coal-tar, 672. Properties, 672. Constitu- tion, 673. Number of substitution-products, 674. Orienta- tion, 674. Homologues, 676. o-Propenylpjrridine, 676. Piperidine, 677. Piperine, 677. Piperic add, 677. Pyridine- carboxylie acids, 677.
Furon, (392, 393) 679
Constitution, 679. Preparation of derivatives, 679. Furfur- aldehyde, 680. Furfuramide, 680. Furfuroln, 680. Hy- droxymethylfurfuraldehyde, 681. Dehydromucic acid, 681. ^yromucic acid, 681.
xvi CONTENTS.
PAGB
PyrroU (394, 395) 582
Preparation, 582. Properties, 582. Ssmthesis, 583. Constitu- tion, 583. Derivatives, 584.
Thiophen (396, 397) 585
Preparation, 585. S3nithesis, 585. Properties, 586. Homo- logues, 586. Derivatives, 586.
PyrazoU (398, 399). • ' 587
Formation of derivatives, 587. S3nithe8is and constitution, 588. Identity of derivatives with substituents at positions 3 and 5, 588. Pyrazoline, 588. Pyrazolone, 589. Methyl- phenylpyrazolone, 589. "Antipyrine," 589. "Salipyrine," 589.
CoNDENSATION-PRODU(:rrS OF BeNZENE AND HeTBROCTCLIC NuCLEI
(400-405) 59C
Quinoline (400, 401) 59C
Properties, 590. S3nithesis, 590. Constitution, 590. Orienta- tion, 591. Nomenclature, 592. Derivatives, 592.
iaoQuinoline (402) 593
Properties, 593. Constitution and 83nithesis, 593.
Indole (403-405) 593
Relation to indigo, 593. ^Constitution, 595. Scatole, 595. Tryptophan, 595. 3-Indolealdehyde, 596. Indigo, 596. Indoxyl, 597. Indigotin, 597. Indigo-white, 598. Vat-dye- stuffs, 599. Indigoids, 599. ''Purple of the ancients," 599. Thioindigo, 599.
Alkaloids (406-416) 600
Classificaium (406) 600
Properties (407) 600
ConstUiUion (408) 602
Individual alkaloids (409-416) 602
Coni'ine, 602. Nicotine, 602. Atropine, 604. Cocaine, 605. Morphine, 606. Heroin, 607. Narcotine, 607. Nornarcotine, J07. Cotamine, 607. Quinine, 608. Cinchonine, 608. Strychnine, 609. iBrucine, 609. Curarine, 609.
INDEX 611
FIGURES.
FIBST PART.
WiaVWB WAQM
1. Organic analysis 5
2. Potash-bulbs 6
3. Tube-fumaoe 9
4. Victor Meter's vapour-density apparatus 12
5. Etkman's graphic method 15
6. Eteman's depressimeter 17
7. Etkman's boiling-point apparatus 17
8. Heating substances in an open flask 20
9. Flask with reflux-condenser 20
10. Distillation-apparatus 21
11. Fractionating-flask. 21
12. Distillation in vacuum 22
13. Fractionating-columns 23
14. 15, 16. Fractk)nal-distillation curves 25
17. Steam-distillation 27
18. Separating-funnel 28
19. Ffltering-flask 30
20. Thiel's melting-point apparatus 31
21. Pyknometer 32
22. Laurent's polarimeter 33
23. Fractionating-column 57
24. Carbon tetrahedron 67
25. 26. Asymmetric C-atoms 68
27» Melting-point curve of the fatty acids 106
28. Preparation of vinegar by the ''quick'' process 109
29. Graphic representation of fluidity 110
30. Graphic representation of the melting-points of the acids C11H211 _ 2O4 . . 199
31. Spacial representation of the bonds between 2-5 C-atoms 208
32. 33. Single bond between two carbon atoms 212
34, 35, 36. Graphic spacial representation of the double bond between
two carbon atoms 213
37. Fumaric acid 214
38. Dibromosuccinic acid 214
39. MaleTc acid 215
40. uoDibromosucdnic add 215
41. Dibromosuccinic add 215
42. Bromomale!c add 215
zvii
xviii FIGURES.
nam paob
43. isoDubromoeuccinic acid 216
44. Bromofumaric acid 216
45. Enicic acid : 224
46. 47. Dibromoerucic acid 225
48. Braasidic acid 225
49, 50. Dibromobrassidic acid 225
61. Acetaldehyde 230
52, 53. Lactonitrile 230
54, 55. Emil Fischer's spacial representation of two C-atoms in union . . 236
56. Electrolysis of an alkaline copper solution 241
57. Maleic acid 244
58. 59. Mesotartaric acid 244
60. Fumaric acid 245
61. Raceinic acid 246
62. Crystal forms of the sodium ammonium tartrates 248
63. 64, 65, 66. Werner's theory of stereoisomerism ^ 251
67. Rye-starch 297
68. Rice-starch 297
69. Potato-starch 298
70. Conversion of an optically active substance into its optical isomeride 327
71. Single linking between two carbon atoms 328
72. Normal reduction-curve 379
73. Abnormal reduction-curve 379
SECOND PART.
74. Kekul^'b benxene-formula 392
75. Thiele's benzene-formula 394
76. Von Baeter's centric formula 395
77. Von Baeyer's stereo-formula 395
78. Willstatter's cyc^ctatetraene 395
79. Fusion-curve of mixtures of o-nitrotoluene and p-nitrotoluene 407
80. Solubility-curve of benzoic add in water 436
81. Enantiotropic substance 442
82. Monotropic substance 442
83. Hartley's absorption-curve ". 471
84. Absorption-curves of p-nitrophenol, p-nitroanisole, and sodium, p-ni-
trophenolate 471
85. Centric naphthalene-formula 554
86. Thiele's naphthalene-formula 554
87. Simple naphthalene-formula 554
88. The system nicotine — ^water 604
,^^
ORGANIC CHEMISTRY.
INTRODUCTION.
1. Organic Chemistry is the Chemistry of the Carbon Com- pounds. The word ''organic" has now lost its historic meaning, given it at a time — the beginning of last century — when it waa thought that the substances which occur in organized nature, in the animal and v^etable kingdoms, could only be formed under the influence of a special, obscure force, called the vital force. Several unsuccessful attempts to prepare artificially such ''or- ganic" substances promoted this belief. Until about the year 1840, it was so general that Berzelius still thought that there was but little hope of ever discovering the cause of the difference between the behaviour of the elements in the mineral kingdom and in living bodies. Organic chemistry included the study of those compounds which occur in plants and animals, as well as of the more or less complicated decomposition-products which could be prepared from these compounds by various means. Among the latter many were known which were not found in nature, but it was thought impossible to build up a compound body from its decomposition-products, or to obtain an oi^anic compound from its elements.
In the year 1828, Wohler had indeed obtained from inorganic sources the organic compoimd urea, a product of the animal economy. This discovery was at first regarded as of small im- portance, for it was thought that this substance occupied a position midway between organic and inorganic compounds. For a num- ber of years the synthesis of urea was in fact the only well-known example of the kind, such observations becoming more numerous
2 ORGANIC CHEMISTRY. [J 2
about the middle of the nineteenth century. At length the syn^ thesis of many substances, including that of acetic acid by Kolbe and of the fats by Berthelot, strengthened the growing convic- tion that organic compounds are formed under the influence of the same forces as are inorganic, and that to this end no special force is necessary.
The natural distinction between organic and inorganic chemr istry was thus destroyed, its place being taken by an artificial one. As it had been already noticed that all organic compounds contain carbon, the name "Organic Chemistry" was appropriated to the Chemistry of the Carbon Compounds,
Through the numerous discoveries which were made in this branch of the science, especially in Germany by Liebig, Wohler, and their pupils, and in France by" Dumas, Laurent, and Ger- HARDT, organic chemistry acquired by d^rees a totally different aspect, and the old division into groups of substances which had either the same origin, as in the case of vegetable chemistry or animal chemistry, or had single properties in common, as, for example, the vegetable acids, the vegetable bases, and neutral vegetable bodies, vanished. Its place was taken by a more rational classification, which gradually developed into its present form, and is based on the mutual relationships found to exist between organic compounds.
2. Since no essential distinction between organic and inoxganic chemistry now exists, and numerous S3mtheses have set at rest all doubt as to the theoretical possibility of building up from their elements even the most complicated carbon compounds, such as the proteins, the question may arise as to the reason for still treating the chemistry of the carbon compounds as a special part of the science. The answer to this question is two- fold.
First, the enormous number of carbon compounds known, amounting to about one hundred and fifty thousand, the number of the compoimds of all the other elements being only about twenty-five thousand. Second, the special nature of certain properties of the carbon compounds. These are either not found at all in the compounds of other elements, or at most in a much less marked degree: for example, many inorganic compounds can be exposed to high temperatures without undergoing any
i 3] QUALITATIVE ANALYSIS. 3
chemical change, whereas the carbon compounds, ahnost with- out exception, are decomposed at a red heat. It follows that the latter are usually much less stable than the former towards chemical and physical reagents, and in consequence different methods are employed in the investigation of carbon compounds and of inorganic compounds.
Another peculiarity is that numerous organic compounds con- tain the same elements in the same proportions, but differ from one another in properties. For example, one hundred and thirty-five compounds of the formula C10H13O2N have been discovered. This phenomenon is called isomerism, and is almost unknown in inorganic chemistry, a fact which necessitates an investigation of the cause to which it is due.
All these reasons make it desirable to treat the carbon com- pounds in a special part of chemistry.
QUALITATIVE AND QUANTITATIVE ANALYSIS.
■
3. Investigation has shown that in most of the compounds of carbon there is only a very small number of elements. The chief of these are carbon, hydrogen, oxygen, and nitrogen. Halogen derivatives are less numerous, and substances containing sulphur or phosphorus occur still less frequently. Carbon compounds are also known in which other elements are found, but they are ex- ceedingly few in comparison with those which contain only the elements named above. Some elements do not occur in carbon compounds.
In order to be able to determine the nature of a compound, it 18 first of all necessary to ascertain what elements it contains by submitting it to qualitative analysis. In the case of the ^carbon compounds, this is very simple in theory, the process being one of oxidation.
On solution of an organic compound, the elements constituting it are usually not present as ions in the liquid. Oxidation, however, either converts them at once into ions, or into oxygen compounds with ionized groups, such as CO3", SO4", and so on. They can then be identified by the ordinary inorganic reactions (''Laboratory Manual," I, 1-5).
Carbon is thus converted into carbon dioxide, wliich can be
t ORGANIC CHEMISTRY. [J 4
detected by the lime-water test; sulphur and phosphorus are oxidized to sulphuric acid and phosphoric acid respectively; hydro- gen is oxidized to water; and nitrogen is evolved in the free state.
If an organic compound contains a halogen, it is oxidized in presence of silver nitrate, the corresponding silver halide being formed. Other elements present are found, after oxidation, in the form of compounds easily identified.
For analytical purposes, oxidation is carried out in different ways, according to the nature of the element suspected to be present. Copper oxide is generally used in testing for carbon^ hydrogen, and nitrogen. The substance is mixed with it, and the mixture heated in a glass tube sealed at one end, the carbon and hydrogen being oxidized by the action of the oxygen of the copper oxide. Nitrogen is evolved in the free state, and can be recognized in exactly the same way as in the quantitative analysis of nitrogen (7). For the halogens, sulphur, phosphorus, etc., it is best to oxidize the substance under examination with con- centrated nitric acid.
The method of oxidation is a general one for qualitative analy- sis: it can always be applied, and yields positive results. There are other methods which in many cases attain the desired end more quickly and easily, but as most of these are not of universal application, the failure of one of them to detect an element affords no certain indication of its absence. In doubtful instances the question must be decided by the oxidation-process.
For example, the presence of carbon can frequently be de- tected by submitting the substance to dry distillation. Charring often takes place, or vapours are evolved which can be recognized as carbon compounds by their smell or other properties, such as their burning with a smoky flame on ignition.
4. The nitrogen in many organic compounds can be converted into ammonia by heating them with soda-lime, or with concen- trated sulphuric acid. Another method very largely used in testing for this element was suggested by Lassaigne. It consists in heating the substance under examination with a small piece of sodium (or potassium) in a narrow tube sealed at one end. Should the com- pound contain nitrogen, sodium (or potassium) cyanide is formed, its presence being readily recognized by converting it into Prussian blue ("Laboratory Manual," I, 3, a).
{( 5, 6J QUANTITATIVE ANALYSIS. 5
5. The halogens can be recognized by heating the substance with quicklime, the corresponding calcium halide being formed. A very delicate method of detecting them is to introduce a small quantity of the compound on a piece of copper oxide into a non- luminous flame. The corresponding copper halide is formed and volatiliKCs, imparting a magnificent green colour to the flame. These two methods are always applicable.
Sulphur can often be detected by heating the compound with a small piece of sodium in a narrow ignition-tube. Sodium aul- *phide is produced, and can be detected by treating the reaction- mixture, placed on a clean silver coin, with water, when a black stain of silver sulphide is formed. Or, the reaction-mixture can be extracted with water, and sodium nitroprusside added: the solution acquires an intense violet colour.
No qualitative reaction is known for detecting oxygen in an organic compound. This can only be effected by a quantitative snalys:s.
6. Following on qualitative, must come quantUative, analysis; that is, the determination of the quantity of each element present in the compound. The methods used for qualitative analysis in inorganic chemistry are oft«n very different from those employed in quantitative determinations: in organic chemistry the methods of qualitative and quantitative analysis are alike in principle, oxidation being employed in both.
Carbon and hydrc^en are always estimated together. The principle of the method of organic analysis chiefly used was worked out by Ltebig (1803-1873). It b usually carried out as follows. In the combustion-furnace, A: (Fig. 1), is a hard glass tube, ob,
Fio. 1. — Organic Analtbib.
open at both ends. A complete drawing of it is shown i» the figure above the furnace. It contains granulated copper oxide.
6 ORGANIC CHEMISTRY. [( 6
//, and a spiral of copper-gauze, c, oxidized by heating to redness in the air or in a stream of ox)'gen. About one-third of the length of the tube is left empty, and into this, after temporary removal of the copper spiral, a platinum or porcelain boat, d, containing a weighed quantity of the substance to be analyzed, is introduced. The end of the tube next the boat is connected with a drying apparatus, g, A, /, in which the air or oxygen is freed from water- vapour and carbon dioxide: g contains concentrated caustic potash, A soda-lime, and / calcium chloride. To the end of the tube^ furthest from the boat is attached a weighed calcium-chloride tube, Z, for the purpose of collecting the water produced by the combustion
of the substance. The weighed potash-bulbs, m (shown enlarged in Fig. 2), are connected to this, and in them the carbon dioxide formed is absorbed by concentrated caustic potash. The gases enter the appara- tus by the tube 6 on the right, pass Fio. 2.— Potash-bulbs. through the three bulbs containing
potash, and escape through the tube a, which is filled with soda-lime. As soon as all the joints of the apparatus are known to be gas-tight, the burners are lighted, except beneath the place where the boat is. When the tube is hot, the substance is burned by carefully heating this part of the tube, while at first a slow stream of air, and later a slow stream of oxy- gen, is led through the drying apparatus into the tube. The oxygen facilitates the combustion of the particles of carbon which have deposited, and the red-hot copper oxide serves to oxidize the gaseous decomposition-products completely to carbon dioxide and water. The increase in weight of the calcium-chloride tube and that of the potash-bulbs respectively give the quantity of water and carbon dioxide formed, from which the amount of hydrogen and carbon in the compound can be calculated.
If the compound contains nitrogen or halogens, a freshly- reduced spiral of copper-gauze is placed at the end of the tube next the absorptioD-apparatus I ^^.A rn. The hot copper decom- poses any nitrogen oxides fon^^* which would otherwise be abaoxhed in the potaah-bvdba; u ^^ combines with and retains the halogens. ^l0^
§71 QUANTITATIVE ANALYSIS. 7
The foregoing is only intended to illustrate the principles on which the methods of organic analysis are based. The experimental details have often to be modified somewhat to suit special circum- stances. For example, substances which burn with great difficulty are mixed with lead chromate instead of copper oxide, the former being the more energetic oxidizing agent. When the compound con- tains sulphur, this substance is also used, the sulphur being con- verted, by heating in contact with the chromate, into lead sulphate, which is stable at red heat. If coppsr oxide is used, sulphur dioxide is formed and is absorbed in the potash-bulbs, thereby introducing an error into the carbon estimation. Another method of retaining sulphur dioxide consists in having a layer of lead dioxide, PbO„ at the end of the tube next to the absorption-apparatus. This layer is gently heated, and retains all the sulphur dioxide in the form of lead sulphate. Combustion tubes of silica are also employed, and are superior to glass in their power of resisting fracture. Contact of the copper oxide with the inner surface of the tube should be pre- vented by means of a layer of asbestos, to obviate the formation of copper silicate.
In Dennstedt's method copper oxide is not employed, but the combustion-tube contains platinized asbestos or a platinum plate to serve as a catalyst during the combustion in oxygen of the gaseous decomposition products. In recent years, methods of micro-elementary analysis requiring only a few milligrammes of substance have also been devised.
7. Nitrogen is usually estimated by Dumas's method. An apparatus similar to that employed in the estimation of carbon and hydrogen (Fig. 1) is used. The drying apparatus g, h, /, is replaced by a carbon-dioxide Kreussler generator, to effect com- plete expulsion of the air from the tube before the combustion is begun. The absorption-apparatus /, m, is replaced by a delivery- tube opening under mercury. As soon as the air has been driven out of the apparatus, the front part of the tube, containing the copper-gauze and the granulated copper oxide, is heated. The combustion is then begun, and the evolved gases are collected in a graduated tube open at the bottom (measuring tube), the end of which dips into the mercury-bath. This tube is filled partly with mercury, and partly with concentrated caustic potash to absorb the carbon dioxide. The reduced copper-gauze has the effect of decomposing any nitrogen oxides formed. When the
8 ORGANIC CHEMISTRY. [{ 8
combustion is over, all the nitrogen remaining in the tube is swept into the graduated tube by a stream of carbon dioxide from the Kbeussler generator. The tube, along with the mercury, potash, and gas which it contains, is then placed in a wide cylinder filled with water. The mercury and potash are displaced by the water, and after the level of the liquid inside and outside the tube has been made to coincide, the number of cubic centimetres of nitrogen is read off. From this the amount of nitrogen in the compound is calculated.
Nitrogen can often be estimated by a method discovered by Kjbldahl and improved by Wilfarth. It depends upon the fact that the nitrogen of many organic substances is wholly con- verted into ammonia by heating the compound for some time with concentrated sulphuric acid in presence of phosphoric oxide and a drop of mercury, the latter going into solution. Usually the mixture first turns black, owing to charring: after heating for one or two hours the liquid again becomes perfectly colourless. The carbon has then been fully oxidized by the oxygen of the sulphuric acid, which has been reduced to sulphurous acid. The process is facilitated by the mercury salt, which probably plays the part of an " oxygen-carrier" between the sulphuric acid and the organic substance, being continually converted from the mer- curic to the mercurous state, and then back again by the boiling acid into the mercuric state. When the liquid has become colour- less, it is allowed to cool, diluted with water, excess of alkali added, and the ammonia distilled into a measured quantity of acid of known strength. Titration gives the quantity of ammonia, and hence the amount of nitrogen. This neat and simple method is usually not applicable to compounds containing oxygen linked to nitrogen. In such compounds the nitrogen is only partially converted into ammonia.
8. The halogens can be estimated by the method either of Ltebiq or of Carius. By the former, the substance is heated with quicklime, and by the latter, at a high temperature with a small quantity of concentrated nitric acid and a crystal of silver nitrate in a sealed glass tube. This is carried out without risk in the tube-furnace (Fig. 3), in which the glass tubes are placed in wrought-iron cylinders with thick walls.
Carius's method can also be applied to the estimation of sul-
§9]
QUANTITATIVE ANALYSIS.
9
phur, phosphorus, and other elements. Non-volati)e substances containing sulphur or phosphorus can also be oxidized by fusion with nitre.
The estimation of halogens in solids can also be readily effected by oxidation with sodium peroxidci the final product being a chlo- rate, bromate, or iodate. On reduction with sulphurous acid, this is converted into a halide, which can be precipitated with silver nitrate in the usual manner.
9. The results of a quantitative anal3rsis are expressed in per- centage-numbers. If the total of these percentage-numbers is very nearly 100, then no other element is present in the compoimd; but if appreciably less than 100, there is another element present which has not been taken account of in the analysis, there being no convenient method for its estimation. This element is oxygen. The percentage-amount of oxygen is therefore found by sub- tracting the total of the percentages of the other elements from
FlO. 3. — TUBE-FUBNACB.
100. This has the disadvantage that all experimental errors are included in the percentage-number of the oxygen.
10 ORGANIC CHEMISTRY. [{0
Carbon-estimations are usually too low, owing to the loss of a small quantity of carbon dioxide through the various connections of the apparatus. Hydrogen-estimations are generally too high, be- cause copper oxide is hygroscopic, and can only be freed from traces of moisture with difficulty. These errors balance one another more or less, so that the want of accuracy in the oxygen-percentage is diminished.
The method by which the percentage composition and formula of a substance are calculated from the results of analysis is best explained by an example.
The analysis of a substance containing nitrogen yielded the fol- lowing numbers:
0.2169 g. substance gave 0«5170 g. CO, and 0-0685 g. HaO.
0*2218 g. substance gave 17*4 c.c. N, measured over water at 6° C and 762 mm. barometric pressure.
Since there are 12 parts by weight of C in 44 parts by weight of COj, and 2 parts by weight of H in 18 parts by weight of HjO, the number obtained for CO, must be multiplied by il=A to find the weight of C, and the number found for HjO by A ^^i to obtain the weight of H. This calculation gives 65-0 per cent, of carbon and 3* 51 per cent, of hydrogen in the compound.
The weight of the nitrogen is calculated as follows. Since it ia saturated with water-vapour, the tension of this expressed in nun. of mercury must be subtracted from the barometric pressure in order to obtain the true pressure of the nitrogen. At 6^ C. the tension of aqueous vapour is 7 -O mm. The actual pressure of the nitrogen is therefore 762—7*755 mm. Since 1 c.c. of nitrogen at (f and 760 mm. weighs 1 -2562 Aig., at 755 mm. and 6** C. the weight of this volume expressed in milligrammes is
1-2562 xZ5|.i.22ii.
1+6X0-00367 760
Therefore the 17 • 4 c.c. of nitrogen obtained weigh 1 • 221 1 X 17 • 4=
21 • 247 mg., from which the percentage of nitrogen is found to be 9- 6.
The sum of these percentage-numbers is 78-1, so that the per«
oentage of oxygen in the substance analyzed is 21 -9. The perceb tage-
eomposition given by the analysis is therefore
C 65-0 H 3-5 N 9-6* 0 21-9
{ 10] DETERMINATION OF MOLECULAR WEIGHT, 11
On dividing these values by the numbers representing the atomic weights of the corresponding elements, there results
|
C H N |
0 |
|
6-4 3-5 0-7 |
1-4. |
|
re divided by 0*7 give |
|
|
C ,H N |
0 |
|
7-7 5-0 1-0 |
2-0. |
These numbers approximate very closely to those required by the formula C,H^O,N. The percentage-composition corresponding to this formula is
C 65-3 H 3-4 N 9 5,
which agrees well with the analysis.
DETERMINATION OF MOLECXTLAR WEIGHT.
xo. An analysis only gives the empirical formula of a com- pound, and not its molecular formula, because C^HbOo has the same percentage-composition asUC«H|>Oo)ii* When the empirical fonnula has been ascertained m analysis, the molecular weight has still to be determined. (/ 1
It cannot be decided by chemical means, although it is possible thus to obtain a minimum value for the molecular weight. For example, the empirical formula of benzene is CH. Benzene readily yields a compound, GeHftBr, which can be reduced again to benzene. It follows that the molecule of benzene must be represented by CeHe at least. The molecular formula, however, could also be C12H12, or, in general, (C6He)n; the bromine com- pound would then have the formula (CeHsBr)^. Assiuning the formula to be C12H12, that of the bromine compoimd would be Ci2HioBr2. It is evident that the formation of a compound of this formula would involve direct replacement of two hydrogen atoms by bromine, and experiments would be made for the pur- pose of obtaining Ci2HiiBr. Should these not attain the desired result, the probability of the correctness of the simpler formula CsHftBr would be increased. This would not, however, be decisive, because the experimental conditions necessary to the formation
12
ORGANIC CHEMISTRY.
[{11
of the compound Ci2HiiBr might not have been attained. The chemical method only proves that the molecular formula of ben- zene cannot be smaller than CeHe, but does not prove whether it is a multiple of this or not.
To ascertain the real molecular weight, physical methods must be employed. These involve the determination either of
the specific gravity of the compound in the gaseous slate, or of certain values depending on the osmotic pressure of the substance in dilute solution. The theory of these methods is fully explained in " Inorganic Chemistry," 31-35 and 40-43. Here it will suffice to describe the practical details of a molecular-weight determination.
In calculating the vapour-density (the specific gravity of the substance in the gaseous state), four quantities — the weight of substance converted into the gaseous state, the volume of the resulting vapour, the temperature at which the volume is measured, and the barometric pressure — must be known.
II. Vapour-density is usually deter- mined by a method suggested by Victor Meyer. The apparatus (Fig. 4) con- sists of a glass tube B with an internal diameter of about 4 mm. This tube is closed at the top with a stopper, and underneath has a wider cylindrical por- ^^ tion of about 200 c.c. capacity, closed
^^^0 At the lower end. Near the top of the
^^^ tube is sealed on a delivery-tube A for
Fio. 4.— Victor Meyer's the gas, which is collected over water in Vapour- DENSITY Appa- , x j x u w m^
RATus. ^ graduated tube E. The apparatus is
partly surrounded by a wide glass (or metal) jacket C. This contains a liquid boiling higher than the substance the vapour-density of wrhich is being determined. This liquiil is heated to bciling, t:cme of |l^ j^iir in B being in consequence
§ 11] DETERMINATION OF MOLECULAR WEIGHT. 13
expelled. A point is soon readied at which no more air escapes from the delivery-tube, that in the wider part of the tube having a constant temperature, almost equal to that of the vapour of the boiling liquid. The graduated tube is then filled with water and placed over the open end of the delivery-tube A. After the stopper has been withdrawn, a weighed quantity of the sub« stance under examination enclosed in a small glass tube is dropped into the apparatus, and the stopper replaced, care being taken to make it air-tight. The substance vaporizes quickly in the heated wide portion of the .tube. Its vapour expels air from the apparatus: the air is collected in the graduated tube, and its volume is equal to that of the vapour. While, however, the air in the hot part of the apparatus has the local temperature, in the graduated tube it acquires the temperature of the latter, and this must be considered in making the calculation. The experi- ment gives a volume equal to that which the weighed portion of the substance in the form of vapour would occupy, if it were possible to convert it into a gas at the ordinary temperature and under the barometric pressure.
For ease of manipulation this method leaves nothing to be desired. It possesses, moreover, the great advantage over the other methods, that it is not necessary to know the temperature to which the apparatus has been heated, this not being employed in the calculation. It is only necessary that the temperature should remain constant during the short time occupied by the experiment.
The result ia calculated thus. Suppose that g mg. of the sub- stance were weighed out, and yielded V c.c. of air, measured over water, with the level the same inside and outside the<tube: sup- pose further that the barometric pressure were i/, the tempera- ture /, and the tension of aqueous vapour b, then, at a pressure of H—b mm. and at i^, g mg. of the substance would occupy a volume of V c.c, so that under these conditions the unit of volume
(1 c.c.) would contain ^ mg. of the substance.
One c.c. of oxygen at H—h mm. of pressure, and at i^^ weighs in milligrammes
1-429 ^H-h
l+0-003G7r" 760'
14 ORGANIC CHEMISTRY. [§12
from which it follows that the vapour-density D referred to oxygen == 16 is
£ 1+0:003^/^60^
The molecular weight M being twice the density,
M='2D.
12. Two other methods are often employed in the determina- tion of the molecular weights of organic compounds. They are based on the laws of osmotic pressure, and involve the determi- nation of the depression of the freezing-point or the elevation of the boiling-point of a dilute solution of the substance, referred to the freezing-point or boiling-point respectively of the pure solvent C* Inorganic Chemistry," 40-43).
In practice, it is necessary to determine first the freezing-point of the solvent; for example, that of phenol. Then one gramme- molecule of a substance of known molecular weight is dissolved in a known weight — that is, in a known volume — of the solvent.
It lowers the freezing-point by a certain amount, which is always the same for the same solvent, no matter what the substance may be, provided that the volume of solution, containing one gramme-molecule, is the same. The depression of the freezing- point caused by a gramme-molecule is, therefore, a constant for this solvent. If a one per cent, solution of a substance of unknown molecular weight M be made in phenol, and the depression {A) of the freezing-point of this determined, then
• i4.Af =Constant;
because the depression of the freezing-point iS; between certain limits, proportional to the concentration.
It is evident that this formula is equally applicable to the elevation of the boiling-point. Here M is the only unknown quantity, and can be calculated from this equation.
The product AM is called the molecxdar depression of the freezing-voint or the molecular elevation of the boiling-point of the solvent.
Example. — Numerous determinations have proved that when
S 13] DETERMINATION OF MOLECULAR WEIGHT. 16 •
phenol is used as the solvent the molecular depression of its freezing-point is equal to 75. We have then for phenol
iiM-75.
A solution of 2*75 per cent, concentration was prepared by dis. solving 0*3943 g. of a substance of empirical formula G^HyONa in 14 •34 g. of phenol. The depression of this solution was 0*712^. For
0*712
a one per cent, solution the depression would have been -77-==- —
2*75
0*258| therefore A — 0*258. It follows that the molecular weight is
;^-291. 0*258
Since C^HyON, corresponds with the molecular weight 135, and
CuHi^OjN^ to 270, the latter comes nearest to the molecular weight
found, so that twice the empirical formula must be assigned to the
compound.
The laws of osmotic pressure only hold when the solutions are very dilute. This is also true of the equation i4Af= Const., since it is derived from these laws.
It is not strictly correct to determine A by means of a solu- tion of finite concentration, as is done in the example given.
To determine M accurately, the value of A should be derived from a solution of infinite dilution; but as this is not possible,
A
E lb
ip.
Eykman has described the following graphic method of determining A for such a solution. A is determined for three or four concentrations, and the values obtained are represented graphic- ally as in Fig. 5, in which the values of A are the ordinates, and those of the percentage-strengths of the solu- FERCEHTAOEt tious ATo thc abscisssB. Eykman states
Fig. 5.— Etkican'b Gbaphio that very often the line drawn through Method. ^j^^ ^^^pg ^f ^y^^ ordinates is very nearly
straight. If it is produced till it cuts the ordinate OA, OPq gives
the value of A for infinite dilution.
13. The constants for the molecular depression of the freez-
ing^oint of a number of solvents are given in the following
table:
16
ORGANIC CHEMISTRY.
[{13
SolTenl.
Water.......
Acetic acid. .
Benzene
Nitrobenzene.
Phenol
Naphthalene. Urethane. . . . Stearic add. . p-Toluidine. .
|
^M %A.* * a |
Molecular Depreosion. |
|
|
lleltiDg-pouit. |
||
|
Obsenred. |
Cateolated. |
|
|
(f |
19 |
18-9 |
|
16.6*» |
39 |
38*8 |
|
6^ |
53 |
53 |
|
b"" |
70 |
69*5 |
|
39.6« |
75 |
77 |
|
80« |
69 |
69.4 |
|
48.7** |
51.4 |
_ |
|
53*» |
45 |
... |
|
42.6^ |
52.4 |
— |
The last five solvents are very useful, and are better than glacial acetic acid, which is still often employed, because they are not hygroscopic. Moreover, they melt above the ordinary tem- perature, so that a cooling agent is unnecessary, and their con- stants are high.
The following table shows that the molecular elevations of the boiling-point are usually smaller than the molecular depressions of the freezing-point.
Solvent.
Water
Ether
Ethyl alcohol
Benzene
Chlorofonn. . Acetone
BoUing-point.
100*^ 36.6** 78.0*» 80.4*» 61.0*» 56.3*^
Molecular ESevation.
Obeerved.
5.1 22*1 11.3 26-0 35*0 17.3
Galoulated.
5.2 21.1 11.5 26.7 36.6 16.7
The numbers in the last column of the tables are cal- culated from VAN 't Hofp's formula
2?:=
0.02X!P
w •
K being the molecular depression or elevation, T the freez- ing-point or boiling-point on the absolute scale, and W the
1141 DETERMINATION OF MOLECULAR WEIGHT. 17
latent he^t of fusion or of evaporation per kilogramme of the solvent.
14. ErKMAN has constructed convenient apparatuses for the determication of the depression of the freeaing-point and the elevation of the boiling-point. The first (Fig. 6) comprises a small thermometer divided into twentieths of a degree with a small flaslc attached as shown in the figure, this being contained in a glasB cylinder: it is held at the top by a stopper, and supported underneath by cotton-wool. The latter has the effect of making
the cooling take place slowly. Being a poor conductor of heat, the cotton-wool retards coding. A weighed quantity of the solvent is placed in the flask, and its freezing-point determined. Then a known weight of the substance is introduced, and the freezing-
18 ORGANIC CHEMISTRY. [{ 15
point again observed. From the depression of the freezing-point thus obtained A can be calculated as in the example given (12).
15. Eykman's apparatus (Fig. 7) for determining the elevar tion of the boiling-point comprises a thermometer, and two glass vessels, A and B. The tube A is about 40 cm. long and 4 cm. wide, and serves both as a heating jacket for the pure solvent, and as an air-oondenser. Into jB, which is only a few millimetres narrower than A, there is fused the boiling-tube C, with a narrow side-tube D. C is suspended from the clamp K by a platinum wire. P, twisted round its neck, and can be raised or lowered at will. The thermometer-scale is divided into tenths of a degree, the graduations being about one millimetre apart, so that with the aid of a lens it is possible to read to one-hundredth of a degree. Besides giving the boiling-point, the graduated scale of the ther- mometer also serves to indicate the volume of solution contained in C, For this purpose the vessel C with the thermometer placed in it must be calibrated by a gravimetric or volumetric method.
When using the apparatus the solvent is introduced into C until the level of the liquid has risen to that of the first gradu- ation on the thermometer-scale, from 5' to 10 c.c. being needed. About 40 or 50 c.c. of the solvent are poured into the jacket A^ and the apparatus heated with a micro-burner, using a large flame at first. When ebullition has begun, the size of the flame is re- duced so that the vapour is completely condensed in the tube A at a height shown in the figure by the letters A or E.
When the liquid has boiled at a constant temperature for a short time, the height of the mercury is noted, and the clamp raised so that the open end of the boiling-tube C is some centimetres above the top of the jacket A, A weighed quantity — 1-2 milligramme- molecules — of the substance under investigation is then introduced into C from a tared weighing-tube, and C gently lowered to its former position in the jacket. While the weighing-tube is being weighed to ascertain how much substance has been added, the boiling-point of the solvent will have become constant. This is noted, the boiling-tube C again raised by the aid of the clamp K^ and the volume accurately determined by reading with a lens the height of the solution-meniscus on the thermometer-scale.
A second determination is made with a solution of greater concentration by introducing a further quantity of the substance
{§ 16, 17] THE ELEMENT CARBON. 19
from the weighing-tube, and repeating the series of operations just described. Since very little more time is needed for each operation than is required to tare the weighing-tube and its contents, a aeries of determinations at different concentrations can be quickly made, and the results plotted on squared paper. From thQ curve thus obtained the value of A for infinite dilution can be readily cal- culated (12).
THE ELEMENT CARBON.
16. Carbon occurs in three allotropic forms: diamond, graphite ^ and amorphous carbon. For a description of these the reader is referred to "Inorganic Chemistry," 176-179, which also treats of the compounds of carbon with metalloids and metals, as well as with the determination of its atomic and molecular weights. The evidence in favour of the assumption that the molecule of carbon contains a great number of atoms is there set forth.
Confirmation of this view is afforded by a consideration of the relation subsisting between the boiling-points of the compounds of carbon and of hydrogen. If these be denoted by the general formula Ct|H2n-p, then, even when n and p are both large num- bers, the boiling-points of these substances are relatively low, and rise with the increase of both n and p. For carbon itself, 2n = p, and, on account of the extraordinary non-volatility of this sub- stance, the value of n must be very great.
The subject of valency is explained in " Inorganic Chem- istry," 76. With univalent elements carbon forms compounds of the type CX4. It is therefore quadrivalent^ and it is on this foundation that the whole superstructure of organic chemistry rests.
LABORATORY-METHODS.
17. To prevent repetition, it is desirable, before proceeding with a description of the organic compounds, to give a short account of the most important operations used in their preparation and investigation.
Heating Substances Together. — ^This process is very often used to induce reaction between bodies, since the velocity of reac- tions increases largely with rise of temperature ("Inorganic Chemistry," 13 and 104). Details vary according to the tem-
20 ORGANIC CHEMISTRY. [\ n
perature to be attained. If this is considerably below the boil- ing-point of the most volatile compound, they are simply mixed together in a flask fitted with a thermometer, as in Fig. 8. The flask is immersed in an air-bath formed of a vertical iron cylinder closed at the lower end, a [aece of stove- pipe being very suitable. The upper end is closed with a
sheet of asbestos mill-board, <
with an opening for the neek of the flask. Should, how- ever, the boiling-point of one of the substances be reached or overstepped, the flask must be connected with a condenser, as in Fig. 9, The invention of this form of con- densing apparatus is usually
— Heatinq p,o 9. — Flasi
SCBSTMJCBB m AK ^^ RbflCX-
Open Flabk.
CONDSNSEB.
attributed to Liebiq, although it was first constructed by Weiget, in 1771. It consists of a glass tube aa, enclosed in ajacket bo( glass or metal, through which a stream of cold water can pass. For substances of high boiling-point a plain vertical glass tube may
I 18] LABORATORY METHODS. 21
be substituted: it is called an "air-condenser," being sufiSciently cooled by the air alone. The effect of the condenser is evident: the boUing liquid is condensed in it and drops back into the flask.
Fia. 10. DlSnUiATION'-APPASATDB.
When substances have to be heated above their boiling-pointe, they are placed in a thick-walled glass tube sealed at one end: this is then sealed at the other, and heated in a tube-fumace (9, !•«■ 3).
l8. DittiUaiion. — ^The apparatus shown in Fig. 10 may be used,
but if the liquid to be distilled
is of such a nature that it would
become contaminated by the
action of its vapour on the cork
or rubber stopper shown in the
figure, a distilling-flask (Pig. 11}
^V is substituted, and, if its neck
M is sufficiently loag, contact of the
11 vapour with the stopper during
|l dbtillatioa is prevented.
1^^^^^ ^ At the ordinary pressure
11 ^^^^^^ * many substances decompose on
A^^ ^^^^^^ heating to their boiling-points,
BI^H ^^^N but distil unchanged under di-
^1^^ minished pressure, because the
Fia. H — FRACTioMATiNO-FLABic. boiling-point is then much lower.
The apparatus shown in Fig. 12 can be used for vacuum-dis-
22 ORGANIC CHEMISTRY. [fis
The liquid to be distilled is placed in d. A glass tube e, drawn out to a very fine point, dips into the liquid, and a thermometer b placed in it. As soon as the apparatus has been made vacuous by the water-pump w, a stream of small bubbles of air escapes from the fine point of the tube e, and serves to prevent the violent "bumping" which otherwise occurs when liquids are boiled under diminished pressure. This bumping, caused by the sudden and intermittent formation of vapour, sometimes causes boiling over, or fracture of the Bask. The receiver b is kept cool by a stream of water from c. wi is a mercury manometer: a is a two-way
Fio. 12. — Distillation in Vacdum. stop-cock which permits access of air to the apparatus after the distillation, and also serves to cut off the connection between the aii^pump and the rest of the apparatus when the pump "strikes back "; that is, when the water rises through the tube » into the apparatus.
It). The separation of a mixture of volatile substances is effected by fractional distillaiion. If a mixture of two liquids, boiling, for example, at 100° and at 130°, is distilled, more of that boiling at 100° distils over at the beginning, and more of that boiling at 130° at the end, of the operation. If the distillate passing over below 110° is collected separately in one fraction, and similarly that between 120° and 130°, a rough separation is effected, while the middle fraction still consists of a mixture. To make the separa-
520]
FRACTIONAL DISTILLATION.
23
tion as complete as possible, the fraction 100^-110^ is returned to the fractionation-flask and distilled till the thermometer reaches 110^, the fraction 110^-120° then mixed with the residue in the fractionation-flask, and the 'distillation then continued till the thermometer again stands at 110^. The receiver is changed, and the distillation renewed till the thermometer reaches 120^. The fraction 120°-130^ is then added to the liquid in the distillation-
YOUNO.
HXICPSL. WURTX. LXNWBIIAN.
FlO. 13. — FRACTIONATINChCOLUMNS.
flask, and the distillate collected in the same receiver, until the ther- ' mometer again indicates 120^. The portion distilling subse- quently is collected separately. By several repetitions of this process it is possible often to effect an almost complete separation, it being usually advantageous to collect the fractions between narrower limits of temperature, and thus to increase their number.
20. The separation is much facilitated by using a fractionating- column (Fig. 13) connected to the neck of the boiling-flask;
24 ORGANIC CHEMISTRY. [§21
the vapour of the least volatile constituents of the mixture is to a large extent condensed in the column. The stream of vapour from the distillation-flask heats the liquid in the fractionating- column, the effect being to vaporize its more volatile part, and simultaneously to condense the higher-boiling constituent of the vapour issuing from the flask.
ax. A change in the composition of most liquid mixtures does not occasion a proportional alteration in their properties, like that expressed in the annexed graphic representation (Fig. 14) by a straight line AB. The abscissae correspond with the molecular-percentage composition of the mixtures: the points A and B on the ordinates give the values of such physical constants as vapour-tension, boiling- point, specific gravity, etc., for the pure substances A and B, and the line AB the values of these constants for mixtures. The curve thus obtained usuaUy varies more or less from a straight line.
The boiling-points of mixtures will be lower Oine c) or higher (line h) than those calculated by the proportion-rule. Sometimes, these boiling-point cmves will depart so much from the straight line as to show such maxima and minima as the curves a and d. Complete separation of such mixtures by fractional distillation at constant pressure is impossible, but is feasible when the boiling- point curves follow the course indicated by h or c. The most volatile, or lowest boiling, constituent of a mixture alwa3rs distils first, so that the vapour is richer in A and the residual liquid in B. If the pure constituents A and B are more, or less, volatile than any mixture of the two, as represented by the boiling-point curves h and c, continued fractional distillation must lead to an approxi- mately complete separation of A and B. But if the boiling-point curve has a maximum or minimum, the mixtures corresponding with it will consist of the most, or least, volatile constituents. On distillation, a fraction with this highest, or lowest, boiling-point will always be obtained, and at constant pressure further separation will be impossible.
Oomprehension of this phenomenon will be facilitated by con- sidering a boiling-point curve h without a maximum or minimum (Fig. 15). Since the most volatile portion of any mixture always volatilizes first, the vapour evolved from a boiling liquid always contains more of A than the liquid itself. When the composition of the mixture is 6, that of the liquid will be b\ The vapour-iermon
21]
FRACTIONAL DISTILLATION.
25
curve AVE throughout the complete trajectory AB lies higher than the boiling-point curve.
If the boiling-point curve has a maximum h (Fig. 16), along the trajectory Ah the vapour will be richer in A than the liquid from
Fig. 14.
Percentage Fig. 16.
100
B
0 PanonfiiiSM 100
Fig. 16. Fraction AirDiSTiLLATioN Curves.
which it is evolved: along the trajectory hB the vapour will contain more of B than the liquid, since B is now the most volatile, or lowest boiling, constituent. It follows that at the maximum 6 the vapour must have exactly the same composition as the liquid; that is, the mixture with maximum boiling-point distils at a constant temperature as though it were a single substance. For a mixture of liquids with a minimum boiling-point analogous results are
26 ORGANIC CHEMISTRY. [§22
obtained, so that in the graphic representation the vapour-tension curve must be tangential to the boiling-point curve, and touch it at the minimum-point.
The separation of a mixture of liquids by fractionation is also impossible when the boiling-points of its constituents are close together, because the essential characteristic of the whole method consists in the unequal volatility of the portions composing the mixture, resulting in the distillation of one substance before the other. If, however, the substances have nearly the same boiling- point, then both attain a vapour-tension of one atmosphere at al- most the same temperature; in other words, they are almost equally volatile. With these conditions it is therefore impossible to apply the method successfully.
22. Steam-distillation. — In the preparation of many organic substances a crude reaction-product is oft^n obtained containing tarry matter along with the required compound. To free the substance from this, use is often very advantageously made of the property possessed by many substances of distilling in a current of steam, the tarry matter remaining behind. Fig. 17 shows the apparatus employed in such a distillation.
Water is boiled in the can a, fitted with a delivery-tube c and a safety-tube fe, the evolved steam being passed into the bottom of the distillation-flask d. If the distillation is interrupted, cooling causes diminished pressure in a, air being then able to enter the tube 6. If b were not used, the liquid in d would flow back into a, owing to the fall in the steam-pressure.
Steam-distillation is also of service in separating compounds volatile with steam from others not volatile. With substances in- soluble in water, the distillate is a milky liquid, because the water in the receiver is mixed with fine, oily drops. There is also an oily layer above or below the water.
In steam-distillations two liquids take part — ^water and the sub- stance to be distilled. Usually these liquids are not miscible in all proportions. In the limiting case, when each liquid is wholly insoluble in the other, the vapour-pressure of each is unaffected by the presence of the other. At the boiling-point of the mixture, the sum of the vapour-pressures of the two constituents must be equal to the baro- metric pressure, since the liquid is boiling. The boiling-point must be lower than that at ordinary pressure of the lower-boiling of the two substances, because the partial pressure is necessarily smaller than
ffil STEAM DIST! LLATIO.V. 27
the totel preBsure, which is equal to that, nf the atmosphere. The same resutt is therefore attained aa by diatillalJon at diminished pressure; that is, the volatilisation of the substance at & tem- perature lower than i\a boiling-point under ordinary pressure.
Whether a substance distils quickly or slowly with steam de- pends on its partial pressure and on its vapour-density, together witli
Pio. 17. — Steam-distillatiow.
the values of these physical constantB for water. If the pressures are pi and pt, and the vapour-densities rfi and d,. the quantities dis- tilling simultaneously are pid, (subatantw) and pA (water). If the ratio pi-J, :p^ is large, the substance distils with a small quantity of water, the distillation being quickly completed. The reverse takes place when the ratio p,d, :jhd, is small.
At a pressure of 760 mm. a mixture of nitrobenzene and water boils at 99°. The steam exerts a pressure of 733 mm., so that the tension of the nitrobenzene-vapour is 27 mm. Since the vapour- densities of water and nitrobenzene are in the ratio of their respective molecular weights, 18 and 123, the proportion of water to nitrobenzene in the distillate should be as 733x18 : 27x123; that is, approximately as 4 : 1. Notwithstanding its small vapour- tension at the boiling-point of the mixture, the quantity of nitro- benzene which passes over is about one-iifth of the total distillate, the rapid volatilization of the nitrobenzene being due to the fact that it has a large, and water a small, molecular weight. £ven
28 ORGANIC CHEMISTRY. [§23
when an organic compound under similar conditions has a vapour- tension of only 10 mm., it distils with steam sufficiently rapidly to render the method applicable to its purification.
23. Separation of Two Immiscible Liquids. — For this purpose, a separating-funnel (Fig. 18) is employed: the method can be
inferred from the drawing without further explanation. It is also applied to the extraction of aqueous solu- tions of substances soluble in a volatile liquid im- miscible with water, such as etfier, light petroleum, chloroform, carbon disulphide. The solution is trans- ferred to a separating-funnel; ether, if that solvent is selected, is added; and after the mouth of the funnel has been closed by a glass stopper, the two liquids ate mixed together by vigorous shaking, whereupon the substance dissolved in the water passes partly into the ether. The ethereal solution is allowed to rise to the surface, and separated from the water by opening the stop-cock after removal 'rating- PUN- ^^ ^^^ stopper. The water dissolved by the ether NEL. during the shaking is removed by chloride of cal-
cium, or some other drying agent, and finally the ether is distilled off. When the dissolved substance is only slightly soluble in water, and easily soluble in ether, the extraction is completed quickly; it is then possible to exhaust the aqueous solution almost completely by several repetitions of the process, using fresh ether for each extraction. Otherwise, the shaking must be repeatedly carried out, and even then the extraction is imperfect.
When two immiscible solvents are simultaneously in contact with a substance soluble in both, the latter distributes itself so that the ratio of the concentrations reached in both solvents is constant (law of Berth elot). If a quantity X^ of the substance is dis- solved in a quantity / of the first solvent (water), and this solution extracted with a quantity m of the second solvent (ether), there will then remain a quantity X, in the first solution, so that X^ —Xi has passed into the second solvent.
The value of the quantity X\ is, in accordance with the above law, given by the equation
Kl
I m m-^Kl
{ 231 EXTRACTION WITH SOLVENTS. 29
X X —X
for — and — ^^ '' are the two oonoentrations after agitation with
I m
the solvents, and K is the number expressing the constant rau'o, or
the coefficieni of distnbtUion,
A second extraction with the same quantity m of the second
solvent gives
I m *
or, substituting the value of Xi from the first equatioD,
and for the nth extraction,
^•"-^•(m+xj •
(
Thus Xii, the quantity remaining in the first solvent (water), diminishes as n increases, and -as m and K are respectively greater and less. Complete extraction is impossible, because although
— ='.) can approach zero very closely, it can never become
equal to it.
Examples will facilitate comprehension of this formula. Sup- pose the problem is to determine how often 1000 c.c. of an aqueous solution of benzoTc acid must be extracted with 200 c.c. of ether to remove all the benzoic acid from the solution. In this instance / = 1000 c.c, and m— 200 c.c. By experiment K is found to have approximately the value i^; that is, if the concentration of the benzoic acid in the ethereal solution is represented by 80, that in the aqueous solution is expressed by 1. On substituting these values for /, m, and K respectively, the formula becomes
X Kl lOOOXA 1
X, m+Kl 200+1000XA 17*
which means that a single extraction with 200 c.c. of ether leaves A of tlie benzoic acid in the aqueous solution. After three extrac-
/ 1\* 1 tions with 200 c.c. of ether, there remains only ( — • I ^Trr:: of the
\17/ 4913
add, so that the extraction of the acid is practically complete. For succinic acid X»6. A single extraction of 1000 c.c. of an
ORGANIC CHEMISTRY. li 24
solution of this acid with 200 c.c. of ether leaves 6000 30
T-- — ^7J3^~?7 of t''^ *'''<1 still dissolved in the w&ter. Repeated '
extraction is neceesary to remove all the succinic add from the
aqueous solution.
Several agitations with small proportions of the solvent e&ect a more complete separa- tion than that attained by employing the whole quantity for a single operation. An example will make this faet clear.
An aqueous solution of a substance is extracted with benzene, the coefficient of distribution being \. When one litre cf the solution is agitated with a like volume of benzene in one operation, the proportion re- maining in the water of the original quantity
of material dissolved is ■rTi = i- On carry- ing out the extraction in two stages, half a litre of benzene being employed for each, the Fio 19. — FiMiiKiNO- proportion of substance remaining dissolved *^'^ in the water after the first agitation ia
7^^— i, and after the second Jxi^j. Since the same volume of benzene was employed in both instances, it follows that extrac- tion in two stages gives a better separation than a single extraction. By employing the differential calculus, it can be proved to be theoretically best to extract an infinite number of times with infinitely small proportions of benzene.
Separation of Solida and Liquids. — This ia effected by filtrar tion, a process materially accelerated by attaching the funnel with a rabber stopper to a flask a (Fig. 19). connected through & to a water air-pump. To prevent rupture of the point of the filter-paper, it must be supported by a hollow platiniun cone c. 34. Separaiion of Solids from one Another. — This process de- pends on difference in solubility. For a soluble and an insoluble substance the operation is very simple. If both substances are soluble, the method of fractional crystallization must be used. The mixture is dissolved in the minimum quantity of a boiling liquid: on cooling the solution the less soluble substance crys^llizes first. The mother-liquor is poured off just as crystals of the second
i 25] MELTING-POINTS AND BOIUNO-POINTS. 31
bodybegJD to separate, and the aecondcompouDdcrystallizedeitber by further cooling or by concentrating the liquid by evaporation. Several repetitions of these processes are esBential to the separa- tion. Even when the pure compounds have very different boIu- bilities, the method is not free from difficulty, because the solu- bility of one substance may be very considerably modified by the presence of another. Water, alcohol, ether, glacial acetic acid, benzene, and other substances are employed as solvents.
3$. From the foregoing it is seen that soliJ substances are usually purified by crystallization, and liquids by distillation. It is an indication of purity when the physical constants remain un- changed after the substance has been purihod anew. All hough every physical constant could serve this purpose, the mdling- poinl and the boiling-point are those most used, liccausc they are easily determined, and slight impurities exercise a very material influence upon them. They also often afford a means of identify- ing substances. If a compound has been ob- tained by some process and is supposed to be one already known, it is strong evidence in favour of the supposition if the melting-point and boiling-point of the substance coincide with those of the compound with which it is supposed to be identical. For this reason determinations of melting-points and boiling- points are very often carried out.
The best method of ascertaining whether two substances are identical is to mix them in i approximately equal proportions and det'.'rmine ' the melting-point of the mixture. When iden- tity exists, the melting-point of the" mixture will d
coincide with that of the two individual eub- j-jg^ 20. Thiele's
stances; when it does not, the mixture melts Melting - point at a much lower temperature, which is not Apparatos. sharply defined.
Thiele has devised a very convenient apparatus for deter- mining the mdting-pcnnt (Fig. 20). A small quantity of the Bubetance is placed in a thin-walled capillary tube sealed at one end. This tube is attached to a thermometer, T, with its bulb dipping into a liquid of high boiHng-point, such as concentrated
32
ORGANIC CHEMISTRY,
[§26
sulphuric acid, olive oil, or liquid paraffin (31), the viscoedty causing the tube to adhere to the thermometer. The liquid is contained in the apparatus ABC. Heating with a small flame at B induces circulation of the liquid, ensuring uniform heat- ing of the thermometer and capillary tube. When the sub- stance fuses, the thermometer is read.
The boiling-point is determined by heating the liquid to boil- ing in a fractionation-flask with a high side-tube. Short ther- mometers are used, so that the whole of the mercury colunm is surrounded by the vapour of the boiling liquid. To avoid in- conveniently small graduations, these thermometers are. con- structed so that they can only be employed for a comparatively small range of temperature, six or seven different instruments being used for temperatures between 0*^ and 360®. These are called " abbreviated " thermometers.
26. Sometimes physical constants other than the melting-points and boiling-points are determined in the investigation of organic
compounds. 1. The specific gravity can be de- mmiinrfc /mumi termined with the pyknomder, the most useful J I form of which is shown in Fig. 21. It consists
^^ of two thick-walled capillaries a and 6, termi-
nating in a wider tube c. The parts a and h are furnished with a millimetre-scale. The capacity of the apparatus is first determined, as well as that of the space between two divisions, by filling it several times up to different divisions with water of known temperature, and then weighing. The liquid under investigation is then placed in the apparatus, and this is weighed after the positions of the menisci in the capillaries have been observed; from the daia thus obtained the specific gravity can be calculated.
The coefficient of expansion of organic liquids is almost always much greater than that of water at ordinary temperatures, and the densities of these substances are greatly influenced by change of temperature. As a rule, there is an alteration of one unit in the third decimal place for each degree of temperature alteration.
As indicated by Mendel^eff , the specific gravity or density of such liquids at different temperatures can be expressed by the formula
\j
Fia. 21.— Pyk-
NOMETER.
6] POLARIMETRY. 33
Do being the density at 0°, D, that at f, and K a constant de- pendent on the nature of the liquid.
■ The number derived by division of the molecular weight by the density is termed the moiecuiar edlume.
2. The rotation of the plane of potaruation is another constant of importance.
Some substances, such as turpentine, a solution of sugar, etc^ have the property of rotating out of its original position the plane of a ray of poluHzed light passing through them. This phenomenon is called the rotation of the plane of polarization, and substances pos- eesBing this property are said to be opticaUy active. Polarimetera bave been coostructed for measuring Uie angle through which the
FiQ. 22. — ^Ladrent'b Polabiukter.
plane of polarization has been rotated by an optically active sub- stance: of these Ladrent's (Fig. 22) is one of the best known. The yellow andium-Itght of the burner TT is polarized in the part of the apparatus marked BD, and then passes through a tube of known length (200-500 mm.) placed in the channel L. This tube contains the hquid or solution under examination. The part OC of the appa- ratus serves to measure the rotation of the plane of polarization.
The extent to which the plane of polarization is rotated is pro* portional to the length of the tube, and is variously expressed. The rotation of a substance can be stated, for example, in terms of the effect produced by a given length of the tube described. The angle of rotation is read off directly from the instrument, and ia
34 ORGANIC CHEMISTRY. [526
usually denoted by a. By convention, the specific rotary power is defined as the quotient obtained by dividing a by the product of the length of the tube into the specific gravity of the liquid. ' This value is denoted by [a] so that
where I is the length of the tube, and d the specific gravity of the liquid. Under these conditions, [a] expresses the rotatoiy power of a substance per unit length of the tube (1 decimetre) , and for unit weight of the substance divided into the unit of volume.
The extent of the rotation is dependent on the colour of the light, on the temperature, and for solutions on the nature of the solvent. The measurement is often carried out with sodium-light, which gives a yellow line in the spectroscope, denoted by D. This is expre.«s5ed by the 83rmbol [aj^.
When the rotatory power of a substance is small, or when, on account of its shght solubility, it can only be obtjiined in dilute solution, the rotation can often be increased by adding a solution of boric acid, molybdic acid, uranium salts, or other substances. These bodies combine with the organic substances to form com- pounds of much higher rotatory power.
The determination of the refractive power or refraction of liquid compounds is of great importance in organic research. A descrip- tion of the appai'atus employed is given in text-books of physics. The index of refraction^ n, depends on the colour of the light em- ployed, and is generally determined for the three principal lines of the hydrogen spectrum, for the yellow sodium line, or for five of the more brilliant lines of the helium spectrum. The difference in refraction for the various colours is called dispersion, and also finds application in organic investigation.
The refraction also depends on the temperature, and therefore on the specific gravity of the liquid. On theoretical grounds, LoreKtz, of Leyden, and Lorenz, of Copenhagen, consider the expression
n«-l 1
to be independent of the temperature, d representing the density.
Within narrow limits of temperature, their view is supported by
numerous experimental determinations. An empirical formula sug-
n*—l 1
gestcd by Eykman, -— : . -j, remains constant over a range of
n-|-0»4 o
temperature of more than 100^, and furnishes a much better expres-
§27] CLASSIFICATION OF ORGANIC COMPOUNDS. 35
sion of the independence of temperature. The product of these ex- pressions by the molecular weight Af ,
a„ n*-l M n«-l M Nil/ s • — or = • —
^^ n«-f2 d n-fO.4 d'
Lorents'a formula Eykman'a formula
is called the tnokcular refraction. Reference will be made sub- sequently to the great importance of this constant. The molecular electric conductivity is considered in 87.
CLASSBFICATION OF ORGANIC COMPOUNDS.
27. The organic compounds are usually classed in two main divisions. One of these includes the fatty or aliphatic com- pounds (c[X€i0ap, fat), and the other the cyclic or ring compounds. The first class owes its name to the fact that the animal and vegetable fats belong to it. They are also called hormathic compounds, their carbon atoms being arranged in a chain or row. The name of the second class is derived from its contain- ing compounds in which the presence of a closed chain or ring of atoms must be assumed.
The aliphatic compounds can be regarded as derived from methane, CH4. The most important cyclic derivatives are the aromatic compounds, so-called because many of them are char- acterized by an agreeable smell or aroma.
It will be shown later that there are important differences between the general properties of these two classes of compounds.
FIRST PART.
THE ALIPHATIC COMPOUNDS.
SATURATED HTDROCASBONS.
28. The aliphatic compounds are defined in 27 as those derived from methane f CH4. It is, therefore, advisable to begin the study of these compounds with this hydrocarbon.
Methane occurs in nature in the gases evolved from volcanoes. It escapes in coal-mines during the working of the coal-seams, and is called fire-damp by the miners. It is also called marsh-ga^, being present in the gases evolved from marshes by decay of vege- table matter. It is an important constituent of coal-gas,. being present to the extent of 30-40 per cent.
It can be obtained by the following methods.
1. By Sabatier and Senderens's synthesis. When a mixture of hydrogen and carbon monoxide is passed over reduced nickel at 260^-300**, methane is formed:
CO+3H2-CH4+H2O.
The nickel undergoes no apparent change, and can be used re- peatedly. At a temperature of 230^-300**, carbon dioxide reacts similarly with hydrogen in presence of finely-divided nickel:
CO2+ 4H2 = CH4 + 2H2O.
2. Methane can also be synthesized directly from its elements by passing hydrogen through a heated tube containing reduced nickel mixed with very finely-divided carbon obtained by previously decomposing methane. An equilibrium is attained, corresponding at 475® and one atmosphere with 51 per cent, of methane:
CH4F±C+2H2.
33
129] - METHANE. 37
Prino has found that pure carbon and pure hydrogen also combine directly without a catalyst at temperatures above 1100°, the equilibrium at 1200° corresponding with about 0«35 per cent, of methane.
3. By the action of water on aluminium carbide:
C3AI4 + I2H2O = 3CH4 + 4A1(0H)3.
Other methods of preparation are referred to in 75 and 83.
Physical and Chemical Properties. — Methane is an odour- less and colourless gas of sp. gr. 0*559 (air=»l). Its critical pressure is 55 atmospheres, and its critical temperature —82°. It boils at ~ 165°, and solidifies at - 186°. It is only slightly soluble in water, but more so in alcohol. It is decomposed into carbon and hydrogen by the sparks of an induction-coil, or in the electric arc. Oxidizing substances, such as nitric and chromic acids, do not attack it, or only very slightly, while concentrated sulphuric acid and strong alkalis have no action upon it. It bums with an almost non-luminous flame. When mixed with air or oxygen it forms a violently explosive mixture, the reaction being in accordance with the equation
CH4 + 2O2 = CO2 -f 2H2O.
This so-called "fire-damp" is the cause of the explosions which sometimes occur in coal-mines. Chlorine and bromine react with methane, replacing its hydrogen atoms by halogen atoms, and forming a hydrogen halide :
CH4+2a=OH3a4-Ha
The replacement of one atom by another is called subetittUion. If chlorine or bromine is present in excess, the final product is 0X^4 or CBr4.
29. There exists a series of hydrocarbons having general chem- ical properties similar to those of methane. Examples of these compounds are ethane C2H6, propane CaHg, butane C4H10; pen- tane C5H12, hexane CeH^, etc., pentatriacontane C35H72, and hexa- contane C6oHi22- These formulae can be summed up in the general expression CnH2B+2: for methane, n=l. The hydrocarbons ^H2i»-|.2 resemble methane in their power of resisting oxidation,
38 ORGANIC CHEMISTRY. "* [§ 30
and are unacted on by concentrated sulphuric acid, while halogens act on them with substitution of hydrogen and formation of compounds CnH2n+iCl, CnH2nCl2, and so on.
The higher hydrocarbons can be obtained by building-up from those lower in the series. For example, ethane is got from methane by replacement of a hydrogen atom by halogen, and treatment of the halide thus obtained with sodium or calcium:
2CH3I + Nag = CgHg + 2NaI.
Propane can be prepared in accordance with tne following equa- tion:
CH3I + CgHfil + Nag = C3H8 + 2NaI :
and, in general, CnH2n+2 is obtained by the action of sodium upon CmH2m+iI-t-CpH2p+iI, when m4-p=n.
In addition to propane, butane, C«H,o, is formed from 2C,HJ, and ethane, C,H,, from 2CHgI, three hydrocarbons being obtained. This is always so in such syntheses.
Since methane can be prepared synthetically, it is evidently possible to synthesize each hydrocarbon of the formula CnH2n+2-
30. Nomenclature, — The hydrocarbons CnH2n+2 are always .denoted by the termination *'ane." The first four members, methane, ethane, propane, and butane, have special names: the others are denoted by the Greek or Latin numeral corresponding with th > number of carbon atom . Thus CgHis is called octane, C12H26 dodecane, C31H64 hentriaconiane, and so on.
It will often be necessary to consider groups of atoms un- obtainable in the free state, but theoretically derivable by re- moval of a hydrogen atom from the hydrocarbons CnH2n+2« These groups have the general formula CnH2n+i, and are called alkyl-groups. They are denoted individually by changing the termination "ane" of the corresponding hydrocarbon into '*yl." Thus CH3 is called methyl, C2H5 ethyl, C3H7 propyl, C4H9 biUyl, C12H26 dodecylf etc.
The hydrocarbons CnH2n+2 have the general name saturated hydrocarbons, because they are saturated with hydrogen; that is, are imable to take up any more hydrogen atoms into the molecule. They are also called paraffins, because paraffin-wax consists of a
§ 31] PARAFFINS, 39
mixture of the higher members. The word paraffin is derived from parum affiniSf and indicates the stability of this substance towards chemical reagents.
31. Occurrence in Nature. — The hydrocarbons CBH2n+2 occur in nature in enormous quantities. Crude American petroleum consists of a mixture of a great number of these compounds, from the lowest to the highest members of the series. Three principal pro- ducts are obtained from this petroleum by fractionaldistillation, after treatment with acids and alkalis to free it from substances other than hydrocarbons of the formula CaH2n+2. The most volatile por- tion is called petrol, light petroleum, petroleum-ether, benzine, naphtha, or ligr&ln: it distils between 40° and 150°, and contains lower members, chiefly CeHn, C7H16, and CgHig. It is exten- sively employed as motor-spirit, as a solvent for fats, oils, and resins, and in the removal of stains from clothing in the " dry- cleaning process."
The portion distilling between 150°-300° is ordinary petroleum, and is used on a large scale for lighting and cooking.
The retention in petroleum of the constituents of low boiling- point is a fruitful source of accidents due to fire. Their presence can be detected by determining the flash-point, effected by heating the sample slowly in an apparatus devised by Sir Frederick Abel, and observing tho^mperature at which the mixture of vapour and air over the petroleum can just be ignited. Experience has shown that there is no danger with a flaifh-point of 40° C. (104** F.).
Further distillation above 300° yields lubricating oil, and then wax-Uke products, the residue in the still ultimately carboniz- ing. The residual product from the evaporation of American petroleum in the air is called " vaseline " or petroleum-jelly. It is semi-solid at ordinary temperatures, white when pure, and finds appUcation in pharmacy as a substitute for fats in the preparation of ointments. It is employed as a lubricant for machinery, and also for covering the surfaces of metallic articles to hinder oxidation. As a protective coating it is superior to vegetable and animal fats, which become rancid in course of time, and thus attack the surface of the metal. Vaseline is free from acid, and remains unchanged by exposure to air.
Paraffin-wax is a mixture of the highest members of the
40 OBOANIC CHEMISTRY, [§ 32
series CnH2n+2) among them the hydrocarbons C22H46) C24H50f C26H64, C28H58.
Some kinds of crude petroleimi, notably that obtained from Java, contain considerable quantities of these highest members. They are present in but small amount in American petroleum. Liquid paraffin is a product of high boiling-point, obtained in the dry distillation of brown coal. Earth-wax or ozokerite occurs in Galicia, and consists chiefly of paraffin-wax. This substance is also obtained in the dry distillation of the brown coal found in Saxony.
Asphalt (from ^^oXros, unalterable) is a mixture of hydro- carbons of high molecular weight, and also contains compounds of oxygen, nitrogen, and sulphur in small proportions. It is present in large quantities in the celebrated " Pitch lake " of Trinidad, and in a similar lake in Venezuela, and is also found in Cuba. Artificial asphalt consists partly of oxidation-products of mineral-oil constituents of high boiling-point, analogous to the brown product formed by the action of atmospheric oxygen on paraffin-wax heated at a high temperature for a long time. It also contains residual pitch from the distillation of coal-tar.
32. The petroleum stored in the interior of the earth at depths up to 600 metres has probably been formed from fats under the influence of high temperature and great pressure. In confirma- tion of this hypothesis, Engler has prepared by distillation of train-oil under pressure a liquid very similar to natural petroleum.
Many diverse suggestions have b^n made as to the origin of the enormous quantities of fats assumed to constitute the basis of petroleum. The best explanation is that of Potoni^, who regards the oil as having originated in the sapropelium or ''putrefying ooze/' a material rich in fats. Shallow fresh-water pools contain floating flora and fauna (plankton) of very minute dimensions {microplankton). They propagate rapidly, but the life of the indi- vidual is short. In consequence, a continuous shower of dead micro- plankton descends to the bottom of the pool, and subsequently decomposes to form sapropelium.
The hypothesis explaining the formation of petroleum as a result of the interaction of water and certain metallic carbides is rendered extremely improbable by two facts : (1) almost every variety of petroleum is optically active, an indication of its derivation from optically active organic material (223) ; (2) petroleum is never
1 331 HOMOLOGOUS SERIES. 41
found in the oldest geological fonnations, but only in those in which the presence of vegetable and animal remains has been demonstrated.
Homologous Series.
33. Each of the hydrocarbons CnH2n+2 differs in composition from the rest by nXCH2, as the general formula shows. It was pointed out (29) that this difference exercises but slight influence on their chemical properties.
Whenever organic compounds show great resemblance in their chemical properties, and have at the same time a difference in composition of nXCH2, they are said to be homologous (6/AoXoyos, corresponding), the name homologoTis series being given to such a group of compounds. As will be seen later, many of these series are known.
It IS easy to understand how much this simplifies the study of organic chemistry. Instead of having to consider the chemical properties of each compound individually, it is sufficient to do so for one member of a homologous series, as this gives the principal characteristics of all the other members. In addition to the main properties common to the members of a homologous series, each individual member has its characteristics. Except in a few instances, this book will not deal with the latter, because they only need to be considered in a more extensive survey of the sub- ject.
The physical propertiest such as the melting-points and boiling-points,' specific gravities, and solubilities, of the members of a homologous series, generally change uniformly as the number of carbon atoms increases. In general it may be said that the melting-points and boiling-points rise from the lower to the higher ' members of a homologous series.
A table of some of the ph3rsical constants of a number of normal (36) members of the paraffin series is given on p. 42.
An inspection of this table reveals that the first four members aie gases at the ordinary temperature, those from C5 to Gie liquids, and the higher members solids. Although methane is odourless, the liquid members have a characteristic petroleum-like smell; the solid members, on the other hand, are odourless. All are nearly insoluble in water.
It should be further remarked that the differences between the. melting-points and boiling-points respectively of successive mem-
42
ORGANIC CHEMISTRY.
[§33
bers of the series become smaller with increase in the number of carbon atoms. This phenomeiton is usually found in homologous series.
For- mula.
CH. C,He
C,H,.
%x
Name.
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
Undecane
Dodecane
Tetradecane
Hexadecane
Eicosane
Heneicosane
Tricosane
Hentriacontane
Pentatriacontane
Hexacontane
Melting' poiot.
-186° -172.1*^
-las"
-130.8**
- 94.03
- 97. 1"
- 56.5°
- 6P
- 31*>
- 26*»
- 12°
4°
18°
36-5^
40- P
47.4^
68.4° 740
101°
Observed Boiling- point.
Calculat'd Boiling- point.
-160°
- 93°
- 45°
- o.r
36.3' 68-9' 08*4 125.6 149-5 173° 194° 214.5° 252.5° 287.5° 205°* 215° 234° 302° 331°
-I66.3*
- 96.3'
- 43.1
- 0.4 36*4 68.9 98-3
125* 1
149.8°
172.8°
194.3°
214.6°
252.0°
285.9°
Specific Gravity.
ft
0.415 (at -160°)
0.446 (atO°)
0.536 (at 0°)
0.600 (at 0°)
0.627 (at 14°)
0.658 (at 20°)
0-683
0.702
0-718
0.730 "
0-774 at melttng-point
0-773 "
0.775 "
0-775 "
07776" "
0.7778" '•
07799" »'
07799" "
07813" ••
i> »t
ti
It
n
* At 15 mm. pressure, and the same for thoee following;
For the boiling-points these differences are functions of the ab- solute temperature. Sydney Younq has induced the empirical formula
144-86
giving the difference in boiling-point of two successive members of the series, when T is the boiling-point on the absolute scale of the more volatile of the two homologues. The boiling-points in the fifth column of the table in this section were calculated by the aid of this formula.
The expression holds not only for this homologous series of hydrocarbons, but also for many other homologous series. The dif- ferences between the calculated and observed boiling-points are greatest for the lower members. For some homologous series the divergences are considerable, but can usually be proved to be due to association of the molecules of the compound in the liquid state; that is, the molecular weight in this condition is twice, or a higher multiple of, that in the normal gaseous state*
§ 34] ISOMERISM AND STRUCTURE, 43
Young's formula holds for nonnal pressure, 760 mm. For the absolute boiling-points of two substances a and b the simple relation
often obtains, T and 7' being the absolute boiling-points of the substances at the same arbitrary pressure. Otherwise expressed, this equation means that the ratio of the boiling-points at different pressures is often constant.
For the critical temperature Tt of the series of saturated hydro- carbons, VAN Laar has derived from theoretical considerations the formula
85*14(n+l)»(l-0'04n)
n+0'22 '
n representing the number of carbon atoms. Except for methane, this expression is in good accord with the results of experiment.
Eykman has determined with great care the molecular refrac- tion of the members of this series and of many other homologous series. His experiments have proved the difference between suc- cessive values not to be constant for the initial members of such series, but to become constant for the third or fourth member and those succeeding. This difference may be regarded as the refraction of the CHs-group. Employing Eykman 's formula (26), the difference for the a-line of the hydrogen spectrum is 10*260, and for the /3-line 10-431.
Molecular refraction is mainly an additive property of the molecules. Despite the slight degree of its constitutive influence, deviaticHis from pure additivity often furnish valuable indications of structural arrangement, as will be frequently indicated in the sequel.
Isomerism and Structure.
34. Only one substance with the formula CH4 is known : it Lb methane. Similarly/ there is only one compound having the formula C2H6, and one with the formula CaHg. There are known, however, two compounds with the formula C4H10, three with the formula C5H]2, five with the formula CeH^, and so on. The phenomenon of two or more compounds being represented by one formula is called isomerism (2), and compounds having the same formula are called isomerides. Isomerism is explained by a con- sideration of the grouping of the atoms in the molecule.
One of two hypotheses may be adopted. In the first place, the
44 ORGANIC CHEMISTRY. [§ 35
arrangement of the atoms may be regarded as continually chang- ing, a molecule being represented as like a planetary system, the configuration of which changes from moment to moment. This hypothesis, however, cannot explain the phenomenon of isomerism. For example, it is not apparent how the four carbon atoms and ten hydrogen atoms in butane could form two different substances if the arrangement were indeterminate, for there are trillions of molecules present in even one cubic millunetre, and all the possible configurations of these fourteen atoms must therefore be supposed to exist at any instant.
Isomerism can at once be understood by assuming a definite and unchanging arrangement of the atoms in the molecule, be- cause the difference in the properties of isomeric compounds may be then explained by a difference in the arrangement of equal numbers of the same atoms.
A definite and unchanging arrangement of the atoms in a mole- cule does not involve their being immovable with respect to one another. For example, they might revolve round a point of equilibrium without alteration in their order of sucoesalon*
35. Since the phenomenon of isomerism leads to the assxunp* tion of a definite arrangement of the atoms in the molecule, it is necessary to solve the problem of how the atoms in the molecules of different compounds are arranged. The basis of the solution is the quadrivalency of the carbon atom. In methane the arrange^ ment of the atoms may be represented by the formula
in which the four Unkings of the carbon atom act, as it were, like four points of attraction, each holding a univalent hydrogen atom fast. This is the only possibility, because the hydrogen atoms cannot be bound to one another, the only point of at- traction, or single linking, of each being already in union with one of the linkings of the carbon atom.
The arrangement of the atoms in ethane, 0^11^, must now be investigated. This substance can be obtained by the action of sodium upon methyl iodide, CH3I (53), with a quadrivalent
S 35] ISOMERISM AND STRUCTURE. 46
carbon atom, three univalent hydrogen atoms, and one univalent iodine atom. It must therefore be represented thus:
/"
Sodium reacts with methyl iodide by withdrawing the iodine atoms from two molecules, with formation of ethane. The re- moval of the iodine atom has the effect of setting free the carbon linking previously attached to this atom, with the production of two groups
H
Since the formula of ethane is C2HQ, it is evident that the only possible arrangement of its atoms is that having the two free linkings of the methyl-groups imited to one another:
H— 7C — C^H .
The arrangement of the atoms in propane can be determined in an exactly analogous manner. It was mentioned (29) that propane is formed by the action of sodium on a mixture of methyl and ethyl halides. Since ethane can be prepared by the action of sodium on methyl iodide, the formula of an ethyl halide can only be
where X represents a halogen atom.
If the halogen is taken away from this substance and from
methyl iodide simultaneously, the residues unite, showing that
propane has the structure
H
H— /C — C — Cr— H, H/ ^ \H
or shortly H3C • CHg • CH3.
46 ORGANIC CHEMISTRY, [§ 35
Such an arrangement of symbols expressing the configuration of a molecule, and indicating the form or structure, is called a structural or constUviional formula.
The following example makes it clear how cases of isomer- ism can be explained by differences in structure. One of the five known hexanes boils at 69^, and has a specific gravity of 0-6583 at 20 • 9*^: another boils at 68**, and has a specific gravity of 0-6701 at 17*5°. The first is obtained by the action of sodium on normal propyl iodide, CH3«CH2*CH2l. From the forgoing it follows that this hexane must have the structure
CH3 • CH2 • CH2 — CH2 • CH2 • CH3,
It is named dipropyl, on the assumption that it has been formed by the imion of two propyl-groups.
In addition to this normal propyl iodide, an isomeride called iaopropyl iodide is known. Both compounds can be readily converted into propane, CH3-CH2'CH3. Assuming that the isomerism is due to a different arrangement of the atoms in the molecule, it follows that the isomerism of the two compoxmds C3H7I can only be explained by a difference in the position occu- pied by the iodine atom in the molecule, because the arrangement of the atoms in propane is known, and the propyl iodides only differ from propane in having one of the hydrogen atoms in the latter replaced by iodine. tsoPropyl iodide must therefore have
the structure
H
CH3»C*CH3,
•
I
if the constitution of normal propyl iodide is CH3-CH2*CH2l,
The hexane boiling at 58° is produced by the action of sodium on tsopropyl iodide, and consequently must have the structure
CHa •U-tl •CHo PTT- PTT
CHa-CH-CHs ^^3 CHa
Hence it is called dOaopropyL
{ 361 CARBON CHAINS. 47
Carbon Chains.
36. The foregomg facts evidently make it reasonable to assume the existence of a bond between carbon atoms in the molecules of organic compounds. This bond is a very strong one, since the saturated hydrocarbons resist the action of powerful chemical reagents (29). The property possessed by carbon atoms of com- bining to form a series of many atoms, a carbon chain, like that in the hexanes above described, furnishes a marked distinction between them and the atoms of all the other elements which either have not this power, or have it only in a very inferior de- gree. The fact that the number of carbon compounds b so enormous is due to this property, in conjunction with the quadri- vaiency of the carbon atom.
A carbon chain like that in dipropyl is said to be normal. On the other hand, an example of a branched chain is fur- nished by dimpropyl. Each carbon atom in the normal chain is linked directly to not more than two others: in branched chains there are carbon atoms directly linked to three or four others. A normal-chain compound is usually denoted by putting n before its name; branched-chain compounds are often dis- tinguished by the prefix iM.
A few other definitions may find a place here. A carbon atom linked to only one other carbon atom is called primary; if linked to two carbon atoms it is named secondary; if to three, tertiary; if to four, quaternary. A carbon atom situated at the end of a chain is called terminal. The carbon atoms of a chain are dis- tinguished by numbers, the terminal one being denoted by 1, the one next it by 2, and so on; for example,
CH3 •CH2 *CH2 *CH8.
12 3 4
Sometimes the terminal atom is denoted by* a, the one linked to it by Pf and the succeeding one by /*, etc., but a terminal C-atom in a CN-group, CHO-group, or COOH-group, is distinguished by W9 the next by a, and so on.
Law of the Even Humber of Atoms. — ^The number of hydrogen atoms in the saturated hydrocarbons is even, since their formula is CnHiD+t. All other organic .compounds may be regarded as
48 ORGANIC CHEMISTRY. [§ 37
derived by exchange of these hydrogen atoms for other elements or groups of atoms, or by the removal of an even number of hydrogen atoms, or by both causes simultaneously. From this it follows that the sum of the atoms with uneven valency (hydrogen, the halogens, nitrogen, phosphorus, etc.) must always be an even number. The molecule of a substance of the empirical composition CsHaOsN must be at least twice as great as this, because 2H + 1N is uneven.
Number of Possible Isomerides.
37, The quadrivaleney of the carbon atom, coupled with the principle of the formation of chains of atoms, not only explains the existence of the known isomerides, but also renders possible the prediction of the existence of unknown compounds. Thus for a compound C4H10 either the structure CH3 -0112 -0112 -CHa or
p^^>CH»CH8 may be assumed, and there are no further possi- bilities. Pentane may have the following structural formulae:
(1) CHs-CHa-CHa-CHa-CHs; (2) CH3-CH:5-CH<^^;
CHs^p^CHa
For hexane the following five are possible:
(1) CH3-CH2-CH2-CH2.CH2-CH3; (2) CH3-CHa.CH2-CH<^g»;
(3) CH3-CH2-CH.CH2CH3; (4) CHs-CH-CH-CHa;
CH3 CH3 CHs
•CH3 (5) CH3»CH2«C^-CH3.
\CH3
If the principles given above be assumed, it will be impossible to find structural formulae other than those mentioned.
Should it be possible actually to obtain the same number of isomerides as can be thus predicted, and no more, and should the products of sjmthesis or decomposition of any existing isomeride necessitate the assumption of the same structural formula as that required by the theory, these facts constitute a very important
1 381 PHYSICAL PROPERTIES OF ISOMERIC COMPOUNDS. 49
confinnation of the correctness of the principles upon which the theory is based. This correspondence of fact with theory has been proved to hold good in many instances, and therefore, on the other hand, affords an important means of determining the structure of a new compound, because if all the structural formulae possible for the compound according to the theory are considered in turn, one of them will be found to be that of the substance.
Frequently the number of isomerides actually known is much smaller than that which is possible, because the number of possible isomerides increases very quickly with increase of the number of carbon atoms in the compound. Cayley has calculated that there are nine possible isomerides for C7H16, eighteen for CgHig, thirty-five for C^Hao* seventy-five for CioH22» one hundred and fifty-nine for C11H24, three hundred and fifty-four for Ci2H26y eight hundred and two for CidHsgy and so on. Chemists have not tried to prepare, for example, every one of the eight hundred and two possible isomerides of the formula CiJ3.2Sf because their atten- tion has been occupied by more important problems. There can, however, be no doubt as to the possibility of obtaining all these compounds, because, as mentioned above, the methods for build- ing them up are known, and there would therefore be no theoretical diflSculties in the way of these experiments, though there might be hindrances of an experimental nature.
^ Physical Properties of Isomeric Compounds.
38. Of the different isomerides the normal compound has the highest boiling-point.
The nearer a side-chain is to the terminal carbon atom, the more it lowers the boiling-point. Two side^chains attached to different carbon atoms produce a considerable reduction in the boiling-point. The isomeride with two side-chains linked to the penultimate carbon atom has the lowest boiling-point. The sub- joined table affords confirmation of these statements.
50
OaOANIC CHEMISTRY.
[§38
|
Name. |
Formula. |
Boiling- point. |
|
n-Octane 2-»Methylheptane |
CH| • (CHs)e • CH» CH| • CH • (CHs) 4 • CHt CH, |
124-7"' iie-o' |
|
3-Methylheptane |
CHt * CUs * CH * (CHt)t * CHs CH, |
117. 6** |
|
4-Methylheptane |
CH, . (CH,), • CH . (CH,), . CH, CH, |
118-0** |
|
2 : 5-Dimethylhezane |
CH, • CH • (CH,), • CH • CH, CH, CH, CH, CH, |
108-3* |
|
2 : 2' : 3 : S'-Tetramethylbutane |
CH, CH, |
104* |
The isomeride with the most branched chain has often the highest melting-point.
ALCOHOLS, CbH2ii+20.
Hethods of Formation and Constitution.
39. The alcohols of this homologous series can be obtained by the action of silver hydroxide on the alkyl halides:
CnH2„^.iI + AgOH = CaH2a+20 + AgI.
It is usual to bring an alkyl iodide into contact with moist oxide of silver, the portion dissolved in the water reacting like silver hydroxide (** Inorganic Chemistry," 246). The preparation of the alcohol from the iodide can also be effected by heating it with excess of water at 100°:
C2H5I + H2O = CzHeO + HI.
When sodium reacts with an alcohol Ci|H2n+20, one gramme- atom of free hydrogen is liberated from each gramme-molecule of the alcohol, and a compound called sodium aikoxide (alcoholate), CnH2n+iNaO, is produced: in presence of excess of water this decomposes into sodium hydroxide and an alcohol The sodium has thus replaced one atom of hydrogen, and neither it nor any other metal can replace more than one hydrogen atom: if excess of sodium is added, it remains unacted upon. It follows that only one hydrogen atom in the alcohol i3 replac3able by sodium.
When an alcohol is treated with trichloride or pentachloride of phosphorus, an alkyl chloride is formed:
3CnH2n+20 + PCI3 = 3C„H2„+ , CH- H3PO3.
From these facts the constitution of the alcohols can be in- duced. Silver hydroxide can only have the structure Ag — O — H, its bivalent oxygen atom being linked to its univalent silver and hydrogen atoms. When silver hydroxide is brought into contact with an alkyl iodide, the reaction must be supposed to take place so that on the one hand the iodine atom is set free from the alkyl- group, and on the other hand the silver atom from the hydroxyl-
61
62 ORGANIC CHEMISTRY. [§39
group. The alkyl-group and the hydroxyl-group are thus afforded the opportunity of uniting by means of the linking set free in each:
C„H2n+1 l + AgJOH -> CnH2n+l— OH.
This method of formation proves that the alcohols contain a hydroxyl-group. Their preparation from alkyl iodides and water leads also to the same conclusion, which is further supported by the two properties of alcohols mentioned on the last page. It is evident that if their structure is expressed by CnH2n+i'0H, all the hydrogen atoms present, except one, are linked directly to carbon, while one hydrogen atom occupies a special position in tho molecule, being attached to the oxygen atom, which is united through its second linking to a carbon atom. It is only natural to suppose that the special position occupied by this hydrogen atom is accompanied by a special property, that of being the only one of all the hydrogen atoms replaceable by alkali-metals. More- over, sodium sets free hydrogen from another compound con- taining without doubt a hydroxyl-group: this compound is water, for which no other constitution is possible than H — O — H.
The fact that the alcohols are converted into alkyl chlorides by the action of the chlorides of phosphorus is additional proof that they contain a hydroxyl-group. The empirical formulse CnH2n+20 and CnH2n+iX show that the halogen has replaced OH. It may be assumed that in this reaction the hydroxyl of the alcohol has changed places with the chlorine of the phosphorus compound: ^^ ^i
3(CnH2n+l-OH)+Cl3P.
A consideration of the possible constitutional formulae for sub- stances having the general molecular formula CnH2n+20 reveals the fact that the linkage of the oxygen atom admits of only two possible formulae; thus, the compound C2HaO could be either
I. CHa-CHg-OH, or II. CHa-O-CHg.
Since all the hydrogen atoms in the second formula have the same value, it cannot be the one representing an alcohol, as it would not account for a very important property of these compounds^ their interaction with the alkali-metals. The action of silver hydroxide on an alkyl iodide, or that of phosphorus chlorides on an alcohol, would accord equally ill with this formula, whereas for- mula I. explains these reactions fully. It must therefore be adopted*
§40]
ALCOHOLS, CnH2n+iOH.
53
The constitutional formulse of the alcohols have thus been induced from their properties. Inversely, the constUvtional far- mvlcB represent all the chemical prapertiea of the compounds, being simply a short way of expressing them. The value of these for- mulae is evident: the structural formula of a compound, estab- lished by the study of some of its properties, reveals the rest of these properties. The existence of properties thus deduced has in miany instances been established by experiment.
Komenclature and Isomerism.
40. The alcohols of this series are named alter the alkyl-groups contained in them; for example, methyl alcohol, ethyl alcohol, propyl alcohol, etc.
Isomerism may arise in three ways: by branching of the carbon chains; by changing the position of the hydroxyl-group; or through both these causes simultaneously.
This is seen from the following table of the isomeric alcohols C3 to C5.
|
Specific |
||||
|
Name. • |
Formula. |
Melting- point. |
Boiling- point. |
Gravity at20'» (dt») |
|
Propyl alcohols CtHiO |
||||
|
1. Normal |
CH,.CH,.CH,OH |
Glass- like |
97° |
0-804 |
|
2. Uo |
CHrCHOHCH, |
-85-8° |
81° |
0789 |
|
Bxdyl alcohols C4H10O |
• |
|||
|
1. Normal primary |
CHrCHjCHjCHtOH |
-79-6° |
117° |
0810 |
|
2. , , secondary |
CHjCHaCHOHOH, |
Glass- like do. |
100° |
|
|
3. iso |
(CH,),CH.CH,OH |
107° |
0-806 |
|
|
4. Trimethylcarbinol |
(CH,),COH |
25-5° |
83° |
0-786 |
|
Amyl alcohols CsHitO |
||||
|
p^. Normal primary |
CH,(CH,).CH,OH >^ |
138° |
0-815 |
|
|
\y2. isoButvlcarbinol 3. Seconciary butyl- |
(CH8),CH.CHJ.CH,0H^ |
-134° |
131° |
0-810 |
|
carbinol ^ |
CHrCH(QH6)CH?0H |
128° |
||
|
A. Methylpropylcar- |
||||
|
^ binol |
CH,.(CH,)2.CH0H.CH, |
119° |
||
|
'^'5. Methvlisopropyl- carbinol |
, |
|||
|
(CH,)rf)HCHOHCH, |
112. 6° |
|||
|
fc^. Diethylcarbinol |
CtHrCHOHCaHj |
117° |
||
|
^^7. Dimcthylethylcar- |
||||
|
binol |
(CH,)rf)(OH)C,H» |
102° |
||
|
y%. Tertiary butylcar- binol |
^ |
|||
|
(CH,),CCH,OH |
112° |
54
OROANIC CHEMISTRY.
[§41
The alcohols with names ending in ''carbinol " are so called because all alcohols may be looked upon as methyl alcohol (car- binot), in which one or more of the hydrogen atoms, with the exception of the one in the hydroxyl-group, are replaced by alkyl- groups (Kolbe). Thus, isohutyl alcohol is called isopropylcarbinol, secondary butyl alcohol methylethylcarbinol, normal butyl alcohol n-propylcarbinol, and so on.
The table also shows that in a primary alcohol the hydroxyl- group is linked to a primary carbon atom (36), and that in a second- ary or a tertiary alcohol the hydroxyl is linked to a secondary or a tertiary carbon atom respectively. Similarly, any compounds which may be regarded as produced by replacement of hydrogen linked to a primary, secondary, or tertiary atom are called primary, secondary, or tertiary compounds. Primary alcohols are repre- sented by the general formula CnHgn+i — CH2OH, secondary by
R
\0H
and tertiary by
CQH2n+l V Cn|H2n,+i-^ CpH2p+l /
General Properties of fhe Alcohols.
41. Some of the physical properties of the alcohols are given in this table, which includes only normal primary compounds.
|
Difference of |
Specific |
||||
|
Name. |
Formula. |
Meltinff- |
BoHinff- |
the BoUing- |
Gravity. |
|
point. |
point. |
pointo. |
do**. |
||
|
Methyl alcohol |
,CH,OH |
- 97-1** |
67.4'' |
0812 |
|
|
Ethyl " |
CH»OH |
-IHIS** |
78** |
13-3** |
0.806 |
|
Propyl " |
CHtOH |
96-6^ |
• 18. 5* |
0-817 |
|
|
Butyl " |
C4H.OH |
- 79-6* |
1167* |
20-2** |
0-823 |
|
Amyl " |
CJfnOH |
137** |
20-3** |
0-829 |
|
|
Hexjl " |
CeHuOH |
157** |
20* |
0833 |
|
|
Heptyl " |
CtHuOH |
- 36-5^ |
175** |
18* |
0836 |
|
Octvl " |
CrHitOH |
- 17.9** |
194. 6* |
19-5* |
0839 |
|
Nonyl »' |
C»H,.OH |
213** |
18. 5* |
0-842 |
This table, with tnat in 40, shows that the normal compounds have the highest boiling-points (38).
§41 GENERAL PROPERTIES OF THE ALCOHOLS. 55
The augmentation of the molecule by addition of the CH2- group is attended by an almost constant rise in boiling-point, although for the first members the rise is somewhat less than for the alcohols higher in the series. The association of the alcohol molecules renders Sydney Young's formula inapplica- ble (33).
The existence of this association is proved in many wajrs: (1) The vapour-densities of the alcohols at temperatures slightly above their boiling-points are greater than indicated by their formulse; (2) the degree of association can be inferred from measuHments of the capillarity and viscosity of the liquids; (3) there subsists between the boiling-point and the molecular weight a relationship of the type
VJIf T
T being the absolute boiling-point, and M the molecular weight. For many compounds the constant has the value 64, but it is much greater for associated substances, and increases with the degree of association; (4) according to Trouton's rule,
-;;r"=21; T
M being the molecular weight, L the latent heat of evaporation, and T the absolute boiling-point of a liquid. For water, the alcohols, and other associated liquids, the value of the quotient approximates to 26.
Various other formulse are available for detecting association, an example being that of Joribsen,
193M«
n being the mmiber of atoms in the molecule, M the molecular weight, T the boiling-point, and d the density at that temperature. For associated liquids T and d are abnormally high, and too low a value is obtained for n.
None of the formula gives an accurate measure of the degree of association.
The lower alcohols (Ci— C4) are mobile liquids, the middle members (C5— Cn) are of a more oily nature, while the higher
56 ORGANIC CHEMISTRY. [§{ 42, 43
members are solid at the ordinary temperature. In thin layers all are colourless. In thick layers they are slightly yellow, the colour becoming more marked with increase in the number of carbon atoms. The first members (Ci— C3) are miscible in all proportions with water, but the solubility of the higher members diminishes quickly as the number of carbon atoms increases.
The lower members have a spirituous, and those intermediate a disagreeable, smell; while the solid members are odourless. Their specific gravity is less than 1.
"^ Methyl Alcohol, CHa* OH.
42. Methyl alcohol is obtained on the largo scale by the dry distillation of wood in iron retorts at as low a temperature as possible; or better, by treatment of wood with hot Tproducer-gas, which is a mixture of carbon monoxide and nitrogen, obtained by passing air over coke at a white heat. To this method of preparation the substance owes its name wood-spirit. The products of the distillation are gases, an aqueous liquid, and tar. The aqueous solution contains 1-2 per cent, of methyl alcohol and a number of other substances, the chief being acetic acid (82) (ca. 10 per cent.) and acetone (iii), (ca. 0*5 per cent.). The acetic acid is converted into calcium acetate by the action of lime, and the methyl alcohol purified by fractional distillation, and other methods. It is used in the arts in the preparation of aniline-dyes and formaldehyde, for the denaturation of spirit to render it unfit for drinking purposes (44), and in other processes.
Methyl alcohol bums with a pale-blue flame, and is miscible with water in all proportions, the mixing being accompam'ed by contraction and the development of heat. It is poisonous.
Ethyl Alcohol, CaHs • OH.
43. Ethyl alcohol, or ordinary alcohol, is prepared artificially in enormous quantities. Its preparation depends upon a prop- erty possessed by dextrose (208), a sugar with the formula CeHiaOo, of decomposing into carbon dioxide and alcohol in presence of yeast-cells:
CeHiaOo =2C2H60 + 2CO2.
V
S431 ETHYL ALCOHOL. fi7
About 95 per cent, of the dextrose decompoees according to this equation. By-products such as glycerol and other substances are also formed. Certain higher alcohols of this series, princi- pally amyl alcohols, and also a small proportion of succinic acid, are produced from the proteins contained in the raw material (24a).
On account of its cost, dextrose itself is not employed in the manufacture of alcohol, some substance rich in starch {125), (CeHioOs)!!, such as potatoes, grain, etc., being used instead. By the action of enzymes (aaa), the starch is almost completely transformed into maltoae (214), C12H22O11, one molecule of this compound being then converted into two molecules of dextrose by the action of one molecule of water:
The enzyme employed in the technical manufacture of maltose from starch is called diastase, and is present in malt. The reaction it induces is called sac- charijtcation. When po- tatoes are used, they are first made into a thin, homogeneous pulp by treatment with steam under pressure at 140° to 150°, malt being added after cooling. At a tem- perature of 60° to 62°, the decomposition into maltose ia completed in twenty minutes. ^
Yeast is then added to the maltose solution, and the fermentation car- ried on between 23° and 25°. To separate the re- sulting alcohol from the Fio. 23.— Fkactionating-column. other substances present, the product is submitted to distillation ; and by using a fraction'
58
ORGANIC CHEMISTRY.
H44
ating-column (Fig. 23), alcohol of 90 per cent, strength can be obtained, although the concentration of the alcohol in the fermented liquid does not exceed 18 per cent.
The thin liquid residue remaining in the still is called sperd wash, and is used for feeding cattle and for the manufacture of hydrocyanic acid (257). It contains, amongst other products, almost all the proteins present in the material from which the spirit has been manufactured.
The crude spirit ({oic wine%) so prepared is again carefuUy fractionated, when alcohol of 96 per cent, by volume (spirite) is obtained. The fractions of higher boiling-point consist of an oily liquid of unpleasant odour, called fusel-^ih it contains chiefly amyl alcohols and other homologues. The residue is called sj^enl lees.
Alcoholic beverages are classified into those that have been dis- tilled, and those that have not.
Distilled (about 50 percent, of alcohol).
Brandy or cognac, from wine.
Whisky^ from fermented solution of malt.
Rum, from fermented solution of sugar.
Gin, like whisky, but flavoured with juniper.
Not diBtUled.
Beer, from fermented malt and hops (3-6 per cent, of alcohol).
JVine, fermented grape- juice (8-10 per cent, of alcohol).
"Fortified" wines ^ such as port, sherry f and madeira. They are wines with added alcohol. (Nat- ural wine never contains more than about 10 per cent, of aioohol.)
44. The alcohol of commerce ("spirits of wine ") always con- tains water. To obtain anhydrous or absolvie alcohol from this, lumps of quicklime are added to spirit containing a high per- centage of alcohol, until the quicklime shows itself above the surface of the liquid. The latter is allowed to stand for some days, or boiled for several hours under a reflux-condenser (17), and then distilled. The preparation is much facilitated, and the loss, rather large by this method, reduced to a minimum, by heating a spirit of high percentage with a small quantity of quicklime in a vat, closed by a screwed-down cover, for some hours at ICXP in a water-bath. The spirit is then distilled. To.
§ 44] ETHYL ALCOHOL. 59
prepare absolute alcohol from dilute alcohol, the latter must first be concentrated by distillation from a water-bath. The de- hydration can also be effected by addition of solid potassium carbonate, which causes the liquid to separate into two layers, the aqueous one below and the alcoholic one above. Alcohol of 91*5 per cent, by weight is thus obtained.
Absolute alcohol is a mobile, colourless liquid of character- istic odour, and bums with a pale-blue, non-luminous flame. Cooling with liquid air renders it very viscid, and ultimately causes crystallization. It is very hygroscopic, being miscible with water in all proportions with contraction and rise in tempera- ture. The maximum contraction is obtained by mixing 52 volumes of alcohol with 48 volumes of water, the volume of ths resulting mixture at 20° being 96*3 instead of 100.
The presence of water in alcohol can be detected by anhydrous copper sulphate, which remains perfectly colourless when in con- tact with absolute alcohol, whereas if a trace of water is present, the copper sulphate develops a light-blue colour after several hours. The specific gravity, a ph3rsical constant ofteA employed to ascertain the purity of liquid compounds, can also be employed for the same purpose.
A simple and rapid method for the estimation of alcohol in mixtures with water is very necessary for industrial and fiscal purposes, and a practical method, due to von Baumhauer, Mendeleepf, and others, consists in the determination of the specific gravity and temperature of such a mixture. A table has been prepared with great accuracy, showing the specific gravities of mixtures of alcohol and water from 0 to 100 per cent., at temperatures between 0® and 30°. When the specific gravity and temperature of a given mixture have been determined, the percentage of alcohol may be found by reference to the table. In practice the specific gravity is usually determined with a delicate hydrometer.
In oommerce and in the arts, the amount of alcohol is usually expressed on the Gontment of Europe in volume-percentagef or the number of litres of absolute alcohol contained in 100 litres of the aqueous solution. In Great Britain the standard is proofspirit. This name is derived from the old method of testing spirit by moisten- ing gunpowder with it, and then bringing the mixture into contact
60 ORGANIC CHEMISTRY, [{ 44
with a lighted match. If the alcohol were "under proof," the powder did not take fire, but if there were sufficient alcohol present, the application of the light ignited the gunpowder, the spirit being then "over proof." When the proportions of alcohol and water were such that it was just possible to set fire to the powder, the sample was described as "proof-spirit." When the spirit is weaker than proof-spirit it is said to be under proof, and when stronger than proof-spirit is said to be over proof; for example, a spirit 5® under proof would contain in each 100 volumes the same quantity of alcohol as 95 volumes of proof-spirit, and a spirit 5** over proof would need 5 volumes of water added to each 100 volumes to con- vert it into proof-spirit. By Act of Parliament "proof-spirit" is defined as "such a spirit as shall at a temperature of 51® F. weigh exactly \i of an equal measure of distilled water," corresponding with a spirit containing 57.1 per cent, of alcohol by volimie, or 49.3 per cent by weight.
For scientific purposes the amount of alcohol is usually ex- pressed in percentage by weight, or the number of grammes of alcohol contained in 100 grammes of the aqueous solution. These percentage-numbers are not the same, the percentages by weight being smaller than those by volume for a spirit of any given con- centration.
The greater part of the alcohol produced is consumed in the form of beverages, their detrimental physiological effects being augmented by the impurities, especially fusel-oil, which they contain. Alcohol is used in commerce for the preparation of lacquers, varnishes, dyes, important pharmaceutical preparations such as chloroform, chloral, iodoform, and others, and as a motive power for motor-vehicles. It is also employed for the preservar tion of anatomical specimens. Alcohol is a good solvent for many organic compounds, and finds wide application in laboratory- work for this purpose.
On account of the extensive use of alcohol for manufacturing processes, some industries would be paralyzed if the necessary spirit were subject to the same excise-duty as alcohol intended for consumption. The alcohol used in manufactures in some countries is accordingly made imfit for drinking (denatured or methylated) by the addition of materials which impart to it a nauseous taste, and is sold duty-free. On the Continent of Europe crude wood-spirit is employed for this purpose, and in Great
S 46] PROPYL ALCOHOL. 61
Britain this is supplemented by the addition of a small quantity of paraffin-oil. The sale of denaturated alcohol is also permitted in the United States.
In the United States the tax on beverage-alcohol was $6.40/ and on non-beverage^lcohol is $2.20, per proof-gallon (50 per cent, alcohol by volume). If the alcohol is stronger than proof- spirit, the tax is computed on the proof-gallon basis. If it is weaker than proof-spirit, the tax is computed on the basis of the wine-gallon. In the United States a gallon is 231 cubic inches.
The duty is much higher in Great Britain, being 758. per gallon of proof-spirit (British standard, p. 60). Besides permitting the sale of methylated spirit containing naphtha, the British Govern- ment allows the sale for manufacturers' use of alcohol denatured with wood-spirit only, under the name " Industrial spirit." It has the important advantage of being wholly miscible with water. In the chemical laboratories of universities and colleges in Great Britain and Ireland the use of duty-free pure alcohol is permitted.
A test for ethyl alcohol is the formation of iodoform on the addition of iodine and caustic potash (146).
Propyl Alcohols, C3H7.OH.
45. Two propyl alcohols are known, one boiling at 97° and having a specific gravity of 0-804, the other boiling at 81° and having a specific gravity of 0-789. In accordance with the prin- ciples which have been stated, only two isomerides are possible:
CHa-CHz-CHgOH, and CH3.CH(OH).C3H8.
Monnal propyl alcohol iwPropyl alcohol
The structure to be assigned to the substance with the higher boiling-point, and that to the substance with the lower, may be determined by submitting the substances to oxidation. From each of these alcohols is thus obtained a compound with the formula CsHeO, but these oxidation-products are not identical. On further oxidation, the compound CaHeO (propionaldehyde), obtained from the alcohol of higher boiling-point, yields an acid C3H6O2, called propionic acid; whereas the substance CaHeO (acetone), formed from the alcohol of lower boiling-point, is con- verted into carbon dioxide and acetic acid, C2H4O2:
\
62 ORGANIC CHEMISTRY. [§ 45
CaHgO (propyl alcohol, B.P. 97**) -> CaHeO (propionaldehyde) -»
— » C3H6O2 (propionic acid) ;
CsHgO (wapropyl alcohol, B.P. 81*^) -> CaHeO (acetone) ->
— » (X)2+C2H402 (acetic acid).
Propionic acid has the constitution CH3-CH2-COOH, and acetone CHs-OO-GHs, as will be shown later. It will be observed that only the normal alcohol is capable of forming propionic acid, because the production of this substance must be due to the replacement of two hydrogen atoms by one oxygen atom, and with the normal alcohol this can only yield a compound with the structure assigned to propionic acid. On the other hand, the formation of a substance with the constitution of acetone by re- moval of two hydrogen atoms from a compound CsHgO is only possible when the latter has the structure of isopropyl alcohol. The alcohol of higher boiling-point must therefore be n-propyl alcohol, and that boiling at the lower temperature must be wo- propyl alcohol. ^
Oxidation affords a general method for distinguishing primary from secondary alcohols. By referring to the formute given in 40, it IS seen that all primary alcohols contain the group — CH2OH,
which is converted by oxidation into the carboxyl-group — C<qtt
the characteristic group of organic acids. Further, all secondary
alcohols contain the group H-C-OH: removal of the two hydro- gen atoms from this yields the group C:0, characteristic of the
ketones (no), the homologues of acetone. The oxidation of a pri^ mary alcohol and that of a secondary alcohol produce respectively an acid and a ketone with the same number of carbon atoms as the original alcohol,
A further induction may be made from these reactions. In the conversion of normal propyl alcohol into propionic acid, as well as of isopropyl alcohol into acetone, the oxidation occurs at the carbon atom already linked to oxygen. This is always so, and the general rule may be stated as follows: when an organic compound is svimiitted to oxidaiion, the molecule is attacked at the
S 461 BUTYL ALCOHOLS. 63
part which already contains oxygen — that is, where oxidation has already begun.
Normal propyl alcohol is obtained by fractionation of fusel- oil, and is a colourless liquid of agreeable odour. It is miscible with water in all proportions. i«o Propyl alcohol is also a liquid: it is not present in fusel-oil, but can be obtained by the reduction of acetone (iii and 150).
Butyl Alcohols, C4H9 • OH.
46. Four biUyl alcohols are known (c/. Table, 40), which is the number possible according to the theory, and it is necessary to consider whether these theoretically possible formulae are in accord with the properties of the four isomerides. On oxidation, the two alcohols boUing at 117*^ and 107° respectively yield acids with the same number of carbon atoms. They must therefore have the structures 1 and 3 (7Wd.), since each contains the group — CH2OH. For reasons referred to later, the alcohol boiling at 117® is considered to have the normal structiue (1), and that boil- ing at 107*^ the structure (3). A third butyl alcohol, boiling at 100*^, is converted by oxidation into a ketone with the same num- ber of carbon atoms, showing that it must be a secondary alcohol corresponding with structure (2). Lastly, for the fourth, which is solid at ordinary temperatures, melting at 25-5° and boiling at 83**, since three of the theoretically possible structural formulse have been assigned to the other isomerides, there remains only the fourth structure, that of a tertiary alcohol. This structure for the alcohol melting at 25* 5**, thus arrived at by elimination, is in accordance with its chemical behaviour. On oxidation, for exam- ple, it yields neither an acid nor a ketone with four carbon atoms, but the molecule is at once decomposed into substances containing a smaller number of carbon atoms. Since to yield on oxidation an acid with the same number of carbon atoms, an alcohol must contain the group — CH2OH, and to produce a ketone with the
same number of carbon atoms, it must contain the group H-C^OH,
I
it is evident that neither of these can be obtained from a tertiary alcohol. If the oxidation takes place in this, as in every other case, at the carbon atom already linked to oxygen, it must result in the decomposition of the molecule.
64 . ORGANIC CHEMISTRY. [§ 47
The foregoing holds for tertiary alcohols in general, so that oxidation affords a means of distinguishing between primary, secondary, and tertiary alcohols. The experimental proof can be summed up as follows.
A primary alcohol yields on oxidaiion an acid wUh the same number of carbon atoms: a secondary alcohol yields on oxidaiion a ketone vrith the same number of carbon atoms: whereas oxidation of a tertiary alcohol at once decomposes the molecule^ yielding com- pounds with a smaller number of carbon atoms.
Many other methods of ascertaining whether an alcohol is primary, secondary, or tertiary are available, one of the simplest being based on the effects of heat. Primary alcohols are stable at 360°, the boiling-point of mercury. At this temperature, secondary alcohols decompose, yielding chiefly hydrocarbons of the series CnH2n (112) and water; but they are stable at 218°, the boihng-point of naphthalene. At the last temperature tertiary alcohols are decomposed, yielding similar products to those formed from secondary alcohols at 360°. In practice, the constitution of any alcohol is ascertainable by determining its vapour-density at both these temperatures with Victor Meyer's apparatus (11), the decision being based on the normal or abnormal character of. the results obtained.
Amyl Alcohols, GsHh-OH.
47. The alcohols containing five carbon atoms are called amyl alcohols. There are eight possible isomerides, and all are known (cf. Table, 40). They are liquids with a disagreeable odour, like that of fusel-oil. woButylcarbinol, (CH3)2CH.CH2-CH20H, and secondary butylcarbinol, CH3-CH(C2H5)-CH20H, are the prin- cipal constituents of fusel-oil (43).
Secondary butylcarbinol furnishes a very remarkable example of isomerism. It is shown in 34 how the arrangement of the atoms in a molecule accounts for the phenomenon of isomer- ism. A careful study of the properties of a compound makes it possible to assign to it a structural formula, to the exclusion of all the other formulae' possible for its known molecular composi- tion. On the other hand, any given structural formula represents only one compound, since such a formula is the expression of
S 47] AMYL ALCOHOLS. 65
a very definite set of properties: when they are unlike for two compounds^ the difference must be indicated by their structural formulae.
Nevertheless, there are three isomeric amyl alcohols which have been shown by careful examination to have the same structural formula:
CH3 pr H
That they have this constitution is proved by the fact that on oxidation they yield valeric acid with the structure
CH3. p H C2H5>'"<CCX)H,
as can easily be proved by synthesis (164).
The three amyl alcohols with this constitution have identical chemical properties and nearly all their physical constants are the same. One of the latter, however, serves to distinguish them from one another. When a beam of plane-polarized light is passed through layers of these alcohols, the plane of polarization is rotated by one isomeride to the left, and by another to the right, while the third alcohol produces no rotation. The first two are said to be apticaUy active (261 2).
Since the difference between optically active compounds de- pends only upon a physical property, while their chemical proper- ties are identical, it may be asked whether this difference is not a purely physical one, arising from differences in the arrangement of the molecules, such as is supposed to exist in dimorphous sub- stances. The objection to this view is twofold.
First, differences in the arrangement of the molecules can only be supposed to exist in the case of solid substances, because it is only in them that the molecules have a fixed position in relation to one another. It is assumed that the molecules of liquids and gases are free to move; but they, too, afford examples of optical activity. For liquids there is still a possibility that not the mole- cules themselves, but conglomerations of them arranged in a defi- nite manner may be free to move. Were this the cause of optical activity, on conversion into gases of normal vapour-density, optic- ally active liquids should produce no rotation in the plane of polarization. That they actually do produce this rotation was
66 ORGANIC CHEMISTRY. [{ 48
proved by Biot, and later by Gernez. This phenomenon cannot be attributed to a difference in the arrangement of the molecules, because in a vapour of normal density each molecule is capable of independent motion.
Second, the optical activity is displayed in derivatives of optically active substances.
Hence it follows that an explanation of the rotation of the plane of polarization by liquids and dissolved substances must be sought for in the internal structure of the molecules,
48. Pasteur regarded optically active molecules as having an asymmetric structure, two configurations being possible. These forms are mirror-images, but cannot be superimposed, their rela- tionship resembling that of a right-handed and a left-handed glove. One of the configurations must belong to the dextro- rotatory isomeride, and the other to the laevo-rotatory modification.
Van 't Hoff imparted a more concrete form to this conception by his discovery of the presence in most optically active com- pounds of at least one carbon atom linked to four dissimilar atoms or groups. He has designated a carbon atom thus linked an asymmetric carbon atom.
When two of the groups attached to such an atom become similar, the asymmetry vanishes, and with it the optical activity of the compound. Consideration of an example will faciUtate the comprehension of this phenomenon.
The UtwHTotatory amyl alcoholy with the constitution
CHa p H
is converted by the action of gaseous hydriodic acid into amyl iodide^ with the structural formula
CHa^pj H
QiS.1 CHtl.
This compound is optically active. On treatment with nascent hydrogen, the iodine atom is replaced by hydrogen, with forma- tion of pentanCy
CHs^^ H
CjHa CHj.
This compound is optically inactive.
§ 48] AMYL ALCOHOLS. 67
If amy] iodide is subjected to the action of ethyl iodide in the presence of sodium, there results a heptane,
CiH» CHi * CiHty
and this substance is optically active.
An examination of these three optically active substances shows that they differ from optically inactive pentane in the respect that, of the four groups linked to the central carbon atom, in the latter two (methyl) are similar, whereas in the others they are all different.
Pasteur's molecular asymmetry for carbon compounds with an asynunetric carbon atom is explained by the following con- siderations.
The quadrivalency of the carbon atom has its origin in four points of attraction, situated on its outer surface, so th^t it is able to link itself to atoms or groups of atoms in four directions. The only supposition about these directions in agreement with the facts is that the carbon atom is situated at the centre of a regular four-sided figure (tetrahedron) with its lirtkings directed toward the angles (Fig. 24). By putting the groups R, P, and Q of com- pounds CR2Q2, CR2PQ, or CR3P in different positions in two atom models,* it is always possible by rotating the models to bring them into such a position that the like groups coincide, showing that the two forms are identical. Such compounds do not exhibit optical isomerism.
For compounds C»RPQS, containing four different groups and therefore an asynometric /
carbon atom, the possibility of the existence /
of two isomeric forms is indicated. It is-seen /J
from Figs. 25 and 26 (and still better from a^it^fii z^o
models) that for these four groups two arrange- ^'tetoahbdron ^ ments are possible, which cannot be made to
* The oomprehension of what follows will be considerably facilitated by the oonatruction of several models of carbon atoms with their linkings. This is easily done by cutting out a sphere from a cork to represent the carbon atom, the linkings being represented by moderately thick wires about ten centimetres long, with ends filed to a point. These wires are fixed in the cork sphere in the manner shown in Fig. 24. To show the linking of the atoms or groups of atoms, cork spheres of different colours are fastened to the ends of the wires, the different colours indicating dissimilar groups.
68
ORGANIC CHEMISTRY,
[§48
coincide in any position, although they resemble one another as an object resembles its reflection in a mirror. Such a figure has no plane of symmetry, hence the name " asymmetric carbon atom.'*
It is thus possible to \mderstand how one isomeride causes as much dextro -rotation as the other tevo-rotation, for the arrangement of the groups relative to the asymmetric carbon atom must be the cause of the rotation of the plane of polarization. If the arrangement of the groups in Fig. 25 produces dextro-rotation,
-<"
Fig. 25. Fia. 28.
Asymmetric C-atoms.
then the inverse arrangement in the isomeride in Fig. 26 must neces- sarily cause an equal rotation, but in an opposite direction.
It was stated above that not merely two, but three, isomerides are possible when there is one asymmetric carbon atom present in the molecule; a dextro-rotatory, a laevo-rotatory, and an optically inactive isomeride. It has been proved that the optically inactive substance is composed of equal parts of the dextro-rotatory and of the tevo-rotatory compound. Since these rotations are equal in amount, but different in direction, their sum has no effect upon the plane of polarization.
. This isomerism in space, called stereochemical isomerism or stereo- isomerism^ is not indicated in the ordinary structural formulae written in one plane: hence the apparent contradiction that a single structural formula may represent two different compounds. Van 't Hoff's theory, however, supports the fundamental prin- ciple that all isomerism has its origin in a difference in the arrange- ment of the atoms in the molecule.
In addition to the explanation of optical isomerism just given, two others might be suggested, although both can be shown to be untenable. Thus, the four linkings of the carbon atom might be supposed unequal in value; so that such a compound as CPsQ could
§§ 49, 50] HIGHER ALCOHOLS— ALKOX I DBS. 69
exist iti isomeric forms. Experience contradicts this assump- tion.
This phenomenon might also be supposed to be due to a differ- ence in the motion of the atoms in the molecule. Then isomerism could no longer exist at absolute zero, since atomic motion ceases at this point; and a falling temperature should cause 'a marked diminution in the difference between the optical isomerides. There is, however, not the slightest indication of such behaviour.
ler Alcohols, CnH22i+i*OH.
49* The properties of the higher alcohols are mentioned in 41. Here may be cited cetyl alcohol, CieHsa-OH, obtained from sper- maceti, and myricyl alcohol, CsoHei •OH, obtained from wax. The nimiber of isomerides of these higher compounds possible is very great, while the number actually known is but small. Of the higher members of the series, only the normal primary compounds are known.
Alkozides.
50. AVcoxides (alcoholates) are compounds obtained from alco^ hols by exchange of the hydroxyl-hydrogen atom for metals (39). The best known are sodium methoxide (methylate), CHa-ONa, and sodium eihoxide (ethylate), C2H6»ONa. Both are white powders, and yield crystalline compounds with the corresponding alcohol. They dissolve readily in the alcohols, and, as will be seen later, are constantly used in syntheses. It was formerly supposed that the addition of water to a solution of an alkoxide converted it com- pletely into an alkali-metal hydroxide, and liberated an equivalent quantity of alcohol; but Lobby de Bruyn has shown this to be only partly true, an equilibrium being reached in the reaction:
C^HgONa + HvO ^ CzHgOH + NaOH.
A proof of this is given in 55. It follows that a solution of sodium hydroxide in alcohol is partly decomposed into water and sodium alkoxJde.
The alcoholic solution of sodium ethoxide, usually obtained by dissolving pieces of sodium in absolute ethyl alcohol, gradually becomes brown in consequence of oxidation to aldehyde (106).
70 ORGANIC CHEMISTRY. [§ 60
On the other hand, the solution of sodium methoxide in methyl alcohol remains unaltered, and therefore is employed in syntheses more than that of sodium ethoxide.
Only the alkali-metals react directly with alcohols to produce aikoxides. Those of other metals can be prepared by the inter- action of solutions in liquid ammonia of a potassium alkoxide and a salt, an example being the precipitation of barium ethoxide by the combination of potassium ethoxide and barium nitrate:
2CH.0K +Ba(NO,), - (C,H,0)5Ba -f 2KN0,.
The aikoxides of calcium, strontium, and lead have been prepared similarly.
ALKYL HALIDES, ESTERS, AKD ETHERS.
51. Many compounds containing a hydroxyl-group are known in inorganic chemistry: they are called bases, and display a close resemblance in properties. This similarity may be attributed to their common possession of the group OH, which is present in their aqueous solutions as an ion.
An aqueous solution of alcohol does not conduct an electric current, so that the alcohol is not ionized. This is supported by the fact that such a solution is not alkaline, and therefore contains no OH-ions.
Notwithstanding this fact, the alcohols possess a basic charac* ter in so far that, like bases, they combine with acids with elimi- nation of water:
M. OH + H .R=M.R+HOH.
Alcohol Acid Ester
The substances formed are comparable with the salts of inor- ganic chemistry, and are called compound ethers or esters. The dif- ferent natures of bases and of alcohols are displayed, however, in the mode of formation of their salts, which is quite unlike that in which esters are produced. A salt is formed from an acid and base instantaneously: it is a reaction of the ions, because the hydrogen ion of the acid unites with the hydroxyl ion of the base ("Inorganic Chemistry," 66):
[B+OHT+[H+Z']=[6+ZT+H20.
fiaae Aoid Salt
The formation of esters, on the other hand, takes place very slowly, especially at ordinary temperatures, the reaction being between the non-ionized alcohol and the acid:
R.0H+[H+Zq=R.Z+H20.
Akohol Add Ertar
71
72 ORGANIC CHEMISTRY. [§ 52
Reactions between ions usually take place instantaneously, those between molecules slowly.
Many bases can lose water, with fonnation of anhydrides or oxides: alcohols behave similarly. By the abstraction of one molecule of water from two molecules of an alcohol, compounds called ethers with the general formula CnH2n+i — 0 — CnH2„^.i are formed. By elimination of water from two different alcohols, com- pounds called mixed ethers with the general formula
CnH2n+l — 0 — CnjH2m+l
are produced.
Alkyl Halides.
$2. The alkyl halides may be regarded as the hydrogen-halide esters of the alcohols, as their formation from alcohol and a hydro- gen halide shows:
CnH2^.nfOHTHiX = CnHsn+iX+HgO.
In preparing alkyl halides by this method, the alcohol is first saturated with the dry hydrogen halide, and then heated in a sealed tube or under a reflux-condenser. The reaction may also be carried out by heating the alcohol with sulphuric acid and sodium or potassium halide:
C2H60H+H2S04+KBr = C2H6Br+KHS04+H20.
Two other methods of formation for alkyl halides are men- tioned in 28 and 39: they are more fully treated below.
Action of Phosphorus Halides on Alcohols, — ^These sometimes react together very energetically. In preparing alkyl bromides and iodides, it is usual to employ phosphorus with bromine or iodine instead of the bromide or iodide of phosphorus itself. For example, in the preparation of ethyl bromide, red phosphorus is added to strong alcohol, in which it is insoluble. Bromine is then added drop by drop, the temperatm^ of the liquid being kept from rising by a cooling agent. Each drop of bromine unites with phosphorus to form phosphorus tribromide, and it reacts with the alcohol, producing ethyl bromide:
PBrs+SCzHfiOH = POaHs+SCaHfiBr.
The careful addition of bromine is continued until a. quantity cor- responding to that required by the equation has been used. The
§63] ALKYL MALI DBS. 73
mixture is then allowed to stand for some time^ so that the reac- tion may be as complete as possible, the final product consisting chiefly of phosphorous acid and ethyl bromide. Since the latter boils at 38*4°, and the acid is not volatile, it is possible to separate them by distillation, which can be effected by immersing the flask containing the mixture in a water-bath heated above the tempera- ture mentioned.
Action of Halogens on Hydrocarbons. — Only chlorides and bromides can be prepared thus, because iodine does not react with hydrocarbons. The method is seldom used for the preparation of alkyl halides, since, from two causes, mixtures of alkyl halides are obtained which are sometimes very difficult to separate: whereas, by employing other methods,' these compounds are produced with- out admixture of similar substances.
One of these causes is that whenever one molecule of a hydro- carbon CnH2n+2 ^ brought into contact with one molecule of chlo- rine or bromine, the reaction does not take place merely as indi- cated by the equation
CnH2m.2+Cl2 = CnH2ii+iCl4-HCl,
but that compounds CttH2nCl2, CnH2„_iCl3, etc., are simultaneously formed, a portion of the hydrocarbon remaining unacted on.
ScHORLEMMER obscrved the possibility of avoiding the formation of these higher substitution-products by bringing the halogens into contact with the vapour of the boiling hydrocarbons.
The other cause is that the halogen replaces hydrogen in dif- ferent positions in the molecule. Thus, chlorine reacts with nor- mal pentane to form simultaneously primary and secondary amyl chlorides,
C/il3 • CH2 • C112 • CH2 • CH2CI and CH3-CH2*CH2*CHC1»CH3,
as can be proved by conveHing these chlorides into the corre- sponding alcohols and oxidizing the latter (45).
53. The following table gives some of the physical properties of the alkyl halides,
74
ORGANIC CHEMISTRY,
[§S3
|
• |
Name. |
Chloride. |
Bromide. |
Iodide. |
|||
|
5 |
Boiling- point. |
Specific Gravity |
Boiling- point. |
Specific Gravity. |
Boiling- point. |
Specific Gravity. |
|
|
CH, C,H. C.H, C,H, C5H11 |
Methyl Ethyl n-Propyl /i-Prim. butyl F*-Prim. amyl |
-23.7** 12.2** 46.5** 78** 107** |
0.952(0**) 0.918(8**) 0.912(0**; 0.907(0**) 0.901(0**; |
4.5** 38.4** 71** 101** 129** |
1.732(0**) 1.468(13**) 1.383(0**) 1.305(0**) 1.246(0**) |
45** 72.3** 102.5** 130** 156** |
2.293(18**) 1.944(14**) 1.786(0**) 1.643(0**) 1.643(0") |
It will be noticed that only the lower chlorides and methyl bromide are gaseous at the ordinary temperature, most of the others being liquids, and the highest members solids. The melting-points of some of these compounds have been determined accurately:
|
Alkyl-Group. |
Name. |
Chloride. |
Bromide. |
Iodide. 1 |
|
CH, coi. CH, |
Methyl Ethyl n-Propyl |
-103.6** -140.85** -122.6'* |
- 96.8" -119.0** -109.85** |
- 66.1** -110.9** -101.4** |
The specific gravities of all the chlorides are less than 1, and diminish as the number of carbon atoms increases. The specific gravities of the lower bromides and iodides are considerably greater than 1, although they also diminish with increase in the number of carbon atoms, so that the highest members of the homologous series are specifically lighter than water. All are very slightly soluble in water, but dissolve readily in many organic solvents. The lower members have a pleasant ethereal odour.
Chemical Properties. — In their action upon silver nitrate the alkyl halides differ very much from the halides of the metals. In aqueous or alcoholic solution the latter at once yield a precipitate of silver halide, the reaction being quantitative. On the other hand, silver nitrate either does not precipitate silver halide from a solution of the alkyl halides, or the reaction only takes place slowly. The explanation is the same as that given in 51, that in the first case the action is one between ions, and in the second between molecules. This proves that there are either no halogen
§ 54] ETHYLSULPHURIC ACID. 75
ions present in an alkyl halide solution, or at least that their number is very small.
The alkyl halides can be converted into one another; for example, alkyl iodides can be obtained by heating the corre- sponding chlorides with potassium or calcium iodide. These reactions are often incomplete.
The alkyl iodides are chiefly used for introducing alkyl-groups into organic compounds:
Alkyl fluorides are also known, and are more volatile than the corresponding chlorides. They are obtained by the action of silver fluoride on an alkyl iodide, and in other ways.
Esters of Other Mineral Acids.
54* Esters of a great number of mineral acids are known. The general methods for their preparation are as follows. 1. By the action of the acid on absolute alcohol:
C2H5>|OH+H|.ON02 « HgO+CaHft.ONOa.
Alcohol Nitric add Etliyl nitrate
2. By the action of an alkyl halide on a silver salt:
S04[Ag2+21jC2Hfi = S04(C2H5)2+2Agl.
Etliyl Hulptiate
3. By the action of mineral-acid chlorides on alcohols or alkox- ides:
PO
Cl3+3Na OC2H5 = PO(OC2H5)3+3Naa.
Phosphorus Normal ethyl
oxyenloride phosphate
The acid esters of sulphuric acid, called alkylsiUphuric acids, are of some importance. Ethylmlphuric acid, or ethyl hydrogen aidphate, C2H60«S02-OH, is obtained by mixing alcohol with con- centrated sulphuric acid. The formation of this compound is never quantitative, because an equilibrium is reached in the reaction (93). The alkylsulphuric acids are separated from the excess of sulphuric acid by means of their barium (or strontium or calcium) salts, these compounds being readily soluble in water, while the sulphates are insoluble, or nearly so. It is only necessary to neutralize the mixture of sulphuric acid and alkylsulphuric acid
76 ORGANIC CHEMISTJtY. [§ 64
with barium carbonate, the product being a solution of barium
ethylsulphate, q jj >S04. The free ethylsulphuric acid is then
obtained by the addition of the calculated quantity of sulphurio acid to this solution. At ordinary temperatures it is an odour* less, oily, strongly acid liquid, miscible with water in all propor- tions. The aqueous solution decomposes into sulphuric acid and alcohol, slowly at the ordinary temperature, but quickly at the boiling-point.
Ethylsulphuric acid forms well-crystallized salts. Its potas- sium salt is used in the preparation of ethyl compounds; for exam- ple, ethyl bromide is readily prepared by the dry distillation of a mixture of potassium bromide and potassium ethylsulphate:
KCSOz-O-lCaHft + BrlK « KO.SOz-OK+CzHgBr.
Potassium ethyl- Potassium Ethyl
sulphate sulphate bromide
When free ethylsulphuric acid is heated, the neutral ethyl ester of sulphuric acid and free sulphuric acid are formed:
S0.<gg2H«^S0,<gJ^jj^ - S02<8g+SO,<gC.H.,
Simultaneously, free sulphuric acid and ethylene are produced (115):
The conversion of ethylsulphuric acid into ether is described
in 5^*
Dimethyl sulphate j (CHj)2S04, is obtained by the vacuum-dis- tillation of methylsulphuric acid:
2CH,HS04 = (CH3),S04 +H2SO4.
It is an oily, very poisonous liquid, boiling at 188^, and is often em- ployed in the introduction of methyl-groups into organic compounds.
• Ka^
ba»iBa.
§§56,66] ETHERS, 77
Ethers,
55. The ethers are isomeric with the alcohols. Their con« stitution is proved by Williamson's synthesis^ the action of an alkoxide on an alkyl halide;
CnH2„+i -O. (NaTl| .C„H2«+i « C„H2„+, .O-C^Ha^+i +NaI.
This synthesis affords confirmation of the constitution of the alkoxides indicated in 39, that the metal occupies the place of the hydroxyl-hydrogen. For, supposing it were otherwise, the metal having replaced a hydrogen atom directly linked to carbon, then sodium methoxide, for example, would have the formula Na -0112 -OH. On treatment with ethyl iodide, this compound would yield propyl alcohol:
CzHg^lI-hNal^CHaOH - C2H6-CH20H+NaI.
This reaction does not take place. Methylethyl ether, with the empirical formula of an alcohol, but none of its properties, is pro* duced instead.
Williamson's synthesis is also possible when the alkoxide is dis- solved in dilute alcohol (50 per cent.). Though so much water is present, the reaction is almost quantitative. It follows that the greater part of the sodium alkoxide must be present as such, and is therefore not decomposed by the water into alcohol and sodium hydroxide (50), because then the formation of the ether would neces- sarily be prevented.
56. The best-known compound of the homologous series of ethers is diethyl ether, C2H6'0-C2H6, usually called "ether." This compound is manufactured, and also prepared in the labora- tory, from sulphuric acid and ethyl alcohol. For this purpose a mixture of five parts of alcohol (90 per cent.) is heated with nine parts of concentrated sulphuric acid at 130^-140®. When ether and water begin to distil, alcohol is allowed to flow into the dis- tillation-flask to keep the volume of liquid constant. Ether passes over continuously, but after about six times as much alcohol has been added as was in the first instance mixed with the sulphuric acid«the distillate becomes richer and richer in alcohol, and finally
78 ORGANIC CHEMISTRY. [§ 56
the formation of ether stops altogether. Methylated gpirit may be substituted for pure spirit, the product being called "methylated ether."
The explanation of this process is as follows. The alcohol and sulphuric acid first form ethylsulphuric acid (54). Ethylsulphuric acid is decomposed by heating with water, the acid and .alcohol being regenerated:
CgHs'lOSOsHTHlOH - C2H6.OH+H2SO4.
When, however, ethyl alcohol instead of water reacts with ethyl- sulphuric acid, ether and sulphuric acid are formed in an exactly analogous manner:
CgHg-IO-SOsHTHl^O-CzHg - C2H6.O.C2H6+H2SO4.
The production of ether depends upon the formation of ethyl- sulphuric acid, and subsequent decomposition of this compound into ethyl ether and sulphuric acid by the addition of more alcohol. Since the sulphuric acid is regenerated in this reaction, it yields a fresh quantity of ethylsulphuric acid, so that the process is con- tinuous. This would lead to the expectation that a small quan« tity of sulphuric acid could convert an unlimited amount of alco- hol into ether, but this is not borne out by experience. The explanation is that in the formation of ethylsulphuric acid from alcohol and sulphuric acid, water is formed as a by-product:
C2H5. OH+H SO4H - C2H5-S04H4-H20.
This water partly distils along with the ether, but partly remains in the flask, decomposing the ethylsulphuric acid as formed into alcohol and sulphuric acid. When the amount of water in the reaction-mixture exceeds a certain limit, it prevents the formation of ethylsulphuric acid altogether, thus putting an end to the pro- duction of ether.
When another alcohol is allowed to flow into the original mix- ture instead of ethyl alcohol, shortly before the distillation begins, a mixed ether is obtained:
C2Hg-|S04H-hHl>0*CfiHii - C2H5-O.C5H„+H2S04.
§ 561 ETHERS. 79
This reaction proves that the formation of ether takes place in the two stages mentioned above.
Senderens foimd that addition to the liquid of 5 per cent, of its weight of sulphate of almninium or lead causes the forma- tion of ether smoothly at 120°.
Ethyl ether is also formed by passing alcohol-vapour over aluminium oxide at 240^-260®.
Higher homologues of ethyl ether cannot be prepared by heat- ing the higher alcohols with sulphuric acid, even in presence of the sulphates named, only unsaturated hydrocarbons of the series CnHan being produced. These higher ethers must be prepared by the interaction of alkyl halides and metallic alkoxides.
The crude ether thus obtained contains water, alcohol, and small quantities of sulphur dioxide. It is left in contact with quicklime for several days, the water, sulphur dioxide, and part of the alcohol being thus removed. It is then distilled from a water-bath heated to about 55**. To remove the small quantity of alcohol remaining, it is extracted several times with small volumes of water, and the water run off. The ether is separated from dissolved water by dis- tillation, first over calciimi chloride and finally over sodium.
Diethyl ether is a colourless, very mobile liquid of agreeable odour, boiling at 35»4°, and solidifying at —117-6°. Pro- longed breathing of it produces unconsciousness, followed by but slightly disagreeable consequences on awakening. Ether is there- fore used in surgery as an anaesthetic. It is slightly soluble in water, one volume dissolving in 11-1 volumes of water at 25°; water also dissolves slightly in ether (2 per cent, by volume at 12°). On account of its low boiling-point, ether is very volatile, and as its vapour is highly combustible, burning with a luminous flame, and producing an explosive mixture with air, it is a substance requiring very careful handling. Intense cold is produced by its evaporation, the outside of a flask containing it becoming coated with ice when the evaporation of the ether is promoted by the introduction of a rapid stream of air.
In the laboratory, ether is an invaluable solvent and crystal- lizing-medium for many compounds, and is used for extracting aqueous solutions (23). It is also of great utility in many manu- facturing processes.
AlETL-RADICALS LINKED TO SULPHUR.
57. The elements grouped in the same column of the periodic system ("Inorgam'cChemistry/'2i6-22i) jdeld similar compounds, a fact traceable to their having equal valencies: they also have similar chemical properties. Experience has shown that organic compounds containing elements of such a group display the proper- ties of their inorganic analogues in every variety of similarity and dissimilarity; their points of resemblance and of difference being sometimes even more marked than those of the inorganic com- pounds. A comparison of the oxygen compounds treated of up to this point with the sulphur compounds of similar structure will serve as an example.
The alcohols and ethers may be regarded as derived from water by the replacement of one or both of its hydrogen atoms by alkyl. The corresponding sulphur compounds are similarly derived from sulphuretted hydrogen, and are represented thus:
CftH2ii +1 • SH and CnH2B +1 • S • CqiHsbi +1 •
The first are called mercaptans, and the second thioethers.
The resemblance of these compounds to the alcohols and ethers is chiefly noticeable in their methods of formation, for if potas- sium hydrogen sulphide instead of potassium hydroxide reacts with an alkyl halide, a mercaptan is formed:
C^H2ii+i* X-hK|*SH =a CnH2ii4.i«SH+KX.
Like the alcohols, the mercaptans have one, and only one, hydrogen atom in the molecule replaceable by metals. It is there- fore reasonable to suppose that the hydrogen atom thus distin- guished from all the others is linked t^ oulphur,tbe other hydrogen atoms being linked to carbon.
80
§681 MERCAPTAN8. 81
Just as the ethers are formed by the action of alkyl halides on alkoxides; so the thioethers are obtained by treating the metallic compounds of the mercaptans, the mercaptidea, with alkyl halides:
CnH2n+l*S« Na + I •CmH2ni+l = CnH2n+l 'S-CmHain+l 4-NaI.
Water is a neutral compound, and sulphuretted hydrogen is a weak acid; in consequence alcohol does not form alkoxides with the bases of the heavy metals, whereas mercaptans yield mercap- tides with them. An alcohol soluble with difficulty in water, such as amyl alcohol, does not dissolve in alkalis; but the mercaptans, although insoluble in water, dissolve readily in alkalis, forming mercaptides. They therefore possess an acidic character.
Mercaptans.
58. The mercaptans can also be obtained by the action of phos- phorus pentasulphide upon alcohols:
5CnH2ii +1 • OH 4- P2S6 —* 5CnH2ii +1 • SH ;
or by distilling a solution of potassium alkylsulphate with potas- sium hydrogen sulphide:
C2H5>|o»so3kTk:]sh = C2H5.SH+K2SO4.
They are liquids almost insoluble in water, with boiling-points markedly lower than those of the corresponding alcohols. Thus, methyl mercaptan boils at 6°, methyl alcohol at 66^, a striking phenomenon, sulphur being much less volatile than oxygen. It may be explained by assuming non-association of the mercaptan molecules, and association of the alcohol molecules. The mercap- tans are characterized by their exceedingly disagreeable odour, a property characteristic of almost all volatile sulphur compoimds. Our olfactory organs are very sensitive to mercaptans, and can detect the merest* traces of them, although quite unrecognizable by chemical means. The smell of the perfectly pure mercaptans is much less objectionable than that of the crude products.
Many metallic compounds of the mercaptans are known, some of them in well-cry staJli zed forms. The mercury mercaptides fur- nish an example of these bodies, and are produced by the action of mercaptans on mercuric oxide, whence the name of these com- pounds is derived (by shortening corpus mercurio apium to nur-
82 ORGANIC CHEMISTRY. [{ 69
captan). Many of the other heavy metals, such as lead, copper, and bismuth, yield mercaptides: the lead compounds have a yellow colour. The mercaptan is liberated from all mercap* tides by the addition of mineral acids.
Thioethers.
59* In addition to the methods given in 57 for the preparation of thioethers, the action of potassium sulphide, KtS, upon the salts of alkylsulphuric acids may be employed:
2aH5 O • SO J^ +K, S = (C ^1^)28 H-2K,S04.
Potassium ethylsulphate
The thioethers are neutral compounds with an exceedingly offen- sive odour, eliminated by heating with copper-powder. They are liquids insoluble in water, and yield double compounds with metallic salts, such as (C2H6)tS.HgCU.
With one molecule of an alkyl iodide the thioethers form remark- able crystalline compounds of the type (C2H5)3SI. These com- pounds, called sulphonium iodides, are readily soluble in water. Moist silver oxide replaces the I-atom by hydroxyl :
(C2H,)3SI + AgOH - (C2H5)3SOH+AgI.
The sidphonium hydroxides thus obtained dissolve easily in water, and are very alkaline in reaction. They are strong bases, absorbing carbon dioxide from the air, and yielding salts with acids. In the sulphonium halides, such as (02115)38 -CI, sulphur is the only element to which the univalent alkyl-groups and univalent 01-atom can be united, so that these substances must have constitutional formulae of the type
S
The mercaptans resemble sulphuretted hydrogen in being slowly oxidized by contact with air, whereby they are converted into disul- phides like diethyl disulphide,
O2H5 "S 'S •O2H5.
The hydrogen linked to sulphur has been removed by oxidation, so
§ 60] SULPHONIC ACIDS. 83
that the disulphides have the constitution given above. A further proof is their formation when potassium ethylsulphate is heated with potassium disulphide, KsSs.
Some inorganic compounds containing oxygen and sulphur exist. Similar substances are also known in organic chemistry.
The svlphoxides, ^°tt^°''"*>SO, are formed by the oxidation of
thioethers with nitric acid. Their constitution is indicated by the
fact that they are very easily reduced to thioethers. If the oxygen
were linked to carbon, they would not behave in this manner, because
neither alcohols nor ethers lose their oxygen by gentle reduction.
C H The svlphones are compounds with theconstitution r>,°TT^ "*" ^ > SOj,
as shown in 6o. They are formed by energetic oxidation of the thioethers, and also by oxidizing sulphoxides. Nascent hydrogen is unable to effect their reduction.
Sulphonic Acids.
6o. The sulphonic acids result when mercaptans undergo vigorous oxidation (with nitric acid). They have the formula CnHsn+i -SOaH. During this oxidation the alkyl-group remains intact, lor the salts of these sulphonic acids are also formed by interaction of an alkyl iodide and a sulphite:
CaH,[r+K|SO.K - KI +C3H^0,K.
Since the sulphur in mercaptans is directly linked to carbon, the same is true of the sulphonic acids. This is further proved by the fact that on reduction the latter 3ield mercaptans. The struc- ture of ethylsul phonic acid is therefore CHg-CHj-SOaH.
The group SO,H must contain a hydroxyl-group, because PQj 3nelds with a sulphonic acid a sulphonyl chl )ride, CnH2n + i*S02Cl, from which the sulphonic acid may be regenerated by the action of water. The structure of the compound is therefore
CH,CH,.SO,.OH.
The alkylsulphonic acids are strongly acidic, very hygroscopic, crystalline substances, and are very soluble in water.
In the sulphonyl chlorides, chlorine can be replaced by hydrogen in the nascent state. The bodies thus obtained have the formula CnH2n+i-S02H, and are called sulphinic acids. When an alkyl halide reacts with the sodium salt of a sulphinic acid, a sulphone (59) is formed :
84 ORGANIC CHEMISTRY. {§ 60
C,H,SO,|Na+Br|C,H> = ^]^»> SO, + NaBr.
This mode of preparation is a proof of the constitution of the sulphones.
Selenium and teUwrium compounds corresponding to most of these sulphur compounds are known, and have also a most offensive odour.
ALEYL-RADICALS LINKED TO NITROGEN.
L AMINES.
6i . At the beginning of the last chapter (57) it was stated that the properties possessed by inorganic compounds are even more marked in their organic derivatives. The compounds to be described in this chapter afford another striking example of this phenomenon.
The term amines is applied to substances which may be regarded as derived from ammonia by exchange of hydrogen for alkyl-radi- cals. The most characteristic property of ammonia is its power of combining with acids to form salts by direct addition:
NH3+H.X=NH4.X.
Tervalent nitrogen is thereby made quinquivalent, a change ap- parently intimately connected with its basic character. This property is also found among the alkylamines. They are, at least those low in the series, better conductors of electricity for the same molecular concentration of their aqueous solutions, and are therefore more strongly basic than ammonia itself ("Inorganic Chemistry," 66 and 238). This applies also to the organic com- pounds corresponding to ammonium hydroxide, NH4OH. The last- named substance is not known in the free state, but it exists in the aqueous solution of ammonia. It b very unstable, being com- pletely der^omposed into water and ammonia by boiling its solu- tion. It has only weakly basic properties, because there are but few NH4-ions and OH-ions in its aqueous solution, apparently because the compound NH4OH has a very strong tendency to break up into NH3 and H2O. Such a decomposition is, however, no longer possible for compounds containing four alkyl-groups in place of the four hydrogen atoms of the NH^-group, and experi- ence has shown that these compounds possess great stability. Since the nitrogen cannot revert to the tervalent condition, their
• 85
86 ORGANIC CHEMISTRY. [§S 62, 63
basic character, in comparison with that of NH4OH, is so strength- ened that they are ionized to the same degree as the alkalis, being almost completely dissociated in j^^f-normai solutions.
The amines yield complex salts fully analogous to the platinum salt, (NH4)2PtCla, and the gold salt, NH4AUCI4, of ammonia.
Nomenclature and Isomerism.
62. The amines are called 'primary, secondary , or ^tertiary, according to whether one, two, or three hydrogen atoms of NH3 have been exchanged for alkyl-radicals. The compounds NR4OH, in which R stands for an alkyl-radical, are called quaternary am- monium bases.
Isomerism of the amines may be due to different causes. First, to branching of the carbon chain, just as in the alcohols and other compounds. Second, to the position occupied by the nitrogen in the molecule. Third, to both causes simultaneously. In addition to these, the primary, secondary, and tertiary nature of the amines must be taken into account. A compound C3H9N, for example, can be propylamine or tsopropylamine, CH3«CH2«CH2'NH2 or
^5'>CH.NH2, primary; methylethylamine, q j| >NH, second-
CH3V ary ; or trimethylamine, CHa-^N, tertiary.
CH3/
Methods of Formation.
63. HoFMANN discovered that when an alcoholic or aqueous solution of ammonia is heated with an alkyl halidc, the following reactions take place:
I. CnH2n+i-Cl-hpNH8 = C„H2„+i-NH2,Ha-h(p-l)NH3.
The alkyl halidc is added to ammonia, NH3, a reaction analogous to the formation of ammonium chloride, NH4CI, from ammonia, NH3, and hydrochloric acid, HCl. Part of the resulting hydro- chloride is decomposed by ammonia, with liberation of the
§031 AMINES, 87
primary amine, the free base reacting with the alkyl halide in accordance with equation II. :
II. C„H2n+l • CI + CnH2n+l • NHg = (CnH2n+l)2NH,HCl.
Part of the secondary amine thus produced is also set free, and reacts according to equation III.:
III. C„H2n+i -01+ (C„H2n+l)2NH = (CbH2»+i)3N,HC1.
The tertiary amine is also partly liberated, and reacts with the alkyl halide to yield the halide of a quaternary ammonium base :
IV. (CaH2n+2)8N-hCnH2„+l-a= (C„H2„+l)4N.Cl.
It is assumed that excess of ammonia is employed; but even when it is otherwise, and in general for every proportion of alkyl halide and ammonia, the reaction takes place in these four phases. The final result is, therefore, that the primary, secondary, and ter- tiary amines, and the ammonium base, are formed together. It is often possible, however, so to adjust the proportion of ammonia and alkyl halide, together with the duration of the reaction, etc., that a given amine is the main product, and the quantities of the other amines are small. The nature of the alkyl-group also exer- cises a great influence upon the character of the reaction-product.
The separation of the ammonium bases from the ammonia and amines is simple, because, while the amines are liquids volatilizing without decomposition, or gases, the ammonium bases are not vol- atile. When, therefore, the mixture of the amine hydrohalides and the ammonium bases is distilled after addition of caustic potash, only the free amines pass over.
To separate the primary amines from the mixture of the hydrohalides of the three amines, fractional crystallization is often employed for the lower members, methylamine, dimethylamine, and 80 on. The propylamines and those succeeding can be sepa- rated by fractional distillation.
Various methods of preparing primary amines unmixed with secondary or tertiary are known (78, 96, 259, 268, and 349),
88 OBGANIC CHEMISTRY, [\ G4
64. The velocity of the formation of tetraalkylammonium iodides from triethylamine and an alkyl iodide or bromide has been investigated by Menschutkin. It is apparently a bimolecular reaction (" Inorganic Chemistry," 50) and therefore takes place according to the equation
« =-jT- = A;(a— x) (6— x),
where s is the velocity, k the constant of the reaction, a and b the quantitites of amine and iodide per unit volume expressed in molecules, and x the quantity of both which has entered into reaction after the time t. Solution of this equation by the integral calculus gives
I standing for the natural logarithm.
For the investigation of these velocities, weighed quantities of the amine and iodide are brought into contact in a suitable solvent, and the solution heated in a sealed tube at 100*^, x being determined after the lapse of known intervals of time t. The value of k is found to be constant for every reaction: that is, if corresponding sets of values are substituted for t and x in the equation, on solving it the same value is always obtained for fc. The greater the molecular weight of the alkyl-radical, the smaller is k, although the decrease is not very marked : for example, when the amine reacts with propyl bromide, A;=0«00165; with octyl bromide fc=0-00110 (with acetone as solvent). The equation is always applicable, being independent of the solvent used, as might be expected from the fact that it does not contain any term dependent upon the nature of the solvent. There was made, however, an unexpected observation of the extraordinarily great influence exercised by the nature of the solvent upon the values of k. Using hexane as a solvent, k =0 • 000180 for the combination of triethylamine and ethyl iodide: for methyl alcohol, on the other hand, A; =0-0516, or 286 -6 times as great.
In many other instances the nature of the solvent exercises an important influence upon the velocity of ^reaction, but a satis- factory explanation of the phenomenon is still lacking.
§66]
AMINES.
89
Properties.
65. The primary, secondary, and tertiary amines are sharply distinguished from one another by their different behaviour towards nitrous acid, HO -NO.
Primary amines yield alcohols, with evolution of nitrogen:
CnH2n+l
-rOH
N N
H2 O
-C„H2n+i-OHH-N2+H20.
The reaction is fully analogous to the decomposition of ammonium nitrite into water and nitrogen:
NH3.HONO
H. HO
N N
H2 O
2H20+N2,
Secondary amines yield nitrosoamines:
(CnH2n.n)2N[HTHOlNO == (C„H2„+,)2N.N0+H20.
The lower members are yellowish liquids of characteristic odour, and are slightly soluble in water. They are easily reconverted into secondary amines by the action of concentrated hydrochloric acid (298) : this is a proof of the structure given above, because if the nitroso-group were directly linked to a carbon atom either by its oxygen or by its nitrogen, it would not be possible thus to recon- vert the nitrosoamine into a secondary amine.
Tertiary amines are either imacted on, or oxidized, by nitrous acid.
Their behaviour with nitrous acid therefore affords a means of distinguishing the three classes of amines from one another. It also serves as a basis for the separation of the secondary and ter- tiary amines in the pure state from a mixture of the two. When a concentrated solution of sodium nitrite is added to a hydrochloric- acid solution of a mixture of the two amines, the secondary amine is converted into a nitrosoamine: this collects as an oil on the sur- face of the aqueous solution, and can be removed by means of a separating-funnel. The tertiary amine is not attacked, but re- mains in the aqueous solution in the form of a salt: it can be obtained by distilling with caustic potash. Any primary amine present is decomposed during the process.
90
ORGANIC CHEMISTRY.
[S66
Another method of distinguishing between primary, secondary, and tertiary amines consists in the determination of the number of alkyl-groups'with which the amine can combine. For example, if a compound C3H9N is propylamine, C3H7NH2, it should yield, when heated with excess of methyl iodide, a compound
(CH3)3^^
CaHieNI:
C,H
or if C3H0N = QTT^>NH, the same treatment should yield
rrw^^NI = CfiHuNI : or lastly, if C3H9N = (CH3) 3N, there would be
obtained (CH3)4NI=C4Hi2NI. A titration of the iodine ion of the quaternary ammonium iodide formed determines whether C3H9N is primary, secondary, or tertiary.
Hofmann's test for primary amines is described in 77.
Individual Members.
66, The lower members are inflammable gases, and are very soluble in water; thus, 1150 volumes of methylamine dissolve in one volume of water at 12-5®. The succeeding members have low boiling-points, and are miscible with water in all proportions. Both they and the lower members have a characteristic ammo- niacal odour, like boiled lobsters. The higher members are odour- less and insoluble in water. The specific gravities of the amines are considerably less than 1, that of methylamine being only 0-699 at— 11°. The following table indicates the variations of their boiling-points.
Alkyl-RadicaL
Methyl
Ethyl
n-Propyl
n-Butyi
7i-Octyl
Primary.
-6^ 180**
Secondary.
70
98*» 160*» 297*»
Tertiary.
3.5*
90«
156^
216<»
366*
Methylamine occurs in MercuricUis perennis: it is readily pre- pared by the interaction of ammonia and dimethyl sulphate. Di- methylamine (299) and trimethylamine are constituents of herring- brine.
$67] . AMINES, 91
Trimethylamine, (CHs)sN, can be readily prepared by heating ammonium chloride with formaldehyde ("Formahn/' xo8) in an autoclave at 120^-160**:
2NHj+9CH,0 -2(CH,)3N +3CO,+3H,0.
Tetramethylammonium hydroxide^ (CH3)4N«OH, is obtained by treating a solution of the corresponding chloride in methyl alcohol with the equivalent quantity of caustic potash. After filtering off the precipitated potassium chloride, the solution is diluted with water, and evaporated in vacuo at 35° to remove the alcohol. The base crystallizes out as hydrates, which are very hygroscopic and absorb carbon dioxide readily. It is decomposed by heat into trimethylamine and methyl alcohol:
(CH3)4N.OH = (CH3)3N+CH80H.
The higher ammonium bases are converted by dry distillation into a tertiary amine, water, and a hydrocarbon CnH2ii:
(C2H6)4N .OH = (C2H5)3N +C2H4 +H2O.
Triethylamioe Ethylene
The structure of the ammonium bases is thus explained. Only the nitrogen atom is able to link to itself the four univalent alkyl- groups and the univalent hydroxyl-group. It must be assumed to be quinquivalent in these compounds, and the constitution of the ammonium bases is therefore
TJu^^tV OH n, m, p, and r being similar or dissimilar.
67. Alkyl-derivatives of hydrazine or diamicfe, HjN -NHj, are also known. Among the methods for their preparation may be men- tioned the direct introduction of an alkyl-group into hydrazine, and the careful reduction of nitrosoamines (65). They have little power of resisting oxidizing agents, reducing an alkaline copper solution, for example, at the ordinary temperature.
92 ORGANIC CHEMISTRY. [§ 68
• n. NITRO-COMPOUNDS.
68. When silver nitrite reacts with an alkvl iodide, two com- pounds ar^ formed, both with the empirical formula CnH2n+iN02, but having different boiling-points. From ethyl iodide, for ex- ample, a substance C2H5NO2, boiling at 17°, and another boiling at 113°-114°. are obtained. The two isomerides are therefore read- ily separated by fractionation.
The compound of lower boiling-point is decomposed into alcohol and nitrous acid by the action of caustic potash. It must there- fore be looked upon as an ester of nitrous acid, being formed thus;
C„H2n+i[rTAg).0N0 = C„H2„^.i.0N0-hAgI.
When these esters, or alkyl nitrites, are reduced, they are con- verted into an alcohol and ammonia.
The compound boiling at the higher temperature behaves quite differently. It is not converted into a nitrite and alcohol by the action of alkalis, and on reduction its two oxygen atoms are replaced by two hydrogen atoms, with formation of a primary amine;
CnH2n+lN02^C„H2n+lNH2.
The last reaction shows that the nitrogen in this class of compounds is directly linked to carbon, because it is so in the amines. The oxygen atoms can be linked only to the nitrogen, because the reduction to amine takes place at the ordinary tem- perature. Under these conditions it is not possible to replace oxygen directly linked to carbon, for neither alcohols nor ethers are reduced at low temperatures to substances not containing oxygen. This leads to the conclusion that these substances, called nitro-compounds, have the constitution CnH2n+i — NO2.
Nitro-compounds therefore contain a group NO2, the nitrogen atom being directly linked to carbon; this group is called the nitro^oup.
The generation of nitrite and nitro-compound may be explained by ajssuming the production of the nitrite to be a regular ionic reaction, and that of the nitro-compound to be preceded by the
Ag-O-N-0 formation of an addition-product, /\ , subsequently
I C,H, decomposed with fission of silver iodide.
§ 69] NITRO-COMPOUNDS, 93
It has, in fact, been stated that a dilute, aqueous solution of potassium nitrite is converted by dimethyl sulphate into methyl nitrite only, but that a concentrated solution yields up to 25 per cent, of nitromethane.
The names of these compounds are formed from those of the saturated hydrocarbons by means of the prefix nitro. The com- pound CH^N02 is thus nitromethane; C2H5NO2 is nitroethane; and so on. The members of this homologous series are called nitro- paraffins. They are colourless liquids of ethereal odour: the lower members are slightly soluble in water. They all distil without decomposition.
69. The nitro-derivatives have a number of characteristic pro- perties, among them the possession of one hydrogen atom replaceable by alkali-metals, especially sodium. This sodium compound is most readily obtained by the action of sodium ethoxide or methoxide upon the nitro-compound in absolute-alcoholic solution. A fine, white, crystalline precipitate is thus formed, that from nitroethane, for example, having the composition C2H4NaN02. The insolubility of these sodium compounds in absolute alcohol is sometimes em- ployed in the separation of the nitroparaffins from other substances.
This power of exchanging hydrogen for sodium only exists when at least one hydrogen atom is linked to the carbon atom carrying the nitro-group. As from nitroethane, a metallic com- pound is obtained from secondary nitropropane,
but tertiary nitrobutane,
CH3.CH<^q3.
CH3V CHs^.NOg,
does not yield any corresponding metallic derivative. The struc- ture of these metallic compounds is considered in 322.
When an alkaline solution of a nitro-compound is brought into contact with bromine, one (or more) of its hydrogen atoms linked to the same carbon atom as the nitro-group is replaced by bromine. This reaction is analogous to the substitution by metals, it being
still possible, for example, to introduce one bromine atom into
/Br CH3.CHBrN02, but not into CHa-C^CHs
\N02.
94 ORGANIC CHEMISTRY. [§ 70
70. The behaviour of nitro-compounds with nitrous acid is very characteristic, and affords a method of distinguishing between pri- mary, secondary, and tertiary nitro-denvatives. The reaction is car- ried out by adding sodium nitrite to an alkaline solution of the nitro-compound, and acidifying with dilute sulphuric acid. From a primary nitro-compound, an alkylnitrolic acid is formed:
CH,-C[h7+^N0H = CH3.C<(JJ^^^+H,0.
xv-Q Ethylnitrolio add
The constitution of these compounds is indicated by their produc- tion from a dibroraonitro-com pound by the action of hydroxylamme, HJ^OH:
[,>ClBr, + H,|NOH - CH,.C^5jQ^+2HBr.
ca
^N0«
Tlie alkylnitrolic acids dissolve in alkalis, yielding metallic com- pounds of blood-red colour, this reaction affording a characteristic test for them. They crystallize well, but are by no means stable.
When similarly treated, tlie secondary nitro-compounds yield
NO pseudoni^oka. They contain the group ^C < xtq :
Propylpseudonitrole.
When solid, the pseudomtrolGB are colourless, crystalline sub- stances, but have an intense blue colour in the fused state or in solution. This characteristic serves as a test for them.
Lastly, the tertiary nitro-compounds are not acted on by nitrous acid.
Among the other properties of nitro-compounds is their decom- position into the acid with the same number of carbon atoms and hydroxylamine, by heating with hydrochloric acid:
CH,-CH,.NO,+HaO - CH..COOH-fH,NOH.
Nitroethane Aoetio acid HydraxyUmina
The mechanism of this reaction is explicable on the assumption that the nitro-compound is first transformed into a hydroxamic add:
R.CH,NO, -> R •C<(qS^-
Hydroxamic acid
1 70] NITRO-COMPOUNDS. 95
The hydroxamic acid is then converted by the water present into the acid and hydroxylamine:
r-c<22^+h,o-r.c<2jj+h,noh.
Acid HydrozyUmine
.'
ALKYL-RADICALS LINKED TO OTHER ELEMENTS.
L ALKYL-RADICALS LINKED TO ELEMENTS OF THE NITROGEN
GROUP.
71. Ammonia unites readily with acids, with formation of salts. Phosphine, PH3, also possesses this property, although the phos- phonium salts, PH4X, are decomposed even by water into an acid and phosphine. The basic character has wholly disappeared in arsine, AsHs, and stibine, SbHa.
Ammonia cannot be easily oxidized, and is unacted on by the oxygen of the atmosphere at ordinary temperatures. On the other hand, the hydrides of phosphorus, arsenic, and antimony are readily oxidized.
All these properties are displayed by the compounds of these elements with alkyl-radicals.
Phosphines.
7a. The amines yield stronger bases than ammonia. Similarly^ the phosphineS' form stronger bases than phosphine. In both cases this property becomes more marked as the number of alkyl-groups replacing hydrogen atoms increases. The salts of the monoalkyl- phosphines, for example, are decomposed by water, whereas those of the dialkylphosphines and trialkylphosphines are not. The quaternary phosphonium bases, PR,OH, are as strongly basic as the ammonium bases. When a phosphonium base is heated, it does not, like an ammonium base (66), decompose into an alcohol (orCnH2n-l-H20) and a trialkyl base, but into a hydrocarbon CnH2n+2 and an oxygen compound :
(C,H*)4P-0H =CH.H-(aH5),P0.
This substance is called trielhylphosphine oxides In this reaction the great affinity between phosphorus and oxygen plays an impor-
96
S 73] ARSINES, 97
tant part. This affinity is also indicated by the ease with which the phosphines undergo oxidation, a change effected even by the action of the air. Nitric acid oxidizes phosphine, PHa, to phosphoric acid, OP(OH)s: in an analogous manner the phosphines take up one oxygen* atom, and in addition as many oxygen atoms as there are hydrogen atoms directly linked to phosphorus:
CHap . CH, p.^ (CH«)2p . (CH8)ip.^.
jj^r gives (HO).^'^' j^ r gives hO^'^'
Monomethylphosphinic DimetbylphoephinM
acid acid
and (CHOaP gives (CH,),P:0.
Trimethylphosphme oxide
The constitution of these compounds is established by a variety of considerations: for instance, by the fact that the monocdkylphos- phinic acids are dibasic, that the dialkylphosphinic acids are monobasic, and that the trialkylphosphine oxides have no acidic properties.
The phosphines are colourless liquids of penetrating, stupefying odour. Methylphosphine, CHjPH,, is a gas: in very small quan- tities triethylphosphine has an odour of hyacinths.
Methods of Formation. — Only tertiary phosphines and phospho- uium compounds are formed by the action of alkyl halides upon phosphine, PHj. Primary and secondary phosphines are obtained by heating phosphonium iodide, PHJ, with an alkyl iodide and zinc oxide.
Arsines.
73. The primary and secondary arsines, HaAsCH, and HAsCCHs),, are obtained by reduction of monomethylarsinic acid and dimethyl- arsinic acid, (CH,)HAsOOH and (CH,)2AsOOH, by amalgamated zinc-dust and hydrochloric acid. Both are immediately oxidized by the air. Tertiary arsines do not yield bases with water. They are formed by the action of a zinc alkide on arsenic chloride, AsClj, and from sodium arsenide and an alkyl iodide :
AsNa,+3C,HJ = As(C,H0,+3NaI.
Quaternary arsonium bases, however, have strongly marked basic properties. They are prepared by the addition of alkyl haUdes to tertiary arsines, and treatment of the resulting halide with silver hydroxide.
98 ORGANIC CHEMISTRY. [j 74
The best-known arsenic derivatives containing alkyl-radicals are
the cacodyl compounds. They were investigated by Bunsen, who gave
them this name in consequence of their offensive smell. They are
very poisonous. The name cacodyl is applied to the univalent group
CH
Qjj*>As— . Cacodyl oxide, [(CH,),AsiO, is formed by distilling
arsenious oxide with the acetate of an alkali-metal. All the other cacodyl compounds are obtained from cacodyl oxide ; thus, cacodyl chloride^ (CH,),AsCl, is prepared by heating the oxide with hydro- chloric acid, and cacodyl, (CH3),As-As(CH8)2, by heating the chlo- ride with zinc in an atmosphere of carbon dioxide. When brought into contact with air, both ignite spontaneously.
n. ALKYL-RADICALS LINKED TO THE ELEMENTS OF THE
CARBON GROUP.
74. The elements in each group or colunm of the periodic system are divided into two sub-groups: in one the elements are electro- positive and base-forming; in the other electro-negative and acid- forming (" Inorganic Chemistry," 216). In the first division of the carbon group are titanium, zirconium, and thorium; in the second, carbon, silicon, germanium, tin, and lead. Only elements belonging to electro-^negative suihgroups are capable of yielding alkyjrcompounds, this being true not only of the carbon group of elements, but also of the elements of the other groups. In 1870 Mendel^eff for this reason predicted that the then unknown element germanium would, in accordance with its position in the periodic system, yield alkyl-derivatives; this prediction was confirmed by the researches of Winkler, to whom science is indebted for the discovery of this element. Titanium belongs to the electro-positive sub-group, and though in many respects it resembles silicon, it has not been possible to prepare its alkyl-derivatives.
Like carbon, the elements silicon, germanium, tin, and lead are quadrivalent. Numerous attempts have been made to prepare com- pounds containing chains of silicon atoms resembling the carbon chains. They have not been successful, no compounds containing a chain of more than three silicon atoms having been prepared. As far, therefore, as is at present known, silicon lacks the power of forming long chains like those present in many carbon compounds. On account of this defect, a " Chemistry of Silicon," analogous to the '' Chemistry of Carbon," is not possible, the phenomenon having a threefold origin:
§ 75] METALLIC ALKIDBS. 99
(1) The linking between silicon atoms (Si — Si) is endothennic, whereas that between carbon atoms (C — C) is exothermic.
(2) Most organic silicon compounds are readily decomposed by both water and oxygen.
(3) Such compounds are very subject to polymerization, with formation of amorphous powders.
Introduction of a single silicon atom into organic substances containing many carbon atoms produces derivatives of a character differing little from the corresponding carbon compounds. For example, silicon teiraethidef Si(C2H6)4, and teiraethylmethnne, C(C2H&)4, are known. Both are liquids, and are not acted upon by either fuming nitric acid or fuming sulphuric acid at ordinary tem- peratures, but yield substitution-products with chlorine. Silicohep- tane, (C2Hs)3SiH, has a petroleum-like odour, a resemblance to (ri- ethylmethane, (C8H6)aCH.
m. METALLIC ALKIDES.
75. When excess of ethyl iodide is warmed with zinc, a white crystalline compound, CaHsZnl, is formed, and on stronger heat- ing it yields zinc elhide, Zn(C2H5)2, and zinc iodide:
2C2H5ZnI = Zn(C2H6)2 -f-Znla.
Zinc ethide can be separated by distillation, which must be per- formed in an apparatus filled with an inert gas, because this com- pound, like the other zinc alkides, bums spontaneously when ex- posed to air.
The metallic alkides are colourless liquids, heavier than water. Zinc methide boils at 46®, zinc ethide at 118*^, and zinc propide at 146®.
When an alkyl iodide reacts with a zinc alkide, a saturated hydrocarbon is formed;
;CHj = Znl2+2CH3.CH3.
Water converts zinc alkides into saturated hydrocarbons and zinc oxide:
Zn(CH3)2+H20 = 2CH4 +ZnO.
The halogens react very energetically with zinc alkides, yield- ing alkyl halides.
100 ORGANIC CHEMISTRY. [5 75
Sodium alkides of the type of sodium m£thide, CHa^Na, are formed by the interaction of sodium and mercury alkides. They are colourless, amorphous powders, are not dissolved by indifferent solvents, and ignite spontaneously on contact with air.
Very remarkable compounds of magnesium have been obtained by Grignard. When magnesium-turnings are brought into con- tact with a dry ethereal solution of an alkyl iodide, one gramme- molecule of the latter being employed for each gramme-atom of magnesium, a reaction ensues, the heat evolved raising the ether to the boiling-point. When sufficient ether is present, all the mag- nesium dissolves, forming an alkyl magnesium iodide^ CnH2n+i -Mg-I. This is combined with one molecule of ether, because on evap- oration to dryness the residue still contains equimolecular propor- tions of ether and the metallic compound.
The alkyl magnesium halides of the type R-Mg«X can also be obtained free from ether by dissolving the alkyl halide in benzene, light petroleum, and other solvents, adding magnesium, and induc- ing the reaction by the introduction of a small quantity ^of a ter- tiary amine or of ether as a catalyst.
Unlike the zinc alkides, the alkyl magnesium halides do not ijnite spontaneously when brought into contact with air. They are often employed for syntheses, notably those of the secondary and tertiary alcohols (102).
The alkyl magnesium halides are decomposed by water, with formation of saturated hydrocarbons:
C„H2n+i .Mg.Cl+HaO = C„H2„+2+Mg(OH)a.
Mercury alkides are prepared similarly to zinc alkides. They do not ignite in the air, are not attacked by water, and are danger- ously poisonous. Such compounds as CsHj-Hg-OH are weak bases.
Alkyl-derivatives of beryllium, magnesium, cadmium, alumin- ium, thallium, and lead have also been obtained, some by the aid of Grignard's alkyl magnesium halides. A typical instance is the formation of tin ethide by the interaction of stannic bromide and ethyl magnesium bromide:
SnBr* +4C2H6 • Mg . Br = SnCCH*)* +4MgBr».
NITRHES AND ISONITRILES.
76. When potassium ethylsulphate is distilled with potassium cyanide or anhydrous potassium ferrocyanide, K4Fe(CN)6, a liquid of exceedingly unpleasant odour is obtained. By fractional distil- lation it can be separated into two substances, both with the formula C3H5N. One is called ethykarbylamine, and is only present in small proportion: it boils at 82^, and has a disagreeable smell like that of the original mixture. The other constitutes the main por- tion, and is called ethyl cyanide: it boils at 97®, and after purifica- tion has a not unpleasant odour, which is much less penetrating than that of ethylcarbylamine.
When acted upon by inorganic acids, these isomerides yield quite different decomposition-products. Ethylcarbylamine is attacked, at ordinary temperatures: the oily layer floating on the surface of the acid dissolves completely, and the disagreeable odour disappears. Formic acid, CH2O2, can be obtained from this solution by distillation; and on addition of caustic potash to the residue in the distilling-flask and subsequent distillation, ethyl- amine, C2H5NH2, passes over, indicating that the nitrogen atom in ethylcarbylamine, C3H5N, is directly united with the ethyl- group:
C3H5N +2H20=CH202 +C2H5NH2.
Ethylcarbylamine Formic acid Ethylamina
Ethyl cyanide is only slowly attacked by inorganic acids at ordinary temperatures, but heating accelerates their action. On warming the mixture in a flask with a reflux-condenser and subse- quent distillation, propionic acid, C3He02, passes over. This acid contains the same number of carbon atoms as ethyl cyanide, C3H5N. On making the residue in the flask alkaline and again distilling, ammonia is obtained. The nitrogen atom in ethyl cyanide can- not, therefore, be in direct union with the ethyl-group:
C3H6N+2H2O =C3H602 + NH3.
Ethyl cyanide Propionic acid
These facts indicate that the nitrogen atom in ethylcarbylamine is in direct union with the ethyl-group, and that the three carbon
101
102 ' ORGANIC CHEMISTRY. [§ 77
atoms are not directly united, since one of them can be eliminated with production of formic acid. In ethyl cyanide, on the other hand, there must be a chain of three carbon atoms like that in propionic acid (80), and the nitrogen cannot be directly linked to the ethyl-group. These facts are expressed by the constitutional formulse
I. C2H5— NC, II. C2H5— CN.
Carbylamine Cyanide
On account of their method of formation, each must contain the group CN.
CJompounds with a structural formula like I. are named carbyl- amines or isonitriles; those with a structural formula like Il.are called cyanides or nitriles. The names of the former are derived from the alkyl-radical they contain, thus methylcarbylaminef ethylcar- bylamine, etc. The latter can be designated analogously methyl cyanide f ethyl cyanide , etc., but are usually called nitriles and are named after the acid from which they are derived. Thus CHa-CN is acetanitrile, and C2H6»CN propionitrile,Si,nd so on.
The constitution of the groups — CN and — NC requires further consideration. They are represented as — C^N and — N^=:C, the first with a triple, and the second with a double, bond betw'cen C and N (c/. 119).
In Nef's view, the carbylamines furnish one of the few examples of compounds with a bivalent carbon atom. He proved the formula R.N:C to represent the constitution of the carbylamines by demonstrating that addition of halogens, hydrogen halides, sulphur, and other substances only takes place at the carbon atom, with formation of compounds of the type R-NCXi, R-NCHX, R-NCS, and so on (c/. 130 and 261}.
Carbylamines.
77, Carbylamines are the principal product of the interaction of alkyl iodides and silver cyanide. They can also be obtained tmmixed with nitriles by the action of caustic potash and chloro- form, CHCI3, upon primary amines:
C2H5N[Ebl+C[HCk| +3KOH = 3KCl+3H20+C2H5.NC.
On account of the disagreeable and characteristic odour of the carbylamines, this reaction affords an exceedingly delicate test for
78] ' NITRILE8. 103
primary amines. Secondary and tertiary amines are not converted into carbylamines by this reaction, since they lack tivo hydrogen atoms in direct union with the nitrogen atom of the amine.
The carbylamines are colourless liquids, very stable towards alkalis, but readily converted by acids into a primary amine and formic acid. With dry hydrochloric acid in ethereal solution they yield unstable addition-products, such as 2CH3NC • 3HC1.
Nitriles.
78. Nitriles are the chief product obtained when potassium cyanide reacts with alkyl iodides (cf. 77), or when it is submitted to dry distillation with potassium alkylsulphate. Sometimes anhydrous potassium ferrocyanide, K4Fe(CN)6, can be advan- tageously substituted for potassium cyanide.
Nitriles can be prepared by the action of an alkaline bromine solution on the higher primary amines:
C7HUCH, -NH: +2Br, +2NaOH = C7H15CH, -NBr, +2NaBr +2H,0; CtHuCIp^nIBt^ -f 2NaOH - CHuCN +2NaBr -f 2H,0.
Nitriles are also formed by passing esters mixed with anmionia over oxide of aluminium or of thorium heated at 480^-500°:
R-COOR'+Na=R.CN+R'-OH+H,0.
Other methods of preparation are mentioned in 96 and 103.
The nitriles are liquids of characteristic odour, soluble in water, and having specific gravities about 0-8. They are converted not only by acids, but also by warming with alkalis, into fatty acids containing; the same number of carbon atoms and ammonia, a process called hydrolysis. They form addition-products with many substances, by conversion of the triple bond between nitrogen and carbon into a single bond. An example of this reaction is the addition of nascent hydrogen (Mendius) :
C2H6.CN+4H = CgHfi.CHg-NHa.
This produces a primary amine (63) with the same number of carbon atoms as the nitrile, the yield being ver>' good for the higher members when sodium is brought into contact with a mixture of the nitrile and boiling absolute alcohol.
A description of a number of other addition-products of the nitriles is given in 97.
ACIDS, CQH2n02.
79. An addition-product is formed by the interaction of Grignard's alkyl magnesiiun halides (75) and carbon dioride. Since magnesium exhibits great affinity for oxygen, this reaction can be explained by assuming the release from the alkyl-radical of the group — ^MgX, X representing halogen; and its subsequent
union with an oxygen atom of the carbon dioxide, C^ being
converted into — CC^ . As this new group and the alkyl- radical previously attached to the group — ^MgX have one free carbon bond apiece, the two groups may be assiuned to unite
to form a compoimd CnHjn+i — C\ This addition-
product is decomposed by water, yielding an acid:
jO jO /OH
In accordance with these reactions the acids CnH2n02 contain
the group — ^\^ ^ imion with an alkyl-radical. This view is
supported by the formation of these compounds by other methods. Amongthemistheirsynthesisby theinteraction of an alkyl iodide and potassiiun cyanide, followed by hydrolysis of the resulting nitrile. This hydrolysis consists in the addition of the elements of water, and entails breaking the bonds between carbon and nitrogen in the
group — C = N. If any other bond in a nitrile CH3 • CH2 • CH2 CN
were released, it would involve a severance of the carbon chain, and prevent the formation of an acid containing the same number of carbon atoms as the nitrile. The hydrolysis of the nitrile, in which an acid and ammonia are formed, may therefore be explained by assuming that the molecules of water are resolved into H and OH, the hydroxyl uniting with the carbon, and the hydrogen with the nitrogen. By a threefold repetition of this the
104
I ft S791 ACIDS, CnHanOa. 105
nitrogen is converted into ammonia, the three bonds between car- bon and nitrogen, in the nitrile, being severed:
yOH Hv CHa-C^OH H-9N.
The formula of the acid formed is not CHa-CX^aHs, but CH3-C02H, containing one molecule of water less. When one molecule of water is eliminated from GHa-GOaHa, there results
CHa-CIOH --^CHa-C^Q^, a substance contaming the carboxylr
6a
group.
In this explanation of the formation of acids, the existence of an intermediate compound containing three hydroxyl-groups is assumed. Such substances are not known, but the assumption seems by no means improbable, because compounds containing
yOC2H5
three alkoxyl-groups exist; for example, GH3'C^OC2H5.
\0C2H5 They are called orthometer 8 (149).
The acids 0^112^02 can be formed by the action of carbon monoxide on metallic alkoxides under the influence of heat:
CHa-ONa+CO = GHa-COONa.
The formation of an addition-product between CHa-ONa and CO can be explained by the assumption that the alkoxide first decom- poses into CHa and ONa.
It is mentioned in 45 and 46 that oxidation converts the primary alcohols into acids of the general formula 0^112^02, with the same number of C-atoms in the molecule. In this reaction the group — CH2OH is oxidized to — COOH.
The higher primary alcohols can also be transformed into the corresponding acids by heating them with soda-lime, free hydrogen being evolved:
CirHa, . CH,OH -f NaOH = C17H,* • COONa +2H,.
Stearyl alcohol Sodium stearate
Other methods are described in 98, 145, 164, 232, and 233. The presence of hydroxyl in the carboxyl-group is proved by
106 ORGANIC CHEMISTRY, [§ 80
the action of the chlorides of phosphorus, which replace the OH- group by CI, as with the alcohols.
In each molecule of the acids of this series there is one hydrogen atom replaceable by metals. Only the carboxyl-hydrogen atom is in direct union with oxygen, and its special position suggests that it is the replaceable atom. The truth of this supposition has been proved by treating silver acetate, C2H302Ag, with ethyl iodide: ethyl acetate is formed, and not butyric acid, which would result if the Ag-atom were attached to the methyl C-atom; thus, CHzAg.COOH.
80. The lower members of this series of acids are liquid at ordinary temperatures. They can be distilled without decomposi-
10 u u
NUMBER OP OARBON ATOHt
Fia. 27. — Melting-point Curvji of the Fatty Acida.
tion, and have a very irritating and strongly 'acid odour in the Qincentrated state. They are miscible in all proportions with water. The middle members (C4 — C9) have a disagreeable rancid smell. They are of an oily nature, and do not mix with water in all proportions. The higher members, beginning at Cio, are solid at ordinary temperature, without odour, and resemble paraflin-wax in character. They are almost insoluble in water, and cannot be distilled at the atmospheric pressure without decomposition. All the acids of this series dissolve readily in alcohol and ether. Except the first member, they are very stable towards oxidizing agents.
580]
ACIDS, CnH2n02.
107
The acids of the series CnH2n02 are called fatty acids, some of the higher members having been first obtained from fats.
Many of the fatty acids are natural products, occurring either in the free state or as esters, and are of great theoretical and tech- nical importance The table contains the names, formulse, and certain physical constants of the normal-chain acids of the series
Name
Formic acid . . Acetic acid . . . Propionic acid Butyric acid . . Valeric acid . . Caprolc acid . . Heptylic acid . Caprylic acid . Nonylic acid. . Capric acid . . . Palmitic acid . Margaric acid. Stearic acid . .
Formula.
CH2O2 C2H4O2
CHfiO,
C4H8OJ
C6H10O2
CfiHxsOa
CtHmO,
CsHieOt
C»Hi80i
C10HJ0O2
CieHwOj
CX7H3402
C18HJ602
Melting-point.
8-3** 16.671** 22**
312**
5**
5° 16-5* 12. 5** 314** 62-618° 60** 69-32°
58
1
10«
Boiling-point.
101**
118°
141°
162°
1^6°
205°
223°
2375
254°
269°
269°
277°
287°
Specific Gravity-
1-2310 10532 0-9985 0-9599 0-9560 .0-9450 0-9186 0-9100 0-9110 0-930
(10°)
(ife*;
(14°)
(i9.r
(0°) (0°) (17-2* (20°)
(M.P.)
(37°)
')
)
* At 760 mm.
t At 100 mm.
Although the boiling-points rise with increase in the number of C-atoms in the molecule, the melting-points of the acids with an even number of C-atoms are higher than those of the acids imme- diately preceding and succeeding them, with an odd number of C-atoms (Fig. 27). This phenomenon has also been observed in some other homologous series.
The residual groups which would result by elimination of hy- droxyl from fatty-acid molecules are unknown in the free state, but named after the corresponding acids by changing the termina- ation"ic"mto"yl"; thus,
H.CO Formyl, CH3.CO Acetyl, C2H5.CO Propionyl, CsHy.CO Butyryl, C4H9.CO Valeryl, etc.
108 [ORGANIC CHEMISTRY. [§ 81
Formic Acid, H-COOH.
8i. Formic add derives its name from its presence in ants (Latin, formica). It is manufactured by passing carbon monoxide at a pressure of eight atmospheres over soda-lime at 210^; and formate is also produced by the interaction of potassium hydrogen carbonate and hydrogen at a pressure of sixty atmospheres and a temperature of 70^. Palladium-black must be employed as a cataljTst.
Moissan discovered a mode of synthesis from carbon dioxide and potassium hydride:
K.H+CO2+H.COOK.
A convenient laboratory method for the production of formic acid is described in 153, Formic esters can be prepared by the interaction of carbon monoxide and alcohols under pressure, with alkoxides as catalysts:
R.OH+CO=H.COOR.
The acid can also be obtained by the oxidation of methyl alcohol.
Pure formic acid is a colourless liquid of irritating odour. Its salts are called formates: they are soluble in water, some only with difficulty.
Formic acid is distinguished from its homologues: first, by its susceptibility to oxidation, and hence its reducing power; second, in. being readily decomposed into carbon monoxide and water. When mercuric oxide is added to a solution of formic acid,a solution of mercuric formate is obtained. If this solution be filtered and warmed, mercurous formate is precipitated with evolution of car- bon dioxide, and on further warming, metallic mercury is liberated: OOCH H COO Hg |OOCH-fH|COO|"g - ^2^^+^^+^^^°'
Merouxio formate fonaate
Hg|OOCH+H|C(X)|Hg - 2Hg+C02+HCOOH.
MerourouB formate
In this process half of the formic acid in the salt is set free, and half is oxidized. When a solution of silver formate is warmed, an exactly analogous reaction takes place; metallic silver is pre- cipitated, carbon dioxide evolved, and half of the acid liberated.
(821 ACETIC ACID. 109
When formic acid ia warmed with concentrated sulphuric acid, water and carbon monoxide are foimed:
[HlCO[OHl = HaO+CO.
The introduction of finely powdered metallic rhodium, or other metaU of the platinum group, into an aqueous solution of the acid effects its decomposition into carbon dioxi^la and hydrogen, the metal acting as an accelerating catalyst.
It is apparent that the properties of formic acid differ somewhat from those of the other acids of the homologous series in which it is the lowest member. A similar phenomenon is of frequent occurrence.
Acetic Acid, CHa-COOH. 82. Acfiic acid has been known longer than any other acid. It is manufactured by two different methods.
a. By oxidation of dilute alcohol, wine, beer, etc., by exposure to the air, with production of vinegar. The oxygen of the atmos- phere acts upon the alcohol by the aid of bacteria, and the process must be so r^ulated that these bacteria produce the greatest pos- sible effect. To this end it is important that the temperature should be kept between 20° and 35°.
In the " quick " process for the preparation of vinegar (Fig. 28), dilute alcohol (6-10 per cent.) is allowed to drop on beech-wood shavings con- tained in a vat with a perforated falne bottom, a. Holes bored in the sides of the vat near the bottom serve to admit an ascending stream of air, opposite in direction to that of the alcohol. The shaving of beech-wood distribute the liquid over a very large surface, thus facilitating the oxidizing action of the (lir, while at the same time they serve as a feeding ground for the bacteria.
b. Acetic acid is obtained in the dis-^ tillation of wood (42). By treatmentl
with quicklime, the acid is converted p,^ 28. - Pbbpaeation of into calcium acetate, which is freed Vinboab by the "Quick" from tarry impurities by heating to 200° Pbocbsb.
110]
ORGANIC CHEMISTRY,
1582
in the air. The acetic acid is then liberated by distilling with an equivalent quantity of concentrated hydrochloric acid. It can be purified by distillation from potassium dichromate, being very stable towards oxidizing agents.
At temperatures below 16-671°/760 nun., anhydrous acetic acid is solid and has much the appearance of ice; hence the name glacial acetic acid. The solid acid has a penetrating odour, and is obtained by allowing a very concentrated solution of acetic acid to solidify, pouring off the liquid residue, melting the solidified acid, again allcrwing it to crystalUze, and so on, these operations being repeated imtil the melting-point is constant. A rise of temperature and contraction of yolume occur when glacial acetic acid is nixed with water, the maximum rise and contraction being produced by mixing in the proportion of one gramme-molecule
of acetic acid to one gramme-moleculeof water. B This fact indicates the existence of a compoimd called ortho-acetic acid(79), with the formula
CH3-COOH.H20 =
CH3.C(OH)3.
A determination of the viscosity of a liquid mix- ture sometimes indicates an association of its molecules. The \'iscosity is measured by determining the rate of efflux of a known volume of the liquid through a capil- lary. During the operation, the maintenance of a constant tem- perature is essential, any alteration producing a marked change in the observed value. The rate of efflux is proportional to the viscosity.
The fluidity (</>) is the reciprocal of the viscosity (?/), so that ^ =-.
As has been indicated by Brigham, the fluidity-curve obtained by plotting the volume-percentages of the Uquid mixture as absciss®
Volume - percentage
Fig. 29. — Graphic Representation of
Fluidity. ACB indicates combination and AB does not.
1 831 ACETIC ACID. Ill
in a co-ordinate system, and the fluidity values as ordinates, is a straight line for many binary liquid mixtures. For mixtures such as alcohol and water, acetic acid and water, and others, instead of a straight line a curve like ACB (Fig. 29) is obtained, a phenomenon possibly indicative of the union of two kinds of molecules.
A fifty-five per cent, solution of glacial acetic acid in water has the same specific gravity as the pure, anhydrous acid. When water is added to glacial acetic acid, the specific gravity of the mixture first rises: further addition of water causes it to fall. This circiunstance makes it impossible to determine the amoimt of acid present in such mixtures by the simple use of the hydrometer.
The strength of very concentrated acetic acid is best determined by an observation of its melting-point, a thermometer graduated in tenths of a degree being used. In accordance with the formula given in 12,
ilAf* Constant,
the presence of 1 per cent, of water (molecular weight 18) would,
since the constant for glacial acetic acid is 39, cause a depression
39 {A) of —, or 2' 16**. Since a thermometer graduated in tenths can
lo
easily be read to within one-twentieth of a degree, the amount of
1 water can be determined to within . ^- — r-, or 0'025 per cent.
Z* lOX'6
This is a degree of accuracy unattainable by titration.
When either no very great accuracy is required, or the acetic acid is dilute, it is best to determine the strength by titrating a weighed quantity of the solution with a standard solution of alkali.
The vapour-density of acetic acid at temperatures slightly above its boiling-point is twice as great as that corresponding with the formula C2H4O2. At about 200^, however, the vapour- density is normal. A similar phenomenon has been observed with many acids of this series and other substances (288).
Absolutely pure acetic acid is not attacked by chlorine or bromine in absence of light. The acid can be prepared in this condition by distilling from phosphoric acid the highly concen- trated acid melting above 16°.
83. The acetates, or salts of acetic acid, are soluble in water, the silver salt dissolving with difficulty. When ferric chloride is
112 ORGANIC CHEMISTRY, [§84
added to a solution of an acetate, such as sodium acetate, a blood- red colour is produced, owing to the formation of a complex acetoferric acetate, the salts of formic and propionic acids react- ing similarly. When this solution is sufficiently dilute, brown- red basic ferric acetate, Fe(OH)2C2H302, is precipitated on boil- ing, acetic acid being simultaneously liberated.
The dry distillation of anhydrous sodium acetate with soda- lime produces methane :
CH3 • COONa + NaOH = CH4 + NagCOa.
This method is not applicable to the salts of the higher members of this series of acids, for the hydrocarbons are decomposed at the high temperature essential for the reaction.
A very delicate test for acetic acid is the formation of cacodyl oxide (73). Owing to the extremely poisonous nature of this sub- stance, great care must be exercised in applying the test. Among the acetates of technical importance are lead acetate ('' sugar of lead ")> basic lead acetate^ and aluminium aceiaJte, The first two are used in the manufacture of white lead, and the third as a mordant in calico-printing (340).
Butyric Acids, C4H8O2. 84. Two isomeric acids with the formula C4H8O2 are known. They are normal hxdyric acid, CH3.CH2-CH2-COOH, and '^aobuty-
ric acidf ^jj^>CH.COOH. The constitution of these acids is
proved by their synthesis, the normal compound being obtained from n-propyl iodide, and the iso-acid from isopropyl iodide:
CH3.CH2-CH21 -^CH3-CH2.CH2.CN -^CHs-CHa-CHg-COOH. ggj>CHI ->^23>CH.CN -->ggj>CH.COOH.
The normal compound is also called "fermentation" butyric acid, from the fact that it can be obtained by the fermentation under certain conditions of such substances as sugar. It has an extremely disagreeable odour, and can only be oxidized with diffi- culty.
Butter contains about 2-3 per cent, of n-but)rric acid, along with smaller quantities of other volatile acids of the fatty series, such
§>5] HIGHER FATTY ACIDS. 113
caproic acid: they are probably present as esters. Since volatile fatty acids are not obtained by saponification of other fats, whether animal or vegetable, their presence furnishes the most characteristic distinction between butter and margarine: the latter is a mixture of animal and vegetable fats. Since the percentage of volatile fatty acids in butter is not a constant quantity, but may vary between wide limits, it is not always possible by estimating these acids to detect adulteration of butter with margarine. Admixture can usually be also identified by other tests, especially by the deter- mination of the refraction of the molten fat.
iaoBiUyric add also has a very disagreeable odour. It contains a tertiary carbon atom, and since such compounds are readily oxidized, oxidation affords a method of distinguishing between the normal acid and the iso-acid.
The calcium salts of these acids also exhibit a remarkable dif- ference, that of the normal acid being less soluble in hot water than in cold, while that of the iso-acid follows the ordinary rule, and is more soluble in hot than in cold water. When heated to about 80°, a solution of normal calcium butyrate saturated at 0° deposits considerable quantities of the salt.
In accordance with the principle of mobile equilibrium ("In- organic Chemistry," 235), calcium n-butyrate should dissolve in water with slight evolution of heat, and calcium isobutyrate with slight absorption of heat. This view is fully supported by the results of experiment.
Higher Fatty Acids, C„H2n02.
85. Many of the higher members of the series of fatty acids are natural products, chief among them being palmitic add, C16H32O2, and stearic add, C18H36O2, both with normal carbon chains (137). In the form of esters of glycerol (154), these two acids occur in large quantities as the principal constituent of most animal and vegetable fats, from which they are obtained by saponification, a process carried out by heating either with slaked lime (95), or with concentrated sulphuric acid. The latter causes slight car- bonization, imparting a dark colour to the fatty acids. They can be purified by distillation with superheated steam.
Another method of decomposing the fats into glycerol and a fatty acid de[)ends upon the action of an enzyme (aaa) present in
114 ORGANIC CHEMISTRY, [{85
castor-seed (Latin, ricinus communis). After removal of the oil, the powdered seeds are intimately mixed with the fat: on addition of a dilute acid, such as decinormal sulphuric acid, an emulsion is formed. If the mixture is kept at a temperature of 30^-40° for two or three days, the fatty acids are set free in a very pure state; on gentle heating, the emulsion then separates into two layers, the upper consisting of the free acids, and the lowBr of an aqueous solu- tion containing 40-^50 per cent, of glycerol.
Twitchell's process also depends on the formation of an emul« sion. A mixture of the fat with water containing a few tenths of 1 per cent, of sulphuric acid is kept in an emulsified condition by means of live steam, the operation being rendered possible by the addition as " Saponifier ** of a fatty-aromatic sulphonic acid such as naphthalenestearosulphonic acid, a substance soluble in both water and fat. ^
Saponification of fats yields a mixture of acids, semi-solid at ordinary temperatures. This mixture contains the two acids men- tioned above, melting at 62° and 69° respectively, when pure; but when mixed; each lowers the melting-point of the other (25). Moreover, liquid oleic acid, belonging to another homologous series, is also present: it can be pressed out of the mixture, leav- ing a white, solid substance used in the manufacture of " stearine " candles. For this purpose the " stearine " is melted, and after addition of a small proportion of parafi^-wax, to prevent crystal- lization of the fatty acids, which would make the candles brittle, the molten substance is poured into moulds, in the axes of which wicks are fastened.
Soaps consist chiefly of the alkali-metal salts of the acids con- tained in fats. They are prepared by saponifying fats with a solution of caustic soda or of caustic potash heated to the boiling- temperature. Potassium-soap is called "soft soap," and is usually yellow. In some countries it is tinted green by the addition of in- digo, and is then known as "green soap." Potassium-soap contains not only the potassium salts of the acids, but also the glycerol pro- duced in the reaction, and a considerable proportion of water. Sodium-soap is hard: it is separated from the reaction-mixture, after saponification is complete, by "salting-out," which consists in the addition of solid common salt to the mixture at th? boiling- temperature. Since the sodium salts of the acids are insoluble in a concentrated solution of sodium chloride, the soap separates out
5861 SOAP, 115
in the molten state, forming a layer on the surface of the brine, in which the glycerol remaina dissolved. The soap thus obtained consists of the sodium salts of the acids, with a small percentage of water.
86. The cleansing action of soap may be explained as follows. When an alkali-metal salt of one of the higher fatty acids is brought into contact with a large excess of water, it decomposes with for- mation of free alkali, a fact that was pointed out by Chevreul as early as at the beginning of the nineteenth century. The acid thus liberated unites with a second molecule of the salt to form an in- soluble substance, which with the water produces the lather. The presence of free alkali in dilute soap-solutions can be experimentally demonstrated. A concentrated soap-solution is only very slightly coloured by phenolphthalein; but the addition of a large propor- tion of water causes the development of the red colour, due to the action of the base thus liberated on the phenolphthalein. The soap has therefore undergone hydrolytic dissociation, owing to the weak acidic character of the higher fatty acids.
The soiling of the skin, clothes, and so on, is partly due to substances of a fatty nature, and partly to soot, iron oxide, or clay. An insight into the mechanism of the removal of the fatty substances is afforded by the following experiment. When a drop of oil or a small piece of fat is placed in water, the two substances do not mix. On addition of a few drops of caustic- alkali solution to the water, followed by vigorous agitation of the mixture, the liquid develops a milk-like appearance, due to the formation of an emulsion (" Inorganic Chemistry," 196) consisting of minute droplets of fat suspended in the liquid, just as in milk. The alkali liberated from the soap has a similar emulsif3dng effect on the dirt. The proportion of alkali set free from soap is small with a small quantity of water, larger with a large quantity; but the addition of a great quantity of water produces no considerable modification of the concentration — the amount of free alkali in unit volume of the liquid — since, although it produces more free alkali, it simultaneously dilutes it. The use of soap has, therefore, the efifect of automatically maintain- ing a small concentration of free alkali in the water. There would be no such adjustment if free alkali were employed instead of soap.
116 ORGANIC CHEMISTRY, I8»7
Soot, iron oxide, and other forms of dirt adhere very tena- ciously to the skin and to textiles, and either cannot be removed by rubbing with water alone, or only with great difficulty, but the cleansing is readily effected by the action of a soap-solution. Its action must be ascribed to adsorption of the dirt by the acid alkali-metal salts of the fatty acids, the product formed no longer adhering to the skin or fabric. An illustrative experiment is described in " Laboratory Manual," IX., 17.
Water containing a certain percentage of calcium salts is called a ''hard" water ("Inorganic Chemistry," 259). Such water does not immediately lather with soap, but causes the formation of a white, flocculent substance, consisting of insoluble calcium salts of the fatty acids. Hard water is therefore unsuitable for washing, because it prevents the formation of a lather, and also because the alkali is neutralized and thus withdrawn by the acid-radical of the calcium salts (sulphate and carbonate) present.
Electrolytic Dissociation.
•
87. Molecules of acids, bases, and salts are assumed to be re- solved, on solution in water, into ions, charged with opposite kinds of electricity ("Inorganic Chemistry," 65 and 66). In such a solu- tion, an acid is partially or completely dissociated into positively charged hydrogen ions, H' (cations), and negatively charged anions: for example, acetic acid is resolved into H* (positive), and (C2H3O2)' (negative). Bases yield a positively charged metallic ion, and a negatively charged OH'-ion; salts a positively chained metallic ion, and a negatively charged acid-radical ion.
It is further stated {Ibid.y 66) that in the solution of a partly ionized substance there is an equilibrium which for a monobasic acid can be expressed by
ZH?=fcZ'-fH-,
where Z' represents the acid-radical. If v is the volume in litres containing one gramme-molecule of the acid, and a is the portion
ionized, then the concentration of the ions is — , and that of the non-ionized portion is ^^. The equation representing the equi-
t88]
ELECTROLYTIC DISSOCIATION.
117
librium in the above example of a monobasic acid is, therefore (/Wd., 49),
1-a /a\2
or
a-
=*.
In this equation k is constant, and is catted the umizalionrconstarU, It has been proved that this equation affords an exact measure of the amount of ionization for the very weak organic acids; that is, expresses accurately the connection between the dilution v and the ionization a. For this reason it is called the law of dilution. It was discovered by Ostwald, who dissolved one gramme-molecule of an acid in different quantities of water, v, and ascertained the ionizations a by determining the electric conductivity. On sub- stituting the values obtained for a and v respectively in the expres-
sion
a'
the latter was always found to have the same value,
as it must if k is constant.
The accuracy of this law is evident from the examples in the following table.
|
Aoetic Add. |
Propionic Acid. |
n-Butyric Acid. |
||||||
|
V |
100a |
lO^Jk |
V |
100a |
lO^Jk |
V |
lOOa |
10'* |
|
8 |
1193 |
OlSO |
8 |
1016 |
0130 |
8 |
1-068 |
0 144 |
|
16 |
1-673 |
0179 |
16 |
1-452 |
0 134 |
16 |
1-636 |
0.160 |
|
32 |
2380 |
0182 |
32 |
2-OfO |
0-134 |
32 |
2-165 |
0149 |
|
64 |
3-33 |
0179 |
64 |
2-895 |
0135 |
64 |
3053 |
0150 |
|
128 |
4-68 |
0-179 |
128 |
404 |
0-133 |
128 |
4-292 |
0-UO |
|
1024 |
12*66 |
0-177 |
1024 |
10-79 |
0-128 |
1024 |
11-41 |
0144 |
88. The "strength" of acids depends upon their degree of ionization, strong acids undergoing considerable, and weak acids but slight, ionization. Since the constant k rises or falls in value simultaneously with a, and is independent of the concentration, it affords a convenient measure of the strength of an acid.
The table shows the values of 10*A; for certain fatty acids.
Formic Acetic Propionic n-Butyric Valeric
2-14, 0-18, 0.13, 0-15, 016.
It is noteworthy that formic acid has a greater ionization-constant, and is therefore stronger, than its homologues, another example of
118 ORGANIC CHEMISTRY. [§88
the difference between it and the other members of the series.
A comparison of these acids with such strong mineral acids as sulphuric acid and hydrochloric acid, from the point of view of the magnitude of their ionization-constants, shows that the former are very much weaker than the latter. When t;=16, then for hydro- chloric acid 100a = 95*55, and for acetic acid only 1-673. It is obvious that 100 a is the amoimt ionized, expressed in percentage.
The weak organic acids follow the law of dilution : the strong mineral acids do not. No perfectly satisfactory explanation of thus phenomenon has been suggested hitherto.
DERIVATIVES OF THE FATTY ACIDS OBTAINED MODIFYING THE CARB0XYL-6R0UP.
89. The carboxyl-group may be modified by the exchange of its oxygen atoms or hydroxyl-group for other elements or groups. The compounds described in this chapter contain such modified carboxyl-groups.
I. Acid Chlorides.
Add chlorides are derived from acids by replacement of the hydroxyl-group by chlorine, and consequently contain the group — COCl. They are obtained from the acids by the action of the chlorides of phosphorus, PCI5 and PCls, or of phosphorus oxy- chloride, POCI3:
3C„H2n+l-COOH + 2Pa3 = 3CnH2n+i-COCl+P203 + 3HCl.
The ease with which the acid chlorides are converted into the cor- responding acids is a proof that the chlorine atom has replaced the hydroxyl-group. For the lower members this conversion is eflfected by merely bringing them into contact with water. If the chlorine atom- had substituted hydrogen of the alkyl-group, there would be no reaction, since an alkyl chloride is not decomposed by water at ordinary temperatures.
The acid chlorides of this series, at least the lower members, are liquid, and have a suffocating, irritating odour. The chloride corresponding to formic acid is not known. Acetyl chloride, CH3COCI, fumes in the air, and can be distilled without decom- position. It boils at 55®, and its specific gravity is 1 • 13 at 0°.
Acetyl chloride is employed in detecting the presence of hy- droxyl in organic compounds. Hydroxyl is replaced by acetyl: thus, alcohols form esters of acetic acid:
R-OIH-f-ClJOCCHs = RO.OC.CH3+HCI.
' ' 119
120 ORGANIC CHEMISTRY. [§§ 90, 91
The compound to be tested is allowed to remain for some time in contact with acetyl chloride, either at the ordinary temperature or with gentle warming. To ascertain whether an acetyl-compound has been formed, the purified product is analyzed or saponified. If saponification yields acetic acid, an acetyl-derivative was present. The homologues of acetyl chloride are also sometimes employed in the detection of hydroxyl-groups.
The acid chlorides also react with the mercaptans, forming sub* stances of the type of acetyl-compounds.
II. Acid Anhydrides.
90. Acid anhydrides are formed by interaction of the alkali- metal salts of acids and acid chlorides:
CH8>CO[Ci + Na|0>OC.CH8 = 0<^;^JJ8+Naa.
Aoetio anhydride
Higher anhydrides are best obtained by heating the sodium salts of the higher acids with acetic anhydride.
The acid chlorides may be regarded as mixed anhydrides of hydrochloric acid and an acid, a view supported by their formation from these two acids by treatment with phosphorus pentoxide as a dehydrating agent.
Mixed anhydrides of the fatty acids themselves exist, although when distilled they decompose into the anhydride? of the two acids.
The lower members of this series are liquids, and have a dis- agreeable, suffocating odour. Acetic anhydride has a specific gravity D420 = 1 . 0820 and.boils at 139 • 53/760 mm. At ordinary temperatures it is soluble in about ten times its volume of water, the solution decomposing slowly with formation of acetic acid. In this respect it differs from acetyl chloride, which reacts momen- tarily and vigorously with water, yielding acetic acid and hydro- chloric acid. Like acetyl chloride it is used in testing for the presence of the hydroxyl-group. No anhydride of formic acid is known.
m. Esters.
91. Esters result from the interaction of acid chlorides, or anhydrides, and alcohols:
CHs-CO Cl+H OCzHs^CHa-COOCaHfi+Ha
i 91] ESTERS. 121
They are also formed by direct treatment of the alcohol with the acid, although extremely slowly at ordinary temperatures:
CHa-COOH+HOCjHft = CHa-COOCaHg+HjO.
The velocity of the reaction is much increased by a rise of tem- perature. Esters are also obtained by the action of the silver salt of an acid upon an alkyl iodide.
The following is a characteristic method frequently used for the preparation of these compounds. Dry hydrochloric-acid gas is passed through a mixture of absolute alcohol and the anhydrous organic acid. After some time the reaction-mixture is poured into water, whereupon the ester separates out, owing to its slight solu- bility. The formation of esters in this manner may be explained on the assumption that a very small quantity of the hydrochloric acid unites with the organic acid, water being eliminated, and a minute quantity of the acid chloride formed:
CH3.COOH + HCI = CH3.COCI + H2O.
It is true that for each molecule of acid chloride formed in accord- ance with this equation an equivalent quantity of water is pro- duced, sufficient to reconvert the chloride into the acid and hydro- chloric acid. There is, however, such an infinitely greater number of molecules of alcohol than of water with which the chloride can react, that the probability of the formation of an ester is very much greater than the probability of the regeneration of the acid. The preponderance continues so long as the proportion of alcohol present greatly exceeds that of the water formed; so that when the object is to obtain the maximum yield of ester, the organic acid cihould be dissolved in a large excess of alcohol. The formation of esters is called eMenflcation.
The esters are colourless liquids of neutral reaction, and do not mix with water in all proportions. They are lighter than water, most of them having a specific gravity between 0-8 and 0*9. Many of them are characterized by their agreeable odour, resem- bling that of fruits, a property which finds practical application in their employment in the manufacture of artificial fruitressences. For example, isoamyl isovaleraie (b.p. 196°) has an odour of apples, ethyl butyrate (b.p. 121°) of pineapples, isoamyl acetate (b.p. 148°) of pears, and so on.
122 ORGANIC CHEMISTRY. [§ 92
Beeswax Is a natural ester, consisting chiefly of melissyl palmitate, CisHsi-COOCsoHoi.
Tertiary alcohols can be synthesized from the esters by means of Gbionabd's alkyl magnesium halides (75) :
Addition-produfll
The addition-product thus obtained reacts with a second molecule of the alkyl magnesium halide:
/OMgBr /OMgBr
R.C^<X^A +R"MgBr - R-C^R" +C,H.O»«gBr. \R' \R'
On decomposition with water the tertiary alcohol is formed:
/OMgBr X)H
R.C^R" +H,0 - R.C^R" +MgBTOH. \R' \R'
R, R', and R" represent alkyl-groupe
Q3« The formation of esters has been carefully investigated by several chemists, first of whom were Berthelot and Pean de St. Gillbs. Their researches have shown that the reaction between the acid and the alcohol is never complete, some of both remaining uncombined no matter how long the process has been carried on. With equivalent quantities of acetic acid and ethyl alcohol, for example, the final product is such that from each gramme-molecule of alcohol and acid used, only two-thirds of a gramme-molecule of an ester and of water are formed, while one- third of a gramme-molecule of the alcohol and of the acid respect- ively remain uncombined. The same limit is reached when equi- valent quantities of an ester and water are brought into contact. An equUibrium between the four substances, alcohol, acid, ester, and water, is ultimately reached, and is due to the reversibility of the reaction C Inorganic Chemistry," 49). It may be represented as follows:
C2H5.0H+CH3.CO*OH i:±CH8.CO.OC2H5+H20,
§ 93] ESTERS. 123
The equation of equilibrium deduced in Ibid,, 49-51, may be applied to the fonnation and decomposition of esters. It is
where p is the initial concentration of the alcohol and q that of the acid, while x represents the quantities of water and of ester re- spectively present when the equilibrium is attained. Ail these are expressed in gramme-molecules, and K ia a, constant. There are here two opposing reactions taking place simultaneously, so that all the statements referred to above (loc. cU.) are applicable to the present instance. Given p, q, and K, the unknown quantity x can be calculated.
Numerous observations have proved that K is equal to 0-25 for the system ethyl alcohol -{- acetic acid. Whea one gramme-molecule of alcohol (46 g.) and one gramme-molecule of acetic acid (60 g.) are brought into contact, both p and q are equal to 1, and the equa- tion is
(l-x)««0*25x«, or a;«-|a:H-i-0.
The positive root of this equation is x»}, but the negative root has no physical significance.
It follows that this system in equilibrium contmns | gramme-moleeule alcohol + i gramme-'molecule acetic acid-¥i gv'omme^moleciile water -^ f gramme-molectile ester.
93* Several deductions can be drawn from the equation
(p— x)(^— a:) = Kofi.
These deductions had been established by experiment long before the development of the theory.
1. The esterification is approximately quantitative only when either the acid or the alcohol is largely in excess.
Putting the equation in the form
X 5— X*
•
it is evident that when the quantity of alcohol (p) is infinitely great, the left-hand side— 00. This is true of the right-hand side when 9=x, that is, when all the acid has been converted into ester.
124 ORGANIC CHEMISTRY. [? 93
It also holds when the ratio of the quantity of acid to alcohol is infinitely great, the whole of the alcohol changing into ester.
Although these considerations indicate that esterification can be complete only in presence of an infinitely great excess of acid or alcohol, in practice the very nearly theoretical yield of ester is obtained when the ratio of the quantity of acid to alcohol, or of alcohol to acid, is finite. When 1 gramme-molecule of acetic acid and 0*05 gramme-molecule of alcohol are employed, the equilibrium corresponds with 0*049 gramme-molecule of ester. When the gramme-molecular proportion of acetic acid and alcohol is 1:8, the equilibrium corresponds with 0*945 gramme-molecule of ester. There is almost complete conversion into ester of the alcohol in the first instance, and of the acid in the second.
2. The alcohol and the acid exercise the same influence on the formation of esters: thus, if a mixture containing a certain num- ber of acid molecules is prepared and n times as many alcohol molecules, and another with the proportions of acid and alcohol reversed, then the number of molecules of acid converted into ester in the first mixture is equal to that of the molecules of alcohol converted in the second.
When p gramme-molecules of alcohol are mixed with np gramme-molecules of acid, the equation becomes
X np—x
Inversely, when np gramme-molecules of alcohol aiB added to p gramme-molecules of acid, we have
np— X p, X X p— x
These two equations are identical.
3. The addition of a quantity of the ester to the mixture of the alcohol and the acid at the beginning of the experiment has the same effect on the formation of ester as would be exerted by an equivalent quantity of water.
When r gramme-molecules of water or of ester are added to a mixture containing p gramme-molecules of alcohol and q gramme- molecules of acid, then for both the equation becomes
(p— a:)(g— a:) — Kx{x-\-r).
i§ 94, 95] ESTERS. 125
It follows that the equilibrium is influenced to the same extent by the addition of equivalent quantities of water or of ester.
94. A typical application of the principle of mobile equilibrium (" Inorganic Chemistry/' 235) may be made to the formation of esters. Although the velocities of formation and decomposition of esters depend greatly upon the temperature, a change in the latter has very small efifect upon the equilibrium. At 10® the limit of esterification is 65 -2 per cent.; at 220® it is 66 • 5 per cent. In accordance with the principle of mobile equilibrium, this necessitates that the heat of formation of the ester should be very small. That it actually is so has been established by experiment.
In the esterification of primary, secondary, and tertiary alcohols with trichloroacetic acid, CCU-CpOH, Michael proved the velocity- constant k to have a much higher value for primary alcohols than for secondary and tertiary. For n-propyl alcohol A; X 10**725, for isopropyl alcohol 98. For secondary and tertiary alcohols the value of the constant is of the same order; for secondary butyl alcohol, CHs-CHOH-CjH,, itXlO*=90, for trimethylcarbinol, (CHjljC'OH, 118. For methyl alcohol the constant has a much higher value than for other primary alcohols, since A;XlO»=3690. All these determinations were made at a temperature of 25^.
9$. The conversion of an ester into an acid and an alcohol by a mineral acid or an alkali is called saponification, from analogy to the formation of soap from alkali and fat (85) . It is represented by an equation of the type
CH3 • COOC2H5 -h H2O = CH3 • COOH + C2H5OH.
The action of the mineral acid is therefore catalytic. Its presence only accelerates the saponification: the same result would be attained without it, though the time required would be incom- parably longer. If the concentration of the ester be Ci, that of the water is C2, and x the quantity of ester saponified during the
dz lime t, then the velocity of saponification 3=-^' for each mo- ment can be represented by the equation for bimolecular reac- tions ("Inorganic Chemistry/' 50):
5-^-*(Ci-x)(C2-x) (1)
126 ORGANIC CHEMISTRY. [{ 95
If the ester is dissolved in- a very large proportion of water, the concentration C2 of the water is only very slightly altered by the saponification, so that it may be included in the constant. The equation is therefore simplified to that for a unimolecular reaction:
— ^kiiCi^x) (2)
The saponification of esters by bases can be represented by an equation of the type
CHs-COOCiHsf+N^OH = CH3-COONa+C2H60H.
It is a bimolecular reaction^ and consequently equation (1) is applicable to it.
The velocity of saponification of esters by acids depends largely upon the acid, being greater the stronger the acid used. It has been proved that the velocity of saponification depends upon the extent of electrolytic dissociation of the acid employed. From this fact it may be concluded that the saponifying action is due to the hydrogen ion common to all acids. The velocity with bases is much greater than with acids; thus, for dilute (decinormal) solu- tions of caustic potash and hydrochloric acid, the ratio of the velocity-constants K for the saponification of inethyl acetate is 1350: 1. The velocity of saponification by bases also depends upon their electrolytic dissociation. Ammonium hydroxide, for example, being considerably less ionized than caustic potash or caustic soda, saponifies much more slowly than either of these bases. Saponifi- cation is therefore caused by the hydroxyl-ion common to all bases.
The velocity of ester-saponification, being proportional to the concentration of the hydrogen ions or hydroxyl-ions, can be em- ployed in determining this concentration. By its aid, the degree of hydrolytic dissociation of potassium cyanide, carbonates of alkali-metals, and other salts can be ascertained, and also the hydrogen-ionization of acid salts, such as potassium hydrogen sul- phate, KHSO4.
In the technical saponification of fats with slaked lime (85) a much smaller amount of this base is used than would be needed to neutralize all the acid obtained: the saponification is nevertheless complete. This is due to the fact that the higher fatty acids are
( 96] ACID AMIDES. 127
very weak, so that their salts undergo partial hydroiytic dissocia- tion. Thus, notwithstanding the excess of acid, there is always enough of the free base (hydroxyl-ions) present to effect the saponification.
IV. Acid Amides, CnH2n+i-CONH2.
96. Add amides are formed by the action of ammonia on acid chlorides or anhydrides, a circumstance affording a proof of their constitution:
CnH2«+i .CO CTfHINHa - C^Hzn+i -CONHg+HCl;
CnH2n+i-CO^f;7lHlNH
C»Hj°+r.CO> ^+H NH2 ^ 2CnH2„+i.CONH2+H20.
Acid amides are also formed when the ammonium salts of the fatty acids are strongly heated, or when the sodium salts are dis« tilled with ammonium chloride, one molecule of water being elim- inated:
CnH2a^l .C0(0|NH2jIE1 « C„H2n+l .CONH2 + H2O.
When the nitriles are warmed with acids, two molecules of water are taken up, with formation of the corresponding acids (79). This reaction can be so modified — for example by dissolving the nitrile in concentrated sulphuric acid — that only one molecule of water is added, when amides are obtained:
C„H2„+i -CN+H2O = C„H2„+i .CONH2.
The acid amides are therefore intermediate products in the con- version of nitriles into acids. Distillation with such a dehydrating agent as phosphorus pentoxide converts amides into nitriles by elimination of water, whereas boiling with dilute acids or alkalis produces the corresponding acids by addition of the elements of water.
The acid amides are also formed by the action of ammonia upon esters:
CHs-CO^C^HT+HlNHa^CHs-CONHa + CzHsOH.
The acid amides are solid, crystalline compounds, with the exception of the liquid Jarmamide, H •CONH2. The lower members
128 ORGANIC CHEMISTRY. [§ 97
are soluble in water, and odourless when pure. Acetamidef CH3-CONH2, melts at 82®, and distils at 222®. Some specimens have a strong odour suggestive of the excrement of mice, due to slight traces of impurities. The remarkably high boiling-point of this substance is worthy of notice.
The acid amides and the amines greatly differ in their behaviour. Unlike the bond between carbon and nitrogen in the amines, that
in the — C ^ ^rr -group of the amides is readily severed by boiling
with acids or alkalis. Further, the basic properties of ammonia are greatly weakened by the exchange of one of its hydrogen atoms for an acid-radical; and although salts of acid amides do exist, they are decomposed b^'' water. Acetamide hydrochloride, CH3 • CO • NH2 • HCl, is such a substance : it is formed by passing dry hydrochloric-acid gas through an ethereal solution of acetamide. The acid amides even possess acidic properties: an aqueous solu- tion of acetamide dissolves mercuric oxide, forming a compound with the formula (CH3-CONH)2Hg.
The behaviour of the amides and amines towards nitrous acid is analogous, the corresponding - acids and alcohols respectively being produced by exchange of NH2 for OH (65).
Amides can be converted into primary amines by a method ' described in 259.
97. Some further derivatives, obtainable from the acids by substitution in the carboxyl-group, are described below.
Amino-chlortdes are produced by the action of phosphorus penta- chloride on the acid amides:
R.CGNHa + Pa, « R.Ca,.NH,+POCl,.
These compounds are only stable when one of the hydrogen atoms of the amino-group, NH2, is replaced by an alkyl-radical, or when both atoms are similarly substituted. They yield imiruxklorides, R*CC1:NH, by the elimination of one molecule of HCl, the same compounds being formed by the addition of HCl to nitriles.
<NH ^p, and may be
regarded as the product of the replacement of the doubly-linked oxygen of the carboxyl-group by the imino-group, NH. They are
( 97] IMINO^OMPOUNDS, HYDRAZIDES, AND AZIDES. 129
obtained by combination of alcohols and nitriles under the influence of dry hydrocbloric-acid gau:
The well-crystallized hydrochlorides of the imino-ethers are con .verted by treatment with ammonia into the hydrochlorides of the amidines:
The amidines are unstable In the free state, but are strongly mono- basic, and form stable salts.
Amidoximes are addition-products of the nitriles and hydroxyl* amine, NHgOH:
R.CN +H^OH - R.C < ^^.
They yield salts with both acids and bases, and give a fiocculent, muddy-brown or green precipitate when treated with an alkaline solution of a copper salt, a reaction which affords a characteristic test for them.
Acid kydrazides are produced by the action of hydrazine, HjN — NHa, on acid chlorides or esters, and therefore have the con- stitution R.CONH.NHt. Nitrous acid converts them into add azides:
R . CONH • NH, +HNOi = R . CON, +2H,0.
The acid azides are volatile, explosive substances, and some yield well-developed crystals.
ALDEHYDES AND KETONES.
gS. Both the aldehydes and ketones have the general formula CbH2bO. They are produced by the oxidation of primary and secondary alcohols respectively. Both classes of alcohols have the general formula CnH2n+20, so that each oxidation involves the elimination of two hydrogen atoms.
On further oxidation, an aldehyde takes up one oxygen atom, forming the corresponding acid with the same number of carbon atoms; thus CnH2iiO is converted into CnH2n02. It follows that an aldehyde is an intermediate product in the oxidation of a primary alcohol to an acid (45) :
CnH2n+20 — > CnH2nO — > CiiH2n02.
Primary alcohol Aldehyde Acid
A primary alcohol has the constitutional formula CnH2ii+i •CH2OH, and on oxidation yields an acid CnH2n+i*C00H. Since in this reaction the alkyl-group, CnH2n+i, is not altered, it must be present in the aldehyde. Hence, it follows that the two hydrogen atoms removed from the alcohol by oxidation must belong to the group — ^CH20H.
Two structural formulae are, therefore, possible,
R.C^ and R-C— OH.
The improbability of the existence of free bonds or bivalent carbon atoms in compounds constitutes a strong reason against the adoption of the second formula. Moreover, this formula points to the presence in an aldehyde of a hydroxyl-group: in reality, the aldehydes possess none of the properties peculiar to substances containing that group. For example, they do not form esters or
130
§ 991 ALDEHYDES AND KETONES. 131
ethers, and phosphorus pentachloride does not replace OH by CI, but effects the exchange of the oxygen atom for two chlorine atoms. Smce the second formula does not represent the properties of the alddiydes, it follows that the first is the correct one. This view is supported by the fact that aldehydes are formed when acid chlorides dissolved in moist ether react with 8odiiuu« the chlorine atom being replaced by a hydrogen atom:
CaHy-C^Q — >C3H7-C'^Q«
fi-Butyryl chloride n-Butyi»ldehyda
The aldehydes therefore contain the group — C'^g.
99. Ketones result from the removal by oxidation of two hydrogen atoms from secondary alcohols (98). Like the alde- hydes, ketones lack the properties peculiar to hydroxyl-compoimds, a proof that one of the hydrogen atoms removed comes from the hydroxyl-group. Putting aside the possibility of the formation of free bonds, the second hydrogen atom eliminated must have been attached to the carbon atom linked to oxygen, or to another carbon atom. The two cases are represented below, R and Bf being alkyl-groups:
L n.-
CH.2R GH2XV GH2XI GHR
CHOH --> CO or CHOH -> CH •
CHaR' CH2R'
2R' CH2R' CH2R' CH2R'
For reasons analogous to those for aldehydes, formula I. is more probable than formula XL The products obtained by the oxida- tion of ketones indicate that formula I. represents the constitution of this class of compounds.
The general formula for secondary alcohols is
R»Cxi2*C>r~CH2«R • X)H
From such an alcohol two acids, R-CH2-C00H and R'-CHa-COOH, are obtained by strong oxidation, the carbon chsin in some of the molecules being severed to the right, and in others to the left, of
132 ORGANIC CHEMISTRY, [§100
the CHOH-group. This reaction furnishes a means of identifying the alkyl-radicals attached to the group — CHOH — in a secondary alcohol. Since on oxidation ketones yield the same acids as the corresponding secondary alcohols, the alkyl-groups of the secondary alcohols must remain unchanged in the ketones. Hence, such a structure as that represented by formula II. is excluded, so that formula I. must be correct.
Ketones therefore contain the carbonyl-group CO in union with two carbon atoms.
Aldehydes may be looked upon as ketones with an alkyl-group replaced by hydrogen.
Nomenclature.
The name aldehyde is derived from aZ(cohol) e2e%€{(rogenatus)» that is, "dehydrogenated alcohol." The word ketone has its origin in the name of the first member of the series, acetone, CHa-CO-CHs (iii).
The aldehydes are named after the corresponding acids: for- maldehyde, H*CHO; acetaldehyde, CHs-CHO; yrojnonaldekyde, C2H5.CHO; valeraldehyde, C4H9 -CHO; etc.
The ketones derive their names from the alkyl-groups which they contain: dimethyUcetone, CHa-CO-CHs; methylfrojjylketone^ CH3.CO.C8H7; etc.
Methods of Formation.
ICO. Several methods besides the oxidation of alcohols are applicable to the preparation of both aldehydes and ketones.
1. Dry distillation of the salts of the fatty acids, calcium acetate yielding acetone:
CHs-COfa
CH3. COO
>Ca
^CHs-CO-CHa+CaCOa.
The conversion of acetic acid and propionic acid into the cor- responding ketones is readily effected by passing the vaporized acids over aluminium oxide heated to a temperature above 400®.
When an equivalent quantity of a formate is nuxed with the salt of the other fatty acid, an aldehyde is produced by the dis- tillation:
CaHj. colore HCOONa
=C3H7-G<2+NaaC03.
§ 1011 ALDEHYDES AND KETONES, 133
When a mixture of the salts of two different fatty acids, excluding formates, is distilled, mixed ketones are obtained:
CH3 .COlONal ^ CH3 .CO .C2H5+Na2C03.
C2H5« COONa Methylethylketono
Ketones are also readily formed by passing the free acids as vapour over precipitated aluminium oxide, AI2O3, at 400°.
2. Aldehydes or ketones can be obtained from compounds containing two halogen atoms linked to a single carbon atom, by heating them with water:
CH3-CH[Cl2 + H2)0 « CH3.CHO+2HCI.
Ethylidene chloride
3. When primary or secondary alcohols in the gaseous state are passed over finely-divided copper-dust, obtained by reduction of copper oxide, at 250*^-400**, they yield hydrogen, and aldehydes or ketones respectively:
CiiH2n+l'0H = H2 + CnH2nO.
4. An important method for the preparation of ketones, but not of aldehydes, is the interaction of acid chlorides and zinc alkides (75)1 and subsequent decomposition with water. An addition- product is first formed, its production being due to the transforma- tion of the double bond of the oxygen atom into a single one:
O CH yOZnCHs
CnH2n + l •C'^Qi+Zn<QTT' = CnH2n + l '^"(^Hs •
When this addition-product is treated with water a ketone is
formed:
.0|Zn|CH3 HJO]
-C^
CnH2„+,-C^H3 + = C„H2n+i-CO.CH3 + ZnO + CH4 +
\
P H
+ HC1.
loi. Common to the aldehydes and ketones is the power of forming addition-products. This property is due to the double bond of the oxygen atom, the conversion of which into a single bond sets free a carbon linking and an oxygen linking, and thus
134 ORGANIC CHEMISTRY. . I§ 101
enables the aldehydes and ketones to form addition-products with the following elements and compounds.
1. Hydrogen, — An addition-product is produced by the action of sodium-amalgam on an aqueous solution of an aldehyde or ketone; or by passing the vapour of the aldehyde or ketone mixed with hydrogen over heated, finely-divided nickel. Primary alcohols are formed from aldehydes, and secondary from ketones.
2. Sodium hydrogen sidphite, — When aldehydes or ketones are agitated with a very concentrated aqueous solution of this com- pound, a crystalline addition-product is obtained:
CaHfi-C^ J+NaHSOa - CzHg-C^SOaNa.
This constitution is assigned to these compounds because of their ready conversion by the action of dilute acids or sodium-carbonate solution into the corresponding aldehydes or ketones, mere solution in water effecting this decomposition for the higher members. For this reason, it is highly improbable that there is a direct bond between sulphur and carbon (59). I he primary sulphite com- pounds— sometimes incorrectly called " bisulphite" compounds^ dissolve readily in water, but are insoluble in very concentrated solutions of the acid sulphite itself.
All ketones do not yield these addition-products. They are most readily obtained from those containing one methyl-group directly linked to carbonyl, or methylketones.
The use of primary sulphite is often exceedingly serviceable for the purification of aldehydes or ketones, or for separating them from reaction-mixtures.
3. Hydrocyanic acid. — When an aldehyde or ketone is brought into contact with anhydrous hydrocyanic acid, and a drop of an alkaline aqueous solution of potassium carbonate, potassium cyanide, or a similar substance, combination takes place:
(CHj>C0 + HCN=c^5j>C<gJ.
On addition of a small proportion of acid, the catalyst is rendered inoperative, and the cyanohydrins or hydrozynUrUes formed can be obtained in a pure state by vacuum-distillation. This syn-
§§ 102, 103] ALDEHYDES AND KETONES, 135
thesis is important, since the cyanohydrins can be converted into hydroxy-acids by hydrolysis, a reaction affording a means of synthesizing such compounds (179, 5).
102. With Grignard's alkyl magnesium halides (75); alde« hydes and ketones form addition-products, and on treatment with water these yield respectively secondary and tertiary alcohols:
R.c5+R'.Mg.I = R.C^.Mg.I, ^ \R'
Aldehyde A-ddition-produel
H
2R.0O.Mg.I+2H2O - 2R.CH0H.R'+MgIa+Mg(0H),;
f^/ Seooodary alcohol
^^>CO+CHs-Mg.Br = CH3>^<CH^'°''
Aeetone AdditioD-produot
2^8>C<2^^^"®^+2H20-2(CH,)3C.OH + MgBr2+Mg(OH)2.
^113 ^Xl3 Trimethylcarbinol
103. Other reactions common to aldehydes and ketones depend upon exchange of the doubly-linked oxygen atom for other atoms or groups.
1. Phosphorus perUachloride replaces the oxygen atom by two chlorine atoms.
2. Hydroxylamine reacts in accordance with the equation
CHa. nrrv . TT IXT/^TT CH
^>C[0TH2|N0H = ^gJ>C:N0H+H20.
Oximes are thus produced, and are called aldoximes when derived from aldehydes, and ketoximes when derived from ketones. This reaction is of very general application. The oximes are either crystalline compounds, or liquids, and possess both acidic and basic properties. When they are treated with bases, the hydrogen of the hydroxy 1-group is replaced by a metal; with acids, additijii- products are formed, the reaction being similar to the production of ammonium salts:
(CH3)2C=N0H.HC1.
Aoetoxime hydrochloride
1
136 ORGANIC CHEMISTRY. [{ 103
On boiling with dilute hydrochloric acid, the oximes take up one molecule of water, yielding hydroxylamine, and either an alde- hyde or a ketone.
The constitution of the oximes is discussed in 337.
Energetic reduction converts the oximes into amines:
R2C=NOH+4H =R2CNH2+H20.
H
The aldoximes are readily transformed into the corresponding nitriles by the action of dehydrating agents, such as acetic anhy- dride:
C„H2n+l >C=N|OH -► C^H2n+i -CsN. H
Ketoximes undergo a remarkable rearrangement of the atoms in the molecule or intramolecidar transfomuUionf called after its dis- coverer the "Beckmann transformation." It takes place, for example, under the iniiuence of acetyl chloride. The ketoximes thus yield acid amides, with substituents m union with the nitrogen atom .
R.C-R'
I -♦ R.CO.NHR'.
NOH
Oxime Amide
~ The behaviour of aldehydes and ketones with phenylhydrcunne, C6H5NH*NH2 (310), is exactly analogous to that with hydroxyl- amine:
R . r.\r. . TT IXT .TXT ^ XT R
g,>C|0-fH2|N-NH.C6H5 - b;,>C=N-NH.C6H5+H20.
Phenylhydrasine Phenylhydruooe
The substances formed, called hydrazonea, are either well-defined crystalline compounds, or liquids. When heated with hydrochloric acid, they take up the elements of water, forming phenylhydrazine and the corresponding aldehyde or ketone. Phenylhydrazine and hydroxylamine are important reagents for detecting the presence of the carbonyl-group.
The constitution of the phenylhydrazones is thus established. Derivatives of phenylhydrazine obtained by replacement of the hydrogen of the imino-group, — NH, by an alkyl-group, react with aldehydes and ketones similarly to phenylhydrazine itself, so
i 1041 ALDEHYDES. 137
NH that the structure R,G< • ^„ is excluded. This is rendered even
more evident by the fact that only phenylhydrazines containing an unsubstituted amino-group can form hydrazones.
ALDEHYDES.
104. In addition to the properties common to both aldehydes and ketones (101-103), aldehydes have their own special pro* perties.
1. Aldehydeammonia. — Acetaldehydeammonla is produced from aomionia and acetaldehyde:
C2H4O+NH3 = C2H4ONH3.
Aoetaldehyde Aoetaldehydeammootft
It is precipitated in the form of white crystals by the slow intro- duction of acetaldehyde into liquefied, anhydrous ammonia, or by gradual addition of a concentrated aqueous solution of ammonia to the aldehyde at low temperature. It is very soluble in water, and melts at 96*^-98°. Acids decompose the aldehyde-ammonias into an aldehyde and ammonia; potassium hydroxide is unable to effect this decomposition.
At ordinary temperatures the molecular formula of acetaldehyde- ammonia is three times its empirical formula. When dried over sulphuric acid, it loses water and is transformed into a substance of the formula (CHj-CHNIDa, (105) a polymeride of ethylidene- imine. Water reconverts this product into acetaldehydeammonia.
2. Acetals, — An aldehyde combines with two molecules of an alcohol, with elimination of water, and production of an acetal:
OC2H6 p„ p„ ^ OC2H6 , XT O
r\ry TT «=z^rl3'^ll<rkr« tj +1^2^-
Acetals are readily obtained by addition of the aldehyde to a one per cent, solution of anhydrous hydrochloric acid in the alcohol. The reaction is not complete; it is limited by the reverse one, since water acts on acetal, regenerating aldehyde and alcohol. Both the formation and decomposition of acetal are considerably accelerated by the presence of a small quantity of a strong mineral acid, which acts as a poweiful catalyst. The acetals are liquids of aromatic odour, and distil without decomposition. They are not attacked by alkalis, but are resolved by acids into. the compounds from which
138 ORGANIC CHEMISTRY. [§ 105
odour, and distil without decomposition. They are not attacked by alkalis, but are resolved by acids into the compounds from which they were produced, a fact which supports the view expressed in the above structural formula, that the alkyi-groups and the alde- hyde-residue are indirectly united by oxygen, the stability of a carbon chain being sufficient to resist the action of such reagents.
3. Reaction with add anhydrides, — Addition-products are ob* tained with acid anhydrides:
CHs -Cq + 0(C0CH3)2 « CH3 • CH < qqqqS*
Aoetio anhydride
These compounds are analogous to the acetals. They are easQy decomposed by water, and still more readily by alkalis, into the corresponding acid and aldehyde.
105. Two kinds of addition-products are also formed by the union of aldehyde molecules with one another. When a few drops of concentrated sulphuric acid are added to acetaldehyde, a liquid boiling at 22^, the mixture becomes warm, and then begins to boil violently. At the end of the reaction a colourless liquid is obtained, similar to the original one, but boiling about 100° higher, at 124°: The empirical formula of this compound is the same as that of acetaldehyde, C2H4O, but its vapour-density is three times as great, so that it has the molecular formula C5H12O3. This substance, paracetaldehyde, is readil/ converted into acetal- dehyde by distillation with dilute sulphuric acid, another example of a reaction limited by the reverse one:
The equilibrium reached must be independent of the nature of the acid, that is, of the catalyst (" Inorganic Chemistry," 49) , as has been proved for this reaction by experiment. The same equihb- rium must be attained without the aid of any catalyst, but the change proceeds so slowly that no experimental proof has yet been possible. A direct union between the carbon atoms. of the three aldehyde molecules in paracetaldehyde is improbable, and the existence of an indirect linking through the oxygen atoms must be assumed, because it accounts for the ease with which the molecule
§ 1061 ALDEHYDES, 139
of paracetaldehyde can be resolved. The compound is not attacked by sodium, and therefore cannot contain hydroxyl-groups. It lacks all the characteristics of aldehydes, proving the absence of
the group — C^Tct- These properties are best expressed by the
constitutional formula
CHs^C C'CHs
I I
o o
CHa
The union of two or more molecules of a substance to form a body from which the original compound can be r^enerated is called pciymerizcUum.
io6. Under the influence of dilute alkali-solutions aldehyde molecules combine with production of compounds of a different kind. When an aqueous solution of acetaldehyde is warmed with concentrated caustic potash, the liquid becomes yellow; after a short time, reddish-yellow, amorphous masses are precipitated. The aldehyde has resinifid, and the reddish-yellow substance formed is called aldehyde-resin. When, however, dilute caustic potash (or sodium acetate, zinc chloride, etc.) is added to acetalde- hyde, a substance is formed having the same empirical composition as acetaldehyde, but with double the molecular formula, C4H8O2. This compound is called aidol: it is a liquid, distilling without de- composition under diminished pressure, and readily undergoing poly- merization. It possesses the properties characteristic of aldehydes, yielding on oxidation, for example, an acid with the same number of carbon atoms. The acid thus obtained has the formula C4ll80^, and is a n-hydroxybutyric acid; that is, n-butyric acid with one H-atom of the alkyl-group replaced by hydroxyl. It can be con- verted into n-butyric acid, with a chain of four carbon atoms, proving the presence of a similar chain in aldol. Hence, in this case, the union of the aldehyde molecules has been effected through the carbon bonds, a view supported by the fact that aldol cannot be reconverted into aldehyde. The combination of the aldehyde molecules to form aldol may be represented by the equa* tion
140 ORGANIC CHEMISTRY. (J 107
CHa-cJ+^HCHa-C^ = CHa-C^CHg-CQ.
Aldol
This constitutional formula expresses the properties of aldol.
Instead of explaining the formation of aldol by assuming the combination of one of the hydrogen atoms of one aldehyde molecule with the oxygen atom of another to form hydroxyl, it might be supposed that an aldehyde molecule unites with a molecule of water, the addition-product formed reacting with a second molecule of aldehyde with elimination of water:
H CH,.c5+H.O -CH,.C<gJJ;
H CH..C<?L^ H ^H
0H+HJCH,.CH0 - CH,.C <cH..CHO+^«°-
Aldol
Reactions are often explained by assuming the formation of sucb addition-products and the subsequent elimination of water. In a few instances this view has been experimentally verified.
Aldol is both an alcohol and an aldehyde, hence its name, aW(ehyde-alcoh)oi. The union of molecules through carbon bonds, as in the formation of aldol, with the production of compounds from which the original substance cannot be regenerated by any simple method, is called condensation.
It is probable that aldehyde-resin is a product resulting from continued condensation of the aldol molecules with elimination of water, just as aldol itself readily loses one molecule of water when heated, with formation of crotonaldehyde (142) :
CH,.CHOH.CH,.Cq-H,0=CH,.CH:CH.Cq.
Aldol Crotonaldehyde
The mechanism of the condensation of the higher aldehydes always involves transposition of a hydrogen atom linked to the carbon atom carrying the aldehyde-group of one molecule, this hydrogen combining with the carbonyl-oxygen of another molecule
fi 1071 ALDEHYDES, 141
to form hydroxy!, the liberated carbon valencies being simulta* neously saturated:
CiJBf CHH H
I Xi V f\C • CmHsm-f 1 =™ CnHin+i • CH • CHOH • CmHtm+l*
o eg
WiELAND has made some interesting experiments on the oxidation of aldehydes to acids. The old theory assumed the direct union of the aldehyde with an atom of oxygen:
R-CHOH-0=R^OBL -
WiELAND has proved the mechanism of acid formation to depend on an initial combination of the aldehyde with water, the addition- product formed subsequently losing hydrogen, which is oxidized to water:
R*CHO+H,0=R.CH(OH),;
R*CH(0H),=R*C(X)H+2H;
2H-|-0=H,0.
Agitation of an aqueous solutioF of aldehyde with palladium-black in absence of air produces the corresponding acid and palladium hydride. On access of air, or addition of an oxidizer, the hydrogen attached to the metal is oxidized, and there is a further formation of acid. The presence of water is essential to the production of acid, for although anhydrous acetaldehyde and dry silver oxide do not react, addition of water instantly induces energetic oxidation. f By means of analogous experiments, Wieland has demonstrated the conversion of primary alcohols into aldehydes to be dependent on the abstraction of two hydrogen atoms from the CHiOH-group.
Tests for Aldehydes.
107. The following tests serve for the detection of aldehydes.
1. Resinification with alkalis.
2. Reduction of an ammoniacal silver solution. This solution is prepared by adding excess of caustic potash to a solution of silver nitrate, and then just sufficient ammonia to dissolve the precipitated silver oxide. When this liquid is brought into a dilute aqueous solution of an aldehyde, and the mixture warmed, a beautiful mirror of metallic silver is deposited on the sides of the tube.
142 ORGANIC CHEMISTRY. \\ 108
3. When an aldehyde is added to a solution of magenta dacolorized by sulphurous acid — Schiff's reagent — the red colour is restored.
Formaldehyde, H • C ^ q .
zo8. Formic acid, the first member of the homologous series of fatty acids, has certain properties not possessed by the higher members (8z). Formaldehyde affords another striking example of this phenomenon of disparity between the first and succeadin^^ members in a homologous series.
It is obtained by the oxidation of methyl alcohol, effected by passing a mixture of air and methyl-alcohol vapour over a hot spiral of platinum or copper. The heat produced by the reaction is sufficient to raise the temperature of the spiral to redness, and to maintain it at that point, provided the stream of gas is passed over it with sufficient velocity. The formaldehyde produced is absorbed by water, in which it dissolves readily.
This aldehyde is a product of the incomplete combustion of wood, peat, and many other organic substances This fact explains its presence in traces in the atmosphere, especially in that of large towns. Its formation from methane and ozone is also noteworthy.
Formaldehyde has a very pungent odour. At ordinary tem- peratures it is gaseous, but when cooled with solid carbon dioxide and ether, it forms a liquid boiling at — 20°. Even at this tem- perature polymerization begins, and at higher temperatures it proceeds with explosive energy. When the aqueous solution is evaporated, para/ormaWeA?/de, a crystalline polymeride of unknown molecular weight, is produced. It melts at 63^. On concentrat- ing a solution of formaldehyde with strong sulphuric acid, only part of the formaldehyde is evolved as gas; the rest polymerizes, and remains as a white, crystalline mass, a mixture of a-, /?-, and Y'polyoxymeihylene. The molecular weights of these polymerides are not known: on heating, they are reconverted into formalde- hyde, proving them true polymerides. Prolonged heating of the ;'-variety with water yields another polymeride, o-poyoxy methylene. On treatment with ammonia at the ordinary temperature, formal- dehyde does not yield an aldehydeammonia, but a complicated
f 108] FORMALDEHYDE, 143
compound, C6H12N4, hexamethylenetetramtnef (CHa)6N4, a crys- talline, very hygroscopic, basic substance, employed as a medicine under the name " urotropine." At 120^-160° and increased pressure, methylamines are formed :
2NH8 + 3CH20=2NH2-CH3+C02+H20; 2NH3 -h 6CH2O = 2NH (CH3) 2 + 2CO2 + 2H2O; 2NH3 + 9CH2O = 2N(CH3)3 + 3CO2 -h 3H2O.
When treated with potassium hydroxide, formaldehyde does not resim'fy, but is converted into methyl alcohol and formic acid :
2CH2O -h H2O =CH30H + HCOOH.
When a fifteen per cent, solution of formaldehyde is mixed with an equal volume of a solution of sodium hydroxide, and a small proportion of cuprous oxide added, formic acid is produced, with evolution of hydrogen:
H.CH0 + H20=H-C00H + H2.
The oxime of formaldehyde also polymerizes readily. For- maldehyde and its derivatives display a much greater tendency towards polymerization than the other aldehydes and their deriva- tives, and differ from them in their behaviour with ammonia and with caustic potash.
An aqueous solution containing 40 per cent, of formaldehyde is a commercial product, and is called "formalin." After dilution, it is employed as a disinfectant, and in the preservation of ana- tomical specimens. It possesses the remarkable property of con- verting protein substances into a hard, elastic mass, quite insol- uble in water. The contents of a hen's egg, for example, undergo this transformation through contact with formaUn for half-an- hour; brain-substance attains the consistency of india-rubber; and a solution of gelatin is converted into a harj, transparent, in- soluble, odourless mass, reducible to a fine powder. Before development, photographic films with a basis of gelatin are immersed in a dilute solution of formaldehyde for a short time to render the gelatin insohible.
The condensation of formaldehyde is discussed in 206.
144 ORGANIC CHEMISTRY. [f 109
The concentration of a formalin solution is determined by adding excess of a solution of twice normal sodium hydroxide, and then hydrogen peroxide, the formaldehyde being converted completely into formic acid. The excess of alkali is estimated by titration, and from the result the amount of formaldehyde can be calculated, since one molecule of the aldehyde yields one molecule of the acid.
Acetaldchydc, CHs-C^q.
ZOQ. Acetaldehyde is the typical aldehyde of this series, since it has all the properties characteristic of aldehydes as a class. It is obtained by the oxidation of ethyl alcohol by means of potassium dichromate and sulphuric acid, and is a liquid with a disagreeable odour, at least in the dilute state: it boils at 22^, and solidifies at — 120-6®. It readily polymerizes to paracet aldehyde. C6H12O3 (105), or to metacetaldehyde. The molecular weight of this product is not known with certainty, but cryoscopic determina- tions point to the formula (C2H40)4, or a polymeric multiple of it. Metacetaldehyde forms well-developed,^ acicular crystals, which begin to sublime at 150°. Neither it nor paracetaldehyde exhibits the aldehyde reactions; for example, neither is resinified by alkalis.
The inter-relationship of acetaldehyde, paracetaldehyde, and metacetaldehyde is still a matter of doubt, but certain facts have been definitely established. Acetaldehyde is converted into par- acetaldehyde by the action of various catalysts, among them sul- phuric acid at ordinary or somewhat higher temperature, met- acetaldehyde being also produced in small proportion. If the liquid is strongly cooled immediately after addition of the catalyst, metacetaldehyde is the main product, and crystallizes out in well- developed needles, but paracetaldehyde is also formed. If the temperature rises, metacetaldehyde is decomposed under the influence of the cataljrst, with prodliction of acetaldehyde and par- acetaldehyde. No direct transfortnation of metacetaldehyde into paracetaldehyde has been observed, the mechanism of the trans- formation probably involving a preliminary complete depol3rmeriza- tion to acetaldehyde, followed by the formation of paracetaldehyde.
Addition of a very small proportion of sulphuric acid to ice-cold acetaldehyde generates metacetaldehyde, but, on further addition of sulphuric acid, the metacetaldehyde disappears, and paracetal-
S 110] KETONES. 146
dehyde is formed. Calcium chloride, a much less energetic catal3r8t| also induces the formation of metacetaldehyde, paracetaldehyde being produced only in traces. The equilibriiun between acetal- dehyde and metacetaldehyde is, therefore, much -more readily attained than that between acetaldehyde and paracetaldehyde. The predominance of paracetaldehyde or metacetaldehyde in the ternary system
Paracetaldehyde ^ Acetaldehyde ^ Metacetaldehyde
is dependent on the experimental conditions, temperature being a very important factor.
In practice, acetaldehyde is transformed into paracetaldehyde by addition of sulphuric acid, the catalyst being rendered inopera- tive by neutralization of the acid after completion of the reaction. The acetaldehyde and paracetaldehyde can then be readily separated by distillation. Inversely, the conversion of paracetaldehyde into acetaldehyde is effected by addition of sulphuric acid, and dis- tillation of the mixture from a water-bath. The volatilization of the acetaldehyde upsets the equilibriiun, causing the catalyst to decom^ pose a fresh portion of paracetaldehyde. The acetaldehyde thus produced distils, and the process continues until the conversion into acetaldehyde is complete.
In- preparing metacetaldehyde, the acetaldehyde is cooled to a low temperature, and dilute sulphuric acid added. Metacetalde- hyde crystallizes out, and can be isolated by filtration. The mode of reconverting it into acetaldehyde is similar to that described for paracetaldehyde.
KETONES.
iio. The properties characteristic of the ketones are described in 101-103. The first member of the homologous series cannot contain less than three carbon atoms.
Ketones have the general formula R»CO»R', and are always divided at the carbonyl-group by oxidation (99) ; that is, oxida- tion occurs at that part of the molecule already containing oxygen (45). The decomposition can, however, take place in two different
ways:
R.|CO.R' or R.CO.|R'.
z n
Thus, methylnonylketone, CHa-jCO-ICoHio, can yield formic
I n
146 ORGANIC CHEMISTRY. [% 111
acid, CH20a, and capric acid, C10H20O2; or acetic acid, C2H4O2, and pelargonic acid, C9HX8O2; the decomposition taking place at the points indicated by the lines I. and II. respectively. The oxida- tion is such that the decomposition takes place at both points simultaneously, so that four acids are obtained. Two of them may be identical; for example, the oxidation of methylethylketone, CH3 -CO -02116, produces acetic acid and acetic acid by decom- position at point II., and formic acid and propionic acid by decom- position at I. Tsually the reaction which leaves the carbonyl in union with the smallest alkyl-residue predominates. Oxidation therefore affords a means of determining the position of the car- bonyl-group in the ketone molecule.
The ketones are further distinguished from the aldehydes by their behaviour towards ammonia : this reaction has been care- fully investigated for acetone, the first member of the series. By elimination of water it yields complicated substances, such as diacetoneamine, CeHisNO or (2C3H6O + NH3 — H2O), iriacetone- amine, C9H17NO or (3C3H6O + NH3-2H2O), and so on.
The ketones do not yield polymerides, but are capable of form- ing condensation-products.
Acetone, CHa-CO-CHs.
III. Acetone is prepared on the manufacturing scale from crude wood -spirit (42), and by the dry distillation of calcium ace- tate. It is present in very smaU quantities in normal urine, but in much greater proportion in pathological cases, such as diabetes mdlitus and acetonuria. It is a liquid of peculiar, peppermint-like odour, boils at 56 • 3°, solidifies at -94-9°, and has a specific gravity of0»812at0®. It is an excellent solvent for many organic com- pounds, and is nuscible in all proportions with water; on addition of certain salts, such as potassium carbonate, the h'quid separates into two layers. It is converted by reduction into isopropyl alcohol (150), and jdelds a crystalline oxime melting at 69®. Condensation-products derived from acetone are considered in 143 and 285.
Sulphonal, an important soporific, is prepared from acetone. In presence of hydrochloric acid, acetone unites with ethylmercaptan with elimination of water:
§ 1111 ACETONE. 147
(CH,),C0+2HS.C,H, - {CH,),C(SC,H.),+H,0.
Dimethyldiethyi- mercaptole
Oxidation with potassium permanganate converts the two sulphur atoms of this compound into SO,-groups, forming diethylsulphonedi- methyhnethane, (CH,)/]!(SO,CaH«),y or sulphonal. It crystallizes in colourless prisms, soluble with difficulty in cold water, and melting at 126°.
The soporific action of sulphonal must be ascribed to its ethyl- groups. Dimethylsidphonedifnethylmethane (I.) lacks this property; but as its methyl-groups are replaced by ethyl-groups, the hypnotic pointer becomes augmented, attaining its maximum in teironal (IV.) (compare 271):
CH, SOjCH. CH, SOiCJI.
L ^>c/ • II.
X
CH, S0.C3H, CH, SO,CH.
Sulphoiud
CH. SO,C,H. CH. SOtCJI,
m. Nc^ '^ , IV. \c/
CH. SOiCiH. CJI. SOiCJI.
Trional Tetronal
UNSATURATED HYDROCARBONS.
I. ALKYLENES OR OLEFINES, C„Hto.
Methods of Formation.
ZZ2. 1. The olefines are formed in the dry distillation of com- plicated carbon compounds, a fact which accounts for their pres- ence to the extent of 4-5 per cent, in coal-gas.
2. By elimination of the elements of water from the alcohols
CnH2n+20:
CsHn'OH = C5H10 + H2O.
This can sometimes be effected by heat alone, as with tertiary alcohols, but it is usually necessary to warm the alcohol with a dehydrating agent, such as concentrated sulphuric acid (54 and 115) or zinc chloride. Water is more readily eliminated from the secondary and tertiary alcohols than from the corresponding pri- mary compounds.
3. By abstraction of hydrogen halide from alkyl halides, effected by heating with alcoholic potash, a solution of caustic potash in alcohol :
CnH2n+ 1 1 + KOC2H5 = CnH2n + KI + C2H5OH.
An ether is also formed (55) :
CnH2n+lI + KOC2H5 = CnH2n+lOC2H6 + KI.
With alkyl iodides the reaction chiefly follows the first equation^ the secondary and tertiary iodides being specially adapted for the production of unsaturated hydrocarbons.
14S i
1113]
OLBFINES.
149
|
Mame. |
Formula. |
Boiling- point. |
Name. |
Fonnuia. |
Boiliot- point. |
|
Ethylene. . . . Propylene. . . fi-Butylene. . n^Amylene. . . Hexylene. . . . |
-103*» - 48** 39* 68*» |
Heptylene . . Octylene. . . . Nonylene. . . Decr^Iene. . . . Undecylene. |
c,fl„ C,oH„ CiiHa |
98*» 124*» 153*» 172*» 195** |
The names of the members of this series are derived from those of the saturated hydrocarbons by altering the termination "ane " to "ylene." These compounds are denoted by the general name olkylenes or olefines.
To indicate the position of the double bond in the molecule, the alkylenes are sometimes regarded as substituted ethylenes: thus, CHs-CHrCH'CHs is called symmetrical dimeihyleihylene; And (CH3)2C:CH2, unsymmetrical dimeihyleihylene.
Properties.
1 13* The lowest members of this homologous series are gases, and are slightly soluble in water: the higher members are liquids or solids, insoluble in water, but soluble in alcohol and ether. At their melting-points the specific gravities of the lower members are about 0»63, rising with increase in the number of carbon atoms to about 0»79. They are only slightly higher than those of the corresponding saturated hydrocarbons; but their refrac- tions are much higher (120). Like the saturated hydrocarbons, the olefines are colourless.
Their most important chemical property is the power of form- ing addition-products, and on account of it they are said to be unmttirated. Addition-products are very readily obtained by the action of the halogens, especially bromine, on the olefines and other substances containing a double bond, the presence of which can be detected by the decolorization of bromine-water. Another test for the presence of a double bond, suggested by von Baeyer, is carried out by agitating the substance with a dilute solution of potassium permanganate and sodium carbonate. Owing to the reducing action of compounds containing a double carbon bond, the violet colour of the permanganate quickly disappears, with formation of a brown-red, flocculent precipitate of hydrated man- ganese dioxide. Compounds of other classes* such as aldehydes,
160 ORGANIC CHEMISTRY. (§114
react similarly with potassium permanganate, so that the test can only be applied in their absence to hydrocarbons, unsaturated acids, and a few other substances.
The hydrogen halides react by addition with the olefines to form the alkyl halides, hydriodic acid combining very readily.
Concentrated sulphuric acid yields the alkylsulphuric acids by addition: it is sometimes necessary to employ the fuming acid. The addition of sulphuric acid, like that of the hydrogen halides^ results in the union of the acid-residue with the unsaturated carbon atom linked to the smallest amount of hydrogen. For example,
CH tsobutylene, pTT^>C:CH2, treated with sulphuric or hydriodic acid
yields
CH3 ^ piTT ^_ CH3
CH, > 9-~CH3 or ^JJ3 > C-CH3. ' SO3H 1
This reaction may be otherwise expressed by stating that there is a tendency for the number of methyl-groups to increase in such Edition-reactions.
Hypochlorous acid, CI -OH, can also form addition-products which are chloro-alcohols:
CH2=CH24-C1 .OH = CHzQ .CH2OH.
Ethylene Qlyoolchlorohydim
114. defines can form condensation-products, butylene and the amylenes yielding them on treatment with moderately dilute sul- phuric acid, although ethylene cannot be similarly condensed. The condensation may l^e explained by assuming that an addition- product with sulphuric acid, or alkylsulphuric acid, is first formed, and then reacts with a second molecule of the olefine:
Qjj (CH3)2C — CH3
s-sn-CHo-^ I
OSQaHH-HHC.CCCHa)^
cgJ>C:CH2
(CH3)2C — CH3
"* H(')=C(CH3)2. The simplest member of this series, CH2, methylene, has not
( 115] ETHYLENE. 151
been obtained. Various attempts have been made to prepare it: for instance, by the elimination of HCl from methyl chloride. Such experiments have always resulted in the formation, not of methylene, but of ethylene, two CHa-groups uniting to form a single molecule.
Ethylene, G2H4.
115. Ethylene is a gas, and is usually prepared by heating a mixture of ethyl alcohol and sulphuric acid. Ethylsulphuric acid is first formed (54), and on further heating decomposes into ethyl- ene and sulphuric acid :
C2H5SO4H =C2H4 + H2SO4.
In the preparation of ether ($6) the temperature is maintained below a certain limit, and fresh alcohol is continually added, but in this reaction a higher temperature is employed, and no alcohol is added. At the temperature of the reaction, sulphur dioxide and carbon dioxide are produced, but can be removed from the ethylene by passing it through dilute alkali.
It has been customary to add sand to the mixture of alcohol and sulphuric acid in the flask, with a view to prevent undue foam- ing of the hquid. Senderens has proved that the sand exerts a catalytic, accelerating influence, producing a more vigorous evolu- tion of gas at a lower temperature. Addition of 5 g. of anhydrous aluminium sulphate per 100 c.c. of liquid is even more effective, and also practicaUy eliminates the tendency to foaming.
A purer product is obtained by passing the vapour of ethyl alcohol over clay balls heated at 300°-400°, water and ethylene being formed. When passed over aluminium oxide at 400°, ether-vapour also gives a good yield of water and ethylene.
Ethylene can also be prepared from ethylene bromide, C2H4Br2, by removal of its two bromine atoms, which is effected by bringing it into contact with Gladstone and Tribe's copper-zinc couple.
Ethylene possesses a peculiar, sweetish odour, and bums with a luminous flame. It is slightly soluble in water and in alcohol. When passed into bromine it is quickly converted into ethylene
152 ORGANIC CHEMISTRY. [§§ 116, 117
bromide, €2114612 (148). It is readily absorbed by concentrated sulphuric acid at 170°, with formation of ethylsulphuric acid. Sabatier found that a mixture of hydrogen and ethylene is changed completely into ethane when passed over finely-divided nickel at temperatures of less than 300° (a8).
Amylenes, G5H10.
116. A mixture of isomeric amylenes and pentane is technically prepared by heating fusel-oil (43) with zinc chloride.
The isomeric amylenes can be separated by two methods, also applicable in other similar cases. One is based on the solu- bility at a low temperature of some of the isomerides in a mixture of equal volumes of water and concentrated sulphuric acid, with formation of amylsulphuric acids; the other isomerides are insol- uble. This treatment, however, converts part of the amylenes into condensation-products, called diamylene and triamylene. The other mode of separation depends upon the different velocities with which the isomeric amylenes form addition-products with hydriodic acid.
The Structure of Unsaturated Compounds.
117. Hitherto the existence of a double carbon bond in the alkylenes has been arbitrarily assumed: the constitution of un- saturated compounds could, however, be represented in a variety of ways.
1. Existence of bivalent or tervalent carbon atoms:
n mm
CH3 — C — CH3, CH2 — CH — CHis*
2. Existence of free bonds:
a. On one carbon atom only:
CH
8
— J^;— CHs.
6. On different carbon atoms:
GH3 — CH — CH^t
I 1
§ 117] STRUCTURE OF UNSATURATED COMPOUNDS. 163
3. Existence of a doiMe carbon bond:
CH3 ^-CH=^3H2» 4» Existence of a closed chain or ring:
CH2 — CHa,
\/
CHa
It is stated in 1x3 that unsaturated compounds are convertible into »aturnted compounds by addition of atoms or groups. The constitution of these addition-products on the one hand, and the method of formation of the unsaturated products obtained by the elimination of a hydrogen halide, etc., from the saturated com- pounds on the other, enable a decision to be arrived at between these four possibilities.
It should be observed that the addition-product is the same, whether the existence of a bivalent carbon atom, or of two free
bonds on the same carbon atom, be assumed. Thus, whether
II propylene be supposed to have the constitution CHa-C-CHs or
CHa-C-CHa, the addition of bromine produces the same substance, A
CHa-CBra-CHa. Similarly, the assumption of tervalent carbon atoms, or of free bonds on different carbon atoms, leads to the
m in
same result; CHj^CHa with two tervalent carbon atoms, and CHa-CHa with free bonds, yielding with bromine the same addi^
I I
tion-product, CHaBr-CHaBr. It follows that for the present it is unnecessary to treat cases 1 and 2 separately.
It is readily proved that addition does not take place at only one carbon of unsaturated compounds, for otherwise ethylene chloride, C2H4CI2J would have the constitution CHa-CHCla, and ethylene itself, CHa-CH. Ethylene chloride would then be iden- tical with the product obtained by the action of phosphorus penta- chloride upon acetaldehyde, CHa«CHO, since the exchange of the oxygen atom in the latter for two chlorine atoms yields a com- pound of the formula CHa-CHCla. But ethylene chloride is differ- ent from the compound C3H4Cla (ethylidene chloride) got from aide-
154 ORGANIC CHEMISTRY. [§ 118
hyde. Similarly, propylene chloride, C3HeCl2, formed by the addition of chlorine to propylene, is not identical with the reaction- product obtained by treating acetone with phosphorus penta- chloride, CH3«CCl2*CH3 (chloroacetane), nor with that from pro- pionaldehyde, CH3.CH2 -011012 (propylidene chloride). Ethylene
n
therefore cannot have either the formula CHa-CH or CHs-CH.
nor propylene any of the formulas CHa-C-CHs, CH3-CH2-CH,
A A
n n
CH3 • C • CH3 , or CH3 • CH2 • CH.
1 18. A further insight into the structure of the unsaturated com- pounds is derived from other considerations. Propylene is obtained by the elimination of HI from n-propyl iodide, CH3«CH2»CH2l. The same compound is produced by the removal of HI from isa- propyl iodide, CH3-CHI-CH3. Hence, it follows that propylene
CH2 — CH2 cannot have either the formula CH2-CH2-CH2 or \.y/ , and
I I CH2
therefore the remaining possibilities are CHs-CH •CH2,
II
CH3-CH.CH2, and CH3.CH:CH2.
isoBuiylene, C4H8; is similarly formed by the elimination of HI from both .iso6i^7/Z iodide j (CH3)2C[H|CH2|T], and tertiary butyl
iodide f (CH3)2Cpr| -CH2JH]. Thus, isobutylene can only have one of
III in
the formula (CH3)2C.GH2, (CH3)2C.CH2, and (CH3)2C:CH3.
Both these examples indicate that the removal of hydrogen halide from an aUcyl halide necessitates the elimination of a halogen atom and a hydrogen atom respectively in union with two carbon atoms directly linked together.
Other examples serve as further illustrations of this principle. It
OH HI be removed from a pentyl iodide, Q^TT^>CH-CH2r, the result- ing amylene, C5H10, should, in accordance with the principle, have
OH the constitution ^i ir^ >C-0H2. That it actually has is proved bv
the fact that the addition-product obtained by the action of hydri- odic acid on this amylene is not the original pentyl Iodide, but one
S 1191 STRUCTURE OF UNSATURATED COMPOUNDS, 166
with the formula a^tJ^>CI-CH3, as is established by replacement
of I by OH, and comparison of the tertiary alcohol thus obtained with that of the same formula prepared by the synthetic method described in 102 •
The constitution of another pentyl iodide, (CH3)jCH -0112 -01121, which yields CsHio on elimination of HI, may be similarly estab- lished. With hydriodic acid this amylene yields another pentyl iodide, (CH3)2CH-CHI-CH3: the constitution of this compound is proved by its conversion into an alcohol which yields a ketone on oxidation, and is therefore a secondary alcohol.
BuTLEROW has proved that the removal of hydrogen halide is impossible when the halogen atom and hydrogen atom are not united with carbon atoms in juxtaposition to one another. He converted isobutylene, (CH,),C:CH„ by addition of two bromine atoms into (CH3),CBr*CH,Br. Elimination of HBr from this di- bromide produced (CHs)tC:CHBr, the constitution of which is in- ferred from its oxidation to acetone :
{CH,),C|:CHBr -* (CH,),0O.
It was not possible again to eliminate HBr from the compound (CH,)sC:CHBr, monobromobiUylene, there being no hydrogen at- tached to the carbon atom in direct union with the CHBr-group.
1x9. From the foregoing considerations it is evident that only three possible constitutipnal formulae remain for the unsaturated hydrocarbons.
1. Two free bonds on two carbon atoms directly linked to one another: R-GH-CH-R'.
m m
2. Tervalent carbon atoms in direct union: R-CH-CH«R'.
3. A double bond between two carbon atoms: R«CH:CH»R'. For several reasons the preference is given to the formula with
the double bond. First, it would be remarkable if only carbon atoms in juxtaposition to one another could have free bonds, or be tervalent. Second, experience has shown that unsaturated com- pounds containing an uneven number of free bonds or tervalent carbon atoms do not exist. Next to the saturated hydrocarbons
156 ORGANIC CHEMISTRY. [§ 120
CnH2a+29 come in order of the number of hydrogen atoms, CnH2nf CnH2n-2i ©tc. Hydrocarbons, CnH2n+i, CnH2n-i, etc., with one or three free bonds, or tervalent carbon atoms, are unknowtr, all attempts to isolate methyl CH3, ethyl C2H5, etc., having failed. The facts afford no support for the assumption of either free bonds or of tervalent carbon atoms. On the other hand, in forming a double linkmg hydrogen halide must be eliminated from adjoining carbon atoms in direct union, thus excluding the possibility of the forma- tion of such compounds as C„H2n+i. Only the existence of the double bond, therefore, explains the observed facts.
The non-existence of free bonds in the unsaturated hydro- carbons has led by analogy to the conclusion that they are also absent from other compounds containing atoms doubly linked, trebly linked, etc., such as nitrogen in the nitriles, oxygen in the ketones, and so on.
120. The assumption of the existence of multiple bonds pre- sents at first sight, however, certain difficulties when the power of forming addition-products fK)ssessed by all such compounds is considered. As has been stated several times, carbon bonds are only severed with difficulty (36), but the double carbon bond is very readily converted into a single one by formation of an addi- tion-product. It is still more remarkable that when a substance containing a double carbon bond is oxidized, the chain is always severed at the double bond. A satisfactory explanation is afforded by the fact that when substances containing a double carbon bond are oxidized, it is often possible to prove that there is no direct rupture of the carbon chain at the double bond, but that an addi- tion-product is first formeil by the taking up of two OH-groups:
\cH \:hoh
II becomes | yCH JCaOK
Such derivatives can often be isolated. Since oxidation always takes place at a point where it has already begun (45), it follows that further oxidation of such a compound must result in a sever- ance of the carbon chain at the position previously occupied by the double bond. The breaking of the unsaturated chain by oxidation therefore depends on the formation of an intermediate addition-
§120] STRUCTURE OF UNSATURATED COMPOUNDS. 157
product, and it is only necessary to find an explanatioi^ for the ease with which the addition is effected, an object best attained by a consideration of the nature of the bonds between the atoms. An affinity or bond may be looked upon as an attraction exercised by one atom upon another. Should an atom possess more than one affinity; it is assumed that the attraction is exercised in more than one direction, and is concentrated at certain points of its surface, somewhat after the manner in which the attraction exercised by a magnet is concentrated at its two poles. Any other assumption, such as that the attracting force is equally distributed over the whole surface of an atom, would make it difficult to understand how each element could have a determinate valency. If the carbon atom is quadrivalent, there must be on its surface foui such points or "poles," situated at the angles of a regular tetrahedron (48). When there is a single bond between two such poles on different carbon atoms, their mutual attraction causes the atoms to approach one another as closelj' as possible.
Von Baeyer has suggested that these poles on the surface of carbon atoms are movable. Such a movement results, however, in a certain " strain," and this tends to make the poles revert to their original position. Thus, on conversion of a single bond between two carbon atoms into a double bond, the directions of the affinities of each carbon atom must undergo an appreciable alteration:
— C C — becomes — C C — .
/\
The resulting strain is therefore a cause of the readiness with which double bonds can be severed. Von Babybr's strain theory affords an explanation of other important phenomena also.
Evidently the double bond must not be regarded as a mere duplication of the single bond, as the expression " double bond " would indicate.
The presence of a double bond exerts a great influence on chemical properties, as has been demonstrated, but its effect on physical properties is no less marked. This phenomenon has been most fully investigated in connection with refraction.
158 ORGANIC CHEMISTRY. [§ 121
The j^iolecular refraction (26) of a large number of unsatu- rated compounds containing a double bond and of the correspond- ing saturated derivatives has been determined by Etkman. His results indicate the molecular dispersion y-a, or the difference between the molecular refraction for the a-line of the hydrogen spectrum and that for the 7-line, to be appreciably greater for unsaturated compounds than for the corresponding saturated derivatives. This phenomenon is exemplified by the molecular refraction of CeHu: for the a-line it is 65*214; for the 7-line it is 66-913; the dispersion is therefore 1-699. For C6H12 the value for the a-line is 64*814, and that for the 7-line is 67*027, the dispersion being 2*213 employing Eykman's formula.
The difference between the molecular refraction of a saturated compound and that of the corresponding unsaturated compound with two hydrogen atoms less in its molecule is denoted by [H2]. Its value for the a-line of the hydrogen spectrum, employing Eykman's formula, may lie between 1*0 and 0*2. Further investigation has proved this variation to depend on the number of carbon atoms in direct union with the group >C=C<. For [H2]i, corresponding with direct union of one carbon atom with the group >C=C<, the mean value has been found to be 0*96; for [H2]2, corresponding with two carbon atoms in direct union, it is 0-59; and for [H2]3 it is 0-24. These examples illustrate the aid furnished by refractometry in Ideating the position in the molecule occupied by a double bond.
There is an important difference between the molecular refrac- tion of a hydrocarbon CnH2n and that of (CHj)^. The value cor- responding with CH2 for the ce-line is given in 33 as 10*260. The molecular refraction a for CcHia is 64*814; whereas that for (CH*)* is 61 • 56. The presence of the double linking causes an increase of the refraction, known as the increment of the double bond.
II. ALICYCLIC COMPOUNDS, CnH,n.
X2X. Isomeric with the olefines is a series of compounds, CnH2n, chiefly distinguished from the former by the absence of, or at least a diminution in, the power of forming addition-producta. Most of these compounds are very stable: thus ct/dopentane, CsHio, closely resembles n-pentane, C6H12. The methods for the
§§ 122, 123] HYDROCARBONS WITH TRIPLE BONDS. 159
formation of these compounds make it evident that there is a ring or closed carbon chain in the molecule (275-280).
III. HYDROCARBONS, CnHa-i.
122. Two structures are possible for these compounds, which contain four hydrogen atoms Ixsss than the corresponding paraffins. Hydrocarbons with two double bonds have the general formula CnH2n-2; for example,
CH2'CH»CH5CH2.
Vinylethylene
Further, substances with a triple bond have the same general for- mula; for example,
CH3 • C^ECIi*
AUylena
The triple linking here is assumed for reasons similar to those applicable to the double bond in the olefines (119).
A. HYDROCARBONS WITH TRIPLE BONDS.
Nomenclattire.
133. The first meml)er, C2H2, is called acetylene: the second, O3H4, aUylene: the higher members are regarded as substituted acetylenes; thus G4H6 is called ethylaceiylene; CeHio, hutylacetylene; and so on.
Methods of Formation.
1. By the dry distillation of complex compounds such as coal; hence the occurrence of acetylene in coal-gas.
2. By the withdrawal of two molecules of hydrogen halide from compounds of the formula CnH2nX2, where X represents a halogen atom, these compounds having been previously formed by the addition of hal(^en to alkylenes:
CH2Br— CH2Br-2HBr=CFlEC?I.
Ethylene bromide Acetylene
The elimination of hydrogen halide is effected by heating with alcoholic potash.
160 ORGANIC CHEMISTRY. [§ 124
A general method for the preparation of unsaturated com- pounds is furnished by this method of adding on halogen, followed by the removal of hydrogen halide. Thus from CnH2n+2, CnH2n+iX is obtained by the action of chlorine or bromine. Heating with alcoholic potash converts this into CnH2n, from which CnH2nBr2 is got by the action of bromine, and is converted into CnH2n_2 by abstraction of 2HBr. This compound can again form an addition- pifoduct with bromine, and so on.
3. By the elimination of 2HX from compounds of the formula CnH2nX2, previously formed by the action of phosphorus penta- halide upon aldehydes or ketones:
CH3-CHC12 - 2HC1 = CH=CH.
Ethylidene ohloride Aoetylene
CH3*CCl2'CH3 — 2HC1 = CHs'CSCH.
ChloroaoetoDe Aliylene
124. Some of the hydrocarbons prepared by the foregoing methods exhibit a characteristic behaviour towards an ammoni- acal solution of cuprous chloride or of a silver salt, which affords a ready means of recognizing them. By replacement of hydrogen, they yield metallic derivatives, insoluble in the ammoniacal solu- tion or in water, which separate out as a voluminous precipitate. These compoimds are explosive, the copper yellow or red, and the silver white. Acetylene, and of its higher homologues, those derived from the dihalogen compounds of the aldehydes, yield metallic compounds of the type C2CU2. The method of formation of these homologues shows that they contain the group ^CH :
CnH2n+l •CH2 'CHO — > CiiH2n+l -0112 •CHCI2 — > C11H211+I -C^CH.
From this it may be concluded that the presence of (he group 3 ia essential to the yielding of metallic derivatives: it is the hydrogen of this group which is replaced by metals. In support of this view is the fact that only the dichloro-derivatives of the methylketones (loi) can be transformed into hydrocarbons yielding metallic compounds:
CnH2n+l •CO-CHs — > CnH2n-|-l •CCl2*CH3 — ► CnH2n+l -CSCH;
Yields metalUc deiivativM
C2H6*C0»C2H5 — >C2H5«0Cl2*CH2*CH3 — ► C2H5«C=C»CH3.
Does not yield metaUie denyatives
§ 125] HYDROCARBONS WITH TRIPLE BONDS. 161
The isomeric hydrocarbons containing two double bonds (127) are also incapable of forming metallic compounds.
The hydrocarbons are readily liberated from their metallic derivatives by the action of dilute hydrochloric acid. This affords a means of isolating from mixtures the members of the series CnH2n-2 which yield such derivatives, and of obtaining them in the pure state.
125. The hydrocarbons of this series can add on four halogfen atoms or two molecules of a hydrogen halide. In presence of mercury salts they can take up water, forming aldehydes or ketones :
CH=CH+H20 = CHa-CHO. CHa-C^CH + HzO = CHa-CO-CHs.
Mercury compounds are first formed by addition: thus, when allylene, C3H4, is passed into a solution of mercuric chloride, there is first formed a precipitate of the composition 3HgCl2,3HgO,2C3H4, which is converted into acetone by the action of hydrochloric acid.
The hydrocarbons of the acetylene series also 3rield condensa- tion-products. The condensation sometimes takes place between three molecules: thus, acetylene, C2H2, condenses to benzene, CeHe; dimethylacetylene, C4H5, to hexamethylbenzene, C12H18; etc. This transformation is effected by the action of heat on acety- lene, and of sulphuric acid on its homologues.
A remarkable reaction, resulting in a change in the position of the triple bond, takes place when the hydrocarbons of the series CnH2n-2 Containing the group =CH are heated to a high tempera- ture in a sealed tube with alcoholic potash:
C2H6-CH2-C=CH is converted into C2H6-CEEC-CH3.
Propylaoetyieiie Methylethylaoetylene
It is probable that addition at one part of the molecule is followed by the elimination of atoms from another part. The displacement of the triple linking in the instance cited is proved by the fact that although propylacetylene yields metallic derivatives, the substance obtained by heating it with alcoholic potash does not, but is con- verted by oxidation into propionic acid and acetic acid. This deter- mines the position of the triple bond, since, for reasons similar to
162 ORGANIC CHEMISTRY. [§ 126
those applicable to the double bond (120), the carbon chain is broken by oxidation at the point occupied by the multiple bond. The substance obtained must therefore have the formula givea above, and be methylethylacetylene.
Acetylene^ G2H2.
126. Acetylene is a colourless gas of disagreeable odour, is somewhat soluble in water, and condenses at 18° and 83 atmos- pheres to a liquid boiling at —82.4**. It can be synthesized from its elements by the aid of an electric-arc discharge between carbon poles in an atmosphere of hydrogen, but the maximum yield of acetylene at 2500° is only 3- 7 per cent. At the same temperature, about 1*2 per cent, of methane and a trace of ethane are simul- taneously formed. The presence of acetylene can be detected by means of an ammoniacal solution of cuprous chloride, which 3de]ds a red precipitate of copper acetylene even from traces of acetylene mixed with other gases. Acetylene is also obtained as a product of the incomplete combustion of many organic substances. It is prepared on the large scale by the action of water on calcium carbide, or calcium acetylene, CaC2:
CaC2+2H20 = Ca(OH)2+C2H2.
The reaction is somewhat violent, and is attended with the evolu- tion of a considerable quantity of heat. Calcium carbide is pre- pared by heating carbon with quicklime, CaO, in an electric furnace. Under the influence of the high temperature, the calcium liberated by the action of the carbon on the quicklime enters into combina- tion with the excess of carbon, forming calcium carbide: when pure, it is white, but has usually a dark reddish-brown colour, due to the presence of small quantities of iron.
Various applications of acetylene have been facilitated by the cheap and simple method available for its preparation from cal- cium carbide. A solution in acetone is usually employed in the arts and manufactures, the gas being compressed at twelve atmos- pheres into steel cylinders containing this solvent. At this pressure, one volume of acetone dissolves about three hundred volumes of acetylene. When the gas evolved from tliis solution is allowed to issue from a fine orifice and ignited, it burns with a smokeless, bright luminous flame, and is employed as an illuminant in railway-car-
§ 127] HYDROCARBONS WITH TWO DOUBLE BONDS. 163
ris^es, motor-car lamps, gas-buo3rs, and so on. Another important application is exemplified by autogenous xcddingt sufficient heat being generated by an oxy-acelylene blowpipe to melt iron readily. Steel plates for safes, rails for railway or tramway use, and other iron or steel material can be readily welded by its aid.
Another important application of acetylene is its conversion into acetaldehyde. As stated in 125, under the influence of mercury salts this hydrocarbon can take up the elements of water. The process is sufficiently developed to be technically applicable, the acet- aldehyde admitting of reduction to ethyl alcohol, and of oxidation to acetic acid.
B. HYDROCABBONB WTFH TWO ]X>UBLE BONDS.
127. A hydrocarbon of this series of great importance is isoprene^ CftHs on account of its close relationship to caoutchouc (370). In recent years many attempts to prepare isoprene technically have been made, some with success. A very good laboratory-method for its preparation is mentioned in 367. A poor yield of the hydrocarbon is obtained by the dry distillation of caoutchouc. It is a liquid boiling at 37^, and has the specific gravity D4** *0«6793.
Isoprene is proved to have the constitution rio*^C • CH=CH2 by the
addition of 2HBr, which yields a dibromide, ^^»>CBr-CH,-CH,Br,
identical with that obtained from dimethylallene, pTT*> C=C=CHi. DimethylaUene is thus obtained. Two carbinol-derivatives,
dimethylethylcarbinol, ^J|» > C(OH ) . CH, • CH3, and methylwopro-
CH pylcarbinol, q|j'>CH-CH0H»CH3, are prepared. by the method
described in zoa, and converted into the corresponding iodides. On elimination of HI, each iodide yields trimethylethylene,
OH
nxj*>C— CH«CH„ its formation from both iodides admitting of no
other position for the double bond. Trimethylethylene takes up 2Br, forming ^^»>CBr.CHBr.CH,. On treatment of this sub- stance with alcoholic potash, two molecules of hydrobromic acid, 2HBr, are eliminated, with the formation of dimethylallene.
This mode of formation does not wholly preclude another
164 ORGANIC CHEMISTRY. [§ 127
arrangement of the double bonds, but other evidence proves thai dimethylallene has the structural formula indicated:
1. On oxidation it yields acetone, proving the'presence of the group (CH8)2C=.
2. Treatment with sulphuric acid of 50 per cent, strength con- verts it into methylt«opropylketone:
gH.>Q^:,Q,^H^^2H,0 - ^^•>CH-C{OH),-CH,-*
Intermediate product
Compounds like this intermediate product are referred to in 149.
When forming an addition-product with two univalent atoms, oiiganic compounds containing the group C=C — C=C, called by Th'ielb a " Conjugated system/' often behave peculiarly, the addition taking place at C-atoms 1 and 4, with formation of a double bond between C-atoms 2 and 3 :
CH2=CH.CH=CH2+Br2 = CH2Br.CH=CH.CH2Br.
The subject of conjugated double bonds is further discussed in 283.
Compounds with a conjugated system of double bonds also exhibit characteristic physical properties. A comparison of their molecular refractions with those of the corresponding saturated compounds, or with those of substances containing only a single double linking, shows them to be much higher for conjugated compounds than would be anticipated from the presence of two double bonds. This phenomenon is termed the exaltaiion of the conjugated system, an$l its existence affords a means of deciding whether two double bonds are conjugated or not.
SUBSTITUTION-PRODUCTS OF THE UNSATURATED
HYDROCARBONS.
I. (HffSATURATED HALOGEV COMPOUUDS.
128. Since the saturated hydrocarbons do not themselves pos- sess any salient characteristics, the properties of their compounds depend upon the nature of the substituents. Hitherto, only com- pounds with properties due to the presence in the molecule of a single group, such as hydroxyl, carboxyl, a multiple carbon bond, etc., have been described. Substances containing more than one characteristic group in the molecule must now be considered.
When these groups are present simultaneously in the same molecule, they exercise a modifying influence upon one another. The extent of this influence varies considerably, as is evident from a consideration of the different classes of unsaiurated halogen compounds.
Halogen derivatives of the type CnH2n-iX are obtained by the addition of halogen to the hydrocarbons GQH2n, and subsequent elimination of one molecule of hydrogen halide:
CH2=CH2+Br2 = CH2Br— CH2Br. CHzBr— CHaBr-HBr = CH2=CHBr.
Ethylene bromide Vinyl bromide
They are also formed by removal of one molecule of hydrogen halide from compounds containing two halogen atoms in union with the same carbon atom:
CH3-CH2-CHC12-HC1 = CH3-CH=CHa.
Piopsdidene chloride a-Chloropropylene
CHj-CClz-CHa-Ha = CH3-CC1=CH2.
Chloroaoetone #-ObioropropylsBe
165
166 ORGANIC CHEMISTRY, [§ 129
The methods employed in the preparation of these compounds indicate that their halogen atom is in union with a carbon atom having a double bond. Their properties differ widely from those of compounds like the alkyl halides, with the halogen atom attached to a singly-linked carbon atom; and this rule is general for such compounds. The halogen atom of the alkyl halides is especially able to take part in double decompositions: it is replaceable by hydroxyl, an alkoxyl-group, an acid-residue, the amino-group, and so on.
This aptitude for double decomposition is almost lacking in com- pounds with halogen in union with a doubly-linked carbon aiovru Alkalis do not convert them into alcohols, nor alkoxides into ethers: but invariably, when they do react, hydrogen halide is eliminated, with formation of hydrocarbons of the series CnH2n-2.
129. An isomeride of a-chloropropylene and p-chloropropylene, which have been referred to above, is called allyl chloride. Its halogen atom takes part in double decompositions as readily as the halogen atom of an alkyl chloride. Allyl chloride is obtained by the action of phosphorus pentachloride upon allyl alcohol, CH2 : CH • CH2OH (132) . This alcohol yields n-propyl alcohol by addition of hydrogen, and its hydroxyl-group must therefore be at the end of the carbon chain. Hence, the halogen atom in allyl chloride must also be at the end of the chain, since it takes the place of the hydroxyl-group. Given the constitutions of a-propylene chloride and /5-propylene chloride, which are deduced from those of propionaldehyde and acetone, the allyl halides can only have the constitutional formula
CH2^^^^H • Cri2X.
The halogen atom is attached to a singly-linked carbon atom, and retains its normal character despite the presence of a double bond in the molecule.
The influence exerted upon the character of a halogen atom by its position in the molecule of an unsaturated compound affords a means of determining whether it is attached to a singly-linked or doubly-linked carbon atom, the indication being its possession or lack of the power to take part in double decompositions.
The following are examples of individual members of the series. Vinyl chloride CH2:GHC1 is a gas, vinyl bromide CH2:GHBr a
§S 130, 131] UNSATURATED ALCOHOLS, 167
liquid of ethereal odour. Both these compounds polymerize readily.
130. AUyl chloride, aUyl bromide, and aUyl iodide, boil respec- tively at 46°, 70°, and 103°. They are often employed in syntheses to introduce an unsaturated group into a compound. They have a characteristic odour resembling that of mustard.
The propargyl compounds, CH=C*CH2X, are a type of the series CnH-in-aX. Their constitution is inferred from the facts that they yield metallic derivatives, indicating the presence of the group zhCH, and that their halogen atoms are capable of taking pert in double decompositions, proving their union with a singly- linked carbon atom. They are obtained from propargyl alcohol (133) by the action of phosphorus pentahalides, and are liquids of pungent odour.
Bromoacetylidene, CHBr:C, which is assumed by Nef to contaia a bivalent carbon atom, can be obtained from acetylene bromide, CHBr:CHBr, by treatment with alcoholic potash. It is a gas, boils at —2°, and takes fire spontaneously in the air. Its solution in alcohol is phosphorescent, owing to slow oxidation, and the gas itself has an odour very similar to that of phosphorus.
II. UNSATURATED ALCOHOLS.
131. The hydroxyl-group of the unsaturated alcohols may be attached to a singly-linked or to a doubly-linked carbon atom:
CH2 : CH .CH2OH, CH2 : CH -OH.
Allyl alcohol Vinyl alcohol
Few compounds of the type of vinyl alcohol are known. It is found that reactions which might be expected to yield them generally result in the formation of their isomerides. Thus, when water is abstracted from ^glycol, CH2OH -0112011, there results, not vinyl
XT
alcohol, CH2=CH0H, but an isomeride, acetaldehyde, CH3 — C^ q.
When ^-bromo propylene, CH3-CBr:CH2, is heated with water, theie is formed not /3-hydroxy propylene, CH3'C(OH):CH2, but the isomeric acetone, CH3 • CO • CH3. The rule is that when a group- ing of the atoms in the form — CH:C(OH) — would be expected, a transformation into — CH2'C0 — usually occurs. Although most substances containing hydroxyl attached to a doubly-linked carbon
168 ORGANIC CHEMISTRY, [§ 132
atom are unstable they have a tendency to become transformed into isomerides. Compounds do exist, however, in which the group — CH : C(OH) — is stable (235-236).
The following compounds either contain hydroxy! in union with a doubly-linked carbon atom, or are related to substances of that type.
Vinyl alcohol^ CHsiCHOH, so called because it contains the vinyl-gToxk^y CHjrCH — , is probably present in ordinary ethyl ether owing to partial oxidation. When such ether is agitated with an alkaline solution of a mercury salt, a precipitate of the composition HgsCiiOsCzH, is formed, and on treatment with hydrogen halide yields vinyl-compounds.
A vinyl-derivative of great physiological importance, called neu-
rinCf is formed in the putrefactive decay of fiesh, and in other fer-
CH'CH mentation-processes. Its constitution is {CH,)8N<QrT' ', as is
indicated by synthesis. When trimethylamine reacts with ethy- lene bromide, a substituted ammonium bromide of the formula
(CH3)3N<^^»"^^'^'' is obtained. HBr is eliminated from the
group — CHj-CHaBr by the action of moist silver oxide, the bromine atom attached to nitrogen being simultaneously replaced by hy- droxy!. A substance of the constitution indicated is thus obtained, and is in all respects similar to neurine.
AUyi Alcohol, CHg-.CH.CHaOH.
232. Many imsaturated alcohols containing hydroxyl attached to a singly-linked carbon atom are known. The most important is aUyl alcohol, the preparation of which is described in 163. Its constitution is inferred from that of the chlorine derivative formed by the action of phosphorus pentachloride (129) ; as well as from that of the products obtained by oxidation, by which allyl alcohol is converted first into an aldehyde, acraldehyde, and then into acrylic acid:
CH2:CH.CH20H->CH2:CH.C<:5-*CH2:CH.COOH.
AUylaloohol Acraldehyde ^ Aorylioaeid
Allyl alcohol must therefore contain the group — CH2OH, charac- teristic of primary alcohols.
§ 133] PROPARGYL ALCOHOL. 169
Allyl alcohol is a liquid of irritating odour, solidifying at —60*, and boiling at 96-5^; and is miscible with water in all proportions. Its specific gravity at 0^ is 0-872. It forms addition-products with the halogens and with hydrogen, with the latter yielding n-propyl alcohol.
Many other compounds containing the allyl-group, CH, : CH •CH,— , are known, amoDg them allyl sulphide (CHs:CH*CH2)sS, the prin- cipal constituent of oil of garlic. It is synthetically obtained by the action of potassium sulphide, K^, on ally! iodide.
It is apparent that the influence of the double bond in the unsaturated halogen compounds and alcohols is very pronounced when it is situated in the immediate neighbourhood of halogen or hydroxy I, but that otherwise its influence is much less marked. When two groups are sitiuUed in immediate proximity to one another in the same molecule, each group exercises a strong influence upon the properties of the other.
•
Propargyl Alcohol, CH^C-CHgOH.
133. Propargyl akohd contains a triple bond, and is prepared from tribromohydrin, CHiBr • CHBr • CHiBr (147) . Potassium hydroxide converts this substance into CHi:CBr*CHsBr, which on treatment with potassium acetate and saponification 3rield8 CHi: CBfCHtOH, since only the terminal Br-atom is capable of taking part in a double decomposition (128). When this alcohol is again brought into con- tact with caustic potash, HBr is eliminated, with formation of pro- paigyl alcohol, the constitution of which is indicated by this method of formation and also by its properties. The presence of the group =CU is indicated by the formation of metallic derivatives: on oxidation it yields propiolic acid, CH=C*COOH, with the same number of carbon atoms, proving that it is a primary alcohol.
Propargyl alcohol is a liquid of agreeable odour, soluble in water, and boihng at 114''-115'': its specific gravity at 21'' is 0*963. Its metallic derivatives are explosive.
MONOBASIC UNSATURATED ACIDS.
I. ACmS OF THE OLEIC SERIES, CoHa,. A-
134. The acids of the oleic series can be obtained from the saturated acids CnH2n02 by the methods generally applicable to the conversion of saturated into unsaturated compounds.
1 . Substitution of one hydrogen atom in the alkyl-group of a saturated acid by a halogen atom, and subsequent elimination of hydrogen halide by heating with alcoholic potash.
2. Removal of the elements of water from the monohydroxy- acids:
CH8-CHOH.CH2-COOH-H20=CH3-CH:CH.COOH.
/9-Hydroxybutyrio acid Crotonic acid
The acids of this series can also be prepared from unsaturated compounds by
3. Oxidation of the unsaturated alcohols and aldehydes.
4. The action of potassium cyanide on unsaturated halogen compounds, such as allyl iodide, and hydrolysis of the resulting nitrile.
Nomenclature.
«
Most of the acids of the oleic series are named after the substances from which they were first obtained, but a few of the middle members have names indicating the number of carbon atoms in the molecule. The first member, CH2:CH-(X)0H, is called acrylic acid: others are crotonic acid, C4H5O2; angelic acid and tiglic acid, C6H8O2; undecylenic acid, CiiBi2(f)2t ol^ ^*^» C18H34O2; erucic acid, C22H42O2J etc,
170
§i 135, 1361 ACIDS OF THE OLEIC SERIES, 171
Properties.
135. In common with all compounds containing a double bond, the acids of this series possess the power of forming addition- products. They are " stronger " acids than the corresponding fatty acids containing the same number of carbon atoms in the molecule: thus, the value of the constant 10*A; (87) for propionic acid, C3H6O2, is 0-134; foracrylicacid, C3H4O2, 0-56; for butyric acid, C4H8O2, 0-149; for crotonic acid, C4H6O2, 0-204; etc. The double bond renders the acids of the oleic series much more susceptible to oxida- tion than those of the fatty series (120). The former are converted by energetic oxidizers into two saturated acids, but when the reac- tion is made less energetic by using a dilute solution >of potas- sium permanganate, a dihydroxy-acid containing the group — CHOH'CHOH. — is formed as an intermediate product, and on further oxidation the chain is severed at the bond between these two carbon atoms (120). This behaviour affords a means of deter- mining the position of the double bond in the molecule. A breaking down of the molecule with formation of saturated fatty acids also results on fusion of an unsaturated acid with caustic potash in presence of air:
CnH2n+i*CH: KO KO O
CH-COOH o|H
S -CnH2n+l-C|OK+CH3-COOH,
OK
Formerly the reaction was employed to determine the position of the double bond, on the assumption that the division of the mole- cule was effected at the point where this bond was situated in the first instance. It is now known that under the influence of fused caustic potash, or even by boiling with a solution of caustic soda, the position of the double bond is displaced nearer that of the carboxyl-group. Fusion with caustic potash cannot, therefore, be employed as a means of determining the position of double bonds. The action of ozone on these acids is described in 198.
AcryUc Add, CH2:CH-C00H.
136. Acrylic acid is obtained by the elimination of HI from ^-iodopropionic acid, CH2I • CH2 • COOH. It is a liquid of pungent odour, boiling at 140°, and is reduced by nascent hydrogen to pro- pionic acid.
172 ORGANIC CHEMISTRY. [\ 136
Adds of the formula C4H6O2. The theoretically possible acids of the formula C4H6O2 are
1. CHaiCH.CHz-COOH; 2. CHg-CHiCH.COOH;
3. CH2:C<^q3^jj; 4. | >CH.COOH;
but five acids of the formula C4He02 are known.
An acid of the constitution indicated in formula 1, vinylacetic add, can be obtained by the action of carbon dioxide on allyl mag - nesium bromide, and decomposition of the primary product by acidulated water:
CH2:CH.CH2MgBr+C02=CH2:CH-CH2-C02MgBr;
CH2:CH-CH2-C02MgBr+H20 =
=CH2:CH.CH2-C00H+MgBr.0H.
Its formation by the action of potassium cyanide on allyl iodide, and hydrolysis of the nitrile thus formed, might be expected:
CH2:CH-CH2l -► CH2:CH-CH2CN -* CHziCH-CHa-OOOH.
Allyl iodide
Actually, however, an acid of formula 2 is obtained, solid croUmic add, which melts at 71° and boils at 180°: careful oxidation with permanganate converts it into oxaUc acid, HOOC — COOH, a proof of its constitution. It follows that during the reaction the position of the double bond must have changed.
Etkman has proved allyl cyanide to have the formula
CHi : CH •CH2 'CN. The molecular refraction for the cr-line based on
his formula is
For propyl cyanide, CaH? 'CN 44*55
For allyl cyanide, CaHs-CN 43-51
Difference 1 '04
This difference corresponds with [Haji, indicating the group > C=C< to be in union with only a single carbon atom, and therefore situated at the end of the chain (120).
moCroionic add, melting at 16 •S® and boiUng at 172°, has also constitution 2, because, on the one hand, like solid crotonic acid
§ 1371 ACIDS OP THE OLElC SERIES, 173
it can be reduced to n^butyric acid, proving that it too contains a nonnal carbon chain; on the other, it is converted by careful oxidation into oxalic acid. Ordinary constitutional formula are incapable, therefore, of accounting for the isomerism of these acids, which is explained in 169.
An acid with formula 3 is obtained by the elimination of HBr from bromoiaobutyric acid; it is called meihacrylic acid:
>CBr.COOH-> >C.COOH. CH3/ CH3/
The acid of formula 4 is described in 275.
Oleic Acid, C18H34O2.
137. OU^ add is obtained by the saponification of oils and soft fats (85). To separate it from the saturated fatty acids, stearic and palmitic, simultaneously liberated, the lead salt is pre- pared. Lead oleate is soluble in ether, while lead palmitate and stearate are not. The oleic acid is liberated from the lead oleate by treatment with acids.
At ordinary temperatures, oleic acid is a liquid without odour and of an oily nature. It melts at 14°. It oxidizes readily in the air, and cannot be distilled at ordinary pressures without decom- position.
Oleic acid contains a normal carbon chain, since on reduction it yields stearic acid.
Krapft has proved the normal structure of stearic acid by con- verting it step by step into acids with a smaller number of carbon atoms. When submitted to dry distillation in a vacuum, barium stearate and barium acetate form a ketone, Ci7Hs5«CO«CH3:
CitHw lOOOba* + baO^OC >CH, -> C„H„.CO.CH,.
Barium stearate Barium acetate MargarylmethyOcetoiie
On oxidation, this ketone yields acetic acid and an acid of the for- mula C17H34O2. This proves that the ketone contains a CHj-group next to the carbonyl-group, and has the formula C1QH33 -CHs -CO •CHg,
* ba = iBa.
174 ORGANIC CHEMISTRY, [§ 138
for only from such a compound could oxidation produce an acid with seventeen carbon atoms. This acid, OiyHs^Oj {margaric acid), is similarly transformed into a ketone, CjeHss-CO-CHa, which on oxidation yields an acid CieHjiOj. The formula of margaric acid must therefore be CigHji-CHj-COOH. and that of stearic acid, CsHa, .CH, . CH, . COOH. The acid CicHajOj, palmitic acid, is in its turn converted into a ketone, and the process continued until capric add, CioHjoO,, is obtained. This acid has been proved by synthesis (333t 1) to contain a normal carbon chain.
The presence of a double bond in oleic acid is indicated by its forming an addition-product with bromine, and by its power of reducing an alkaline permanganate solution (113). The double bond is situated at the centre of the chain, the constitution of oleic acid being
CH3 - (CH2)7 .CH : CH . (CH2)7 -COOH.
.This constitution is inferred from the products of careful oxida- tion, which yields pelargonic add, CsHiyCOOH, and azelalc add, HOOC.(CH2)7-COOH.
The hardening, or conversion into solid fats, of oik which are glyceryl esters of the higher unsaturated acids, has in recent years developed great technical importance. The process involves the combination of the unsaturated acids with hydrogen to form the corresponding saturated derivatives. Hydrogen under pressure is passed through a thoroughly agitated mixture of the oil and nickel-powder heated to approximately 200°, the reaction taking place readily under these conditions.
138. Oleic acid reacts in a remarkable manner with nitrous acid, even when brought into contact with a mere trace of this substance. The best method is to pass the red gaseous mixture of nitrogen peroxide and nitric oxide, obtained by heating arsenic trioxide with nitric acid, into oleic acid, or to add nitric acid of specific gravity 1-25. The oleic acid soon solidifies, having been converted into an isomeride, elaidic add. The reaction is called the "elaidic trans- formation." Other acids of this series are similarly transformed: thus, erudc add, C22H42O2, is converted by a trace of nitrous acid into hrassidic acid.
Elaidic acid has the same structural formula as oleic acid, the double bond occupying a similar position in the molecule of each.
§§ 139, 140] ACIDS OF THE PROPIOUC SERIES. 175
since each acid readily forms a bromine addition-product from which elimination of 2HBr yields sUarolic acid, C18H82O2:
C18H34O2 -^ Ci8H34Br202 — > C18H32O2. Olelo and elaldio Bromine addition- Steait^o add adds product
Oleic acid and elaidic acid yield the same hydroxystearic acid by the addition of one molecule of water, a reaction elGfected by the action of concentrated sulphuric acid. Their isomerism is, therefore, like that of erucic acid and brassidic acid, analogous to the isomerism of the two crotonic acids (136).
n. ACmS OF THE PROPIOLIC SERIES, CnH„_,0,-
139. The acids of the propiolic series have one triple bond, or two double bonds, in the molecule. The first-named are formed by the action of carbon dioxide upon the sodium compounds of the acetylene hydrocarbons:
CH^CNa+002=CI^C-C00Na.
Sodium pn^iolata
The a-carbon atom of these acids has a triple bond, and such acids are very readily decomposed into an acetylene hydrocarbon and CO2; for example, by heating their silver salts.
A general method for the preparation of acids with triple bonds involves the addition of two bromine atoms to acids containing a double bond, and subsequent elimination of 2HBr:
CHa.CH-.CH.COOH-^CHa.CHBr.CHBr.COOH-^
Croionio aoid Dibromobutyric acid
-*CH3.C3C-COOH.
Tetrolio aoid
140. In presence of concentrated sulphuric acid, substances with a triple bond take up water with formation of ketones (125) :
—CSC > — CH2-C0— •
In this manner stearolic acid is converted into a ketostearic acid of the formula
C8Hi7-CO-CH2-(CH2)7*CXX)H,
176 ORGANIC CHEMISTRY. [J 140
and treatment with hydroxylamine transforms this compound into the corresponding oxime:
CsHiy -C •CH2 • (CHa)? •COOH.
NOH
Under the influence of concentrated sulphuric acid, this oxime undergoes the Beckmann transformation (103), among the prod- ucts being the substituted acid amide
CgHiT-CO
I NH.(CH2)8-COOH,
which is proved to have this formula by its decomposition into pelargonic acid, CgHij-COOH, and the 9-aminononoic * acid, NH2*(CH2)8*COOH, by the action of fuming hydrochloric acid. This is a confirmation of the constitution above indicated for oleic acid and elaidic acid, since they can be converted into stearolic acid in the manner already described.
Geranic acid, C10H16O2, a compound with two double bonds, is considered in 143.
* If the carboxyl-carbon atom is denoted by 1, the amino-group is in union with the ninth carbon atom of the chain.
UNSATURATED ALDEHYDES AND KETONES.
141. The lowest unsaturated aldehyde is acr aldehyde or acrol^n, CH2:CH*CH0. It is obtained by removal of water from glycerol (153), effected by heating with potassium pyrosulphate, K2S2O7. It is a colourless liquid, boiling at 52*4^, and has an extremely powerful, penetrating odour, to which it owes its name {(u^eTf sharp, and oleum, oil). The disagreeable, pungent smell produced when a tallow candle or an oil-lamp is extinguished is due to the formation of acraldehyde. On reduction, it yields allyl alcohol, from which it is regenerated by careful oxidation. It is converted into acrylic acid by further oxidation.
It has the properties peculiar to aldehydes — the susceptibility to reduction and oxidation, resinification in presence of alkalis, and the power of forming pol3nnerization-products. It possesses this last property in such a marked degree that it usually becomes completely converted into a polymeride in the course of a few days or even hours, probably under the catalytic influence of traces of impurities. The presence of the double bond in acraldehyde modifies to some extent the aldehydic character. This is exhibited in its behaviour towards ammonia, with which it does not com- bine like acetaldehyde (104), but in accordance with the equation
2C3H4O + NH3 = CeHoON + H2O.
Acraldehyde-ammom'a is an amorphous, basic substance, is
soluble in water, and in its appearance and behaviour towards
water bears a close resemblance to glue.
Acraldehyde does not unite with one molecule of an acid sul-
phite, but with two, yielding a compound from which the aldehyde
cannot be regenerated by the action of acids, which eliminate only
177
178 ORGANIC CHEMISTRY. [§§ 142, 143
one molecule of the acid sulphite. This indicates that the other molecule of acid sulphite has been added at the double bond.
142. CroUmaldehyde, CH,*CH:CH-CHOy results on eliminatioD
rVi ^H
of water from aldol, CH..CHOH|>CHjH >Cg (106), by heating to
140°. It is a liquid boiling at 104^-105°, and is converted by oxida- tion with silver oxide into solid crotonic acid (136), proving that it has the constitution indicated.
XT
Propiolaldehyde, CH=C-C<;7J, can be obt^ned from acrolein-
acetal by the addition of two bromine atoms, and subsequent removal by means of caustic potash of 2HBr from the addition- product thus formed:
CH,:CH.C(Q^jj^) -*CH.Br-CHBr.C(Q^jj^j^-*
Acrolelnao6tal Dtbromo-oompound
Propiolaldehydeaoetal
Propiolaldehydeacetal is converted by warming, with dilute sul- phuric acid into the corresponding aldehyde, which has the same irritating action on the mucous membrane as acrolein.
The behaviour of propiolaldehyde towards alkalis is remark- able. It decomposes into acetylene and formic acid:
CI^C-CHO +NaOH -CH=CH +C^Na.
\o
143. An important unsaturated aldehyde is geranial (citral), CioHieO, characterized by its agreeable odour. It is a constituent of various essential oils; among them oil of orange-rind, the cheap oil of lemon-grass, and oil of citron. At the ordinary temperature it is liquid, and boils at 110°-112° under a pressure of 12 mnu Its aldehydic nature is shown by its reduction to an alcohol, geranid, and its oxidation to an acid with the same number of carbon atoms, geranic acid,
Geranial is 2 : 6-dimethyI-A^ ' ®-octadiene-8-al,
pTT > C=CH»CH2»CH2*C(CH3)=£JH»C|-|,
S 1431 UNSATURATED ALDEHYDES AND KETONES. 179
since on oxidation it yields acetone, laevulic acid (234), and carbon dioxide, the molecule breaking down at the double bonds:
^» >C==CH-CH2-CH2-C(CH3)=CH-cg ->
Geranial
~* m^ >^^ +HOOC.CH2-CH2.COCH8 +CO2 +OO2.
Aoetone Leerulio acid Carbon dioxide
When boiled with a solution of potassium carbonate, geranial takes up one molecule of water, forming methylheplerwne and acetal- dehyde:
^3 >c=CH-CH2-CH2-C(CH3)=CH.c5->
Geranial
— ^^>C=CH.CH2.CH2-CX)-CH3+CH3-C^.
Methylheptenone Aoetaldebyde
On oxidation, methylheptenone also yields acetone and laevulic acid. This reaction indicates its constitution, which is further proved by synthesis.
Baryta-water converts a mixture of geranial and acetone into a condensation-product, pseudoiono/ic;
(CH3)2C==CH.CH2-CH2-C(CH3)=CH.CH0fH2CH.C0-CH3=
Geranial Aoetone
=H20+(CH3)2C=CH-CH2-CH2-C(CH3)=CH.CH=CH-CO-CH3.
jwetidolonone
When boiled with dilute sulphuric acid, psendoionone yields ianone:
CH3 CH3 CH3 CH3
\/ \/
c c
/ /\
HC CH.CH:CH'00«CH8-»H2C CH-CHiCH-OO-CHa.
HjC C-CHs HaC C-CHg
\/ \y
CH2 CH
IRfrndoIonone lonooe
180 ORGANIC CHEMISTRY. il43]
The structure of ionone is proved by its decbrnposition-products. It is manufactured as an artificial perfume, as it has a powerful, violet-like odour, and is closely related to irone, the active principle of violets. The formula of irone is
GH3 GH3
\/
c
HC CH-CHiCH-OO-cas,
HG GH • GH3
\/
CSHa
which differs from that of ionone only in the position oocuined by the double bond in the carbon ring.
COMPOUNDS CONTAmiNG MORE THAN ONE
SUBSTITUENT.
L HALOGEN DERIVATIVES OF METHANE^
144. The balogen derivatives of the saturated hydrocarbons obtained by replacement of a single hydrogen atom by halogen are called alkyl halides, and are described in 52-53. This chapter treats of the compomids formed by exchange of more than one hydrogen atom for halogen.
It is possible to replace all four hydrogen atoms in methane, in successive stages, by the direct action of chlorine or bromine in presence of sunlight. Iodine does not react with methane, or with its homologues, while the action of fluorine is very energetic, effect- ing complete substitution.
In practice, however, this is not the method adopted for the preparation of the compounds CH2X2, CHX3, or CX4. They are obtained from the trihalogen derivatives: these are readily prepared by another method, and on chlorination or bromination yield tctra- chloromethane or tetrabromomethane; on reduction they are con- verted into dihalogen-substituted methanes. On account of their important therapeutic properties, the compounds CHXa are pre- pared on the large scale.
Chloroform, caci^.
145. Chloroform is obtained by distilling alcohol — or on the manufacturing scale, acetone — with bleaching-powder. This reac* tion involves simultaneous oxidation and chlorination, and it is assumed that aldehyde is first produced by oxidation of the alcohol, and is then transformed into trichioroaldehyde, or chloral, CCU-CHO.
181
182 ORGANIC CHEMISTRY. [§ 145
This substance is converted by bases, in this instance by the slaked lime present in the bleaching-powder, into chloroform and formic acid (201). ,
Chloroform is a liquid boiling at 61®, and solidifying at —70°. Its specific gravity at 15® is 1*498: it is very slightly soluble in water, and possesses a characteristic ethereal odour and sweet taste. In 1847, Simpson discovered that its prolonged inhalation pro- duces unconsciousness, whence it derives its value as an anaesthetic in surgical operations.
Its use for this purpose is not wholly unattended with danger. Notwithstanding the fund of experience resulting from the fre- quency of its application, it occasionally happens that the inhala- tion of chloroform is attended by fatal results. Ordinarj' ether and ethyl chloride are less dangerous, do not produce such disagreeable after-effects, and hence have latterly been preferred as anaesthetics (56).
Chloroform is a somewhat unstable substance, decomposing under the influence of light and air, and yielding chlorine, hydro- chloric acid, and carbon oxychloride, COCI2. A considerable amount of this oxy-derivative is produced by bringing chloroform- vapour into contact with a flame. Its suffocating effect renders it very dangerous. The decomposition of the liquid can be almost prevented by adding one per cent, of alcohol, and keeping the chloroform in bottles of non-actinic glass.
The halogen atoms of chloroform take part in double decom- positions: thus, sodium ethoxide yields the ethyl ester of ortho- formic acid:
CH|Cl8+3Nal .OC2H6=CH(OC2H5)3 +3Nan.
Formic acid can be obtained by warming chloroform with dilute alkalis, orthoformic acid being probably formed first, although it has not been isolated. When chloroform is treated with a 40 per cent, aqueous solution of caustic potash, carbon monoxide is evolved : it is assumed that chloromethylene, CCI2, is formed as an inter- mediate product.
When chloroform is warmed with alcoholic ammonia and caustic potash, its three chlorine atoms are replaced by nitrogen, with production of potassium cyanide. The formation of isoni-
§ 146] IODOFORM. 183
triles from chloroform, alcohob'c potash, and primary amines, has been already mentioned (77).
Exposure to dark electric discharge converts chloroform into a series of highly chlorinated products, such as C2CI4, C2HCI5, CjClfi, C3HCI7, and others of similar type.
Methylene chloride, CHaCU, is obtained from chloroform by reduc- tion with zinc and hydrochloric acid in alcoholic solution. It is a liquid, boils at 40°, and has a specific gravity of 1 •337.
Tetrachloromethane, or carbon tetrachloride, CCI4, produced bj the action of chlorine on chloroform or carbon disulphide, is also a liquid, and boils at 76°. When heated with excess of water at 250° it yields HCl and CO,. Its specific gravity is 1»593 at 20°: the high specific gravities of these polychloro-compounds is noteworthy. The bromine and iodine compounds are specifically much heavier than the corresponding chlorine compounds.
Bromoform, CHBr,, is obtained by methods analogous to the preparation of chloroform. It melts at 7*8°, boils at 151°, and has a specific gravity of 2*904 at 15°. It is used for therapeutic pur- poses.
Iodoform, CHI3.
146. Iodoform is a substance of great importance, and is ob- tained from alcohol by the action of potassium carbonate and iodine. The intermediate product iodal, Cla-CHO, analogous to chloral, has not been isolated. On the manufacturing scale acetone, being less expensive than alcohol, is often employed.
Iodoform can also be prepared by the electrolysis of a solution containing 60 g. of potassium iodide, 20 g. of sodium carbonate, and 80 c.c. of alcohol per 400 c.c, the temperature being kept between 60° and 65°. Iodine is liberated at the anode, so that the alcohol, potassium carbonate, and iodine necessary to the formation of iodoform are all present in the mixture. By this method about 80 per cent, of the potassium iodide is converted into iodoform, the remainder of the iodine being obtained as potassium iodate. The formation of iodate can be avoided to a great extent by surrounding with parchment the cathode, at which caustic potash is formed: this prevents contact of the potassium carbonate with the iodine set free at the anode.
Iodoform is a solid, and crystallizes in yellow hexagonal plates, well-developed crystals about a centimetre in length being obtained by the slow evaporation of a solution in anhydrous acetone. It
184 ORGANIC CHEMISTRY. [§ 147
has a peculiar, saffron-like odour, sublimes very readily, and melts at 119^.
These characteristic properties of iodoform make its formation an important test for alcohol, although aldehyde, acetone, and several other substances similarly yield iodoform. Substances containing the group CH3*C in union with oxygen answer to the iodoform^ test. It is carried out by adding iodine to the liquid under examina- tion, and then caustic potash drop by drop until the colour of the iodine vanishes. If a considerable quantity of alcohol is present, a yellow precipitate forms -at once: if only traces, the precipitate forms after a time. The reaction is sufficiently delicate to show traces of alcohol in a sample of well-water or rain-water, after con- centration by repeated distillation, the first fraction in each case being collected.
Iodoform is employed ia surgery as an antiseptic. It is note- worthy that it does not kill the bacteria directly, its action on the niicro-organisms being subsequent to a decomposition resulting, under the influence of the heat of the body, from fermentation induced by the matter exuded from the wound.
Methylene iodide, CH2l2y is a liquid, and is obtained by the reduction of iodoform with hydriodic acid; phosphorus is added to regenerate the hydriodic acid. Its specific gravity, 3*292 at 18^, is remarkably high.
IL HALOGEN DERIVATIVES OF THE HOMOLOGUES OF MET&AHE.
147. It is evident that among these derivatives numerous cases of isomerism are possible. For example, replacement by chlorine of three hydrogen atoms in normal pentane may yield several dif- ferent compx)unds: thus, a methyl-group may be converted into CCI3; two chlorine atoms may replace the hydrogen of one methyl- ene-group, while the third replaces another hydrogen atom in the molecule; or the three chlorine atoms may unite with different carbon atoms; and so on.
The preparation of many of the halogen compounds included under this heading has aheady been described, 'the compounds CnHsn^i-CHX;! and CpH2p4.rCX2-GqH:iq^i being obtained by the
S 1481 HALOGEN DERIVATIVES OF PARAFFINS. 185
action of phosphorus pentahalide on aldehydes and ketones respect- ively (gS). Compounds with two halogen atoms attached to two adjoining carbon atoms are obtained by addition of halogen to the hydrocarbons CnH2n; those having four halogen atoms, two being directly united to each of two adjoining carbon atoms, are produced by addition of halogen to hydrocarbons with a triple bond; while compounds of the type
CpHsp+i -CHX-CHX-CrHjr-CHX-CHX.C^Ham+i
result on addition of halogen to the hydrocarbons CnH2n-49 con* taining two double bonds; etc.
A method for the preparation of compounds rich in halogen from the saturated hydrocarbons is the exchange of one hydrogen atom for halogen, elimination of hydrogen ha.id ^ by means of alco- hoUc potash, halogenation of the hydrocarbon CnH2n thus obtained, removal of HX, renewed halogenation of the product, and so on.
CH3-CH3->CH3-CH2Cl-HCl->CH2:CH2+2a->
Ethane Ethyl chloride Ethylene
-> CH2CI . CH2CI - 2HC1 -> CH=CH -I- 4C1 ->
Ethylene chloride Acetylene
-> CHCI2 .CHCI2-HCI -»CHC1 :CCl2 +2C1 -♦
TetraohloroethAoe Trichloroethylene
-i CHCI2 • cx:;i3 - Hci -♦ (XI2 : CCI2 + 2C1 -► CCI3 • caa.
Pentachloroethane Tetrachloroethylene HexaohloroethAoe
A method for the preparation of polybromo-compounds was discovered by Victor Meyer, and involves the direct action of bromine on the hydrocarbons of the series CnH2n+2 In presence of a small quantity of anhydrous iron bromide, or iron-wire. These conditions greatly facilitate substitution, each carbon atom of a normal chain taking up only one bromine atom. Thus, propane yields <rifcromo&i/dnn, CH2Br»CHBr«CH2Br, since the product is identical with the addition-product obtained by the action of bro- mine on allyl bromide, CH2-CH-CH2Br (130).
Nomenclature and Individual Members.
148. The notation adopted by the Chemical Society of London 18 that " In open-chain compounds Greek letters must be used to
186 ORGANIC CHEMISTRY. (§ 148
indicate the position of a substituent, the letter a being assigned to the first carbon atom in the formula, except in the case of CN", CHO, and COgH." Thus, CHs-CHa-CHa-CHal is a-iodobutane; CH3.CH2-CH2-CN a-cyanopropane; CH2Br*CH2»CH2Br aa'- dibromopropane; CH2Br»CHBr»CH3 a^-dibromopropane.
Only a few of the numerous compounds of this group will be described.
TetracJUoroeihane, CHClfCHClj, is prepared technically by the interaction of chlorine and acetylene, with antimony pentachloride as catal3rst. It is a liquid boiling at 147^. When it is boiled with milk of lime, hydrochloric acid is eliminated, with formation of tnMoroethyleney CCla^CHCl, a liquid boiling at 88®. On addition of zinc-dust to an aqueous suspension of tetrachloroethane, heat is developed, and pure dichloroethylenef CHCl: CHCl, distils. It is a liquid boiling at 55®. All these substances are excellent solvents for fats and oils; they also dissolve sulphur readily, and are employed in vulcanizing caoutchouc.
Ethylene chloride, CH,C1-CH,C1, is called "Dutch Liquid," or the "Oil of the Dutch Chemists," it having been first prepared at the • end of the eighteenth century by four Dutch chemists, Deiman, BoNDT, Paets van Troostwyk, and Lauwebenburgh, by the action of chlorine upon ethylene. It is a liquid boiling at 84*9®, and has a specific gravity of 1 -28 at 0°.
Hexachloroethane (perchloroethane), CiCU, is formed by the direct union of carbon and chlorine under the influence of a powerful arc- discharge between carbon poles in an atmosphere of chlorine.
Ethylene bromide is employed for syntheses and ,as a solvent. It is prepared by passing ethylene into bromine covered with a layer of water to prevent evaporation, the addition taking place very readily. Ethylene bromide is a colourless liquid of agreeable odour, solidifies at 8®, boils at 131®, and has a specific gravity of 2-189 at 15^
Trimeihylene bromide, CHiBr*CHi-CH,Br, aa '-dibromopropane, also plays an important part in S3mtheses, and is obtained by addi- tion of HBr to allyl bromide, CHj: CH»CHiBr, produced from ally! alcohol. This method of formation suggests the constitution CHj«CHBr*CH2Br, that of the addition-product obtained by the action of bromine upon propylene, CHj-CH:CHt. Since the two compounds are not identical, trimethylene bromide must have the
§S 149, 150]
POLYHYDRIC ALCOHOLS,
187
ao'-formula. It is a liquid, boiling at 165 '^y and has a specific gravity of 1-974 at 17°.
Pentamethylene dibromide is mentioned in 388.
m. POLTHTDRIC ALCOHOLS.
Z49. When more than one hydrogen atom of a saturated hydro- carbon is replaced by hydroxyl, it is theoretically possible to have more than one hydroxy 1-gro up in union with a single carbon atom, or to have each attached to a different one. It should be possible to obtain compounds of the first class by replacement of halogen by hydroxyl in the halogen derivatives R*CHX2, R-CXa, and R-CX2-R'. Silver acetate converts halogen compounds of this
type into stable acetates, such as CJH2<q/-.^tt q. On saponifica- tion, however, dihydric alcohols like CH2(OH)2 are not obtained, but aldehydes result by elimination of one molecule of water. When compounds of the type RCCI3 are treated with sodium ethoxide, substances with the general formula R"C(OC2H5)3, called ortho- esters, are obtained. On saponification R-C(0H)3 does not result, the corresponding acid being formed instead, through loss of water.
Ethers of dihydric alcohols, such as CH3-CH<Qp jj^ are known,
and are called acetals (104, 2). The saponification of these sub- stances does not yield R -011(011) 2, but an aldehyde. It follows from these facts that compounds with mare than one hydroxyl-growp attached to the same carbon atom are unstable, although it is some- times possible to obtain such compounds (127, 201, 230, and 234). Many compounds are known contaimng several hydroxyl- groups, of which not more than one is in union with each carbon atom.
I. Glycols or Dihydric Alcohols.
150. The glycols are obtained from the corresponding halogen compounds analogously to the monohydric alcohols (39) :
0-0C-CH3
CH2' CHo
•O'OC'CHs CH2'
O-OC-CHs+H
O-OC-CHs+H
OH CHa'OH
Trimethylene bronude
Trimethyleneglycol diaoctate
OH CHs-OH
Trimethyleii»- glycol
188 ORGANIC CHEMISTRY, H 150
The exchange of halogen for hydroxyl can be brought about by treatment with acetate of silver or the acetate of an alkali-metal, and saponification of the diacetate thus obtained. It can also be effected directly by boiling with sodium-carbonate solution, or water and lead oxide.
Glycols of the type R-CHOH-CHOH-R, with the CHOH- groups in direct union, are formed from olefines either through the medium of their bromine addition-products, or by the direct addi- tion of two OH-groups by means of careful oxidation with potassium permanganate. Thus, ethylene yields the simplest dihydric alcohol, called glycol:
CHj.-CHg+HgO+O^CHaOH.CHaOH.
Another method for the formation of glycols of this type consists in the reduction of ketones. This may be either carried out with sodium in aqueous solution, or by electrolysis. Acetone yields ptnor cone and isopropyl alcohol. Glycols of the type of pinacone — called pinaconea — can be obtained without admixture of a secondary alco- hol by reduction of aldehydes or ketones with magnesium-amalgam, addition-products being first formed with evolution of heat:
2CH,.C^ +Mg -CH,.CH — CH-CH, \j * * §
Q.Mg.O or 2CH,-C0-CH,+Mg-g?g»>C C<^-.
0*Mg.O
Water decomposes the addition-product, with formation of the pinacone:
CB> ^f j' <Ch! +2H,0 -^2|> C(OH)-C<ioH) + MgO.
The constitution of pinacone is indicated by its synthesis:
CH,.CO.CHg H CH».C{OH).CH,
+ - I
CH,-OO.CH, H CH,-C(OH).CH.
Aoetooa Pinaooiw
S 150] GLYCOLS. 189
When distilled with dilute sulphuric acid, pinacone luidergoes a remarkable intramolecular transformation, explicable on the assump- tion that a hydroxyl-group changes place with a methyl-group:
yOK y 0|H
(CH,),C(OH) .C^CH, — (CH,),C.C^[OH - H,0 - (CH,),C -CO -CH,.
Pinacone ^CHj P H PinAoolin
The constitution of pihacolin may be deduced from its synthesis by the action of zinc methide on trimethylacetyl chloride, (CH,),C«C0C1, and in other ways.
Most of the glycols are colourless, viscous liquids of sweet taste, whence the series derives its name. Their boiling-points and speci- fic gravities are considerably higher than those of the monohydric alcohols with the same number of carbon atoms. Thus, glycol boils at 197 '5°, and ethyl alcohol at 78®: at 0® the specific gravity of glycol is 1»128, and of ethyl alcohol 0-806. The nature of the hydroxyl-groups in glycol and that in the monohydric alcohols is perfectly analogous: exchange of OH for halogen, the formation of ethers, esters, and alkoxides, and the oxidation of primary glycols to aldehydes and acids, may take place in connexion with one or both of the hydroxyl-groups. For instance, the compounds CH20H-CH2C1, glycolchlarohydrin; CH2OC2H5.CH2OH, glycol- manoethyl ether; CIl20C2H.5'CH20C2fl5, glycol diethyl ether; etc.; are known. The glycols possess, however, one property due to the presence of two hydroxyl-groups, the power of forming anhydrides. The first member of the series, glycol, CH20H*CH20H, does not yield an anhydride by the direct elimination of water, but a com- pound of the formula C2H4O is obtained by first replacing one hydroxyl-group by CI and then eliminating HCl:
C5H2CI CIH2V
I -Ha- I >o.
CH2OH CHj/
Glycolchlorohydrin Ethylene oxide
This compound, ethylene oxide, boils at 14®, and is therefore gas- eous at ordinary temperatures: it readily takes up water, forming glycol; or hydrochloric acid, forming glycolchlorohydrin. To ethylene oxide is assigned the constitutional formula indicated, because it yields ethylene chloride when treated with phosphoiiis pentachloride, the oxygen atom being replaced by two chlorine
190 ORGANIC CHEMISTRY. [§151
CHa
atoms. If the compound had the constitution || , which is
CHOH
also possible but less probable (131), it would not yield ethylene
chloride when thus treated.
Some of the higher homologues of glycol with a chain of foui
or five carbon atoms between the hydroxy l-groups yield anhydrides
with a constitution analogous to that of ethylene oxide. They
show a marked diminution in the power of forming addition^
products with water; or, in other words, the closed chain of carbon
atoms and one oxygen atom is more stable than in ethylene oxide
itself.
2. Trihydric Alcohols.
151. The principal representative of the group of trihydric alcohols is glycerol^ or "glycerine," C3H6(OH)3. In accordance with the rule that two hydroxyl-groups cannot attach themselves to the same carbon atom, glycerol can only have the structure
CH2OH . CHOH . CH2OH.
This structure finds support in other proofs.
1. On careful oxidation of allyl alcohol by means of potassium permanganate, two OH-groups are added at the position of the double bond:
CH2:CH-CH20H -► CHaOH-CHOH-CHaOH.
2, When glycerol, CaHgOs, is carefully oxidized, glyceric acid, CsHeOi, is first formed, corresponding to the formation of acetic acid, C2H4O2, from ethyl alcohol, CaHeO, by exchange of two hydrogen atoms for one oxygen atom: this indicates that glycerol contains one — CHaOH-group. Further oxidation converts gly- ceric acid into tartronic acid, C3H4O5, two hydrogen atoms being replaced by one oxygen atom, with formation of a new carboxyl* group. Hence, glycerol contains two — CHaOH-groups in thff molecule, so that its constitution is CH20H«CH^«CH^H. Since tartronic acid, COOH-CHaO-COOH, still possesses alcoholic properties, the group CH^O must have the constitution >CHOH, and since it must have the same constitution in the molecule
(( 152, 153] GLYCEROL. 191
of glycerol, the structure of the latter is proved to be CHj^H.CHOH.CHaOH.
3. A further proof of the constitution given above is the forma- tion of glycerol from tribromohydrin (147) .
152. Glycerol is a colourless, oily liquid of sweet taste, is very hygroscopic, and miscible in all proportions with water and alcohol, but insoluble in ether. When cooled to a low tempera- ture for some time, it solidifies, but the crystals thus formed do not melt below 17^. It boils at 290^, and has a specific gravity of 1-265 at 15^ Its chemical behaviour accords completely with the constitution of a trihydric alcohol. Thus, it yields three esters, by replacement of one, two, or three hydroxyl-groups. When borax is dissolved in glycerol or in a solution of this sub- stance and the mixture introduced into the flame, the green colour characteristic of free boric acid is observed: on this reaction is based Senier's test for glycerol.
^ce glycerol is a substance which plays a very important part in the economy of nature as a constituent of the fats (154)9 its synthesis from its elements is of great interest. This was effected by Fri^dbl and SiLVA, the starting-point being acetic acid. This substance can be synthesized from its elements in several ways, for example by the oxidation of acetaldehyde obtained by the action of water on acetylene (las). The dry distillation of calcium acetate gave ace- tone, which was reduced to i«opropyl alcohol. On elimination of water from this alcohol, propylene was formed, and on addition of chlorine, was converted into propylene chloride, from which tri- chlorohydrin was obtained by treatment with iodine chloride. Tri- chlorohydrin was converted into glycerol by heating with water at 170^:
CH,.COOH -> CH,.CO.CH, -* CH,.CHOH.CH, -♦ CH,.CH :CH, -^
Aoetie acid Aoetooe iioPropyl alcohol Propylene
-> CH,.CHa .CH,a -♦ CH,CI .cHa .ch,ci -► ch,oh .choh .ch,oh.
Propylene chloride Trichlorohydiin Olyoerol
IS3- Acraldehyde (141) is produced by elimination of water from glycerol:
OHH
CH2.C— CHOH. OHlkl
192 ORGANIC CHEMISTRY, [§§ 154, 155
CH2: C: CHOH should be obtained, but immediately changes to acraldehyde, CH2:CH.Cq (131).
Large quantities of acraldehyde can be prepared by passing glycerol-vapour over anhydrous magnesium sulphate at 330*'-34O*', the yield corresponding with 60 per cent, of the glycerol employed. For the preparation of small quantities, 250 g. of glycerol can be heated with 10 g. of potassium pyrosulphate, KtSsO?.
154. Glycerol occurs in nature in large quantities in the form of esters. The fats and oils are glyceryl tri-esters of the higher fatty acids and of oleic acid: glycerol and the fatty acids are obtained from them by saponification (85 and 95). Glycerol is also present in small proportion in the blood.
Inversely, the fats can be S3mthesized from glycerol and the fatty acids: for instance, tristearin is obtained by heating glycerol Tdth excess -of stearic acid under reduced pressure at 200® until separation of water ceases.
Many fats gradually become rancid, and develop a disagreeable smell and taste. This is due to atmospheric oxidation, which is facilitated by the influence of light. The unsaturated fatty acids become converted into others containing a smaller number of car- bon atoms, and with a characteristic odour and taste.
The digestion of fats is attended by decomposition into glycerol and fatty acid, effected by an enz3rme present in the pancreas.
155. Glycerol is extensively employed in the arts and in medi- cine. One of its most important applications is to the preparation of the so-called " nitroglycerine.'' This explosive has a mislead- ing name, since it is glyceryl trinitrate,
CH20-N02
CHO.NO2,
CH2O.NO2
and not a nitro-compound (68) ; for on saponification with aikalis it yields glycerol, and the nitrate of the corresponding alkali-metal. Nitroglycerine is prepared by bringing glycerol into contact with a mixture of concentrated sulphuric acid and nitric acid, rise of temperature being prevented. Other polyhydric alcohols are converted analogously into nitrates. After a time, the reac*
J 156] TETRAHYDRIC AND POLYHYDRIC ALCOHOLS, 193
tion-mixture is poured into water, whereupon the nitrate separates in the form of an oily, very explosive liquid of faint, headache- producing odour. It can be purified by washing with water; when perfectly pure it does not explode spontaneously.
The specific gravity of nitroglycerine is 1-6. Its metastable form solidifies at 2*2^, and its stable modification at 12 •2^.
Nitroglycerine is a liquid, and as its use in this form for technical purposes would be attended with difficulties, it is mixed with infu- sorial earth ("kieselguhr*'), which absorbs it, forming a soft, plastic mass, dynamite, containing usually 75 per cent, of nitroglycerine and 25 per cent, of the earth. Nitroglycerine can also be obtained in the solid form by dissolving in it a small amount of guncotton (238), which converts it into an elastic solid resembling jujubes in con- sistence, called '^ blasting gelatine.'' This substance has the advan- tage over dynamite of not leaving any solid residue after explosion. Dynamite cannot be used as ammunition, its velocity of explosion being so great as to produce an impulse too violent for a gun to resist without bursting: that is, it exerts a '^brisant" or detonating
effect.
«
3. Tetrahydric and Polyhydric Alcohols. 156. Among the tetrahydric alcohols is eryihriiol,
CH2OH . CHOH . CHOH . CH2OH,
which is a natinral product. It contains a normal carbon chain, since reduction with hydriodic acid converts it into n-secondary butyl iodide, CHs-CHI-CHg-CHa.
Examples of pentahydric alcohols are arabiiol and xylitol, C6H12O6, which are stereoisomerides, as are also the hexahydric alcohols didcUol and mannUol, C0H14O6, both of which are found in nature. These all have normal carbon chains, since, like erythritol, they yield n-secondary iodides on reduction with hydriodic acid: thus, mannitol is converted into
CH3 • CH2 • CHI • CH2 • CH2 • CH3,
•
They can be obtained artificially by the reduction of the corre- sponding aldehydes or ketones, dulcitol being formed from galactose, and mannitol from mannose and Isevulose. The reason for assuming their stereoisomerism is explained in 205,
194 ORGANIC CHEMISTRY, .[§§157,158
but here it may be pointed out that the polyhydric alcohols contain asymmetric carbon atoms, indicated in the formulas by asterisks :
CHaOH.CHOH.CHOH-CHOH.CHzOH;
Arabitol and Xylitol
CH2OH . CHOH . CHOH . CHOH . CHOH • CHjOH.
Dulcitol and Mannitol
157. The presence of polyhydric alcohols prevents the pre- cipitation of the hydroxides of copper, iron, and other metals by means of alkalis. Thus, a solution of copper sulphate and glycerol does not yield a precipitate of copper hydroxide with caustic potash. This is due to the formation of soluble metallic compounds of the polyhydric alcohols, the hydroxyl-hydrogen being replaced by the metal. The acidic nature of the hydroxyl-group, almost lacking in the monohydric alcohols, is therefore in some measure developed by increase in the number of these groups present in the molecule. This property is possessed not only by the polyhydric alcohols, but also by many other compounds containing several 'hydroxyl-groups (191).
IV. DERIVATIVES CONTAINING HALOGEN ATOMS, HTDROXTL- GROUPS, NTTRO-GROUPS, OR AMINO-GROUPS.
158. Only a few of the numerous compounds belonging to this class will be considered: the chemical properties of its members are determined by the substituents.
No compounds containing halogen and hydroxy 1 in union with the same carbon atom are known: when their formation might be expected, hydrogen halide is eliminated, with production of alde- hydes or ketones. It has been mentioned more than once that stable alkyl-derivatives of compounds themselves unstable or un- known, such as the ortho-esters, exist (149). This is true in this
CI instance, for while compounds of the type R-CH < qtt are unknown,
CI derivatives of the formula R«CH<rk r« xj are known. These
substances are called ehloroethers. When chlorine is passed into ethyl ether, kept cool and in the dark to avoid explosion, the
i 158] CHLOROETHERS AND CHLOROHYDRINS. 196
hydrogen atoms are replaced by chlorine. The monosubstitution- product has the constitution
CH3 • CH2 • O • CHCl • CHg,
Monoohloroether
as is proved by the action of sulphuric acid, under the influence of which it takes up one molecule of water, forming ethyl alcohol, aoetaldehyde, and hydrochloric acid:
C2H5 H CaHfiOH
CHa-CHCl OH CHa.CH<XlT - CHa-CHO+HCl.
Ck>mpounds containing halogen and hydroxyl in union with different carbon atoms are obtained from the polyhydric alcohols by partial exchange of hydroxyl for halogen, and have the general name halogen^hydrina. Glycerol dicfdorohydrin, C3H5(OH)Cl2, is formed when a solution of glycerol in glacial acetic acid is saturated with hydrochloric-acid gas. It has the symmetrical formula
CHzCl.CHOH-CHzCl,
since it differs from the dichlorohydrin obtained by addition of chlorine to allyl alcohol, this having the constitution
CH20H-CHC1.CH2C1.
On treatment of both dichlorohydrins with potassium hydroxide,
epichlorohydrin,
CH2 •CH •CH2CI,
Y
is obtained.
Dinitro-compcunda with both nitro-groups in imion with the same carbon atom are formed from primary bromo-nitro-com- pounds by the action of potassium nitrite:
CHs •CHBrN02+KN02 = CH3 .CH(N02)2+KBr.
The hydrogen atom belonging to the carbon atom carrying the nitro-groups can be readily replaced by metals, so that
196 ORGANIC CHEMISTRY, [§§ 159, 160
these primary dinitro-compounds have an acidic character (322).
159. Diamines with the two amino-groups attached to the same carbon atom are not numerous: most of them have their amino-groups in union with different carbon atoms. Some of these compoimds are formed by the putrefaction of animal matter, such as flesh; and are classed as ptomaines with other basic substances similarly formed. Such are cadaverine (pentamethylenediamine) , NH2-CH2'(CH2)3*CH2-NH2, and putrescine {tetramethylenedia- mine), NH2-CH2«(CH2)2*CH2-NH2. The constitution of these substances has been proved by synthesis, pentamethylenediamine being thu^ obtained. Trimethylene bromide, Br«CH2'CH2-CH2-Br, is converted by treatment with potassium cyanide into trimethylene cyanide, CN-CH2*CH2'CH2-CN. This substance is reduced with sodium and boiling alcohol, which converts the CN-groups into CH2NH2-groups (78), with formation of the diamine:
|
CN |
CH2NH2 |
|
(CH2)3 |
-^(CH2)8 . |
|
CN |
CH2NH2 |
When pentamethylenediamine hydrochloride is heated, it loses one molecule of ammonia, and is converted into piperidine, which has the character of a saturated secondary amine. For this and other reasons (388) it is assigned a ring or cyclic formula :
CH2 • CH2NH2 /CH2 • CH2
•V^XJ.2->^i-12-»-^AX2 y
\,
CHa -NHa = CHj ^NH. *
\CH2-CH2NH2 \)H2-CH2
Pentamethyienediamine Piperidine
When heated, tetramethylenediamine and trimethylenediamine yield analogous cyclic compounds, but less readily, whereas ethylene- diamine does not.
160. A substance, partly amine and partly alcohol, should be mentioned on account of its physiological importance: it is choline, C5H16O2N, which is widely distributed in the vegetable kingdom. Its constitution is inferred from its synthesis by the interaction of trimethylamine and ethylene oxide in aqueous solution:
$ 1601 CHOLINE AND LECITHIN. 197
(CH3)3N CH2-CH2 /CH2.CH2OH
+ + \/ =(CH3)8N OHH , 0 \0H
Choline
Ethylene oxide can also combine with substances like ethyl- amine, with formation of amino-alcohols.
Choline is a constituent of a very complicated compound, lecithin, present in brain-substance, yolk of egg, many seeds, and elsewhere. It is glycerophosphoric acid in which the alcoholic hydroxyl-groups are esterified by palmitic, stearic, and oleic acid; and the acidic hydroxyl-groups are combined with choline.
On treatment with baryta-water, lecithin yields choline, one or more of the fatty acids named above, and glycerophosphoric acid. This acid is optically active, and has the formula
CH,OH
H— O-OH
CH,-0— PO(OH),,
the central C-atom being asymmetric.
Lecithin, likewise, is optically active, and may have the formula
CHiOR
CHOR'
I /OH
CH,*0— P:0
\0-CH, • CH, .N(CH,), -OH,
R and R' being similar or dissimilar acid-radicals.
Many varieties of lecithin are known. The difference in type is partly due to the position occupied by the phosphoric-acid radical, since it may be in union either with the central or a terminal hydroxyl- group of the glycerol; it is also occasioned by variation in the acid- radicals united with the other two hydroxyl-groups to form esters.
The lecithins are optically active, the central glycerol carbon atom in the foregoing formula being asymmetric. When the phosphoric- acid radical (Ph) is in union with the central carbon atom, asymmetry is contingent on the dissimilarity of the groups R and R':
CH2OR -CHOPh • CH,OR'.
Natural lecithin is always a mixture of different varieties.
The lecithins dissolve readily in alcohol, but with difficulty in ether. As the structural formula indicates, they yield salts with both bases and acids.
POLYBASIC ACmS.
L SATURATED DIBASIC ACIDS, CM^n^fi^
i6i. Many isomerides of the acids Ci|H2ii(COOH)3 are theoretic- ally possible, and differ from one another in the positions at which the carboxyl-groups are linked to the carbon chain. For many reasons, the most important are those with carboxyl-groups attached to the terminal carbon atoms of the normal chain, the aa'-acids
(148).
The general methods for the preparation of the dibasic acids
and the monobasic acids are analogous. The former are produced by the oxidation of the corresponding glycols and aldehydes, and by the hydrolysis of the dinitriles, although many of them are pre- pared by special methods.
Physical and Chemical Properties.
These acids are well-defined crystalline substances: those with more than three carbon atoms can be distilled in vacuo with- out decomposition. When distilled under ordinary pressure, many of them lose water.
The melting-points of these acids exhibit the same peculiarity as those of the fatty acids (80) : the members with an even number of carbon atoms have higher melting-points than those imme- diately succeeding them, with an uneven number of carbon atoms, as is seen from the table on next page.
This relation is graphically represented in Fig. 30, which indi- cates that the melting-points of the even and uneven series approximate more and more closely as the number of the carbon atoms increases.
A similar peculiarity is displayed by other physical constants of these acids, that of the solubility in water being given in the last
198
i )6i\
SATURATED DIBASIC ACIDS, C^b-«0»
column of the tabic. The solubility of the acids with an uneveo number of carbon atoms is much greater than the solubility of thoee with an even number, and for both it diminishes with increase in the number of carbon atoms.
|
Nuno. |
Fonniilk. |
UelllDC poi«. |
|
|
COOH.COOH COOH.CH,-COOH COOH.(OH,),.COOH COOH.(CH,),-COOH COOH.(CH,).*COOH COOH.(CH,)»-COOH COOH.(CH,),-COOH COOH.(CH,)..COOH COOH.(CH,).-CX)OH COOH.(CH.),.COOH COOH.(CH,)...COOH COOH.(CH,)„.COOH COOH.(CH,)„.COOH |
189-5°* 133° 183° 97.6° 1S3' 105.5° 140° 108° 134-5° 110° 126° 112° 124° |
||
|
Pimdic acid |
|||
|
Suberic acid |
|||
|
SdMcicscid |
|||
|
• |
Oxalic acid is a very much stronger acid than ito homologues, as the dissociation-constants indicate. For oxalic acid 10*ifc is
about 1000, for malonic acid 16-3, and for succinic acid 0-65: for the remaining acids it has values which diminish with increase io
200 ORGANIC CHEMISTRY, [§ 162
the number of carbon atoms, but are of the same order as the last number. The longer the carbon chain between the carboxyl- groups, the weaker is the acid (172). The values of the dissocia- tion-constants remain considerably higher than those of the cor- responding saturated monobasic acids with the same number of carbon atoms.
OxaUc Acid, C2H204,2H20.
162* Between oxalic add and formic acid there exists a genetic mterdependence: it is possible to prepare formic acid from oxaliC; or conversely, oxahc from formic acid. On rapidly heating potas- sium or sodium formate, hydrogen is evolved from the fusing mass, and potassium or sodium oxalate is produced:
KOOG KOOC
H H
KOOC
I + H2. KOOC
The reverse transformation of oxalic acid into formic acid is described in 163, and constitutes the ordinary method for the preparation of formic acid.
Oxalic acid frequently results in the oxidation of organic sub- stances with nitric acid: thus, it is formed by the action of this acid on sugar. It is prepared on the manufacturing scale by heat- ing a mixture of caustic potash and caustic soda to the point of fusion along with sawdust. A formate is an intermediate pro- duct, and on further heating loses hydrogen, being converted into an oxalate. After cooling, the mass is lixiviated with water, the oxalate going into solution: the oxalic acid is then precipitated as calcium oxalate by the addition of milk of lime, and finally obtained in the free state by the action of sulphuric acid.
The production of this acid by the interaction of carbon dioxide and potassium or sodium at about 360®, and its formation by the hydrolysis of cyanogen, CN«CN, are of theoretical importance.
Oxalic acid occurs in nature in different plants, chiefly in species of oxalis, in the form of potassium hydrogen, or calcium, salt. It is sometimes found as a crystalline deposit of calcium oxalate, called raphides, in plant-cells. It crystallizes with two molecules of water of crystallization, which it begins to lose at 30°. On careful heating the anhydrous acid sublimes, but when
§ ie2] OXALIC ACID. 201
strongly heated, either alone or with concentrated sulphuric acid, it decomposes into CO2, CO, and H2O. The velocity of this decomposition is largely dependent on small differences in the amount of water present in the* samples of concentrated acid employed, one of the few instances of a reaction being retarded by the influence of water. A similar decomposition ensues when a solution of uranium oxalate is exposed to sunlight, CO and CO2 being energetically evolved. Oxalic acid is very readily oxidized : a volumetric method for its estimation depends upon the use of potassium permanganate in sulphuric-acid solution, each molecule of oxalic acid requiring one atom of oxygen :
C2H204-f-0 = 2CO2+H2O.
The oxidation with permanganate accords with the equation
2KMnO, +5C,HA +3H^0, -K^O, +2MnS04 + lOCO, +8H,0.
The manganese sulphate formed has a catalytic accelerating action on the process, so that, although the first few drops of permanganate solution are very slowly decolorized, after further addition of per- manganate the disappearance of the colour is instantaneous. When manganese sulphate is added to the oxalic-acid solution before the titration, the permanganate is at once decolorized.
Only the salts of the alkali-metals are soluble in water. Calcium oxalate, CaC204,2aq, is insoluble in* acetic acid, but soluble in mineral acids; its formation serves as a test both for calcium and for oxalic acid. As a dibasic acid, oxalic acid yields both acid and normal salts, and the so-called qiLodroxalaies are known — compounds of one molecule of acid salt with one molecule of acid: among these is "salt of sorrel," KHC204,H2C204,2aq. A great number of complex salts of oxalic acid are known : many of them contain aJkali-metals, and are soluble in water. They are employed in electro-analysis.
A t3rpe of these complex salts is potassium ferr<yus oxalate^ KjFeCCjO^),, which yields a yellow solution. This indicates the presence of a complex ion, probably (FeCCaOJ^)", since ferrous salts are usually light-green. Potassium ferrous oxalate is a strong reduc- ing agent: it is employed for the development of photographic plates.
Potasnum ferric oxalate, KjFeCCyOJai yields a green solution, which must, therefore, also contain a complex ion, possibly
202 ORGANIC CHEMISTRY. U 163
(FeiCtOi)^)'". Its solution is rapidly reduced by sunlight, in accord- ance with the equation
2K,Fe(C,0i), =2K,Fe(C,04)f +K,C,04 +2C0,.
This property b made use of in the preparation of T^Iottno^pes. The photographic negative is placed upon a sheet of paper saturated with potassium ferric oxalate: reduction to ferrous salt only takes place where the light is transmitted through the negative, and when the paper is placed in a solution of a platinum salt, the metal is only deposited on the parts coated with potassium ferrous oxalate.
Eder's solution has remarkable properties. It consists of a mixture of two volumes of a four per cent, solution of anmionium oxalate, and one voliune of a five per cent, solution of mercuric chloride. In the dark it remains unaltered, but under the influence of light it decomposes with precipitation of mercurous chloride:
2HgCl2 -h (NH4)2C«0« = 2HgCl +2C0, +2NH«a.
The decomposition is much accelerated by the presence of certun fluorescent substances, such as eosin (348).
163. Dimethyl oxdUUe is solid, and melts at 54^ : it is employed in the preparation of pure methyl alcohol. Diethyl oxalate is a liquid. Both are prepared by distilling a solution of anhydrous oxalic acid in the absolute alcohol.
Oxalyl chloride, COCl^COCl, is prepared by the interaction of two gramme-molecules of phosphorus pentachloride and one gramme-molecule of oxalic acid. It is a colourless liquid, boils at 64°, and at — 12° solidifies to white crystals. When its vapour is brought into contact with steam, oxalic acid and hydrochloric acid are formed. Liquid water, however, converts it quantitatively into carbon dioxide, carbon monoxide, and hydrochloric acid.
Oxamide, GONH2-CONH2, is a white solid, nearly insoluble in water, alcohol, and ether, and is obtained as a crystalline precipi- tate by the addition of ammonia to a solution of a dialkyl oxalate. The monoamides of the dibasic acids are called amic acids, that of oxalic acid being oxamic add, CONH2-0OOH. It is a crystal- line compoimd, readily soluble in cold water, and insoluble in alcohol.
The interaction of oxalic acid, HOOC-COOH, and glycerol 3rields either allyl alcohol (132) or formic acid (81), the product formed being dependent on the experimental conditions. This
CH20H ^ CH20H
§ ie4] MAWNIC ACID. 203
aetion constitutes the basis of the laboratory method of preparing each of these compounds.
On dissolving anhydrous oxalic acid in excess of glycerol at a temperature of approximately 50^, the initial product is an oxalic ester of glycerol (I.)i since addition of alcoholic ammonia produces oxamide, as with other oxalic esters. Rise of tem- perature causes elimination of two molecules of carbon dioxide, with production of allyl alcohol (II.) :
CH2O.CO CH2 CH2O.CO.CO2H
I • II I
CHO-CO -2C02=CH ; CHOH -CQ2
I CH2OH
L II. III.
CH2O.CO.H + H2O CH2OH
= CHOH -> CHOH + H.CO2H.
CH2OH CH2OH
IV.
The quantity of allyl alcohol thus formed is equivalent to that of the oxamide which can be precipitated from an equal volume kA the reaction-mixture.
With oxalic acid containing water of crystallization, the initial product is the acid oxalic ester of glycerol (III.). On warming, this compoimd readily loses one molecule of carbon dioxide, with formation of glyceryl monofomKUe or monoformin (IV.). On adding more oxalic acid, formic acid is liberated, and distils. Simultaneously, the acid oxalic ester of glycerol is regenerated, and becomes available for the production of more formic acid. Since the glycerol is always reproduced, it is evident that a given weight of this substance is capable of transforming an unlimited quantity of oxalic acid.
Acid, COOH.CH2.COOH.
x64« The constitution of malonic acid is proved by its synthesis from monochloroacetic acid. When an aqueous solution of potas- sium monochloroacetate is boiled with potassiiun cyanide, cyano-
204 ORGANIC CHEMISTRY. [§ 164
acetic acid is formed, and can be converted into malonic acid by hydrolysis of the nitrile-group :
^*^2<C00H ~*^"2<C00H ~*^**2<COOH-
HoQochloroaoetio acid Cyanoaoetio acid Malonic acid
Malonic acid is a crystalline substance: some of its physical properties are given in the table in i6i. When heated somewhat above its melting-point, it loses one molecule of carbon dioxide, being converted into acetic acid:
C00H-CH2-iC00|H - CX)2 + OOOH.CH,.
It is found that wlfien a compound with two carboxylrgroupa in union with one carbon atom is heated above its meUing-^point, its molecule loses one molecule of carbon dioxide.
The most important derivative of malonic acid is diethyl malo- note, many important syntheses being accomplished by its aid. It 18 a liquid of faint odour, boiling at IdS^, and having a specific gravity of 1-061 at 15®. On treatment with sodium, in the pro- portion of one atom to each molecule of ester, hydrogen is evolved, and the diethyl malonate converted into a solid mass. In this reaction, hydrogen is replaced by sodium, yielding diethyl mono- sodiomalonate, a compound of the structure
COOCgHs CHNa • COOCgHfi
This is proved by treating it with an alkyl halide (iodide), a sodium halide and an ester being obtained;
CgHfill +Na|CH(COOC2H5)2 = C2H5-CH(COOC2H6)2+NaI.
On saponification, this ester yields a homologue of malonic acid.
If two atoms of sodium, instead of one, react with one molecule of diethyl malonate, two hydrogen atoms are replaced. Both of these hydrogen atoms are in the methylene-group, because, on treatment of the disodio-compound with two molecules of an alkyl iodide, the two sodium atoms are replaced by alkyl, with
§ 1641 MALONIC ACID, 205
production of a substance which on saponification is converted into a homoiogue of malonic acid:
COOC2H5 COOC2H6
C Nag +21 C2H5 - 2NaI -f C(C2H5)2 .
COOC2H5 COOC2H5
It is also possible to introduce two different alkyl-groups into diethyl malonate. Thus, when diethyl monosodiomafenate is treated with methyl iodide, the diethyl ester of methylmalonic acid is formed: on treatment with sodium this again yields a sodio-com- pound, which is converted by ethyl iodide into the diethyl ester of methylethylmalonic acid. The reaction is discussed further in the chapter on tautomerism (235).
From these examples it is evident that it is possible to synthe- size a great number of dibasic acids from diethyl malonate. More- over, since all these acids contain two carboxyl-groups linked tc the same carbon atom, and have in common with malonic acid the property of losing CO2 when heated above their. melting-points, it is evident that the so-called ''malonic-ester synthesis" is also available for the preparation of the monobasic fatty acids. Thus, methylethylmalonic acid loses CO2 on heating, yielding methyl- ethylacetic acid, identical in constitution with active valeric acid (51}, and resoluble into two active components:
COOH COOH
CH3*C«C2H5 = CH3»C»C2H5.
• •
|500Th H
Methylethylmalonio Valerie aeid
aeid
The malonic-ester S3mthesis is much employed in the prepara* tion of acids, and will be the subject of frequent reference.
Details of the malonic-ester synthesis. — One gramme-molecule of diethyl malonate is mixed with a ten per cent, solution of sodium ethoxide (I equivalent) in absolute alcohol, obtained by the action of sodium on alcohol. To this mixture is added one gramme-mole- cule of an alkyl iodide, and the reaction-mixture heated on a water- bath under a reflux-condenser until the liquid is no longer alkaline. After the alcohol has been distilled off, the residue is treated witii
206 ORGANIC CHEMISTRY. [§§165, 166
water to dissolve the sodium iodide formed, and the diethyl alkyl* malonate extracted with ether. The ethereal solution is dried over calcium chloride, the ether distilled, and the residue purified by fractionation.
If it is desired to introduce two alkyl-radicals or other groups, two equivalents of sodium ethoxide and two gramme-molecules of an alkyl iodide are employed. When two different groups are to be substituted, one of them is first introduced into the molecule, and on subsequent treatment with a second gramme-molecule of sodium ethoxide and of alkyl iodide, the diethyl dialkylmalonate is produced. Otherwise, the procedure is identical with that described above.
165. Carbon suboxide, C3O2, is formed by the distillation of dry malonic acid with ten times its weight of phosphoric oxide:
CH2(COOH)2=C302+2H20.
This mode of formation indicates that carbon suboxide has the constitutional formula
C< •
Carbon suboxide is stable only at low temperature; at ordinary temperature it polymerizes in the course of a single day to a blackish-red, amorphous mass.
It is a gas of very pungent odour, which can be condensed to a Uquid boiling at 7^. With water, it regenerates malonic acid, and may, therefore, be regarded as an anhydride of this acid. The true anhydride,
CH2<gg>0,
analogous to the anhydrides of the higher homologues of malonic acid, is unknbwn.
Compounds containing the group CH2==C0 are known, and are designated keiens. Carbon suboxide is the simplest diketen.
Succinic Acid, COOH.CH2-CH2.COOH.
166. Succinic add is a crystalline substance, melting at 182^, and dissolving with difficulty in cold water. It is present in
i 166] SUCCINIC ACID. 207
amber, in fossilized wood, and in many plants, and can be syn- thetically prepared by the following methods.
1. From ethylene bromide by treatment with potassium cya- nide, which converts it into ethylene cyanide, CN»CH2-CH2-CN: on hydrolysis, this yields succinic acid.
2. From malonic acid by treating diethyl monosodiomalonate with ethyl monochloroacetate:
(COOC2H6)2CH Na+Cl H2C-COOC2H6
= NaCl + (COOC2H5)2CH.CH2-COOC2H5.
In this reaction an ester of ethanetricarhoxylic acid is formed; and when heated above its melting-point, the corresponding acid loses CX32y yielding succinic acid:
CHa-COOH CH2-C00H |COOlH.CH-COOH "" CH2-C00H
Succinic acid, and symmetrically substituted succinic acids, can also be obtained by the action of an ethereal solution of iodine or bromine upon diethyl monosodiomalonate or its monoalkyl- derivatives:
COOC2H6 OOOC2H6 COOC2H5 COOC2H5
A-CNa -fU + NaC-A' -A-C ■ CA +2NaI.
COOC2H5 COOC2H5 COOC2H5 COOC2H5
A — Hydrqaon or alkyl Tetnoarboxylio aster
By saponification, and elimination of CO2, the ester formed is con- verted into the dibasic acid:
COOH COOH . • • ,, A.CH.COOH
A-C C-A' - • -f-2C02.
' , • , A'.CH.COOH^ *
|COO|H|COO|H
Unlike calcium oxalate, calcium atxeinate is soluble in water. A characteristic salt is ferric stuxtnakf deposited as an amorphous, flocculent, brownish-red precipitate by mixing solutions of ferric chloride and an alkali-metal succinate.
208
ORGANIC CHEMISTRY.
I§167
Formation of Anhydrides.
167. Oxalic acid and malonic acid do not yield anhydrides (165) , while succinic acid, C4He04, and glutaric acid, C£H804, do so very readily. The formation of anhydride is due to the elimination of one molecule of water from one molecule of the dibasic acid, as is proved by a determination of the molecular weights of the anhydrides:
CH2— COOlH
rJ -H2O OH
CHy— Cof
/CH2— COOIH
CH2 ]— — H2O
\CHa— colon
CHjr— COv
I >0;
CH2-€0/
Succinio anhydride
/CH2— C0\
CH2 o.
XCHr- CO/
Qlutario anhydride
Fig. 31. — Spacial Representation of thh Bonds betwesn 2-6
C-ATOM»
i 1671 ANHYDRIDES OF DIBASIC ACIDS. 209
These anhydrides are reconverted into the corresponding dibasic acids by dissolving them in water.
CH2-C0. A derivative of succinic acid, succinimide, \ /NH, has
CHa-CCr
a ring of four carbon atoms and one nitrogen atom: it is formed by the rapid distillation of ammonium succinate. The atoms situ- ated at the extremities of a carbon chain of four or five C-atoms interact very re&dily : those in shorter chains only interact with difficulty, or not at all. Analogous phenomena are the elimina- tion of one molecule of water from aa'-glycols (150), and of anunonia from aa'-diamines (159), both very readily effected from a carbon chain of four or five C-atoms, but impossible' or leading to the formation of very unstable compounds, when the chain is shorter. A satisfactory explanation of these phenomena, and others of the same type, may be attained by a consideration of the direction of the bonds in space. It was assumed (48) that the four affinities of the carbon atom are directed towards the angles of a regular tetrahedron with the carbon atom at the centre. For a single bond between two carbon atoms it is assumed that one affinity of each of these atoms is linked to one affinity of the other (Fig. 31). The position in space of the C-atoms in a chain of three or more members, and the direction of their affinities, are represented in the figure.
It is evident that in a normal chain of four C-atoms the affinities at the extremities approach on^ another closely, and in a chain of five C-atoms still more closely, so that they can interact readily.
A few instances of compounds with a closed chain containing
CH2 • CH2 only two C-atoms, such as ethylene oxide, \/ , are known.
O
The figure indicates that for two C-atoms the direction of the affin- ities must undergo a considerable change to render the formation of a ring possible. Such compounds are unstable, the closed chain being very readily opened, as is indicated by the "strain-theory " of VON Baeter (120).
210 ORGANIC CHEMISTRY. [{ 168
The Saponification of Esters of Polyhydric Alcohels and of
Polybasic Acids*
x68. Esters can be saponified by means of either acids or alkalis. For the saponification with acid of the esters of sym- metrical dibasic acids and of the esters of dihydric alcohols, the process does not take place step-by-^tep, and the remarkable fact has been established that the ratio of the saponification-constants of the neutral and the acid esters^ or of the neutral and the alcoholic esters, b as 2:1, For instance, when ^ycol diacetate is saponified with acid, there is no intermediate formation of mono- acetate, and the velocity-constant is twice as great as that for glycol monoacetate; and there is a similar ratio between the constants for diethyl malonate and ethyl hydrogen malonate.
There is a simple theoretical explanation of this phenomenon. In the acid saponification the hydrogen ions exert a catalytic action, and the saponification may be assiuned to be due to the impacts of the ions with the ester molecules. The hydrogen ions being much smaller than these molecules, localization of the impacts to ester-groups can be considered the cause of saponifica- tion. For equimolecular concentration the impacts are then twice as niunerous for the esters of dihydric alcohols or dibasic acids as for mono-esters ; as can be tested by a doubling of the concentra- tion of the ester of a monohydric alcohol and a monobasic acid.
For esters like those of methylsuccinic acid,
COOH.CHCCHs) .CH2-C00H,
the structure is not symmetrical, so that the molecule does not consist of two similar parts, and the velocity-constants are not in the ratio 2:1. On saponification, such esters should behave like a mixture of two dissimilar esters, and experiment has con- firmed this view.
In the saponification with alkali of the esters of polyhydric alcohols, the saponification-constants exhibit a similar ratio. If the constant for glyceryl monoacetate is 1, that for the diacetate is 2, and for the triacetate 3. In this instance the hydroxyl-ions exert a catalytic action, and the explanation of the simple ratio of the constants is similar to that given for the hydrogen ions. The existence of these ratios is obviously contingent on instan-
§ 1691 PUMARIC ACID AND MALElC ACID. 211
taneous saponification of the esters, and would be incompatible with the step-by-step process formerly assumed to occur.
When esters of polybasic acids are saponified by alkalis, the ratio of the constants is entirely different, the numerical value of the constant for the neutral ester being many times greater than that for the acid ester. This phenomenon is exempUfied by the saponification-velocities of diethyl malonate and ethyl hydrogen malonate, their ratio being almost 100: 1. This fact is explicable on the assumption of step-by-step saponification in this case, causing the presence of many anions, such as
C2H6OOC.CH2-COO',
in the alkaline solution of the acid ester, in which this acid ester is present as a highly ionized salt. The saponifying action of the negatively charged hydroxyl-ions is in great measure inhibited by the repellent influence of the similarly charged anions.
n. UNSATURATED DIBASIC ACIDS.
Fumaric Acid and Maleic Acid, C4H4O4.
169. The most important members of the group of imsaturated dibasic acids are fumaric add and maleic add, both with the formula C4H4O4. They have been much investigated, a complete explana- tion of their isomerism having been finally arrived at by an appli- cation of the principles of stereoisomerism.
Fumaric acid is somewhat widely distributed in the vegetable kingdom. It does not melt at the ordinary pressure, but sub- limes at about 200**: it dissolves with difficulty in water. Maleic acid is not a natural product: it melts at 130**, and is very readily soluble in water.
Both acids can be obtained by heating malic acid (187),
C00H-CH0H.CH2-C00H,
the result depending on the temperature and duration of the reac- tion. Fumaric acid is the principal product when the temperatm^ is maintained at 140^-150° for a long time, but when a higher tem- perature is employed, and the heating is quickly carried out, the anhydride of maleic acid distils along with water. This anhydride readily takes up water,, regenerating the acid. This is the ordinary
212
ORGANIC CHEMISTRY,
[§169
method for the preparation of these acids, and it indicates that both have the same structural formula:
COOH-CH-CH-COOH-HgO = COOH.CH:CH.COOH.
OHH
This view of their constitution is supported by the fact that on treatment with sodium-amalgam and water both acids yield suc- cinic acid, and also by the formation of monobromosuccinic acid by addition of HBr, and of malic acid by heating with water at a high temperature. Both acids have therefore the same constitutional formula,
COOH.CHiCH.COOH.
The isomerism of the crotonic acids is similar (136). It remains to consider how this isomerism can be explained by the aid of stereochemistry*
A single bond between two carbon atoms may be represented as in Fig. 32 (167). If the tetrahedra are drawn in full, then the
Hr:::^ -^r-yH
Fig. 32. Fig. 33.
Single Bond between two Carbon Atoms.
single bond will be as in Fig. 33. If the tetrahedra are free to rotate round their common axis, isomerism cannot be expected for compounds Cabc — Cdefj nor has it ever been observed.
When a double bond is present, then two affinities of each carbon atom come into play, as graphically represented in Figs. 34, 35, and 36. Free rotation of the tetrahedra relative to one another is then no longer possible.
S169]
PUMARIC ACID AND MALElC ACID,
213
The figures indicate that difference of grouping depends on the position of the groups a and b of one tetrahedron with reference to
Fio. 34. Fig. 35. Fia. 36.
Graphic Spacial Representation op the Double Bond between
TWO Carbon Atoms.
the similar groups a and b of the other, a may be over a, and 6 over 6, as in Fig. 35: or a may be over 6, and b over a, as in Fig. 36. This can be represented by the formulae
a — C — b
II
a — C — b
a— O— 6
and
i^— C— a
Thus, the two crotonic acids would be
Cxi3 — C — H
II
H— C— COOH
TranM
H— C— CHs and II ,
H— C— COOH
Cif
aad famaric and maleic acids would have the fonnuUe
COOH— C— H H— C— COOH
I. II and II. II
H— C— COOH H— C— COOH
Trana CU
It must now be proved which of these two formulse belongs to fumaric acid, and which to maleic acid.
Maleic acid yields an anhydride, while fumaric acid does not. In formula II. the carboxyl-groups are in juxtaposition to one another, but in formula I. they are as far removed from each other
214
ORGANIC CHEMISTRY.
I§170
as possible. Only in the acid with the cts-formula are the carboxyl- groups represented in a position to interact readily:
H-C-COOIH
H— C-COIOH
Maleleacid
H— C— CO
II >o.
H— C— CO
If alelo anhydride
From this it is inferred that fumaric acid has the constihdion indu ceded in formula L, and maldc acid that in formvla II.
170. Further consideration indicates that this view also accounts for the other known properties of these acids. Neither formula contains an asymmetric C-atom, so that neither optical activity nor the great resemblance in such properties as specific gravity, melting- point, solubility, etc., due to the similarity in internal structure characteristic of the isomerism occasioned by an as3munetric carbon atom, is to be expected. Fumaric acid and maleic acid do, in fact, display great differences in these physical properties.
Both fumaric acid and maleic acid combine with bromine, but the dibromo-addition-products thus obtained are different. Fu- maric acid yields dibramosuccinic add, soluble with difficulty in water; and maleic acid iaodibroino8y4:cinic acid, much more readily soluble in water. Figs. 37 to 40 indicate that different acids must result from this reaction. Figs. 38 and 40, representing dibromo-
HOOC
HOOC
+ 8Brs=s
H i^ CO'OH
Fig. 37. — ^Fumaric Aero.
COOE
Fig. 38. — ^Dibromosoccinic Acid.
succinic acid and t^odibromosuccinic acid respectively, cannot be made to coincide by rotation; and this is made more evident by comparing Figs. 40 and 41. The latter is obtained from Fig. 38 by
41701
PUMARIC ACID AND MALBIC ACID.
215
rotation of the upper tetrahedron round the vertical axis, the posi- tion of the lower tetrahedron remaining unaltered. In the figures the order of the groups linked to both carbon atoms of the i>o-acid is H, Br^ COOH from left to right : for the lower carbon atom of
CO'OH
+ JBBr
CO-OH
Fio. 39. — ^IIaudIc Acid.
00-OH
zri-:z=5»A COOH
Fio. 40.— ^Dibbohosuccinic Acid.
dibromosuccinic acid (Fig. 38) the order is similar, but for the upper carbon atom it is from right to left.
When HBr is removed from dibromosuccinic acid (Fig. 41), the H-atom linked to one carbon atom and the Br-atom linked to the other are eliminated, yielding an acid COOH •CH:CBr- COOH. This removal of HBr could not be effected if the tetrahedra were
CO'OH
CO«OH
Fig. 41. — Dibromobuccinic Acm.
CO-QH
CO-OH
FiQ. 42. — ^Bromomaleic Acid.
in the position shown in Fig. 38: rotation round the vertical axis is essential to bring H and Br into " corresponding " positions, as
216
ORGANIC CHEMISTRY,
(§171
in Fig. 41: elimination of HBr produces the acid represented in Fig. 42. This acid readily yields an anhydride, since the COOH- groups are in the corresponding positions: it is therefore bromo- maleic add.
When HBr is removed from i^odibromosuccinic acid, repre- sented in Fig. 43 (obtainable from Fig. 40 by rotation in the same
HOOC
— HBr =
00-Off
-H4^ + :=^ CO-OH
Br Be
Fig. 43. — woDibromobuccinic Acn>. Fio. 44. — ^Bromofuuabic Acm.
way as Fig. 41 from Fig. 38), an acid results which does not yield a corresponding anhydride, but is converted by elimination of water into the anhydride of bromomaleic acid. This behaviour resembles that of fumaric acid, which under the same conditions yields maleic anhydride. This acid must therefore be bramo^ fumaric acid {Fig. 44).
It follows that the constitution assumed for these acids on stereochemical grounds accounts for their chemical properties. Another example in support of this explanation is mentioned in ig4.
171. Maleic acid can be converted into fumaric acid by keeping it for some time at a temperatiu^ above its melting-point; by bringing it into contact with hydrogen halides at ordinary tem- peratures; by exposing its concentrated solution in presence of a trace of bromine to the action of sunlight, a slow reaction in absence of light; by treating ethyl maleate with small quantities of iodine; or by other means. The facility of all these decom- positions indicates that maleic acid is the unstable, and fumaric acid the stable, modification. Inversely, fumaric acid is con-
S 172] AFFINITY-CONSTANTS OF UNSATURATED ACIDS. 217
verted by distillation into maleic anhydride. Fumaric acid is also converted into maleic acid by the action of ultraviolet light, as is maleic acid into fumaric acid. With increasing concentra- tion of the initial solution, the equilibrium attained is displaced towards the side of the maleic acid.
AflSnity-€onstant8 of the Unsaturated Adds.
172. Like the monobasic unsaturated acids (135), the dibasic unsaturated acids have greater affinity-constants than the corre- sponding saturated acids. For succinic acid, 10^^ = 0 •665, and for fiunaric acid, 10^A; = 9*3. The strength of acetylenedicar- boxylic acid, COOH.C^C»COOH (obtained by the interaction of alcoholic potash and dibromosuccinic acid,
COOH .CHBr— CHBr .COOH),
is about equal to that of sulphuric acid. Thus the presence of a double bond, and even more of a triple bond, intensifies the acidio character. For maleic acid 10^^ = 117, or about twelve times aa much as for fumaric acid. This indicates the great influence exerted by the distance between the carboxyl-groups in the mole- cule upon the strength of these acids.
The ionization of dibasic acids is a step-by-step process. An
acid H2A first 3rields H + HA', and then on further dilution HA' is
ionized to H+A''. In this dissociation remarkable differences have been observed. For some acids the second stage of ionization does not begin until the first is almost complete, but for other acids it is already begun when about half of the first stage is over. The degree of ionization depends upon the relative position of the carboxyl- groups in the molecule. The nearer these groups are to each other, the more extended is the first, and the smaller the second, stage of ionization; and mce^i^ersa.
This phenomenon is rpadily explained by assuming that the nega- tive charge of the anion is concentrated on the hydroxyl-oxygen of the ionized carboxyl-group. During the ionization of the first H-atom, the presence of one carboxyl-group promotes the ionization of the other. This influence is greatest when the carboxyl-groups are dose together. Other negative groups produce a similar effect (178
218 ORGANIC CHEMISTRY. [{{ 173, 174
and 183). When, however, the ionization of the first H-atom is
complete, the HA'-residue is decomposed with difficulty into H and A", on account of the attraction exerted by the negative charge of this residue on any positively-charged H-ion liberated, this attraction being greatest when the negative charge is close to the H-atom of the HA'-residue. On the assumption that this charge is situated on the hydroxyl-oxygen of the first carboxyl-group, its attraction is greatest when the two carboxyl-groups in the non-ionized acid are in close proximity. When, however, the H-atom of the first car- boxyl-group and the negatively-charged hydroxyl-oxygen of the HA'-residue are further apart, the second stage of the ionization meets with \&v resistance, and therefore takes place more readily.
IMbasic Acids with more titan one Triple Bond.
173. VoN Baeter has prepared dibasic acids containing more than one triple bond in the molecule, from acetylenedicarboxylic acid. When heated with water, its potassium hydrogen salt is converted into potassium propiolate (139), with loss of COi:
KOOCCSC.fCOilH - CO,+KOOC.C=CH.
When the copper derivative of this salt, KOOC-C=Ccu,* is treated with potassium ferricyanide in alkaline solution, CuO is formed, while the two acid-residues simultaneously unite with production of the potassium salt of diacetylenedicarboxylic acid,
KOOC .C^C-€=C -COOK.
The potassium hydrogen salt of this acid also loses 00, readily, and the copper derivative of the monobasic acid thus formed is converted by similar oxidation into CuO and the potassium salt of tetra-dcetylenedicarboxylic acid:
2K00C.C=C.C=Ccu* -♦ KOOC.CEC.C^C.CEC-C=C.COOK.
These compounds are very unstable, being decomposed by the action of light, and otherwise.
m. POLYBASIC Acms.
174. Acids with three carboxyl-groups in union with one car- bon atom are unknown, except as esters. The triethyl ester of
♦cu=JCu.
§ 174] POLYDASIC ACIDS. 219
methanetricarboxylic acid is obtained by the action of ethyl chloro- carbonate (263) on diethyl monosodiomalonate:
C2H5OOC|CPHNalCH(C00C2H5)2 -►C2H500C-CH(COOC3H5)2.
Hthyl chlorocarbonate
When this ester is saponified , CO2 is simultaneously eliminated, malonic acid I^ing formed instead of the corresponding tribasic acid. This is another instance of the phenomenon that several negative groups do not remain in union with one carbon atom, two being the maximum number for carboxyl (149 and 177).
A description of the syntheses of a few of the polybasic acids will afford examples of the methods adopted for the preparation of compounds of this class.
A type of the tribasic acids is afia^-^opanetricarboxylic acid, or tricarballylic acid, obtainable by several methods.
1. From tribromohydrin by treatment with potassium cyam'de, and hydrolysis of the tricyanohydrin thus formed:
CH2 — CH — CH2 CH2 — CH — CH2 CH2 CH CH2
Br Br Br ~* CN CN CN ~* COOH COOH COOH.
2. From diethyl disodiomalonate and ethyl monochloroacetate;
(CaHsOOQaClNaa +2CIICH2.COOC2H8 =
C2H600C^p^CH2'COOC2H5 , „^ p, CzHsOOC^^^CHa-COOCjHs'''''^*^'-
On saponification of this ester, an acid is obtained which an heating loses CO2, with formation of tricarballylic acid:
CHj-COOH CH2-C00H
HOOC^^ CH-COOH.
HIO2C • .
' ' CHa-COOH CH2-C00H
A synthesis peculiar to the polybasic acids consists in the addition of ethyl monosodiomalonate to the esters of unsaturated acids, such as fumaric acid:
NaCH.COOC2H6 Na CH.COOC2H6
I +11 = CH-COOCaHe
HC(C00C2H6)2 CH-CXXXJaHs |
CH(COOC2H8)8
220 ORGANIC CHEMISTRY, [§ 174
Saponification, with subsequent elimination of CO2, yields tiicar- ballylic acid. It melts at 166^, and dissolves readily in water.
Aconitic acid, melts at 191^ : . it is a type of the unsaturated tribasic acids. It is obtained from citric acid (197) through removal of water by heating. The constitution of aconitic acid is
CH==<} CHa
COOH COOH COOh'
for on reduction it is converted into tricarballylic acid.
SUBSTITUTED ACIDS.
L HALOGEN-SUBSTirUTED ACIDS.
Z75. The hcdogen-^ubstUuted acids can be obtained by the direct action of chlorine or bromine upon the. saturated fatty acids, but this process is not very satisfactory. The monochloro- acids and monobromo-acids are best prepared by the action of chlorine or bromine, not upon the acid, but upon its chloride or bromide. The process involves treating the acid with phosphorus and a halogen, the phosphorus halide produced reacting with the acid to form an acid chloride or bromide, R-COX, which is then attacked by the excess of halogen present.
Some acids cannot be thus brominated: such are trimethyl- acetic acid, (CH3)3C*COOH, and tetramethylsuccinic acid,
(CH3)2C-COOH
. In these acids there is no hydrogen in union (CH3)2C.COOH
with the a-carbon atom, which is du-ectly linked to carboxyl.
As a general rule, it is only possible to brominate acids of which
the a-carbon atom is linked to hydrogen, the acids formed being
called a-bromo-acids. The constitution of these is proved by
converting them into hydroxy-acids (179), which are shown to be
a-compounds through their synthesis by another method.
Halogen-substituted acids can also be prepared by addition of hydrogen halide or halogen to the unsaturated acids, or by the action of phosphorus halides on the hydroxy-acids. The iodo- acids can sometimes be advantageously obtained from the corre- sponding chloro-derivatives by heating them with potassium iodide.
The formation of a-substituted acids only in this process is
explicable on the assumption of the initial transformation of
the acid bromide into an isomeride:
X)H R.CH2.C0Br-^R.CH:C< .
^Br
221
222
ORGANIC CHEMISTRY.
[§176
Addition of bromine to this compound yields a substance of the formula
/OH R.CHBr.C^Br ,
converted by elimination of HBr into an oe-bromo-acid bromide.
176. The introduction of halogen into the molecule causes a marked increase in the strength of an acid, as will be seen from the table below of dissociation-constants, 1(HA;. This table indicates that the strength of an acid is increased to a greater extent by chlorine than by bromine, and by bromine than
|
Nftme. |
Formula. |
10«Jb. |
|
Acetic acid |
CH,.CO,H CHjCl.COiH CHjBr.COiH CH,I .CO,H CHClj.COjH ccu.coja CH3 • CHj • Cxii • COtH CH,.CH,.CHC1.C0,H CHs-CHCl-CHi-COJI CH,Cl-CH,-CH,-COja |
0*18 |
|
Monochloroacetic acid |
15*5 |
|
|
Monobromoacetic acid |
13.8 |
|
|
Monoiodoacetic acid |
7.5 |
|
|
Dichloroacetic acid |
514 |
|
|
Trichloroacetic acid |
12100 |
|
|
Butvric acid |
0*152 |
|
|
a-Chlorobutvric acid |
13*9 |
|
|
fi-Chlorobutvric acid |
0*89 |
|
|
Y-Chlorobutvric acid |
0*3 (ca.) |
|
by iodine, and that a marked increase is occasioned by the intro- duction of more than one chlorine atom. The position of the halo- gen atom also exerts an influence: for iodoacetic acid with the I-atom in the a-position the value of the constant is 32 times as great as for acetic acid, while for ^-lodopropionic acid 10*fc is only 7 times as great as for propionic acid.
The influence of the carboxyl-groups upon the halogen atoms is such that the properties of the monohalogen^ubstUuted acids depend chiefly upon the reUUive position of the halogen atom and the carboxyl-group.
On boiling with alkalis, the a-halogen-substituted acids are readily converted into the a-hydroxy-acids by exchange of halogen for hydroxy 1:
CH2Cl.COOH-f2KOH = KCl+CH20H.C00K-f H2O.
Monochloroftcetic acid
Potaasium glycollate
{§ 177, 178] HALOGEN-SUBSTITUTED ACIDS. 223
On similar treatment, the /7-halogen-substituted acids lose hydrogen halide, with formation of unsaturated acids:
CH3.CHCl.CH2-COOH«CH3-CH:CH.COOH+HCL
^-Chlorobutyrio aoid Crotonic acid
The behaviour of the )9-haIogen-sub6tituted acids with sodium carbonate is very characteristic. When they are warmed with its aqueous solution, hydrogen halide and CO, are simultaneously eliminated from the molecule; with formation of an unsaturated hydrocarbon:
/CH,
CH,.CH.CH|CO,|Na
r= '
CH, . CH : CH . CH, + NaBr + 00,.
pvciMfoButylene
On boiling with water or with an alkali-metal carbonate, the Y-halogen-substituted acids readily lose HX, forming lactones (z8o and 185-186) :
CH3-CH.CH2-CH2-CO->CH3-CH-CH2-CH2-CO
I Br H-0
I i
Valerolaotone
Chloroacetic Acids.
177. MonocHoroacetic acid, CH2C1-C00H, is obtained by the action of chlorine upon acetic acid, in presence of sulphur as a chlorine-carrier. It is a crystalline solid, melting at 63°. Di- chloroacetic acid, CHCl2*C00H, a liquid boiling at 191°, and trichloroacetic add, CC13-C00H, a solid melting at 57° and boiling at 195°, are best prepared from chloral (201). Trichloroacetic acid is unstable, and on boiling with water decomposes into carbon dioxide and chloroform :
CCl3.[C0^H = CCI3H + CO2.
This is another example of the fact that " loading " a carbon atom with negative elements and groups renders the molecule unstable.
Acids with more than one Halogen Atom in the Molecule.
178. Isomerism in this type of compounds may be occasioned by a difference in position of the hald^en atoms in the molecule.
224 OROANIC CHEMISTRY, [§ 178
Addition of halogen to an unsaturated acid produces a compound with the halogen atoms linked to adjoining carbon atoms.
The elimination of hydrogen halide from acids of this class affords a striking example of the value of stereochemistry in explaining phenomena for which the ordinary constitutional formulae are unable to account. Among them is the fact that in the series of unsaturated acids the dibromide of one modification loses 2HBr very readily, yielding an acid with a triple bond, while the dibromide of the other modification either does not react thus, or only with difilculty. An example of this is afforded by erucic and brassidic acids, which have been proved, by the method indicated in 140, to have the constitution
Q,H„*CH:CH-CuHtt.COOH.
When heated with alcoholic potash at 150^-170^, dibromoerucic acid, obtained by addition of bromine to erucic acid, readily loses 2HBry yielding behenolic acid, C8Hi7*C=C*CiiH»*GOOH; whereas one molecule of hydrobromic acid is eliminated from dibromobrassidic acid, with production of a monobromoerucic acid. This difference is accounted for by assigning the (ran«-formula to erucic acid and the OS-formula to brassidic acid, as indicated in Figs. 45 to 50.
C«H„
OuH,^CX>aH
Fia. 46. — ^Erucic Acu>» rmn«-fonnuIa,
In the formula for dibromoerucic acid, the tetrahedra may be rotated so as to bring each Br-atom above a H-atom (170), making the elimination of 2HBr possible {Figs. 46 and 47): in that for dibromobrassidic acid, only one Br-atom and one H-atom can be brought into the " corresponding positions " to one another (Figs. 49 and 60).
HAWGENSUBSTITUTED ACIDS,
Br
225
Rotated -#-
OuHa-CO,H
Fia. 46. — DlBROMOERUClC
Acid.
CiHjf
H*^
CuHi^OOaH
FlO. '47. — DlBROMOKRUCIC
Acid.
Each H-atom in corresponding position to a fir^tom.
C«Hi|
Br,
CuHi^COtH
Fia. 48. — Brassidic Acid. Ct8-fonnula«
Rotated
CuHtfCOiH
Fig. 49. — ^Dibromobrassidic Acid.
CuHvOQiS
Fig. 50. — ^Dibromobrabsidic Acid.
Only one H-atom in corresponding position to one Br-atom.
226 ORGANIC CHEMISTRY. [f 179
IL MONOBASIC HTDROZT-ACIDS.
179. The hydroxy-acids are substances with one or more hydroxyl-groups and carboxyl-groups in the molecule. The general methods for their formation depend upon the introduction of hydroxyl-gn)ups and carboxyl-groups. They are produced in the following reactions.
1. By the careful oxidation of polyhydric alcohols:
CHs-CHOH.CHaOH -^CHa-CHOH.COOH.
PropyleDaglyoQl Laetie add
2. By replacement of the halogen in halogennsubstituted acids by hydroxyl, as aheady described (150).
3. By reduction of the aldehydic acids and ketonic acids, which contain both a carboxyl-group and a carbonyl-group:
CH3-CO.COOH-f2H = CHs-CHOH-COOH.
Pyroraoemio aoid Laotio acid
4. By the action of nitrous acid upon acids with an amino-group in the alkyl-residue:
NHa-CHz-COOH+HNOg = CHaOH-COOH+Ng+HaO.
Glycine Glycollic acid
5. By addition of hydrocyanic acid to aldehydes or ketones, and hydrolysis of the nitrile thus obtained (loi. 3), a method yield- ing only a-hydroxy-acids:
C„H2„+i.CH0+HCN = C„H2„+, -CM^N;
Aldahyda nQH
Cyanohydrin
C„H2„+i.Cf<:;N+2H20 = C„H2„+i.Cf<XX)H+NH8. \0H \0H
Cyaoohydrin a-Hydrozy-acid
By exchange of Br for OH, acids brominated by the method de- scribed in 175 yield hydroxy-acids identical with those obtained by this cyanohydrin-synthesis. It follows that in these acids the bromine is in union with the a-carbon atom.
6. Oxidation with potassium permanganate effects the direct
5180]
MONOBASIC HYDROXY-ACIDS.
227
replacement of hydrogen by hydroxyl in acids with a hydrogen atom linked to a tertiary carbon atom:
^g»>CH.COOH+0 - ^»>C(OH).COOH.
^ MoButyrio acid a-Hydroxjriaobutsrrio acid
Properties.
i8o. Different compounds are obtained from the hydroxy-acids by substitution in the hydroxyl-group and carboxyl-group respect- ively. When the H-atom of the hydroxyl-group is replaced by alkyl, an acid ether is obtained :
CH2OH.COOH -^CHaOCaHfi.COOH.
GlyooUio acid EthylgiyooUio aoid
Like an ordinary ether, CnH2n+i'0-CmH2m+i, ethylglycoUic acid cannot be saponified. When, on the other hand, the H-atom of the carboxyi-group is exchanged for alkyl, an ester is produced:
CH2OH . COOH ^ CH2OH . COOC2H6.
Ethyl slycoUate
Like other esters, these compounds can be saponified.
The introduction of hydroxyl strengthens the fatty acids to an extent dependent on its position relative to the carboxyl-group, an effect analogous to that produced by the halogens (176), This is indicated by the table, which contains the values of the dissociation- constant, 10**, for several acids.
|
Name. |
Formula. |
10<*. |
|
Acetic acid |
CH,.COOH CH,OH.COOH CH,.CH,.COOH CH,.CHOH.COOH CH,OH.CH,.C(X)H |
0*180 |
|
Glyoollic acid (Hydroxy acetic acid) ProDionic acid |
1-52 0*134 |
|
|
I#actic acid (a-Hydroxypropionic acid) . . ^HvdroxvDroDioiiic acid. ^ |
1*38 0-311 |
|
On heating, the a-hydroxy-iicida readily lose water, two mole- cules being simultaneously eliminated from two molecules of acid: this reaction takes place between the hydroxyl-group of one mole- cule and the carboxyl-group of the other. Lactic acid yields lactide:
228 ORGANIC CHEMISTRY, [§ 181
CH3.CHIOH HJOOC CHg-CH.OOC
1 : \ i -2H2O+ I I
COOIH HOI— CH.CH3 COO — CH -CHa.
3-
Laetide
The formula of this compound indicates that it is a double ester, its constitution being proved by its behaviour when boiled with water or dilute acids: like the esters, it is saponified, yielding lactic acid. p'Hydroxy-acida readily give up water, with formation of un- saturated acids:
CHa-CH-CH-COOH
= H20+CH3.CH:CH.COOH.
Ootonio aoid
OHH
^Hydroxybut}rrio aeid
When a )9-hydroxy-acid is boiled with excess of a 10 per cent, solution of caustic soda, it is partly converted into an a/9-unsaturated acid, and partly into a ^^^-unsaturated acid, while a portion remains unchanged. An equilibrium is thus reached:
R.CH:CH-CH,.COOH ^ R.CH,.CHOH.CH,.COOH ?=±
?=t R -CH, .CH : CH .COOH.
If this reaction is reversible, the same equilibrium should be attained by starting from the hydroxy-acid, or from either of the two unsat- urated acids. FiTTiG proved that this is actually the case.
Y'Hydroxy-ojcids and d-hydroxy-ncids lose water, with formation of inner anhydrides, called lactones (176 and 185-186) :
CH2*CH2»CH2*CO CH2»CH2*CH2*CO, I ,1 =H20+ I
5H HlO 0
(OH
r-Hydrozybutyrio abid Butyrolaotone
GlycoUic Add, C2H4O3.
z8i. GlycoUic acid is present in unripe grapes^ It is usually pre- pared by treating monochloroacetic acid with caustic potash:
COOH.CH,pTK]OH - C00H.CH,0H + KC1.
GlycoUic acid is a crystalline solid, melting at 80°. It is very readily soluble in water, alcohol, and ether : the calcium salt dissolves
§ 1821 LACTIC ACID. 229
with difficulty in water. When distilled in vacuo , glycoUic acid loses water, with formation of glycoUide:
CH,OHHOCO CH,O.CO
I .' ^1 «2H.0+| I
COO|H HO|CH, CO.O.CH,
GlycoUide
Hydroxypropionic Adds, C3H6O3.
182. Two hydroxypropionic acids are known, differing in the position occupied by the hydroxy l-group: they are a-hydroxypro- pionic add, CHs-CHOH-COOH, and ^-hydroxypropionic acid, CH2OH .CH2-C00H. The first is ordinary lactic acid.
a-Hydroxypropionic acid can be obtained synthetically by the methods described in 179, although it is usually prepared by other means. In presence of an organized ferment, called the " lactic-acid bacillus," certain sugars, such as lactose, sucrose, and dextrose, undergo "lactic fermentation," the principal product being lactic acid. These bacilli are present, for example, in decaying cheese, and cannot live in a solution of lactic acid of more than a certain concentration: to make fermentation possible, chalk is added to neutralize the lactic acid formed. Lactic acid can also be prepared by heating dextrose or invert-sugar with caustic soda.
Lactic acid derives its name from its presence in sour milk, as a result of the fermentation of the lactose present. The faint acid odour possessed by sour milk is due, not to lactic acid, but to traces of volatile fatty acids simultaneously formed: lactic acid itself is odourless. Lactic acid is also present in other fermented substances; and in large quantities in ensilage, a cattle-food prepared by submitting piles of grass or clover to pressure.
Lactic acid is purified by distilling the aqueous acid at very low pressures (1 nmi.), when it is obtained as a crystalline solid melting at 18®. The commercial product is a colourless, syrupy liquid of strongly acid taste, and contains water. When heated under ordinary pressure, with the object of removing water, it is partially converted into the anhydride (180) even before dehydra- tion is complete: this can be detected by the diminution of the acid-equivalent on titration. Its racemic zinc salt forms well- defined crystals with three molecules of water.
The constitution of lactic acid is deduced from its formation
230
ORGANIC CHEMISTRY
[§183
from acetaldehyde by the cyanohydrin-synthesis (179, 5), and by the oxidation of propyleneglycol. When lactic acid is heated alone, or with dilute sulphuric acid, it yields acetaldehyde and formic acid:
H
CHs-CHOlH^COOH] -^CHs-Cq+H-COOH
This decomposition mayberegardedasareversalof thecyanohydrin- synthesis, and is characteristic of many a-hydroxy-acids.
H
Lactic acid, CHg-C-COOH, contains one a8>Tnmetric carbon
OH
atom. In accordance with the principles laid down in 48, it ought to exist in three isomeric modifications, and all these are known. Ordinary lactic acid obtained by synthesis is racemic: that is, it consists of equal quantities of the dextro-acid and laevo-acid, and is therefore optically inactive. Dextro-lactic acid and laevo- lactlc acid can be obtained from the inactive modification by methods described in 195. The dextro-rotatory variety is a constituent of meat-juices, and is therefore sometimes called " sarcolactic acid."
183. The sjrnthetic lactic acid is inactive, and hitherto optically active products have not been prepared from inactive substances by wholly chemical means. Since the inactive modification con- sists of equal parts of dextro-rotatory and laevo-rotatory substance, both must be formed in equal quantities in the synthesis. An explanation of this phenomenon is aftorded by a consideration of the following examples.
The nitrile of lactic acid is obtained by the addition of hydro- cyanic acid to acetaldehyde (179, 5), the structural formula of which is represented in Fig. 51 :
CHs
CHs
or
Fio. 61.
ACETALDEHTDB.
Fia. 62. Lactonitrilb.
OH Fig. 63.
LACTONrnULB.
S 1841 LACTIC ACID. 231
The addition of H-CN can take place in two ways, the oxygen doubly linked to the central carbon atom of the figure becoming severed either from the bond c or from d. In the first case the group CN becomes linked to c (Fig. 52), and a hydroxyl-group is formed at d: in the second case this is reversed (Fig. 53). The configurations thus obtained are mirror-images, and cannot be made to coincide: they represent asymmetric C-atoms.
The possibility of the formation of both active components is thus evident, and that these must be formed in equal amounts is made clear by a consideration of the probability of their formation. This is alike for both, since d and c occupy similar positions with respect to a and 6, and there is therefore no tendency for the oxygen to remain linked to the one more than to the other.
In this example an asymmetric carbon atom has resulted from an addilioTi'VesiCixoii. An example of the formation by substitution of a compound containing such an atom is that of a-bromopro*^
pionic acid, jj ^^'^COOH' ^^^^ propionic acid, ^jj'^^'^COOH By replacement of He and Hd respectively, two acids of opposite rotation are produced, the probability of the formation of one being equal to that of the formation of the other.
Compounds containing an asymmetric carbon atom can also result from the elimination of a group, as in the formation of methyl-
ethylacetic acid, p t? >C<qqqjj, from methylethylmalonic acid,
c
?H ^^'^COOH' ^^ '^®^ ^^ ^^2. The probability that this will
^ * d
take place at c and at d is equal, so that an inactive mixture is produced.
184. When optically active lactic acids and othar optically active substances are strongly heated, they are converted into the corresponding optically inactive form, containing equal propor- tions of the dextro-modification and laevo-modification. This necessitates the conversion of one-half of the optically active substance into its optical isomeride.
Optical inactivity is sometimes attained without the aid of heat. Walden found that the dextro-rotatory wobutyl bromopropionate, CHi • CHBr • COOCJHg.and other compounds with a Br-atom in union
232 ORGANIC CHEMISTRY. [§ 185
with an asymmetric C-atom, became optically inactive through being kept for three or four years at the ordinary temperature. The veloc- ity of transformation under such conditions, for most substances too small to be appreciable after the lapse of even long periods — and only measurable at higher temperatures, which have an accelerating effect upon most reactions — ^has for these compounds a measurable value.
Lactones.
185. The ;--hydroxy-acids lose water very readily, with forma* tion of lactones (176 and 180). So great is this tendency that some y-hydroxy-acids, when liberated from their salts, at once give up one molecule of water, yielding a lactone. This phenome- non is another example of the readiness with which ring-com- pounds containing four carbon atoms are formed (167). Many y^hydroxy-acids are not known in the free state, but only in the form of esters, salts, or amides. The lactones are stable towards an aqueous solution of sodium carbonate, but are converted by the hydroxides of the alkali-metals into salts of /'-hydroxy-acids, a reaction proving their constitution. They may be looked upon as the inner esters of the hydroxy-acids.
The lactones can be prepared by several methods. Thus, acids containing a double bond at the ^y-position or /'^-position (J^-acids or J''*-acids) are readily converted into lactones by warming with dilute sulphuric acid. This formation of lactones may be regarded as an addition of the carboxyl-group at the double bond:
R.cfH:CH.CH2-C0 -> R.CH.CHa.CHg-CO.
H.A I A
Unsaturated i^r-acids can be obtained by several methods, one being the action of aldehydes upon sodium succinate in presence of acetic anhydride:
CH,.c5 + H,C-COOH CHa-C^HC.COOH
H,C-COOH " pi] ^.
Aldehyde Succinic acid
H,C>COO[H].
By elimination of one molecule of water, there results a lactonlc acid,
§ 1861 LACTONES, 233
CH,.CH.CH.OOJi CH, CO
0—i
On dry distillation, this loses CO,, yielding the unsaturated add:
CH,.CH.CH.|CO,|H
CH, -♦CH,.CH:CH.CH,.COOH.
O— CO
Another method for the preparation of lactones is the reduc* tion of /'-ketonic acids (233, 3). ^-Lactones and ^-lactones are also known.
186. On boiling with water, the lactones are partly converted into the corresponding hydroxy-acids, the quantity of acid formed being in a measure dependent upon the amount of water present. An equilibrium is attained between the system acid and lactone + water:
CH2OH . GH2 • GH2 • COOH <^ CH2 • CH2 • CH2 • CO + H2O.
T-Hydrozybutyrio aoid I I
Butyrolactone
If the molecular concentration per litre of the /'-hydroxy- butyric acid is A, and if, after the lapse of a time t, x molecules have been converted into lactone, the velocity of lactone-forma- tion at that instant, 8, is given by the equation,
k being the reaction-constant. But the reverse also takes place, the acid being regenerated from the lactone and water. If the lactone is dissolved in a large excess of water, no appreciable error is in- troduced by assuming the quantity of the latter to be constant. The velocity «' of this reverse reaction is then represented by the
equation
8'^k%
in which kf is again the reaction-constant. The total velocity of
^34 ORGANIC CHEMISTRY. [§ 187
the lactone-formation for each instant is^ therefore, equal to the difference between these velocities:
«-5'=^=jfc(A-x)-*'a:. (1)
at
When equilibrium is reached, s = 8'; and if the value of x at this pomt has become equal to xi, then
Aj(A-xi)-fc'xi=0, or p = jl^' ... (2)
Equations 1 and 2 can be solved for k and V. The same method of calculation may be applied to ester^formation from acid and alcohol, by which the reaction-constant of the ester-formation, and of the ester-decomposition, can be computed.
The lactones form addition-products with hydrobromic acid as w^U as with water, yielding y-bromo-acids, the constitution of which is inferred from their reconversion into lactone (176). The lactones also form addition-products with ammonia, yielding the amides of the ;--hydroxy-acids.
m. DIBASIC H7DR0XT-ACIDS.
•
187. The Eomplest dibasic hydrazy-acid is tartronic acid, COOH.CHOH.COOH. It can be obtained by the action of mobt oxide of silver upon bromomalonic acid, and is a crystalline solid, melting at 187® with evolution of COj. The glycollic acid, CHjOH.COOH, thus formed, at once loses water, yielding a poly- meride of glycollide (181).
A substance of greater importance is malic acid, C4He05, which IS present in various unripe fruits, and is best prepared from unripe mountain-ash berries. It is a crystalline solid, melting at 100^, and is readily soluble in water and in alcohol. Natural malic acid is optically active.
It is possible to prove in several ways that malic acid is hydroxy- succinic acid, COOH.CHOH.CHa-COOH. Among these are its reduction to succinic acid by heating with hydriodic acid, its con- version into monochlorosuccinic acid by the action of phosphorus pentachloride, and so on. Its alcoholic character is indicated by the formation of an acetate when its diethyl ester is treated with acetyl chloride.
i 188] MALIC ACID AND TARTARIC ACIDS. 235
The conversion of malic acid under the influence of heat into fumaric acid and maleic acid has been already mentioned (169). In addition to the natural kevo-rotatory acid, both a dextro-rota- tory and an inactive modification are known. The latter can be resolved by fractional crystallization of its cinchonine salt into its two optically active components. As indicated by its structural formula, malic acid contains an asymmetric C-atom.
Tartaric Acids, C4H6O6.
188. Four acidis of the composition C4HQO6 are known, all with the constitutional formula
COOH • CHOH . CHOH • COOH.
They are called dextro-rotatory tartaric addf hevo-rotatory tartaric acid, racemic acid, and mesotartaric add: the last two are optically inactive. Their constitution is proved by their formation from the dibromosuccinic adds — obtained from fumaric acid or maleic acid by the action of bromine — by boiling their silver salts with water, as well as by their production from glyoxal (198) by the cyano- hydrin synthesis. The inactive modifications are produced by these reactions (183).
In accordance with the constitutional formula given above, the tartaric acids contain two asymmetric C-atoms in the molecule, and it is necessary to consider how many stereoisomerides are theoretically possible.
With a single asymmetric C-atom there arc two optical isomerides, which can be denoted by ri and li (I.), Addition of a second asymmetric C-atom, which may be dextro-rotatory or IflBvo-rotatory, produces the combinations II. of the subjoined scheme. Increase in the number of C-atoms to three gives similarly eight isomerides (III.). It is evident that for n asym- metric C-atoms the number of possible isomerides is 2":
I. ^1 li
II. Tir2 Tih lir2 III
^\
1*2
III. rir2r3 TirJLz Til2rz r\l2lz ^1^*2^3 ii^2i3 'i^2r3 IM:^*
236 ORGANIC CHEMISTRY. [§ 189
In this scheme, all the asymmetric C-atoms are assumed to be dissimilar, and the racemic combinations are left out of con- sideration.
Since tartaric acid, however, contains two similar asymmetric C-atoms, that is asymmetric C-atoms in union with similar groupi, l\T2 and ^2^1 become identical, leaving so far three isomerides possible. rir2 and hh being able to unite to form a racemic compound, the total number of poasible isomerides is raised to four:
12 3 4
CH(OH)(COOH) Dextro Dextro L»vo j ^. ,.
I ^ '^^ Inactive combma-
CH(OH)(COOH) Dextro Lsdvo Lsevo tion of r^rg and /iZo
The four tartaric acids, C4H6O6, correspond in properties with the four theoretically possible isomerides. Dextro-tartaric acid and IsBVO-tartaric acid must be represented respectively by 1 and 3, since in these both C-atoms rotate the plane of polarization in the same direction, and should therefore reinforce each other's influence. The optically inactive mesotartaric acid is represented by 2: its two asymmetric C-atoms rotate the plane of polarization equally, but in opposite directions, and thus neutralize each other's effect. Finally, isomeride 4 is racemic acid.
An important difference exists between the two optically in- active isomerides, racemic acid and mesotartaric acid. The former, obtained by mixing equal quantities of the dextro-acid and laevo-acid , can be resolved into its components: the latter, consisting only of one kind of molecules, cannot be resolved. The rotation caused by the dextro-acid is equal in amount but opposite in sign to that due to the laevo-acid.
189. Emil Fischeb has introduced a simple mode of writing the spacial formulae of optically active compounds, of which frequent
FiQ. 64.
§1901
TARTARIC ACIDS.
237
use will be made later. The representation in space of two Oatoms
Cabc in union, in a compound | , is shown in Fig. 54 (167).
Cabc If the two bonds uniting the two carbon atoms are supposed to lie in the plane of the paper, then the positions of a and c are to the back, and of 6 to the front. If a, b, and c are imagined to be projected upon the plane of the paper, and a and c simultaneously so altered in position that they lie in the same straight line at right angles to the vertical axis, and b lies in this axis produced, then projection-figure I. is obtained :
6 I.
-6
a II.
If Fig. 54 is rotated round its vertical axis, so that a, for example, lies in front of the plane of the paper, Fig. 55 results, its projection being represented by II. These apparently different configurations are identical.
For a chain of four carbon atoms there is obtained analogously the projection-figure
This will be imderstood if it is imagined that the figures in 167 (Fig. 31) are so placed that the plane in which the carbon bonds lie is at right angles to that of the paper, and the figures in this position are projected in the manner just described.
190. The projection-formulae for the four isomeric tartaric acids are thus obtained. If the projection figure for two asym- metric C-atoms is divided in the middle of the vertical line, and the upper half of the figure rotated through 180*^ in the plane of the paper, the similar grouping of HO, H, and COOH about the asymmetric C-atoms in both halves,
238
ORGANIC CHEMISTRY.
K190
Ha
H and Ha
COOH
H,
COOH
indicates that both Oatoms rotate the plane of polarization in the same direction. We shall arbitrarily {uasume that this grouping occasions dextro-rotation.
When the two carbon atoms are again united by transposing one of the halves in the plane of the paper, the figure
COOH
H-
Ha
■OH
COOH
results and is therefore the projection-formula for the dextro* rotatory acid.
The grouping with respect to the two C-atoms m the Isvo- rotatory acid must be the mirror-image of that in the dextro- rotatory (48): thus, '
H-
■OH and H-
OH.
COOH COOH
The combination of these two gives the projection-formula
COOH
Ha
H
H OH
for the Iffivo-rotatory acid.
COOH
§1901
TARTARIC ACIDS.
239
These representations of the constitutions of dextro-tartarie acid and Isvo-tartaric acid cannot be made to coincide by altering their position in the plane of the paper * and are therefore different.
When the acid contains a dextro-rotatory and a Isevo-rotatory C-atom, as in mesotartaric acid, the arrangement of the groi^ will be
Deztio
LSTO
HO
OH,
COOH
COOH
and th^ projection-formula
COOH
HO-
Ha
-H
-H
COOH
The projecticm-formtila for racemic acid is
Dextro
COOH
H-
Ha
OH
■H
COOH
Ha
H-
Levo
COOH
H
OH
COOH
* These projection-formulse can be made to coincide by rotating one of them through 180^ about the line HO — H. It will be seen from a model, however, that the spacial formuls cannot be made to coincide by this treat- ment. To determine by means of projection-formuhe whether this is possible for spacial formuke, it is only admissible to transpose them in the plane of the paper.
240 ORGANIC CHEMISTRY. (§ 191
Dextro-tartaric Acid.
191. Potassium hydrogen drlartrale, C4H50QKy is present in the juice of grapes, and during alcoholic fermentation is deposited on the bottom of the casks, being even more sparingly soluble in dilute alcohol than in water. The crude product is called "argol "; when purified, it is known as "cream of tartar." To obtain dextro^ tartaric acid, the crude argol is boiled with hydrochloric acid, and the acid precipitated as calcium tartrate, PaC4H406, with milk of lime. After washing, the calcium salt is treated with an equivalent quantity of sulphuric acid, which precipitates calcium sulphate and sets free the tartaric acid: this can be obtained by evaporation in the form of large, transparent crystals, without water of crystalliza- tion, and having the composition C4H6O6.
Dextro-tartaric acid melts at 170®, is very readily soluble in water, to a less extent in alcohol, and is insoluble in ether. When heated above its melting-point at atmospheric pressure, it loses water and yields various anhydrides, according to the intensity and duration of the heating. On stronger heating, it turns brown, with production of a caramel-like odour, and at a still higher tem- perature chars, with formation of pyroracemic acid (231) and pyrotartaric acid, COOH.CH(CH3)-CH2-COOH. It can be converted into succinic acid by the action of certain bacteria.
In addition to the potassium hydrogen tartrate may be men- tioned the normal potassium salt, C4H4O6K2, which is readily soluble in water, and potassium antimonyl tartrate,
2[C00K . CHOH . CHOH . COO(SbO)] +H2O.
On accoxmt of its medicinal properties, the latter is known as "tar- tar emetic." It is obtained by boiling potassium hydrogen tartrate with antimony oxide and water, and is readily soluble in water.
The precipitation of hydroxides from metallic salts — ^for exam- ple, copper hydroxide from copper sulphate — ^is prevented (157) by the presence of tartaric acid. The liquid obtained by dissolving copper sulphate, tartaric acid, and excess of potassium hydroxide in water is called " Fehling's solution." It is an important means of testing the reducing power of compounds, since reducing ag^its precipitate yellowish-red cuprous oxide, or its hydroxide, from the dark-blue solution. In this alkaline copper solution the hydroxyl- Croups of the central C-atoms have reacted with the copper hydroxide, since one gramme-molecule of normal alkali tartrate can
§1911
TARTARIC ACIDS.
241
dissolve one gramme-molecule of copper hydroxide. These copper alkali tartrates have also been obtained in a crystalline form: thus, the compound C4H206Na2Cu+2H20 is known, and must have the constitutional formula
^ O.CH.COONa „ ^ Cu< . +2H2O.
O.CH.COONa
Experiment has proved that in aqueous solution this compound
is ionized to Na* and the complex anion Cu < • • First,
CCH-COC
the reactions of the solution are no longer those of copper ions:
although the liquid is alkaline, copper hydroxide is not precipitated.
Second, on electrolysis the copper goes towards the anode. This has
been studied by Kuster by the aid of the apparatus shown in Fig.
56. One U-tube contains coppernsulphate solution at 5; the other,
Fig. 56. — ^Elbctroltbis of an Alkaline Confer Solution.
Fbhung's solution at di into both limbs of each is then carefully poured a solution of sodium sulphate, a and c. The common sur- faces of the sodium-sulphate and coppernsuiphate solutions in the two U-tubes lie in the same horizontal plane. When an electric current is passed through the tubes, preferably arranged in parallelj and not in series, a different effect is produced on the level of the surfaces of the copper solutions in each tube. In the copper-sulphate solution a rise takes place at the cathode, since the Cu-ions are cations, and tend towards the cathode. The reverse effect is observed in the Fehling's solution, indicating that in it the copper is a constituent of the anion. The arrows in the figure show the direction in which the ions in each solution tend.
Moreover, the colour of Fehling's solution is a much more in- tense blue than that of a copper-sulphate solution of equivalent concentration, this being evidence of the presence in Fehling's solution of a complex ion containing copper.
Fehling's solution decomposes gradually, so that it is best pre-
242
ORGANIC CHEMISTRY.
[§192
pared as required. Ost has discovered a much more stable alkaline copper solution, applicable to the same purposes as that of Fehlino. It is a mixture of copper sulphate with potassium hydrogen carbon- ate and potassium carbonate, and contains a soluble double carbon- ate of copper and potassium.
Lsevo-tartaric Acid.
L(BVo4artaric acid is obtained from racemic acid. With two exceptions, the properties of the laevo-acid and its salts are identical with those of the dextro-modification and its salts. First, their rotatory power is equal, but opposite in sign: second, the salts formed by the laevo-acid with the optically active alkaloids differ in solubility from those derived from the dextro-acid (195).
Racemic Add.
192. It is stated in 184 that optically active substances can be converted by the action of heat into optically inactive compounds; that is, changed into a mixture of the dextro-modification and IsBvo-inodification in equal proportions. This change is often facilitated by the presence of certain substances: thus, dextro- tartaric acid is readily converted into racemic add by boiling with excess of a concentrated solution of sodium hydroxide. Meso- tartaric acid is simultaneously formed (193).
The optical inactivity is occasioned by conversion of one-half of the dextro-acid into the laevo-modification. If formula I. represents the dextro-acid, then formula II. will correspond with the Isevo-acid; and the formula indicate that the exchange of groups, by which an active compound is converted into its optical isomeride (184), must in this instance take place at both as3rmmetric C-atoms, in order that the dextro-acid may yield its Isevo-isomeride.
COOH
COOH
H- HO-
-OH ■H
HO-
H-
COOH I.
-H ■OH
COOH IL
§193]
TARTARIC ACIDS.
243
Racemic acid is not so soluble in water as the two optically active acids, and differs in crystalline form from them: the crystals have the composition 2C4H606H-2H20. In many of its salts the amount of water of crystallization differs from that in the corre- sponding optically active salts. Racemic acid is proved to consist of two components by its synthesis from solutions of the dextro- acid and the laevo-acid. If the solutions are concentrated, heat is developed on mixing, and the less soluble racemic acid crystallizes out. Racemic acid can also be resolved into the two optically active modifications (195).
Although racemic acid in the solid state differs from both dextro- tartaric acid and laevo-tartaric acid, yet in solution, or as ester in the state of vapour, it is only a mixture of them. The cryoscopic depression produced by it corresponds with the molecular formula C4H6O5; and the vapour-density of its ester with single, instead of with double, molecules.
The term " racemic " is applied to substances which consist of isomerides of equal and opposite rotatory power in equimolecular proportions, and are therefore optically inactive. This phenom- enon was first observed by Pasteur in his researches on racemic acid (195).
Mesotartaric Add.
193. like racemic acid, mesotartaric acid is optically inactive but cannot be resolved into optically active components. It is formed when dextro-tartaric acid is boiled for several hours under a reflux-condenser with a large excess of sodium hydroxide (192).
If formula I. is assigned to dextro-tartaric acid, it is evident that to convert it into mesotartaric acid, formula II., it is only necessary
CX)OH COOH
H Ha
OH -H
HO- HO
COOH I.
H H
COOH II.
for two groups in union with a single asymmetric C-atom to change places, while racemic acid can only result through exchange of the
244
ORGANIC CHEMISTRY,
I§m
groups linked to both C-atoms. This affords an explanation of the fact that when dextro-tartaric acid is heated with dilute hydrochloric
CO-OH
20H
CO'OH
Fio. 57. — MalbIc Acid.
COOH H
or
COOH
H OH
Fig. 58. — Mbsotartaric Acid. Fig. 59. — Mbsotartaric Acid.
acid, or boiled with dilute sodium hydroxide, mesotartaric acid is first formed, and racemic acid only after prolonged heating.
Potassium hydrogen mesotartrate is readily soluble in cold water, differing in this respect from the corresponding salts of the other tartaric acids.
194. This view of the structure of the tartaric acids is in complete accord with their relation to fumaric acid and male!c acid (169), which, on treatment with a dilute aqueous solution of potassium perman- ganate, yield respectively racemic acid and mesotartaric add by addi- tion of two hydroxyl-groups. Addition of 20H to maleic acid may result from the severance of the bond 1 : 1' or 2: 2' in Fig. 57, with
§1W1
TARTARIC ACIDS.
245
production of the configurations represented in Figs. 58 and 59. The projection-formuls corresponding with Figs. 58 and 59 are
OH
HO-
Ha
-COOH H-
and ■COOH H-
H
I.
<XX)H
-COOH
OH II.
These apparently different configurations are identical, as becomes evident on rearranging I. (189):
OH
COOH-
OOOH-
H H
OH
If the last projection-formula is rotated in the plane of the paper through 180°, it will coincide with II. A comparison of this scheme with that in 193 shows it to be the configuration representing meso- tartaric acid. It follows that addition of two hydroxy 1-groups to malelc acid produces only mesotartaric acid.
A different result is obtained by addition of two OH-groups to fumaric acid, as is indicated by Figs. 60 and 61.
HO'OC
+ 2(0H),
CG-OH
Fia. 60. — Fumaric Acid.
246
ORGANIC CHEMISTRY.
[S195
H HOOO
H OH
FiQ. 61. — Racbmic Acid.
Severance of the bonds 1 : 1' or 2:2' by addition yields two ooq- figurations which cannot be made to coincide by rotation. This is made clearer by the projection-forznuke
COOH
OOOH
HO-
HO-
-H <X)OH
HO-
H OH
-H
OH
CXX)H OOOH
COOH- H-
-H OOOH
H- HO-
OH
OH -H
COOH
These projection-formulse are identical with the configurations repre- senting dextro-tartaric and Isevo-tartaric acid (190).
Racemic Substances^ and their Resolution into Optically Active
Constituents.
195. Optically active isomeridcs display no difference in their physical or in their chemical properties, except the rotation of the plane of polarized light in opposite directions, and certain physio-
( 195] RESOLUTION OF RACEMIC SUBSTANCES. 247
logical effects not yet explained. They have, therefore, the same solubility, boiling-point, and melting-point; their salts crystallize with the same number of molecules of water of crystallization; and so on. It follows that the resolution of an optically inactive substance into its optically active components cannot be effected by the ordinary methods, since these are based on differences in physical properties.
Pasteur has devised three methods for effecting this resolution. The first depends upon the fact that racemates sometimes crystal- lize from solution in two forms, one corresponding to the dextro- salt, and the other to the tevo-salt: these can be mechanically sep- arated. Pasteur effected this for sodium ammonium racemate, C8H80i2Na2(NH4)2,2H20. Crystals of the dextro-tartrate and IjEvo-tartrate are only obtained from this solution at temperatures below 28°, the transition-point for these salts (" Inorganic Chemistry," 70):
2Na(NH4)C4H406-4H204:±C8H80i2Na2(NH4)2-2H20+6H20.
I>extro-+lavo- Na-NH^-tartrate Na-NH«-raoemate
Fig. 62 represents the crystal-forms of the two tartrates, the difference between them being due to the positions of the planes a and fe. The crystal-forms are mirror-images, and cannot be made to coincide.
Sometimes separation can be effected by inoculating a super- saturated solution of the racemic compound with a crystal of another substance isomorphous with only one of the components. By thus inoculating a supersaturated solution of sodium ammonium racemate with {-asparagine (243), von Ostromisslenskt isolated sodium ammonium dextro-tartrate in crystalline form.
Pasteur's second method of resolution depends upon a differ- ence in solubility of the salts formed by the union of optically active acids with optically active bases. When a dextro-acid or a Isevo- acid is united with an optically inactive base, as in the metallic salts, the internal structure of the molecule remains unchanged: the constitution of the salt-molecules, like that of the free acids, can be represented by configurations which are mirror-images. But it is otherwise when the dextro-acid and the Iffivo-acid are united with an optically active (for example, a dextro-rotatory) base: the
248
ORGANIC CHEMISTRY.
[§105
configurations of the salt-molecules are then no longer miiTOr- images, and identity of physical properties must of necessity cease. Racemic acid can be thus resolved by means of its cinchonine salt, since cinchonine laevo-tartrate is less soluble than the dextro- tartrate, and crystallizes out from solution first. Strychnine can be advantageously employed in the resolution of lactic acid; and other similar examples might.be cited.
FiQ. 62. — Crystal-forms op the Sodium Ammonium Tartrates.
The conversion of enantiomorphic isomerides into derivatives with configurations which are no longer mirror-images of one an- other can be otherwise effected: thus, for acids, by the formation of an ester with an optically active alcohol. The velocity of ester- formation with an optically inactive alcohol must be the same for both isomerides, on account of the perfectly symmetrical structure of the esters formed; but with an optically active alcohol the two isomerides are not esterified at the same rate, since the compounds formed are no longer mirror-images of one another. Marckwald found that when racemic mandelic acid (324), is heated for one hour at 155° with menthol (365), an active alcohol, the non- esterified acid is IsDvo-rotatory.
The third method of fission devised by Pasteur depends on the action of mould-fungi (PeniciUium glaucum), or of bacteria. Thus, when racemic lactic acid in very dilute solution is treated with the BaciLlua acidi Icevolactici, after addition of the necessary nutriment for the bacteria, the optically inactive solution becomes tevo-rotatory, since only the dextro-rotatory acid is converted by the bacilli into other substances. A dilute solution of racemic acid, into which traces of the mould-fimgus Penicillium gUmcum have been introduced, becomes tevo-rotatory, the fimgus propagating itself with decomposition of the dextro-rotatory acid.
§ 196] RESOLUTION OF RACEMIC SUBSTANCES, 249
The second and third methods of resolution are alike in prin* ciple. During their growth the bacteria and fungi develop sub- stances called enzymes (222), which decompose compounds by means hitherto unexplained. These enzymes are optically active; hence, a difference in their action on the optical isomerides, analo- gous to that described in the previous paragraph, is to be expected.
When a racemic substance is liquid or gaseous, it consists only of a mixture of the two enantiomorphic isomerides: an ex- ample of this is afforded by racemic acid in solution and in the form of esters (192). If the substance is crystalline, there are three possibilities.
First, the individual crystals may be dextro-rotatory or l»vo- rotatory, so that the two modifications can be mechanically separated. This is expressed by the statement that the racemic substance is a conglomerate of the isomerides.
Second, it may be a true compound of the dextro-modification and laevo-modification, a racemic compound or racemoid, its forma- tion being comparable to that of a double salt, when a solution containing two salts is allowed to crystallize imder certain conditions.
The third possibility is also analogous to the crystallization of Bait-solutions, whereby crystals are sometimes obtained containing both salts, but in proportions varying in different crystals. It sometimes happens that the salts crystallize together in all propor- tions, but usually these can vary only between certain limits. This simultaneous crystallization of salts yields the so-called mixed crys" tola; and optical isomerides produce pseitdoracemic mixed crystals.
The variety of crystals obtained from a given solution or fused mass of a racemic substance — a conglomerate, a racemic compound, or pseudoracemic mixed crystals — depends upon the temperature of crystallization, and upon other conditions. An example of this is afforded by sodium ammonium racemate. When concen- trated above 28° the racemate crystallizes from the solution of this salt; below this temperature a mixture of the individual tartrates — the conglomerate -is obtained.
Bakhuis Roozeboom has indicated a method of distinguishing between these three classes of compounds. For a conglomerate, this is simple. A saturated solution is made: it must be optically inactive, and saturated alike for the dextro-rotatory and for the tevo-rotatory body. If now the solid dextro-compound or l»vo-
250 ORGANIC CHEMISTRY. I§ 196
compound is added, and the mixture agitated, nothing more will dissolve, the liquid being already saturated with respect to the two isomerides: the amount of dissolved substance is still the same, and the solution remains optically inactive. On the other hand, if a racemic compound was present, althou^ the solution was saturated in the first instance with regard to this, it is unsaturated with respect to the two optically active modifications: addition of the solid dextro-rotatory or laevo-rotatory substance will cause a change in the total quantity of solid dissolved, and the liquid will become optically active. Less simple methods are sometimes necessary to detect psetidoracemic mixed crystals.
Optically Active Compounds with Asymmetric Atoms Oflier
Than Carbon.
196. The methods of separation outlined in 195 have also made possible the resolution into optical isomerides of other compounds of asymmetric structure, a result in accord with Pasteur's principle of the " Dissymm^trie mol^culaire " (47). The presence of an n-valent atom of any kind in union with n dissimilar substituents always necessitates a structure capable of existence in two configurations, which are mirror-images of each other, but cannot be superimposed.
By employing the highly rotatory d-bromocamphorsulphonic acid and its Isevo-isomeride it is possible to resolve into their optical components basic substances of the types indicated. Substitution of acetone or some other solvent for water in the fractional crystal- lization of the salts prevents hydrolytic dissociation. Optically active compounds with as3rmmetric nitrogen, sulphur, selenium, tin, phosphorus, and silicon atoms are known, examples being C7H7V •CgHs C2H5V •CH3
>N< , >s<r
;h2.cooh
CaHiK yCHa C2H8V ^CHa CaHsv y^CsHs
Cl/XJO.CeHs* CsH/ "^S * (y XJHs
C2H5 C2H6
HOaS .C6H4 .CH2 .Si— O— Si .CH2 •CoH* .SOaH.
JsHt C3H7
I.
§196]
OPTICALLY ACTIVE COMPOUNDS.
251
Although the tetrahedron-grouping is assigned to compounds with a quadrivalent, asymmetric atom such as carbon, there is no general agreement as to the position and the direction of the Unkings of the quinquivalent, asynunetric nitrogen atom.
As a general rule, an asymmetric molecular structure induces optical activity, and the fine researches of Webneb on asjrmmetric metallic atoms have furnished fresh evidence in support of this statement. In the complex derivatives of cobalt, chromium, iron, and other metals, Webneb assumes ("Inorganic Chemistry," 318) the presence of six atoms or groups in direct union with the metallic atom, these groups being supposed to be situated at the angles of a regular octahedron with the me- tallic atom at its centre. Two groupings are pos- sible for compoimds of
Fig. 65.
the tjrpe Me*g^, as indi- cated in Figs. 63 and 64, resulting either from "Axial-substitution " (Fig. 63), or from "Edge- substitution " (Fig. 64). The possibility of the existence of two stereo- isomerides is made evi- dent, and many examples of this type of isomerism are known. The possi- bility of the existence in two stereoisomeric forms of compoimds
Me^^ is also clear.
As a basis for determining wh^^her a compound MeAsB^ has the configuration represented in Fig. 63 or that in Fig. 64, Werner has made the very plausible assumption that the union of a bivalent
* Me represents a metallic atom.
Fig. 66.
Figs. 63, 64, 65, and 66.— Wernbb's Theoht OF Stebeoisomerism.
252 ORGANIC CHEMISTRY. [§ 197
groupi such as ethylenediaiuine, carbon dioxide, or oxalic acid, is only possible through edge-substitution. In accordance with this view, exchange of the carbon dioxide or other bivalent group for two univalent groups must produce compounds also with the configura- tion of Fig. 64.
Since both stereoisomerides have a plane of symmetry, optical activity is impossible for compounds MeAsBi with univalent groups A and B. An octahedral arrangement of a bivalent group and two univalent groups, or three bivalent groups, around the metallic atom makes possible the existence of two non-superimposable forms without a plane of symmetry (Figs. 65 and 66), and some com- pounds of this t3rpe have been resolved into their optical antipodes. They are often characterized by a very high specific rotatory power, that of a complex iron derivative of the tri-tc-di-pyridyl-ferrous series being about 500^.
IV. POLYBASIC HYDROZY-ACmS.
197. Of these acids it will be suflScient to describe the tribasic citric add, CeHsOz, which is widely distributed in the vegetable kingdom, and is also found in cows' milk. It is prepared from the juice of unripe lemons, which contains 6-7 per cent. Tricalcium citrate dissolves readily in cold water, but very slightly in boiling water: this property is employed in the separation of the acid from lemon-juice, it being obtained in the free state by addition of sul- phuric acid to the citrate. Another technical method for its prepa- ration depends upon the fact that certain mould-fungi {Citromyces pfefferianus and C. glaber) produce considerable quantities of citric acid from dextrose or sucrose.
Citric acid can be obtained synthetically by a method prov- ing its constitution. On oxidation, symmetrical dichlorohydrin, CH2C1-CHOH.CH2C1 (158), is transformed into symmetrical di- chloroacetone, CH2CI • CO • CH2CI. The cyanohydrin-s)mthesis con-
X)H verts this into CH2C1«C^CH2C1, and hydrolysis yields the hydroxy-
\CN
yOH acid, CH2C1-Ce-CH2C1. On treatment of this compound with
\COOH potaasium cyanide, a dicyanide is formed, which can be hydro- lyzed to citric acid:
( Wn CITRIC ACID. 253
CHa-CN CH2-C00H • .OH ^A^OH V^COOH~'V COOH • CH2-CN CHa-COOH
The alcoholic character of citric acid is indicated by the forma- tion of an acetyl-compound from triethyi citrate and acetyl chloride.
Citric acid forms well-defined crystals containing one molecule of water of crystallization, and is readily soluble in water and alco- hol. It loses its water of crystallization at 130^, and melts at 153^. It is employed in the manufacture of lemonade, and in calico- printing.
DIALDEHYDES AND DIKETONES: HALOGEN-SUBSnTUTED
ALDEHYDES AND KETONES.
Dialdehydes.
198. The simplest member of the series of dialdehydes, glyoxal,
is a combination of two aldehydo-groups, q^C — C^q. It is best
prepared by carefully floating a layer of water on the surface of strong nitric acid contained in a tall glass cylinder, and pouring ethyl alcohol on the surface of the water, care being taken that the layers do not mix. The nitric acid and alcohol diffuse into the water; and the alcohol is slowly oxidized to glyoxal, glycollic acid, oxalic acid, and other substances.
Thus prepared, gl3roxal is a colourless, amorphous substance: when moist, it dissolves readily in water, but very slowly after complete drying in vacuo at 1 10*^-120®. It is a polymeride of un- known molecular weight, although its aqueous solution reacts as though it contained only simple molecules. Distillation of this polymeride with phosphoric anhydride evolves an emerald-coloured gas, condensable by cooling to beautiful yellow cr3rstals, which at a lower temperature become colourless. They melt at 15®, and the yellow liquid thus obtained boils at 51®. It is unimolecular glyoxal, and can only exist as such for a short time: traces of water readily polymerize it. The unimolecular form is the simplest type of coloured compound, containing only carbon, hydrogen, and oxygen.
The combination of glyoxal with two molecules of sodium hydrogen sulphite, and the formation of a dioxime, prove it to be a double aldehyde. It also has the other properties pecul- iar to aldehydes, such as the reduction of an ammoniacal silver solution with formation of a mirror. On oxidation, it takes up two atoms of oxygen, 3rielding oxalic acid, of which it is the dial-
264
i 1931 DIKET0NE8. 255
debyde. Treatment with caustic potash converts glyoxal mto gly collie acid, one aldehydo-group being reduced and the other oxidized. This reaction may be explained by the assumption that an addition-product with water is formed; in accordance with the scheme
C^.cJ + HaO - CH2OH.COOH.
^ ^ GlyooUie add
H H
Succindialdehyde, qC«CH2*CH2-Cq, has been prepared by
Harries by the action of ozone upon a chloroform solution of diallyl, CH2:CH.CH2— CH2-CH:CH2. An addition-product— a diozoiiide — ^is formed,
CH2 • CH • CH2 — CH2 • CH • CH29
\/ \/
Oz Qs
each double linking uniting with one molecule of ozene. This diozonide is a syrup-like, explosive liquid. When heated slowly with water, it decomposes, forming succindialdehyde.
Harries has prepared several analogous ozonides, each double linking always taking up O3. Water decomposes these ozonides in accordance with the scheme
>C— C<+H20 -= >CO+OC<+H202.
O3
The formation cf these ozonides and their decomposition by water afford an excellent method for determining the position in the molecule of double linkings. Its application to the case of oleic acid has confirmed the formula indicated in 137.
Diketones.
199. Thediketones contain two carbonyl-groups: their proper- ties and the methods employed in their preparation depend upon the relative position of these groups. l:2-Diketones with the
12 12 3
group —CO • CO— are known : 1 : 3-diketones with —CO • CH2 • CO— :
12 3 4
l:4-diketones with — CO-CH2*CH2'CO— : and so on.
1:2-Diketanes cannot be obtained by the elimination of chlorine
256 ORGANIC CHEMISTRY. [{ 200
from the acid chlorides by the action of a metal, in accordance with the scheme
R.COCl+Naa+ClOC.R.
Their preparation is effected by the action of amyl nitrite and a small proportion of hydrochloric acid on a ketone, one of the CH^ groups being converted into C=NOH:
R.CO.C
o
•R' R.CO-C.R'
NOH NOH
These compomids are called moniirosoketonea. When boiled with dilute sulphuric acid, the oxime-group is eliminated as hydroxyl- amine, with formation of the diketone. The ketoaldehydea are both
XT
ketones and aldehydes, and contain the group — CO-C^ : they,
too, can be obtained by this method.
Diacetylj CHa-CO-CO-CHa, can be prepared from methylethyl- ketone in the manner indicated. It is a yellow liquid of pungent, sweetish odour, and is soluble in water: its vapour has the same colour as chlorine. Diacetyl boils at 88°, and has a specific gravity of 0-973 at 20*^. Its behaviour points to the presence of two car- bony 1-groups in the molecule: thus, it adds on 2HCN, yields a mono-oxime and a dioxime, and so on. The adjacency of the two carbonyl-groups in diacetyl is proved by its quantitative con- version into acetic acid under the influence of hydrogen peroxide:
CH3.CO— + OH
CO.CH3 _^2CH8-CO.OH.
OH
200. 1 iS'Dikeiones can be prepared by a condensation-method of general application discovered by Claisen and Wisliceniis. Sodium ethoxide is the condensing agent. An addition-product is formed by the interaction of this substance and an ester:
''•<c
O Na ry^^^
2H5 OC2H6 \OC2H5
The addition-product is then brought into contact with a ketone R'-CO'CHs, two molecules of alcohol being eliminated with forma- tion of a condensation-product:
5 20tg DIKBTONES. 257
,ONa
^ ONa
R.(^
OC2H5 H
^5*+5CH.CO.R'-R.C< +2C2H6OH.
CH.CO.R'
On treatment of this compound witk a dilute acid, the sodium atom is replaced by hydrogen. This might produce a compound with a hydroxyl-group attached to a doubly-linked carbon atom; but usually compounds of this type are unstable, the group OH
— C=CH — changing to — CX) — CH2 — . The principle applies in
the present instance, ^ yielding a l:3-diketone,
R«C=CH»CO«R
R.C0-€H2-C0.R'.
Claisei^ has foimd that sodamide, Na«NH2, can be substituted advantageously for sodium ethoxide in the condensation of ketones with esters. Frequently, it not only facilitates the reaction, but increases the yield.
Another method for the preparation of 1 : S-diketones is the action of acid chlorides on the sodium compounds of acetylene homologues:
CH,.{CH,),.C^Cpa+alOC-CH, — CH,-(CH,),.C^C.CO-CH,.
Sodio-n-amylaoetylene Acetyl chloride
By treating this ketone with concentrated sulphuric acid, water is added, and the desired diketone obtained:
CH,.(CH,)4.C=C-C0-CH,-CH,.(CH,),.C0.CH,.C0-CH,. + O H,
These^diketones have a weak acidic character, their dissocia- tion-constants being very small. Among others, that of acetyU acetone, CH3*CO-CH2*CO*CH3, has been determined. They contain two H-atoms replaceable by metals. These atoms must belong to the methylene-group between two negative carbonyl- groups, since diketones of the formula R«C0«(Alk.*)2-C0*R can- not yield metallic derivatives.
Acetylacetone is obtained by the condensation of ethyl acetate and acetone. It is a colourless liquid of agreeable odour, boils at 137^, and has a specific gravity of 0*979 at 15^. When boiled with water,
* Alk, s methyl or its homologues.
268 ORGANIC CHEMISTRY. [| 201
it decomposes into acetone and acetic acid, a reaction affording another example of the instability of compounds containing a car- bon atom loaded with negative groups.
Among the salts of acetylacetone is the copper salt, (C^fi.^^}x, which is sparingly soluble in water; and the volatile aluminium salt, (G|H702)sAl. By a determination of the vapour-density of this compound, Combes has shown that the aluminium atom is tervalent.
These metallic compounds have properties differing from those of ordinary salts. Unlike true salts, they are soluble in benzene, chloroform, and other organic solvents. Their aqueous solutions are almost non-conductors of electricity. They either do not answer to the ordinary tests for the metals, or else react very slowly. The ferric and aluminium salts, in which both base and acid are very weak, do not undergo hydrolytic dissociation, but diffuse unchanged through parchment-paper. In these respects they resemble mercuric cyanide (''Inorganic Chemistry/' 274), which is practically not ionized in aqueous solution, and therefore lacks all the properties characteristic of ordinary salts.
A type of the I'A-diketones is acetanylacetone,
CH3 • CO • CH2 • CH2 • CO • CHs,
the preparation of which is described in 233, 4. It is a colour- less liquid of agreeable odour; it boils at 193**, and has a specific gravity of 0-970 at 21°. Acetonylacetone and other l:4-dike- tones yield cyclic compounds, which are dealt with in 392-396.
Halogen-substituted Aldehydes.
M 201. Chloral or trichloroacetaldehyde, CCl3*C^ , is of great
therapeutic importance, since with one molecule of water it forms a crystalline compound known as chloral hydrate, and employed as a soporific. Chloral is technically prepared by saturating ethyl alcohol with chlorine. The alcohol must be as free from water as possible, and the chlorine carefully dried. At first the reaction-mixture is artificially cooled, but after a few days the process becomes less energetic, and the temperature is slowly raised to Q(f, and finally to 100^
The reaction may be explained by assuming that the alcohol is first converted into aldehyde, which is then transformed into acetal, dichloroacetal, and trichloroacetal: the last compound is
201]
CHLORAL.
259
converted, by the hydrochloric acid produced, into chloral alcohol - ate, CXI!l3-CH<QTT **. Dichloroacetal and other intermediate products of this reaction have been isolated:
CHs-CHaOH-hClz = CH3-CH< ^jj + HCl - CH3-Cq+2HC1;
Alcohol
CH3.cS + ^
OC2H5 OC2H5
CHa.CH<^«^J
Aoetal
Aldehyde
OC H CH8-CH<^n^^ Tj H-H20,'
CHCl2.CH<^2|»-H.
Diehloroaoetal
OC H
TciehloroaoeU^
CCla-CH<
OC2H5
Chloral alooholate
The final product of chlorination is a cr3rstalline mixture of chloral
p.Icoholate, chloral hydrate, and trichloroacetal, from which chloral
is obtained by treatment with concentrated sulphuric acid. It is
an oily liquid of penetrating odour, boiling at 97^, and having a
specific gravity of 1-512 at 20°. When treated with water, it is
converted with evolution of heat into the well-crystallized chloral
hydrate, m. p. 57°. To this compound is assigned the formula
OH CCl3*CH<QTT, as it does not show all the aldehyde-reactions.
For example, it does not restore the red tint of a solution of magenta (374) which has been decolorized with sulphurous acid (107, 3). Chloral hydrate is, therefore, one of the few compounds containing two OH-groups in union with a single C-atom (127, 149, 230, 234).
Otherwise, chloral behaves as an aldehyde: for instance, it reduces an ammoniacal silver solution with formation of a mirror, combines with sodium hydrogen sulphite, and is oxidized by nitric acid to trichloroacetic acid. Solutions of the alkalis decompose it at ordinary temperatures with formation of chloroform and formic acid :
ca3*
+ H
H
^O « CClsH+HCr HO ^
^0
OH
260 ORGANIC CHEMISTRY. [§ 201
On account of its purity, chloroform prepared in this manner is preferred for anaesthetization.
In dilute solutions of about centinormal strength, and at low
temperatiue, this reaction has a measurable velocity. Experiment
has proved it to be unimolecular, and not bimolecular as indicated
by the equation. This phenomenon is explicable by assuming
preliminary combination of the base and chloral hydrate to form a
OH salt of the tjrpe CCU*CH<Q^» subsequently decomposed into
chloroform and formate. The electric conductivity of a mixture of solutions of chloral hydrate and a base also indicates a union of the ^molecules.
The formation of chloroform from chloral by the action of alkaline liquids originally suggested the use of chloral as a soporific: it was expected that the alkaline constituents of the blood woidd decompose it with the formation of chloroform in the body itself. LiEBREiCH showed that chloral has in fact a soporific action, but more recent investigation has proved this to be independent of the formation of chloroform, since the chloral is eliminated from the system as a complicated derivative, yrochloralic acid.
ALDEHTDO-ALCOHOLS AND KETO-ALCOHOLS OR
CARBOHYDRATES.
202. Aldehydo-alcohols and keto-alcohols are natural products, and are very widely distributed. They are called carbohydrates, sitgars, or saccfuirides. They contain one carbonyl-group and several hydroxyl-groups. One of the hydroxyl-groups rmist be linked directly to a carbon atom in union with the carbonyl-group ^ so that the characteristic group of these compounds is — CHOH — CO — .
The sugars are classified as polyoses and monoses. On hydrolysis, the polyoses yield monoses, which have lower molecular weights than their parent substances, but possess all the properties charac- teristic of the sugars. The monoses do not admit of further hydrolysis to simpler sugars. They will be considered first.
iromendature and General Properties of the Monoses and their
Derivatives.
When the monoses are aldehydes they are called aldoses, and when ketones,* ketoses. The number of carbon atoms in the molecule is indicated by their names: thus, pentose , hexose, heptosCy etc. To distinguish between aldoses and ketoses the prefixes "aldo-" and "keto-" respectively are used; as aldohexose, keto- hexosCj and so on.
When the polyoses may be regarded as derived from two monose
molecules by the elimination of one molecule of water, they are
called dioses; thus, hexodioses when they are formed from two
molecules of hexose. The polyoses derived from three monose
molecules by the elimination of two molecules of water are called
triosea; as hexotriose, etc.
261
262 ORGANIC CHEMISTRY. [§203
Like other aldehydes, the aldoses are converted by oxidation into monobasic acids containing the same number of cairbon atoms, the pentoses yielding the monobasic perUonic acids, the hexoses the hexonic acids, etc. The oxidation can be carried further; for the
/H
general formula of an aldose is CH20H-(CH0H)n-C< (204),
and the group — CH2OH can be oxidized to carboxyl, yielding a dibasic acid containing the same number of carbon atoms as the aldose from which it is derived. On oxidation, the ketoses jrield acids containing a smaller number of carbon atoms.
On reduction, the aldoses and ketoses take up two hydrogen atoms, with formation of the corresponding alcohols: thus, hexose yields a hexahydric alcohol, and pentose a perUahydric alcohol (204 and 207).
203. Four reactions are known which are characteristic of all monoses : two of these they possess in common with the aldehydes (107).
1. They reduce an ammoniacal silver solution on warming, forming a metallic mirror.
2. When warmed with alkalis, they give a yellow, and then a brown, coloration, and ultimately resinify.
3. When an alkaline copper solution (Feeling or Ost, igi) is heated with a solution of a monose, reduction takes place, with formation of yellow-red suboxide of copper.
4. When a monose is heated with excess of phenylhydrazine, C6H6«NH«NH2, in dilute sulphurous-acid solution, a yellow com- pound, crystallizing in fine needles, is formed: substances of this type are insoluble in water, and are called osazones. Their for- mation may be explained as follows.
It is mentioned in 202 that the sugars are characterized by containing the group — CHOH — CO — . The action of phenyl- hydrazine on a carbonyl-group has already been explained (103) ; water is eliminated, and a hydrazone formed:
CfOTH^N.NHCeHfi =» CtN-NHCeHfi+HzO. 1^ I
.\ second molecule of phenylhydrazine then reacts with the group — CHOH — , from which two hydrogen atoms are eliminated, the
1 204] MONOSES. 263
molecule of phenylhydrazine being decompoeed into ammonia and aniline:
FfaeoylhydruiDe AnOina
+ H H
The elimination of two hydrogen atoms from the group — CHOH — converts it into a carbonyl-group, — CO — , with which a third molecule of phenylhydrazine reacts, forming a hydrazone, so that
CHOH C=N.NHC6H5
the group I is converted into | . This group
00 C=N.NHCftH5
1 I
is characteristic of the osazones. ,
The osazones dissolve in water with difficulty. This property makes them of service in the separation of the monoses, which are very soluble in water, and crystallize with great difficulty, especially in presence of salts, and hence often cannot be purified by crystal- lization. By means of the sparingly soluble osazones, however, they can be separated: the osazones are readily obtained in the pure state by crystallization from a dilute solution of pyridine (387). Moreover, the identity of the monose can be established by a deter- mination of the melting-point of the osazone obtained from it.
Constitution of the Honoses.
204. It is shown later that the constitution of all the monoses follows from that of the aldohexoses, the structure of which can be arrived at as follows:
1. The aldohexoses have the molecular formula C6H12O6.
2. The aldohexoses are aldehydes, and, therefore, contain a carbonyl-group in the molecule. This follows from the facts that they show the reactions characteristic of aldehydes; that they are converted by oxidation into acids containing the same number of C-atoms, and by reduction iato an alcohol; and that they form addition-products with hydrocyanic acid.
3. All known hexoses contain a normal chain of six carbon atoms, since they can be reduced to a hexahydric alcohol, which,
264 ORGANIC CHEMISTRY. [J 205
on further reduction at a high temperature with hydriodic acid, yields n-flecondary hexyl iodide, CH3-CH2'CHI«CH2*CH2-CH3.
The constitution of this iodide is inferred from the fact that it can ' be converted into an alcohol, which on oxidation yields
CH3.CH3.CO-CH3.CH3.CH,;
for on further oxidation this is converted into n-butyric acid and acetic acid.
4. The hexoses have five hydroxyl-groups, since, when heated with acetic anhydride and a small quantity of sodium acetate or zinc chloride, they yield penta-acetyl-derivatives.
These facts indicate the existence in an aldohexose of
a normal carbon chain, C — C — C — C — C — C;
an aldehydo-group, C — C — C — C — C — C^ ; and
five hydroxyl-groups, I I I I I ^
6H0H0H0H0H
There are six other hydrogen atoms in the formula G6H12O6, and these will fit in with the last scheme, if the C-atoms of the chain are singly linked to each other: the formula of an aldohexose will then be
i
H OH OH OH OH
205. In these formulse a somewhat arbitrary assumption has been made as to the distribution of the hydroxyl-groups and hydro- gen atoms relative to the carbon atoms; it is, however, in accord- ance with the principle (149) that a carbon atom cannot u^ally have linked to it more than one hydroxyl-group. A more con- vincing proof of the fact that the monoses do not contain two hydroxyl-groups attached to the same carbon atom, is afforded by the following considerations.
When a hexose, C6H12O6, is reduced to a hexahydric alcohol, C6H14O6, only two hydrogen atoms are added, and this addition
S 205] M0N0SE8. 265
must take place at the doubly-linked oxygen atom, since the carbon chain remains imbroken. If the hexose contains two hydroxy!- groups attached to one carbon atom, so must also the hexahydric alcohol derived from it. Compounds containing a Oatom linked to two OH-groups readily lose water, with formation of aldehydes or ketones: they also possess most of the properties characteristic of these substances (201). The hexahydric alcohols, however, have an exclusively alcoholic character, and do not exhibit any of the reactions of aldehydes and ketones. It follows that the hexahydric alcohols, and hence the hexoses, cannot contain two hydroxyl-groups linked to a single carbon atom.
The possibility of the attachment of three hydroxyl-groups to one carbon atom is also excluded, since, when the production of a compound with such a grouping might be expected, water is always eliminated, with formation of an acid (79) :
The monoses have none of the properties which distinguish acids: their aqueous solutions do not conduct the electric current; whereas the dissociation-constant for an acid containing so many OH- groups should be considerably higher than for a saturated fatty acid, such as acetic acid (180).
With calcium and strontium hydroxides, and other bases, the carbohydrates form compounds called mcchanUes, which are, there- fore, to be looked upon as aikoxides (50).
It follows from these considerations that the constitution of the aldohexoses cannot be other than that given above, and, since the same method of proof is applicable to each member, they must all have the same constitutional formula, and are therefore stereoiso- mevides. This is due to the presence in the molecule of asymmetric carbon atoms: an aldohexose has four such atoms, indicated by aaterisks in the formula
CH3OH.CHOH-CHOH.CHOH.SHOH.CQ.
266 ORGANIC CHEMISTRY. [{ 206
Methods of Formation of the Monoses.
206. 1. The monoses are produced from the polyoses by hydrolysis, the transformation being attended by the taking up of the elements of water. They are also formed by the hydrolysis of glucosides. These substances are natural products, decomposed by enzymes or by dilute acids into a carbohydrate, and one or more other compounds often of very divergent character. An example is amygdalin (256).
2. The monoses are also derived from the corresponding alcohols by the action of oxidizing agents, such as nitric acid. Arabitol, C6H12O6, yields arabinose, CsHioOs; xylitol yields xylose; mannitol yields mannose; etc.
When glycerol is carefully oxidized with hydrogen peroxide in presence of ferrous salts, or with bromine and sodium carbonate, a syrup-like liquid called glycerose is obtained, with the four reac- tions typical of monoses (203). Prepared by the first method, it is essentially glyceraldehyde (I.); by the second method, only di- hydroxyacetone (II.) is produced. Both compounds yield the same osazone, glycerosazone (III.), a substance crystallizing in yellow leaflets, melting at 131^:
CH,OH CH,OH CH,OH
CHOH CO C=N • NH • C.H,
*H CHiOH C=N-NH«C,H» ^O H
I. II. III.
In accordance with the nomenclature already indicated, glycerose is a triose.
When sorbose-bacteria are cultivated in a solution of glycerol, the final product obtained by the action of the atmospheric oxygen is dihydroxyacetone. These bacteria can also oxidize other poly- hydric alcohols to ketoses.
3. Another method of formation depends on replacement by hydroxyl of the bromine in bromo-derivatives of aldehydes, effected by the action of cold baryta-water.
In this manner the simplest member of the sugars, glycolUm or
-a
glycoUdldehyde, CHaOH^C , is obtained from monobromoaldehyde,
( 206] MONOSES, 267 g
CHsBr*C : it shows all the reactions of themonoses. Glycollose
crystallizes well, and melts with decomposition at about 97^. It polymerizes readily, and is volatile with steam.
The addition of bromine to acraldehyde (141) yields
CHiBr«CHBr*C . which is converted by the action of baryta- water into glyoeraldehyde.
4. Monoses are also derived from formaldehyde by the action of lime-water (aldol-condensation). The crude condensation- product, called formose, is a sweet, syrup-like substance: it consists of a mixture of compounds of the formula C6H12O6. In this reaction, six molecules of formaldehyde undergo the aldol- condensation (106) :
•H ^ — H H ^ — ^H
HaCXT + HCO + HCO + HCO + HCO' + H(30- .H,C0H*CQg-CQjj-CQg-CQ2«CQ.
A hexose can also be obtained from glyoeraldehyde, two molecules of which yield, by the aldol-condensation, one molecule of the hexose. This hexose is called acrose^ on account of its relation to acraldehyde, from which glyoeraldehyde can be obtained by method 3. Acrose is a constituent of formose, and, like all compounds prepared by purely chemical synthesis, is optically inactive.
5. Monoses can also be transformed into other monoses with one carbon atom more or less in the molecule by the aid of step- by-step methods of building up or breaking down, as indicated in the subjoined examples. Monoses can form an addition- product with hydrocyanic acid. An aldohexose yields a cyano- bydrin which is converted on hydrolysis into a monobasic acid containing seven C-atoms,
7 j8 a
CH20H-CH0H-CH0H-CH0H-CH0H-CH0H-C00H. 1 2 3 4 5 6 7
268 ORGANIC CHEMISTRY. [| 207
The 7-hydroxyl-group reacts easily with the carboxyl- group, forming a lactone,
CH20H-CH0H-CH0H-CH-CH0H-CH0H-C0.
I i
In aqueous solution, these lactones can be reduced by sodium- amalgam to the corresponding aldehydes, the aldoses.
By repeated application of the cyanohydrin-synthesis, . and reduction of the lactone thus obtained, it has thus been possible to prepare nonoseSy with nine C-atoms, by conversion of an aldohexose into a heptonie acidy the lactone of which can then be reduced to a heptose. This compound can be converted into an octose, and the latter into a nonose, by the same process.
The step-by-step breaking down of monoses can be effected by other agencies, an example being the conversion of pentoses into tetroses. The calcium salts of the pentonic acids, obtained from these pentoses by oxidation, can be further oxidized by hydrogen peroxide in presence of ferric acetate:
CH20H.(CHOH)3.COOH + 0 = CH20H.(CHOH)2-Cq
Pentonic acid Tetroee
+ CO2 + H2O.
Another process consists in the application of Hoogewebff and VAN Dorp's method (259) with sodium hypochlorite to the amides formed from monobasic acids, such as gluconic acid:
NaClO CHaOH . (CH0H)4 • CONH, > CH2OH • (CHOH)* -NCO
Gluconamide
I
NaOH TT
> CH.OH • (CHOH), 'Cq + NaNOO.
ArabinoM
L MONOSES.
Pentoses.
207. A number of different pentoses have been identified, among them arabinose and xylose, both of which are present in many plants as polyoses, called pentosans.
Arabinose can be prepared by boiling gum-arabic or cherry-gum with dilute acids, but the best method is to hydrolyze sliced sugar-
§ 207] MONOSES. 269
beet after extraction of the sugar, the resulting mixture of galac- tose and arabinose being freed from galactose by fermentation. A yield of 8 to 12 per cent, can be produced from the husks of cotton-seed.
Xylose, or wood-sugar, can be obtained similarly from bran, wood, straw, and other substances, especially the shells of apricot- stones. Arabinose aud xylose can be prepared from any plant- cells which have been converted into wood, and which show the reaction of lignin (228). The racemic modification of arabin- ose is present in the urine of patients suffering from the disease known as pentosuria.
Arabinose forms well-defined crystals, melts at 160®, and has a sweet taste. Its osazone melts at 157®. Xylose also crystallizes well, and yields an osazone which melts at 160®.
Arabinose and xylose are aldoses, and have the same formula,
CH2OH.CHOH-CHOH.CHOH.CQ.
This constitution is proved by their conversion, on gentle oxidation with bromine-water, into arabonic add and xyUmic add respectively, both of which have the formula CHgOH. (CH0H)3.C00H, and are therefore stereoisomeric. On stronger oxidation, both arabinose and xylose yield trihydroxygluiaric add, C00H«(CH0H)3.C00H, the constitution of which follows from its reduction to glutaric acid. The acid obtained from arabinose is optically active, and that from xylose is inactive, so that they, too, are stereoisomerides. On reduction, these two pentoses yield respectively arabUol and xylitol, which are stereoisomeric pentahydric alcohols. Arabinose and xylose can be converted into hexoses by the cyanohydrin- synthesis, a proof that neither contains a C-atom in imion with more than one OH-group (205), and that each has a normal carbon chain:
CH20H.(CHOH)3.C? -> CH20H.(CHOH)3.CH<?^->
Pentooe ^ ^^
-* CH2OH . (CH0H)3 . CHOH . COOH.
Hexonio acid
This hexonic acid yields a lactone which, on reduction, gives the hexose. Arabinose and xylose contain three asynmietric C-atoms, and are optically active.
Apiose is considered in 213.
270 ORGANIC CHEMISTRY. [{
The pentoses cannot be fermented. They have one property in common, by which they may be recognized and distinguished from hexoses. When boiled with dilute sulphuric acid, or hydro- chloric acid of sp. gr. 1-06, the pentoses and their polyoses form a volatile compound, furfuraldehyde, C5H4O2 (393), which, on treatment with aniline and hydrochloric acid, yields an intense red dye.
The presence of the polyose of xylose can be detected in such a substance as straw by distillation with hydrochloric acid of sp. gr. 1*06. With aniline and hydrochloric acid, the distillate gives an intense red coloration, and with phcnylhydrazine yields a phenyl- hydrazone very sparingly soluble in water. Both these reactions indicate the presence of furfuraldehyde.
Hexoses.
20S. The hexoses are colourless compounds of sweet taste, which are diflScult to crystallize, and cannot be distilled without decomposition. They dissolve readily in water, with difficulty in absolute alcohol, and are insoluble in ether. Since all the aldo- hexoses are stereoisomerides (205), their oxidation-products, the monobasic and dibasic acids, are also stereoisomerides.
1. Dextrose {d-gliLcose or grape-sugar) is present in many plants, notably in the juice of grapes, and in other sweet fruits: it is found in the urine of diabetic patients, and in small quantities in normal urine. It can be obtained from many polyoses: for example, cane-sugar is converted by hydrolysis — inversion (216) — into a mixture of dextrose and laevulose (209), called invert-sugar. The technical preparation of dextrose from starch, by boiling with dilute acids, is Ukewise a case of hydrolysis.
Dextrose crystallizes from water, or alcohol, with some diffi- culty; the crystals obtained from methyl alcohol contain no water of crystallization, and melt at 146^. It is mentioned in 43 that dextrose can be readily fermented, producing chiefly alcohol and carbon dioxide. Natural dextrose is dextro-rotatory: a laevo- rotatory and an optically inactive modification have been arti- ficially prepared. The dextro-rotatory, laevo-rotatory, and optically inactive isomerides are respectively distinguished by the prefixes d {dexter), I {Icsvus), and i {inactive); thus, (f-glucose, Z-giucose, i-glucose.
n
§ 2081 MONOSES. 271
By convention, all other monoses derived from a (f-hexose, {-hexose, or i-hexose are also distinguished by the letters dy Z, or i, even when they possess a rotatory power opposite in sign to that indicated by these letters. Thus, isevuiose or ordinary fructose, which can be obtained from dextrose or (f-glucose, and is kevo- rotatory, is also called d-fructose on account of its genetic relation to c2-glucose. The same method of classification is adopted for the hexahydric alcohols, the hexonic acids, and in general for all deriva- tives of the hexoses.
Dextrose is an aldose, as is proved by its oxidation to a hexonic acid, d-glucanic acid, CH2OH. (CH0H)4*C(X)H: further oxidation produces the dibasic (i-saccharic acid,
C00H.(CH0H)4-C00H.
Saccharic acid forms a characteristic potassium hydrogen salt of slight solubility, which serves as a test for dextrose. The substance suspected of containing dextrose is oxidized with nitric acid: sac- charic acid is produced from this hexose, if present, and can be pre- cipitated as potassium hydrogen salt by addition of a concentrated solution of potassiiun acetate.
On reduction, dextrose yields a hexahydric alcohol, d-sorbitol: it also gives an osazone, d-gliicosazone, which is soluble with diffi- culty in water, and crystallizes in yellow needles wl.ich melt at 205^
Solutions of dextrose and many other sugars furnish examples of a phenomenon called mittcarotatian. When freshly dissolved, such substances have a rotatory power other than that possessed by them after the lapse of a comparatively short interval of time. Thus, an aqueous solution of dextrose at first produces a rotation [a]jy = 110^ : after some hours it produces a constant rotation [a]o«52'5°. The attainment of a constant rotatory power is much hastened by boiling the solution, and is effected at once by addition of a small quantity of caustic potash or ammonia.
The explanation of this phenomenon must be sought in the par- tial conversion of the dextrose or other sugar into another modifica- tion of different rotatory power. When the rotation has become constant, there is equilibrium between the two modifications.
Tanret has prepared three different crystalline modifications of dextrose, denoted by a, fit and c Ordinary dextrose is the a-modi- fication: it crystallizes with one molecule of water. When dissolved
272 ORGANIC CHEMISTRY. [{ 208
quickly in cold water, the solution produces a rotation [a\j^ « 1 IQP, When the solid a-form is heated for some day^ at 105^, it is changed to the ^-form. In aqueous solution the ^-modification at first only rotates the plane through [a]r> — 19*^: when allowed to remain for some time, or boiled, or mixed with a trace of sQkali, the rotation rises to [«]!,=» 52 -5°. When dissolved in water, the e-modification at once causes a rotation [a]o~52-5^, indicating that it is not an independent form, but a mixture in equilibrium of the a-modifica- tion and ^-modification.
Tanret has proved by experiment that this surmise is correct. A very concentrated solution of the (-modification was made, and crystallized at 0^. When a solution of the crystals thus obtained was prepared at a low temperature, its rotation was diminished by addition of a small quantity of ammonia, proving that the crystals belonged to the CK-modification. If the e-form is a mixture of the a-modification and the /9-modification, the latter must have remained in solution in the mother-liquor, and addition of alkali should increase the rotation of this residual solution. Experiment has proved that alkali has this effect.
The results of these researches, in conjunction with other facts, have led to the adoption of a somewhat modified type of constitu- tional formula for the monoses (317).
With a small quantity of water, dextrose yields a colourless syrup used in the preparation of liqueurs and of confectionery.
The mechanism of the formation of ethyl alcohol and carbon dioxide by the fermentation of dextrose is probably best explained by assuming alterations in the relative positions occupied by the hydroxyl- groups and hydrogen atoms. It may be supposed that elimination of water in the usual manner first takes place, being followed by the migration of one hydrogen atom. These changes involve the transformation of the group — CHOH-CHOH — by abstraction of water into — CH=C(OH) — , which then changes to — CH,-CO — . The result is the same as that produced by an exchange of position between hydrogen and hydroxy I, followed by elimination of water :
-<;H0H-CH0H > — CHj-C(0H)2 > — CH,.CO— .
Analogous phenomena are known, among them the formation of acraldehyde from glycerol (141), of pyroracemic acid from tartaric acid (231), and of oxalacetic acid, COOH-CO-CHa-COOH, from tartaric acid.
Methylglyoxal, which was isolated as osazone, is an inter-
§ 2091 MONOSBS. 273
mediate decomposition-product in the interaction of dextrose and dilute alkalis, as indicated in the following scheme:
CHjOH .CHOH .CHOH -CHOH -CHOH -C
(Migration of H and OH)
-* CHa.C(0H),.C(0H),.CH,.CH0H.c5 -»
H OH ^
(Deeomposition with addition of IHaO)
-♦CHs.CO.Cq and CHaOH-CHOH.C^ — H3O "♦CHa-CO.CQ.
Methylglyoxal Methylglyoxal
Lactic acid has been identified as an intermediate product in alcoholic fermentation, and may be regarded as derived from methyiglyoxal in accordance with the scheme
CHs.C(OH),.Cq -^ CHa-CHOH.C^^,
Methyiglyoxal Lactic acid
resulting from a change of position between hydroxyl and hydrogen. The lactic acid then loses carbon dioxide, yielding ethyl alcohol :
CHa.CHOH.COjH - CHs-CHjOH+COj.
It is not improbable that two enzymes play a part in these reactions. One of them may occasion the interchange of position leading to the formation of lactic acid; the other may effect th« decomposition of the lactic acid into alcohol and carbon dioxide.
The converaon of dextrose into butyric acid by the butyric fermentation can also be explained by assuming the intermediate formation of lactic acid, and its subsequent transformation into formic acid and acetaldehyde. Condensation of acetaldehyde pro- duces aldol, which 3rield8 butyric acid by transposition of H and OH :
ch,.cho+ch,.cho=ch,.choh-ch,-cho-k:h,.ch,.ch,.cooh.
Aldol Butyric acid
209. LcBVtdose (d'fructose or fruit-sugar) is present along with dextrose in most sweet fruits. It is a constituent of invert-sugar (216), and of honey, which is chiefly a natural invert-sugar. When hydrolyzed, inulin, a polyose contained in dahlia-tubers, yields only Uevulose, just as starch yields dextrose. Laevulose crystal- lizes with difficulty, being readily soluble in water, although less so than dextrose. It is Iflevo-rotatory, and can be fermented.
274 ORGANIC CHEMISTRY. [§209
Lsevulose is a type of the ketoses, but few of which are known. Its formula, CH20H.(CHOH)3-CO-CH20H, is inferred from the followmg considerations. First, when oxidized with mercuric oxide in presence of baryta-water, it is converted into glycollic acid, CH20H'C(X)H, and trihydroxyglutaric acid,
COOH • (CH0H)3 . COOH.
Since oxidation takes place in the carbonyl-group, the production of these acids necessitates the adoption of this constitutional formula. Second, application of the cyanohydrin-synthesia to a compound of this constitution would yield a heptonic acid with
the formula
CH2OH. (CHOH)3-C(OH).CH20H.
COOH
That the heptonic acid obtained from lsevulose has this ccHisti- tution, is proved by heating it at a high temperature with hydriodic acid, whereby all the hydrpxyl-groups are replaced by hydrogen, and a heptylic acid is formed. This acid is identical with the sjmthetic methylr-n-btUylacetic acid (233, 2),
CH3 • (0112)3 • CH • CH3
i
OOH
The osazone of bevulose is identical with that of dextrose. A comparison of the formula of dextrose,
CH20H- (CH0H)3-CH0H.Cq,
with that of lsevulose, CH20H.(CHOH)3-CO.CH20H, shows that the two osazones can only be identical if the a-C-atom of dextrose, and the terminal C-atom of lsevulose, respectively unite, after for- mation of the hydrazone, with the second phenylhydrazine-residue: that is, when in both cases this reaction takes place at a C-atom directly linked to a carbonyl-group. For this reason, it is assumed that the formation of an osazone always results in the union of two phenylhydrazine-residues with neighbouring C-iatoms. d-GlnrCosazane, or d-fructostizone, has therefore the constitution
i 210] MONOSES. 275
CH2OH
(CH0H)3
C=N.NH.CBHe
C=N-NH-C8H5
•
H
Methylphenylhydrazine, Q jj >NNHi, yields osazones with
ketoses only, but converts aldoses into colourless hydrazones, readily separated from the intensely yellow osazones. This reagent is a valuable aid in the detection of ketoses.
When osazones are carefully warmed with hydrochloric acid, two molecules of phenylhydrazine are eliminated, with formation of com- pounds, osonesy containing two carbonyl-groups. For example, d-glucosazone yields d-glv/^osone,
CH.X)H.(CHOH),-CO.Cq.
The osones can be reduced by treatment with zinc-dust and acetic acid, and it is found that addition of hydrogen always takes place at the terminal Oatom. (2-GIucosone yields Isevulos^
CH/)H.(CHOH),.CO-CHX)H.
The reaction affords a means of converting aldoses into ketoses:
Aldose -+ Osazone -+ Osone — > Ketose.
Inversely, an aldose can be obtained from a ketose. On reduction, the latter yields a hexahydric alcohol, which is converted by oxida- tion into a monobasic hexonic acid. This substance loses water, yielding the corresponding lactone, which on reduction gives the aldose:
Ketose -♦ Hexahydric Alcohol -♦ Hexonic Acid — ♦ Lactone — ♦ Aldose.
210. d'Mannose is an aldose, and is present as a polyose inthe v^etable-ivory nut: it is also obtained by the careful oxidation of the hexahydric alcohol mannitolf found in several plants. d-Mannose, a hard, amorphous, hygroscopic substance, can be readily fermented, and is very soluble in water. It yields a characteristic hydrazone which melts at 195^-200°, and, unlike the hydraaones
276 ORGANIC CHEMISTRY. [j210
of the other monoses, dissolves with diffi^culty in water. On oxi- dation, d-mannose is first converted into the monobasic A-mannonic acid, CH2OH- (CH0H)4.C(X)H, and then into the dibasic d-wianno- saccharic acid, C00H.(CH0H)4.C00H. It yields dextrose by a method generally applicable to the conversion of aldoses into their stereoisomerides. For this purpose, it is first converted into d-mannonic acid. On boiling the solution of this substance in quinoline (400), it is partly transformed into the stereoisomeric d-gluconic acid, the lactone of which can be reduced to dextrose. Inversely, d-gluconic acid is partly changed into d-mannonic acid, by boiling its quinoline solution, so that dextrose can thus be con- verted into d-mannose.
Mannonic acid is one of the intermediate products in Emil Fischer's isynthesis of dextrose, pe converted glyceraldehyde into acrose (306, 4), and this into t-mannitol, by reduction with sodium- amalgam. On oxidation, t-mannitol yields first t-mannose, and then t-mannonic acid, which can be resolved, by means of its strychnine salt, into its optically active modifications. When the d-mannonic acid thus obtwned is heated with pyridine, it is converted into d-gluconic acid, the lactone of which, on reduction with sodium- amalgam, yields dextrose.
The stereoisDmorism of d-mannose and dextrose^ as well as of d-mannonic acid and d-gluconic acid, is occasioned only by different grouping round the a-C-atom, since the osazone of d-mannose is identical with that of dextrose. As this has the constitution
a H CH2OH.CHOH.CHOH.CHOH.C— C=N.NH.C6H6,
N.NH.CeHfi these osazones can only be identical when the residue
CH2OH . (CH0H)2 • CHOH—
in d-mannose and dextrose is also identical: their stereoisomerism can then only result from a difference in the arrangement of the groups linked to the a-C-atom.
So far as the transformations of the monobasic hexonic acids when boiled with quinoline or pyridine have been studied, it has
( 211] MONOSES. 277
always been found that the alteration takes place, as in the above instance, at only one C-atom, and this the one adjoining the aldehy do-group, the a-C-atom.
drGaladose can be obtained by the hydrolysis of lactose, or by the oxidation of the hexahydric alcohol dtUcUol, which occurs in certain plants. d-Galactose is crystalline, melting at 168^; it is strongly dextro-rotatory, is capable of undergoing fermentation, and exhibits mutarotation. Galactose is proved to be an aldose by its conversion, on oxidation, into the monobasic d-galactonic acid, C6H12O7. Further oxidation yields the sparingly soluble dibasic miunc add, C00H«(CH0H)4«C00H, which is optically in- active, and cannot be resolved into optically active components: its formation serves as a test for d-galactose. This is carried out by oxidizing the hexose under examination with nitric acid.
Their conversion into Icevxdic add (234), on treatment with hydrochloric acid, constitutes a general reaction for the hexoses. Brown, amorphous masses, known as humic substances, are pro- duced at the same time. Laevulic acid can be identified by means of its silver salt, which dissolves with dif&culty, and yields characteristic crystals.
The identification of the constituents of a mixture of monoses can often be readily effected by the aid of phenylhydrazine and its substitution-products (310), the tendency of each monose to form a phenylhydrazone or osazone depending on the particular hydrazine-derivative employed. Thus, from a solution containing arabinose and dextrose imsymmetrical methylphenylhydrazine, C6H5N(CH3)-NH2, dissolved in acetic acid precipitates arabinose- methylphenylhydrazone. If this is filtered ofif and the liquid warmed after addition of an acetic-acid solution of phenylhydra- zine, phenylglucosazone crystallizes out.
Synthesis of the Monoses.
211. As mentioned in 206, 4, condensation of formaldehyde or glyceraldehyde yields compounds of the formula C6H12O6. Similar derivatives are produced by the condensation of glycoU- alJehyde. These substances are obtained in the form of a syrup or concentrated aqueous solution. A phenylhexosazone identical with the osazone of inactive glucose, fructose, or mannose
278 ORGANIC CHEMISTRY, [§ 212
is obtained from thece syrups by the action of phenylhydrazine, such synthetic products being always racemic mixtures. Elimi- nation of two phenylhydrazine-residues yields an osone, convertible by reduction into dl-fructose (209). Further reduction of this monose gives dZ-mannitol, transformed by oxidation into dZ-mai.- nose as primary product, and then into dZ-mannonic acid. Reso- lution of this acid into its optical components yields d-mannonic acid, convertible by reduction into d-mannose. This substance can be transformed into dextrose (d-glucose) by the method of 210, and from either monose it is possible to obtain laevulcsc (d-fructose) by the method described in 209. From these hexoses the preparation of pentoses such as d-arabinose and i-xylose can be effected by oxidation with hydrogen peroxide of the calcium salt of the hexonic acid in presence of ferric acetate as catalyst. Oxidation of Z-xylose produces Z-xylonic acid, a substance converted by boiling with pyridine into the isomeric ly^conic acid, which can be reduced to d-lyxose. By means of the cyanohydrin-synthesis this derivative can be transformed into c?-gala:tonic acid, a com- pound reducible .3 d-galactose.
Stereochemistry of the Monoses.
212. It was stated (205) that all the aldohexoses and aldopen- toses have the same structure, and that, in consequence, their isomerism must be stereoisomerism. Although it would be beyond the scope of this book to deduce the configuration of all the p>entoses and hexoses mentioned here, it is desirable to indicate how this is determined for such compounds; that is, for those containing several asymmetric carbon atoms in the molecule.
It was mentioned (188) that the presence of two dissimilar asym- metric C-atoms in a molecule causes the existence of a greater num* ber of stereoisomerides than that of two similar asymmetric C-atoms. It will be seen from a projection-formula that the principle applies to a greater niunber of asymmetric C-atoms in the molecule. The projection-formulffi for two aldopentoses,
CH2OH CH2OH
HO ^ H H OH
HO ? H and H OH,
H H OH
i HO
pH
KJ
H
O O
§212]
STEREOCHEMISTRY OF* THE MONOSES,
279
cannot be made to coincide by rotation in the plane of the paper (190): the aldopentoseSy therefore, are not identical. The corre- sponding trihydroxyglutaric acids
HO- HO-
Ha
COOH
-H -H -H COOH
2
3
and
COOH
H OH
H OH
H OH
COOH
, however, identical^ since their projection-formuke can be made to coincide. In these compounds the asymmetric C-atoms 1 and 3 are similar, while in the pentoses they are dissimilar.
Assuming that the determination of the configuration of a tri* hydroxyglutaric acid is possible, and that it leads to the projection- formula given above, it follows that the pentose from which this acid is obtained by oxidation must have one of the above configurations, and that aU others are excluded. It thus only remains to distinguish between these two configurations.
In order to determine the stereochemical structure of a pentose, it is, therefore, first necessary to determine that of the corresponding trihydroxyglutaric acid. The optical behaviour of these acids affords a means of determining their stereochemical structure. Xylose, which is optically active, is converted by oxidation into an optically inactive trihydroxyglutaric acid which melts at 152^. Since an optically inactive substance is here obtained from an optically active one, not from a racemic compound, the inactivity must be due to intramolecular compensation, a fact which must find expression in the configuration allotted to this particular trihydroxyglutaric acid. The projection-formula of a compound which is optically inactive on account of intramolecular compensation must fulfil this condition: itself and its mirror-image must be capable of being made to coincide by rotation in the plane of the paper; that is, itself and its mirror- image must be identical. For, if it were otherwise, two enantio- morphous configurations — the formula and its mirror-image — would be possible, while for intramolecular compensation only one con- figuration is possible.
The above reasoning may be applied to the determination of the stereochemical structure of arabinose. Eight stereoisomeric for- mulae are possible for a pentose, but, by arranging these in pairs of mirror-images, and taking one of each pair, four different types are obtained:
230
ORGANIC CHEMISTRY.
[f213
H- H- H-
CH2OH ■OH -OH -OH
CH2OH
.H O
H —
H —
HO —
OR ■OH -H
H- HO
CH2OH —OH
HO —
I.
^O
II.
— H — H ,H ^0
III.
H-
Ha
H-
CH2OH —OH — H .
— OH ,H O
IV.
The mirror-image of I. is repreaented on p. 278.
Arabinose is converted by oxidation into an optically active tri> hydroxyglutaric acid. This excludes the trihydroxyglutaric acids which could be obtained from types I. and IV., since each of these could be made to coincide with its mirror-image, and thus would be optically inactive:
COOH COOH
I.
H- H- H-
■OH ■OH ■OH
identical with its miiTor^mage,
Ha
HO
Ha
COOH COOH
-H -H. H
COOH COOH
IV.
H-
Ha
H-
OH
-H
-OH
identical with its mirror4mage.
HO H-
Ha
COOH
H
OH.
H
COOH
The fact that by the aid of the cyanohydrin-synthesis arabinose can be converted into a mixture of dextrose and mannose, which on ondation yields the optically active saccharic acid and mannosac- charic acid, enables a choice between types II. and III. to be made.
Since in the cjranohydrin-syntheffls only the group Cq in CHOH .c5
is altered, the configuration of the rest of the O^toms remaining unchanged, saccharic acid and mannosaccharic acid must have the stereochemical structure
COOH
COOH
H-
K-
HO
HO
■OH ■OH ■H ■H
or
H- H-
Ha
H-
OH OH -H ■OH
COOH COOH
if arabinose is represented by formula II. Neither of these can be
i 213] DIOSES. 281
made to coincide with its mirror-image, so that formula II. is assumed to represent arabinose. Formula III. is excluded, since otherwise one of the acids mentioned above must have the stereochemical constitution
COOH
H-
Ha
H-
OH ■H , -H OH
COOH
which is identical with its mirror-image : one of the acids would then be optically inactive, which is not the case.
Arabinose has, therefore, a formula of the type II., but it is still uncertain whether it should be represented by the formula given above, or by its mirror-image.
Important aid in the determination of configuration is furnished by the building-up and the breaking-down of the monose molecules. Thus, oxidation of eiythrose yields mesotartaric acid, and this fact establishes the grouping round the central C-atoms of this tetrose. Since erythrose is a decomposition-product of ({-arabinose, this reaction affords a partial insight into the configuration of that pentose. As already indicated, S3mthesiB by the cyanohydrin- method enables the grouping in the hexoses to be inferred from the known configuration of the pentoses.
n. DIOSES.
213. Most of the dioses (or Moses) known are exclusively derived from hexoses, and therefore, have the formula
C12H22O11 = 2C6H12O6 — H20.
Dioses hydrolyzable to a pentose and a hexose are of very rare occurrence. Hydrolysis of vicianin, a glucoside present in the seed of the vetch {Vicia angustifolia) , yields hydrocyanic acid, benzaldehyde, and a diose, vicianose, built up from dextrose and I-arabinose, as is proved by its hydrolysis:
CiiH2oOio + H20=C6Hi206 + C5Hio05. Vicianose Dextrose (-Arabinose
Apiin, a glucoside present in parsley, is converted by the action of acids into a diose, transformed by further hydrolysis into
282 ORGANIC CHEMISTRY. [§ 214
dextrose and apiose, a pentose with a branched carbon chain, as is proved by its oxidation to isovaleric acid.
The hydrolysis can be effected not only by boiling with dilute acids, but also by the action of enzjones (222). On account of the readiness with which decomposition with water takes place, it is assumed that the monoses from which a diose is formed are not linked together through the carbon atoms, but through one or more oxygen atoms.
Hitherto, all attempts to S3rnthesize natural dioses have failed.
EMHi Fischer has, however, prepared artificial dioses synthet- ically from monoses, such as dextrose. Acetic anhydride and hydrobromic acid convert this sugar into acetobramodextrose, probably with the formula
CHjOAc* • CHOAc • CH . CHOAc • CHOAc • CHBr.
I 0 1
Silver carbonate eliminates bromine from this compound, two molecules becoming united by an oxygen atom. On careful saponi* fication with barium hydroxide, the eight acetyl-groups are removed, and a diose with reducing properties synthesized (224). A biochemical S3mthesis of dioses is described in 217.
Maltose. 214. Maltose in the crystallized state has the formula
Cl2H220ll,H20,
and can be prepared from starch by the action of diastase (43}. It is an important intermediate product in the industrial pro- duction of alcohol.
Maltose crystallizes in small, white needles, and is strongly dextro-rotatory. When boiled with dilute mineral acids, it yields only dextrose. It exhibits all the characteristics of the monoses: thus, it reduces an alkaline copper solution; yields an osazone, maUosazone (C12H22O11-2H2O-2H+2C6H5NH.NH2); and it can be oxidized to the monobasic maltobionic acid, C12H22O12, which, on hydrolysis, splits up into dextrose and d-gluconic acid, CH^OH . (CH0H)4 . COOH.
♦A^=CHa.CO— .
§ 215] DIOSES, 283
These properties show that maltose contains only one of the two carbon yl-groups present in two molecules of dextrose: thus, it forms an osazone with two, instead of four, molecules of phenyl- hydrazine, and yields a monobasic instead of a dibasic acid. The linking of the two molecules of dextrose must, therefore, involve in the reaction the carbonyl-oxygen of only one molecule. Such a linkage between two monose molecules is called a monocarhonyU bond. If this is denoted by the sign < , and a free carbonyl-group in a molecule by < , then maltose can be represented by
C6Hn05<O.C6Hn06<.
Dextrofle Dextrose
Lactose.
2i5« Lactose {milk'Sugar) is present in milk, and is prepared from it.
W?iey is usually employed for this purpose : it is the liquid whirh remains after the cream has been separated and the skimmed milk has been used for making cheese. In these processes the milk is deprived of most of its fats and proteins; the whey contains nearly all the lactose, and a large proportion of the mineral constituents of the milk. The lactose is obtained by evaporation, and purified by recrystallization.
Lactose crystallizes in well-defined, large, hard cr3r8tal8. It has not such a sweet taste as sucrose, and in the mouth resembles sand, on account of the hardness of its crystals.
On hydrolysis, lactose splits up into d-galactose and dextrose. It shows the reactions of the monoses, and can be proved, by a method analogous to that employed for maltose, to contain one free carbonyl-group in the molecule: it is, therefore, made up of dextrose and d-galactose, linked by a monocarbonyl-bond. The free carbonyl-group belongs to the dextrose molecule, since lactose is converted by oxidation with bromine-water into lactdbionic acid, which is converted by hydrolysis into d-galactose and d-gluconic acki. Lactose is, therefore, represented by
C6H„06<O.C6H„Ofi<.
(Mjalactofie Dextrooe
284 ORGANIC CHEMISTRY. [§ 218
Sucrose.
2i6. Sucrose (cane^stigar or saccharose) is present in many plants, and is prepared from sugar-beet and sugar-cane. It crystallizes well, and is very soluble in water. It melts at 160°, and on co^^ling solidifies to an amorphous, glass-like mass, which after a consid- erable time becomes crystalline. When strongly heated, it turns brown, being converted into a substance called carameL On hydrolysis, sucrose yields dextrose and tevulose in equal propor- tions. This mixture is called invert-sugar, and is tevo-rotatory, since Isevulose rotates the plane of polarization more to the left (209) than dextrose does to the right. Sucrose itself is strongly dextro- rotatory, so that the rotation has been reversed by hydrolysis. This is called inversion, a term also applied to the hydrolysis of other dioses and of polyoses. Sucrose does not show the reactions characteristic of the monoses: thus, it does not reduce an alkaline copper sotution, is not turned brown by caustic potash, and does not yield an osazone. Hence, it is evident that there are no free carbonyl-groups in its molecule; it may, therefore, be concluded that both of these have entered into reaction in the union of the two monoses. Such a linking between two monoses is called a dxcarbonyl-bond, and is represented by the sign <0>; so that sucrose has the formula
C6Hn05<0>C6Hii06-
Dextrose LievuloBo
217. The discovery that alcohols are able, under the influence of hydrochloric acid, to unite with monoses with elimination of water, affords an insight into the nature of the monocarbonyl-bond and ,the dicarbonyl-bond. The substances thus formed are called glucos- ides, since they are in many respects analogous to the natural glucos- ides, substances which are decomposed into a sugar, and one or more compounds of various kinds, on boiling with dilute acids. The arti* ficial glucosides are obtained by the action of one molecule of an alcohol upon a monoae:
C,H»0,+CH,OH - CeH„Oe-CH,+aO,
Methyl glucoside
These compounds were discovered by Emil Fischer, who has assigned to them a constitution analogous in some respects to that of the acetals (104, 2):
S2171
DIOSES.
285
H R.C
Aldehyde
OCH, OCH,
Alcohol
H
Aoetal
In the formation of glucoside, only one molecule of alcohol acts upon the aldose, so that one of the hydroxyl-groups of the latter plays the part of a second alcohol molecule:
CH2OH CHOH yCHOE /SCHOlT oCHOH
CO +H
OCH,
CHjOH
CHOH
7CHO—
iSCHOH oCHOH
C— OCH. H
The grounds for the assumption of tlus constitution are: first, these gluoosides are readily resolved into their components, which argues against the existence of a carbon bond between the lattSr; second, the hydroxyl of the 7-C-atom is assumed to be the one which reacts, since a number of instances of similar behaviour are known, such as that of the acids yielding lactones (185). The possibility of the other hydroxyl-groups reacting is by no means excluded, and in some instances amounts to a probability.
The combination of two monoses with elimination of one mole- cule of water may be represented as being analogous to the forma- tion of a glucoside from an alcohol and a monose. Maltose and lactose, which are united by a monocarbonyl-bond and contain one free carbonyl-group, are combined thus:
CH,OH CHOH
|
rCHOjir iflCHOH oCHOH |
|
|
cp |
+H |
,H
(CHOH), OC]
)H,
CH2OH CHOH CHO-^ H2O+CHOH CHOH
'0 (CHOH)«.
H
H
By analogy the constitution of sucroiM, in which Isvulose and dex- trose are united by a dicarbonyl-bond, will be
286 ORGANIC CHEMISTRY. [§ 217
CH/)H CH,OH
CHOH fCHO-
CHO-^ CHOH CHOH C=
aCHOH
rCHOH
i9
^C-
0 aCH/)H
H
The methylglucoside previously mentioned exists in two isomeric forms, denoted by a and /3, and closely related to a-dextrosc an'd /^-dextrose. Hydrolysis of a-methylglucoside with the enzyme maltase yields a-dextrose; that of /^-methylglucoside with emulsin forms /^-dextrose. These facts have led to the adoption of a formula of lactone-type for dextrose:
CHjOH . CHOH . CH . CHOH . CHOH . CHOH.
I 0 I
The stereoisomerism of a-dextrose and /9-dextrose therefore dependl on variation in grouping at the carbon atom indicated by an asterisk (*). Similar reasoning is applicable to the other monoses. The absence of an aldehy do -group from the constitu- tutional formulae of dextrose and the othsr monoses accords with their inability to restore the colour to Schiff's reagent (107).
Interesting syntheses of these methylglucosides by means of enzymes have been discovered by Bourquelot. An appreciable amount of ^-methylglucoside is produced by keeping a methyl- alcoholic solution of glucose, containing the a-form and the j3-form, for one month in contact with emulsin ^ the enzyme of bitter almonds. a-Methylglucoside is formed similarly under the influence of an enzyme present in yeast. Alkylglucosides of this tjrpe can be synthesized from many other alcohols. An equilibrium is attained, for the glucosides formed are decomposed by the same enzymes into the corresponding alcohols and glucose.
Bourquelot also tried to build up dioses from monoses by this method, and succeeded in synthesizing gentiobiose, a carbohydrate containing two glucose-residues, and obtainable from the glucoside gentianose. The great difficulty of isolating small proportions of dioses in presence of a large excess of monoses prevented him from demonstrating with certainty the possibility of synthesizing sucrose.
S 2181 DI0SE8, 287
lactose, and other dioses by the aid of enzymes, although there is some probability of his having been successful.
Sucrose forms compounds with bases, called saccharates: among them are Ci2H220ii,CaO,2H20 and Ci2H220ii,2CaO, which are readily soluble in water. When the solution is boiled, the nearly insoluble tri calcium saccharate Ci2H220ii,3CaO,3H20 is precipitated.
Manufacture of Sucrose from Sugar-beet.
2i8. Sucrose is present in solution in the cell-fluid of the sugar- beet. The cell-walls are lined with a thin, continuous layer of protoplasm, constituting a semi-permeable membrane, which pre* vents the diffusion of the sugar from the ceils at ordinary tempera- tures. When placed in water at 80*^-90®, the protoplasm is killed, coagulates, and develops minute ruptures, through which the cell- fluid can diffuse. The process is facilitated by cutting lip the beet into pieces 2 to 3 mm. in thickness. In order to make the diffu- sion-process as complete as possible with a minimum amoimt of water, the slices are placed in vats through which water circulates in such a manner that the nearly exhausted material is acted on by fresh water, while that which is only partly exhausted comes into contact with the solution already obtained, so that the material richest in sugar is treated with the strongest extract, and vice versa (principle of the coimter-current). The solution obtained contains 12-15 per cent, of sugar, which is about the proportion contained in the beet itself.
Slaked lime is added to this solution, whereby a double object is attained. First, the free acids in the juice, such as oxalic acid and citric acid, are precipitated, along with the phosphates: their removal is necessary, since on concentrating the solution they would cause inversion. Second, proteins and colouring mat- ters are precipitated from the solution. To accomplish these objects, it is necessary to add an excess of lime, part of which goes into solution as saccharate. The saccharate is then decomposed by a current of carbon dioxide, care being taken to leave the liquid faintly alkaline. The precipitate is separated by a filter-press, and the filtrate concentrated. To obtain the maximum yield of sugar, the concentration must take place at a low temperature.
288 ORGANIC CHEMISTRY. [§ 219
This is attained by the use of vacuum-pans, in which the sugar- solution boils under diminished pressure. The first product of the concentration is a thick syrup, more strongly alkaline than the original solution. Calcium carbonate is precipitated by repeated treatment with carbon dioxide until the thick syrup is almost neutral. After filtration, the syrup is concentrated imtil crystals of sugar begin to separate. It is then allowed to cool, when more crystals are obtained, mixed with a sjrrupy liquid, which is removed in a centrifugal machine. This syrup is further crystallized by slow agitation with a stirring apparatus, and the crystals are again separated by means of the centrifugal machine. The residual syrup (molasses) is worked up in the preparation of alcohol.
The sugar thus prepared is not pure: it is brown, and contains a certain amount of syrup. The crude product is purified by dis- solving it, decolourizing with animal-charcoal, and concentrating in vacuum-pans.
Quantitative Estimation of Sucrose.
219. The great practical importance of sucrose makes it de- sirable to have a quick and accurate method of estimating it quantitatively. This is effected almost exclusively by examining its aqueous solution with the polarimeter (26, 2). Since sucrose is strongly dextro-rotatory ([a]z)= +66-5®), a small quantity produces an appreciable amount of rotation, which, moreover, is almost independent of the temperature, and for practical purposes may be considered as proportional to the concentration. It is obvious that this method will only yield accurate results when no other optically active substances are present in the solution. If such substances are present, either they must be removed, or their effect taken into account. The former method is adopted in the determination of the amount of sugar in beet. The sample ia grated with a fine rasp to destroy the cell-walls, and a weighed quantity is made up to a certain volume with cold water, which dissolves not only the sucrose, but also optically active proteins. The latter are precipitated with lead acetate, filtered off, and the amount of rotation observed.
When another sugar is present in the solution along with the sucrose, it is necessary to proceed by the second method. Suppose
i 220] DIOSES. 289
dextrose is the other sugar present. The rotatory power of the solution, which will be dextro-rotatory, is first determined. If it be now inverted, the solution will either diminish in dextro-rota- tion, or wiU become tevo-rotatory, since invert-sugar is l»vo- rotatory. The rotatory power of an invert-sugar solution obtamed from a sucrose solution of given strength being known, these two observations furnish the data by which the percentage of dextrose in cane-Bugar or beet-sugar can be calculated.
Velocity of Inversion of Sucrose*
220. The equation for unimolecular reactions (95) may be applied to the inversion of a dilute solution of sucrose. If the original amount of the latter present was p, and after a certain time the quantity x has been inverted, then the velocity 8 in the fraction of time immediately following can be expressed by the equation
in which i is a constant. The inversioii can be effected by means of differ^t acids of the same molecular concentration: the velocity of the reaction is dependent upon the natiu^ of the acid employed, so that different values are obtained for the velocity- constant k. When the values of this constant and of the electrolytic dissociation-constant for these acids are compared, they are found to be proportional to one another. An acid which is ionized strongly effects- inversion much more rapidly than one but slightly ionized, from which it follows that only the ionized part of the acid exer- cises an inverting influence. Since only the hydrogen ion is com- mon to all acids, it must be concluded that inversion is the result of the catalytic action of the hydrogen ions. Inversely, the concentra- tion of the hydrogen ion in the solutions of acid salts, for example, may be determined by measuring the velocity of inversion.
290 ORGANIC CHEMISTRY, [§ 221
Fermentation and the Action of Enzymes.
221. The alcoholic fermentation of liquids is one of the longest known reactions. During the nineteenth century a number of other reactions were identified as fermentation-processes, such as the lactic fermentation and butyric fermentation of sugar, putre- factive fermentation, and others. Fermentation-processes include a number of reactions which take place slowly and at ordinary temperatures: they are usually attended by the evolution of a gas and of heat, and depend upon the action of micro-organisms, such as yeast-cells, bacteria, and schizomycetes.
The part played by these micro-organisms in fermentation- processes has been the subject of much diversity of opinion. Liebiq thought that yeast contained certain easily decomposed ferments, and that it was their decomposition which, as it. were, induced the; fermentation of the substance. Pasteur, however, after a series of brilliant researches, became convinced that fermentation can only be brought about by living yeast-cells, and that the process is, therefore, a physiological phenomenon; that is, a complicated biological function of these cells. Thus, he concluded that there could be no fermentation without living yeast-cells, a theory which was universally accepted, Liebig's supposition that the part played by the cells is only a secondary one being definitely abandoned.
In accordance with Pasteur's theory, the process of fermenta- tion is inseparable from the presence and propagation of yeast- cells. If it were found possible to bring about fermentation with- out their presence, his theory would fall to the ground. Edward Buchner has effected this. He triturated fresh yeast with sand, whereby' the cell-walls were destroyed. The dough-like mass was submitted to great pressure, which expressed a liquid: this expressed yeast-juice was separated by filtration from the cells still floating in it. Buchner proved in various ways that this yeast-juice contains neither living cells nor living protoplasm: for instance, the yeast may be first killed by the action of acetone; the extract from it can nevertheless set up active fermentation in a solution of sugar similarly to that obtained from living yeast. The fermentation is caused by a dissolved substance, which, on account of its properties, such as coagulation on warming, must
i 222] FERMENTATION AND THE ACTION OF ENZYMES. 291
be classed with proteins: it is a kind of enzyme^ to which Buchner has given the name zymase. The yeast-cells only have the func- tion of producing Z3rmase.
Buchner has proved by analogous methods that other fermen- tation-processes, such as the lactic fermentation and acetic fermen- tation, are not caused by the bacilli themselves, but by the enzyme they contain.
222. The chemical structure of the enzymes is still imperfectly understood. Those capable of decomposing proteins probably consist of a mixture of amino-acids and pol3rpeptides, but the diastatic ferments seem to be degradation-products of the car- bohydrates. Most of them have not been obtained in the pur state. Their power of decomposing compounds is also not understood. Hitherto, only small insight has been obtained into the conditions upon which their action depends.
First, the enzymes only act at the ordinary, or at a slightly elevated, temperature: below the freezing-point their activity is suspended, but returns at the ordinary temperature: on heatmg, they are decomposed. Second, they are sometimes rendered in- active ("poisoned") by the presence of small quantities of certain substances, such as hydrocyanic acid. Third, it is very remark- able that a given enzyme can only produce changes in a few sub- stances, and has no action on other similar compounds. Thus, of the different monoses containing two to nine C-atoms, only the trioses, hexoses, and nonoses undergo the alcoholic fermentation: in fact, these are the only monoses which, according to their formula, can be readily converted into CO2 and C2H5OH; for instance,
CsHeOa^CaHfiOH+COg.
Only the monoses are capable of being fermented by enzymes: dioses must first be converted into monoses. Yeast contains an enzyme, invertase, which first decomposes sucrose into a mixture of tevulose and dextrose. This is proved by the fact that certain varieties of yeast, which do not contain invertase, are incapable of fermenting sucrose: thus, Schizosaccharomyces octosporuSf discov- ered by Beyerinck, can ferment maltose, but not sucrose. This variety of yeast contains no invertase, but only maltase, the enzyme by which maltose is hydrolyzed.
292
ORGANIC CHEMISTRY.
[S222
The aptitude for decomposition by enzjrmes, possessed by the monoses, has been proved by Ehil Fischer to be intimately con- nected with their i;tereochemical configuration. The three naturally occurring sugars, dextrose, d-mannose, and Isevulose, are capable of undergoing fermentation, and there is a great similarity in their configurations, since they differ only in the grouping round two C-atoms:
H-
Ha
H- H
,H O
—OH — H — OH — OH IHzOH
Deztroae
HO —
HO —
H —
H —
CI
,H
'O
H H
— OH
—OH
JHzOH
Ha
H- H
d-MaDDoae
CH3OH
I
CO — H —OH —OH
CH2OH
Lcevulose
H
Ha Ha
H-
,H
o
— OH — H — H — OH CH2OH
d-Galaetose
d-Galactose, which is also a natural product, has a somewhat dif- ferent configuration, and is either more slowly fermented by certain varieties of yeast, or not at all. The mirror-images of these com- pounds, i-glucose, etc., are not capable of undergoing fermentation.
The cause of these phenomena is probably the asynmietric struc- ture of the enzyme molecule. Although these substances have not been obtained in the pure state, their great resemblance to the pro- teins, and the probability of their formation from them, render their optical activity undoubted : that is, they are to be looked upon as built up of asymmetric molecules. This has led to the hypothesis that there must be a similarity in molecular configuration between the enzymes and the substances which they decompose; and that when this similarity is wanting, no reaction can take place. Emil Fischer appropriately compares this resemblance in structure to that necessary between a lock and a key, in order that the latter may pass the lock.
The application of these views to the chemical processes which go on in the more highly developed organisms leads to the concep- tion that generally in reactions in which proteins take part, as is undoubtedly the case in the protoplasm, the configuration of the molecule has the same importance as its structure. Various phe- nomena may be thus explained: the sweet taste possessed by one of the optically active asparagines, and the absence of taste in the other; the different degrees to which the three stereoisomeric
§2231 FERMENTATION AND THE ACTION OF ENZYMES. 293
tartaric acids are oxidized in the body of a dog fed with them; the fact that, on subcutaneous injection of a rabbit with Z-arabinose or d-arabinose, of the first only 7 per cent., of the latter 36 per cent., are excreted from the body unchanged in the urine; and so on.
Asymmetric Synthesis.
223. Laboratory-s3mtheses effected with optically inactive material always yield inactive compounds: plants employ such inactive material as carbon dioxide and water for the synthesis of dextro-rotatory dextrose and numerous other optically active compounds. They also produce optically active nitrogenous compounds^ such as proteins and alkaloids, although the nitrogen reacts either in the free state or as nitric acid. Two problems present themselves for solution:
1. The mode of formation of the first optically active substance from inactive material.
2. The production of active substances from inactive material imder the influence of an already existing optically active body.
The solution of the first problem is still unattained. It has been suggested that the formation of the first optically active compound took place imder the influence of the circularly- polarized light present at the earth's surface; but although this hypothesis is plausible, it still lacks experimental confirmation.
More progress has been made towards the solution of the second problem. Emil Fischer has found that in the cyano- hydrin-synthesis (183) the use of optically active substances does not always lead to the production of the two possible optical isomerides. An example is furnished by mannose, convertible by the cyanohydrin-synthesis into mannoheptonic acid. From analogy with other cyanohydrin-syntheses, the formation of two stereoisomeric mannoheptonic acids in equal proportions would be anticipated, but only one acid is obtained. It follows that the building-up of a molecule from one already asymmetric can continue in an asymmetric sense. If mannose were converted by a triple appUcation of the cyanohydrin-synthesis into a manno- nonose, the building-up being in every instance in an asymmetric sense; and if it were possible to decompose this nonose into the original hexose and a product with three carbon atoms, this new substance would also be optically active. One optically active molecule would thus have occasioned the formation of another.
294 ORGANIC CHEMISTRY. [§ 224
The formation of sugar in plants is probably the result of an analogous process. Dextrose is formed in the chlorophyll-grains, themselves composed of optically active substances. It may be assumed that prior to the formation of sugar these substances combine with carbon dioxide or formaldehyde (206, 4), and that the condensation to sugar is asymmetric on account of the asym- metric character of the participating substances.
Some asymmetric sjTitheses of this type have been efifected, particularly by McKenzie and his coadjutors.
Reduction of bemoylfonnic add, CeHs-CO-COOH, yields inactive mandelic acid, CeHs-CHOH-COOH. But reduction of an ester of this ketonic acid derived from an optically active alcohol, such as the Isevo-rotatory menthol, produces a mixture of the ester of the dextro-acid with a small excess of that of the Iffivo-acid. On saponification, active mandelic acid is obtained, despite the elimination of the asymmetric structure occasioned by the menthol-residue. The formation of Z-lactic acid by the reduction of Z-bomyl pyroracemate with aluminium-amalgam is / a similar reaction:
CH3.CO.COOC10H17 -^ CH3.CHOH.COOH.
2-Borxiyl pyroracemate /-Lactic acid
Another example is tlie formation of excess of Z-tartaric acid by treating monobomyl fumarate with permanganate (324).
The occurrence in nature of all the possible optical isomerides of a compound is exceptional. Only the dextro-rotatory forms of dextrose, tartaric acid, and lactic acid are natural products. Why nature has not produced the chemical mirror-images of all optic- ally active substances found in the existing flora and faima, since, as far as is at present known, the probability for the formation of both must have been equal, is a problem by no means solved^
m. POLYOSES.
RaflBnose, Ci8H320i6,5H20.
334. Raffinose is the most important of the hexotrioses, of which but few are known. Their formula is CisHasOie; that is,
3C«Hi,0«-2HsO.
§ 2251 POLYOSES. 296
Raffinose is a hexotriose, eince, on hydrolysis, it takes up two molecules of water with formation of an equal number of molecules of Isvulose, dextrose, and d-galactose. By careful hydrolysis, raf- finose can be split up quantitatively into Isevulose and a diose {mde^ diose) : from the latter, dextrose and (^galactose can be obtained in the same way as from lactose, with which, however, melediose is not identical. The action of emulsin converts r&ffinose into d-galactose and sucrose. Raffinose exhibits none of the monose reactions: thus, it does not reduce an alkaline copper solution. This proves the absence of a free carbonyl-group, so that raffinose must be repre- sented by
CeHuOs<0-C.H,oO, <0>C.HnO,.
Melediose exhibits the sugar reactions, and therefore contains one free carbonyl-group, so that its formula is
C.HnO,<0-CJI„05<,
which proves that the decomposition of raffinose into monose and diose takes place at the dicarbony]>bond, as otherwise there would have been obtained a diose, C«Hii04<0>CeHn04, lacking a free carbonyl-group.
Raffinose crystallizes with five molecules of water. When sucrose contains a certain proportion of this polyose, it yields pointed crystals.
Manneotetroae is a tetrose present in manna. On hydrolysis it yields two molecules of galactose, one molecule of dextrose, and one molecule of Isevulose:
C,,H4A. + 3H,0 - 2C.H„0.+CeH„0e+C.H„0e.
Manneotetroee Galactoae Dextrose Lnvulose
Higher Polyoses.
225. Most of the higher polyoses are amorphous, and do not possess a sweet taste: many of them are insoluble in water. On hydrolysis, they yield monoses, either pentoses or hexoses, so that it may be assumed that the monose-residues are united by the oxygen atom. The molecular weight of the polyoses is unknown, but must be very great. Their formula may be represented as being derived thus:
nC6Hi206-(n-l)H20.
296 ORGANIC CHEMISTRY, [§ 225
If n is very great, this constitution approximates to
nC6Hi206— nH20= ^(CsHioOs),
which is the formula indicated by the results of analysis. On hydrolysis, nearly all the polyses yield monoses with the same number of G^toms.
Starch.
Starch is the first observable assimilation-product of plants. It occurs in large quantitites in the tubers, roots, and seeds of many plants, in which it is present in the form of granules differing in form and size in different plants. Some of these granules are represented in Figs. 67, 68, and 69.
Starch is insoluble in cold water: in hot water it swells up without dissolving. It yields an intense blue coloration with a dilute solution of iodine, for which this reaction serves as a test.
On addition of a concentrated solution of tamiin under the microscope to the liquid obtained by boiling 1 g. of potato-starch with 100 c.c. of water, the starch-granules are seen to consist of a skin, filled with a liquid which is coagulated by the action of the tannin. Starch is therefore built up from two distinct individuals: the skin, called amylocellnlose; and the soluble part, termed granidose, Amylocellulose constitutes about forty per cent, by weight of starch, and can be prepared from it by extraction of the granulose with a dilute solution of sodium hydroxide. Only the granulose produces the blue coloration with iodine.
When boiled with dilute acids, starch is converted into dex- trose. On treatment with diastase, starch-paste first liquefies, its molecules then decompose, and ultimately maltose and iso^ maltose, C12H22O11, are formed. Both these methods of treat- ment yield intermediate products, however; they are gum-like substances, polyoses containing a smaller number of atoms in the molecule than starch, called dextrins. Dextrin is also obtained by heating starch alone, or to 110^ with a small quantity of nitric acid.
Starch does not show any of the reactions of the monoses: it
Fia. 67 .^Rite-starch. X 3
FlQ. 68.— RlCB-ATABCH. X
298 OROANIC CHEMISTRY. [(225
does not reduce an alkaline copper solution, nor resinify with alka- lis, and yields no compound with phenylhydrazine. This proves
Fia. 69, POTATO-STASCH.
the absence of a free carbonyl-group, so that ite molecule must be represented by
C6Hio06<0 . . . . CeHio04<0>C8HioOi OCeHwOs.
It might be ai^geated that the molecule of starch coottUDs more than one dicarbonyl-bond, when the fonnula would be, for example,
CgH,oOB<0 CaH,(Oj<0>C,H,oO,-0>C,H„0( 0>
>CJI,oO*<0>C,H,oO,.0>CsHiA-0>CJi,o<^ 0>C,H„0,.
It does not, dnce hydrolysia of a compound of this type must yidd, in addition to dextrose, a substance >CiHiiOi,< awitaining two free carbonyl-groups, and no such product has been obtained by the hydrolysis of starch.
Dextrin can unite with phenylhydrazine, and exhibits the reac- tions of the monoses, such as reduction of an alkaline copper solution, and the formation of a yellow coloration with alkalis. It must, therefore, be assumed to contain a free carbonyl-^roup,
Certain dextrins have also been prepared in crystalline form.
§i 226, 2271 POLYOSES. 299
Glycogen, (CeHioOs)
z«
Glycogen is a substance resembling starch, and is present in the animal organism: the other polyoses are vegetable products. It 18 usually prepared from liver, and is a white, amorphous powder, dissolving in wat^'r with formation of an opalescent solution. On hydrolysis, it yields only dextrose. Apparently there are different kinds of glycogen, according to the animal from which it is isolated.
Manufacture of Starch.
226. The process by which starch is manufactured is theoretically very simple. Potato-starch is prepared by first finely grinding the potatoes, whereby the cell-tissue is destroyed. The starch-granules, thus laid bare, are washed out of the cell-tissue by treatment with water in a specially constructed apparatus, somewhat resembling a sieve. They are allowed to settle on standing, are then carefully washed, and finally dried slowly.
Starch is employed for many purposes in the arts, as an adhesive paste, and for stiffening linen in laundries. In the latter process, the Btarch-paste is converted by the heat of the smoothing-iron into a stiflf, shining layer of dextrin, coating the fibres of the linen. Starch is of great impK)rtance as a large constituent of foods. It is more fully dealt with in this connexion in physiological text-books.
Cellulose, (CeHioOs),.
227. Cellulose is a polyose of very high molecular weight. The cell-walls of plants consist principally of this substance, together with lignin, which is probably not a polyose.
The formula of lignin is unknown, but it contains the groups methoxyl, acetyl, and formyl. The formation of methyl alcohol by the dry distillation of wood depends on the presence of lignin, since the process does not produce this alcohol from pure cellulose. A test for lignin is described in 228.
Cellulose is very stable towards dilute acids and alkalis, a property which is made use of in the technical preparation of cellulase, in order to free it from the substances present along with it in the plant-material. Linen, cotton, and paper consist almost exclusively of cellulose: pure filter-paper is nearly chem- ically pure cellulose. When it is dissolved in strong sulphuric
300 ORGANIC CHEMISTRY, . [§ 228
acidy and the solution boiled, after dilution with water, it is completely hydrolyzed. Cellulose from cotton-wool, paper, etc., jrields exclusively dextrose; from coffee-beans, cocoa-nibs, etc., d-manno3e. Cellulose is converted by treatment with sulphuric acid containing half its volume of water into a colloidal modifica- tion, amyloidy which gives a blue coloration with iodine: this reaction furnishes a test for cellulose. The latter is soluble in an ammoniacal solution of copper oxide (Schweitzer's reagent) : from this solution it is precipitated chemically unchanged by- acids and salts, and forms an amorphous powder when dried.
The action of acetic anhydride and concentrated sulphuric acid on the cellulose of filter-paper, cotton-wool, and other mate- rials, yields the octoacetyl-compound of a diose, named cellose, obtained by saponification of the acetyl-derivative with alcoholic potash. Inversion converts cellose into dextrose. It is the simplest polyosc obtained from cellulose, just as maltose is the simplest polyose formed from starch. This fact furnishes an important argument from the chemical standpoint, supported by observations in vegetable physiology, in favour of the view that cellulose and starch are essentially different substances, and against the theory that cellulose is a higher polymeric form of starch.
Technical Applications of Cellulose; Nitrocelluloses; Artificial
Silk.
328. Linen is prepared from the stalk of the flax-plant. The linen fibres can be obtained from the flax, cellulose being very stable towards chemical reagents. For example, the flax is steeped in water for from ten days to a fortnight. The consequent decay of the external fibre gives rise to an impleasant smell. The material is then dried by spreading it out, and passed between corrugated rollers. This loosens the external woody fibre, which is then stripped off by revolving wooden arms named "wipers," a process called "scutch- ing." The linen-fibres have a grey colour, and are bleached by either being spread out in the open or by means of blcaching-powder.
Paper was formerly prepared almost exclusively from linen-rags, iDUt is now largely manufactured from wood and straw, which must be divided into fibres; the fibres are then separated as much as possible from the other, so-called incrusting, substances present. This is effected either by the aidphite-method, in which the wood is
§ 2281 NITROCELLULOSES. 301
heated under pressure with a solution of calcium hydrogen sulphite; or for straw by heating with sodium hydroxide under pressure. By these processes most of the incrusting substances are dissolved, and the wood or straw bleached at the same time: the cellulose which remains can be readily separated into fine fibres, which is necessary - to. the manufacture of paper-pulp. It is not, however, possible to remove all the lignin by these means; in consequence, wood-paper and straw-paper answer to the tests for lignin, and can be recognized thereby. Lignin gives a yellow coloration with salts of aniline (297), and a red coloration with a solution of phloroglucinol (337) iu^ concentrated hydrochloric acid.
Parchmentr-paper is prepared by converting the outer surface of paper into amyloid (227), a process which imparts toughness to it.
The nitroceUvloses are of great technical importance. When cotton-wool is treated with a mixture of nitric and sulphuric acids, a mixture of mononitrocelliUoae, dinitrocellidose, and trinitrocellulose is obtained, the extent of the nitration being dependent upon the concentration of the acids and the duration of the process. Cellulose is arbitrarily assumed to have the molecular formula CeHioOt. In the nitration of cellulose the final product is trinitro-oxycellulose. For, on treatment with ferrous chloride, trinitro-oxycellulose yields oxyceUuIose, but no cellulose, proving that the formation of the trinitro-compound is accompanied by oxidation of the cellulose; whereas nitromannitol, for example, is reconverted by this reagent into mannitol, without oxidation of the latter. Oxyceliulose has the formula
(C,4H«0„)x or [(C*HioO»),-h(C«H,oOe)]x;
and its trinitro-derivative is
[CeHzCNOOA], +C Jl7(N0,),0e.
The solution in a mixture of alcohol and ether of mononitroceliu- lose and dinitrocellulose is known as collodion: on evapK)rat]on it leaves an elastic skin, and is employed in photography, and in the manufacture of celluloid. The trinitrocellulose is guncoUon, which looks like cotton-wool, but feels somewhat rough to the touch, and is extensively employed as an explosive. It bums readily when a loose tuft of it is ignited, but can be made to explode by the detona- tion of a small quantity of mercury fulminate, and yields only gaseous products, nitrogen, hydrogen, water-vapour, carbon mon- oxide, and carbon dioxide. It exerts a detonating or brisani (155) action, and without modification is, therefore, unsuitable for use in artillery.
302 ORGANIC CHEMISTRY, [§ 228
When guncotton is dissolved in acetone or^ethyl acetate, a gelatin- ous mass is obtained: after removal of the solvent, an amorphous, transparent substance is left, having the same chemical composition as guncotton, but burning and exploding more slowly. The velocity of explosion of guncotton being thus moderated, it is made available in this form for use in artillery, imder the name of ''smokeless pK)wder."
Artificial silk is manufactured by forcing a solution of cellulose through very narrow orifices immersed in a bath which repre- cipitates the cellulose in lustrous threads resembling silk in appear- ance. Photographic film is made similarly, the orifices being replaced by a narrow slot.
On the manufacturing scale the cellulose is brought into solution by one of three processes: (1) by means of Schweitzer's reagent (227); (2) by preliminary nitration to mononitrocellulose and dinitrocellulose, and solution of these nitro-compK)unds in alcohol and ether, the threads being then denitrified by the action of various reducers; (3) by conversion of the cellulose into a xanthate (264), a very thick liquid being formed, the so-called viscose. To coagulate the fibres, the solution obtained by the first method is pressed out into dilute acid; that produced by the second method into a large amoimt of water; and that formed by the third method into a solution of ammonium sulphate or dilute sulphuric acid.
AHINO-ALDEHYDES AND AMINO-KETONES.
sag. Very few amino-cddehydea and amino-ketones are known. Aminoacetaldehyde, CH2NHs«Cq, a very unstable compound, can be
obtained from aminoacetal, CH2NHs*C,qq tj \ , which can be pre- pared from monochloroacetal, CH2*Cl*CH(C)CaH,)s. Muscarine is possibly the corresponding trimethylammonium base:
CHaN(CH.),OH
It is a crystalline, excessively poisonous substance, and is present in certain plants — for example, toad-stool (AgariciLS miLscariiLs).
Apart from inorganic substances, chitin is the principal con- stituent of the shells of the Crustacea, and is best prepared from the shell and claws of the lobster. When boiled with concentrated hydrochloric acid, chitin is almost wholly converted into gluco- samine hydrochloride^ C6Hi305X,HCl, a well-crystallized salt. Chitin contains an NH2-group, since like primary amines it evolves nitrogen on treatment with nitrous acid, yielding chitose, C6H12O6, with the properties of an aldose. Thus, it is oxidized by bromine-water to the monobasic chiUmic acid : further oxidation with nitric acid converts this substance into the dibasic isosaccharic acid.
Bromine converts glucosamine hydrochloride into d-^lixosamic acid, CH20H.(CHOH)3-CHNH2-COOH, which Emil Fischer has sjmthesized by the following method. Ammonia and hydro- cyanic acid react with d-arabinose to form a compoimd (240, 3),
CH2OH . (CH0H)3 .CHNH2 -CN,
and with concentrated hydrochloric acid this yields
CH2OH . (CH0H)3 .CHNH2 .COOH,
identical with glucosamic acid. Since this acid is reduced to glucosamine by the method of 206, 5, the identity of the synthetic amine with the natural product is established.
303
ALDEHTDO-ACIDS AND EBTONIC ACIDS.
GlyoxyUc Acid, COOH-cJ+HaO.
230* Glyoxylic acid is the first member of the series of aldehydo- acids. It is present in unripe fruits, and can be prepared by heat- ing dibromoacetic acid, CHBra-COOH, with water, or by the electro-reduction of oxalic acid. It also results on the oxidation of alcohol with nitric acid, by the method described under glyoxal
(198).
As the above formula shows, glyoxylic acid contains one mole- cule of water, which cannot be separated from the acid or its salts without their undergoing decomposition. For this reason, the water is often assumed to be in chemical combination (149) ; thus, CH(0H)2'C00H, as it is in chloral hydrate (201). In each of
H these substances the aldehydo-group, — Cq, is under the influence
of a strongly negative group; — CCI3 in chloral, and — COOH in glyoxylic acid. The latter, moreover, possesses all the properties characteristic of aldehydes: it reduces an ammoniacal silver solu- tion, forms an addition-product with sodium hydrogen sulphite, yields an oxime, etc. When boiled with caustic potash, it is con- verted into glycollic acid and oxalic acid, the formation of which may be explained by the assumption that one molecule of the acid takes up the two hydrogen atoms, and another the oxygen atom, from one molecule of water:
2C00H.CH0 -> COOH.CH2OH +(XX)H •COOH.
§ 2311 PYRORACEMIC ACID. 305
Pyroracemic Acid, CHa-CO-COOH.
231. Pyroracemic (pyruvic) acid, the first member of the series of ketonic acids, owes its name to its formation by the distillation of either tartaric acid or racemic acid with potassium hydrogen sulphate. It is probable that carbon dioxide is first eliminated from tar- taric acid^COOH . CHOH . CHOH . COOH, with formation of glyceric acid, CH20H- CHOH 'COOH, which yields pyroracemic acid by loss of one molecule of water; for glyceric acid itself is con- verted into pyroracemic acid by heating with potassium hydrogen sulphate:
CH2OH. CHOH. COOH -H2O =
= CH2=C(0H) .COOH ->CH3-C0.C00H.
Pyroracemic acid can be obtained synthetically by hydrolysis of the nitrile formed by the action of potassium cyanide on acetyl chloride:
CH3.COCI -> CH3-CO.CN -> CH3.CO.CO2H.
This is a general method for the preparation of a-ketonic acids.
When heated to 150*^ with dilute sulphuric acid, pyroracemic acid yields carbon dioxide and acetaldehyde:
CHa-CO.fCO^H = CHs-Cq +CO2.
At ordinary temperatures p3rroracemic acid is liquid, but is solid at low temperatures. It melts at 9°, boils at 165°, and is miscible with water in all proportions: its specific gravity is 1.27 at 20*^, and it has an odour resembling that of acetic acid. It is a stronger acid than propionic acid, for which 10*A; is 0-134; for pyroracemic acid 10*fc is 56, which must be explained by assuming the presence of a n^ative carbon yl-group in juxtaposition to the carboxyl-group.
Pyroracemic acid has all the properties characteristic of ketones: it yields an oxime, a hydrazone, an addition-product with hydro- cyanic acid, etc.
Addition of boric acid to an aqueous solution of pyroracemic acid causes a marked rise in the value of the electric conductivity of the organic acid. This phenomenon is characteristic of a-hydroxy- acids (180), and indicates each molecule of pyroracemic acid to be in imion with one molecule of water, in accordance with the structural formula CH,-C(OH), •COOH.
The electrolysis of a very concentrated solution of potassium pyroracemate yields acetic acid and diacetyl. The formation of
306 ORGANIC CHEMISTRY. [§ 232
acetic acid may be looked upon as due to the interaction of the anion of the acid and the hydroxyl-ion, after discharge at the anode:
CH,-CO-COO'+OH' - CH,-COOH+CO,;
and that of diacetyl as resulting from the union of two acid anions, with elimination of CO2:
cS::C0ic00' - CH,.CO.CO.CH.+200,.
The potassium salts of other ketonic acids are decomposed by electrolysis in an analogous manner.
Acetoacetic Add, CHa-CO-CHz-COOH.
23a. Acetoacetic acid is a ^-ketonic acid. It is not of much importance; but its ester, ethyl acetoacetatej CH3*CO*CH2«COOC2H5, is an interesting compoimd.
Ethyl acetoacetate is obtained by Claisen's condensation- method (200) through the action of sodium on ethyl acetate in presence of ethyl alcohol:
ONa H
,0 ..„ ry
Ethyl acetate
OC2H6+H
OC2H6 H
C.C00C2H8
Addition-product
.ONa -2C52H60H + CH3 . C=CH • COOC2H6.
Ethyl sodioacetoaoetate
The foregoing explanation of the condensation was proved to be correct in this instance by Claisen, who found that ethyl aceto- acetate cannot be prepared by the action of sodium on ethyl acetate which has been carefully purified from alcohol. The free ester, CH3«CO»CH2*COOC2H5, can be obtained by treatment of the sodium compound with acetic acid, since in the substitu- tion of sodium by hyarogen the group — C(OH):CH — is first formed, and subsequently transposed into — C0«CH2 — (131).
Ethyl acetoacetate is a colourless liquid, slightly soluble in water, and characterized by an agreeable odour: it boils at 181®, and has a specific gravity of 1-030 at 15®. It can be hydrolyaed in two ways, respectively known as the ketone decomposition (weak hydrolysis) and the add decomposition (strong hydrolys^is) , on account of the nature of the products.
The ketone decomposition is effected by heating ethyl aceto-
§ 232] ACETOACETIC'ESTER SYNTHESIS. 307
acetate with dilute sulphuric acid, or with a dilute aqueous solution of alkali, the products being acetone, carbon dioxide, and alcohol:
CH3 • CO • CH2 • + H
CO^
g2^5=CH3-CO.CH3+C02 + C2H50H.
The acid decomposition takes place when ethyl acetoacetate is heated with a ver}- concentrated solution of alcoholic potash or soda :
CH3.CO + 0H
CHz-COO H + H
C2H5
Q^""^ CHs-COOH+CHa-COOH+CaHfiOH,
The great importance of ethyl acetoacetate for S3aitheses arises from its capability of undergoing these two decompositions, together with the existence of a great many derivatives with one or two of the hydrogen atoms of the CH2-group replaced by substituents. Replacement of one or two hydrogen atoms by one or two groups R gives the compound
CH3-CO.CHR.COOC2H5 or CH3-CO-CR2-COOC2H5,
converted respectively by the ketone decomposition into the ketone
CH3-CO.CH2R or CH3.CO-CHR2,
a reaction affording a general method of synthesizing methyl- ketones (loi).
The acid decomposition converts the compounds
CH3-CO-CHR.COOC2H5 and CH3-CO-CR2-COOC2H5
into acetic acid and an acid with either the formula
CH2R-C00H or CHRa-COOH,
the reaction furnishing a general method for the synthesis of monobasic acids.
The mechanism of the formation of such derivatives of ethyl acetoacetate Involves interaction of sodium ethoxide and the ester to form a sodium compound, CH3-C(ONa):CH«COOC2H5 (235).
308 ORGANIC CHEMISTRY. [§ 233
Addition of an organic halide, R«X, in which X represents a halogen atom, gives the product
ONa H
CH3-C C.COOC2H6.
X R
EL'mination of NaX from this substance yields the compound CH3-CO.CHR.COOC2H5, the hydrogen atom of its CHR-group being capable of analogous replacement.
233. A few examples of this synthetical method are appended.
1. Methylnonylketone, the principal constituent of oil of me (from Rida graveolens), can be obtained by the action of n-octyl iodide upon ethyl sodioacetoacetate:
CH,-C(ONa) :CH»COOCH, CH,-CO-CH-COOC,H»
+ - -^ I
I — CgHn CsHiT
It yields, by the ketone decomposition, methylnonylketone^
CH, • CO -CHi -081117.
Ethyl n-octylacetoacetate yields, by the acid decomposition, capric acidi^CioHaoOs, which must therefore have a normal carbon chain
(137).
2. Heptylic acid, which is obtainable from laevulose by the cyano-
hydrin-sjrnthesis (209), can be synthetically built up from ethyl acetoacetate by the successive introduction of a methyl>group and a n-butyl-group: this proves it to be methyl-n-butylacetic acid:
CH,* C(ONa) :CH • COOCH, /COOCyai
+ -► CH,-CO-CH<' -♦
I — CiHj \!/4Ht
Ethyl n-buiylaoetoaeetata
CH,'C(ONa):C<p^^'^ /COOCH,
_» + ^«^ _» CH,'CO'<><;«H,
I— CH, \::h.
Ethyl nlHhyl-n-butyUoetoaoeiate
Ethyl methyl-fv-butylacetoacetate yields, by the add decompqmtion, methyl-41-butylacetic acid,
/COOH
X3H,
§ 2341 LjEVULIC ACID, 309
3. T-K^etonic acids are obtained by the action of ethyl aoetoaee- tate upon the esters of the o-halogen-substituted fatty acidSi followed by the ketone decomposition:
CH. • C(ONa) : CH • COOaH. yCOOCHi
+ -♦ CH.-CO-CH<
X — CHR-COOCH, X)HR-COOCiHi
This yields, by the ketone decomposition,
CH,-CO-CH,-CHR-COOH.
T p a
4. When iodine acts upon ethyl so4ioacetoacetate, two molecules unite thus:
CH..C(ONa):CH.COOCH. cH..C^^H.CX)OC.H.
2t - \l I
CH,-C(ONa):CH-COOCH, Ca-O^— CH-COOCA
Elimination of two molecules of sodium iodide converts this com- pound into diethyl diaceiyhuccinaiey
CH,-CO*CH CH-CO-CH,
I I
COOCH, COOCH,
When boiled with a 20 pef cent, solution of potassiimi carbonate, diethyl diacetylsuccinate loses carbon dioxide and alcohol, with formation of aceUmylacetane (200) :
CH, • CO • CH— CH • CO • CH,
|
|H |H |
||
|
CHtlOiC OH |
CO. |
CJI. OH |
CH,«CO'CH.'CH,'CO«CH^
AcetonyUoetone
icAcid, CH3-CO.CH2-CH2-COOH.
334. Lctwlic acid is the simplest ^^-ketom'c acid: it can be obtained by the synthetical method described in 233, 3 — from ethyl acetoacetate by the action of ethyl monochloroacetate; in this instancOi in the formula given R=H. When hexoses are
310 ORGANIC CHEMISTRY. ^ (§235
boiled with concentrated hydrochloric acid, lavulic acid is pro- duced (210): it is usually prepared by this method, which has not yet been fully explained.
Lsevulic acid is crystalline: it melts at 33* 5^, and bdils with slight decomposition at 250^. It yields an oxime and a hydrazone, and an addition-product with hydrocyanic acid: in short, it exhibits all the reactions characteristic of ketones.
Mesoxalic Acid, C3H205,H20.
Mesoxalic acid is a type of the dibasic ketonic acids. Its constitution is proved by the formation of ethyl mesoxalate when diethyl dibromomalonate, Br2C(COOC2H5)2, is boiled with baryta- water:
(C2H500C)2C|Br2-hBaJ (0H)2 = (C2H600C)2C(OH)2 + BaBra.
Mesoxalic acid is an important decomposition-product of uric acid. Like glyoxylic acid (230), it can only be obtained with one molecule of water. An ester of the anhydrous acid is, however, known: it very readily adds on water. The constitution (COOH)2C(OH)2 must therefore be assigned to the free acid (149) which has most of the properties of ketones, just as chloral hydrata (201) and glyoxylic acid show most of the reactions of aldehydes. When boiled with water, mesoxalic acid loses carbon dioxide^ forming glyoxylic acid ;
C02H.C(0H)a-C00H.
It is not surprising that a compound containing a carbon atom loaded with four negative groups should break down thus. The decomposition takes place more readily than that of malonic acid, which does not lose carbon dioxide till heated above its melting- point, to 140°- 150^.
TAUTOMERISM.
235. The conversion of ethyl acetoacetate into its sodium derivative, and the interaction of this substance with an alkyl iodide, yield derivatives in which the alkyl-group introduced is undoubtedly attached to a carbon atom (232). Sometimes the reaction proceeds differently, the metallic atom of the sodium derivative being replaced by a substituent which becomes linked
( 235] TA UTOMBRISM. 31 1
to the molecule through oxygen. An example is furnished by the interaction of ethyl sodiocetoacetate and ethyl chloroformate (263)1 two compounds being formed. The one produced in smaller proportion is the C-derivative :
ONa ONa
CHa.CiCH.COOCaHfi -► CHa-C — CH-COOCaH^-
CLCOOCaHft CI COOC2H5
COOC2H5
-=GH3.00.GH +Naa
C00C2H^
The identity of this product with that formed by the interaction of acetyl chloride and diethyl sodiomalonate proves its con- stitution :
CH3*CO[CHNa|>CH(COOC2H6)2 -► CH3-CO.CH(COOC2H5)2. The main product is an isomeride, the O-derivative:
CH3-C(0Na) :CH.C00C2H6 CH3-C:CH.COOC2H6
+ = I +Naa.
CI— COOC2H5 6 • COOC2H5
The presence of a double carbon bond in the molecule is proved by the instantaneous formation of an addition-product with bromine.
The mechanism of the interaction of ethyl chlorocarbonate and sodioacetylacetone is exactly analogous, the C-derivative being produced in small proportion:
CH3-C(ONa):CH-CO.CH3 CH3-CO.CH.CO.CH3
+ -> I .
CI— COOC2H5 COOC2 H5
The constitution of this compound follows from its ready decom- position into potassium acetate and ethyl acetoacetate by heating with an equimolecular proportion of potassium hydroxide:
H.
+ CHa-CQ.CH-
OK Cq-CH3=CH3-CO.CH2.COOC2H6+CH3.COOK.
■ Ethyl aoetoacetate Potaasium
COOC2H5 '"''*'
312
ORGANIC CHEMISTRY.
[(235
The 0-derivative, however, is the principal product:
CH3-C(0Na) iCH-CO-CHa CHa-CiCH.CO.CHj
+ = I +NaCL
CI— COOC2H5 O . COOC2H6
Its formula is proved by the ready formation of an addition- product with bromine, and its decomposition into acetylacetone, ethyl alcohol; and carbon dioxide by dilute alkalis at ordinary temperature:
CH3.C:CH.CO.CH3
=CH3-G(0H) :CH.CO.CH3+C2Hfi«OH+OQ2-
AoetyUoetone
The interaction of ethyl acetoacetate and acid chlorides can be completely controlled so as to produce either a C-derivative or an 0-derivative. If the usual method is employed, ethyl sodio- acetoacetate being first prepared, and then brought into con- tact with the acid chloride, a C-derivative is produced. But slow addition of the acid chloride to a solution of ethyl acetoacetate in pyridine (387) results in the exclusive formation of the O- derivative:
GH3--CO-CH.COOC2H6 CH3-C=CH.COOC2H6
I
lO-CHs
C-derivative (Gives DO addition-product with bromine)
i
CO-CHs
O-derivative (Gives an addition-produoi with bromine)
Similar equivocal reactions have been observed for many compounds with the grouping — CO • CH2 • CO — . It was formerly beheved that the production of a C-derivative was occasioned by direct linkage of the sodium atom to carbon, — CO«CHNa-CO — ^ and that of the O-derivative by direct union of the sodium atom with oxygen, — C(ONa) :CH-CO — . It was accordingly assumed that in compounds of this type there was continual alternation between the groupings — CO-CHz-CO— and — C(OH) rCH^CO— . The phenomenon received the name tatUomerism or desmotropy.
(236] TAUTOMERISM, 313
Although later investigation proved the metallic atom in the sodium compounds to be in union with oxygen, as will be shown subsequently, it has also demonstrated the liquid derivatives, such as ethyl acetoacetate, to be a mixture of two isomerides of the type indicated, each being very readily transformed into the isomeric compound. This view is based on direct isolation of the tautomeric forms.
Ethyl acetoacetate is the classic example of a tautomeric substance. By cooling it to a low temperature, Knorr isolated the ketonic form, CH3*CO*CH2*COOC2H6, in crystals melting at —39**. By the action of an equivalent quantity of anhydrous hydrogen chloride on a suspension of ethyl sodioacetoacetate in strongly cooled h'ght petroleum, followed by filtra* tion of the sodium chloride and evaporation of the solvent at a low temperature, Knorr isolated the endic form CH3-C(OH):CH-COOC2H5, a substance requiring for solidifica- tion the refrigerating action of liquid air. This separation proves the sodium derivative to have the enolic structure.
236. The ketonic form aQd the enolic form of a tautomeric substance admit of ready identification by both physical and
■
chemical means. The most important physical method is furnished by refraction, the presence of a double carbon bond in the enoh'c form, and its absence in the ketonic form, making the refraction of the enoUc compound higher than that of the ketonic compound (120). By the aid of this physical property, the proportion of the two isomerides present in a liquid mixture can be determined, provided the refraction of each component in the pure state is known.
Two main chemical methods of distinguishing the two forms are available :
1. Addition of a small proportion of ferric chloride to a dilute aqueous or alcoholic solution of an enolic compound produces a deep coloration, usually violet; but ketonic derivatives remain colourless.
2. The action of bromine in alcoholic solution, K. H. Meter having discovered that in this solution enolic compounds form addition-products with bromine instantaneously, but that ketonic compounds do not. The method has been appUed by him to determine the proportion of the enolic form present in a tauto- merie mixture.
314
ORGANIC CHEMISTRY.
IS 236
The introduction of alkyl-groups into diethyl malonate being also effected by means of the sodium derivative, it is reasonable to anticipate complete analogy between the mechanism of that reaction and that characteristic of ethyl acetoacetate. The bromine- reaction affords confirmation of the accuracy of this assumption, and indicates diethyl monosodiomalonate to have the tautomeric formula
/ONa C,BUOOC*CH:C<
Interaction of this substance and an alkyl halide first yields an addition-product of the formula
/ONa CHftOOC-CH-C^X
^ ^OCH.
X representing a halogen atom, and R an alkyl-radical. On elimi- nation of sodium halide from this compound, the diethyl alkylmalo- nate is produced.
These aids can be applied to the elucidation of the conditioiis governing the ketonization of an enolic compoundi and the inverse enolizoHon of a ketonic compound. The nature of the solvent is of primary importance. For ethyl acetoacetate in the liquid state the equilibrium between the two forms corresponds with a small percentage of the enolic derivative, and about 90 per cent, of the ketonic form. The subjoined table indicates the percentage of the enolic form of ethyl acetoacetate in various solvents at 18°, the amounts being determined by titration with bromine.
|
Solvent. |
Percentage of Enolic Form. |
Solyeni. |
Pereentace of Enolic Form. |
|
Methyl alcohol Ethyl alcohol |
6.9 12.0 15.3 0*4 |
Methyl alcohol (50 per cent.) |
1.5 |
|
Amyl alcohol |
Ether |
27.1 |
|
|
Water |
Carbon disulphide. . . . Hexane |
32*4 |
|
|
46*4 |
|||
For ethyl acetoacetate itself the temperature has little influence on the equilibrium, but the freshly distilled product contains about 20-25 per cent, of the enolic form, which becomes trans- formed slowly into the ketonic modification. There are other in-
§2371 TAUTOMERISM. 315
stances of rise of temperature causing displacement of the equi* librium towards the enolic side, although usually not to any great extent.
The velocity of translation of each form can be determined by starting with the pure modifications, and noting the proportion of each component present after the lapse of known intervals of time. The velocity-constant of the ketonization of ethyl aceto- acetate has been proved to be much greater than that of the enoli- zation. Different tautomeric compounds generally exhibit wide divergence in the velocity of transformation in either direction.
A qualitative demonstration of the transformation of the enolic form of ethyl acetoacetate into the ketonic modification can be made by addmg an equivalent amount of hydrochloric acid to a dilute aqueous solution of ethyl sodioacetoacetate. The enolic form separates m fine drops, its solubility in water at 0^ being about 0-5 per cent. Owing to transformation of the enolic form into the ketonic modification, the drops gradually dissolve, the solubility of the ketonic derivative in water at 0^ being about 11 per cent«
Enolic compounds dissolve instantly in caustic alkali; but ketonic compounds do not, their solution proceeding slowly as they change to the enoh'c form. On subsequent addition of acid, the enolic modification is first obtained, but not the ketonic component.
Tautomerism of Ozimes.
R 237. The structural formula, j^/> C=NOH, has been assigned
to the oximes (103). The action of hydroxylamine on aldehydes and ketones admits of another explanation, indicated in the scheme:
HO. yO
>C0+ >NH=H,0+>C<; I .
Experiments directed to proving which of these formulae is right, have shown that the oximes are tautomeric in the sense of the scheme
>C=NOH <=> >C
<1h-
316 ORGANIC CHEMISTRY. [§ 238
The following exemplifies the method. When acetoxime is treated * with methyl iodide, the methyl-group becomes linked to nitrogen, as is proved by reduction of the resulting compound to methyl- amine and acetone:
(CH,),(X^ I +2H- (CH,),CO+NH,.CH,. MCH,
But when sodium methoxide is added to a mixture of methyl iodide and the oxime — whereby the sodium derivative of the ketoxime is first formed — there results an isomeric substance convertible by hydrochloric acid into acetone and a compound, NHj^OCHi. Heat- ing with hydriodic acid transforms this body into hydroxylamine and methyl iodide, proving that its methyl-group is linked to oxygen.
PTRONE DERIVATIVES.
238. A number of compounds assumed to contain the group
CO
hc/Njh
Ah
are known: they are called jnprone derivatives, and some of them occur naturally.
An important pyrone derivative is dimethylpyrone:
vCH=C •CH3
do \) .
'\CH=C.CH3
It can be synthesized from ethyl copper-acetoacetate and carbonyl chloride (263):
CHs-CO CO.CH3 CH3.CO CO-CHs
J, I i I
HC— Cu— CH = CuCk +HC\ X!H
/ \ /\:!0/\
CaHsOOC + CI2 COOC2H5. C2H5OOC COOC2H5
CO
§2391 PYRONE DERIVATIVES. 317
On sapK)iiification with dilute sulphuric acid, two molecules of car- bon dioxide are simultaneously eliminated from the molecule, whereupon
CHa CO CX).CEa
HjCv vCMj
should result. The tautomeride,
HO OH
/^
CHa'C C'CHg
II II »
H.C C-H
\c/
O
however, is formed, and loses one molecule of water, yielding di- methylpyrone.
339. Dimethylpyrone is characterized by its ability to form addition-products with acids, which must be looked upon as salts. These " salts " are formed by dissolving dimethylpyrone in an aqueous solution of hydrochloric acid, oxalic acid, etc. : they are obtained in a crystalline form by the spontaneous evaporation of the solutions. By dissolving them in a large quantity of water, they are completely hydrolyzed. Collie and Tickle, the dis- coverers of these comp)ounds, assume the qiiadrivalency of the oxygen atom closing the carbon chain, thus attributing to dimethylpyrone hydrochloride the structure.
•CH=C -CHa
C.OH \).C1.
^CH— C.CH3
This mode of expressing the constitution of dimethylpyrone has been adopted instead of the earlier formula C0C4Hi(CHs)t> 0 <p|.
Yon Baeter having proved the addition-product of dimethylp3rrone with methyl iodide to have formula I., and not formula II., his proof being based on the conversion of the addition-product by the action of ammonia into methoxyltUidine (389), formulated in III.:
318 ORGANIC CHEMISTRY, [§ 239
|
CH, I |
||
|
\y |
||
|
O.I |
0 |
N |
|
CH,-G C-CH, |
CHi'C C'CH, |
CH,.C C-CH, |
|
H« Ah |
1 II HC CH |
HC CH |
|
\/ |
^ |
X/' |
|
C'OCH, |
C-OCH, |
|
|
I. |
II. |
ITT. |
These compounds have been named oxonium salts, on account of their analogy to the ammonium salts. They are to be regarded as true salts or electrolytes, because they possess all the properties characteristic of the salts formed by weak bases with strong acids: thus, their aqueous solutions are strongly acidic in reaction in consequence of extensive hydrolytic dissociation; their electric conductivities in solution are almost equal to those of the free acid ; and so on.
The power of forming oxonium salts does not seem to be hmited to dimethylpyrone and analogous compounds. Von Baeyer and ViLLiGER have shown that oxygen-containing compounds, belong- ing to various classes of organic bodies, such as alcohols, aldehydes, esters, and other substances, are able to yield crystalline com- pounds with complex acids, such as hydroferrocyanic acid. It is possible, though not fully established, that these are oxonium salts. They also attempted to obtain trimethyloxonium iodide, (CH3)30 • I, analogous to the tetra-alkylammonium salts, but were unsuccessful. They are of opinion that Grignard's compounds of alkyl magne- sium iodides and ether (75), such as CH3«Mg«I+(C2H6)20, must be regarded as oxonium derivatives,
U2-tt5 UXI3
The power of forming true salts by the addition of acids is especially developed in the alkyl-compounds of the elements of the nitrogen group. Examples also occur among the sulphur com- pounds (59). Carbon compounds of the type RaC-OH also exhibit basic properties, tertiary alipha ic alcohols reacting readily with hydrogen halides to form tertiary halogen derivatives.
f 239] PYRONE DERI V A TI VES, 319
The replacement of the hydroxyl-group by halogen is completely analogous to the production of salts by the interaction of bases and acids.
WiLLSTATTER proved the anthocyaninSf or colouring principles of many plants, to be oxonium salts (345).
AHmO-ACIDS.
340. The amiruHieids contain one or more amino-groups in direct union with carbon! They are of physiological impor- tance, since many are decomposition-products of proteins, and some are natural products. They are synthesized by several methods.
1. By the action of the halogen-substituted fatty acids on ammonia, a method analogous to the formation of amines:
H2N[H+C1JH2C.C00H> H2N.CH2-COOH+HC1.
2. By reduction of oximes with sodium amalgam: R.C(N0H).C00H-|-4H = R.CHNH2.COOH-I-H2O.
This is a method of converting ketonic acids into amino-acids.
3. a-Amino-acids are formed by the action of ammonia upon the cyanohydrins of aldehydes or ketones, and subsequent hydrol- ysis of the nitrile-group (Strecker):
H yH
CH3-C<^ -^CHa-C^OH; +NH8
Aoetaldehyde LaetonitrUe
-»CH3.C^NH2-^CH3.C^NHa . \CN MXX)H
Alanine ntthle Alanine
The araino-acids possess two opposite characters: they form salts with both bases and acids, and are therefore both basic and acidic simultaneously.
Replacement of the hydrogen of the amino-group by radicals yields amino-acids of a more complicated character. Thus, like
320
§ 241] AMINO'ACIDS. 321
ammonia, with acid chlorides they yield an acid amide with one hydrogen atom of the amino-group replaced:
R>COp+qHN^CHa-COOH - R-(X).NH.CHa.COOH+HCl.
Compounds of this kind are therefore both amino-acids and acid amides.
Amino-acids with the hydrogen of the amino-group replaced by alkyl-groups are also known. They are obtained by the action of amines, instead of ammonia, on the halogen-substituted acids:
(CH3)2NfHTci]HaC>COOH - (CH3)2N.CH2.COOH+HCl.
The amino-acids undergo most of the decompositions charac- teristic of amines; thus, with nitrous acid they yield hydroxy- acids, just as the amines yield alcohols.
.241. Like those of the halogen-substituted acids and hydroxy- acids (176 and 180), the properties of the amino-acids depend on the position of their characteristic group — the amino-group — relative to the carboxyl-group. The a-amino-acids readily yield anhydrides (acid amides) by the elimination of two mole- cules of water from two molecules of acid :
CH2>NH(in!0l0C . CH2NH-0C CO|OH H[HNCHa ^ CO HNCHa
The ^-amino-acids easily lose ammonia, with formation of unsaturated acids. Thus, )9-aminopropionic acid, obtained from ^iodopropionic acid, is converted by heat into acrylic acid and enmionia:
j?JH^-CH2>CHlg|>C00H - NHg+CHarCH.COOH.
Like the /--hydroxy-acids, the ^-amino-acids yiekl inner anhy- drides. On account of their similarity to the lactones, these sub- stances are called lactams:
CII2 • CH2 • CH2 • CO CIi2'CH2»Cii2*CO
I I -HaO+l
NH H OH NH
l-i
y-Amlnobiityrio acid Lactam of y-axninobutyrio acid
322 ORGANIC CHEMISTRY. [§242
Emil Fischer proved that the esters of amiruHicids can be obtained by the ordinary method, dissolving the acids in absolute alcohol and treating this solution with hydrochloric-acid gas (91). Hydrochlorides are the primary products, the amino-group in these esters retaining its basic character: an example is the ethyl ester of glycine hydrochloride , C2H600C-CH2-NH2-HC1. The esters ar» prepared by treating aqueous solutions of the hydrochlorides with concentrated potassium hydroxide at a low temperature, and im- mediately extracting with ether. Emil Fischer found these esters well adapted for the purification and separation of amino-acids. This is of great importance in the chemistry of proteins, which are resolved into a mixture of such acids by the action of acids or bases.
Individual Members.
242. Glycine (glycocoll or aminoacetic acid), NH2-CH2»CXX)H, can be obtained by boiling glue with dilute sulphuric acid or with barium hydroxide: it owes the name "glycocoll " to this method of formation, and to its sweet taste {y\vKvs, sweet; xoXXa, glue). It is also prepared from hippuric acid, a constituent of the urine of horses. Hippuric acid is glycine with one hydrogen atom of the amino-group replaced by benzoyl, CeHsCO; and it therefore has the formula C6H5-CO.NH.CH2-COOH. Like all acid amides, it is decomposed by boiling with dilute acids, with addition of the ele- ments of water:
CeHfiCO. NH.CH2-C00H = CeHs-COOH+NHa-CHg-COOH.
OH
pj Beniolo acid Glycine
Hippuric acid
A method well adapted for the preparation of glycine and its derivatives depends on the interaction of formaldehyde, ammonium chloride, and potassium cyanide in well-cooled aqueous solution. Methyleneaminoacetonitnlef CHt : N*CHi*CN, crystallises, being formed in accordance with the scheme
•OH yNH,
CH,0 + HON = CH/ ; + NH, -* GRtK i
/N : CH, + CH,0 -* CH,<
On boiling the nitrile with alcoholic hydrochloric acid, the CN-group is exchanged for — COOCaHfi, and the methylene-group of — N:CHj
§242] AMINO'ACIDS. 323'
replaced by Hs, with production of the hydrochloride of the ethyl ester of glycine:
/N : CH, /NH, + HCl y NH,,HC1
XJN x:;ooc,H* x:;ooc.H5
Glycine is a crystalline solid, and melts at 232^ with decom- position: it is very readily soluble in water, and insoluble in absolute alcohol. Like many amino-acids, it forms a well- crystallized, blue copper salt, soluble with diffitjulty in water, and obtained by boiling copper carbonate with a solution of glycine. This derivative crystallizes with one molecule of water of crystal- lization, and has the formula (NH2-CH2-COO)2Cu+H20.
Betdine, C5H11O2N, is a derivative of trimethylglycine: it is found in the juice of the sugar-beet, and accumulates in the molasses during the. manufacture of sugar. It is an inner ammo- nium salt^
(CH8)3N-CH2-(X)
k
H OH
since it is s}mthetically obtained from trimetbylamine by the action of monochloioacetic acid, with elimination of HCl:
(CH8)8N + Cl.CHa-COOH=(CH3)3N.CH2.CO
^ I 6
This reaction is analogous to the interaction of alkyl halides and tertiary amines to form the salts of quaternary ammonium bases
(63).
Betalne yields large crystals with one molecule of water, which it loses at 100®, or when allowed to stand over sulphuric acid. On heating it decomposes, with formation of trimetbylamine.
Many tertiary amines can be converted into substances with a constitution analogous to that of betaine; that is, inner salts of ammonium bases. These compounds are called betaines.
Alanine, or a-aminopropionic acid, CH3-CH(NH2)'COOH, is synthetically prepared by the action of ammonia on a-chloropropi- onic acid.
324 ORGANIC CHEMISTRY. [f
Leucine^ or cr-aminotsobutylacetic acid,
(CH3)2CH-CH2.CH(NH2)-COOH,
results along with glycine from the decomposition of proteins by the action of acids or alkalis, or by putrefaction. It is synthetic- ally obtained from tsovaleraldehyde-ammonia by the action of hydrocyanic acid, and hydrolysis of the resulting nitrile:
/H
(CH3)2CH.CH8.C^|OH +H]CN -♦
NH2
woValeralddiyde-ammonia
-♦ (CH8)2CH.CH2-CH(NH2)-COaH.
Leueine
isoLeudne, or a-amino-^-methylvaleric acid,
^^ >CH.CH(NH2)-C00H,
is also a decomposition-product of proteins. Its constitution is proved by synthesis. The aldehyde formed by oxidation of secondary butylcarbinol — the optically active amyl alcohol — yields by the method of 240, 3, an amino-acid identical with tsoleucine.
Fusel-oil is a by-product in the alcoholic fermentation (43). Erhlich has proved that it is not derived from the sugars, but from leucine and t^oleucine formed by decomposition of the proteins present in the fermenting liquid. These proteins arc con- stituents of the grain, potatoes, and other material employed in the manufacture of alcohol. When sugar is fermented with a pure yeast-culture in presence of leucine, isobutylcarbinol is formed as a by-product: with tsoleucine secondary butylcarbinol results. These two amyl alcohols, are the principal constituents of fusel-oil
(47).
The mechanism of the decomposition of amino-acids by yeast, or their alcoholic fermentation, is, in general, expressed by the equation
^•CH(NH,)-COOH+H,0 = R-CH,OH+CQ,+NH,. The leucine obtained from proteins is optically active: its for- mula contains an as}rmmetric carbon atom.
243. Asparagine is often present in sprouting seeds; to the ex- tent of 20-30 per cent, in dried lupine-seeds. It is aminosuccinamic
§ 2431 AMINO-ACIDS, 325
CLcid, C2H3(NH2) <coOH^' since on hydrolysis it is converted into aminosuccinic acid (dspartic acid), COOH •CH(NH -) •CH2 •COOH, the structure of which is inferred from its conversion into malic acid by treatment with nitrous acid. Asparagine prepared from seeds is sometimes dextro-rotatory, but generally l«vo-rotatory. The former is sweet, the latter tasteless.
Homologous with asparagine is glviamine or glutamic acid, a con- stituent of the seeds of sprouting plants. It is the amic acid (163) of o-aminoglutaric acid, C00H.CH(NH2) .CH2CH2-COOH.
In addition to the monoamino-acids, diamino-acids are also obtained by decomposing proteins with acids. Some of them merit description.
Lysine, C6H14O2N2, is decomposed by putrefaction-bacilli with formation of pentamethylenediamine (159): it has the formula
NH2-CH2'(CH2)3*CH<QQQ2, and is an ac-aminocaproic acid.
Emil Fischer has proved this formula by synthesis. On bring- ing ethyl monosodiomalonate into contact with 7-chlorobutyro- nitrile, ethyl y-cyanopropylmalonate m formed:
(C00GH,)2CHNa+a-CH,-CH,-CHa-CN -
Ethyl moDOflodiomalonate 7-ChlorobutyTonitrile
- (COOC.H,).CH . (CH,), • CN.
Etbyl y-cyanopropylmalonatc
IVeatment with ethyl nitrite and sodium ethoxide converts this ester by elimination of a carbethoxyl-group into the sodium salt of an oxime :
Oxime
Reduction of this oxime with sodium and alcohol converts the NOH- group into NH„ and the CN-group into CH2NH2, with formation of inactive lysine,
CHjNHj. (CHa)8.CH < ^J^j^.
Ornithine is the next lower homologue of lysine, and has the formula CjHijOjN, or NHa.CHj.CHj.CHj.CHCNH,) -COOH. Bao- teria convert it into putrcscine or tetramethylencdiamine (159)' Its structure is proved by Emil Fischer's synthesis (349)-
326 ORGANIC CHEMISTRY. [f 244
THE WALDBN INVERSION AND THE MODE OF LINKING OF
ATOMS.
344. When one group attached to an asymmetric carbon atom 13 replaced by another, it is impossible to predict the sign of the rotation of the new compoimd: sometimes it is the same as that of the original substance, and sometimes opposite to it. By a series of substitutions, Walden has transformed an optically active compound into its optical antipode. On treatment with moist silver oxide, 2-chlorosuccinic acid was converted into Z-malic acid, and this substance was transformed by means of phosphorus penta- chloride into <i-chlorosuccinnic acid On the other hand, starting from <f-chlorosuccinic acid, the same operation yielded ^hlorosuc- cinic acid. These transformations are indicated in the cyclic scheme
AgOH i-Chlorosuccinic acid ►i-Malic acid.
] ^' AgOH 1 ^
i^Malic acidi d-Chlorosuccinic acid.
The following is another reaction-^ycle, worked out by Eiol
Fischer:
NOBr d-Alanine >i-Bromopropionic acid.
I^H. NOBr INH.
cI-Bromopropionic acid* ^Alanine.
Here the transposition probably took place during the replacement of the amino-group by bromine under the influence of nitrosyl bromide, and not by the action of ammonia, since, with widely different experimental conditions, the same product with a similar sign of rotation always resulted in the latter operation. Although d-alanine reacted with nitrosyl bromide to form Z-bromopropionic acid, its ester under identical conditions yielded d-bromopro- pionic acid.
Senter has discovered many other examples cf the Walden inversion, and demonstrated the complex nature of the phenomenon.
The conversion of an optically active compound into its optic&l isomeride necessitates an interchange of position between two of the groups or atoms linked to the as3anmetric carbon atom. In Fig. 70,'the transformation of I. into II. only requires B and D, for example, to exchange positions. An experimental demonstra-
1244] THB WALDEN INVERSION. 327
a
I. II.
Pig. 70. — Conversion of an Optically Actiye Subbtancb into itb Optical
IsOlfSRIDB.
tion of this fact has been attained by the series of changes indi- cated in the scheme
H^ X^OOH ~* H^ X^OOCHs ^
C3H7V yCOOH C3H7V yCOOH
H/\C00CH3~* h/^\C0NH2'
Although there was no change of position^ the group CONH2 was transformed mto COOH, and COOH into CONH2. The rotation of the initial product proved to be opposite in sign to that of the final product.
In Walden's inversion or in a racemisation there must be a true exchange of position between two groups. In accordance with the views ot atomic Unking hitherto accepted, this process could only be possible through a momentary severance of the two groups from the asynunetric carbon atom, followed by a reunion at the reverse positions. The transformation of maleic acid into fumaric acid and its reversal (171) would also involve either a momentary rupture of the double bond, followed by reunion of the residues at the reverse positions; or an exchange of posi- tion between H and COOH would be necessary.
There is one very important objection to the acceptance of this view. Almost all reactions of this t3n[)e are quantitative, a result not to be anticipated in a process involving the molecular disintegration attendant on the scission of two groups from one carbon atom. (,
\
328 ORGANIC CHEMISTRY. [§ 244
•
The modem view of atomic structm^ has eliminated this difSculty. It assmnes the atoms to consist of an eleetroposi- tively charged sphere and negatively charged electrons, the dimensions of the electrons being very small in comparison with those of the sphere. Stark postulates the presence of a number of electrons within the sphere, and also assumes a number equal to the valency of the atom to be situated on the surface of the sphere. For the carbon atom this niunber is four. He has suggested the name " Valency-electrons " for those on the surface. In the union of two carbon atoms by a single bond, Stabk regards one electron of each carbon atom to be involved, the lines of force of each being partially directed towards the positively
charged sphere of the other carbon atom, as indicated in Fig. 71.
The theory thus outlined does not demand a rupture of the linkings during an exchange of position by two
Fig. 71.— Single Linking between Two groups, but only requires a Carbon Atoms. simple transposition on the
surface of the sphere of the valency-electrons and the attached atoms. It affords an explanation of the quantitative nature both of racemisation and of the conversion of a doubly-linked cis-form into the correspond- ing frarw-modification.
This hypothesis also serves to explain the Walden inversion. The mteraction of d-bromopropionic acid (I.) and silver hydroxide can follow two different courses. One of them involves direct action on the bromine atom, and its replacement by the hydroxyl- group. The lactic acid thus formed has the same configuration as the bromopropionic acid, and there has been no mveroion. Substitution of bromine for the hydroxyl-group by the aid of phosphorus pentabromide or another reagent regenerates the original acid.
In the other type of reaction, the molecule of silver hydroxide attacks that of the bromopropionic acid as indicated in I., the valency-electron of the silver atom penetrating between CH3, H, and COOH. After fission of the silver bromide, the repul-
§ 2451 ETHYL DIAZOACETATE. 329
sion exerted by the valency-electron of the hydroxyl-group on the valency-electrons of the other three groups compels them to assume the positions indicated in II. On replacing the hydroxyl- group by bromine by the aid of phosphorus penta-bromide or another reagent, a substance of formula III. is obtained. It is the optical antipode of I., as can be proved by rotating III. through 180®, the resulting configuration being represented by IV. In this instance a Walden inversion has taken place.
H P'
;00H CH^sX/^COOH
CH^^ "^COOH I T COOH-^y^H,
Br H
II. III. IV.
Stabk's hypothesis also indicates a tetrahedral grouping round the carbon atom. Since the electrons repel one another, but are also attracted to the sphere by its positive charge, they take up positions as far apart as possible on the spherical surface. Location of the electrons at the angles of a regular tetrahedron with its centre coincident with that of the sphere fulfils this condition.
The strain-theory of von Baeyer (120) is also in accord with Stark's hypothesis. When the valency-electrons are forced into closer contiguity, their mutual repulsion operates in an endeavour to restore them to their original positions.
ETH7L DIAZOACETATE.
245. CuRTius has obtained a yellow oil of characteristic odour by the action of nitrous acid on the ethyl ester of glycine: this substance has the formula C4H6O2N2, and explodes when heated. The method of its formation is indicated in the following equation:
C2H5OOC . CH2 • NH2 + HNO2 = C2H5OOC . ch/ I
Glycine ethyl e«ter NJy
N + 2H2O.
It is eihyl diazoacetatej and is also called diazoacetic ester.
The structural formula indicated is proved by numerous trans- formations: they can be classified in three divisions.
I. The first group includes the reactions involving the elimina-
330 ORGANIC CHEMISTRY. (§ 245
tion of the diaso-nitrogen. As an example may be cited the conversioii of ethyl diazoacetate into ethyl glycollate by treat- ment with dilute acids:
G2H6OOC.CH
/
\
N
I
N
H M
+6h-C2H500c.ch< +n,.
X)H
Bredig discovered that this reaction is greatly accelerated by the catalytic agency of hydrogen ions, and on this observation he has based one of the best methods for the detection and quan- titative estimation of such ions.
Concentrated hydrochloric acid yields analogously ethyl monochloroacetate; and iodine ethyl di-iodoacetate. Organic acids produce acidylgly collie acid esters:
? K H
CHs-COOH- |^H.COOC2H6=(.jj^^(.QQ>CH-COOC2H5+N2.
Near its boiling-point ethyl diazoacetate loses all its nitrogen, with formation of ethyl fumarate:
CH.COOC2H6 2N2CH . COOC2H5 = 2N2 + 1 1
CH.COOC2H5
II. In the second group of reactions the nitrogen is not evolved as gas, but one of the bonds between the diazo-group and carbon is severed, with formation of pyrazole-derivatives (399).
III. The third group comprises addition-reactions involving the transformation of the double bond between the nitrogen atoms into a single bond. An example is the addition of hydrogen to form hydrazinoacetic add, a compound decomposed by acids at the ordinary temperature into glyoxylic acid and a hydrazine salt:
NHv I >CH . COOH + H2SO4 + H2O = N2H4 . H2SO4 + CHO • COOH.
Hydraanoaoetic acid Hydraiine Glyozylie add
sulphate
The hydrogen atom of the CHN2-group is replaceable by metals, sodium dissolving in ethyl diazoacetate with evolution of hydrogen.
proteIns.
246. Proteins are compounds of great importance in the animal and vegetable kingdoms, but of such complex structure that their chemical investigation is a matter of extreme difficulty. Their great physiological importance is made apparent by the fact that the dry material in animal bodies — apart from the mineral constituents and fats — consists almost wholly of pro- teins, by their being an essential constituent of each living plant-cell, and by their forming the most important part of human and animal food. An animal can exist without ^fats f ' and carbohydrates for a protracted period, but its death is assured by the withdrawal of proteins from its nourishment.
The investigation of the proteins is rendered difficult not only by their complex structure, but also by the fact that, with few exceptions, they do not crystallize, and cannot be distilled without undergoing decomposition, so that advantage cannot be taken of these valuable aids in the isolation of individual substances. Moreover, many proteins change very readily into other sub- stances, and the distinctions between the different varieties are sometimes by no means well defined.
A number of groups of nitrogenous compounds are classed as proteins. Since they sometimes exhibit great differences in physical and chemical behaviour, it is necessary first to state the general properties characteristic of them. They contain only five elements, and do not differ much from one another in com- position, as the table indicates.
Carbon 50-55 per cent.
Hydrogen 6-5-7-3 "
Nitrogen 15-17-6 "
Oxygen 19-24 **
Sulphur 03-5 ''
Those of one variety, called phospho-proteina, also contain phos- phorus.
331
332 ORGANIC CHEMISTRY, [§247
The solutions of all proteins are optically active and laevo- rotatory. The proteins are colloids (" Inorganic Chemistry," 196) ; they are, therefore, unable to diffuse through parchment-paper. Advantage is often taken of this property in separating them from salts and other crystalloids {loc. dt.). Some of them have been obtained crystalline, among them serum-albumin: most of them are white, amorphous powders without definite melting-points. On heating, they carbonize, with evolution of gases.
Many, but not all proteins can be " salted out " from solution. This " salting-out " is an important aid in identifying and separat- ing the different varieties: usually common salt or magnesium sulphate is employed. It is remarkable that all proteins can be completely salted out from their solutions in both neutral and acid liquids by saturation with ammonium sulphate. The albumins can be fractionally precipitated from aqueous solutions by gradu- ally increasing the concentration of the ammonium-sulphate solu- tion. The point of concentration at which a salt begins to pre- cipitate a protein is just as characteristic for the latter as, for example, the solubility is for a crystalline substance. When the salting-out is effected at ordinary temperatures, it causes no change in the properties of the proteins: their solubilities after the opera- tion are the same as before it.
247. Addition of alcohol precipitates proteins unchanged from aqueous solution: strong alcohol coagulates them, as also does boil- ing with water. For each albumin there is a definite coagulation- point: in other words, each albumin coagulates at a definite temperature. On coagulation, the differences in solubility between the proteins vanish: all are rendered insoluble in neutral solvents, and can be brought into solution again only by treatment with dilute caustic alkalis or with mineral acids. A solution, which behaves exactly like the solutions thus obtained, can be prepared by boiling uncoagulated albumins with a large excess of acetic acid or caustic alkali.
In this process the albumins undergo a change called denatura- tion. They cease to be coagulable by heat, but their composition remains unaltered. The products are called m^eta-proteins. When the hydrolysis was' effected with alkali, the product was formerly termed an albuminate or alkali-albumin, when an acid was em- ployed, a syntonin or acid-albumin. The meta-protelns are
§ 2481 PROTEINS. 333
insoluble in water, but soluble in dilute acids and alkalis. They are precipitated by neutralizing their solutions.
The proteins are precipitated from solution by various sub- stances, either by coagulation or by the formation of compounds insoluble in water. Coagulation is effected by the addition of mineral acids, preferably nitric acid.
The formation of compounds insoluble in water results on addition of salts of most of the heavy metals, especially copper sulphate, ferric chloride, and an acidified solution of mercuric chloride. The proteins, therefore, behave like weak acids, which with the oxides of these metals yield compounds of the nature of salts.
Some weak acids yield insoluble compounds with the proteins, which, therefore, also behave as bases: in this respect they ex- hibit complete analogy to their main decomposition-products, the amino-acids. Among these weak acids are tannic acid, picric add. phosphotungstic acid, and others. The proteins are completely precipitated from solution by phosphotungstic acid : this method, in addition to coagulation by boiling, and precipitation by alcohol, is employed to separate dissolved proteins from solution.
Various tests for proteins are known, among them the following:
1. MiUon's reagen'f a solution of mercuric nitrate containing nitrous acid, yields a red, coagulated mass on boiUng.
2. The xarvthoproteiU'Teaciicm consists in the formation of a yellow coloration on treatment with warm nitric acid.
3. The hiurct-rcaciion depends upon the formation of a fine red to violet coloration when potassium hydroxide is added to a protein, and then a 2 per cent, solution of copper sulphate drop by drop. This reaction derives its name from the fact that biuret, on similar treatment, gives the same coloration (267).
4. Addition of 1 drop of formaldehyde to a solution of 5 drops of egg-albumin in 3 c.c. of concentrated sulphuric acid produpes a yellow coloration, changed to violet by addition of 1 drop of a solu- tion of a nitrite. The reaction is due to the presence of tryptophan.
Nomenclature.
248. The Chemical Society of London, the English Phys- ioiX)GiCAL Society, the American Physiological Society, and the American Society of Biological Chemists have adopted the following system of nomenclature for the proteins.
334 ORGANIC CHEMISTRY. [§248
1. Protamines. — They are the simplest members of the group. Examples are salmine and aturine, isolated from fish- sperm.
2. Histones. — ^They are more complex than the protamines, but probably each class gradually merges into the other. They are exemplified by the histones separated by Kossel from blood- corpuscles. Precipitability by ammonia is one of their distin- guishing features.
3. Albumins. — Egg-albumin, serumrolbumin, and lactHjIbumin are typical examples.
4. Globulins. — ^They differ from the albumins in solubility. They are more readily salted out from solution than the albumins. Examples are serunirglobtdinf fibrinogen, and such globulin- derivatives as fibrin and myosin.*
5. Glutelins. — ^Alkali-soluble proteins of vegetable origin. They are closely related to the globulins.
6. Gliadins. — Alcohol-soluble proteins found in the vegetable kingdom. The principal member of the group is gliadin, and Rosenheim has suggested that the class to which it belongs should be designated by its name.
7. Phospho-protelns. — Examples are vitdlin, caselnogen (the principal protein of milk), and casein (obtained from caseinogen by the action of rennet).t
8. Sclero-proteIns.t — ^This class includes such substances as gelatin, chondrin, elastin, and keratin. The prefix indicates the
* The carbohydrate-radical eeparable in small quantities from many mem- bars of Classes 3 and 4 is probably not to be considered as a "prosthetic group''; as it is in the glucoprotelns (9, c). The term myosin is restricted to the final product formed during rigor mortia. Von FtJRTH's "soluble myogen-fibrin '' should be called soluble myosin. The two chief protelzia of the muscle-plasma are termed paramyosinogen and myosinogen,
t The prefix ** nucleo-" frequently used in relation to this class is incorrect and misleading. The American Societies include this group with the oonju* gated proteins (9). Since the phosphorus-containing radical is not eliminated from the phospho-protelns like a true prosthetic group, and their cleavage- products contain phosphorus, the English Societies prefer the arrangement indicated.
t This term replaces the word "albuminoid "in the limited sense in whieb most physiologists have employed it, but the American Societies retain the old name.
S 2481 PROTEINS. 335
skeletal origin of its members^ and the insolubility of many of them.
9. Conjugated Proteins.'*' — ^They are substances in which the protein molecule is united to a prosthetic group. The principal subdivisions are
a. NucLEo-PROTEiNS. — An example is guanylic add, isolated from the pancreas, liver, spleen, and mammary gland. 6. CHROMo-PROTEiNS.t — HoBmoglobin is a type. c. GLUCO-PROTEiNS. — ^They are exemplified by the mucins.
10. Proteln-derivativcs.J — ^They comprise the products of protein-hydrolysis, and are classed in four divisions.
a. Meta-proteIns. — ^This group includes the substances formerly classed as " albuminates " or " alkali-albumins," and " syntonins " or " acid-albumins," obtained by the action of an alkali or an acid respectively on albumins and globulins. The name meta-proteins is preferable because (1) they are derived from globulins as well as albumins, and (2) the termination ate implies a salt.
b. Proteoses. — They include such substances as albitmose, globulose, and gelatose.
c. Peptones. — Further products of hydrolysis which resemble the proteins in answering the biiu'et-test, but, unlike them, cannot be salted out from solution.
d. Polypeptides. — Products of cleavage beyond the peptone stage containing two or more amino-acid-residues. Most of them are synthetical substances, but some of them have been separated
* The American Societies add "lecitho-protelns" to this class, but their English amfrbres object on account of the uncertainty as to whether these substances are mechanical mixtures, adsorption-compounds, or true chemical combinations.
t The American Societies employ the term "Hnmoglobins" for chromo- pxotelus.
X The American Societies include two additional classes in this group: ^'pioteans," insoluble products apparently resulting from the incipient action of water, very dilute acids, or enzymes; and "coagulated proteins," formed by the action of heat or of alcohol. They are of an ill-defined nature, and the English Societies consider that it is better not to single out for special mention a few of the infinite varieties of insoluble modifications exhibited by prottibis.
336 ORGANIC CHEMISTRY. (§249
from the products of protein-hydrolysis. Most of those hitherto prepared do not answer the biuret-test.
249« Particulars of some of the classes named are appended.
The albumins are the best known and most readily obtained of the proteins: all form well-defined crystals, and they are therefore probably among the few proteins known to be individual chemical compounds; although it has not been proved that these crystals are not mixed crystals containing two or more analogous individuals. They dissolve in water.
Their neutral solutions cannot be salted out with sodium chloride, magnesium sulphate, or a semi-saturated solution of ammonium sulphate — a method of separating them from the globulins, which always occur along with them.
The globulins are further distinguished from the albumins by being insoluble in water, although they dissolve in dilute, neutral salt solutions, and in solutions of alkali-metal carbonates. At 30° they can be completely salted out by magnesium sulphate, and partly by sodium chloride. They have not been obtained crystal- line.
The phospho-proteins contain phosphorus, and have a distinctly acidic character. All of them turn blue litmus red, and in the free state they are only slightly soluble in water, though their alkali-metal salts and ammonium salts are freely soluble. The solutions of their salts do not coagulate, and can be boiled without undergoing any change.
The sclero-proteins differ somewhat in character from the albumins. They occur in the animal economy only in the undis- solved state, being the organic constituents of the skeleton and the epidermis. They include various substances, such as keratinj elastin, gelatin, collagen, and chondrin.
Keratin is the principal constituent of the epidermis, hair, nails, hoofs, and feathers. It is particularly rich in sulphur, of which it contains between four and five per cent. Its decomposition- products resemble those of the albumins. With nitric acid it gives the xanthoprotein-reaction, the origin of the yellow colour developed when nitric acid comes into contact with the skin.
Elastin is the substance constituting the fibres of connective tissue. Its decomposition-products have the same qualitative
S 250] PROTEINS. 337
composition as those obtained from the albumins. It is insol- uble in dilute acids and caustic alkalis.
The coUagens are the principal sclero-proteins of the animal body, and the main constituent of connective tissue, such as bone and white fibrous tissue. In several respects they differ from the albumins: they contain 17 '9 per cent, of nitrogen; they have not an aromatic nucleus; on hydrolysis, they do not yield tyrosine (352), their chief decomposition-product being glycine, which is accompanied by leucine, aspartic acid, and glutamic acid.
When boiled with water, the collagens are transformed into gelatin. This substance is not precipitated from solution by nitric acid or other mineral acids, but it is precipitated by mercuric chloride in presence of hydrochloric acid and by tan- nic acid.
Chondrin is obtained by extracting cartilage with boiling water, the solution gelatinating as it cools. Acetic acid precipitates chondrin from solution. When boiled with dilute acids, chondrin yields a decomposition-product, chondrosin, which reduces Feh- ling's solution. Chondrin is a derivative of gelatin and chon- droitinsulphuric acid.
In the inferior orders of animal life a series of substances has been discovered approximating more or less closely in chemical properties to the collagens and to elastin. Among them is spongin, the principal constituent of sponges, which is much more stable towards caustic soda and baryta-water than collagen. When completely hydrolyzed by boiling with dilute sulphuric acid, it yields leucine and glycine, but no tyrosine, proving it to be a collagen.
On prolonged boiling with water, silk is converted into fibroin, which is not decomposed by water even at 200°, and sericin, or silk-gum,
Comein is the organic constituent of coral. On hydrolysis, it yields leucine and an aromatic substance of unknown com- pK)sition.
250. Nearly related to the albumins are the coujugated proteins, compounds of proteins with other substances, usually of a very complex nature. Like the albumins, they are insoluble in alcohol, by which most of them are coagulated.
338 ORGANIC CHEMISTRY. [§ 260
NtLcleo-proteins derive their name from the fact that they the principal constituents of the cell-nuclei. They are com- binations of proteins with phosphoric acid or nudelc adds (Nucleus, important part of the cells of animals or plants). A nucleic acid is phosphoric acid which is partially saturated by imion with basic substances; such as hypoxanthine, guanine, xanthine, etc. The composition of the nucleo-proteins differs considerably from that of the albumins: they contain about 41 per cent, of carbon, 31 per cent, of oxygen, and 5*7 per cent, of phosphorus.
The nucleo-proteins have a markedly acidic character: they are soluble in water and very soluble in caustic alkalis. They answer to the protein colour-tests.
Chromo-proteins are compounds of proteins with substances containing iron, JuBmoglobin being the dye of red blood-corpuscles. It decomposes into globin and hcematin. In the lungs it unites readily with the oxygen of respired air, yielding oxyhcemoglobin. This substance readily gives up its oxygen, and thus the oxidation- processes which maintain the heat of the animal body are carried on. It unites with carbon monoxide to form carbonyl-hoemoglobin, which is unable to combine with oxygen: on this reaction depends the poisonous nature of carbon monoxide.
On treatment with acetic acid and sodium chloride, oxyhsemo- globin yields the hydrochloride of haematin, called hosmin, which crystallizes in characteristic, microscopic plates of a brown-red colour. The reaction furnishes a delicate test for blood.
Gluco-proteins are compounds of proteins and carbohydrates. They include the mucins, which, like the nucleo-proteins, are acidic in character. They are insoluble in water, but soluble in a small quantity of lime-water or alkali solution. The liquid thus obtained is neutral, has a glutinous appearance, and is not coagu- Jated by boiling. Unlike the solutions of the albumins, these solutions are not precipitated by nitric acid. When boiled with acids or caustic alkalis, they yield either syntonins or peptones, together with carbohydrates. The presence of the nitrogen-free carbohydrates makes the percentage-amount of nitrogen in the mucins considerably less than in the albumins: its value lies between 11 • 7 and 12.3 per cent.
Meta-proteins are mentioned in 247.
§2511 PROTEINS. 339
Proteoses and peptones can be obtained from all proteins by suitable hydrolysis. They have the protein-character, being insoluble in alcohol, and answering the xanthoprotein-test and biuret-test (247, 2 and 3). They are produced during digestion by the action of gastric juice on proteins, and are to be regarded as intermediate products in the hydrolysis of proteins, the pro- teoses being nearer the proteins, and the peptones nearer the amino-acids.
The Structure of the Protem Molecule.
251. During last century experimental evidence of the complex structure of the protein molecule was accumulated, an important point being the great number of substances formed by the decom- position of albumin. On dry distillation it yields a black oil containing many nitrogen bases; hydrocyanic acid, sulphuretted hydrogen, carbon dioxide, water, benzene, and its homologues, and numerous other bodies being also formed. Both putrefaction and fusion with potassium hydroxide yield ammonia, sulphuretted hydrogen, volatile fatty acids such as butyric acid and valeric acid, amino-acids like leucine and tyrosine, scatole, ptomaines, 2><jresol, and other products. By oxidation with various agents it has been possible to isolate hydrocyanic acid, nitriles, benzoic acid, numerous volatile fatty acids, and other substances.
New products have resulted from each fresh mode of attack, but the analytical methods employed have not shed any light on the structure of the protein molecule, since they yield chiefly amorphous and ill-defined substances. The first important step towards the solution of the problem was made by Schutzex- BERGER when he obtained only crystalline derivatives by heating proteins with bartya-water in an autoclave at 200® for several hours. After removal of the barium, the weight of the decom- position-products formed exceeded that of the initial proteins, proving that the baryta-water had effected addition of the elements of water, thus hydrolyzing the proteins to crystalline derivatives.
It was impossible to effect complete separation of the very complex mixture thus obtained, but some of the less soluble con- stituents, such as leucine and tyrosine, were isolated. The
340 ORGANIC CHEMISTRY, [§ 252
presence in the reaction-product of a number of amino-acids was proved by its properties and the results of analysis. Schutzen- berger's brilliant research was rendered more difficult by the necessity of making several hundred analyses. The most import- ant conclusion to be drawn from it is^ that the amino-acids con- stitute the foundation-stones of the proteins, just as the monoses are the basis of the polyoses (225). The fission-products obtained by earlier experimenters were formed by decomposition of the amino-acids.
252. ScHUTZENBERGER did not succccd in separating the various amino-acids from the mixture obtained by his method of fractional crystallization, but the identification of the various amino-acids derivable from the individual proteins would be insufficient for a complete comprehension of the structure of the protein molecule: the proportion of each acid must also be deter- mined by separation of the complex mixture into its individual constituents. By esterification of the amino-acids (241) and fractional distillation in vacuo of the mixture of esters, Emil Fischer succeeded not only in isolating the principal constituents, but also in attaining an approximate insight into their relative proportions in the different proteins. His classical researches have enabled the products of protein-hydrolysis to be classified in six divisions.
1. Monobasic monoamino-acids. — Glycine, alanine, a-amino- valeric acid, leucine (242), and phenylalanine,
CgHs • CH2 • CHNH2 • COOH.
2. Dibasic monoamino-acids. — Aspartic acid and glutamic acid or aminoglutaric acid.
3. Diamino-acids. — Ornithine and lysine (243). In the same category may be included argininc, obtained by addition of cyan- amide to ornithine (270).
4. Hydrozyamino-acids. — ^Tyrosine (352) has been known for a long time. Of more recent date is serine^ CH20H- CHXH2- COOH, which is S3mthesized from glycollaldehyde :
CH2OH . C Q -h HCN -^ CH2OH • CH^g ;
+ NH3-^CH20H.CHXH2-COOH (240, 3).
This synthesis indicates the constitution of serine, and further confirmation is afforded by its reduction to a-alanine.
S 2521 PROTEINS. 341
To this class also belongs the complicated diaminoirihydrox^ dodecanic acid, C12H26O5N2, a decomposition-product of casern.
5. Compounds with a closed chain containing nitrogen. — a-Tetrahydropyrrolecarboxyltc add or proline , and hydroxytetra- hydropyrrolecarboxylic acid or hydroxy proline, are examples of such derivatives. Tryptophan (403), C11H12O2N2, contains a similar chain: probably scatole (403) which causes the character- istic odour of human fseces, is derived from this fission-product of proteins. Tryptophan is characterized by the formation of a violet coloration or precipitate on addition of bromine-water.
NH-CHv Histidine, I >C.CH2-CH(NH2)-COOH, in its Isevo-modifi-
cation is a degradation-product of almost all albumins. Its racemic form lias been S3mthesized, and resolved into its optical isomerides.
6. Compounds containing sulphur. — ^The only representative of this class is cystine, C6H12O4N2S2, which as early as the begin- ning of last century was identified by Wollaston as the principal constituent of certain gall-stones. It has the formula
COOH . CHNH2 . CH2S— SCH2 • CHNH2 . COOH.
On reduction it is converted into cysteine, COOH •*CHNH2 -0112811, from which atmospheric oxidation regenerates cystine.
The constitution of cystine is proved by its formation from the benzoyl ester of serine (in which the benzoyl-group is attached to nitrogen): fusion with phosphorus pentasulphide converts the CH20H-group in this ester into a CH2SH-group. On elimination of benzoyl, cysteine is obtained.
Emil Fischer has found that the hydrolysis of proteins can be more readily effected by boiling with concentrated hydro- chloric acid, or sulphuric acid of 25 per cent, strength, than by Schutzenberger's baryta-water method.
Emil Fischer's ester-method has rendered possible the approximate quantitative estimation of the products of protein- hydrolysis. In the following brief summary of the results ob- tained it should be noted that usually not more, and often less, than 70 per cent, of the protein is recovered in the form of definite compounds, there being a considerable residue which cannot be identified on account of experimental difficulties.
342
ORGANIC CHEMISTRY.
[|253
On decomposition, some proteins yield almost exclusively a single amino-acid. Examples of such relatively simple proteins are salmine and clupeLne, isolated by Kossbl from the testicles of the salmon and herring respectively. On hydrolysis the first yields 84-3 per cent, of arginine, and the second 82-2 per cent.
Usually, however, the proteins yield a series of amino-acids, th^ proportions of the individual constituents varying between wide limits. In most proteins leucine (242) is the principal con- stituent, as in haemoglobin (250), keratin, and elastin (249). It is only in fibroin and in gelatin (249) that glycine predomi- nates. Of the dibasic amino-acids, aspartic acid (243) is generally present in small proportion. Casein (248, 7) contains a relatively large amount of glutamic add. Tyrosine is the principal decom- position-product of fibroin: alanine and glycine are formed in smaller proportions. Cystine is an important constituent of keratin: from cow-hair as much as 8 per cent, of it has been obtained, and, on hydrolysis, human hair also yields a large proportion.
The table summarizes the percentage-composition of a few proteins with respect to certain constituents.
Glycine ,
Alanine. ....
Leucine
Aspartic acid . Glutamic acid
Arginine
Histidine
Tyrosine. ...
Proline
Cystine
|
Hnmo- globin. 0 |
Casein. |
GMatio. |
Keraun (from hair) |
|
0 |
16-6 |
4.7 |
|
|
4 |
0.9 |
0*8 |
|
|
27-8 |
10-6 |
2-1 |
7-1 |
|
4-3 |
1-2 |
0-6 |
|
|
1.7 |
10-7 |
0-9 |
3-7 |
|
5*2 |
4-8 |
7.6 |
|
|
10-6 |
2-6 |
0-4 |
|
|
1-3 |
4-5 |
3-2 |
|
|
23 |
3-2 |
5-2 |
3-4 |
|
0-3 |
0-1 |
8 |
Fibroin
High 21 1-6
1
10
253. Having elucidated the basis of the protein molecule, Emil Fischer applied himself to the solution of the greatest problem of organic chemistry — ^the synthesis of the proteins. It has long been thought that the amino-acids of the protein molecule are linked by their amino-groups, as in glyq/lglycine,
NH2 . CH2 . CO— NH . CH2 . COOH,
§2531 PROTEINS. 343
in which the amino-group of one molecule of glycine has become united with the carboxyl-group of another molecule, as in the formation of acid amides. This hypothesis was confirmed by the researches of Emil Fischer. He succeeded, by employing a number of synthetic methods, in uniting various amino-acid- residues, and named the resulting compounds polypeptides. They display great analogy to the natural peptones (248, 10, c). Their synthesis proves that they have the structure indicated.
It is not possible to give here a detailed description of these synthetic methods, but a brief review will not be out of place. On heating, the esters of amino-acids are converted into anhydrides, with elimination of two molecules of alcohol, the reaction some- times taking place even at ordinary temperatures:
2NH,.CH,.C00C,H, - 2C,H,0H+NH <cHl^a)^ ^^'
Qlydne ethyl ester Diketopiperasine
(Glycine anhydride)
Under the influence of dilute caustic potash, this anhydride takes up one molecule of water, yielding a dipeptidej glycylglycine:
NH<^^~^^»>NH + H,0 - NH,.CH,.CO--NH.CH,.COOH.
Glycylglycine
When a dipeptide is treated with phosphonis pentachloride in acetyl.chloride solution, the carboxyl-group is changed to COCl, and the residue of this acid chloride can be introduced into other amino-acids :
NH, . CH, . CO—NH . CH, . COQ 4- H,N . CH, . COOC,H, - - NH, . CH, . CO—NH . CH, . CO—NH . CH, . COOC,H, -h HQ.
Saponification of this substance yields a tripepiide, and so on.
The polypetides, especially from the tetrapeptides to the octapeptides, are very like the natural peptones, as a short sum- mary of the characteristics of both classes will indicate. Most of them are soluble in water, and insoluble in alcohol: those less soluble are, however, readily dissolved by acids and bases. They usually melt above 200° with decomposition, and have a
344 ORGANIC CHEMISTRY. [\ 253
bitter and insipid taste, and are precipitated by phosphotungstic acid. They answer the biuret-test (247, 3) : for the pol^^- peptides the sensitiveness of the reaction augments with increase in the length of the chain. Boiling with concentrated hydrochloric acid for about five hours effects complete hydrolysis. At ordinary temperatures they are stable towards alkalis. They are hydrolyzed by the action of pancreatic juice.
The highest polypeptide prepared by Emil Fischer is an octadecapeptide containing eighteen amino-acid-residues, fifteen of them being glycine-residues and three being leucine-resiJues. It has all the characteristics just enumerated, and had it been first discovered in nature, it would certainly have been classed as a protein.
This octadecapeptide has the molecular weight 1213 : that of most of the fats is much smaller, the figure for tristearin being 891. It is the most complex substance of known structure hitherto obtained by synthesis. Abderhalden's researches have demonstrated the power of animal organisms to form protein from a mixture of amino-acids in correct proportion, the basis of the proof being the continued existence of animals fed on such a mixture.
The mechanism of this synthesis of proteins must be wholly different from that involved in their production in the laboratory , and the same general rule is applicable to the synthetic formati :i of all natural products. Plants generate dextrose from carbon dioxide and water, and in presence of ammonia they form proteins and alkaloids. In the animal organism, the synthesis of proteins is accompanied by that of fats. All these processes take place at ordinary temperature, and without the aid of concentrated acids, phosphorus pentachloride, and other substances essential in artificial syntheses; but their mechanism is still very obscure.
The natural proteins are probably mixtures of various poly- peptides for which no mode of separation has been discovered.
The step-by-step decomposition of fibroin (249) also indicates that the amino-acids in the proteins have an amino-linking. Wlicn it is treated with concentrated hydrochloric acid, sericotn results, and is converted by further boiling with the same acid into a peptone. Pancreatic juice converts this substance into tyrosine (352), and another peptone, which answers the biuret-test. On wanning
1 254] PROTEINS. 345
this second peptone with baryta-water, however, it no longer answers this test, and a dipeptide, glycylalanine, can be isolated from the products of decomposition.
254. Nothing is known about the molecular weight of the proteins, except that it must be very great. Attempts to deter- mine it by the cryoscopic method have yielded very small depres- sions of the freezing-point. Better results have accrued from measurements of the osmotic pressure of their solutions, a depres- sion of the freezing-point of 0*001^ corresponding with an osmotic pressure of approximately 9 nmi. of mercury or 125 nmi. of water, as is proved by a simple calculation.* A solution of the albiunin of a hen's egg containing 12*5 g. per litre has an osmotic pressure of 20 mm. of mercury, and that of a gelatin-solution of similar con- centration is 6 mm., the corresponding molecular weights being 11,000 and 36,000
The proportion of sulphur in the proteins supports the hypoth- esis of a high molecular weight. In some varieties it is about 1 per cent. Since there cannot be less than 1 atom, or 32 parts by weight, of sulphur in the protein molecule, this percentage points to a molecular weight of 3200, assuming the presence of only one atom of sulphur in the molecule. The percentage of iron in haemoglobin indicates for this protein a molecular weight of about 12,500. Other data give 10,000 as • the approximate molecular weight of many proteins. But there is no gainsaying the fact that these conclusions rest on a very uncertain basis: the close analogy between the higher polypeptides and the natural proteins makes it probable that the chains of the protein molecule do not contain more than about 20 amino-acid-residues.
* Since the molecular depression (12) AM of water is 19, a 1 per cent.
aqueous solution of a compound of molecular weight M = 19,000 causes a
19 depression of the freezing-point of =0'001°. At 0**, the osmotic
pressure of an aqueous solution of a granmie-molecule of the substance, or 19,000 grammes, diluted to 22 •4 litres is equal to 760 mm. of mercury (" Inor- ganic Chemistry,'' 34 and 42). Each litre of such a solution contains 848*2 grammes. The osmotic pressure exerted by a solution containing 10 granmies
per litre, or 1 per cent., would therefore be 760X-.. ,, or approximately
848 • 2
9 millimetres.
346 ORGANIC CHEMISTRY. [§ 254
Even if the difference in the nature and in the number of the amino-acids in the protein molecule is alone considered, it is evident that an almost infinite variety of proteins is theoretically possible. Assuming that the protein molecule contains 20 different amino-acid-residues, it can be represented by the scheme
-^20* -^19' -^18- • •'^2*'4l;
A being an amino-acid-residue. Each fresh grouping of these residues produces a new isomer ide. According to the theory of permutations, there are possible 20Xl9Xl8X...X2xl or approximately 2»3Xl 0^^ = 2.3 trillion groupings, and hence a like number of isomerides. For other reasons this number must be greatly increased, the first of them being based on stereo- chemical considerations. Some amino-acids contain asymmetric carbon atoms: if the protein molecule contains n of them, the number of stereoisomerides possible is 2^. Assuming that the value of n in the foregoing example is 10, each of the 2*3 trillion substances could exist in 2^^=1024 optically isomeric forms. The second reason is that the group — CO-NH — can also exist in the tautomeric form (235) — C(OH):N — . It is evident that the number of possible isomerides is almost unlimited. It is so great as to make it possible that each of the different kinds of living material has its own individual protein; and that the infinite variety of forms found in organic nature is partly the result of isomerism in the protein molecule.
CTAirOGEl^ DERIVATIVES.
Cyanogen, C2N2.
255. When mercuric cyanide, Hg(CN)2, is heated, it decom- poses into mercury, and a gas, cyanogen. A brown, amorphous polymeride, paracyanogen, (CN)x, is simultaneously formed: on heating to a high temperature, it is converted into cyanogen. A better method for the preparation of cyanogen is the interaction of solutions of potassium cyanide and copper sulphate; cupric cyanide is formed, and at once decomposes into cuprous cyanide and cyanogen:
4KCN+2CUSO4 = 2K2S04+Cu2(CN)2 + (CN)2.
The reaction is analogous to that between potassium iodide and a solution of copper sulphate, from which cuprous iodide and free iodine result.
Cyanogen is closely related to oxalic acid. Thus, when ammo- niimi oxalate is heated with a dehydrating agent, such as phos- phoric oxide, cyanogen is produced: inversely, when cyanogen is dissolved in hydrochloric acid, it takes up four molecules of water, with formation of ammonium oxalate. These reactions prove cyanogen to be the nitrile of oxalic acid, so that its constitutional formula is N=C — C=N.
Cyanogen is also somewhat analogous to the halogens, as its preparation from potassium cyanide and copper sulphate indi- cates. Moreover, potassium bums in cyanogen as in chlorine, with formation of potassium cyanide, KCN; and when cyanogen is passed into caustic potash, potassium cyanide, KCN, and potas- sium cyanate, KCNO, are produced, the process being analogous
347
348 ORGANIC CHEMISTRY. [§ 256
to the formation of potassium chloride, KCI, and potassium hypo- chlorite, KCIO, by the action of chlorine on potassium hydroxide (" Inorganic Chemistry," 56). Silver cyanide, like silver chloride, is in consistence a cheese-like substance, insoluble in water and dilute acids, and soluble in ammom'um hydroxide.
On reduction with sulphurous acid, cyanogen is converted slowly into hydrocyanic acid, HCN, whereas the corresponding reduction of halogens to hydrogen halides takes place instan- taneously.
At ordinary temperatures cyanogen is a gas of pungent odour : its boiling-point is ~ 20* 7^. It is excessively poisonous. At high temperatures it is stable, but at ordinary temperatures its aqueous solution decomposes slowly, depositing a brown, amorphous, flocculent precipitate of azviminic acid. Cyanogen is inflammable, burning with a peach-blossom coloured flame.
Hydrocyanic Acid| HCN.
256. Hydrocyanic acid is produced by passing a mixture of nitrogen and hydrogen over red-hot carbon. An equilibrium is attained at one atmosphere of pressure and 2148*^, corresponding with 4-7 per cent, of hydrocyanic acid.
When sparks from an induction-coil are passed through a mixture of acetylene and nitrogen, hydrocyanic acid (" prussic acid ") is formed, and, since acetylene can be obtained by direct synthesis (126), this reaction furnishes a method of building up hydrocyanic acid from its elements. Its synthesis is also eflfected by electrically raising the temperature of a carbon rod to white heat in an atmosphere of hydrogen and nitrogen, 4*7 per cent, of hydrocyanic acid being formed at 2148°. It is usually pre- pared by heating potassium ferrocyanide (257) with dilute sul- phuric acid, anhydrous hydrocyanic acid being obtained by fractional distillation of the aqueous distillate. It is a colourless liquid with an odour resembling that of bitter almonds: it boils at 26°, and the solid melts at - 14°.
When pure, hydrocyanic acid is stable, but its aqueous solu- tion decomposes with formation of brown, amorphous, insoluble substances: the solution contains various compounds, among them ammonium formate.
i 257] CYANIDES. 349
Like most cyanogen derivatives, hydrocyanic acid is an exces- sively dangerous poison. The inhalation of hydrogen peroxide, or of air containing chlorine, is employed as an antidote. Like the mer- cury compounds (" Inorganic Chemistry," 274), its toxic effect de- pends upon the degree of ionization, so that it must be the cyanogen ions that exert the poisonous action. Other evidence leads to the same conclusion : thus, potassium ferrocyanide, the aqueous solution of which contains no cyanogen ions, is non-poisonous.
Hydrocyanic acid must be looked upon as the nitrile of formic acid: H-COOH^H-CN. Its formation by the distillation of ammonium formate, and the reverse transformation — referred to above — of hydrocyanic acid into ammonium formate by addition of two molecules of water, favour this view, as does also the forma- tion of hydrocyanic acid when chloroform, H-OCla, is warmed with alcoholic ammonia and caustic potash (145). Methylamine is obtained by reduction of hydrocyanic acid:
H.C^N+4H = H3C.NH2.
Hydrocyanic acid is one of the weakest acids, its aoueous solu- tion having low electric conductivity.
' Hydrocyanic acid can be obtained from amygdalin, CjoHjjOnN, which is a glucoside (217), and is found in bitter afanonds and other vege^ble-products. In contact with water, amygdalin is decom- posed by an enzyme (222), emtdsirif also present in bitter almonds, into benzaldehyde, hydrocyanic acid, and dextrose:
C,oH270nN-h2H,0 = C7H.O-|-HCN-|-2CJIi,0,.
Amygdfljin Benxaldehyde Deztroee
Substitution of maltase from yeast for emulsin yields only a single molecule of dextrose, amygdalic nitrile glucoside^ CuHnOfN, being simultaneously formed.
Cyanides.
257, The alkali-metaJ salts of hydrocyanic acid are manu- factured chiefly for the lixiviation of gold and silver ores (" Inor- ganic Chemistry," 245 and 248), three methods being employed in their preparation.
1. Wood-charcoal is heated with metallic sodium in a current
350 ORGANIC CHEMISTRY. [§ 257
of gaseous ammonia at 500°-600°, the primary product being sodium cyanamide^ Na2CN2 (260). At a higher temperature this substance combines with carbon to form sodium q^anide^ NaCN:
2NH3+2Na+C = Na2CN2+3H2;
Na2CN2+C = 2NaCN.
2. Crude coal-gas also furnishes a source of hydrocyanic acid (" Inorganic Chemistry," 308).
3. Spent wash (43) is evaporated, and the residue submitted to dry distillation. Hydrocyanic acid is a constituent of the gaseous mixture evolved, and can be extracted by absorption in alkali.
When barium carbide is heated in nitrogen, it yields barium cyanide:
BaC2+N2 = Ba(CN)2.
This reaction affords a means of preparing cyano-derivatives from atmospheric nitrogen.
A good yield of potassium cyanide, KCN, or sodium^ cyanide, XaCN, is readily obtained by heating magnesium m'tride with potassium or sodium carbonate and carbon:
MgaNa + NazCOa + C = 2NaCN + 3MgO.
The isolation of the nitride can be avoided by passing mitrogen over a mixture of magnesium-powder, sodium carbonate, and carbon at elevated temperature:
3Mg+Na2C03+C+N2=2NaCN+3MgO.
The cyanides of the alkali-metals and of the alkaline-earth- metals, and mercuric cyanide, are soluble; other cyanides are in- soluble. All have a great tendency to form complex salts, many of which, particularly those containing alkali-metals, are soluble in water and crystallize well. The preparation and properties of some of these salts are described in " Inorganic Chemistry,*' 308.
Potassium cyanide, KCN, is obtained by heating potassium ferrocyanide, K4Fe(CN)6, to redness:
K4Fe(CN)6 -4KCN -h FeC2 + Ng. Potassium cyanide is readily soluble in water, and with difficulty
S 258] CYANIC ACID, 351
in strong alcohol: it can be fused without undergoing decomposi- tion. The aqueous solution is unstable; the potassium cyanide takes up two molecules of water, slowly at ordinary temperatures and quickly on boiling, with elimination of ammonia, and produc- tion of potassium formate:
KCN+2H2O = HCOOK + NH3.
Potassium cyanide always has an odour of hydrocyanic acid, ow'mg to the fact that it is decomposed by the carbon dioxide of the atmosphere into this compound and potassium carbonate.
The aqueous solution of potassium cyanide has a strongly alka- line reaction, the salt being partially hydrolyzed to hydrocyanic acid and caustic potash ("Inorganic Chemistry," 66). Evidence of this decomposition is also afford ?d by the possibility of saponi- fying esters with a solution of potassium cyanide, this furnishing at the same time a method of determining the extent of the hydro- lytic decomposition of the salt.
Poto««iwm/erroc2/ani(fe, K4Fe(CN)6, crystalli zesin large,8ulphur- yellow crystals, with three molecules of water, which can be driven off by the application of f ent!e heat, leaving a white powder. It is not poisonous (256). When warmed with dilute sulphuric acid it yields hydrocyanic acid. On heating with concentrated sulphuric acid, carbon monoxide is evolved; in presence of the sulphuric acid, the hydrocyanic acid first formed takes up two molecules of water, with production of ammonia and formic acid, the latter being immediately decomposed by the concentrated sulphuric acid into carbon monoxide and water (8i). This method is often employed in the preparation of carbon monoxide.
Cyanic Acid, HCNO.
258, Cyanic acid is obtained by heating its polymeride, cyanuric acid (262), and passing the resulting vapours through a freezing- mixture. It is a colourless liquid, stable below 0®. If the flask containing it is removed from the freezing-mixture, so that the temperature rises above 0®, vigorous ebullition takes place, some- times accompanied by loud reports, and the liquid is converted into a white, amorphous solid. This transformation was first observed by Liebig and W5hler, by whom the product was called
352 ORGANIC CHEMISTRY. [§ 258
" insoluble cyanuric acid/' or cyamelide, which is a pol3rmeride of cyanic acid, and probably has the formula (HCN0)3. It has, however, been shown by Senier that the transformation-product contains only about 30 per cent, of cyamelide, the remainder being cyanuric acid: they can be separated by treatment with water, in which cyamelide is very sparingly soluble, much less so than cyanuric acid.
The relationship subeistiiig between cyanic acid, cyanuric acid, and cyamelide is explained by the following considerations. At ordinary temperatures cyamelide is the stable modification. When cooled below 0^, the vapour of cyanuric acid yields cyanic acid, a transformation analogous to the condensation of phosphorus-vapour at low temperatures to the yellow, and not to the stable red, modi- fication. This is due to the fact that at low temperatures the velocity of transformation of both the unstable forms is very small. Above (f the velocity of transformation of cyanic acid is much greater, and the polymeric, stable cyamelide is formed, the process, moreover, being considerably accelerated by its own calorific effect. Above 150° cyamelide is converted into the isomeric cyanuric acid. This transformation is analogous to that of rhombic sulphur into mono- clinic sulphur, the transition-pK)int being about 150°, although the process is so slow that it could not be determined accurately. A similar slowness prevents observation of the reverse proceds, the direct transformation of cyanuric acid into cyamelide, so that cyanuric acid remains unchanged for an indefinite period at the ordinary temperature, although it is an unstable modification. In this respect it is comparable with detonating gas (''Inorganic Chemistry," 13).
Above QP an aqueous solution of cyanic acid changes rapidly inro carbon dioxide and anmionia:
HCNO+H2O = H3N+CO2.
The constitution of cyanic acid itself is unknown, but it yields two series of derivatives which may be regarded as respectively
OH
derived from normal cyanic add, C4 jr , and from iaocyanic add,
Cyanogen chloride, CNCl, may be looked upon as the chloride of normal cyanic acid. It is a very poisonous liquid, and boils at 15*5®: it can be obtained by the action of chlorine on hydrocyanic
§ 2591 CYANIC ACID. 863
acid, and polymerizes readily to cyanuric chloride^ C3N3CI3. Cyanogen chloride is converted by the action of potassium hydrox- ide into potassium chloride and potassium cyanate:
CNC1+2K0H = CNOK+KCI+H2O.
259. Esters of cyanic acid have not been isolated : they are probably formed in the first instance by the action of sodium alkoxides upon cyanogen chloride, since the polymeride, ethyl cyanuraie (CNOC2H6)3, can readily be separated from the reaction- product (262).
Esters of iaocyanic add, on the other hand, are well known, and are obtained by the action of alkyl halides on silver cyanate:
CO:N[AiTriC2H5 = CO.NC2H5+AgI.
The isocyanic esters are volatile liquids, with a powerful, stifling odour: they, too, polymerize readily, yielding iaocyanuric esters, such as (CONC2H6)3 (262).
The constitution of the wocyanic esters follows from their decom- ]>osition into carbon dioxide and an amine, by treatment with water, or better with dilute alkalis:
CO:N-CH3+H20 = C02+NH2-CH3.
This reaction was first applied by Wurtz to the preparation of primary amines, for obtaining them pure, and free from secondary and tertiary amines.
Primary amines can be obtained from acid amides by the action of bromine and caustic potash (96). This is more economically effected by distilling a mixture of the acid amide and bleaching- powder with lime-water. The mechanism of the reaction has been investigated by Hoogewerff and van Dorp. The first product has been isolated; it is a substituted amide, with bromine linked to nitrogen : R • CO • N H, -> R • CO • N HBr . The hydrogen of the amino- group can be replaced by metals, owing to the influence of the acid- residue, and this replacement is considerably facilitated by the intro- duction of a Br-atom. The caustic potash present causes the forma- tion of a compK)und, R*CO*NKBr, which is unstable, but can be iso- lated. This potassium bromoamide readily undergoes an intra- molecular transformation, similar to the Beckmann tranaformation (103) :
R-C-GK Br-C-OK
I changes to || •
Br-N R.N
Potassium bromoamide
354 ORGANIC CHEMISTRY, [§260
The tnuQflformation-product loses £[Br, with formation of an iso-
N.R
cyanic ester, || , which is decomposed by the water present into OC
a primary amine and carbon dioxide.
Thiocyanic Acid, HCNS.
260. Thiocyanic acid (sidphocyanic acid) resembles cyanic acid in its properties, but is much more stable towards water. It can be obtained by treatment of barium thiocyanate with the calculated proportion of dilute sulphuric acid. The anhydrous acid is obtained by the action at low temperature of concentrated sul- phuric acid on a mixture of potassium thiocyanate and phosphoric oxide, the oxide being added to prevent excess of moisture. At 0** it forms a white, crystalline solid, melting at about 5°, and quickly changing to a solid polymeride after removal from the freezing- mixture. When warmed with dilute sulphuric acid, thiocyanic acid takes up one molecule of water, and decomposes similarly to cyanic acid (258), with production of carbon oxjrsulphide, COS, instead of carbon dioxide:
HCNS+H2O = H3N+COS.
Potassium ihiocyanaie is obtained by boiling a solulion of potas- sium cyanide with sulphur. Among other applications it is used in Volhard's method of silver-titration. When silver nitrate is added to a solution of potassium thiocyanate, silver ihiocyanaie, AgCNS, is deposited in the form of a white, cheese-like precipitate, insoluble in dilute mineral acids. Ferric ikiocyanaie, Fe(CNS)„ has a dark blood-red colour : its formation is used as a test for ferric salts. The red colour is due to the non-ionized molecules Fe(CXS)„ since neither the ferric ion nor the thiocyanic ion are coloured in solution, and the colour is intensified if ionization is diminished ; for example, by the addition of more of the ferric salt or of the thiocyanate. The red colour is removed by agitating the solution with ether, whereas ions cannot be extracted by this means. Mercury thiocyanate has the property of intumescing when decomposed by heat ("Pharaoh's serpents ")•
The constitution of thiocyanic acid, like that of cyanic acid, is unknown, and it resembles the latter in giving rise to two series of
§ 2601 THIOCYANIC ACID. 365
esters, the thuKyanic esters, C^^ , and the iaothioq^nic eaters,
•^
N.R
Thiocyanic esters are obtained by the action of alkyl iodides upon the salts of thiocyanic acid:
CN-S[kTi]C2H5 « CN-SCaHfi+KI.
They are liquids, insoluble in water, and characterized by a leek- like odour. That the alkyl-group in these compounds is in union with sulphur is proved by the nature of the products obtained both by reduction and oxidation. Reduction yields mercaptans and hydrocyanic acid, methylamine being formed from the latter by further reduction :
CN-S-C2H6+2H = CNH+H.S-CaHfi.
Alkylsulphonic acids, such as C2H5-S020H (60), are obtained by oxidation.
Under the influence of heat the thiocyanic esters are trans- formed into tsothiocyanic esters: thus, distillation of allyl thio- cyanate, CN-SCsHs, effects this change.
The tsothiocyanic esters are also called mustard-oils, after allyl
isothiocyanate, to which the odour and taste of mustard-seeds
are due. The following reactions prove that these compounds
contain an alkyl-group attached to nitrogen, and have the con-
,^N-R stitution Cf . When treated with concentrated sulphuric acid,
they take up water, yield'mg a primary amine and carbon oxy- sulphide:
R.N:CS+H20 = R.NH24-COS.
They are converted by reduction into a primary amine and trithio- methylene, (CH2S)3, the latter probably resulting from the polymeri- zation of the thiomethylene, CH2S, first formed, which is unknown in the free state:
R.N:CS+4H = R-NH2+CH2S.
Addition-products of the mustard-oils are described in 269 and 270.
366 ORGANIC CHEMISTRY, [§ 261
Cyanamide, CN-NH2, is obtained in various reactions; for instance, by the action of ammonia upon cyanogen chloride. It is a crystalline, hygroscopic solid, and poljrmerizes readily. Its hydrogen atoms can be replaced by metals; thus, silver jrields silver qjanamide, CN-NAg2, which is yellow, and insoluble in dilute ammonium hydroxide, wherein it differs from most silver compounds.
When calcium carbide is heated to redness in a current of nitrogen, calcium cyanamide is formed:
CaC2+N2 = CN.NCa+C.
The absorption of nitrogen is much facilitated by addition of 10 per cent, of calcium chloride. This compound can also be obtained by heating lime and carbon to a red heat in an atmos- phere of nitrogen. The crude product is called " Lime-nitrogen " and finds application as an artificial fertilizer, being decomposed slowly by water at ordinary temperatures into ammonia and cal- cium carbonate:
CaCN2+3H20 = 2NH3+CaC03.
The reaction is much accelerated by heating under pressure. Ammonia can be obtained directly from the nitrogen of the at- mosphere by this method.
Fulminic Acid.
36x. Salts of fulminic add are obtained by the interaction of mercury or silver, nitric acid, and alcohol, in certain proportions* The best known of them is mercwric fuLminate, HgCjOaNj, which is prepared on a large scale, and employed for filling percussion-caps, and for other purposes. Guncotton can be exploded by the detona- tion of a small quantity of this substance (228) ; and it produces the same result with other explosives, so that the so-called ''fulminating mercury " plays an important part in their application.
Silver fulminate, Ag(CNO), is much more explosive than the mer- cury salt, and hence is not employed technically. The explosion of these salts has a hrisant (155), though only local, effect: this enabled Howard, the discoverer of mercuric fulminate, to explode a small quantity in a balloon without injury to the latter, the only effect being to shatter the leaden shells containing the explosive.
§ 2621 CYANURIC ACID AND ISOCYANURIC ACID, 367
Free fulminic acid is a very unstable, volatile substance: it has an odour resembling that of hydrocyanic acid, and b excessively poisonous.
According to Nef, the formula of fulminic acid is C=N*OHy con* taining a bivalent carbon atom. When mercuric fulminate is treated with acetyl chloride, a compound of the formula CH,-CO{CNO) is obtained. In presence of hydrochloric acid the fulminate takes up water, with formation of hydroxylamine and formic acid. It is con- verted by bromine into a compound, Br^C^aNs, with the constitu- tional formula
Br— 0=N— O
I I*
Br— C=N— O
Cyanuric Add and isoCjanvaic Acid.
262. Cyanwric bromide, CsNsBra, is obtained by heating potas- sium ferricyanide with bromine at 220^. By heating with water, the bromide is converted into q/anuric acid, (CN0H)3. The latter, however, is usually prepared by the action of heat on urea (267). Two series of esters are derived from this acid, the normal cyanuric and the iaoq^anuric esterSf the former being called " O-esters," and the latter " iV-esters."
The normal cyanuric esters are obtained by the action of sodium alkoxides on cyanuric chloride or bromide. The formation of alco- hol and cyanuric acid on saponification proves the alkyl-group in these esters to be in imion with oxygen. For this reason constitu- tional formula I. is assigned to them:
N N.R O
RO-C C-OR OC CO HN:C C:NH
i i •
II ; I
N N R'N N-R
N/ \y V
C CO C:NH
OR
I. n. III.
The isocyanuric esters result when silver cyanurate is heated with an alkyl iodide. Their alkyl-groups are linked to nitrogen, since, on boiling with alkali, such an ester yields a primary amine
358 ORGANIC CHEMISTRY, [§ 262
and carbon dioxide, a decomposition accounted for in constitu- tional formula II. The O-esters are formed when an alkyl iodide reacts with silver cyanurate at ordinary temperatures, but their conversion into the JV-esters by heating explains the difference in the product obtained at ordinary and at elevated tem- peratures.
Klason has suggested that cyameUde (258) is wocyanuric acid, and that its relation to the isocyanuric esters resembles that of cyanuric acid to the normal cyanuric esters. The formation of cyanuric chloride by the action of phosphorus pentachloride on the normal esters and normal cyanuric acid, and the fact that the iso-esters, and, as Senier has shown,' cyamelide, do not yield chlo- rides under this treatment, support this view.
Important evidence in favour of the imino-formula for cyanuric acid has been furnished by Chattaway and Wadmorb, who have succeeded in replacing the metal in potassium cyanurate by chlorine. They regard the compound formed as (0:C:N«CI)3.
Formula III., containing imino-groups, possibly represents the structure of cyamelide.
DEIOVATIVES OF CARBONIC ACID.]
263. Carbonic acid, H2CO3 or C0(0H)2, is not known in the free state, but is supposed to exist in the solution of carbon dioxide in water: it decomposes very readily into its anhydride, carbon dioxide, and water. It is dibasic, and is generally described, with its salts, in inorganic chemistry ("Inorganic Chemistry," 184). Some of its organic derivatives are dealt with in this chapter.
Carbonyl Chloride, COCI2
Carbonyl chloride (phosgene) is prepared by heating chlo- rine and carbon monoxide; an equilibrium
Cl2 4-CO;=tCOCl2, is attained, corresponding at 505^ with about 67 per cent, of dissociation. It was called phosgene (0o>s, light; yevvdw, to produce) by J. Davy in 1811, under the impression that its formation by this means can only take place in presence of simUght, a view since proved to be incorrect. Carbonyl chloride is a gas with a powerful, stifling odour. It dissolves readily in benzene, and the solutioiwis employed in syntheses, both in the laboratory and in the arts.
At ordinary temperature, carbonyl chloride is decomposed by ultraviolet light, especially by the rays of short wave-length, into carbon monoxide and chlorine, the mechanism of the process being similar to that described in "Inorganic Chemistry," 79. Carbon monoxide and chlorine also combine under the influence of this light, so that an equilibrium is established.
The reactions of carbonyl chloride indicate that it is the chloride of carbonic acid. It is slowly decomposed by water, yielding hydro- chloric acid and carbon dioxide. With alcohol at ordinary tem- peratures it first forms ethyl chlorocarbonate:
/[CT^OCgHc /OC2H6 CO + ->C0
\31 ^Cl
359
360 ORGANIC CHEMISTRY. [§ 264
By more prolonged treatment with alcohol, and also by the action of sodium ethoxide, diethyl carbonate, CO(OC2H5)2, is produced. By the action of anmionia, the two Cl-atoms in carbonyl chloride can be replaced by amino-groups, with formation of the amide of carbonic acid, urea, CO(NH2)2 (266). All these reactions are characteristic of acid chlorides.
The chlorocarbonic esters, also called cMoroformic esters, are col- ourless liquids of strong odour, and distil without decomposition. They are employed for the introduction of the group — COOCjHi into compounds (235).
The carbonic esters are also liquids, but are characterized by the possession of an ethereal odour: they are insoluble in water, and are very readily saponified.
Carbon Disulphide, CS2.
264. Carbon disulphide is manufactured synthetically by passing sulphur-vapour over red-hot carbon. The crude product has a very disagreeable odour, which can be removed by distilling from fat. The pure product is an almost colourless, highly refractive liquid of ethereal odour. It is insoluble in water, boils at 46**, and has a specific gravity of 1-262 at 20**. Carbon disulphide is poisonous: being highly inflammable, it must be handled witjj great care. It is an excellent solvent for fats and oils, and finds extensive applica- tion in the extraction of these from seeds. It is also employed in the vulcanization of india-rubber.
Carbon disulphide is a stable compound, and resists the action of heat, although it is endothermic (''Inorganic Chemistry," 119). It is, however, possible to make its vapour explode by means of mercuric fulminate. The halogens have little action on it at ordi- nary temperatures; but in presence of a halogen-carrier, chlorine and bromine can effect substitution, with production of carbon tetra- chloride and tetrabromide respectively.
Carbon disulphide, like carbon dioxide, is the anhydride of an acid, or an anhydrosulphide. With alkali-metal or alkaline-earth- metal sulphides it yields trUhiocarbonates:
BaS+CS2 « BaCSa.
Barium * trithiooarbonate
§§ 265,2661 XANTHIC ACID AND CARBON OXYSULPHIDE. 361
The barium salt is yellow, and dissolves in cold water with dif- ficulty. By the addition of dilute acids to its salts, free trUhio- carbonic acid^ H2CS3, can be obtained as an unstable oil. The potassium salt is employed in the destruction of vine-lice.
The potassium salt of xarUhic acid is fonned by the action of potassium ethoxide on carbon disulphide:
XKJ2HJ1 CS2+KOC2H5 ■= CS •
^K
This IS effected by agitating carbon disulphide with a solution of caustic potash in absolute alcohol, when potassium xanlhaie sepa- rates in the form of yellow, glittering needles. Free xanthic acid is very unstable: it owes its name (foj^os^, yellow) to its cuprous salt, which has a yellow colour, and results from the spontaneous transformation of the brownish-black cupric salt, precipitated from a solution of copper sulphate by the addition of a xanthate.
Carbon Ozysulphide, COS.
265. Carbon oxysulphide is a colourless, odourless, inflammable gas, and is obtained by the action of sulphuretted hydrogen on isocyanic esters:
2CO.NC2H5+H2S = COS+CO(NHC2H5)2.
Its formation from isothiocyanic esters is mentioned in 260. It is also produced when a mixture of carbon monoxide and sulphur- vapour is passed through a tube at a moderate heat.
Carbon oxysulphide is but slowly absorbed by alkalis. It yields salts with metallic alkoxides: these compounds may be regarded as derived from carbonates by simultaneous exchange of oxygen for sulphur:
yOC2H«
COS+C2H5-OK = CO
Urea,CO<JJg|
NH2
266. Urea owes its name to its occurrence in urine, as the final decomposition-product of the proteins in the body.
362 ORGANIC CHEMISTRY. [§ 266
An adult excretes about 1500 grammes of urine, containing ap- proximately 2 per cent, of urea, in twenty-four hours, so that the daily production of this substance amounts to about 30 grammes. To obtain urea from urine, the latter is first concentrated by evapon^ tion. On addition of nitric acid, urea nitrate, CO{NH2)2'HNOj, (267) is precipitated, and, on account of impurities, has a yellow colour. The colouring is removed by dissolving the precipitate in water, and oxidizing with potassium permanganate. Urea Ls set free from the solution of the nitrate by treatment with barium carbonate:
2CON2H4-HN0i+BaCO8 « 2CON,H4+Ba(N08)j+HaO+CO,.
Urea nitrate
On evaporation to dryness, a mixture of urea and barium nitrate is obtained from which the organic compound can be separated by solution in strong alcohol.
Urea is to be looked on as the amide of carbonic acid, on account of its formation, along with cyanuric acid and cyamelide, from the chloride of this acid, carbonyl chloride, COCI2, this reaction proving its constitution (263) :
.NH.
/ClHjNHa /''"2 CO -f =C0 +2HCL
XjGThJNHj \i
NH2
Carbonyl Urea
chloride
A confirmation of this view of the constitution of urea is its fonna- tion by the action of ammonia on diethyl carbonate.
Urea is formed by addition of ammonia to isocyanic acid:
<NH /NH2
+NH3 = CO O \NR«
\NH2
Ammonium isocyanate dissolved in water is transformed into urea on evaporation of the solution. This is the method by which WoHLER effected his classic synthesis of urea, by heating a mixture of potassium cyanate and ammonium sulphate in solution (i).
This reaction, which has an important bearing upon the history of organic chemistry, has been studied in detail by James Walker and Hamblt. Their researches have shown that the reverse trans- formation of urea into ammonium taocyanate occurs also, since, on addition of silver nitrate, a solution of pure urea in boUing water
§ 266] UREA, 363
yields a precipitate of silver cyanate. An equilibrium is at- tained:
C0(NHt),?=^C0N.NH4.
»T Aixiinoniuin
»«ocyanate
When this equilibrium is reached, the solution only contains a small percentage of taocyanate. It is almost independent of the tempera- ture, proving that the transformation of the systems into one another is accompanied by but slight calorific effect (94).
Urea is manufactured as an artificial fertilizer by heating ammo- nium carbonate at 130-140** under pressure, each molecule of the salt giving up two molecules of water:
C0(0NH4), - CO(NH,)t f 2H2O.
isoCyanic esters are decomposed by water, with formation of primary amines and carbon dioxide (259). If the primary amine formed is brought into contact with a second molecule of tsocyanic ester, addition takes place, with production of a symmetrical diaikyl^urea:
xNHR CO:NR+HaNR' -= CO .
\nhr'
This is a general method for preparing symmetrical dialkylureas.
A monocdkylurea is obttuned by the action of ammonia, instead of an amine, upon an iaocyanic ester.
vNRR'
Unsymmetrical dialkylureaa, CO , are prepared by the action
of isocyanic acid on secondary amines. The method of procedure is analogous to that employed in Wohler's synthesis of urea, and con- sists in warming a solution of the isocyanate of a secondary amine:
^NRR' CONH-NHRR' - CO
The unsymmetrical dialkylureas are converted by treatment with absolute (100 per cent.) nitric acid into nitro-compoimds, which were discovered by Francpiimont, and are called nitroaminea:
364 OBGANIC CHEMISTRY. [§ 267
(CHs),N +N0,
CONHj
— (CH3)^.N0,. OH
267. Urea crystallizes in elongated prisms, the crystals resembling those of potassium nitrate. They are very soluble in water, and melt at 132^. Like the amines, urea forms salts by addition of acids, but only one NH2-group can react thus. Of these salts the nitrate, CON2H4,HN03, and the oxalate, 2CON2H4,C2H204, dissolve with difficulty in solutions of the corresponding acids.
In some of its reactions, notably in certain condensatioa-pn)-
NH
oeeaes, urea behaves as though it had the structure C — OH. An
^NH, ether of this laourea is obtained by addition of methyl alcohol to cyanamide, the reaction being facilitated by the presence of hydro- chloric acid;
^ /OCH.
C +H0CH8-C=NH . ^NH, ^NH,
Oanamide Methyluourea
Tliis method of formation indicates the constitution of the com* pound. Another reaction confirming this view is the production of methyl chloride on heating with hydrochloric acid, which points to the fact that the CH,-group is not in union with nitrogen, since under
this treatment meihylurea, CO , splits off methylamine,
"^NHCH, CHj.NHy
When heated, urea melts; it then begins to evolve a gas, consisting principally of ammonia, but also containing carbon dioxide; after a time the residue solidifies. The following reactions take place. Two molecules of urea lose one molecule of ammonia, with pro- duction of biuret:
/NH2 H2NV CO >C0 = NH2.CO.NH.CO.NH2+NH3.
\ TWTTT TtI TT1.t/ BiUWt
NH2H HN
§267] UREA. 365
Biuret is a crystalline substance which melts at 190^. When copper sulphate and potassium hydroxide are added to its aqueous solution, it gives a characteristic red to violet coloration (" biuret- reaction ")•
On further heating, biuret unites with a molecule of unaltered urea with, elimination of ammonia, and formation of eyanuric acid (363):
NH
IglNH>CO-NH>CO.NH[H] ^ ^C CO H^CO[NH^ Hfl kH
\/ CO
Like the acid amides, when heated with bases urea decomposes, yielding carbon dioxide and ammonia.
The quantitative estimation of urea in urine is an operation of considerable importance in physiological chemistry, and is effected by different methods. Bunsen's process depends upon the decom- position of urea into carbon dioxide and ammonia, on heating with an ammoniacal solution of baryta: the carbon dioxide is thus con- verted into barium carbonate, which can be collected and weighed. In Knop's method the nitrogen is quantitatively liberated by treat- ment of the urea solution with one of potassium hydroxide and bromine, in which potassium hypobromite is present: the percentage of urea can be calculated from the volume of nitrogen liberated. LiEBio's titration-method is based upon the formation of a white precipitate of the composition 2CON2H4«Hg(N03)j»3HgO, when mercuric-nitrate solution is run into a solution of urea of about 2 per cent, concentration. When excess of the mercury salt has been added, a drop of the liquid brought into contact with a solution of sodium carbonate gives a yellow precipitate of basic nitrate of mer- cury. Urine, however, contains substances which interfere with these methods of estimation: an account of the mode of procedure by which the correct percentage of urea can be ascertained will be found in text-books of physiological chemistry.
Potassium cyanate.and hydrazine hydrate, H2N»NHt-fH20, react together, with formation of semicarhazidey NHi«C0«NH»NH2,
366 ORGANIC CHEMISTRY. [J 268
a base which melts at 96^, and combines with aldehydes and ketones similarly to hydroxylamine:
Ra-CO+H,N.NH.CO.NH,-^R,.C:N.NH«CX).NH,.
The compounds thus fonned are called semicarbazones; they some- times crystallize weU, and are employed in the identification and separation of aldehydes and ketones.
Derivatives of Carbamic Acid. 263. Carbamic acid, NH2«C0«0H, which is the semi-amide of carbonic acid, is not known in the free state, but only as salts, esters, and chloride. Ammonium carbamate is formed by the union of dry carbon dioxide with dry ammonia:
/OH /OHNHa
COa+NHs-C^O ; +NH3 = c4:0
XNHa NNHa
Ammonium oarbamsta
When carbon dioxide is passed into an ammoniacal solution of calcium chloride, no precipitate results, since the resulting calcium
/Oca* carbamate^ CO , is soluble in water. XNHa When the salts of carbamic acid are heated in solution, they readily take up water, forming carbonates.
The esters of carbamic acki are called urethanea. They are formed by the action of ammonia or amines upon the esters of carbonic acid or chlorocarbonic acid:
/lOCaHs-fH NHa /NHa
CO^ - CO +CaHi^H;
XOCaHs \OC2H5
Diethyl carbonate Uretbane
/P+HJNHa /NHa \OC2H8 XOCaH,
Ethyl ohloronrbonate
• ca = JCa.
i 2801 URBTHANES AND THIOUREA. 367
Urethanes also result in the action of alcohol upon tsocyanic esters:
<
O /OC2H5
+HOC2H6 = C^O NCHs XnHCHs
Urethanes are also obtained by boiling acid azides(97) with alcohol:
R.C0N,+C,H,OH - R.NHCOOC,H,+N,
Binoe the asides are easily prepared from the corresponding acids, and the urethanes readily yield the corresponding amines, the car- bozyl-group can be replaced by the amino-group:
R-COOH -♦ R.C00C,H5 -^ R-CONHNH, ^ R-CON, -*
Acid EBter Hydraside Aside
-* R-NHCOOCjHs -♦ R-NHa.
Urethane Primary
Urethanes distil without decomposition: ordinary urethane,
/OC2H6 CO , melts at 51®, and is very readily soluble in water. When
\NH2
boiled with bases, it decomposes into alcohol, carbon dioxide, and ammonia. Concentrated nitric acid converts it into nitrourethane, C2H50-CO-NH«N02; and on careful hydrolysis this substance yields nitroamine, NH2-N02.
Thiourea, CS(NH2)a.
269. Ammonium tsothiocyanate yields thiourealn a manner analo- gous to the formation of urea from ammonium t>ocyanate (266). The transformation of the thio-compound can in this instance be effected by heating it in the dry state, but is no more complete than that of ammonium cyanate, since thiourea is converted by heat into ammonium iwthiocyanate. Alkyl-derivatives of thiourea result from addition of ammonia or amines to the mustard-oils (260) the reaction being similar to the formation of alkyl-substituted ureas from Mocyanic esters (266).
These modes of formation prove that the constitution of thiourea 18 expressed by the formula CSCNH,),, being similar to that of urea. Derivatives of thiourea are known, however, which point to the
existence of a tautomeric form Cr-SH (267); thus, on addition of
368 ORGANIC CHEMISTRY, [§ 270
an alkyl iodide, compounds are obtained in accordance with the equation
C^S|H + IlCaHs - ( C^SQHg IHI.
The alkyl-group in this compound is linked to sulphur; for it de- composes with formation of mercaptan, and on oxidation 3rields a milphonic acid.
Thiourea forms well-defined crjrstals, melting at 172^, and readily soluble in water, but with difficulty in alcohol. On treatment with mercuric oxide, it loses sulphuretted hydrogen, forming cyanamide:
C|S = Cf 4-H.S. \NH7 ^NH,
Guanidine, CH5N3.
2yorGiuinidine is formed by the interaction of ammonia and orthoearbonie esters, or chloropicrin, CCI3NO2, obtained by nitrating chloroform. This probably results from addition of four amino-groups to the carbon atom, the compound formed then losing one molecule of ammonia:
NH2
C(OC2H5)4 -> C(NH2)4; - NHs -> (^NH .
iraethyl ort carboaate
c^
Tetraethyl ortho- \NH2
Ouanidiae
This method of preparing guanidine establishes the constitutional formula indicated. Further evidence is afforded by its synthesis by heating cyanamide with an alcoholic solution of ammonium chloride:
cf +NH4CI « ( C=NH HCL \NH2 \ \NH2/
Guanidme is generally prepared by heating anomonium thiocyanate for six hours at temperatures rising from 180® to 205^, air being blown through the melt to oxidize the evolved sulphuretted hydrogen to sulphur and water, and thus obviate the formation of secondary products:
2S : C : NH . NH3 = H2S + (CH5N3) HCNS.
{2701 GUANIDINE DERIVATIVES. 369
It is obtained in the form of guanidine tkiocyanate, the reaction taking place in the following stages:
SCNH-NHs -> CS(NH2)2 -> H2N-CN.
Ammonium thiocyanate Thiourea Cyanamide
The cyanamide unites with a molecule of the unaltered ammonium thiocyanate:
<+NH3-HCNS « (c^NH )HCNS. NHa \ XnHz/
Quanidixie thioeyaxiata
Guanidine is a colourless, crystalline substance, and readily absorbs moisture and carbon dioxide from the atmosphere. It is a strong base, unlike urea, which has a neutral reaction: the strengthenmg of the basic character, occasioned by exchange of carbonyl-oxygen for an imino-group, is worthy of notice. Guani- dine yields many well-defined, crystalline salts.
/NH-N02 Nilrogiianidinef C^NH , is obtained in solution by the
\NH2
action of fuming nitric acid upon guanidine: dilution with water
precipitates the nitroguanidine, which is v^ry slightly soluble in
/NH.NHg water. On reduction, it yields aminogiuinidine, C=NH , which,
\NH2
on boiling with dilute acids or alkalis, decomposes with formation of carbon dioxide, ammonia, and diamide or hydrazine, H2N«NH2 ("Inorganic Chemistry," 114). This reaction proves the consti- tution of nitroguanidine and aminoguanidine.
An important derivative of guanidine is arginine, C6Hi402N4^ obtained from proteins. It can be sjmthesized by the action of cyanamide on ornithine (243) :
COOH.CH(NH2)-(CH2)8-NH2+CN2H2 «
Ornithine Cyanamide
COOH.CHNH2. (CH2)3NH
"^C.NH. NH2
Arginine
370 ORGANIC CHEMISTRY. [§ 270
The cyanamide is added at the ^NH2-group, as represented in the equation, so that arginine is onxmino-^uanino^Tk-valeric acid. The muscular tissue of the human body contains, about 0*3 per cent, of creatine. Its structure is proved by its synthetic formation from methylglydne or sarcosine and cyanamide:
<
NH2 XJHs /NH2
+ HN< = C^NH
X;h2.cooh S?/^^*
N:!H2.COOH
Crefttina
By elimination of one molecule of water, creatine is converted into creaHnine,
/NH
VHcH3
CO
CrMtinina
URIC-ACID 6R0XTP.
271. Urie acid, C5H4O3N4, derives its name from its presence in small amount in urine: it is the nucleus of an important group of urea derivatives. It is closely related to the vrelcUhacids and the acid^ure^idea {ureldea), which are amino-acids and acid amides, con- taining the urea-residue, NH2'C0«NH — , instead of the NHygroup.
Parabanic acid, C3H2O3N2, is an acid-ureide: it is obtained by the oxidation of uric acid. When warmed with alkalis for a long time, parabanic acid takes up two molecules of water, forming urea and oxalic acid, a reaction which proves it to be oxalyhirea:
yNH OHH do\ COOH ^^N
!0+ - I + >00.
COOH „x<
^>
HaN NH OHH
Farabanio add (Oxalylurea)
On careful treatment with alkalis, it takes up only one molecule of water, yielding oxaluric add:
CO— NH-CO-NH, COOH
Ozaluiioadd
Alloxan, C4H204N2,4H20, is an important decomposition- product of uric acid, from which it is obtained by oxidation with nitric acid: it can also be prepared by other methods. It is
371
372 ORGANIC CHEMISTRY. (§ 271
mesoxalylurea, since, on treatment with alkalis, it takes up two molecules of water, with production of urea and mesoxalic acid:
CO NH+OHH CO-OH NH,
00 CO -CO +C0.
CO-
NH+OHH CO-OH NHj
Alloxan Mesoxalic acid .
Carbon dioxide and parabanic acid are produced by the oxidation of alloxan with nitric acid.
Alloxan is converted by reduction into alloxantine :
Alloxantuie
Alloxantine is also formed directly from uric acid by evaporating it to dryness with dilute nitric acid. When treated with ammoniai it forms a purple-red dye, murexide^ CgHgOeNs. The formation o( murexide is employed as a test for uric acid. Alloxantine dissolves with difficulty in cold water, and gives a blue colour with baryta- water. There is still doubt as to the constitution of these com- pounds.
AUarddine, C4H6O3N2, is formed in the oxidation of uric acid with potassium permanganate, a fact which has an important bear- mg on the constitution of this acid. Allantoine has the structure '
/NH.CH— NH.CO.NH2 CO I \NH.CO
AUantoIn*
since it can be obtained synthetically by heating glyoxylic acid with urea:
H
/NH|H H0|— C— |OH+H|HN.C0.NHa
CO +
\NHfH~HO
—CO
Urea Glyoxylic add
/NH-CH— NH.CO.NH2 CO I \NH.CO
Allan tol OB
S 271] ALLOXAN AND ALLANTOINE. 373
The formatioD of alloxan and allantoihe from uric acid gives an insight into its constitution, the production of the first indicating
C-N
the presence of the complex G yC; and of the second, the pre»-
C-IT
ence of two urea-residues, together with the complex C^ 1.
These are accounted for in the structural formula
NH— CO
CO C-NHv
I II >X). NH— C-NH^
Urioacid
This formula also gives full expression to the other chemical proper- ties of uric acid.
The following synthesis affords confirmation of the accuracy of the constitution indicated. Malonic acid and urea combine to form malonylurea or barinturic acid :
NH— 00 I I
CO ca,
I I
NH— CO
On treatment with nitrous acid, this substance 3ne1ds an t^onitroso- eompound which can also be obtained from alloxan and hydroxyl- amiDe, violunc acid :
NH-00
00 O=N0H.
1 I NH-CO
On reduction, violuric acid gives aminobarhiluric acid:
NH-€0
Ao A<S^^
H NH
T-00
374 ORGANIC CHEMISTRY, [f 272
which, like the aminesi adds on one molecule of iK>cyaiiic add oa contact with potassium cyanate, forming
NH— CO
CO CC ^CO.
I I^IHl I
NH-CIO H|HN
This substance is pseudourtc acid, and differs from uric acid onl> in containing the elements of another molecule of water. Boiling with a large excess of 20 per cent, hydrochloric acid eliminates this molecule of water as indicated in the formula, the treatment yieldin;^^ a substance with the constitution assigned to uric acid, and identical with this compound.
Uric acid dissolves with difficulty in water, but is soluble in concentrated sulphuric acid, from which it is precipitated by addi- tion of water. It forms two series of salts, by exchange of one or two hydrogen atoms respectively for metals. Normal sodium urate, C5H203N4Na2 + H20, is much more soluble in water than sodium hydrogen urate, 2C6H303N4Na +H2O. Normal lithium urate is mod- erately soluble in water.
Uric acid is present in urine, and is the principal constituent of the excrement of birds, reptiles, and serpents: it can be convoiiently prepared from serpent-excrement. In certain pathological diseases of the human organism, such as gout, uric acid is deposited in the joints in the form of sparingly soluble primary salts. On account of the solubility of lithium urate, lithia-water is prescribed as a remedy.
272. A number of compounds with the same carbon-nucleus as uric acid occur in nature, partly in the animal, and partly in the vegetable, kingdom. To the former belong hypoxarUhine, C6H4ON4; xanthine, C6H4O2N4; and guanine, CsHsONs: to the latter belong the vegetable bases ife€ofer<wiin«,C7H802N4; and caffeine, C8H10O2N4. To assign a rational nomenclature to these substances and other members of the same group, Emil Fischer regards them as deriva* tives of purine (273), the C-atoms and N-atoms of which are numbered as indicated in the formula
iN=^-«CH NH
C2 fiC.7NH or |i « »]
HC2
3N_C.Nyi^ \5^
0
N
S 2721 URIC ACID. 376
Xanthine, theobromine, and caffeine have the following structural formuls and rational names:
NH— CO NH CO
CO C— NHv CO C— N(CH8).
>CH; I II >H;
NH— C — N^ N(CH3)— C N
XaatbiQe or 3: 0-diozypurine Dimethybcanthino. theobromine, or
3 ; 7-dimethy 1-2 : 6-diozypiiriiie
N(CH3)— CO
00 C— NCCHaK
I II >H.
NCCHa)— C N^
TrunethylxADthine. caffeine, thelne. or 1 :3 : 7-trimethyl-2: 6-dioxy purine
Theobromine and caffeine result from the introduction of methyl- groups into xanthine.
Xanthine, CsH^OaN^, is present in all the tissues of the human body. It is a colourless powder, soluble with difficulty in water, and possessing a weak basic character. On oxidation, it yields alloxan and urea.
Theobromine, C7H8O2N4, exists in cocoa, and is prepared from this product. It is only slightly soluble in water, and is converted by oxidation into monomeihylaUoxan and monomethylurea.
Caffeine or theine, QH10O2N4, is a constituent of coffee and tea It crystallizes with one molecule of water in long, silky needles, and is moderately soluble in water. It is generally prepared from tea- dust. On careful oxidation it yields dimethylalloxan and mono- meihylureat
The position of the methyl-groups in theobromine and caffeine is proved by the formation of these oxidation-products.
There is an evident resemblance between the constitution of uric acid and that of xanthine:
NH-CO NH-€0
ho i-NH^ ; io LnH^ I II >0 I II >CH. NH— C— NH/ NH— C W
Urio aoid Xanthine
These formute indicate the possibility of obtaining xanthine by the reduction of uric acid, and up to the year 1897 numeroiis un-
376 ORGANIC CHEMISTRY, [{ 273
successful attempts were made to prepare it by this method, a reaction ultimately effected by Emil Fischer in that year. He has discovered several methods of converting uric acid into xanthine and its methyl-derivatives mentioned, including one by which the manufacture of the therapeutically important bases, theobromine and caffeine, seems to be possible.
273. Direct replacement of oxygen in uric acid by hydrogen does not seem possible. Emil Fischer has, however, substituted chlorine for oxygen by means of phosphorus oxychloride. Various methods of replacing the chlorine atoms in these halogen derivatives by other groups or atoms have been devised.
When uric acid is treated with phosphorus oxychloride, the first product is S-oxy'2:^-dichlor(ypurine: on further careful treatment with the same reagent, this substance is converted into 2:6:8- irichloropurine:
N==C— OH N=CC1
HO-C C— NHv ^Cl-C C— NHv
II II >.0H II II yc.CL
N— C N^ N— C N^
TftUtomerio f onn of 2: 6: 8<Trichloropurine
uric add
The behaviour of uric acid in this reaction accords with the tauto- meric (235) formula of trihydroxypurine, the phosphorus oxychlo- ride replacing the hydroxyl-groups with chlorine atoms in a normal manner.
« At 0^, and in presence of hydriodic acid and phosphonium iodide,
trichloropurine changes into di-iodopurine:
C5HN4CI3+4HI - C5H2NJ2+3HCI+2L
Reduction of the aqueous solution of di-iodopurine with zinc-dust 3rields purine, a white crystaUine substance, melting at 216^-217®, and very readily soluble in water. It has a weak basic character, but does not turn red litmus blue.
Xanthine is thus obtained from trichloropurine.
Cl-atom 8 in this compound is very stable towards alkalis, whereas Cl-atoms 2 and 6 are displaced with comparative ease: when trichloropurine is treated with sodium ethoxide, Cl-atoma
§2731 ELECTRO-REDUCTION OF PURINE DERIVATIVES. 377
2 and 6 are exchanged for ethoxyl-groups. On heating the com- pound thus obtained with a solution of hydriodic acid, the ethyl- groups are replaced by hydrogen, Cl-atom 8 being simultaneously exchanged for a H-atom, with formation of xanthine:
N=C.OC2H6 N=C.OH NH— CO
CjjHaO-C C— NH -♦HO-C C— NH -►CO C— NH
)ch"
■N N— C— N NH— r "
N-
1 >■" I I >"
3:<l-Dietboxy-8-ehloropuriiie Xanthine (tautomeiio form) Xanthina
When 2:M.iethoxy-%<hlor<ypunne is heated with hydrochloric acid, only the ethyl-groups are replaced by hydrogen, with produc- tion of a compound of the formula
HN— CO
coc— :
NH
HN— C— N
the tautomeric enolic form changing to the ketonic modification. On methylating this substance, its three H-atoms are exchanged for methyl-groups, yielding chlorocaffeine, which can be converted by nascent hydrogen into caffeine. This process, therefore, affords a means of preparing caffeine from uric acid.
Emil Fischer has discovered a very characteristic and simple mode of effecting this methylation — agitating an alkaline, aqueous solution of uric acid with methyl iodide, whereby the four hydro- gen atoms are replaced by methyl-groups, with formation of a tetra- rnethyluric add. On treating this with phosphorus oxychloride POCI3, chlorocaffeine is formed:
3C503N4(CH3)44-POCl3 = 3C502N4(CH3)3Cl + PO(OCH3)8.
It can be converted by nascent hydrogen into caffeine.
Electro-reduction of Purine Derivatives.
Tafel has stated that caffeine, xanthine, uric acid, and sim- ilar compounds reducible with difficulty by the ordinary methods readily take up hydrogen evolved by electrolysis. For this pur-
378 ORGANIC CHEMISTRY. I§ 273
pose the compounds are dissolved in sulphuric acid, the strength of which is varied to suit the particular compound, and lies between 53 and 75 per cent. This solution is contained in a porous cell, and has a lead cathode immersed in it. This cell is placed in sulphuric acid of 20 to 60 per cent, strength, which contains the anode. The hydrogen evolved at the cathode by the ciurent readily effects the reduction of these compounds.
Electro-reduction transforms xanthine and its homologues into deoxy-derivatives, the process requiring four atoms of hydrogen:
C8H10O2N4+4H « C8Hi20N4-hH20.
Oaflfebie Deozycaffelne
The deoxy-compounds are stronger bases than their parent-sub- stances, which have very weakly basic properties.
The reduction of uric acid requires six hydrogen atoms, and yields purone:
C6H4Q3N4+6H = C6H8O2N4+H2O.
Urio acid Purone
The oxygen atom of carbon atom 6 is replaced by hydrogen. Two hydrogen atoms are simultaneously added at the double bond of the uric-acid molecule:
iNH— «C0 NH— CH2
2C0 »C— ^NHv^ -> CO CH— NHv^
Urio add Purona
This structure is proved by the fact that on heating with baryta- water purone yields two molecules of carbon dioxide: it must, therefore, contain two unaltered urea-residues, which necessitates the presence of carbonyl-groups 2 and 8. It can be proved that carbonyl-group 6 is also the group reduced in xanthine and its homologues.
Purone is neither a base nor an acid, and is not attacked by oxidizing agents. When warmed with a 10 per cent, solution of caustic soda, it is transformed into isopurone, which has acidic properties, and is readily oxidized.
§2731 ELECTRO-REDUCTION OF PURINE DERIVATIVES, 379
The application of the electro-reductitm method was at first attended by many difficulties, yields varying between wide limits being obtained, even when the process was apparently carried out in exactly the same way. Tafel has both discovered the cause of this anomaly, and indicated a method by which the reaction can be kept under control. His investigations are of interest, and are worth describmg in some detail.
To be able to watch the course of the reduction-process, Tafel closed the porous cell with a stopper, through which the cathode and a delivery-tube for the gas were introduced, care being taken to make the connections air-tight. A second apparatus, exactly simi- lar to that used for the reduction, but containing acid alone, with- out the purine derivative, was introduced into the same circuit. Periodically, the gas from both was collected simultaneously during one minute. The difference between these volumes of gas is a direct measure of the course of the reduction during that minute, since it indicates the quantity of hydrogen used in the reduction.
When this quantity is represented graphically, the abscissse standing for the time which has elapsed since the beginning of the experiment, and the ordinates for the quantity of hydrogen used in the reduction, the normal course of the reduction is indicated by Fig. 72, since the quantity of hydrogen absorbed in the unit of
O TIME IN MINUTE*
Fio. 72.— Normal Reduction-
CURVE.
0.04110^,
Fia. 73. — Abnormal Reduo-
nON-CURVB.
time must diminish in the same proportion as the quantity of unreduced purine derivative.
Tafel has, however, observed that the addition of traces of a platinum or copper salt, as well as of certain other salts, very quickly reduces the quantity of hydrogen absorbed to nearly zero.
380 ORGANIC CHEMISTRY. [j 273
The graphic representation in this case for the addition of 0*04 milligrammes of platinmn for each 100 square centimdtres^of cathode surface is shown in Fig. 73. This curve indicates that the slightest contamination of the lead of the cathode by certain other metab is almost sufficient to stop the electro-reduction.
The following considerations afford an insight into the cause of this phenomenon. Hydrogen is only evolved by the passage of an electric current through dilute sulphuric acid when the contact- difference of potential between the electrodes and the solution exceeds a certain value. This is a minimum when platinum electrodes are used, and very nearly coincides with the contact- difference of potential to be expected on theoretical grounds for a reversible hydrogen — sulphuric-acid — oxygen-element.
When the cathode is made of other metals, the contact- difference of potential is greater before the evolution of hydrogen begins: for this a swpertermon is necessary. This supertension has a very large value for lead, but as soon as the least trace of platinum or of certain other metals is brought into contact with the surface of the lead cathode, the supertension disappears, and with it the power possessed by the evolving hydrogen of reducing purine derivatives. T
The explanation is that the contact-difference of potential regulates the energy with which the discharged ions can react, for the pressure under which a discharged ion leaves the solution depends only upon the contact-difference of potential between the electrode and the liquid in which it is immersed. Nernst states that by varying the contact-difference of potential it is possible to obtain pressures from the smallest fraction of an atmosphere up to many millions of atmospheres. Hence, reductions unattain- able by other methods, and without supertension, are possible at cathodes where it exists.
SECOND PART.
CYCLIC COMPOUNDS.
INTRODUCTION.
274. With but few exceptions, the compounds described in the first pait of this book contain an open chain. Examples of these exceptions are cyclic compounds such as the lactones, the anhy- drides of dibasic acids, and the uric-acid group. The closed chain of such compounds is very readily opened, and the close rela- tionship of their methods of formation and properties with those of the open-chain derivatives, makes it desirable to include them in a description of the aliphatic compounds.
There exists, however, a large number of substances containing closed chains of great stability towards every kind of chemical reagent, and with properties differing in many important respects from those of the aliphatic compounds. They are called cyclic compounds, and are classified as follows:
A. Carbocyclic compounds, with a closed ring of carbon atoms only, subdivided into
1. Alicyclic compounds, such as the cycZoparaffin derivatives (121), and
2. Aromatic compounds, or benzene derivatives. In this class are included the compounds having condensed rings, or two closed chains with atoms common to each. The typical representative of this type of condensed ring is naphthalene, CioHg, with two benzene-nuclei.
B. Heterocyclic compounds, with rings containing carbon atoms and one or more atoms of another element. This class is exemplified by pyridine, CsHsN, and its derivatives, with a
381
382 ORGANIC CHEMISTRY. U 274
ring of five carbon atoms and one nitrogen atom; furan, €41140, with four carbon atoms and one oxygen atom; pyrrole, C4H5X, with four carbon atoms and one nitrogen atom; thiophen, C4H4S, with four carbon atoms and one sulphur atom; pyrazole, C3H4N2, with three carbon atoms and two m'trogen atoms; and numerous other combinations.
Two dissimilar rings can also have atoms in common, as in quinoline, C9H7N, which contains a benzene-nucleus and a pyridine-nucleus.
Since numerous derivatives of all these compounds are known, the scope of the cyclic division of organic chemistry is much more extended than that of the aliphatic division.* The descrip- tion of the cyclic group is, however, greatly simplified by the fact that in it the properties of alcohols, aldehydes, acids, etc., already described for the aliphatic compounds, are again met with.
* Its wide range is indicated by the fact that 319 ring-systems have been described.
A. CARBOCYCLIC COMPOUNDS.
!• ALICYCLIC COMPOUNDS. I. q/ddProfsne Derivatiyes.
CHr.
375. cycloPrapane, CtHs or | /CHs, is obtained by the action
ch/
of sodium on trimethylene bromide, CHftBr*CHt*CHtBr (148). It is a gas, which liquefies at a pressure of five to six atmospheres. It IS not identical with propylene, CHs:CH-CHi, since with bromine it forms an addition-product only very slowly under the influence of sunlight, yielding trimethylene bromide; nor is it oxidized by per- manganate. These properties and its synthesis prove its constitution. cycloPropylcarboxylic acid is formed by saponifying the primary product of the interaction of ethylene bromide and diethyl disodio- malonate, and eliminating carbon dioxide:
OH, CH,
Br ^COOCH, CH,v /COOC,H,
4- Na,CC =- 2NaBr4- 1 >0(
Br NCOOCjH, CH^ \0OOC,H,
CH,v /COOH CH^. -*| >CC -*J >CH-COOH.
CH,/ \COOH CH/^
II. c^cZoButane DeriyatiYes.
376. cycloBiUane derivcUives are obtained when diethyl di- sodiomalonate reacts with trimethylene bromide, the diethyl ester of a cyclobutyldicarboxylic acid being formed:
OH, CH,
Br CH,
/\ + Na, C(0OOCH.), - CH, C{C00C,H,),+2NaBr.
\/ Br I CHa
383
384 ORGANIC CHEMISTRY. U 277
When heated, the dibasic acid obtained by the saponification of this ester loses one molecule of carbon dioxide (164), yielding cyclo- butylcarboxylic acid.
cycloBiUane is obtained from this acid by a method applicable to the preparation of other hydrocarbons. The acid amide (I.) is converted by the method of 259 into cyclobutylamine (II.). Treat- ment of this amine with excess of methyl iodide yields the iodide of the quaternary ammonium base III., from which the base is then prepared. On dry distillation, it decomposes (66) into trimethyl- amine, water, and c^c/obutylene (IV.) :
CHr-CH.OONH, CHr-CH-NH,
CHf— CHj CHjf— CHj
CHr-CH.N(CH0,OH CHr-CH
-»in.r I -IV.] \\ +N(CH,), + H,0.
OH] — CH] CH|! — CH
t On careful reduction with hydrogen and nickel, cyc^obutylene is converted into cycZobutane.
CHr-CHOH
The main product of the oxidation of cyclcjbutanol, \ \ ,
CH,-CH,
is cyclopropanoZ, | X^H-C^,cyclo6w(anone being also formed.
ch/ ^
This reaction is remarkable as an illustration of the transformation of a ring of four carbon atoms into one of three carbon atoms. The converse change of a cyc2obutyl-ring to a cyc^pentyl-ring
CH,— CH-CH,OH is exemplified by digesting cyclobtUylcarbinol, \ \ ,
CHr-CH,
with concentrated hydrobromic acid, the corresponding bromide being formed. This bromide is transformed by nascent hydrogen into cyc^pentane, instead of methylcyclobutane.
III. cyddPentane DerivatiYes.
377. cycloPentane denvaiives can be obtained by a similar method the action of tetramethylene bromide on diethyl disodiomalonate.
When calcium adipate is submitted to dry distillation, cydo- pefiianofM is formed:
} 278] ALICYCLIC COMPOUNDS. 385
CH,.CH,-OO.I(X CH,'<
I I >Ca = CaC0,4- I
CH,.CH,r0O"o/ CH,.«
CH,'CH,v CHjX
Calcium adipate cyefoPentanone
It IB aJso obtained by heating adipic anhydride:
CH,.CH,«COv CH,-CHiv,
I >0 - 00,+ I >00.
CH,.CH,.CO/ CHj.OH,/
The structure of this compound is proved -by its oxidation to glutario acid:
OH,.OH,v OHa-CHa-OOOH
I >C0 -> I
CHj-CH,-^ CHa-COOH
Olutaric add
This reaction presents a contrast to the oxidation of a straight- chain ketone to two acids. The possibility of the compound being an aldehyde is excluded by the impossibility of oxidizing it to a monobasic acid with the same number of carbon atoms.
cj/cZoPentanone is a constituent of the residue obtained in the fractionation of methyl alcohol (4a). It is a liquid of peppermint- like odour, and boils at 130^.
cycloPenton^ is obtained by the reduction of this ketonic deriv- ative, the carbonyl-group taking up two H-atoms, with formation of a CHOH-group. By treatment with hydriodic acid, hydroxyl is first replaced by iodine, and finally by hydrogen:
CH,.CH,. CHfCHx
I >C0 -* I >CHOH -^
ch,.ch/ ch,-ch/
^ T >CHI -* I >CH,.
ch,-ch/ ch,-ch/
c2^c2oPentaiie is a colourless liquid boiling at 50^. It is a constituent of Caucasian petroleum.
378. Croconic acidy CJIjOj, is a remarkable cyctopentyl-deriv- ative, obtained by the oxidation of hexahydroxybenzene (337) in alkaline solution. It has an intense yellow colour, and is con- verted by weak reducing agents into a colourless substance, oxidizable to croconic acid. On oxidation, croconic acid is transformed into leuconie acid, CiOi,4HsO. This compound has the constitution
386 ORGANIC CHEMISTRY. [§279
CO .CO OC<r NcO,4HA
since it yields a pentoxime of the formula (C:NOH)».
IV. Higber Alicyclic Deriyatiyes.
379* cycloHexane and its derivatives form the group of hydro- aromatic compounds. On accoimt of their relationship to the ter- penes and camphors, they are described in a separate chapter. (363-364).
Several methods are applicable to the preparation of substances containing rings of seven carbon atoms. The first member of this class to be prepared was suberone, obtained by the dry distillation of calcium suberate:
CHrCH,-CH,-COOv CH,.CH,-CH,v
I >Ca = CaCO,+ T >00.
CH,-CH,.CH,.COQ^ CH,.CH,.CH/
Calcium suberate Suberone
Hydrolysis of the nitrile obtained by addition of hydrocyanic acid to suberone and reduction of the resulting a-hydroxy-acid yield suberanecarhoxylic acid:
CH,.CH,.CH,v yOH CH,-CH,-CH,v
I X -> I >CH-COOH,
CH,-CH,-CH,/ \CN CHa.CHj.CH/
This acid is also obtained by the interaction of ethyl diazoacetate and benzene, ethyl paeudophenylacetate being formed as an inter- mediate product:
CH HCy\CH
CeH, + N«HC-COOC,H*
)>CH-COOC,Hi + N„
. HCS^CH CH
The acid corresponding with this ester can be transformed into the isomeric iaophenylacetic acid:
CH
HC
i HC
^CH.
)>CH.COOH. ^^CH
CH
§280]
ALICYCLIC COMPOUNDS,
387
Reduction converts this isomeride into suberanecarboxyiic acid, proving the presence of an unsaturated ring of seven carbon atoms. A third mode of preparing cyclic compounds with seven carbon atoms is exemplified by the conversion of q/c^hexylmethylamine (I.) and other similar primary amines into stable nitrites (II.) :
yCH,— CH,v CH< > CH.CHj.NH, -> (CH,)i>CH.CH,.NH,.NO,H.
NCH,— CH/
I. n.
On boiling in acetic-acid solution, these nitrites are transformed by elimination of nitrogen into the alcohols of the next higher ring-system:
(CH,),>CH.CH,.NH,.NO,H -* (CH,),>CHOH.
The conversion into suberone by oxidation of the alcohol formed from cT/c^hexylmethylamine affords a proof of the course of this reaction. The synthesis of cyclic compounds containing eight carbon atoms is effected similarly.
380. The cyclic hydrocarbons, CnH2n, from cyclopropane to cyclo- odane have been definitely isolated. The table contains a com- parison of some of their physical constants, with the corresponding constants of the normal hydrocarbons of the saturated series CDH2n+2) and the unsaturated series, CnH2n*
|
Number |
CnH2n + 2 |
CnH2n. Unsaturated. |
CnH2o. CycUc. |
|||
|
of Carbon Atoms. |
Boilinc- point. |
Specific Gravity. |
BoiUnc- point. |
Specific Gravity. |
Boiling, point. |
Specific Gravity. |
|
3 4 5 6 7 8 |
-45° 1° 36-3° 68-9° 98-4° 125-6° |
0-536 (0°) 0-600 (0°) 0-627 (14°) 0-658 (20°) 0-683 (20°) 0-702 (20°) |
- 48-2° - 5° 35° 68° 98° 124° |
0-648 (0°) 0-683 (15°) 0-703 (19-5°) 0-722 (17°) |
ca.-35° 11°-12° 49° 81° 117° 147° |
0-7038 0-7635 0-7934 0-8252 0-850 |
The saturated cyclic hydrocarbons have higher boiling-points and much higher specific gravities (about 0«12) than their unsatu- rated isomerides. The saturated hydrocarbons contain two hydro- gen atoms more than the corresponding olefines. The correspond- ing members of both series have almost the same boiling-points, but their specific gravities are about 0*02 lower.
388 ORGANIC CHEMISTRY. [§ 280
The molecular volumes of the unsaturated compounds are appre- ciably higher than those of the corresponding isomeric cyclic deriva- tives. For hexylene the molecular volume is 123*0, and for cyclo- hexane 106' 4. The presence of a double bond obviously augments the volume appreciably.
In 6tud3ring the refraction of the c^c2oparaffins and their deriv- atives, Eykman found the difference between their molecular refractions and those of the corresponding saturated compounds with the formula CnHan+a not constant, but dependent on the number of carbon atoms in the nucleus, and also on the presence or absence of side-chains. The smaller the number of carbon atoms in the nucleus, the greater is the molecular refraction of isomerides, and its value is still higher in substances with a double bond. The most probable explanation of this phenomenon is the strain char- acteristic of these ring-systems (120). The double linking involves the greatest strain, the carbon bonds being deflected from the normal position to the extent of 54** 41'. For a ring of three carbon atoms the deflection is 24"^ 44', for a ring of four carbon atoms 9^ 34', and for a ring of five carbon atoms only a few minutes.
The refraction method affords a valuable aid in ascertaining (h<> nature of the ring-systems present in compounds (370).
2. AROMATIC COMPOUNDS.
CONSTITUTION OF BENZENE.
281. Certain substances found in the vegetable kingdom are characterized by the possession of an agreeable aroma: such are oil of biUer almonds, oil of caraway, oil of cumin, balsam of Tolu, gumr-benzoin, vanilla, etc. These vegetable-products consist prin- cipally of substances of somewhat similar character, which differ from the aliphatic compounds in containing much less hydrogen in proportion to the other elements: thus, cymene, C10H14, is obtained from oil of carraway; toluene, CjHg, from balsam of Tolu; and benzoic add, C7H6O2, from gum-benzoin. The saturated aliphatic compounds with the same number of C-atoms have the formulsB C10H22, C7H16, and C7H14O2, respectively.
Before the nature of the so-called aromatic compounds had been closely investigated, and on account of their external similarity, it was customary to regard them as members of a single group, just as ordinary butter and "butter of antimony," SbCla, were classed together because of their similarity in consistency. This method of classification is still adopted for compounds wath analogous properties, but of imperfectly imderstood constitution, such as the bitter principles, some vegetable alkaloids, and many vegetable dyes.
A closer study of the aromatic compounds has shown that the old and somewhat arbitrary classification according to external re^ semblance is well founded, since all these substances may be looked upon as derivatives of one hydrocarbon, benzene, CeHe, just as the aliphatic compounds can be regarded as derived from methane, CH4. Thus, on oxidation, toluene yields benzoic acid, the calcium salt of which is converted into benzene by distillation with limr. The dibasic terephthalic acid, C8H6O4, is formed by the oxidation of cjrmene, and can be similarly transformed into benzene.
The discovery of this relation by Kekule brought into promi- nence the question of the constitution of benzene, the basis of all
380
390 ORGANIC CHEMISTRY. [§ 282
the aromatic compounds. Its formula, GeHe, contains eight hydro- gen atoms less than that of the saturated paraffin with six C-atoms, hexane, CeHi 4. Benzene, like other hydrocarbons poor in hydrogen, such as C6H12 and CeHio, might be supposed to contain multiple carbon bonds, but its properties do not admit of this assumption. Ck)mpounds with a multiple carbon bond readily form addition- products with the halogens, are very sensitive to oxidizing agents, and easily react with von Baeyer's reagent (113): benzene lacks these properties. It yields halogen addition-products ver}*^ slowly, whereas compounds with a multiple carbon bond form them instan- taneously. It must, therefore, be concluded that benzene does not contain multiple carbon bonds, and that the carbon atoms in its molecule are linked together in a special manner.
282. To understand the manner of linking of the bnnzene carbon atoms, it is necessary to know the relative distribution of its hydro- gen and carbon atoms. Two facts suffice to determine this dis- tribution. First, there are no isamerides of the monosubstHuiion- jjToducts of benzene. Second, the disubstittUion'products exist in three isomeric forms. Hence, there is only one monobromobenzene, CsHsBr; but three dibromobenzenes are known, and are distin- guished by the prefixes ortho, meta, and para.
It follows from the first of these facts that the six hydrogen atoms of benzene are of equal value (359) : that is, replacement of any one of them yields the same monosubstitution-product. Three formute. in which the six hydrogen atoms are of equal value, are possible for benzene:
I. C4(CH3)2; II. C3(CH2)3; HI. (CH)6.
It has now to be considered which of these formuke agrees with the second fact stated over-leaf.
A disubstitution-product of a compound with formula I. can be either j CH2X _ ^ 1 CHX2
^MCH2X ^^ ^MCHs •
No other isomerides are possible, so that this formula is inadmis- sible as leading to two, instead of to three, isomerides. With formula II. four isomerides seem possible:
o. rCHX b. (CHX c. (CX2
Ca \ CHX C3 \ CH2 C3 \ CH2
( CH2 ( CHX ( CH2
§283]
CONSTITUTION OF BENZENE.
391
The hydrogen atoms in benzene being equivalent, the CH2-group8 in the benzene molecule must be similarly linked, so that a=b, and c=d: in other words, the number of possible isomerides is reduced to two. Formula II. cannot be accepted either, since it also fails to explain the formation of three isomeric disubstitution-products.
There remains only formula III., in which each carbon atom is in union with one hydrogen atom. The question of the constitution of benzene therefore narrows itself to this: given a compound CgHe, in which each carbon atom is linked to one hydrogen atom, the problem is to find a formula which accounts for the equivalence of all the hydrogen atoms, the formation of three disubstitution- products, and the absence of double or multiple bonds. It is evi- dent that an open carbon-chain formula cannot fulfil the prescribed conditions, since the hydrogen atoms attached to such a chain con- taining terminal and intermediate CH-groups could not be equi- valent. The six hydrogen atoms can only be of equal value with a ring of six C-atoms:
HG HC
CH
A
8
CH
OH OH
This arrangement of the CH-groups also fulfils the second condition, as is evident from the scheme:
HC HO
cx
CH
CH
ZO HG
CX
GH
GH OH
HO HG
CX
V
CH
CH
ox
HC XO
CX
A
V
CH
CH CH
HG HO
CX
A
V
OX
CH CH
in which the compounds C6H4X2, 1:2=»1:6, 1:3 = 1:5, and 1 :4 are isomeric. The formation of three isomerides is, therefore, also accounted for.
283. This hexagonal formula finds support in the evidence afforded by very many investigations of isomeric benzene deriv- atives, and affords a partial elucidation of the constitution of
392 ORGANIC CHEMISTRY. [( 283
benzene. But despite exhaustive investigation by the most eminent chemists, an entirely satisfactory explanation of the
inner structure of the benzene molecule, and of the mode of Unking of the fourth bond of each of the six carbon atoms, is still lacking.
Kekul^ assumed the presence of three double bonds in the benzene molecule, as in- ^H dicated in Fig. 74.
There are two objections to Kekul^'s FiQ. 74.— Kekul6'8 formula, the first being the representation of Benzene-formula, benzene as an unsaturated compound. The
sceond drawback is the dissimilarity of the two or^Ao-positions, the carbon atoms being singly linked on one side, and doubly linked on the other.
WiLLSTATTER attempted the synthesis of the compound cyclohexatriene, CoHe, with the constitution assigned by Kekul^ to benzene. The starting point was cyclohexanol (I.)i a substance readily converted into cyclohexene (II.) by elimination of water. A dibromide (III.) is formed by addition of bromine, and one of its bromine atoms eliminated as hydrobromic acid by the action of dimethylamine, the other bromine atom being replaced by the dimethylamino-residue (IV.). The cyclohexylamine thus formed reacted with methyl iodide and then with sUver hydroxide, the product being a base (V.), converted by dry distillation at reduced pressure (276) into cyclohexddiene (VI.). Compounds II. and VI. had all the properties characteristic of unsaturated derivatives. Addition of bromine to VI. gave VII. (compare 127 and below), a substance converted into the corresponding di- ammonium base by a process similar to that involved in the trans- formation of III. into V. At the very low pressure of one- hundredth of a millimetre, this base was found to decompose at 0^ into water, trimethylamine, and the compound with formula IX., a substance resembling benzene in all respects. The disappearance of the unsaturated character is an indication of the complete change in properties occasioned by the introduction of a third double bond into the ring of six carbon atoms.
The objections to Kekul^'s formula have been met by a modi- fication proposed by Thiele, who has made a special study of substances containing a conjugated linking (127), and has found
§283]
CONSTITUTION OF BENZENE.
303
!
t
S
s
I
%..
5>
o o
» »
!
» H
t
8
I n
o
8 u
was
394 ORGANIC CHEMISTRY. [§ 283
that addition of two univalent atoms to such compounds converts them into others with a double bond at the centre:
— CH^CH-CH=CH— +2X -^ — CHX— CH=CH— CHX— .
To explain this phenomenon, he assumes that the whole of the affinity of the double bond is not employed, but that a part — the residual affinity — ^remains free at atoms 1 and 4, the remainder being satisfied between atoms 2 and 3, as indicated in the scheme
12 3 4 C-O— C— C.
The dotted lines denote partial valencies. The hypothesis of valency-electrons (244) affords an insight into the possibility of the existence of such partial valencies. There is a double bond between C-atoms 2 and 3, but it is inactive, since addition takes place only at 1 and 4.
The application of Thiele's hypothesis to Kekul£'s formula gives a graphic representation (Fig. 75) with three inactive double bonds, but lacking free partial valencies. This peculiar type of structure might explain the difference between the properties of benzene and those of unsaturated compounds.
By a method similar to that employed in his attempt to prepare q/cZohexatriene, Will- STATTER has Synthesized cyclooctatetraem. In Fia. 75.— Thiele's accordance with Thiele s hypothesis, this sub- stance must possess only inactive double bonds, but the product has the character of a highly unsaturated compound.
This fact has brought von Baeyer's centric formula (Fig. 76) into prominence again. In this representation the fourth valency of each carbon atom is directed toward the centre of the hexagon, the attraction of the valencies for each other keeping them in equilibrium. There are important stereochemical objections to the centric formula. As is evident from the stereo-formula (Fig. 77), it indicates the possibility of the existence of two modifica- tions of benzene derivatives with two dissimilar or^Aosubstituents, although no example of this phenomenon has been observed.
Contradictory evidence has also been afforded by the results
§283]
SUBSTITUTION'PRODUCTS OF BENZENE,
395
obtained from physico-chemical experiments instituted with the object of solving the complex problem of the constitution of benzene, the refractometric method furnishing an example.
When two double bonds are conjugated, the molecular refrac- tion exhibits an exaltation (127), and this phenomenon is much more marked with three conjugated double bonds. This pecu- larity is exemplified by hexatriene, CH2^CH • CH=CH • CH=CH2,
Hc/jNcH
Fig. 76. —Von Baeter's Centric Formula.
Fig. 77. — Von Baeter's Sterbo-forhula.
HO
OH
OH CH
OH
OH
OH OH
Fig. 78.— WillbtXtter'b c2^c2ooctatetraenb.
a compound discovered by van Romburoh. There is no exalta- tion in the observed value of the molecular refraction of benzene compared with that calculated on the assumption of the presence of three ordinary double bonds, and the same holds for qjdo- octatetraene (Fig. 78). Since the closing of the chain to form a ring of either six or eight carbon atoms exerts very Uttle influence on the molecular refraction, the absence of exaltation must be ascribed to the disappearance of the residual affinities in consequence of the closing of the carbon chain. Although benzene and q/cZooctatetraene are entirely analogous in refractometric character, they display wide differences in chemical properties.
Thiele's modification of Kekul^'s formula is the best avail- able representation. As can be seen from a model, its six carbon atoms and six hydrogen atoms lie in the same plane. Despite the remarkable character of this conception, its accuracy is proved by the fact that any other of the spacial formulae proposed for benzene presents a serious difficulty, since it involves the possibility of the existence of non-superimposable mirror-images of compounds C6H4AB, and therefore of optically active isomerides. Compounds of this type have never been prepared, nor found in nature.
396
ORGANIC CHEMISTRY.
[J 284
Nomenclature and Isomerism of the Benzene Derivatives.
284. The different isomeric disubstitution-products are distin- guished by the prefixes ortho, meta, and para, or the positions of their substituents are denoted by numbers:
1:2«=1:6 substitution-products are called orf Ao-compounds. 1:3=1:5 " " »» 11 Tweto-compounds.
1:4 " " ff ff para-compounds.
The number of isomeric substitution-products is the same for two similar or dissimilar substituents, but not for three. When the three groups are similar, three isomerides exist:
XXX
|
X |
||
|
Adjacent or Vicinal |
Symmetrical |
Unsymmetrioal |
|
1:2:3 |
1:3:5 |
1:3:4 |
When one of the groups is dissimilar to the other two, different vicinal derivatives result by substitution at 2 and at 3 respectively, and, for the unsymmetrical compound, substitution at 3 produces a different compound from that resulting on exchange at 4. For four similar groups the same number (three) of isomerides is pos- sible as for two, since the two remaining hydrogen atoms can be in the ortho-position, meto-position, or para-position to one another. The nimiber of isomerides possible in other cases can be readily determined.
An alkyl-radical or other group linked to a benzene-residue, as in CoHs'CHs or C6H5»CH2»CH2»CH3, is called a, side-chain, the benzene-residue being called the ntJtcleus. Substitution can take place both in the nucleus and in the side-chain; when in the former, it is usual to refer to the position of the stibstituent rela- tive to those already present, the determination of which is called the determination of position, or orientation, of the substituents. The methods of orientation are given in 354 to 358.
PROPERTIES CHARACTERISTIC OF THE AROMATIC COM- POUNDS: SYNTHESES FROM ALIPHATIC COMPOUNDS.
285. The saturated hydrocarbons of the aliphatic series are not attacked by concentrated nitric acid or sulphuric acid, and only to a small extent by oxidizing agents: their halogen-substituted derivatives react with great ease. The aromatic hydrocarbons differ from the aliphatic hydrocarbons in all these respects.
1. The aromatic hydrocarbons are readily attacked by concen- trated nitric acid, with formation of nUro-ampaunds:
CeHfi- IH+HCSNOa = CeHs-NOa+HaO. x
Nitrobenaene
These substances yield amino-derivatives on reduction, and are consequently true nitro-compounds.
2. On treatment with concentrated sulphuric acid, the aromatic compounds yield sidphonic acids:
CeHfi. gTHOj-SOsH -CeHs-SOaH-f-HaO.
BenseneBulphonio acid
The sulphur of the SOsH-group is linked to a carbon atom of the benzene-nucleus, since thiophenol, CeHs-SH, also yields benzene- sulphonic acid on oxidation:
G6H5 • SH —> GqHs • SO3H.
3. The aromatic hydrocarbons with side-chains are oxidized without difficulty to acids, the whole side-chain being usually oxi- dized to the carbon atom in union with the nucleus, with formation of carboxyl.
4. Chlorobenzene and bromobenzene have their halogen atoms so firmly attached to the phenyl-group, CeHs, that they are almost incapable of taking part in double decompositions with such com- pounds as metallic alkoxides, salts, and so on.
397
398 ORGANIC CHEMISTRY. {% 285
Two syntheses of aromatic from aliphatic compounds are cited here: other examples are given in the chapter on hydro- cyclic derivatives (363-364) .
1. When the vapours of volatile aliphatic compounds are passed through a red-hot tube, aromatic substances are among the products. The condensation of acetylene, C2H2, to benzene is a typical example, although passage through a red-hot tube transforms benzene-vapour into acetylene, proving that both reactions are incomplete. In addition to benzene, other aromatic compounds are also formed. A synthesis of benzene from car- bon monoxide is described in 337.
2. On treatment with sulphuric acid, acetone is converted into mesitylene, or l:3:5-trimethylbenzene (288):
BCsHeO - 3H2O = C9H12. Other ketones condense similarly to aromatic hydrocarbons.
BENZEITE Ain> THE AROMATIC HYDROCARBOHS WITH
SATURATED SIDE-CHAINS.
Gas-manufacture and its By-products : Tar.
286. The aromatic hydrocarbons are employed in large quanti* ties in the manufactm^ of coal-tar colours, and are obtained from coal-tar, a by-product in the manufacture of gas. A short descrip- tion of this process will not be out of place, since it also yields other products of importance in the organic chemical industry.
Coal is gradually heated in fire-clay retorts of o -shaped cross section, and is finally raised to a red heat: the gases and vapours are removed as completely as possible by means of exhaust- pumps. Coke remains in the retorts, and is employed as fuel and in many metallurgical processes, although for the latter pur- pose the coke has usually to be prepared by special means.
The distillate contains three main products. 1. Gases (illumi- nating-gas). 2. An aqueous liquid, containing anmionia and other basic substances, such as pyridine bases. 3. Tar. These products are separated from one another as completely as possible by a series of treatments. The crude gas is passed over iron-ore and lime, to remove the cyanogen derivatives and sulphur compounds. The former purifying material is employed subsequently for the prepara- tion of potassium ferrocyanide (257), an important source of the cyanogen compounds.
Tar is a thick, black liquid with a characteristic odour. Its colour is due to suspended particles of carbon. It is a complicated mixture of neutral, acidic, and basic substances. The first are principally hydrocarbons, chiefly belonging to the aromatic series. About &~10 per cent, of the tar consists of naphthalene, and 1-1 -5 per cent, of a mixture of benzene and toluene. Phenol (294) is the
3d9
400 ORGANIC CHEMISTRY. [| 287
principal acidic constituent of tar. Basic substances are present only in small proportion: the chief are pyridine, quinoline, and their homologues.
In the arts, the separation of the tar-prpducts is effected partly by chemical means, and partly by fractionation. The tar is first distilled, a considerable portion remaining in the retort as a black, either soft or somewhat brittle mass, known as pUch, The dis- tillate is submitted to fractional distillation, four fractions being obtiuned.
1. Light oil, between 80° and 170°; D 0- 910-0* 950.
2. Middle oil, or carbolic oil, between 170° and 230°; D l-Ol.
3. Heavy oil, or creosote-oil, between 230° and 270°; D 1*04.
4. Green oil or anthracene-oil, above 270°; D 1» 10.
The light oil contains benzene and its homologues, which can be separated by further fractionation. Only a limited number of the homologues of benzene are present in the light oil — ^principally toluene, or methylbenzene, and xylene, or dimethylbenzene.
Benzene and its Homologues.
287. The homologues of benzene can be prepared by the method of Fmia, and by that of Friedel and Crafts.
1. Fittig's synthesis is carried out by treating bromo- benzene, or, in general, a hydrocarbon containing bromine in the nucleus, with an alkyl bromide or iodide and sodium (29) :
CeHs
Br -fBr
Na Na
C2H5 - C^Hir- C2H5+2NaBr.
Ethylbensene
A series of by-products is sometimes obtained, among them par- affins and diphenyl, CoHg-CJli. The yield of alkylbenzene is, however, very good when the higher normal primary alkyl iodides are employed.
2. Friedel and Crafts's synthesis is peculiar to the aromatic series, and depends upon a remarkable property of aluminium chloride. This substance is obtained by the action of dry hydro- chloric^acid gas on aluminium-foil. On bringing it into contact with a mixture of an aromatic hydrocarbon and an alkyl chloride, clouds of hydrochloric acid are evolved, and hydrogen of the nucleus is exchanged for the alkyl-group:
CbHs- |H-hCl|CH8 - CeHs-CHg +Ha
S 287] BENZENE AND ITS HOMOLOOUES. 401
In the synthesis of Friedel and Crafts more than one alkyl- group is generally introduced, the monosubstitution-products and the higher substitution-products being simultaneously formed. The mixture can be separated by fractional distillation.
This reaction constitutes a method both for the building-up and breaking-down of a hydrocarbon. When toluene, CeHj»CHi, is treated with aluminium chloride, benzene, CJIe, and xylene, CeHiCCHs)!, are formed. The alkyl-groups of one hydrocarbon are exchanged for the hydrogen of the other. The reaction can also be effected by the action of concentrated sulphuric acid upon aromatic hydrocarbons with a number of side-chains.
There are many different types of the reaction of Friedel and Crafts, and there has been much diversity of opinion as to its mechanism. Sometimes only a very small proportion of aluminimn chloride suffices; in other reactions there must be at least one molecule of the chloride for each molecule of the reacting substance. Boeseken regards the process as one of simple catal- ysis, having proved reactions requiring a large excess of aluminium chloride to be attended by a combination between it and the other reacting substances, most of the aliiminiiun chloride being thus rendered non-reactive.
3. By heating an alcohol, an aromatic hydrocarbon, and zinc chloride at 270°-300°. The zinc chloride acts as a dehydrating agent :
CeHsiH + HO • CsHn = CqHs • C5H1 1 + H2O.
The following reactions are also available for the preparation of both benzene and its homologues:
4. Like the saturated aliphatic hydrocarbons, the aromatic hydrocarbons are obtained by the distillation of the calcium salts of the aromatic acids with soda-lime (83) :
CeHs- C02ea*+caO H=C6H6+CaC03.
5. Benzene and its homologues can be obtained by heating the 0ulphonic acids with sulphuric acid or hydrochloric acid, the decom- position bein^ facilitated by the introduction of superheated steam:
^ /•« —9
ca = §Ca.
402
ORGANIC CHEMISTRY.
I§288
C6H3(CH3)2lS03H -f-HOIH - C6H4(CH3)2+H2S04.
This method can be employed in the separation of the aromatic hydrocarbons from the paraffins. When warmed with concentrated sulphuric add, the former are converted into sulphonic acids, soluble in water: the paraffins are unacted upon and are insoluble in water. A mechanical separation is thus possible.
This method can also be applied to the separation of the aromatic hydrocarbons from one another, since some of them are more readily converted into sulphonic acids than others.
288. Benzene and the aromatic hydrocarbons with saturated side-chains are colourle^, highly refractive substances, liquid at ordinary temperatures, and possessing a characteristic odoiir. They are immiscible with water, but mix in all proportions with strong alcohol. Some of their physical properties are indicated in the table.
Name.
Benzene
Toluene
m-Xylene
Mesitvlene
Ethylbensene
i«o Propyl benzene ^Cumene) p-Methylisopropyibenzene 1
(Qymene) /
Fonnulft.
CeH,.CH,
C.H,(CH,), (1:3:6) C,H,-CH(CH,),
P XT ^CHj 1
Boilioc- poini.
Specifio Gnnty.
0-874 0-809
(2<r») (ie»)
(14*')
(0^) (16^)
0-856 (2(r*}
0-881
0-865 0-883 0-866
The boiling-points of the isomeric benzene derivatives are usually very close together, but the melting-points display wide divergences. It is an almost invanable rule throughout the entire aromatic series for the paro-compound to have a higher melting-point than the m^to-compound and the orfAo-compound.
Benzene was discovered by Faraday, in 1825, in a liquid obtained from compressed coal-gas. It melts at 5*4®.
The molecular weights of alcohols, phenols, and aliphatic acids determined by the cryoscopic method, with benzene as solvent, ar« sometimes twice as great as the accepted values, whereas normal
§288] BENZENE AND ITS HOMOLOGUES. 403
results are obtained for other substances not containing a hydroxyl- group..
The formation of double and multiple molecules in solution de- pends in large measure upon the nature of the solvent. In addition to benzene, other hydrocarbons, acetic acid, and formic acid induce the formation of complex molecules. The results obtained with such solvents by the cryoscopic method for the determination of molecular weights are unreliable (83).
Xylene, or dimethylbenzene, exists in three isomeric forms: m-xylene is the principal constituent of the xylene in tar, forming 70-85 per cent, of the whole.
The isomeric xylenes are separable with difficulty: their boiling- points lie very close together, that of o-xylene being 142*', while m-xylene and p-xylene boil at 139® and 138® respectively. This makes thrir separation by fractional distillation impracticable, but it can be effected by treating them with sulphuric acid at ordinary temperatures: m-xylene and o-xylene go into solution as sulphonic acids, while p-xylene remains undissolved. The sulphonic acid of the meto-compound and that of the or^^compound can be separated by fractional crystalUzation of their sodium salts, the ortho-aalt crys- tallizing first.
Cymene, C10H14, is closely related to the terpenes CioHiq, and to the camphors CioHieO, since it can be obtained from them. Cymene is a constituent of certain essential oils, such as oil of cara^ tjoay, oil of thyme, and oil of eucalyptus.
It is obtained in large quantities from the terpenes present in the coniferous woods employed for the production of celhUose (228) by the " Bisulphite " process.
MONOSTJBSnTUnON-PRODUCTS OF THE AROMATIC
HYDROCARBONS.
I. HONOHALOGEN COMPOUNDS.
289. Simple contact of the halogens with benzene does not produce substitution-products. Fluorine reacts with this hydro- carbon very energetically, decomposing the molecule completely, with formation of hydrogen fluoride and carbon tetrafluoride. Chlorine and bromine dissolve in benzene, and convert it slowly into the addition-products hexachlorobenzene, CeHeCle, and hexabromobemene, CeHeBro, both reactions being accelerated by sunlight. Iodine has no action, except at very high temperature. The substitution of hydrogen in benzene by chlorine or bromine can only be effected in presence of a catalyst, anhydrous ferric chloride or bromide being specially suitable. The process is exemplified by the preparation of monobromobemene, CsHsBr, by the addition of bromine drop by drop to cooled, dry benzene in presence of a small proportion of iron-powder. Ferric bromide is formed first, monobromobenzene being then produced with evolution of hydrogen bromide. Monoiodobemene, CeHsI, is prepared by heating benzene with iodine and iodic acid in a sealed tube, the iodic acid oxidizing the hydrogen iodide formed to iodine and water, and thus preventing it from reconverting the monoiodobenzene into benzene. Replacement by chlorine or bromine of the hydrogen of the nucleus in the homologues of benzene also necessitates the presence of a catalyst, such as iron. Another method of preparing the halogen derivatives of benzene is described in 307.
The halogen atom in the monohalogen derivatives of benzene can be induced to react only with great difficulty. They can be boiled with alkali, with potassium hydrogen sulphide, with potassium cyanide, or can be heated with ammonia, without substitution of the halogen atom. The replacement of chlorine or bromine by the amino-group proceeds tolerably smoothly, however, in presence of cupric sulphate, a reaction exemplified
40i
§ 289] MONOHALOGEN COMPOUNDS. 405
by the formation of aniline^ C6H5NH2, by heating monochloro- benzene with a concentrated aqueous solution of ammonia in presence of a small proportion of this salt in an autoclave at a temperature of about 180^. Replacement of halogen by the methoxyl-group can be eflfected by the action at 220® of the powerful reagent sodium methoxide.
The character conferred on a halogen atom by union with the benzene-nucleus is in alf respects analogous to that possessed by halogen attached to a doubly-linked carbon atom in an aliphatic unsaturated halogen derivative (128).
FrmG's synthesis (287, 1) is one of the few examples of the ready displacement of a halogen atom in union with the benzene- nucleus. Magnesium reacts with an ethereal solution of mono- bromobenzene in a way resembling its action on a similar solution of an alk3^1 halide (75). It yields a solution of a compound of the formula CeH^Mg-Br, a substance available for the synthesis of tertiary alcohols with the group CeHft, as described in loa.
Monochlorobemene is a colourless liquid: it boils without decomposition at 132®, and has a specific gravity of 1» 106 at 20®. Monobromobenzene, B.P. 157®, sp. gr. 1«491 at 20®. Monoiodo- benzene, B.P. 188®, sp. gr., 1-861 at 0®.
lodobenzene, and other iodine compoimds substituted in the nucleus, can add two atoms of chlorine, with formation of sub- stances such as phenyliodide chloride or iodobemene dicMoride, C«Hf*ICl2. ' When digested with alkalis, these derivatives give iodo8(hcompound8f such as iodosobemenCf CeHt-IO, which are amor- phous, yellowish solids. When heated, or oxidized with bleaching- powder, these compoimds yield iodoxy-compounda:
2Cja[| • 10 = C A • I +C.H, • 10,.
lodozybeniene
lodoxybenzene is crystalline, and explodes when heated.
The constitution of these compounds is inferred from their ready converuon into iodobenzene, effected for iodosobenzene by means of potassium iodide, and for lodoxybenzene by hydrogen dioxide, with evolution of oxygen. These substances would not be so readily converted into iodobenzene if the oxygen were attached to the benzene-nucleus.
406 ORGANIC CHEMISTRY, {{ 290
n. MONONITRO-DERIVATIVES.
290* A point of characteristic difference between the aromatic and aliphatic compounds is that the former are vefy readily con- verted into nitro-derivatives by the ar^tion of concentrated nitric acid (28s, 1). This process is the only method employed in prac- tice for the preparation of aromatic nitro-compounds. The substance is treated with a mixture of nitric acid and sulphuric acid, or with excess of fuming nitric acid of ^cific gravity 1»52:
CeHs- |H+HQ| .NO2 ^CeHg- NO2+ H2O.
If the sulphuric acid or an excess of nitric acid were not present, the water formed in the nitration would dilute the nitric acid and retard the action. This effect is explicable on the assump- tion that dilution causes ionization of the nitric acid, the m'tration-process requiring an unionized acid, the hydroxyl-group of which can react with a hydrogen atom of the benzene to form water. Increase in the number of alkyl-groups attached to the benzene-nucleus is often accompanied by a corresponding increase in the ease with which nitration is effected.
The mononitro-compounds are very stable, and can be dis- tilled without decomposition: their nitro-groups are very firmly attached to the nucleus. Unlike the primary and secondary nitro- compounds of the aliphatic series, the aromatic nitro-derivatives do not contain hydrogen replaceable by metals, since their nitro- group is linked to a tertiary carbon atom: such an exchange is therefore impossible (69). On reduction, the nitro-compounds yield amines, and the reaction can be modified so as to isolate various intermediate products (296-304).
Most of the mononitro-compounds have a pale-yellow colour and an agreeable odour: they are usually liquids heavier than water, in which they are insoluble. They are volatile with steam.
Nitrobenzene is manufactured in large quantities in the aniline- dye industry. Cast-iron vessels fitted with a stirring apparatus, and kept cool by water, are employed. They are charged with benzene, and into this a mixture of nitric acid and sulphuric acid is allowed to flow. At the end of the reaction, the nitro- benzene floating on the surface of the sulphuric acid, which contains only small quantities of nitric acid, is washed with water and purified by distillation with steam.
§290]
MONONITRO'DERJVATIVES.
407
Nitrobenzene is a yellowish liquid: it has an odour resembling that of bitter almonds, and for this reason is employed in per- fumery. Its boiling-point is 208*^, its melting-point 5»5®, and its specific gravity 1-1987 at 25°. It is poisonous, inhalation of its vapour being specially dangerous. Its preparation on the large scale is carried out in order to obtain aniline by its reduction (297 and 302).
Nitrotoluenes, — ^When toluene is nitrated, the chief products are the or^A(M;ompound and para-compound: only a small percentage
51»4
para 1100 90 80 70 eO SO 40 30 20 10 0
0 10 20304050ti0 70 8090 VX) artho
FiQ. 79. — Fusion-curve of Mixtures of o-NrntoroLUENB and
p-NlTROTOLUENB.
of the meta-compound is formed. The proportion of ortho^ derivative is greater than that of the para-isomeride, as is exem- plified by the percentage-yields obtained by nitration at (P, 58*8 of o-nitrotclueney 36 • 8 of p-nitrotolitene, and 4 • 4 of m-nitrotoluene. Usually, when there is simultaneous production of ori/w-com- pounds and para-compounds, the para-isomeride is formed in greater proportion. o-Nitrotoluene is liquid at ordinary tem- perature, its melting-point being — 3»4°; p-nitrotoluene is solid, and melts at 51 •4°. These isomerides are separated by a com- bination of repeated solidification by cooling and of fractional distillation. Fig. 79 represents the fusion-curve ("Inorganic Chemistry," 237) of mixtures of o-nitrotoluene and p-nitrotoluene.
408 ORGANIC CHEMISTRY. [5291
Since the nitration-product contains about 40 per cent of the para-isomeride, its freezing-point lies on the para-section of the curve, so that cooling causes crystallization of p-nitrotoluene. This substance can be separated from the liquid residue by filtra- tion, or on the manufacturing scale by centrifuging. On fractional distillation of the oil, o-nitrotoluene, boiling at 218*', distils first, and subsequently p-nitrotoluene, boiling at 234®. Several repetitions of the fractional distillation, with intermediate solid- ification by cooling, finally )rield an initial fraction so rich in the ori/io-compound that its composition lies on the ori/k>-section of the curve. On cooling this fraction, o-nitrotoluene crystallizes.
m. MONOSULPHONIC ACIDS.
291. The formation of these compounds is described in 285: they are produced by the action of concentrated sulphuric acid upon aromatic compounds. In separating them from the excess of sulphuric acid, advantage is taken of the ready solubility of their calcium and barium salts in water: the process is similar to the separation of ethyl hydrogen sulphate from sulphuric acid (54). They can also be separated from their concentrated solutions con- taining sulphuric acid by the addition of common salt imtil no more will dissolve, when the sodium salt of the sulphonic acid pre- cipitates in the solid state. This salt is dissolved in water, the equivalent quantity of mineral acid added, and the free sulphonic acid isolated by repeated extraction with ether.
The sulphonic acids are colourless, crystalline substances, generally hygroscopic, and freely soluble in water. They can be reconverted into the aromatic hydrocarbons by treatment at a high temperature with hydrochloric acid, or with superheated steam (287, 5), a reaction discovered by Armstrong.
Most of the sulphonates crystallize well, and are employed in the purification of the sulphonic acids. On treatment with phosphorus pentachloride, the latter are converted into chlorides:
GeHfi-SOa-OH ^ CeHs-SOg-CI.
The sulphonyl chlorides can also be obtained directly by the interaction of chlorosulphonic acid and aromatic hydrocarbons:
C6H6+H0.S02-C1 = C6H5.S02-Cl-f-H20.
S 202] PHENOLS. 409
They are very stable towards cold water, being but slowly recon- verted into sulphonic acids. Benzenesidphonyl chloride melts at 14-5^. Like the other sulphonyl chlorides, it has a very dis- agreeable odour.
The sylphonamides, are formed by the action of excess of con- centrated ammonia on the chlorides:
C6H6.SO2CI -> C6H5-S02-NH2.
The sulphonyl chloride first dissolves, the sulphonamide being then precipitated by addition of acid.
They are well-crystallized compounds: the determination of their melting-points is often employed for the identification of an aromatic hydrocarbon. On account of the strongly negative character of the group C6H5SO2 — , the hydrogen atoms of the NH2-group are replaceable by metals; hence the sulphonamides are soluble in alkalis and anmionia.
Prolonged reduction of sulphonic acids yields Oiiaphenols of the type CeHs^SH, substance reconvertible into sulphonic acids by oxidation.
The sulpho-group can be replaced by the hydroxyl-group and the cyano-group (292 and 311).
IV. MONOHYDRIC PHENOLS.
292. The phenols are. compounds derived from the aromatic hydrocarbons by replacement of one or more of the hydrogen atoms of the nucleus by hydroxyl.
Phenol, CeHs-OH, and some of its homologues, such as cresol and others, are found in coal-tar. During its fractional distillation they are accumulated in the carbolic oil and creosote-oil (286). They arc isolated by agitating these fractions with caustic alkali, which dissolves the phenols, leaving the hydrocarbons. They are liberated from the solution with sulphuric acid, and are then separated by fractional distillation. By far the larger proportion of the phenol of commerce is obtained from this source.
Phenol and its homologues can also be obtained by othe r methods.
1. By fusion of the salt of a sulphonic acid with alkali:
C6H5-S03K-I-2KOH = CeHs-OK+KaSOa + HaO.
410 ORGANIC CHEMISTRY. [{ 203
2. By the action of nitrous acid on aromatic amines, a method analogous to the preparation of alcohols of the ahphatic series from amines (65). But whereas on treating an aliphatic amine with nitrous acid the alcohol is produced directly, in this reaction very important intermediate products, the diazonium compounds (305)1 can be isolated.
3. By the action of oxygen upon benzene in presence of aluminimn chloride, phenol is formed.
293. The phenols are in some respects comparable with the tertiary alcohols, since in both the hydroxyl is Imked to a carbon atom in direct union with three others, although in the phenols one of these bonds is of a special kind. Like the tertiary alcohols, therefore, they cannot be oxidized to aldehydes, ketones, or ackls containing the same number of C-atoms. The phenols exhibit many of the characteristics of the aliphatic alcohols: they form ethers by the interaction of alkyl halides and their alkali-metal salts; they produce esters, forming, for example, acetates with acetyl chloride. Phosphorus pentachloride causes the exchange of CI for their OH, although not so readily as in the aliphatic series. But in addition to these properties, the phenols possess special characteristics due to their much stronger acidic character. When describing the separation of phenols from carbolic oil (292), it was mentioned that they dissolve in caustic alkalis: phenoxides, such as CeHs'ONa, are formed. The alcohols of the aliphatic series do not possess this property in the same degree. If they are insoluble in water, they do not dissolve in caustic alkalis, and are only con* verted into metallic alkoxides by the action of the alkali-metala. This increase in acidic character can only be occasioned by the presence of the phenyl-group; in other words, the phenyl-group has a more negative character than an alkyl-group. Otherwise, the phenols behave as weak acids: their aqueous solutions are bad conductors of electricity, and the phenoxides are decomposed by carbonic acid.
It is thus evident that the properties of the hydroxyl-group are considerably modified by union with the phenyl-group. Inversely, the influence of the hydroxyl-group on the benzene-nucleus is equally marked: it makes the remaining hydrogen atoms much more readily substituted. Benzene is only slowly attacked by bro- mine at ordinary' temperatures,but the addition of bromine-water to
52941 PHENOLS. 411
an aqueous solution of phenol at once precipitates 2:4: Q-tribromo- phenol — a reaction employed in its quantitative estimation. Tl.e conversion of benzene into nitrobenzene necessitates the use of con- centrated nitric acid, but phenol yields nitrophenol on treatment with the dilute acid. Phenols are also much more readily oxidized than the aromatic hydrocarbons. When they are heated with zinc ammonium chloride, the hydroxyl-group is replaced by the amino-group.
On distillation with zinc-dust, the phenols are reduced to the corresponding hydrocarbons. They can be detected by the formation of a violet coloration when ferric chloride is added to their aqueous solutions, probably due to the production of a ferric salt of the phenol.
294. Phenol, or carbolic acid, is a colourless substance, crystal- lizing in long needles. It melts at 39 '6^, boils without decom- position at 181°, has a characteristic odour. On account of its powerful antiseptic properties, it was introduced into surgery by Lister, but to a great extent its place has been taken by. mercuric chloride. Phenol is soluble in water, 1 part dissolving in 15 at 16° : it can also dissolve water. On account of the small molecular weight of water, and the high molecular depression of phenol (75), a small percentage of water renders phenol liquid at ordinary temperatures (12). It follows from the equation AM =7 5y in which M is the molecular weight of water (18), that A, the lowering of the freezing-point occasioned by the presence of 1 per cent, of water, is about 4 •2°.
The hydroxytoluenes, CH3«C6H4«OH, are called cresols: they are present in coal-tar, but are usually prepared from the corre- sponding amino-compounds or sulphonic acids. On oxidation, they are completely decomposed, but when the hydrogen of the hydroxyl-group is replaced by alkyl or acetyl, they can, like toluene itself, be oxidized to the corresponding acids. The cresols resemble phenol in their behaviour towards an aqueous
solution of bromine. p-CresoZ, CHa^ /OH, is a decomposi- tion-product of albumin.
Thymol is also used as an antiseptic. It is hydroxycymene,
/CH3 1
CySa^OH 3.
\CH(CH3)2 4
412 ORGANIC CHEMISTRY, l§§ 295, 296
Acid sulphuric esters of phenol are present in urine: they result from the fermentation (putrefaction) of proteins, since the propor- tion present depends upon the extent of this process.
Ethers.
295* A distinction is drawn between the aromatic-aliphatic ethers, such as anisole, CeHs-O-CHa, and the true aromatic ethers, like diphenyl ether, CeHs-O-CeHs- Compounds of the first class are formed by the interaction of alkyl halides or dimethyl sulphate and phenolates (293):
C6H6.0.|Na+I|C2H5 = C6H5.0.C2H5+NaL
The true aromatic ethers cannot be prepared by this method, since the halogen atom attached to the nucleus is exchanged only with difficulty (289). Diphenyl ether is obtained by passing vapor- ized phenol over heated thorium oxide:
CeHs* OH+H O-CeHs = C6H6«0*C6H6+H20.
The mixed aromatic-aliphatic ethers are stable compounds, and resemble the true aliphatic ethers closely in behaviour. Many of their reactions are similar to those of the aromatic hydro- carbons themselves. When heated to a high temperature with a hydrogen halide, they 3deld a phenol and an alkyl halide:
CeHs-O'CHa+HI = CoHs-OH+CHs-I.
AnUole
The true aromatic ethers, such as diphenyl ether, are not decom- posed by hydriodic acid, even at 250**.
Anisole, CeHs-O -CHa, is a liquid, and boils at 155®. PhenetoUf C6H5.O.C2H6, is also a liquid, and boils at 172^. Each of these compounds has a lower boiling-point than phenol itself (294), and each has a characteristic odour.
v. MONOAMINO-COBC>OUNDS.
296. The amino-compounds of the aromatic series, with the NH2-group attached to the*ring, are almost exclusively obtained by reduction of the corresponding nitro-compounds. This pro- cess is effected by various means.
; : • ;
§ 296] MONOAMINO-<:OMPOUNDS. 413
Amines can be obtained from phenols by heating them at 300° with ammonium zinc chloride.
The aromatic amines are colourless liquids, or solids, and have a characteristic odour. They are only slightly soluble in water. Their specific gravities approximate to 1, and their boiling-points lie above 180°. With water, the aliphatic amines form stronger bases than ammonia, but the aqueous solutions of the aromatic amines possess only weakly basic properties: thus, they do not turn red litmus blue, and scarcely conduct an electric current. The aromatic amines yield salts, however, although these have an acid reaction in solution, on account of partial hydrolysis. The negative character of the phenyl-group, already alluded to in -connexion with phenol (293), considerably modifies the nature of the amino-group: the difference in the behaviour of diphenylamine and of triphenylamine in particular betrays this influence. With strong acids the former can yield salts, which, however, are completely hydrolyzed by the addition of a considerable quantity of water: the second does not unite with acids. _
Diphenylamine picrate furnishes another example of the hydro- lysis of salts of the base. The picrate is brown, picric acid yellow, and diphenylamine colourless. The salt and the free base are only slightly soluble in water, and picric acid is moderately soluble. Since the hydrol3rtic equilibrium corresponds with the expression
Salt + Water ^ Acid+Base,
and since the mass of the water may be regarded as constant owing to the large amount present, application of the law of mass action in this instance gives the expression
Concentrationocfd = Constant.
The concentrations of the salt and of the diphenylamine are also constant, owing to the solution being continually saturated by con- tact with the solids.
At 40*6° the constant concentration of the acid has been deter- mined to be 13 grammes per litre. When a solution of picric acid of this concentration is poured on solid diphenylamine, the formation of the salt does not take place; that is, the salt is completely hydro- lyzed. Increase in the concentration of the picric acid imparts a brown colour to the diphenylamine owing to the formation of the
414 ORGANIC CHEMISTRY. [§ 296
salt, and this phenomenon persists until the concentration has fallen to 13 grammes per litre.
Substitution of the amino-group for hydrogen produces the same efifect upon the benzene-nucleus as substitution of the hydroxyl- group for hydrogen, making the rest of the hydrogen atoms of the nucleus much more easily replaced: thus, aniline is readily converted by bromine-water into 2:4:6-tribromoaniline. More- over, the amines are much more readily oxidized than the hydro- carbons.
By means of an alkyl halide, the hydrogen atoms in the amino- group of the primary aromatic amines, like those in the amino- group of the primary aliphatic amines, can be replaced by an alkyl-
group (63) :
CeHfi.NHa+CHsI - C6H5-NH(CH3)-HL
Secondary and tertiary bases and also quaternary ammoniimi bases, such as C6H6.N(CH3)3.0H, are known. The last are as strongly basic as the corresponding true alipha*^ic compounds.
The anilidea are derivatives of aniline, C6H6-NH2, and its homo- 1 3gues: they are acid amides, in which one amino-hydrogen atom has been replaced by a phenyl-group. Acetoanilide, CeHs-NH-COCHs, employed' as a febrifuge under the name " antifebrine," is a type of these compounds. The anilides are produced by boiling aniline with the corresponding acid. Acetoanilide is obtained by heating aniline with glacial acetic acid:
CeHfi.NHJHTHOlOC.CHa - CeHs-NH-COCHs+HaO.
Like the acid amides of the aliphatic series (96), the anilides are readily decomposed into their parent substances by boiling with a dilute solution of an alkali-metal hydroxide or of a mineral acid.
Menschutkin found that the velocity of formation of aceto- anilide is much less for an excess of aniline than for an excess of glacial acetic acid, although on theoretical grounds the velocity of :* formation should be the same in both cases; for at each moment it should be proportional to the product of the concentrations of the glacial acetic acid (c) and of the aniline (c'), being therefore exi»esBed
by
in which k is constant.
•W".
297) ANILINE. 415
The difference between theory and experiment admits of various explanations: one is that the reaction in the two cases takes place in different media. The important influence of the medium is mentioned in 71.
Aldehydes react with aromatic amines with elimination of water:
xj oln _L H HNCeHs _ tt pt^NHCeHs i tt r\ ^^^P + HHNCeHg " "2^^NHC6H5+"^^-
Formaldehyde Meihylenediphenyldi*mine
The combination of aromatic aldehydes and aromatic amines is exemplified by the equation
CsHs-CHlQ+H^N-CeHs = C6H5-CH:NH.C6H5+H20.
Bensaldehyde Benialaniline
Primary aromatic amines show the carbylamine-reaction: with nitrous acid they yield diazonium compounds (305).
Aniline.
297. Aniline was first obtained by the dry distillation of indigo (Portugese, anil; from Sanskrit, ntZa, dark-blue, and mid, the indigo-plant); hence its name. It is manufactured by the action of hydrochloric acid and iron-filings on nitrobenzene con- tained in a cast-iron cylinder fitted with a stirring apparatus:
CeHsNOz+SFe + eHCl = C6H5NH2-h2H20 + 3FeCl2.
It is remarkable that in this process only about one-fortieth of the hydrochloric acid required by the equation is needed for the reduction. This is probably because iron-filings and water are able to effect the reduction in presence of ferrous chloride. Lime is added as soon as the reduction is complete, and the aniline is distilled with steam.
Aniline is also obtained by the electro-reduction of nitro- benzene (303).
Aniline is a colourless liquid, and, unless perfectly pure, turns brown in the air, the colour-change being probably due to the pres- ence of traces of sulphur compounds. It is only slightly soluble in water: it boils at 183®, and has a specific gravity of 1-024 at 16®. Formaldehyde yields with aniline a remarkable condensation- product, anhydroformaldehydeaniline, (C6H5N==CH2)3. This sub-
416 ORGANIC CHEMISTRY. [i298
stance melts at 40®, and dissolves with difficulty. It is employed in the identification of both formaldehyde (io8) and aniline.
An aqueous solution of free aniline gives a deep-violet colora- tion with bleaching-powder solution, the primary product in the reaction being probably phenylchloroaminej C6H5-NHC1, analo- gous to the formation of chloroamine, NH2CI, from ammonia. The phenylchloroamine condenses with the aniline to form coloured substances. An am'line salt in acid solution is coloured dark-green to black by potassium dichromate. These two reac- tions, and that with wood (228), serve as tests for aniline. The bleaching-powder reaction is particularly delicate. The oxidation of aniline is discussed in 338.
Homologues of Aniline.
Ortho-ioluidine and para-toZuidine, CH3-C6H4-NH2, are formed by the reduction of the corresponding nitro-compounds- The ortho-compound is a liquid, B.P. 199' 4°; the para-compound is a solid, M.P. 45°. The different solubilities of their oxalic-acid salts afford a means of separating them.
The monoamino-derivatives of the xylenes are called xylidines. Six isomerides are possible, due to differences in the relative posi- tions of the methyl groups and the amino-group in the ring, .^gme of the toluidines and the xylidines are employed in making ooal- tar colours, and are, therefore, manufactured in large quantities.
Secondary Amines.
298. Diphenylamine, CeHs-NH-CeHs, melts at 64®, and boils at 310®. It is a type of the true secondary aromatic amines. They are formed by heating the hydrochlorides of the primary amines with the free amines :
C6H5INH2 ' HC1Th[HN > CeHs = NH4CH-HN(C6H6)2.
Diphenylamine can also.be obtained by the action of bromobenzene on potassium anilide, C6H5-NHK.
Diphenylamine has an agreeable, floral odour.
Diphenylamine is a very sensitive reagent for the detection of nitric acid, which produces a deep-blue colour with its solution in concentrated sulphuric acid. This reaction can only be applied to
i 299] SECONDARY AND TERTIARY AMINES. 417
the detection of nitric acid in the absence of other oxidizing sub- stances, such as bromine- water, permanganate, etc., since diphenyl- amine also gives a blue coloration with many of these i*eagents.
The method of formation of the mixed aromatic-aliphatic amines, such as methylaniline, CeHs-NH-CHa, is indicated in 296. The action of the alkyl iodide upon aniline results in the substitu- tion of more than one hydrogen atom of the amino-group by an alkyl-group, so that a mixture of the unchanged primary and the secondary and tertiary amines is formed. The secondary amine is obtained pure by first replacing one hydrogen atom of the amino- group by an acid-radical, such as acetyl, and subsequently treating the acetyl-derivative with an alkyl iodide.
To prepare such a compound as methylaniline, for example, aniline is first converted into acetoanilide, CeHs-NH^CCX^Ha, by boiling with glacial acetic acid. The hydrogen atom linked to nitrogen in this compound can be replaced by sodium, yielding CgHs-NNa-COCHs, which on treatment with methyl iodide yields rnelhylacetoanUide, C^Us • N (CH3) • COCH3. Saponification with alkalis converts this compound into monomethylaniline.
The secondary aromatic amines, like those of the aliphatic series, are readily converted by nitrous acid into nitrosoamines,
such as nitrosomethylaniline, CqRs*^ <n^ • Liebermann's
reaction for nitroso-compounds is described in " Laboratory Manual," XXVII, n.
Careful oxidation of the nitrosoamines transforms them into
nitroamiTies, CftH»-N<p *. Compounds of this type are also
produced by the direct action of fuming nitric acid on secondary amines, such as methylaniline or ethylaniline, three nitro-groups simultaneously entering the nucleus. Franchimont has prepared a large number of nitroamines belonging to the aliphatic series.
Tertiary Amines.
299. Triphenylamine, (C6H5)3N, is a type of the true aromatic tertiary amines : only a few of them are known. It is obtained by the action of sodium and bromobenzene on diphenylamine, and is a solid, melting at 127°. It does not possess a basic character.
It is true that perchloric acid, HCIO4, can unite with triphenyl-
418 ORGANIC CHEMISTRY, [§ 299
amine, but this acid displays a special aptitude for combination with many substances, both nitrogenous and non-nitrogenous.
CH
Dimethylaniline, C6H6«N<^it', is the most important member
of the series of mixed aromatic-aliphatic tertiary amines. They can be obtained by the action of alkyl halides upon anilines, but are manufactured by heating aniline hydrochloride with the alcohol, a method in which alkyl halides react in the nascent state. Methyl alcohol and hydrochloric acid yield methyl chloride, and this com- pound then reacts with the aniline.
On heating the hydrochloride of an alkyl-aniline at 180**, in a current of hydrochloric-acid gas, the alkyl-groups are eliminated, with formation of aniline and alkyl chlorides. When the hydro- chlorides of the alkyl-anilines are strongly heated, the alkyl-groups linked to nitrogen are transferred to the benzene-ring. This reac- tion can be explained by assuming that decomposition into alkyl chloride and aniline first takes place as just described:
I. C6H6-NH(C2H6)HC1 = CeHs-NHj+CgHaa The reaction indicated in equation II. ensues:
II. C6H5.NH2+C2H5CI - C6H4<52h^jjC1-
The formation of the hydrochloride of p-toluidine, by the inter- action of methyl alcohol and aniline hydrochloride at a high tem- perature, is analogous. By this process it is possible to obtain even perUamethylaminobenzene, C6(CH3)6«NH2.
The para-hydrogen atoms of dimethylaniline and other dialkyl- anilines are replaceable by various groups. Thus, dimethylaniline reacts readily with nitrous acid, with formation of nUrosodimethyl' aniline,
ON<^N(CH8)2,
effected by the addition of potassimn nitrite to the solution of the tertiary base in hydrochloric acid. This nitroso-compound crystal- lizes in well-defined leaves of a fine green colour. It melts at 85^, and yields a hydrochloride crystallizing in yellow needles. On oxi- dation with potassium permanganate, the nitroso-group is con-
i 289] SECONDARY AND TERTIARY AMINES. 419
verted into a nitro-group, with fonnation of p-nilrodimethyl" aniline,
p„ .N(CH3)2l
On boiling with caustic soda, the amino-group of nitrosodi- methylaniline is removed, with formation of dimethylamine and nitrosophenol:
NitroMphenol
This reaction is employed in the preparation of pure dimethyl- amine (66).
The para-hydrogen atom of dimethylaniline can react with substances other than nitrous acid: thus, aldehydes readily yield a condensation-product :
CH..CH|0 + g|ggj^[gg;j; = C8H5.CH[C3»H4N(CH8)2l2.
The constitution of this compoimd is inferred from its relation to triphenylmethane^ CH(CeH5)3 (373). With dimethylaniline, car- bonyl chloride yields a p-derivativeof benzophenone,C6H5*CO-C6H5, called Mighler's ketone:
C6H4.N(CH3)2 ,/C6H4.N(CH3)2
- CO ^ +2Ha
C6H4-N(CH3)2 \C6H4.N(CH3)2
Heating with fuming nitric acid converts dimethylaniline into irinilraphenylniiToamine,
/CH3
(N02)8C6H2.N< ,
\N02
the reaction being accompanied by a copious evolution of gas, This compound is employed as an explosive. In its formation one of the methyl-groups is removed by oxidation, and replaced by the nitro-group, three additional nitro-groups being simul- taneously introduced into the nucleus. The reaction affords a general method for the formation of nitroamines.
420 ORGANIC CHEMISTRY. [§ 300
Quaternary Bases.
Quaternary bases are formed by the addition of alkyl halides to the tertiary aromatic-aliphatic amines, and treatment of the salts thus formed with moist silver oxide. These substances are strong bases. On heating, they yield an alcohol and a tertiary amine, differing in this respect from the aliphatic ammonium bases (66).
VI. INTERMEDUTE PRODUCTS IN THE REDUCTION OF AROMATIC
NITRO-COMPOUNDS.
300. On reduction, the nitro-compounds of the aliphatic series yield amines directly, from which the alkyl-groups can be removed by oxidation: for example, ethylamine'is converted into acetic acid and ammonia. In the aromatic series, on the other hand, intermediate products can be obtained in the reduction of nitro- compounds, and sometimes also in the oxidation of amines. Only the compounds derived from nitrobenzene and am'line will be described here, although numerous substitution-products of the same type are known.
In acid solution the nitro-compounds are directly reduced to the corresponding amino-derivatives, but in alkaline solution yield substances containing two benzene-residues. Nitrobenzene yields in succession azoxybenzenSf azabenzene, hydrazohenzene, and aniline:
1. Nitro-compound, C6H5«N02 02N«C6H6;
2. Azoxy-compoundf
CeHs-N N.QHs;
\o/
3. Azo-compoundy CeHs-N^N-CeHs;
4. Hydraz(H^ompound, CeHs-NH— ^^NH-QHs;
5. Amino-compound, C6H6-NH2 H2N*C6H5.
Azoxybemene is obtained by boiling nitrobenzene with alcoholic potash, and is also formed in the oxidation of aniline with potas- sium permanganate in alcoholic solution, tt forms light-yellow crystals melting at 36°. When warmed with concentrated sulphuric acid, it is transformed into p-hydrozycizohemene:
CeHi.N N.CeH. - C6H5.N=N.C(iH4.0H.
\ -. / Hydroxyaiobensene
§301] REDUCTION OF NITRO-COMPOUNDS. 421
It is readily attacked by various reducing agents. Under the influ- ence of direct sunlight, concentrated sulphuric acid converts azoxy- benzene into o-hydroxyazobenzene.
IhAzoxypherietole, CaHO.CeH^.N— N.CeHi.OCaH., is distin-
O
quished by its power of forming liquid crystals, a property char- acteristic of a considerable number of other substances. When heated, it melts at 134° to'a turbid liquid, which suddenly becomes clear at 165®. The crystalline structure of the turbid liqiud cannot be detected by the microscope, but is indicated by the double refraction exhibited by the liquid, and by the formation of the figures characteristic of double- refracting cr3rstals between crossed Nicol prisms in converging light. Turbidity is not an essential characteristic of liquid crystals, as VoRLANDER has discovered perfectly clear liquids which display phenomena like those of double-refracting crystals.
301 . Azobemene, CeHs • N : N • CeHs, is formed by the reduction of nitrobenzene with a solution of stannous chloride in excess of caustic potash, and also by distilling azoxybenzene with iron-filings. It is produced along with azoxybenzene by the oxidation of aniline with potassium permanganate.
Azobenzene forms well-defined, orange-red crystals, melting at 68°, and boiling without decomposition at 295®. It is a very stable compound, and is insoluble iu water. Its constitution follows from its yielding aniline on reduction.
Hydrazobenzeney Cells* NH — NH-CeHs, is formed by the action of zinc-dust and alcoholic potash upon azobenzene or nitrobenzene. It is a colourless, crystalline substance, and melts at 126°. Strong reducing agents convert it into aniline: on the other hand, it is readily oxidized to azobenzene, the transformation being slowly effected by atmospheric oxygen. It is also oxidized to the azo- compound by ferric chloride.
The most characteristic reaction of hydrazobenzene is its con- version into benzidine J whereby the benzene-nuclei are, as it were, turned end for end. This " benzidine-transformation " is effected by the action of strong acids:
^77)nH-Ne(7^ ^ H2N.C6H4— C6H4.NH2.
Hydrazobenzene Benzidine
That a diaminodiphenyl is thus formed is proved by the conversion
422 ORGANIC COMPOUNDS, [§ 302
of benzidine into diphenyl; CeHs • CeHg. The amino-groups occupy the para-positions:
o-o
By reducing azobenzene in acid solution, benzidine is formed directly. It is characterize^ by the sparing solubility in cold water of its sulphate.
The amino-groups in benzidine are proved in various ways to occupy the para-position: for example, a hydrazobenzene the p-hydrogen atoms of which have been substituted cannot be con- verted into benzidine. In certain instances compounds of this kind can undergo a remarkable intramolecular transformation, known as the "semidine-transformation," forming derivatives of diphenyla- mine by the turning of only one of the benzene-nuclei:
h/q^NH-NH .CeH,NH .COCHs->H,N (^ NH -CeH^NH .OOCH,.
p-Aoetaminohydrasobeniene p-Aminophenyl-p-acetamino-
phenylamine
Electro-reduction of Nitro-compounds.
302. There is reason to believe that in the future electroljrtic methods will be used more and more in chemical work, for the elec- trie current afifords a means of varying the pressure and concentra- tion of the substances taking part in reactions in the preparation of organic compounds, which is not otherwise attainable. By its aid it is possible to effect new S3mtheses or to improve those ahready known. An explanation of this mode of altering the pressure and concentration is necessary here.
Alteration in the contact-difference of potential between the elec- trodes and the electrolyte causes considerable variation in the pres- sure at which the discharged ions leave the solution (273). la reduction-processes the same effect is attained by using different re- ducing agents. When a compound yields a series of intermediate products on treatment with different reducing agents of increasing strength, this can also be effected by increasing the contact-difference of potential (273) at the cathode, where hydrogen is evolved.
Regarding variation in the concentration, it must be remem- bered that the electrolytic process takes place only in the immediate neighbourhood of the electrodes. When the surface-area of the electrodes is altered, the strength of the current remaining the same,
§ 3081 ELECTRO-REDUCTION OF NITROCOMPOUNDS. 423
the number of ions discharged at unit surface varies in direct pro- portion: it is therefore possible, by selecting suitable electrodes, to cause the concentration of the ions discharged at them to vary within wide limits. The '^ strength " of the reducing agent depends upon the contact-difference of potential, but its concentration is controlled by the density of the ciurent. In reactions in which the discharged ions must interact, a^ in the synthesis of dibasic acids (loc. cU.), a current of high density is necessary: on the other hand, in reductions which must take place as far as possible at all parts of the liquid, large cathodes, which give a current of small density, must be used.
On reduction, nitro-compounds ultimately jdeld amines, but a number of intermediate reduction-products can be isolated. For this reason the electro-reduction of nitro-benzene and its derivatives is of both theoretical and practical importance. It is possible to give a complete and satisfactory explanation of the mechanism of this process.
303. A distinction must be drawn between primary or elec- trolytic, and secondary or chemical, reduction-products. The primary process is
C6H5.NO2 -♦ CeHfi.NO -♦ CeHg.NHOH -♦ CeHs-NHj.
Nitrobensene Nitrosobeniene Phenylhydroxyl- Aniline
amine
The presence of nitrosobenzene can be detected by the addition of hydroxylamine to the liquid, with which it reacts with loss of one molecule of water, and formation of diazoniuni hydroxide, C«H(*Ns*OH: on adding o-naphthol, an azo-dye is produced (340).
The formation of phenylhydroxylamine can be proved by adding benzaldehyde, with which it yields benzylidenephenylkydroxylamine:
CA-NHOH+OCH-CeHj - H2O+ X
Bensaldehyde ^
On rapid reduction of nitrobenzene dissolved in moderately con- centrated sulphuric acid, with addition of alcohol to increase the solubility, the primary process just described takes place, about 90 per cent, of the theoretical yield of aniline being obtained. In a strongly acid solution, however, the phenylhydroxylamine is very quickly converteJTnto p-aminophenol:
CeHg.NHOH -> HO.C6H4-NH2.
424 ORGANIC CHEMISTRY, [§ 301
This substance is not further reduced. Since phenylhydroxylamine undergoes the same transformation, though much more siowiy, in presence of more dilute acid, it is evident that the theoretical yield of aniline cannot be obtained, even when the solvent is dilute, and the velocity of reduction great.
304. In alcoholic-alkaline solution the electro-reduction of nitrobenzene is accompanied by two secondary processes.
1. Nitrosobenzene reacts with phenylhydroxylamine, yielding azoxybenzene: ^^^^^^ ^.^^jj^
CeHs-NHOH+CeHfi.NO - \/ -hHgO.
0 In presence of alkali this reaction proceeds much more quickly ^han the further reduction of phenylhydroxylamine, so that only small quantities of aniline are formed, and higher reduction-products of azoxybenzene, chief among them hydrazobenzene, obtained as the main part of the yield.
2. Hydrazobenzene is attacked by the unreduced nitrobenzene with formation of azobenzene and azoxybenzene:
3C6H6-NH.NH.C6H5+2C6H6.N02 = 3C6H6.N:N.C6Hij+
CeHfi-N N.CeHs
+ \/ +3H20,
O
Since hydrazobenzene in alkaline solution is quickly oxidized by atmospheric oxygen to azobenzene, the yield of azobenzene is very good.
A much higher contact-difference of potential at the cathode is required to reduce hydrazobenzene to aniline; since for the formation of nitrosobenzene and phenylhydroxylamine a difference of about 0-93 volt is necessary, while with a difference of 1-47 volt only traces of aniline are formed from hydrazobenzene.
Haber has combined these primary and secondary reactions in the scheme given on next page, the vertical arrows indicating primary, and the oblique arrows secondary, reactions.
Bamberger pointed out that the reduction of nitrobenzene by purely chemical methods yields the same intermediate products. Thus, nitrosobenzene is formed by its interaction with zinc-dust and water. In accord with this view is the fact that the velocity of reduction of nitrobenzene by stannous chloride in presence of a great
§305]
DIAZO-COMPOUNDS.
425
C,H,.N:N.C,H,
C,H,-NO, C. H,- N(0H)2
CH.-n^.cTh. j
CeHj.NO
1
C, H,-NHiQH: C,H,-NH-NH.C,H,
Haber'b Electro-reduction Scheme.
excess of hydrochloric-acid solution indicates that the reaction is bimolecular, and must therefore be represented by the equation
R.NOj+Snaa+nHCl - R-NO+SnCl4 + H,0+(n-2)HCl.
This reaction has a measurable velocity. The further reduction of the nitroso-compoimd to the amino-compound should be very rapid: experimental evidence confirming this theoretical view is afforded by the fact that when nitrosodimethylaniline is brought into con- tact with stannous chloridoi it is at once reduced.
Vn. DIAZO-COMPOXmDS.
305. The diazo-compounds of the aromatic series, discovered by GuiEss in 1860, are not merely of theoretical importance, but play an important part in the manufacture of dyes. In the aliphatic series only amino-compounds of a special kind yield diazo-com- pounds (245), while their formation is a general reaction of the primary aromatic amines. The "property of undergoing diazotizaJtion 18 characteristic of aromatic amines.
All diazo-compounds contain the group — N2 — . Hantzsch has classified them in two divisions.
Ar.N.X
I. Substances with the structural formula
N
, in which
426 ORGANIC CHEMISTRY. [\ 305
Ar represents phenyl, CeHs, and its homologues and derivatives. They are called diazonium salts, and are analogous to the anunonium salts.
II . Substances with the structural formula Ar • N=N • X. These derivatives are called diazo-compounds, and resemble the azo-com- pounds. They are known in two stereoisomeric modifications.
Ar.N
1. Compounds with the stereochemical formula ||. They
X-N
are called syndiazchcompounds, are imstable, and can be isolated only in certain cases.
Ar-N
2. Compounds with the stereochemical formula || , or
N.X
Antidiazo-compoundSj which are stable.
Intrinsically, the diazonium compounds are of slight import- ance, but the numerous transformations which they can undei^, with formation of a great number of derivatives, render them much more important than the diazo-compounds, and account for their great significance in the chemistry of the aromatic compounds.
Diazonium compounds are formed by the action of nitrous acid upon the salts of aromatic amines:
C5H6-NH2.HN03+HN03 = 2H20+C6H5.N2-N03.
AnifiDe nitrate tBenwnediasonium nitnit*
This is effected by adding a solution of sodium nitrite to a solution containing an cquimolecular proportion of the amine-salt and an equivalent quantity of a free mineral acid, the reaction-mixture being cooled by the addition of ice, as the diazonium compounds decompose very readily. A solution of the benzenediazonium salt is thus obtained.
The preparation in the solid state of such a salt as bemenedta- zonium nitrate, C«H«.Ni.N08, is effected by passing nitrogen tri- oxide, generated from nitric acid and arsenious oxide, into a solution of aniline in dilute nitric acid. On addition of alcohol and ether, the nitrate separates in crystalline form. On ignition or percus- sion, the dry salt explodes with great energy, so that only a few deci- grammes should he isolated in the dry stale. Almost all the dty dia- - zcrJum salts are excessively explosive, and must, therefoiei be
§306] DIAZO-COMPOUNDS. 427
handled with great care. In aqueous solution they are harmless and as they 3aeld derivatives without being isolated, they are seldom prepared in the solid state.
306. The constitution indicated for the diazonium salts is inferred from the following considerations.
The group N2X of the diazonium compounds, in which X represents an acid-residue, is only linked to one carbon atom of the benzene-nucleus, for all their transformations produce sub- stances containing a group likewise linked to only one carbon atom of the nucleus.
In many respects the group C6H5-N2 — behaves similarly to an alkali-metal, and still more to the ammonium radical. With strong mineral acids it forms colourless salts of neutral reaction, like KCl and NH4CI, while its salts with carbonic acid resemble the alkali- metal carbonates in having an alkaline reaction, due to hydrolytic dissociation. The conductivity of the diazonium salts of hydro- chloric acid and other acids indicates that they are as strongly ionized as KCl and NH4CI. Similarly, diazonium chlorides yield complex platinum salts, such as (C6H5N2Cl)2PtCl4, soluble with diffi- culty in water. Other analogous salts, such as (C6H5N2Cl)AuCl3, have also been obtained. Free benzenediazonium hydroxide^ C6H6*N2'0H, is only known in the form of an aqueous solution, which haa a strongly alkaline reaction. It is obtained by treating the aqueous solution of the chloride with silver oxide, or by the addition of the equivalent quantity of baryta-water to the sulphate. Like caustic-potash solution, it is colourless, but through decom- position gradually deposits a flocculent, resin-like substance.
The existence of a quinquivalent N-atom in the diazonium salts, as in the ammonium salts, must therefore be assumed, the basic properties of the members of each class being due to its presence. Two formulae are thus possible:
C6H5N=N.X or CeHsN^J.
For reasons given in 308, the preference must be given to the second.
Benzenediazonium hydroxide is a strong base, but reacts with alkalis in a manner quite unknown among the strong mineral bases. When a diazonium salt is added to a strong solution of caustic potash,
428 ORGANIC CHEMISTRY. I§ 307
a potassium derivative, CcHi -Ni -OK, separates out. The reaction takes place not only in concentrated, but also in dilute, solutions. When a dilute solution of benzenediazonium hydroxide is treated with an equivalent quantity of caustic soda in dilute solution, the molecular conductivity of the mixture is considerably less than the sum of the two electric conductivities of the solutions separately. It follows that a portion of the ions (CeHgNjOy + H* and Na*+OH% which have been brought into contact, have changed to the non- ionized state — union of H* and OH'; that is, a salt must have been formed.
Thus, the diazonium hydroxide, which is a strong base, appears to behave like an acid also. Since this is very improbable, HANTzdCH assumes that an equilibrium exists in the aqueous solution between the diazonium hydroxide and the ^ndiazohydroxide (308):
CHjN.OH -►CeHsN
II - II
N HON
Diasonium ^i^Diaso* hydroxide hydroxide
He supposes that the alkali-metal compounds are derived from the latter substance.
Reactions of the Diazonium Compounds.
307. Many of the reactions of the diazonium compounds are characterized by the elimination from the molecule of the group — N2 — as free nitrogen, and its replacement by a substituent linked by a single bond to the benzene-nucleus. Extended research has revealed the conditions best suited for obtaining nearly quantita- tive results in most of these reactions.
1. Replacement of the N2'group by hydroxyl. — This reaction is effected by allowing the aqueous solution of the diazoniunktelt to stand, or by warming it:
CeHs-Nz-Cl+HOH = CeHs-OH+Ng-fHCl.
2. Replacement by an alkoxylrgroup, — 0'CnH2n+i. — ^This re- placement is carried out by boiling a diazonium salt with alcohol:
CeHs-Ng-lHSOT+HlG.CaHg = C6H50-C2H5+N2+H2S04.
In some instances, sunlight exerts an accelerating influence on reactions of the type described in 1 and 2.
S 307] REACTIONS OF THE DIAZONIUM COMPOUNDS. 429
3. Replacement of the diazonium-group by hydrogen. — Under certain conditions the diazonium salts do not yield alkoxyl- compounds with alcohols, but produce the corresponding hydrogen compound, the alcohol being converted into aldehyde;
N02-C6H4-N2-a+C2H50H=N02-C6H5-fC2H40-fN2 + HCl.
p-Nitrobenienediasonium Nitro- Acetal-
chloride bensene debyde •
Usually reactions 2 and 3 proceed simultaneously; but if the lenzsne-nucleus is already attached to several negative sub- stit lents, such as halogen atoms or nitro-groups, replacement by hydrogen predominates, even with the higher alcohols.
Another method of substituting hydrogen for the amino- group is mentioned in 310.
4. Replacement of the diazoniumrgroup by chlorine. — ^This reac- tion is effected by treating a solution of diazonium chloride either with cuprous chloride dissolved in concentrated hydrochloric acid (Sandmeyer), or with finely-divided copper (Gattermann):
CeHs-Na-Cl- CeHs-Cl+Na.
Cuprous chloride and finely-divided copper have a catalytic action: it is probable that a copper compound is formed as an inter- mediate product, and afterwards decomposed.
Heplacement by bromine is carried out similarly: thus, in the preparation of bromobenzene, a solution of potassium bromide is added to an aqueous solution of benzenediazonium sulphate con- tidning free sulphuric acid; on addition of copper-dust to this mix- ture, nitrogen is evolved, and bromobenzene formed.
Replacement by iodine takes place readily when a warm solution of potassium iodide is added to a diazonium-sulphate solution : it is unnecessary to employ copper or cuprous chloride.
5. Replacement of the diazonium-group by the CN-group. — This replacement, too, readily takes place in presence of copper com- pounds. The solution of the diazonium salt is added to one of potassium cuprous cyanide:
. CeHs-Na-Cl+KCN = C6H6-CN+N2+KC1.
This reaction is of great importance for the synthesis of aromatic acids, which can be obtained by hydrolyzing the resulting nitriles.
430 ORGANIC CHEMISTRY. [{ 306
6. Replacement of the diazonium-group by sidphur. — ^Addition of a solution of potassium xanthate (264) to one of a diazonium salt usually pretcipitates the diazonium xanthate :
C6H5-N2-Cl + KS-CS.OC2H5=C6H5.N2-S.CS.OC2H6-fKa.
On wanning the precipitate with its mother-liquor, nitrogen is evolved, and sulphur becomes directly attached to the nucleus, with formation of phenyl xanthatej C6H5-S-CS*OC2H5. The con- stitution of the product is proved by its oxidation to benzene- sulphonic acid. This reaction was discovered by Leuckart, and furnishes a valuable method for the introduction of sulpho-groups into benzene derivatives at positions not accessible through direct treatment with sulphuric acid.
These reactions illustrate the importance of the diazonium salts as intermediate products in the preparation of numerous sub- stances. Since they are derived from the amines, which are pre- pared by the reduction of nitro-compounds, it is evident that the nitration of aromatic derivatives is a reaction of great importance, for the nitro-group can be replaced at will by almost all other elements or groups by means of the amino-compounds and diazonium compounds.
308. The reactions of the diazonium compounds can be explained by assuming that they themselves do not enter into reaction, but wre first converted into ^ndiazo-compounds, which then decom- pose with evolution of nitrogen. The formation of phenol may be represented thus: _j
C5H5 OH CeHs OH CeHsOH
N=N +
h.
Phenol
-Ha+ N— N N=N:
•ynDiaso-
ii TT hydroxide
DiaBonium chloride
and that of chlorobenzene thus:
CeHj CI CeHs Ci CeHeO
I I I .> Chlorobenae
N3^+ -HC1+ N=N N=N.
I I tynDiaBo-
fy ]^ chloride
The reactions between diazonium salts and alcohol are explained as follows:
§ 309] REACTIONS OF THE DIAZONIUM COMPOUNDS. 431
CA OCA /CaHsOCaUX C.Hs--OC,H, tF^^tionM . a H Cl— H CI— H
C«H« H CeHj — H IFormation of • hydrocarbon. J
N=N + -» N3!^
CI CjHfiO ClOCaHg [Deoompoeition into Haand aldehyde, OAO-J
As these transformations of diazoniiim salts cannot be repre- sented by the aid of the other possible structural formula, CoH»'N^N-X, it is evident that it must be rejected (306).
Most of the syndiazo-compounds are very unstable. They change readily into art/idiazo-compounds, in which it is assumed that the phenyl-group and acid-residue are not contiguous, and therefore can no longer unite:
I I N=N
N=i i
«ynI>iaao-com pound; afih'Diaso-eompound!
CsH« and X can unite CeHs and X cannot unite
In certain cases, such as that of the diazocyanides, Hantzsch has been able to isolate these intermediate products, and thus afford a proof of these views. For example, when cyanides are added to diazotized p^hloroaniline, Cl*CoH4-NH2, p-chlorobemonUrUe, C1*C«H4-CN, is not immediately formed: it is possible to isolate a yellow intermediate product, Cl'C«H4«N2«CN, which yields p- chlorobenzonitrile after addition of copper-dust, the action being accompanied by an energetic evolution of nitrogen. This yellow intermediate p^hlorobenzenesyiuiicLZoq^arnde is, however, very un- stable, and speedily changes to an isomeride (the a7i/i-compound) which does not react with copper-dust. Stereochemical theory thus affords a satisfactory explanation of the observed phenomena.
309. The importance of the diazonium compounds is not con- fined to reactions in which the nitrogen atoms are eliminated, since important derivatives in which they are retained are known.
1. Diazoamiruhcompounds are obtained by the action of primary and secondary amines upon diazonium salts:
Csgs'Na-ICl+HINHCeHfi^ CeHg-Ng'NHCeHfi+HCL
Diasoaminobeniene
They are also produced when nitrous acid reacts with free aniline,
432 ORGANIC CHEMISTRY. [\ 309
instead of with an amline salt. It may be supposed that in this reaction benzenediazonium hydroxide, or benzenediazohydroxide iB first formed, and is at once attacked by a molecule of the aniline gtill present:
I. CeHg-NHa+HNOa - CsHg-Na-OH+HaO. n. CeHg.Nz- lOH+HINHCftHfi « CeHg-NiN-NHCsHfi+HjO.
Benienediaxohydrozide
The diazoamino-compounds are crystalline, and have a yellow colour. They do not unite with acids. In acid solution, they are converted by treatment with nitrous acid into diazonium salts:
CeHfi.N-.N.NHCeHs-f HN02+2Ha = 2C6H6-N2-C1+2H20.
The most characteristic property of the diazoamino-compounds is the readiness with which they can be transformed into isomerideB, the aminoazo^(ym'pofwnd8:
CoHfi.NiN-NH^O^H ->CeH6-N:N<[^NH2.
Diazoaminobensene Amiooaiobenwna
This is effected by adding aniline hydrochloride to a solution of diazoaminobenzene in aniline, and wanning the mixtiure on the
water-bath.
The amino-group in aminoazobenzene is in the para-position to the azo-group. Wh6n the paro-position is abeady occupied, the amino-group takes up the or^Ao-position. Aminoazobenzene and many of its derivatives are dyes (340) .
The equation indicates that the transformation of diazoamino- benzene into aminoazobenzene is a unimolecular reaction ("Inor- ganic Chemistry," 50). Goldschmidt proved by experiment that this view is correct. He dissolved diazoaminobenzene in aniline, and determined the quantity of diazoaminobenzene stiQ present after the lapse of known periods of time.
The aniline hydrochloride added in this reaction has merely a catalytic, accelerating effect upon the reaction,, as is proved, tni«r alia, by the uniform rise in the velocity-constant with increase in the amount of aniline hydrochloride.
2. Diazonium salts unite with tertiary amines at the para^
position: C8H5-Na-[cr+HlC6H4»N(CH3)2-C6H8-N:N.C6H4'N(CHa)8+HCl
Dimethylaniline DimethsrUminoasobenieiM
S 310] PHENYLHYDRAZINE. 433
3. They react similarly with phenols, forming hydroxyaz(hc(nnr^ pounds. This combination takes place in presence of alkalis:
(VHg - Na > pTHlCeHjOH - C6H5-N:N.C6H40H4-HC1.
Phenol HydroxyuobenwDe
Important dyes are also derived from hydroxyazobenzene (^41).
Vm. HYDRAZINES.
310. The typical derivative of hydrazine is phenylhydrazine, CeHs'NH^NHa, referred to several times in the aUphatic series in connection with its action on aldehydes, ketones, and sugars (103, 203, and 209). It is formed by the reduction of the diazonium salts; for example, from benzenediazonium chloride by the action of the calculated quantity of stannous chloride dissolved in hydro- chloric acid:
C6H6.N2-C1+4H = CeHs-NH— NH2.HCI.
It can also be obtained by transforming the diazonium salt into a diazosulphonate by means of an alkali-metal sulphite, reducing the diazosulphonate with zinc-dust and acetic acid, and eliminating the sulpho-group by boiling with hydrochloric acid:
I. CeHfi-Ng-a+NagSOg = CeHfi.NiN.SOgNa-f NaCl.
Sodium diasobenaeiiesulphonate
IL GjHe-N:N.S03Na-i-2H = CeHs-NH-NH-SOaNa.
Sodium pbeDylhydrasineBulphonate
m. CsHe.NH.NH-SOaNa+HaO = CaH5-NH.NHa+NaHS04.
, Phenylhydnuuke
In practice, this apparently roundabout way is simple, since the intermediate products need not be isolated. It is sufficient to mix solutions of the diazonium salt and of the sulphite, add the acetic acid and zinc-dust, and filter off the excess of zinc. The filtrate is then boiled with fuming hydrochloric acid, whereupon the hydrochloride, C6H5-NH.NH2«HC1, separates out, being soluble with difficulty in water, and almost insoluble in hydrochloric acid
Phenylhydrazine is a colourless, oily liquid, turning brown in the air. Its melting-point is 19.6°, and its boilmg-point 241°: when boiled under ordinary pressure, it undergoes slight decom- position. It is only slightly soluble in water.
Phenylhydrazine is decomposed by energetic reduction into aniline and ammonia. It is very sensitive towards oxidizing agents,
434 ORGANIC CHEMISTRY, [8311
its sulphate being oxidized to the diazonium salt by mercuric oxide. Oxidation usually goes further, however, the nitrogen being eliminated from the molecule. Thus, an alkaline copper solution converts it into water, nitrogen and benzene. Phenyl- hydrazine has a wholly basic character: it yields well-defined crysfalline salts.
Phenylhydrazine is proved thus to have the constitutional for- mula C6H5-NH-NH2. A secondary amine is converted by nitrous acid into the corresponding nitrosoamine:
^H6-N<^jj^-.C6H5.N<NO^.
MonomethyUniline Nitrosomethylaniline
On careful reduction, this substance yields methylphenylhpdrcLzine,
NH C6H6»N<QTT^, which can also be obtained from phenylhydrazine
by the action of sodium, one hydrogen atom being replaced by the metal. On treatment of this sodium compound with methyl iodide, the same methy Iphenylhydrazine is formed :
IX. AROMATIC MONOBASIC ACIDS: BENZOIC ACID AND ITS
HOMOLOGUES.
311. Benzoic acid, CeHs^COOH, can be prepared by many methods, of which the most important will be described.
1. By the oxidation of any aromatic hydrocarbon with a side- chain:
CeHs • CnH2n+i "-♦ CeHs •COOH.
Being inexpensive, toluene is specially serviceable for this purpose. In the manufacture of benzoic acid, toluene is not directly oxidized, but is treated at its boiling-point with chlorine. Benzotrichloride^ CfiHs-CCls, is first formed, and is converted into benzoic acid by heating with water:
OH CsHfi.CCl-fHOH-HaO = CeHs-COOH+SHCl.
OH
§311] BENZOIC ACID, 435
Benzoic acid thus prepared often contains traces of chlorobemoic ocuZ, CCH4CI.COOH.
2. By the oxidation of aromatic alcohols or aldehydes, such as
benzyl alcohol, CeHs -0112011, or benzaldehyde, CeHsC^ ^ : also by
the oxidation of alcohols, aldehydes, or ketones with longer side- chains: in fact, from all compounds containing a side-chain with OZ12 carbon atom directly linked to the benzene-nucleus.
3. By the introduction of the nitrile-group into the benzene- nucleus, and hydrolysis of the benzonitrUe, CeHs-CN, thus formed. The introduction of the nitrile-group can be effected in two ways.
(a) By diazotizing aniline, and treating the diazonium salt with potcussium cyanide (307, 5).
(b) By distilling potassium benzenesulphonate with potassium
cyanide (compare 78) :
CsHs-SOsK+KCN = CeHs-CN + K2SO3.
4. By the action of carbon dioxide and sodium on bromoben- zene, whereby sodium benzoate is formed:
C6H5Br+C02+2Na = NaBr+C6H5-C02Na.
5. By the action of various derivatives of carbonic acid, other than carbon dioxide, upon benzene, substances readily convertible into benzoic acid are formed.
(o) In presence of aluminium chloride, benzene and carbonyl chloride react together, with formation of benzoyl chloride^ the chloride of benzoic acid, and hydrochloric acid:
CfiHBlH+Cll.COCl = CeHfi.COCl+HCl.
BenioyI chloride
Benzoyl chloride is converted into benzoic acid by treatment with hot water.
(b) Benzene and aluminium chloride react with carbamyl Mo- ride J C1*C0NH2 (formed by passing carbonyl chloride over heated ammonium chloride) , yielding benzamide, the amide of benzoic acid :
C6H5H + Cll>CONH2 = C6H6-CONH2 + Ha
Bensamide
436
ORGANIC CHEMISTRY,
15312
(c) Bromobenzene is converted by sodium and ethyl chloro- formate into ethyl bemoaie:
+
Br-fCl
Na Na]
•COOC2H6 ^ CeHg-COOCzHs+Naa + NaBr.
312. Benzoic acid is a constituent of many natural resins and balsams, such as gum-benzoin, Peru-balsam, and Tolu-balsam. A derivative, hippuric acid (242), is present in the urine of horses. It was formerly prepared principally from gum-benzoin, from which source the benzoic acid used as a medicament is still sometimes obtained. It is a white solid, crystallizing in leaf-like crystals melting at 121-4^. It sublimes readily, and boils at 250^: it volatilizes with steam, and can be purified by steam-distillation. Its alkali-metal salts dissolve readily in water, most salts of other bases being soluble with difficulty.
The solubility-curve ("Inorganic Chemistry," 235) of benzoic acid has been the subject of careful investigation, on account of its interesting character (Fig. 80). The solubility increases somewhat rapidly with increase of temperature up to 90® {AB), At this tem- perature, the acid melts beneath the water, so that two liquids result: one is an aqueous solution, containing 11*2 per cent, of acid (point B)\ the other consists principally of the acid, containing 95*88 per cent, (point D), The mutual solubiUty of these layers is repre- sented in the part BCD of the curve, of which BC corresponds with the aqueous, and DC with the acid layer. The composition of the two
116" 121 •4»
Fig. 80. — Solubility-cur vb op Benzoic Acid in Water,
§ 3131 DERIVATIVES OF BENZOIC ACID. 437
layers becomes more and more alike as the temperature rises, since the water dissolves more benzoic acid, and the acid more water. At 116® they are identical in composition: that is, the liquid has again become homogeneous.
If more benzoic acid is added to the acid layer only, at 90°, it is necessary to raise the temperature to ke3p all the acid fused: the line DF is thus obtained, ending at F at the melting-point of pure benzoic acid, 121 •4°. DF therefore represente the melting-point- curve of the acid, on addition of increasing amounts of water.
Derivatives of Benzdlc Acid.
313. Benzoyl chloride, CeHfi-COCl, can be obtained by the action of phosphorus pentachloride or oxy chloride upon benzoic acid, or by the method of 311, 5a. It is a liquid of disagreeable odour, and boils at 194°. It is manufactured by treating benzaldehyde,
XT
C^Hs-Cq, with chlorine. Unlike acetyl chloride, which is rapidly
decomposed, it is very slowly acted upon by water at ordinary temperatures.
Benzoyl chloride is employed in the introduction of the benzoyl- group, CeHfi'CO^, into compounds. This is effected bv a method discovered by Baumann and Schotten, which consists in agitat- ing the substance in alkaline solution with benzoyl chloride.
Amines are readily benzoylated by suspending their hydrochlo- rides in benzene, adding the equivalent quantity of benzoyl chloride, and heating until evolution of hydrogen chloride has ceased.
Benzoic anhydride, CeHsCO-O-COCeHs, is formed by the inter- action of a benzoate and benzoyl chloride:
CeHg.CO.ONa+Cl .OCCeHg = NaCl-hCeHsCO.O.COCoHfi.
At ordinary temperatures it is very stable towards water, but is decomposed when boiled with it, yielding benzoic acid.
The formation of ethyl benzoate (311, 5c) is sometimes employed as a test for ethyl alcohol, since it possesses a characteristic pepper- mint-like odour.
Bemamide (311, 56), CeH6«CONH2, can be prepared by the
438 ORGANIC CHEMISTRY. I§ 314
action of ammonia or ammonium carbonate on benzoyl chloride. It is crystalline and dimorphous, melting at 130^. It is stated in 96 that the influence of the negative acetyl-group causes the hydro- j^en atoms of the amino-group in acetamide to be replaceable by metals. Benzamide displays this property to an even greater extent, on account of the more negative character of the benzoyl- group; for the values of the dissociation-constants for acetic acid and for benzoic acid respectively are 10*A; = 0-18 and 10*A; — 0-60. When the silver compound of benzamide is treated with an alkyl iodide at ordinary temperatures, an O-ether, benzoic iminoeiher,
CeHs-CC I is formed. The constitution of this substance is
proved by its yielding ammonia and alcohol, instead of ethylamine
and benzoic acid, when treated with alkalis. When, however, the
silver compound is treated with an alkyl iodide at 100°, a iV-aJkide,
/NHCjHj CflHs • C V > is formed. This is proved by the decomposition of
the latter substance into ethylamine and benzoic acid.
Benzonitrile, CeHs-CN, the methods of producing which are described in 311, 3, can also be prepared similarly to the aliphatic nitriles: for example, by the action of phosphoric oxide upon benzamide. It is a liquid with an odour resembling that of bitter almonds, and boils at 191^. It has all the properties characteristic of the aliphatic nitriles.
The honiologues of benzoic acidj such as the toluic acids, CH3.C6H4-COOH, the xylic acids, (CH3)2C6H3.COOH, and so on, are crystalline solids, very slightly soluble in water. They are prepared by methods analogous to those employed for benzoic acid.
X. AROMATIC ALDEHYDES AND KETONES.
Aldehydes.
XT
314. BenzoLdehyde, CgHs-Cq, is the best-known of the aromatic
aldehydes. Like the aliphatic aldehydes, it is formed by the oxida- tion of the corresponding alcohol, benzyl alcohol, CcHs.CH20H, and by distillation of a mixture of a benzoate and a formate. It is manufactured by heating benzal chloride, CeHs-CHCU, with water
S 315] ALDEHYDES. 439
and calcium carbonate, a method the aliphatic analogue of which is of no practical importance:
CgHfi-CH CM^0H"^20 « C6H6.C^+2HC1.
The following methods are employed in the preparation of the homologues of benzaldehyde.
1. When ethyl chloro-oxalate is brought into contact with ani aromatic hydrocarbon in presence of aluminium chloride, the ethyl ester of an a-ketonic acid is produced:
C«H,+C1C0— COOQHfi = C^H^.CO-COOCjHg + HCl.
Ethyl chloro-ozalate
The free acid is obtained by saponification, and on dry distillation loses CO2, with formation of the aldehyde :
CJHfi-CO-COjH - CHj.Cq + CO,.
2. An aromatic hydrocarbon is treated with a mixture of carbon monoxide and hydrochloric acid in presence of aluminium chloride and a trace of cuprous chloride. It may be assumed that formyl. chloride, HCOCl, is obtained as an intermediate product:
CHi-aa+ClOCH = CH3-C6H4-C^+HC1.
315. Benzaldehyde occurs in the natural product, amygdalin, C20H27O11N (256) ; on this account it is called oil of bitter almonds. It is a liquid of agreeable odour, is slightly soluble in water, boils at 179°, and has a specific gravity 1-0504 at 15°. It has most of the properties of the aliphatic aldehydes: it is readily oxidized, even by the oxygen of tlie atmosphere (especially when exposed to sun- light), reduces an ammoniacal silver solution with formation of a mirror, yields a crystalline addition-product with sodium hydrogen sulphite, adds on hydrocyanic acid and hydrogen, forms an oxime and a phenylhydrazone, and so on.
It displays, however, points of difference from the fatty alde- hydes. Thus, with ammonia at the ordinary temperature it does not } ield a compound like acetaldehyde-ammonia, but produces hydrobenzamide, (C6H5CH)3N2, formed by the union of three molecules of benzaldehyde and two molecules of ammonia:
3C6H5.C§+2H3N = (CeHfiCHjsNa + SHzO.
440 ORGANIC CHEMISTRY. I§ 315
At — 20^y however, ammonia combines with benzaldehyde to henzdldehyde^ininonia, 2CeHg«CH0,NH,, probably
NH[CH(C,Hs).OH]„ which separates in plates melting at 45^. After a time it decomposes into hydrobenzamide, benzaldehyde, and water. It is an intermediate product in the preparation of hydrobenzamide.
The behaviour of the aromatic aldehydes towards alcoholic potash is characteristic, one molecule of the aldehyde being oxi- dized, and the other reduced (c/., however, io8). Thus, benzalde- hyde yields potassium benzoate and benzyl alcohol:
2C6H6-C^+KOH = CeHfi-COOK+CeHfi.CHgOH.
The aromatic aldehydes condense readily with dimethylaniline or phenols, forming derivatives of triphenylmethane (373) :
CeHs-cg+^l
C6H4OH _„ _,-, C6H4OH „ _ C6H4OH ^*"**^^<C6H40H+"2^-
Benzaldehyde also reacts very readily with aniline. When a mixture of equal volumes of the two substances is heated gently, drops of water separate, and, on cooling, benzyHdeneaniline, CeHs . CH : N . CeHg, m. p. 45^, crystallizes.
• The action of chlorine on benzaldehyde is described in 313.
Benzcddehydephenylhydrazonej CeHs-CHJN-NH^CeHs, is very readily precipitated, with evolution of considerable heat, by addition of benzaldehyde drop by drop to a sulphurous-acid solution of phenylhydrazine. It forms pale-yellow crystals, melting at 152^, and is transformed by the action of violet or ultraviolet light into a scarlet-red isomeride, the original colour being restored by exposure to yellow or green light.
AUTOXIDATION.
It has been observed that during the oxidation of various sub- stances in the air as much oxygen is rendered "active" as is taken up by the substance under oxidation: this phenomenon is displayed in the atmospheric oxidation of benzaldehyde. If it is left for several weeks in contact with water, indigosulphonic acid, and air,
i 316] KETONES. 441
the same amount of oxygen is absorbed in oxidizing the indigo derivative as in converting the benzaldchyde into benzoic acid. Von Baeteb has shown that benzoyl-hydrogen peroxide C»HiCO'0*OH, is formed as an intermediate product, and oxidizes the indigosul- phonic acid, being itself reduced to benzoic acid:
CeH,.CHO+0, - CeH..CO.O-OH;
CeH..CO-0-OH+Indigo - CeH..COOH+ Oxidized indigo. The oxidation of benzaldehyde in the air must be considered, there- fore, to take place thus:
C.H,.CHO+Oa - CeH,.CO-0-OH; C.H».CO.O-OH+C«H».CHO « 2C,H,.C00H.
Von Baeter has, in fact, proved that benzoyl-hydrogen peroxide dissolves when added to benzaldehyde, but that the liquid gradually solidifies to pure benzoic acid.
Ketones.
316. The aromatic ketones can be subdivided into the mixed aromatic-aliphatic ketones and the true aromatic ketones. The typical member of the first class is acetophenone, CeHs-CO'CHs. It can be obtained by leading a mixture of the vapours of acetic acid and benzoic acid over thorium oxide, Th02, at 430°-460°; or more readily by the addition of aluminium chloride to a mixture of benzene and acetyl chloride. It is a crystalline sub- stance of agreeable odour, melting at 20® and boiling at 200°: it is slightly soluble in water, and possesses all the properties of the aliphatic ketones. It is employed as a soporific under the name " hypnone."
Bemophenone, CeHs-CO-CeHs, is a true aromatic ketone, and can be obtained by the drj' distillation of calcium benzoate, or by the action of benzene and aluminium chloride upon benzoyl chloride, or carbonyl chloride. This compound, although a true aromatic derivative, behaves exactly like an aliphatic ketone: on reduction, it yields benzhydrol, CeHs-CHOH-CeHs; benzpinacone,
(C6H6)2C C(C6H5)2 . . ,^ , , , ^ ^
• • IS simultaneously formed (150).
OH OH
Fusion of benzophenone with potassium hydroxide jrields benzene and potassium benzoate:
CcHs-CO.CeHfi+KOH = CeHe+CeHs-COOK
442
ORGANIC CHEMISTRY.
[§317
317. Benzophenone exists in two modifications: one is unstable
and melts at 27°
the other is stable and melts at 49°.
The relation of these substances to one another is one of mono- tropy; that is, at all temperatures up to its melting-point the meta- stable form changes to the stable form, but the process is not reversible. The explanation is that the transition-point of the two modifications is higher than the melting-point of the metastable isomeride.
For a substance with a transition-point (0), the vapour-pressure, p, in the neighbourhood of this point is represented by Fig. 81
Fig. 81. — Enamtiotrofig Substance.
Fig. 82. — Monotbopic Substance.
("Inorganic Chemistry," 70). AB is the vapour-pressure curve of the fused substance. Its direction must be such that on the right it lies lower than any other curve; that is, it must be nearest to the horizontal axis. Since rise of temperature ultimately occasions the fusion of all solid forms, above a certain temperature, definite for each substance, the liquid phase must be the most stable; in other words, it must have the lowest vapour-pressure. O/i is the melting- point of the metastable modification, which is higher than the transition-point: O/i is that of the stable modification.
AB can, however, be so situated that/i and/, are below 0 (Fig. 82). Here the melting-point is lower than the transition-point 0, so that the latter cannot be attained. The metastable modification then remains in the metastable state up to its melting-point, the substance being monotropic. In the more usual case of enantiatropyt on rise of temperature the compound first attains the transition-point, then undergoes transformation, and finally melts.
§318] OXIMES. 443
Ozimes.
318. Some of the oximes of the aromatic aldehydes and ketones exhibit a peculiar kind of isomerism. Thus, there are t'AO .isomerides of benzaldoxime : benz&ntialdoxime (a), melting at 35°; and bemsynaldoxime (/? or iao), which melts at 128**, and on treatment with acetic anhydride readily loses water, forming benzonitrile:
CSeHfiClH
I j = CbHs-C^N+HjO. NiOH
With acetic anhydride, the on/mldoxime yields an acetyl-derivative.
It has been proved that no isomerides of the ketoximes p T^,>C:NOH exist, when R and R' are similar: when these groups
are dissimilar, two isomerides are known. Benzophenoneoxime and its derivatives furnish examples. Despite many attempts to prepare an isomeride, benzophenoneoxime is known in only one modification. When, however, hydrogen in one phenyl-group is sub- stituted, two isomeric oximes can be obtained. Monochlarobenzophe- none, CeHg-CO-CoHiCl, numobromobenzophenone, C6H5«CO«C6H4Br. phenyUolylketone, CH3 • C6H4 • CO • CeHs, and phenylanisylketone, CH30«C6H4«C0«C6H6, are examples of ketones which yield two isomeric oximes. Many other compounds of this type could be cited.
After several ineffectual attempts to explain such isomerism by the ordinary structural formulae, the following stereochemical explanation of the observed facts has been adopted. It is assumed that the three affinities of the N-atom are directed towards the angles of a tetrahedron, the nitrogen atom itself being situated at the fourth angle:
N
When the three nitrogen bonds are linked to carbon, as in the nitriles, the following spacial representation is obtained:
444 , ORGANIC CHEMISTRY, [% 318
CH
CH
III = N
Stereoisomerism is here impossible: experience has shown that none of the numerous nitriles known occurs in two forms due to isomerism in the CN-groups.
When, however, the nitrogen atom is linked to carbon by two bonds, two isomeric forms become possible:
and
These can be more readily represented by
X— C— Y X— C— Y
and II
— Z Z— N
It is apparent that different configurations for such compoimds are only obtained when X and Y are different, since when they are similar the figures become identical. This agrees with the facts stated at the beginning of this section. ^
i It can also be determined which configuration represents each
isomeride. The two isomeric benzaldoximes have the formulse
CfHj^—- C— "H CeH5~~C— H
I and II
N— OH HO— N
BeiiB«i/n«ldoxime Bensonhaldoxime
1. 11.
In formula I., H and OH are nearer together than in formula IL This proximity explains the facility with which one molecule of water is eliminated from one aldoxime (syn)^ and not from the other [anli). On this accoiwt configuration I. is assigned to the ^ynaldox- ime, and configuration II. to the an/taldoxime.
The configuration of the ketoximes can be determined by the
§319] AROMATIC DERIVATIVES. 445
Beckmann transformation (103), as is made clear in the following example. Two isomer! des of pfienylanisylketoxime are known,
CHsO-CcH^— C— C,Hj CHsO-CeH^— C-€eHs
I and I ,
N— OH HO— N
I. • II.
the first melting at 137^ and the second at 116^. By the Bbckmann transformation, the oxime of higher melting-point yields the anilide of anisic acid; tliat of lower melting-point, the aniside of benzoic acid. The former must therefore have configuration I., and the second configuration II.. because in I. the groups OH and CeH« are adjacent, and exchange places:
CHsO • C,H,— C— OH CH3O • CeH4— C=0
I - I .
N— C0H5 NH— CeHj
The anilide of anisic acid, CH80*CeH4«COOH, is thus produced. In . II., anisyl (CHsO •C^H^ — ) and OH are adjacent, and exchange plaoea, yielding the aniside of benzoic acid :
HO— C— CoHs 0=C-CcH.
CH,0-CoH4— N CH,0.CeH4— NH
XI. AROMATIC PHOSPHORUS AND ARSENIC DERIVATIVES.
319. Compoimds of phosphorus and arsenic with aromatic hydro- carbons, having constituents similar to those of the nitro-com- poimds, azo-compounds, and amino-compounds, are known.
Phosphinobemeney CeHft-POi, cannot be obtained analogously to nitrobenzene, by the interaction of metaphosphoric acid and benzene. It is prepared by the action of phenylphosphinic add (72) upon its chloride:
CeH5.PO(OH)a+CflH5.POCl, - 2CoH5.PO,+2Ha.
Phenylphosphinio (^^ride
aoid
It is a white, crystalline, odourless powder.
Phenylphosphine, CqHs'PH,, is obtained by distilling pJwaphenyl chloride, CoH5«PCl2, with alcohol, in a current of carbon dioxide. It is a liquid of very penetrating odour. It cannot be obtained by the reduction of phosphinobenzene.
446 ORGANIC CHEMISTRY, (J 320
Phosphobenzene, CeH^-PiP-CeHi, is got by treating phenyl phosphine with phosphenyl chloride:
CcHs'PICla + HalP'CcHs - CeH5-P:P-CoHg+2HCl.
It is a pale-yellow powder, insoluble in water, alcohol, and ether. It is energetically oxidized by weak nitric acid, forming phosphenf^ouM
acid, OP^H . \0H
Phosphenyl chloride, CaHs* PQ,, the starting-point in the prepara- tion of these and other aromatic phosphorus derivatives, can be pre- pared, as can its homologues, by heating aromatic hydrocarbons with phosphorus trichloride and aluminium chloride under a reflux- condenser.
Arsinobemenef CeH^'AsOj, is obtained by the elimination of water from phenylarainic acid, CftHi«AsO(OH)t, under the influence of heat.
Arsenobemene, CeHi-AslAs-CfH*, is formed by the reduction of pkenylarsine oxide, CeHe'AsO, with phosphorous acid. It forms yello.v needles, and is converted by oxidation into phenylarsinic acid, CJL-AsO(OH),.
Other aromatic arsenic derivatives are mentioned in 339.
The following series of compounds are known:
CJI6-N0, CJI».N,-C,H* CJI».NH,
Nitrobenaene Aiobeniene Phenylamine
CJIj'POi CsHi'Pj'CeHi CeHj'PHj
Phosphinobensene Phosphobeiuene Phenylphosphiiie
CeH,.AsO, CeH».As,.CJI» —
[Aninobenaene Anenobensene
Although these compounds have analogous formulae, both the methods employed in the preparation of the individual members of each series, and the properties of the individuals themselves, exhibit wide divergences.
Xn. AROMATIC METALLIC COMPOimDS.
3ao. Mercury, tin, lead, and magnesium are the only metals which 3rield aromatic compounds: they are much less important than the metallic compounds of the aliphatic series. Mercury phenide, HgCCtHs)], is obtained by the action of sodium-amalgam
5 320] AROMATIC METALLIC COMPOUNDS. 447
upon bromobenzene. It is crystalline, and resembles the corre- sponding alkyl-derivatives in its stability towards atmospheric oxygen. When its vapour is passed through a red-hot tube, it decomposes into mercury and diphenyl (371): the same effect is partially produced by distillation.
When mercury acetate is heated with benzene at 110^, there results phenylmercury acetate, CeHi-Hg-OOC-CHa, the acetic-acid salt of the base phenylmercury hydroxide, CeHi^Hg^OH. The homologues of benzene, nitrobenzene, and other substances yield analogous compounds.
Aromatic magnesium compounds are referred to in 289.
BENZENE H0M0L06UES WITH SUBSnTUTED SIDE- CHAINS.
321. The introduction of a substituent into a homologue of benzene can take place not only in the nucleus, but also in the side-chain. The second t3rpe of substitution has been exhaustively investigated for the toluene derivatives with hydrogen of the methyl-group replaced by various substituents. These substances are to be regarded as methane with one hydrogen atom replaced by phenyl, and one or more of the other hydrogen atoms exchanged for a corresponding number of atoms or radicals. A close approximation between the properties of these compounds and those of the corresponding aliphatic derivatives would be anticipated, and this view finds abundant confirmation in the facts recorded in this chapter.
L COMPOUNDS WITH HALOGEN IN THE SIDE-CHAIN.
In the interaction of chlorine or bromine with toluene, the entrance of the halogen into the nucleus or into the side-chain is determined by the experimental conditions. Compounds of the type X«C6H4«CH3 are called halogen-iolv^enes, and those of the formula C6H5-CH2X benzyl halides, A summary of the influence exerted by the experimental conditions is subjoined.
1. Temperature. — ^At low temperatures, halogens substitute in the nucleus, and at high temperatures, in the side-chain: thus, on treatment with chlorine, cold toluene yields o^hlarotoluene and p^hlorotoluene; when, however, chlorine or bromine is brought into contact with boiling toluene (110°), benzyl chloride, CeHs -011201, or benzyl bromide, C6H5»CH2Br, is almost exclusively formed.
2. Sunlight, — A striking example of the influence of light is furnished by the dark-brown mixture of toluene and bromine. At ordinary temperature in absence of light, interaction is very slow, an interval of many days being necessary for the complete
448
8321] HALOGEN ATION OF TOLUENE, 449
disappearance of the bromine, with formation of hydrogen bromide and bromotoluenes. On exposing the mixture to daylight; it becomes decolorized in a few minutes, the bromine entering the side-chain only.
Many instances of the influence of light on chemical reactions have been observed. They include the intramolecular rearrange- ment of atoms and groups, the acceleration of reactions, and, as in the example just cited, the formation of compounds entirely different from those formed in absence of light. •
3. Concentration. — ^The proportion of halogen to toluene has an important influence. At 50° in absence of light, the product obtained by the interaction of bromine and toluene in the molec- ular ratio 1:4-26 contains 24-1 per cent, of benzyl bromide, but in the ratio 1 : 28*55 it has 95*3 percent, of this substance.
4. Catalysts. — ^Aluminium or ferric halides have a very power- ful catalytic action. So small a proportion of ferric bromide as 0*002 gramme-molecule to each granmie-molecule of bromine completely over-rides all other influences, causing substitution in the nucleus only, quite irrespective of the reaction being carried on in the presence of light, at high temperature, or at different concentrations.
The benzyl halides, C6H5»CH2X, are readily distinguished from the isomeric halogen derivatives of toluene. In the first place, their halogen atoms display the same aptitude for reactions involving double decomposition as' those of the alkyl halides, but the halogen atoms of the isomeric halogen-toluenes are as firmly linked as those in the monohalogen-benzenes. In the second place, the benzyl halides are converted by oxidation into benzoic acid, CeHs-COOH, but the halogen-toluenes into halogen-benzoic acids, C6H4X-COOH. In the third place, the halogen-toluenes are characterized by their faint, but not dis- agreeable, odour; but the benzyl halides have a most irritating effect on the mucous membrane of the eyes, a property specially noticeable in benzyl iodide.
Benzyl chloride is a colourless liquid of stupefying odour, intensified by warming: it boils at 178°, and has a specific gravity of 1-113 at 15°. Benzyl bromide is also a colourless liquid. Benzyl iodide is prepared by heating benzyl chloride with potas- sium iodide: it melts at 24°, and decomposes when boiled. It
450 ORGANIC CHEMISTRY. [§ 322
has a powerful and unbearably irritating odour, productive of tears, and was employed for filling lachrymatory shells in the great European war.
The prolonged action of chlorine on boiling toluene yields henzal chloride, C6H6*CHCl2, and bemotrichloridej CeHs-CCla.
n. PHENYLNITROliETHAIYE AND THE PSEUDO-ACIDS.
32a. PJienylnitromethane, CeHi-CHsNOs, is an aromatic com- pound with a fiitro-group in the side-chain, as is evident from its formation by the action of benzyl chloride or iodide on silver nitrite:
CeH, • CH, CI -f Ag NO, = CJEi • OH,NO, + AgQ.
It can be reduced to benzylamine, which proves it to be a true nitro- compound. Phenylnitromethane, and its derivatives with substitu- ents attached to the nucleus, exist in two tautomeric modifications readily transformed into each other. Phenyhiitromethane is a liquid: its aqueous solution does not react with ferric chloride. After it has been converted into its sodium derivative by the action of sodium alkoxide, addition of excess of a strong mineral acid causes the separation of a crystaUine substance of l^e same composition as phenylnitromethane: the aqueous solution of this compound gives a -coloration with ferric chloride. On standing for some hours, these crystals are completely reconverted into the ordinary liquid phenyl- nitromethane. It is very probable that the sodium compound and the imstable modification corresponding with it have the constitutions
CJIi-CH:NO-ONa, and C*Hi-CH:NO'OH.
The presence' of a hydroxyl-group is proved by the formation of dibemhydroxamic add on treatment with benzoyl chloride:
C.H6.CH:n/ H-CIOC-CH, - C,H,*CH:N^ -
^ONa ^0-OC-CeH.
Sodiophenyli«o- nitrometbane
-► CHfi-CO— N-O-OC-CJI,.
H
Dibenxhydrozamio acid
Another proof of the presence of a hydroxyl-group is that tMnitro- compounds, unlike ordinary nitro-compounds, react vigorously with phenyl tsocyanate at low temperatures (259).
S 323] PSEUDO'ACIDS. 451
From these facts it may be inferred that when phenylnitro- methane, CoHi-CHiXOj, is converted into a salt, it first changes to an isomeric modification. Inversely, when it is liberated from its sodium compound, the wormodification, or oa-modification, is first produced, and slowly changes to the ordinary form.
The dilute aqueous solution of m-nitrophenylnitramethane affords a striking example of this phenomenon. This compound is colour- less, but its sodium salt has a deep-yellow colour. On the addition of an equivalent quantity of hydrochloric acid to its deeply-tinted solution, the yellow colour disappears somewhat slowly, indicating the conversion of the t«o-compound into its normal isomeride.
The discharge of the colour is attended by another phenomenon: the electric conductivity of the liquid is considerably greater imme- diately after the addition of the hydrochloric acid than it is several minutes later, when the colour has nearly vanished. The explanar tion of this is that the iso-iorm is a true acid, and is therefore a conductor in aqueous solution, while the solution of the normal modi- fication is a non-conductor, and therefore possesses no acidic character*
The formation of an oa-modification is characteristic of various compounds, notably the nitroparaffins, pyrazolones, oximes, and nitrophenols.
323. Besides the properties indicated above, the psendo-SLcids possess others by which they may be detected. It has just been stated that the addition of a strong acid to a pseudo-Sicid salt liberates the oa-form, which is slowly converted into the normal modification. Inversely, the addition of an equivalent quantity of caustic alkali to the normal modification results in its gradual neutralisation. This " slow neutralization " is a characteristic of the psettdo-ACida.
Another of the characteristics by which they may be recognized is illustrated by dinitroethaney which, after being liberated from its sodium salt in accordance with the equation
.NO, .NO3
CH,-C<: + Ha - CHs-CC +NaC9,
^NO-ONa ^NO-OH
aci-DinitioethaDe
NO is so rapidly converted into the normal compound, CH8-CH<j^q^
that a change in the electric conductivity of the solution can scarcely be observed even at 0°. The neutral reaction of the alkali-metal derivatives of the non-conducting or weakly-conducting hydrogen compound nevertheless indicates the existence of a pseudo-e^^d. An acid which is so weak that it^ solution is a bad conductor of elec-
452 ORGANIC CHEMISTRY. \ § 32^1
tricity yields alkali-metal salts which undergo strong hydrolytic dissociation, and therefore have a strongly alkaline reaction ("Inorganic Chemistry," 66). Such a substance as sodiodinitro^- thane forms a non-alkaline solution,. and must therefore be derived from an acid other than diiiitroethane, since this substance has a neutral reaction and is a non-conductor in aqueous solution.
The difference in structure between the salt of a psetido-acid and the free acid can also be detected by their refraction. Compar- ison of the molecular refraction of an aqueous or alcoholic solution of an acid with that of its sodium salt reveals a constant difference, even for weak acids. For a solution in the equivalent quantity of caustic alkali of a nitro-compound which yields a pseiido-acid, the difference between the molecular refraction of the acid and that of the salt formed is much greater. This phenomenon indicates the transformation of the p«etM^o-acid into its oci-form to be an intermediate process preceding the formation of the salt.
UI. ACmS WITH CARBOXTL IN THE SIDE-CHAIN.
324. One of the compounds with a saturated sideH^haln is phenylacetic acid, C6H5-CH2-COOH. It is prepared by the interaction of potassium cyanide and benzyl chloride, followed by hydrolysis of the resulting nitrile, benzyl cyanide, C6H5-CH2-CX. Phenylacetic acid melts at 76**, and is converted by o^dation
OH
into benzoic acid ; whereas the isomeric toluic acids, C6H4 <qqqti »
are transformed by oxidation into the dibasic phthalic acids.
Manddic acid has both hydroxyl and carboxyl in the side- chain. Its constitution is CeHs-CHOH-COOH, as its synthesis from benzaldehyde and hydrocyanic acid indicates. In this reaction manddoniirile, CeHs-CHOH^CN, is an intermediate product. Addition of quinine to the mixture of benzaldehyde and hydrocyanic acid makes the S3mthesis asymmetric, so that an optically active mandelonitrile is formed. The quinine functions as an optically active catalyst, its action being similar to that exerted by the enzyme emulsin. The mandelic acid found in nature is Isevo-rotatory. The synthetical acid can be resolved by the action of cultures obtained from mildew (PenicUUtim glaiuyum), the dextro-rotatory acid being left intact. The decomposition is also effected by the formation of the cinchonine
§3251 BENZYL ALCOHOL. 453
salts, when the salt of the dextro-rotatory acid crystallizes out first.
Inactive mandelic acid is also called " para-mandelic acid." It melts at 119°, and dissolves very readily in water: the optically active modification melts at 134°, and is lesG soluble in water.
Tropic acid is one of the parent substances of atropine (411). Its constitution follows from its synthesis by the condensation of ethyl phenylacetate and ethyl formate under the influence of sodium ethoxide, and reduction of the condensation-product with aluminium-amalgam:
^[H + C2H50|OC>H /C5
[( -^ CeHs.CHC
\cooC2H6 N:ooc2H6
yCHzOH
N^OOH
Tropic acid
IV. AROMATIC ALCOHOLS.
325. Benzyl alcohol^ C6H5»CH20H, is the typical aromatic alcohoh it possesses nearly all the properties of an aliphatic alcohol. It can be obtained by treatment of benzyl chloride with potassium acetate, and saponification of the ester of acetic acid thus formed. It can also be prepared by electro-reduction of benzoic acid in sulphuric-acid solution with lead cathodes. It reacts readily with phosphorus pentachloride, yielding benzyl chloride, and forms esters, ethers, etc.: being a primary alco- hol, it can be oxidized to the corresponding aldehyde, bemaldeki/de (314), and also to henzoic acid (312). It differs from the aliphatic alcohols in its behaviour towards sulphuric acid, which causes resinification, instead of the formation of the corresponding sulphuric ester. Benzyl alcohol possesses no phenolic properties: it is insoluble in alkalis, and does not yield the characteristic phenol coloration with ferric chloride.
Benzyl alcohol is a liquid which dissolves with difficulty in water : it boils at 206°, and possesses only a faint odour.
454 ORGANIC CHEMISTRY. [§ 326
V. COMPOUNDS WITH THE AMZNO-GROUP IN THE SIDE-CHAIN.
326. BeTLzylamine, C6H6-CH2«NH2, is a type of the amines with NH2 in the side-chain. It can be obtained by the various methods employed in the preparation of aUphatic amines, such as the action of benzyl chloride upon ammonia, by which dibenzyl" amine and tribemylamine are also formed ; the addition of hydrogen to benzonitrile, CeHs^CN; the reduction of phenylnitromethane, C6H5*CH2*N02; and so on. The method for its formation and its properties prove that benzylamine belongs to the primary amines of the aliphatic series: thus, it does not yield diazonium compounds; and its aqueous solution has a strongly alkaline reaction, proving it to be a much stronger base than aniline, in which the NH2-group is under the direct influence of the phenyl- group.
Benzylamine is a liquid of ammoniacal odour: it boils at 185^ , is volatile with steam, and has a specific gravity of 0*983 at 19**. It absorbs carbon dioxide from the air.
COMPOUNDS CONTAINING AN UNSATURATED SIDE- CHAIN.
Hydrocarbons.
327. Siyrene or phenylethylene, GHfCH : CHj, derives its name from its presence in storax, an exudation from trees of Liquidambar orienidUs, The hydrocarbon can be obtained by heating cinnamic acid (328), C«H6*CH:CH«C0JI, carbon dioxide being eliminated. It is a liquid of agreeable odour, and boils at 146^. Heating converts it into a vitreous mass called meiasiyrene^ a polymeride of unknown molecular weight, the same transformation taking place slowly at ordinary temperature. Like other substances with a double linking, styrene has the power of forming addition-products. On treatment with nitric acid, it yields nitrostyreney CeHft-CH: CH*NOj, with the nitro-group in the side-chain. The constitution of this compound follows from its formation by the condensation of benzaldehyde with nitromethane, under the catalytic influence of alcoholic potash:
H
CH^>C|OTh;]CH>NQ, -CeH5.CH:CH-N0,+H,0.
Phenylacetylene, CeHj-CSCH, can be obtained by treating acetophenone with phosphorus pentachloride, and acting on the resulting compound, CcHg-OCl^-CH-, with caustic potash; or from phenylpropiolic acid, CoHj-CiC-COOH, by heating its cupric salt with water. In many respects it resembles acetylene; for example, it yields metallic derivatives. On solution in concentrated sulphuric acidi it takes up one molecule of water^ forming acetophenone.
Alcohols and Aldehydes.
Cinnamyl alcohol, CJI»-CH:CH-CH,OH, is the only repre- sentative of the unsaturated alcohols which need be mentioned. It is a cr3rBtalline substance with an odour of hyacinths, and is present
455
456 ORGANIC CHEMISTRY. [{328
as an ester in storax. Careful oxidation converts it into cinnamic
acid (338), and more vigorous oxidation into benzoic acid.
H Cinnamcddehyde, CeHfCH :CH«Cq, is the chief constituent
of oil of cinnamon, from which it can be obtained by means of its sulphite compound. It is an oil of agreeable odour, and boils at 246^. It is resinified by strong acids, and with ammonia yields hydrodnnamide, Nt(CtHiCtHj)s, analogous to hydrobenzamide (315).
Acids.
328. Cinnamic add, C6H5-CH:CH*COOH, is the most im- portant unsaturated acid. It is present in some balsams, and in storax. It is manufactured by a synthetic method discovered by Sir William Perkin. Benzaldehyde is heated with acetic anhy- dride, in presence of sodium acetate as a catalyst:
CeH6-CQ+H2CH.CO.O.CO.CH3-=C6H5.CH:CH.CO.O.CO-CH84^
BeoBaldehyde Aoetie anhydride
+H2O = CaHj-CHiCH-COOH+HOCO-CHa.
Cinnamio add Aoetio acid
Perkin's synthesis can be carried out with substituted benz- aldehydes on the one hand, and with homologues of acetic acid or with dibasic acids on the other, so that it is possible to obtain a great number of unsaturated aromatic acids by its aid.
Cinnamic acid can also be got by the action of benzal chloride (321), CeHj'CHCla, upon sodium acetate. It can further be synthe- sized by the condensation of malonic acid with benzaldehyde, which takes place readily under the catalytic influence of ammonia, one molecule of carbon dioxide being eliminated:
(H00C),c|H| + 0^'C*^6 - CoHft.CHiCH-COOH+OOa+HA
H
Malonio add
Cinnamic acid is a crystalline substance, melts at 134^, and dis- solves with difficulty in cold water. . In all respects it possesses the character of a substance with a double bond, and therefore forms addition-products and reduces von Babyer's reagent (113).
Its constitution indicates that two stereoisomerides are possible:
C cHi — C — H C eHf — C — ^H
II and II
H— C— COOH COOH— C— H
§ 328] CINNAMIC ACID. 457
Four modifications, however, are known: ordinary cinnamic acid; alloannamic acid, melting at 68^; and two iaocinnamic acids, melting at 58° and 42° respectively. Biilmann has proved that the last three acids are modifications of a single form, and therefore afford an example of trimorphism. On inoculating the liquid, obtained by fusion of any of them, with one of the forms, that form cr3rstallize8 out. iiZ^innamic acid and the tsocinnamic acids can be prepared by partial reduction of phenylpropiolic acid, C«Hi-C^^-COOH (327)! cmd must, therefore, have the os-^onfiguration (I.), as is evident from a model. It follows that ordinary cinnamic acid has the (raris-configuration (II):
H-C-CJI, CHi-C-H
I. II ; IL II
H-C-COOH H-C-COOH
Cit Trana
It can be converted into the os-form by exposing its solution in benzene to the ultraviolet rays of a '^uviol" lamp for ten days.
POLYSUBSTlTUTJfD BENZENE DERIVATIVES.
339. A great number of polysubstituted derivatives of benzene is known, but only a few of special theoretical or technical interest will be considered. For the sake of systematic treat- ment, the substitution-products will be taken in the same order as has been adopted in the preceding pages for the monosub- stituted derivatives. The polyhalogen compounds will be dis- cfussed first, then the substituted nitrobenzenes, sulphonic acids, phenols, and so on.
The general rule holds that substituents simultaneously present exercise their normal functions, although the effect of a given substituent is also often greatly modified by the presence of the ' other atoms or groups.
I. POLYHALOGEN DERIVATIVES.
The polyhalogen derivatives can be prepared by the direct action of chlorine or bromine on the aromatic hydrocarbons in presence of a catalyst, the anhydrous ferric halides being specially suitable for this purpose. The mode of procedure is to introduce a small proportion of dry iron-powder into the liquid, and pass in chlorine or add bromine drop by drop. If a halogen atom is already attached to the nucleus, replacement takes place mainly at the pard-position, but the oriAo-compound and a small pro- portion of the ?m;to-compound are simultaneously formed. m-Dichlorobenzene and m-dibromobemene can be prepared by reduction of ?7Miinitrobenzene (331), and subsequent diazotiza- tion of the product. The para-dihalogen compounds are solid, the isomeric or^Ao-compounds and ma^a-compounds are liquid. When three halogen atoms enter the nucleus, the main product is the 1^2: 4-trihalogenbenzene;
458
§ 330] POLYSUBSTITUTED DERIVATIVES, 459
since the same product is obtained from each of the throe dihalogenbenzenes. Prolonged chlorination of benzene sub- stitutes its six hydrogen atoms, with formation of Julin's chioro- carbon, CeCIe, colourless needles melting at 229**. It is very stable, soluble with difficulty in most solvents, and is often a product of the energetic chlorination of various benzene deriv- atives, the substituents already present being displaced by chlorine.
n. HALOGBN-NITRO-COMPOUITDS.
330. Nitration of a monohalogenbenzene yields only the artfuh compound and the para-compound, the second being formed in larger proportion. An example is furnished by the nitration of monochlorobenzene; at ordinary temperature the product con- sists of about 70 per cent, of p-chloroniirobenzene, and about 30 per cent, of o-chloronitrobenzenef C1-C6H4- NO2. m-ChloronUroben' zene is readily prepared by chlorination at elevated temperature of a mixture of nitrobenzene with 20 per cent, of its weight of antimony pentachloride. w-Halogen-nitrobenzenes can also be prepared from m-nitroaniline by the diazotization-method.
Unlike the halogen in the monohalogenbenzenes, that in the p-halogen-nitrobenzenes and the o-halogen-nitrobenzenes is char- acterized by its power of taking part in double decompositions. When these substances are heated with an alcoholic solution of sodium methoxide, the halogen atom is replaced by OCH3; with alcoholic ammonia the halogen atom is exchanged for NH2. A contrast is presented by the m-halogen-nitrobenzenes, their halogen being almost as difficult to replace as that in the unsub- stituted monohalogenbenzenes.
The presence of several nitro-groups in the nucleus at the or^o-position and the para-position to halogen causes a marked increase in the adaptability for double decomposition. The Cl-atom in picryl chloride,
a
V
^2
NO2
is replaceable by a great variety of substituents. This substance
460 ORGANIC CHEMISTRY, [§ 331
has the character of an acid chloride, being converted by hot water into hydrogen chloride and picric acid, C6H2(N02)30H,
and by ammonia into picramide, C6H2iTTT ^^^ * " .
nL POLTinTRO-DERIVATIVES.
331. mrDinitrobemene is obtained by the nitration of benzene with a mixture of concentrated sulphuric acid and fuming nitric acid. It forms colourless needles melting at 90°. On reduction, it yields m-phenylenediamine, and is therefore employed in the preparation of coal-tar dyes: it is also used in the manufacture of explosives, since it can be exploded by merciuy fulminate. In addition to the m-compound, small quantities of o-dinilrch bemene and traces of p-dinitrobemene are formed. Stronger nitration, efifected by a mixture of nitric acid and fuming sulphuric acid heated to 140°, converts m-dinitrobenzene into symmetrical trinitrobemene (1:3:5), which melts at 121°.
Symmetrical trinitrotoliiene, known as T.N.T., is manufactured by the nitration of toluene in successive stages. It is one of the most powerful explosives known, and was extensively employed in the great European war of 1914-1918.
The hydrogen atoms and nitro-groups in the polynitrobenzenes are much more readily replaced than those in mononitrobenzene. Thus, T^i-dinitrobenzene is converted by oxidation into 2:6- dinitrophenolj and liS^S-trinitrobenzene into 2:4:6-trinitro- phenol, or picric acid:
NO2 NO2
NO2 NO2
By the action of sodium ethoxide and methoxide respectively one of the nitro-groups in o-dinitrobenzene and p-dinitrobenzene can be replaced by OC2H5 and OCHa:
C6H4 < ^^l +NaOCH3 = C6H4< g^^^ +NaN02.
It is remarkable that this substitution does not take place with m-dinitrobenzene, although in l:3:5-trinitrobenzene, with each
§332] POLYSUBSTITUTED DERIVATIVES. 461
of its substituents in the meto^position to the other two, one of the nitro-groups can be readily replaced by OCH3 (" Laboratory Manual," XXXIII, 3).
When boiled with sodium hydroxide, o-dinitrobenzene yields o-nitrophenolf and when heated with alcoholic ammonia, o-ni^o- anUine:
C6H4<^
INOal + NalOH /OH
= CbH^C +NaN03.
NO2 2 \nO
2
C^H,<|Ng4±HlNH, ^ CH,<NH^+HNO..
NO22 " ' NO2
It has not been possible to introduce more than three nitro- groups into beiizene by direct nitration, substitution even by the third nitro-group meeting with considerable opposition. The homologues of benzene are much more readily converted into their higher nitro-derivatives than benzene itself.
Trinitrobtdylxyleney containing a tertiary butyl-group, has a power- ful odour resembling that of musk. It is a perfume, and is called "artificial musk." I
IV. SUBSTITUTED BENZENESULPHONIC ACIDS.
332. Digestion of monochlorobenzene or monobromobenzene with concentrated, or better fuming, sulphuric acid yields exclu- sively ihchlorobenzenesvlphonic acid or p-bromobemenesidphonic \ acid. The properties of these substances approximate closely to
those of the unsubstituted benzenesulphonic acid.
I
On fiision with potassium hydroxide, each of the three bromoben-
OHl
zenesulphonic acids is converted into resorcinol, CeHi <qu3' one of
the few instances of substitution at a position other than that occu- pied by the group replaced. Additional examples of the same phenomenon will be mentioned subsequently (333).
Both nitration of benzenesulphonic acid and sulphonation of nitrobenzene yield chiefly m-nitrobenzenesulphonic acid, with simultaneous production of a small percentage of the isomeric ortho-compound and para-cowipound.
When benzene and its homologues are heated at a high tem-
462 ORGANIC CHEMISTRY. [§ 333
perature with fuming sulphiiric acid; disulphonic adds and tri- sidphonic acids are produced, but it has not been found possible to introduce more than three sulpho-groups. Addition of silver sulphate greatly facilitates the formation of benzenetrisvdphonic acid. With respect to the production of disulphonic acids, benzene yields chiefly benzene'ra-disulphonic acid, a substance partially converted into bemene-p-disidphonic acid by prolonged heating at a high temperature with sulphuric acid. Inversely, under the same conditions the para-compound is partially trans- formed into benzeneHoa-disidphonic add. Bemene-CHlisulphonic and is not produced by direct sulphonation of benzene.
V. SUBSTITUTED PHENOLS AND POLYHTDRIC PHENOLS.
Halogenpbenols.
333, The direct action of chlorine or bromine on phenol yields cxhlorophenol and p-cfdorophenol, or o-broinophenol and p-bromophenol. These compounds are also formed by reduction of the halogen-nitrobenzenes, with subsequent diazotization of the products. In aqueous solution the halogenation is not limited to the entrance of one halogen atom, but yields higher products, an example being the precipitation of 224:6-tribromophenol by add- ing bromine-water at ordinary temperature to an aqueous solution of phenol (293). The or^Ao-compounds have a pungent, very penetrating odour. At ordinary temperature, the ortfco-isomerides and w€to-isomerides of the chlorophenols and bromophenols are liquid; the para-isomerides are solid (288). Fusion with potassium hydroxide replaces their halogen by hydroxyl, although the corresponding hydroxy-derivative is not always formed (332). The acidic character of the phenols is considerably strengthened by the introduction of halogen, exemplified by the power of trichlorophenol to decompose carbonates.
Iodine can substitute hydrogen in phenol only in presence of an oxidizer, the hydrogen iodide being oxidized, and thus pre- vented from eliminatmg the iodine atom from the iodophenol.
Nitrophenols.
The increased aptitude for substitution displayed by the hydrogen atoms of the benzene-nucleus after introduction of a
§ 334] NITROPHENOLS. 463
hydroxyl-group is illustrated by the behaviour of the phenols towards nitric acid. To obtain nitrobenzene from benzene, it is necessary to employ concentrated nitric acid, whereas phenol is converted by dilute nitric acid at low temperatures into o-nitro- phenol and p-niiraphenoL The two isomerides can be separated by distillation with steam, with which only the ar(Ao-compound is volatile. m-Nitrophenol can be prepared from m-nitroaniline by the diazo-reaction. o-Nitrophenol has a yellow colour, and a characteristic odour. m-Nitrophenol and p-nitrophenol are colourless, but resemble the or^Ao-compound in forming highly coloured phenoxides. Further particulars of the nitrophenols are given in 330 and 331.
334. The most important nitrophenol derivative is picric add, or 1 : 2 : 4 : 6-trinitrophenoI|
NO, KO,
NO,
o
This substance has been known for a long time, and is produced by the action of concentrated nitric acid upon many substances, such as silk, leather, resins, aniline, indigo, etc. It is prepared by dis- solving phenol in concentrated sulphuric acid, and carefully adding small quantities of this solution to concentrated nitric acid of 1*4 specific gravity. An energetic reaction ensues, after which the mixture is warmed for some time on a water-bath: on cooling, picric acid crystallizes out. It cannot be further nitrated : in other words, it is the final product of the action of nitric acid upon phenol. This fact explains its production by the action of nitric acid upon such heterogeneous substances.
When pure, solid picric acid has only a very faint-yellow colour, but its aqueous solution is deep yellow. It is a strong acid, and, therefore, undergoes considerable ionization on solution in water: the yellow colour is characteristic of the anion, since the solution of this acid in light petroleum, in which there is no ionization, is colourless; the anion, however, also undergoes tautomerization (373)- I* is slightly soluble in cold water, and is not volatile with steam. It melts at 122^; and has an excessively bitter taste, which suggested its name (irucpof, bitter).
464 ORGANIC CHEMISTRY. [§ 334
A consideration of the following reactions shows that picric acid is comparable with the carboxylic acids. Phosphorus penta- chloride replaces the hydroxyl-group by chlorine, with formation of picryl cWortde (330). Silver pi crate and methyl iodide jdeld methyl picrate: it has the properties of an ester, being saponified by boiling with concentrated caustic alkalis, and yielding picramide on treatment with ammonia. These facts afford further evidence of the remarkable increase in the reactivity of the hydroxyl-group, due to the presence of the three nitro-groups. t Picric acid yields well-defined crystalline, explosive salts, of a yellow or red colour. The potassium salt dissolves with difficulty in water, and, like the ammonium salt, explodes by percussion, although the acid itself docs not. Prolonged consumption of small quantities of potassium picrate imparts a yellow colour first to the conjunctiva of the eyes, and later to the entire skin.
It yields molecular compounds with many aromatic hydrocar- bons; for example, with naphthalene a compoimd of the formula CioH8-C6H2(N02)3-OH, melting at 149^ These derivatives crystallize well, and have definite melting-points. They are sometimes employed with advantage in the separation of hydro- carbons, or in their identification. Picric acid is eliminated from them by the action of ammonia.
The acid can be detected by an aqueous solution of potassium cyanide, which yields a red coloration due to. the formation of tsopurpuric acid.
Picric acid is employed as an explosive, which leaves no residue on explosion, and is called ** lyddite." It was" formerly used as a dye, since it imparts a yellow colour to wool and silk.
Phenolsulphonic Acids.
o-PhenoUvlphonic acid and i>-phenolsidphonic acid are ob- tained by dissolving phenol in concentrated sulphuric acid. m-Phenolsidphonic acid is produced by fusing m-benzenedi- sulphonic acid with caustic potash. The o-acid is characterized by being easily converted into the p-compoimd. Phenol sulpho- nates more readily than benzene, its solution in sulphuric acid t)eing transformed into the o-sulphonic acid and p-sulphonic acid even at ordinary temperatures.
il 335, 336] NITBOSOPHBNOL. 465
NitrosophenoL
335. In certain respects nitrosophenol reacts ajs though it had
NO the constitution C6H4 <qu, although its formation from quinone
.NOH and hydroxylamine points to the constitution C6H4^ . It is
prepared by the action of nitrous acid upon phenol, or of caustic potash upon nitrosodin^ethylaniline (299) :
CeH.<^^NO^C^H^<NO^jj^O.
ON<^^^[N(C^^
Like other oximes, nitrosophenol, or quinone mono-oxime, unites with bases. It is a colourless compound, crystallizing in needles which soon turn brown on exposure to air. On oxidation and reduction, it behaves as though it were nitrosophenol, yielding nitrophenol and aminophenol respectively,
336. Phenol is much more readily attacked by oxidizing agents than benzene (293). The polyhydric phenols possess this property to an even greater extent, many of them behaving as powerful reducing agents when dissolved in alkalis.
Dihydric Phenols.
OH 1 The o-compound, C6H4<QrT ^, catechol (" pyrocatechol '* or
" pyrocatechin ")i is a constituent of many resins, and can be prepared by fusing o-phenolsulphonic acid with caustic potash.
Catechol is crystalline and readily soluble in water, alcohol, and ether. It melts at 104°. Its alkaline solution is first turned green by atmospheric oxidation, and then black. Its aqueous solution precipitates metallic silver from silver-nitrate solution at ordinary temperatures, and gives a green coloration with ferric chloride.
OOH 1 . The monomethyl ether, (^^4<Qir.^2' ^^ c^^^d guaiacol; it is
466 ORGANIC CHEMISTRY. [§ 336
present in the tar obtained by the dry distillation of beechwood. When heated with hydriodic acid, guaiacol yields catechol and methyl iodide. The dimethyl ether of catechol is named veratroU, and is characterized by its agreeable odour.
OH 1
Resorcind (" resorcin "); or ?n-dihydroxybenzene, C6H4<qtt q,
can be obtained by fusing 77i-phenylenedisulphonic acid,
SO HI C6H4 < gQ^TT Q, with potassium hydroxide, the method for its man- ufacture. It yields a deep-violet coloration with ferric chloride: bromine-water converts it mto 2: A: Mribromoresorcinol. It is a colourless, crystalline substance melting at 118^, and is readily soluble in water, alcohol, and ether. It quickly turns brown, owing to the action of the air. A delicate test for resorcinol is mentioned in 348.
Styphnic acid, CeH^^^QV W;4:6) ^ * *^^ ^^ * nitrated dihy-
droxybenzene, and is obtained by the action of cold nitric acid upon resorcinol, as well as from certain gum-resins by the same means. The conversion of m-nkrophenol into styphnic acid by the agency of nitric acid involves the intermediate formation of a tetranitro-com- pound, in which one of the nitro-groups is so reactive as to be replaceable by hydroxyl on treatment with water, with formation of 8t3rphnic acid:
OH OH
NOt/\NO, NO,/NnO,
'no, "" V/NO, "" \yOR'
NO. NO,
m-Nitrophenol 2: 3: 4: 6-Tetraiutrophenol Styphnic add
Quinol (" hydroquinone ")> or p-dihydroxybenzene, melts at 170°. Its chief characteristic is the loss on oxidation of two hydrogen atoms with formation of quinone, C6H4O2 (338), which is readily reconverted into quinol by reduction. The reducing effect of quinol is employed in photography for the development of negatives. With ammonia it gives a red-brown coloration, due to the formation of complex derivatives. Like its isomerides, it is readily soluble in water.
The dihydroxybenzenes can be separated from one another by the action of lead acetate. With tliis reagent, catechol gives
J 3371 TRIHYDRIC PHENOLS. 467
a white precipitate, resorcinol does not yield a precipitate, and qulnol gives a precipitate only in presence of ammonia.
Trihydric Phenols. 337. PyrogaUol (" pyrogallic acid ") ,
.OH 1 GeHsf-OH 2, X0H3
is obtained by heating gaUic add (345)i CO2 being split off:
C6H2(OH)3-COOH - C6H3(OH)3+C02.
Gallic acid PyrogaUol
PyrogaUol forms crystals melting at 132°, and is readily soluble in water. It is a strong reducing agent in alkaline solution: for example, it rapidly absorbs the oxygen of the atmosphere, with formation of a brown coloration. For this reason it is employed in gas-analysis to remove oxygen from mixtures. It also finds application as a developer in photography, and as an agent for dyeing furs.
Mention has been made of the influence exerted by boric acid on the conductivity of hydroxy-derivatives (157 and 231). The results obtained by Boeseken in his investigation of the effect of this acid on the polyhydric phenols possess a general significance. Of the three dihydroxybenzenes, catechol alone has its electric conductivity in aqueous solution greatly augmented by the addition of boric acid. With pyrogallol the effect is similar, but not with the other polyhydric phenols. A seminormal solution of boric acid was found to have a conductivity of 25 •7x10"', that of a similar solution of catechol being 13«6XI0~^ A solution containing both substances in seminormal concentration had the conductivity 555-2x10"*, the sum of the conductivity values for boric acid and catechol separately being only (25 -7 -|-13 -6) X 10"* =39 -3 X lO"*.
The conductivity of a seminormal solution of resorcinol was found to be 5*7x10"', and that of an equivalent solution of boric acid and resorcinol being 25»0xl0"' instead of (25 •7+5-7) X 10"* =31 •4x10"*. For catechol there is an enormous increase in conductivity, but for resorcinol a slight diminution.
Both catechol and pyrogallol have two hydroxyl-groups in union with two directly linked carbon atoms, but this fact does not explain
468
ORGANIC CHEMISTRY.
[§337
the increase of conductivity, since ^ycol, GHiOH*CHsOH, lacks the characteristic. An explanation is furnished by assuming the hydroxyl-groups of these two phenols to be situated in the same plane as the carbon atoms (283), so as to make possible the formation of a ring-syst^oa of the type
\)--0
\
>B.OH
with a d^ree of dissociation much higher than boric acid alone.
The influence exerted by boric acid on the conductivity of poly- hydric alcohols in aqueous solution obviously affords an aid in the determination of the configuration of these substances. Applied to glycol, this method indicates the two hydroxyl-groups not to be
HO-CH, in corresponding positions, but as in the configuration |
H,C-OH The conductivity of boric acid is raised by glycerol, erythritoly mannitol, dulcitol, and sorbitol, indicating the presence in each of these substances of at least two hydroxyl-groups in corresponding positions.
BoESEKEN has discovered a very important relationship between the influence of boric acid on the conductivity of a-dextrose and jS-dextrose and the phenomenon of mutarotation (ao8). This property of mutarotation is explained by assuming the partial con- version of the two forms a and fi (217) into one another until equi- librium is attained. Investigation of the stereochemical constitu- tions of a-dextrose and /^-dextrose (2x2) indicates the two possible configurations to be
OH H OH H
H OH
CHOH CH2OH
and
CHOH CH2OH
I.
II.
the pentagon in each formula representing the plane of the ring of four carbon atoms and one oxygen atom contained in dextrose. Prior to Boeseken's work there was no evidence available as to which formula represents the a-modification, and which the /^-modification.
§ 3371 TRIBYDRIC PHENOLS. * 469
In formula I. there are two hydroxyl-groups on the same side of the plane of the ring, but not in formula II. A substance with the first formula should show a greater increase in conductivity on addition of boric acid than one with the second formula. As a result of the approach to equilibrium between I. and II., the increased conductivity of I. must diminish slowly, the change being accom- panied by a gradual rise in the conductivity of II. This phenomenon is analogous to the diminution with lapse of time of the optical rotation produced by one modification and the corresponding rise in rotatory power of the other isomeride.
Experiment has proved boric acid +a-dextrose to have diminish- ing conductivity, and has demonstrated an increasing conducti\nty for boric acid +/3-dextrose. Formula I. is accordingly assigned to a-dextrose, and formula II. to j?-dextrose.
Phloroglucinol (symmetrical trihydroxybenzene), CeHg^OH 3,
X)H5
is formed by fusing various resins with potassium hydroxide. It is
crystalline, and gives a deep-violet coloration with ferric chloride.
A remarkable synthesis of phloroglucinol from diethyl sodio-
malonate was discovered by von Baeyer.
The mechanism of the reaction involves the preliminary forma- tion of sodium ethoxide under the influence of heat, followed by the combination of this substance with part of the diethyl malonate to form ethyl acetate and ethyl carbonate:
CH,(COOCH»)a +CiH*OH = CH, • COOCzft-l-CO.CCiH,)..
Ethyl acetate Ethyl carbonate
The ethyl acetate condenses with diethyl malonate to form the diethyl ester of unsymmetrical a:etonedicarboxylic acid:
(C(X)CiH»),CH,-f CH»OOC • CH,
- (C00C2H»),CH • CO • CH,+C2H*0H.
Diethyl acetonedicarbozyUte
This product then condenses with another molecule of diethyl malonate, with production of di^kyl phloroglticinoldicarboxylate:
(CXXK),H.)tCjHl • CO-CHifH] (COOCiH»),C— CO— CH,
ItCjHl- COjOCaH^'Cft CO
OCtH, CO-CH,-CO
Diethyl phloroglucinol- dicarbozylate
470 ORGANIC CHEMISTRY. [§ 337
On fusing this substance with potassium hydroxide, the ethyl-car- boxyl-groups ( — COOCiHj) are replaced by hydrogen, with forma- tion of phloroglucinol.
Phloroglucinol should therefore have constitution I.
CO
H
-^ nvt TTn/x
H,C CH, HO
I I
OC CO
\/
CH, I. II.
OH
H\/H OH
In other words, it is cycZohexane in which three of the methyl- ene-groups, CHj, have been replaced by carbonyl, CO; it must, therefore, be called triketocydohexane. It has been proved that phloroglucinol does behave as though it had this constitution: thus, with three molecules of hydroxylamine it yields a trioxime. On the other hand, phloroglucinol has the character of a phenol : for example, it yields a triacetate with acetyl chloride. It exists, therefore, in two tautomeric forms — as a hexamethylene derivative, I., and as trihydroxybenjsene, II.
This is a remarkable example of the alteration of the positions of the atoms (the hydrogen of the OH-groups) in the molecule, result- ing in the conversion of a benzene derivative into a derivative of hexamethylene .
This view expl^ns the interaction of phloroglucinol, and other polyhydric phenols, and a mixture of caustic potash and an alkyl iodide to form derivatives with alkyl-groups. attached to carbon and not to oxygen; for the hydrogen in the methylene-groups of the
tautomeric form must be replaceable by metals (200).
•
The problem of assigning the enolic or ketonic formula to free phloroglucinol has been solved by the aid of a method which has rendered valuable service in many other examples of analogous nature. The process was discovered by Hartley, and involves the study of the absorption-spectra in the ultraviolet region of the spectrum.
An electric arc between iron electrodes is arranged, the light from this source being very rich in bands in the ultraviolet region. After resolution by means of a quartz prism, the beam is passed
§337]
TRIHYDRIC PHENOLS.
471
through an aqueous or alcoholic solution of known strength of the substance under examination. The resulting absorption-band or absorption-bands can be photographed. They are caused by the presence of the dissolved substance, because they are not produced by water or alcohol alone. By this method the absorption-bands for a number of solutions of increasing dilution, or better for a nimiber of liquid layers of diminishing thickness, are reproduced.
I
Fig. 83
-Hartley's Absorption- Fig. 84. — Absorption-Curves op p-Ni-
CURVB. TROPHENOL, p-NlTROANISOLE, AND
Sodium p-Nitrophenolatb.
and the process is continued until the absorption-bands vanish owing to the dilution being too great, or the thickness of the layer too small.
The photographs thus obtained are then placed so as to
bring the wave-lengths X or the oscillation-frequencies ^ (the
abscissse) together. On drawing a line through the edges of the various absorption-bands, a curve like that depicted in Fig. 83 is produced. To reduce the length of the figure, it is constructed by employing the logarithms of the layer-thicknesses as ordinates instead of these thicknesses themselves. The figure indicates
472 ORGANIC CHEMISTRY. H 337
the substance under examination to have two absorption-bands, at ABC and DEP. The second band is much more persisterU than the first, and therefore does not vanish until the layer has become correspondingly thinner.
From numerous measurements by this method, Habtlet established the general rule that aliphatic compounds do not give absorption-bands, whereas aromatic compounds do; and that the absorption-bands produced by aromatic tautomerides sometimes exhibit marked differences in position and persistence. The method affords an exceUent aid in the detection of obscure examples of isomerism indistinguishable by pure chemical tests.
AppUcation of Hartley's method to phloroglucinol shows that it and its trimethyl ether give nearly the same absorption- band. Since the ether is converted into phloroglucinol by heating with hydrochloric acid, its methyl-groups must be in imion with oxygen. The absorption-band also occupies almost the same posi- tion as that of p3rrogallol, a substance which does not display tautomerism. On the analogy of cj/clohexadione, the tautomeric form of phloroglucinol or cycZohexatrione should not give an absorption-band.. It is therefore reasonable to assign the enolic formula to free phloroglucinol.
This method also furnishes valuable evidence of a difference in constitution between free nitrophenol and its deeply coloured salts. Fig. 84 represents the absorption-curve of a neutral solution of p-nitrophenol (I.), that of a solution of the methyl ether 2>-nitroanisole (II.), and that of a solution of sodium p-nitro- phenolate (III.). Curves I. and II. almost coincide, and the difference in character of curve III. is explained by ii-<Miiniing a quvnonaid structure (373) for the nitrophenolate:
H0<^^N02; 0=/^\=NO.ONa.
Free p-nitrophenol Sodium p-nitropbenoUte
Higher Phenols.
The chief of the higher phenols is hexahydroxyhemene, Ct(OH)i. Its potassium derivative, potassium carbonyl, Cfi(0E)6, is formed in the preparation of potassium, and acquires an explosive char- acter on exposure to the air (" Inorganic Chemistry," aay). It can be obtained by heating potassium in a current of carbon mon-
§ 3381 QUI NONES. 473
oxide, a direct synthesis of a derivative of benzene. Distillation with zincMlust converts hexahydroxybenzene into benzene. It is a white, crystalline substance, and undergoes oxidation very readily.
Quinones.
338. The quinones are substances derived by the elimination of two hydroxyl-hydrogen atoms from aromatic dihydroxy-deriva- tives:
C6H4(OH)2-2H = C6H4O2.
Dihydroxybenxene Quinon*
The simplest quinone is benzoquinone, C6H4O2: it is also called quinone. It is obtained by the oxidation of many p-derivatives of
benzene, such as p-aminophenol ^^4<qjj^ At sulphanilic acid,
C6H4<gQ^|j ^, and p-phenolsulphonic acid, C6H4<gQTTi, and
also by the oxidation of aniline with chromic acid — the ordinary method of preparation. It is also formed in the oxidation of quinoi (336), though the latter is usually prepared by the reduction of quinone. Oxidation of quinoi by ferric chloride yields quin- kydrane, a compound in equimolecular proportions of quinone and quinoi; crystallizing in beautiful, intensely coloured, long needles.
o-Dihydroxybenzene or catechol can also be converted by the action of silver oxide into an unstable quinone. m-Dihydroxyben- zene or resorcinol does not yield a quinone.
A great number of pora-quinones are known. Like benzo- quinone, they can be prepared by oxidizing the corresponding para-compounds.
The quinones are yellow, and have a peculiar, pungent odour.
They volatilize with steam with partial decomposition, and have
oxidizing properties. The constitution of benzoquinone is best
expressed by
CO
/\ HC CH
II II • HC CH
\/ CO
474
ORGANIC CHEMISTRY.
H339
Such a formula requires that benzoquinone should be a diketone, and contain two double bonds: its properties show that it fulfils both conditions. Its ketonic character is inferred from its yielding with hydroxylamine first a guinone mono-oxime (335), and then a quinone-dioxime:
|
C— NOU |
C=NOH |
|
/\ |
/\ |
|
HC CH |
HC CH |
|
1 and HC CH |
HC CH |
|
\/ |
\/ |
|
00 |
C=NOH |
The presence of double linkings is proved by its power of forming addition-products: benzoquinone in chloroform solution can take up four atoms of bromine. According to this constitution, benzo- quinone is not a true benzene derivative, but the diketone of a p-dihydrobenzene :
CH2
/\ HC CH
II II . HC CH
\/ CHa
This formula is supported by the oxidation of benzoquinone to maleic acid, effected by an alkali-metal persulphate in presence of silver sulphate and sulphuric acid:
^^ X!OOH
HC + 3O2 - II + 2CO2.
HC CH HC
HC
/
CH
\,
OOH
VI. SUBSTrnXTION-PRODUCTS OF ANILmS.
339. Aniline is attacked very energetically by chlorine and bromine. The direct introduction of these halogens must be
S 3301 SUBSTITUTION-PRODUCTS OF ANILINE. 475
effected by their slow addition to a solution of acetoanilide in glacial acetic acid, the main products being the para-compounds. The orifto-halogenanilines and the TM^to-halogenaniUnes are pre- pared by reduction of the corresponding halogen-nitrobeazenes. The production of 2:4i^'tnbromoaniline .is described in 396. The basic character of aniline is weakened by the introduction of halogens. '
Nitroanilines.
Nitroanilines, or compounds containing m'tro-groups and an amino-group, can be obtained by the partial reduction of dinitro- compounds by means of ammonium sulphide. Another method for their production consists in the nitration of aniUnes, though if nitric acid is allowed to act directly on this base the resulting products are mostly those of oxidation. If nitration is to be car- ried out, the amino-group must be " protected " against the action of this acid, either by first converting the aniline into acetoanilide, or by causing the nitric acid to react in presence of a large quan- tity of sulphuric acid. When the acetyl-compoimd is employed, 'p-nitroanHine is the chief product : with sulphuric acid, m-nt/ro- aniline and p-nitroaniline are formed in almost equal ratio, and a very small proportion of o-nitroaniline. The formation of nitro- anilines from chloronitrobenzenes and bromonitrobenzenes is men- tioned in 330.
The nitroanilines can also be prepared from the corresponding ehloronitrobenaenes and bromonitrobenzenes (330). There is a marked weakening of the basic character in these substances, most pronounced in the or^/io-derivatives, and least in the meta- compounds.
On dissolving o-nitroaniline in concentrated sulphuric acid, and pouring the solution into a large excess of water, the yellow o-nitro- aniline is precipitated owing to almost complete hydrolysis of the salt. With p-nitroaniline there is no precipitation, but the solution develops a yellow colour, the hydrolysis being very much less. Similar treatment of m-nitroaniline yields a colourless solution, since the salt is not hydrolyzed.
o-Nitroaniline; m-nitroaniline, and 2>-nitroaniline, C6H4 <^tt^> are yeUow, crystalline compounds, almost insoluble in cold water.
476 ORGANIC CHEMISTRY. [§339
but readily soluble in alcohol. Their melting-points are respec- tively 71°, 114^ and 147°.
The amino-groups in o-nitroaniline and 2>-nitroanillne, but not that in m-nitroaniline, are exchanged for hydroxyl by heating with a solution of potassium hydroxide, the corresponding potassium nitrophenoxide being formed. The amino-group in picramide or 2*A:64rinitroaniline, C6H2(N02)3*NH2, is very readily replaced by hydroxyl.
p-Aminobenzenesulphonic Acid or Sulphanilic Acid.
Sidphanilic add is obtained by heating aniline with fum- ing sulphuric acid; or by heating p-chlorobenzenesulphonic acid at 200° with ammonia, in presance of copper as a catalyst. like its isomerides, it dissolves with difficulty in cold water. The basic properties of aniline are greatly weakened by the intro- duction of the sulpho-group into the ring, for sulphanilic acid cannot yield salts with acids, whereas the sulpho-group reacts with bases, forming salts. The formula of sulphanilic acid is
.SO
probably C6H4 <tvtj| > ; that is, it is an inner salt. On fusion
with potassium hydroxide, it does not yield aminophenol, in ac- cordance with precedent, but aniline. Oxidation with chromic acid converts it into quinone. On pouring a mixture of sodium sulphanilate and sodium nitrite in aqueous solution into dilute sulphuric acid, an innen salt of benzenediazoniumstdphonic add is precipitated, being nearly insoluble in water:
This compound is of great impoHance in the preparation of a20- dycs, such as hdianihine (341).
Aminophenols.
Aminophenols are formed by the reduction of nitrophenols. The acidic character in these compounds is so weakened that they do not combine with bases: on the other hand, they yield salts ^jvith acids. In the free state the aminophenols are colourless solids, crystallizing in leaflets, and readily turned brown by atmcspheric
S 339] AMINOPHSNOLS. 477
oxidation with formation of a resin. Their hydrochlorides are more stable.
o-Aminophenol yields compounds by the substitution of acid- residues in the amino-group, which at once lose water, forming anhydro-bases:
/\NH
ry
H
0Co>-^
\/0H \/0[H
Aoetylpderivanve Ethenylaminophenolf
Anhydro-MM
On treatment with acids, aminophenol and acetic acid are regen- erated.
jHAminophenol is obtained by the electro-reduction of nitro- benzene in acid solution (303).
The alkaline solution of p-aminophenol rapidly acquires a dark colour, unless sodium sulphite is preseut. The trade-name of this solution is "rodinal." It finds application as a photographic developer.
LuMi)2RB has discovered certain general conditions which aro- matic compounds must fulfil to be available as photographic devel* opers. They must either contain some hydrozyl-groups or amino- groups, or at least one of each class. In order that the developing action may not be interfered with when substituents are present in the amino-group and in the hydroxyl-group, not less than two such unsubstituted groups must be present in the molecule.
A derivative of j>-aminophenol used in medicine is "phenacetin "
OC H or aeetylphenetidinef ^^4<|jiq. Arj q' ^® acetamino-derivative of
phenetole, G«Hs • OC ^Hs.
When aniline hydroarsenate, C«Hi - NHi,H»As04, Lb heated, a mole- cule of water is eliminated, with formation of p-aminoplienylarsinic acidy NHt*CcH4*AsO(OH)2. The presence of a free amino-group is proved by the possibility of diazotising the compound; iodine converts it into p-iodoaniline, with elimination of the arsinic-acid residue. The fcnration of p-aminophenylarsinic acid is analogous to that of sulphanilic acid by heating aniline hydrogen sulphate:
C,H» • NH,,H,S04 - H,0 = NH, • C JH* • SO,H.
Aniline bvdrogen Sulphftnilic acid
' tulphate
478 ORGANIC CHEMISTRY? [| 339
Sodium p-aminophenylar8inaie or " atoxyl/' and sodium p-aeetul- aminophenylarnnate or " arsaoetin/'
CH..CO-NH.C,H4-AsO<^^^,
are valuable remedies for the treatment of trypanosomiasis or sleeping sickness.
When phenol is heated with arsenic acid, it yields the analogous p-hydroxyphenylarsinic add, HO*C6H4-AsO(OH)2, converted by careful nitration into Z-nitroA-hydroxyphenylarsinic acid,
O2N
Reduction transforms this product into the corresponding diaminodihydroxyarsenobemene,
HO<^^A^=As/^ H2N NH2
The dihydroMoride of this substance is the " salvarsan ''
discovered by Ehrlich and Hata, and has been employed with
50od results in the treatment of diseases of protozoal origin. It
s a crystalline powder, readily soluble in hot water, but the
lolution decomposes rapidly.
Polyamino^ompounds are obtained by the reduction of poly-
nitro-derivatives. xa-Phenylenediamine, C6H4 <mjj^ 3; is formed
from benzene by nitration and subsequent reduction.
Xy-Phenylenediamine can be prepared by the reduction of amino- azobenzene (309) with tin and hydrochloric acid, aniline being also formed :
C6H6-N:!N.C6H4-NH2 = C6H6-NH2+H2N.C6H4-NH2.
+ 1 + 2H|2H
Triaminobenzenes are prepared similarly (341).
§ 340] POLYAMINCKIOMPOUNDS. 479
When heated with aqueous ammonia at 180^-200^, in presence of cupric sulphate as a catalyst, p-dichlorobenzene and p-chloro- aniline are converted into the corresponding diamine.
Most of the polyaminobenzenes are crystalline solids, and distil without decomposition. They dissolve readily in warm water.
The three diaminobenzenes are distinguished by the following series of reactions. The o-diamines react readily with l:2-dike- toneSy yielding quinoxalines:
HTO
Ha O
C-R /\N=G— R I = r ] I -h2H20.
C— R' \/N=C— R'
fTi-Phenylenediamine in aqueous solution gives an intense brown coloration with nitrous acid, even when the acid solution is very dilute (341). p-Phenylenediamine is converted by oxidation into benzoquinone.
Like the polyhydric phenols, the polyamino-compounds are very readily oxidized. They are colourless, but many of them are turned brown by oxidation in the air.
Quinonedi-imide, HNiCeHi^NH, a compound derived from p-phenylenediamine, has the same relationship to this amine as benzoquinone to quinol. Aniline-black is a complex derivative of this substance, and is formed by the oxidation of aniline. It is a condensation-product of eight molecules of aniline, and is con- sidered to have the constitutional formula
Ctfl*-N:C,H4:N-C,H4-NH.C6H4-NH-C6H4-N:C6H4:N.C5H4-
N:CeH4:NH,
indicating union of the eight aniline-residues by nitrogen and not by carbon. One of the arguments in favoiu- of this formula is the almost quantitative conversion of aniline-black by further oxidation into benzoquinone, also a proof that each of the eight aniline-residues IB linked at the paro-position.
Azo-dyes.
340. The azo-derivatives of the polyamino-compounds are known as azo-dyes. They are of great technical importance, being
480 ORGANIC CHEMISTRY. (i 340
extensively employed in dyeing wool, silk and cotton. Tb^ are azobenzenes in which hydrogen atoms have been replaced by amino-groups. They are not the only dyes: derivatives of azo- benzene with hydrogen replaced by hydroxyl or by the sulpho- group can likewise be employed in dyeing. Some of these com- pounds will also be described.
It is necessary first to state certain facts regarding dyes in general. It has been proved by experiment that not every colour- ing-matter can dye the substances named above; that is, colour them so that the dye cannot subsequently be removed by rubbing, or washing with water or soap. It b necessary, therefore, to draw a distinction between coloured substances, or ckromogens, and dyes: for example, azobenzene has a deep yellowish-red colour, but it is not a dye. The introduction of an amino-group, however, converts it into a dye, aminoazobenzene. Wrrr has propounde I the theory that the colouring-power of a compound depends upon two factors. The first of these is the presence of certain groups, which he calls chromophore-groupH, among them being the azo- group, — N=N — , the nitro-group, the nitroso-group, the double carbon linking — C=C — , the carbon ring present in benzo-
quinone or quinonoid'group =^ y^^> *^^ other groups.
Substances containing a chromophore-group, along with an auxockrom^-group, such as NH2, OH, SO3H, or in general any group which imparts to them an acidic or basic character, are dyes: an example is aminoazobenzene. Another example is nitrobenzene, which has a pale-yellow colour, and contains the chromophore nitro-group, but is a chromogen, not a dye : on the other hand, p-nitroaniline and p-nitrophenol are dyes.
Baly has shown that many colourless compounds, especially those with double carbon linkings, are characterized by absorption- bands in the ultraviolet spectrum. The introduction of auxc chromeic groups into such substances displaces these bands to the visible part of the spectrum; in other words, transforms these compounds into dyes.
It is often sufficient to immerse the silk, wool, or cotton to be dyed in a solution of the dye. Although primarily dissolved, the dye cannot be removed by washing the fabric after dyeing. The dye must, therefore, have undergone a change. Several theories to explain this phenomenon have been suggested. In sonie instances
S 341] AZO-DYES. 481
the dye fonns a solid solution (" Inorganic Chemistry/' a6o) with the fibre, becoming distributed between the water or other solvent and the material as between two.immiscible substances, an equilib- rium being attained.
In other types of dyeing adsorption comes into play.
The fabric does not alwa3r8 take up the dye when immersed in its solution. It has been repeatedly observed that dyes which become directly fixed on animal fabrics, such as silk and wool, do not dye vegetable fabrics, like cotton, unless the material to be dyed has undergone a special process, called ''mordanting": that is, a sub- stance must be deposited in the fabric to ''fix" the dye, since it will not imite with the fibres themselves. Such substances are called "mordants": they are usually salts of weak bases or acids. Such are aluminium acetate; ferric salts; compounds of tin, such as "pink salt," SnCl4,2NH4Cl. The woven material is thoroughly soaked in a solution of one of these salts, and then spread out and exposed to the action of steam at a suitable temperature. The salt undergoes hydrolytic dissociation, and the base or acid, for example aliuninium hydroxide or stannic acid, is deposited in a fine state of division in the fabric. The dye imites with this base or acid, forming an insoluble, coloured c(»apound which is not removed by washing.
Direct dyes are those capable of colouring the fabric without previous mordanting.
341. Azo-dyes are obtained by treating diazonium chlorides with aromatic amines or with phenols:
CoH5>N2pTH]<^^N(CH3)g=CeH5>N;N*C6H4*N(CH3)2+HCl;
Diasonium ehlorid« DimethyUailino Dimetbylaminoaiobeiiseno
C6HB.N2pTH|<^^OH=C8Hg-N;N-C6H4»OH+HCl.
y*^-/^ HydrozyaiobenMne
Basic and acidic dyes respectively are produced. It is mentioned in 309 that the combination of a diazonium chloride and an aro- matic amine sometimes yields the diazoamino-compound as an intermediate product, which can be converted into the aminoazo- derivative by wanning with the amine hydrochloride. In this formation of aminoazo-compounds and hydroxyazo-compounds, the para-H-atom always reacts with the diaizonium chloride : when this atom is replaced by a substituent, the formation of dye either does not take place, or is very incomplete.
482 ORGANIC CHEMISTRY. H 341
In preparing hydroxyazo-dyes, the solution of the diazonium chloride is cooled with ice, and is slowly added to the alkaline solu- tion of the phenol or its sulphonic acid. The reaction-mixture is kept slightly alkaline, since otherwise the hydrochloric acid liberated would hinder the formation of the dye. After the solutions have been mixed, the dye is *' salted out " by the addition of common salt, which precipitates it in flocculent masses. It is freed from water by means of filter-presses, and packed either as a powder or a paste.
Aminoazo-dyes are prepared by mixing the aqueous solution of the diazonium chloride with that of the aromatic amine salt, the colouring-matter being subsequently salted out. It is sometimes necessary to employ an alcoholic solution.
The simplest azo-dyes are yellow. The introduction of alkyl- groups or phenyl-groups, and, in general, increase of molecular weight, change their colour through orange and red to violet and blue. They are crystalline, and most of them are insoluble in water and soluble in alcohol. Instead of the azo-dyes themselves, it is often better to employ their sulphonic acids, obtainable from them by the usual method — ^treatment with concentrated sulphuric acid.
Aniline-yellow is a salt of aminoazobenzene : it is seldom used now, it.s place having been taken by other yellow dyes.
NH
Chrysdidine or diaminoazobenzene, C6H6*N:N*C6H3<*j.tt^, is
obtained from benzenediazonium chloride and ?7i-phenylenedia- mine. It yields a hydrochloride, crystallizing in needles of a reddish colour and fairly soluble in water: this salt dyes wool and silk directly, and cotton which has been mordanted.
Bismarck-brown or vesuvine is formed by addition of nitrous acid to an aqueous solution of m-phenylenediamine. It is a mixture of various dyes, among them triaminoazobemene, manu- factured by diazotizing one of the NH2-groups in m-phenylene- diamine, and treating the product thus obtained with a second molecule of this base :
<(^^N2[crTg<^~^
HoN H2N H2N H2N
TrlaminoaiobenBMie
Bismarck-brown consists mainly of more complex derivatives,
i 341] AZO-DYBS. 483
formed by diazotization of both the amino-groups of m-phenyl- enediamine and union of the products with two molecules of this base.
Even a very dilute solution of nitrous acid gives a brown colora- tion with wi-phenylenediamine, due to the formation of Bismarck- brown or related substances. This reaction furnishes a very delicate test for nitrous acid, and is employed in water-analysis.
Hdianthinef or dimethylaminoazobenzenesulphonic acid, is pre- pared by the interaction of p-sulphobenzenediazonium chloride and dimethylaniline hydrochloride in aqueous solution:
H03S.C6H4-N2 Cl + H C6H4-N(CH3)2=-
=HCH-H03S.C6H4-N:N.C6H4-N(CH3)2.
Helianthine
It is not often used as a dye, but its sodium salt, which has a yellow colour, and is turned red by acids, is employed as an indicator in volumetric analysis under the name niethyl-orange, Resordyi' yellow or dihydroxyazobenzenesulphonic acid,
H03S.C6H4-N:N-C6H3<q2.
is obtained from resorcinol (336) and p-sulphobenzenediazonium chloride.
The azo-dyes are converted into amino-compounds by energetic reduction with tin and hydrochloric acid. Thus, aminoazobenzene yields aniline and p-phenylenediamine:
C6H5-N=N.C6H4-NH2 -^ CeHg-NHa-i C6H4<^2j i
This decomposition on reduction affords a means of determining the constitution of these dyes, and indicates the methods by which they are obtained. For exany)le, if reduction of a dye with tin and hydrochloric acid yields a mixture of equimolecular amounts of diaminobenzene and triaminobenzene, it follows that the constitution of this compound is
r
NH2 . C6H4— N : JN-^Ha <^.
484 ORGANIC CHEMISTRY. U 342
This decompofsition also indicates that the dye can be obtained by diazetizing a molecule of diaminobenzene, and treating the product with a second molecule of diaminobenzene, in accordance with the equation on the pre^ous page.
Vn. SUBSTITUTED BENZOIC ACIDS; POLTBASIC ACIDS AUD THEIR
DERIVATIVBS.
Halogenbenzolc Acids.
342. Direct chlorination, with ferric chloride as catalyst, con- verts benzoic acid into a complex mixture of acids. The only monochloro-constituent of the product is jn-chhrobenzaic acid, it being associated with polychloro-acids very difficult to separate. m-Ghlorobenzo!c acid can also be obtained from the corresponding amino-derivative by the diazotization-method, a reaction well adapted to the preparation of the halogenbenzolc acids. The interaction of phosphorus pentachloride with the hydroxybenzofc acids proceeds less smoothly, p^hlorobenzdlc add and p-bromo- benzoic acid are usually prepared by oxidation of the corre- sponding halogentoluenes.
As would be expected, the acidic character of benzoic acid is strengthened by the introduction of halogen. The dissociation- constant lO^A; of the halogenbenzolc acids is greater than that of benzoic acid itself. For benzoic acid 10*t is 0*6; for o-chloroben- zoic acid 13*2; for m^chlorobenzolc acid 1*55; f or p-chlorobenzolc acid 0* 93. These values prove that the chlorine atom in the ortho- position exercises the greatest iniSuence and that in the para- position the least, while for the m-compound lO^A; is intermediate in value.
Nitrobenzolc Acids.
m-Nitrcbem&lc acid is the principal product obtained by nitrating benzoic acid; about 20 per cent, of o-nt^obeneoic add and a very small proportion of p-nifrobeiuoic acid are simul- taneously formed. The ar<Ao-compound is best obtained by the oxidation of o-nitrotoluene, and is characterized by an intensely sweet taste.
The introduction of the nitro-group causes a large increase in the value of the dissociation-constant lO^A;, which for benzoic
§ 343] SULPHOBENZOiC ACIDS. 486
acid itself is 0*6, for o-nitrobenzolc acid 61*6, for the mr-add 3*45, and for the p-acid 3*96. The melting-points of these acids are respectively 148^, 141°, and 241.°
Sulphobenzoic Adds. 343. o-Benzcic stdphinidej
C6H4 < co'> NH,
the imino-derivative of o-sulphobenzoic acid, is known as " sac- charin." It is about five hundred times as sweet as sugar, and on this account is sometimes employed as a substitute for it. It has no dietetic value, being eliminated unchanged from the body. Dii*ect sulphonation of benzoic acid yields m-stdphobenzaic acid almost exclusively, so that saccharin cannot be prepared by this means. It is obtained from toluene, which, on treatment with chlorosulphonic acid, S02(0H)C1, yields a mixture of p-totuene- sulphonyl chloride and o-toltienesvlphanyl chloride, the former being the chief product. The o-chloride is converted into its sidphon" amide, the methyl-group of which is then transformed into carboxyl by oxidation with potassium permanganate. On heating, this oxidation-product loses one molecule of water very readily, form- ing saccharin :
UIls- ^Hs -► UII4 <QHg 2 ^^* ^CHs
Toluene o-Toluenesulphonyl chloride o-SuIphonamide
— ♦ GeH4 <QooH ^"^ ^^4 '^ CO ^ ^^*
•-Sulphonamide of Saoolwrin
beniolc acid
"Saccharin" is awhite, crystalline powder, soluble with difficulty in cold water, and readily soluble in alcohol and ether. It takes up one molecule of water, yielding the sulphonamide of (H3u1- phobenzolc acid, which does not possess a sweet taste.
Rbmsen found that the "saccharin *' of commerce is a mixture of 0- benzoic sulphinide; p-stdphaminobenzoic acid, COOK •CMa •SO j!^Kt; and poia98iuin hydrogen o-8ulphobemoaU, COOH*CeH4*SOsOK, containing less than 50 per cent, of the sulphinide. The melting- point of the pure sulphinide is 220**.
486 ORGANIC CHEMISTRY. [{ 344
Monohydroxy-acids.
344. The most important of the monohydroxy-acids is
OH 1
o-hydroxybenzoic acid, or salicylic acid, ^^^^<qqqh 2* ^^
derives its name from salicin, a glucoside in the bark and leaves of the willow (salix). On hydrolysis, this substance yields scUigenin and dextrose:
C13H18O7+H2O = C7H8O2 +C6H12O6.
Salicin Saligenin Dextrose
Saligenin is the alcohol corresponding to salicylic acid, into which it is converted by oxidation:
^^* ^ CH2OH ^ ^^^ ^ COOH-
Saligenin S&llcylio acid
Salicylic acid is present as methyl ester in oil of wintergreen (GauUheria procunibens) , from which the acid is sometimes obtained for pharmaceutical use. A good yield of the acid is obtained by fusing o-cresol with caustic alkali and lead peroxide as an oxidizer:
.CH3 yCOOH
^OH X)]
>H
Salicylic acid is manufactured by a process discovered by KoLBE and improved by Schmidt, in which sodium phenoxide is heated with carbon dioxide in an autoclave at 130^.
At the ordinary temperature at a pressure of about 1} atmos- pheres, sodium phenoxide and carbon dioxide react to form todvum pfienylcarhonate:
CeHs-G-Na+COj - CeHs-O-COONa.
This compound is to be regarded as an intermediate product in the synthesis of salicyclic acid. Its conversion into this substance ia represented by the scheme
. COONa yOH
H \COONa
§ 344] DIHYDROXY'ACIDS. 487
Salicylic acid is a white, crystalline powder, which dissolves with difficulty in cold water, and melts at 159^ When carefully heated, it sublimes, but on rapid heating decomposes into phenol and carbon dioxide. With bromine-water it yields a precipitate of the formula C6H2Br3«OBr. It gives a violet coloration with ferric chloride, both in aqueous and in alcoholic solution, whereas phenol dissolved in alcohol does not. When boiled with calcium chloride and ammonia, a solution of salicylic acid precipitates basic
calcium salicylate, C6H4C^Q^,^Ca: this reaction affords a means of
separating salicylic acid from its isomerides, which do not give this reaction.
Salicylic acid is a powerful antiseptic, and is employed as a preservative for foods and such beverages as beer. It is not, how- ever, completely innocuous. Sodium salicylate and the acetyl-
.O.CO.CH3 derivative, " aspirin," C6H4/^ , are employed in
medicine. XJOOH ^
When the acid is heated to 220^, it loses carbon dioxide and
water, with formation of phenyl salicylate:
^^^<COO[H] ^^^K[CO^H " ^°2"^^20+C6H4<cooCeH6-
This compound is employed as an antiseptic under the name '*salol." By heating to 300°, its sodium derivative is converted into sodium phenyhalicylate:
<^6il4 < coOCeHs '"^^ ^ COONa "
ra-Hydroxybenzdlc add and p-hydroxybenzolc acid 3deld no coloration with ferric chloride. Their basic barium salts are in- soluble.
Dihydrozy-acids. Among the dihydroxy-acids is protocalechuic acid,
/COOH 1 CeHsr-OH 3. M)H 4
488 ORGANIC CHEMISTRY. [§ 345
It is obtained from many resins by fusion with potash, and syn- thetically by heating catechol with ammonium carbonate, the latter method being a striking example of the readiness with which the carboxyl-group can sometimes be introduced into the ring. It is freely soluble in water. It reduces an ammoniacal silver solution, but not an alkaline copper solution. It gives a characteristic reaction with ferric chloride, yielding a green colour, which changes to blue and finally to red on addition of a very dilute solution of sodium carbonate.
Trihydrozy-acids.
345* The best-known trihydroxy-acid is gallic acid^
yCOOH 1 p „ /oh 3 ^^2\<0H 4'
\0H 6
It is a constituent of gall-nuts, tea, and '' divi-divi," a material used in tanning. It is usiially prepared by boiling tannin with dilute acids. It crystallizes in fine needles, readily soluble in hot water. It is mentioned in 337 that, on heating, the acid loses CO2, forming pyrogallol. Gallic acid reduces the salts of gold and silver, and gives a bluish-black precipitate with ferric chloride. In alka- line solution it is turned brown in the air by oxidation, like pyro- gallol.
Gallic acid is employed in the manufacture of blue-black ink. For this purpose its aqueous solution is mixed with a solution of ferrous sulphate containing a trace of free sulphuric acid. Without the acid, the ferrous sulphate would quickly oxidize in the air, giving a thick, black precipitate with the gallic acid: this oxidation is re- tarded in a remarkable manner by the addition of a very small quan- tity of sulphuric acid. As soon as the solution is brought into con- tact with paper, the free acid is neutralized by the alumina always present in the latter, and, as oxidation is no longer prevented, the writing in drying turns deep black. As the mixture of the solutions of ferrous sulphate and gallic acid has only a faint-brown colour, which would make the fresh writing almost invisible, indigo-carmine is added to the mixture. This imparts to the ink coming from tlie ^ pen a dark-blue colour, which changes by the process^described to a deep black.
1346]
VEGETABLE DYES AND TANNINS.
489
Vegetable Dyes and Tannins.
346. The various vegetable dyes and tannins are very important natural products related to the hydroxybenzolc acids.
A considerable proportion of the vegetable dyes are connected with salicylic acid, most of them being characterized by a yellow colour. They are classified in two groups, the xanthonee and flavoneSf and have been investigated mainly by von Eostanbcki. Distillation of salicylic acid with acetic anhydride yields first the
phenyl ether of salicylic acid, C6H4 <qq^qi a substance further
converted into xanOwne
O
by elimination of water. EuxanJOume or Indian yeUaw is a di- hydroxy-derivative of xanthone, with a hydroxyl-group in each benzene-nuclexis.
FUwone is formed by the condensation of methyl phenyl- propiolate and sodium phenolate:
^ONa CeHiT + CHaOOC -0=0 -CeHs
II
c
COOCHs
Saponification of this intermediate product and replacement of sodixun by hydrogen yields the corresponding unsaturated acid. The chloride of this acid condenses quantitatively to flavone under the influence of aluminium chloride:
CeH H
a
./^\..
II
CH
C»H5
Ha +
0
CO
\8' B'X«
)CH
nATone
r
490 ORGANIC CHEMISTRY. [(346
Among the flavones are dtrymi or 1 : S-dihjrdroxjrflayone, the yellow dye of poplar buds; luieolin or 1:3:3' :4'-tetrahydroxy- flavone; the colouring matter of dyers' weld {Reseda liUeola); and morin or li3:2'i4'-tetrahydroxyflav(me, the dye of mulberry {Moms tindoria) ; and other products.
Willstatter's remarkable researches on the colouring prin- ciples of flowers and fruits have identified among the constituents of these substances 2>-hydroxybenzoic acid, protocatechuic acid, or gallic acid. These colouring matters are glucosides, and have the name anihocyanins. Their extraction from the plants is facilitated by the formation of well-crystallized salts with mineral acids and also with organic acids. Since the anthocyanins do not contain nitrogen, Willstatteb regards these salts as oxoniimi derivatives (239).
On heating with hydrochloric acid, the anthocyanins are decomposed * into carbohydrate and the characteristic colour- components, known as ardhocyanidins. Investigation of antho- cyanidins derived from a great variety of coloured flowers and fruits has led to the surprising conclusion that they all contain the same atomic grouping combined with the three acids cited previously. The oxonium salts formed with hydrochloric acid have a structure of the type
CI H0/\ •
=0 C • C6H4 •OH
II =CH — C.OH
the group =C-C6H4*OH derived from p-hydroxyben2oIc acid being replaceable by ^D-C6H3(OH)2 from protocatechuic acid, or by =C-C6H2(OH)3 from gallic acid. The variegated wealth of colour displayed by flowers is partly due to the union of these compounds with acids to form oxonium salts, and partly to their combination with bases to produce phenolates, all these deriva^ tives having different characteristic colours.
The blue colour of the corn-flower is caused by an alkali* metal salt of an anthocyanin identical with that which imparts its colour to the rose and geranium in the form of red oxonium salt.
J 347] VEGETABLE DYES AND TANNINS, 491
Lichens also contain characteristic colouring matters, and some of these products have been synthesized from hydroxy-acids. Emil Fischer has prepared from these acids a whole series of derivatives of this type, and given them the collective name depsides (8c^av, tan). The number of phenolcarboxyUc acid residues in the molecule is indicated by a Greek prefix, di-, tri-, tetra-depsides, and so on, being known.
Sjmtheses of this type are exemplified by the formation of the didepside of p-hydroxybenzoic acid. In alkaline solution, methyl chlorocarbonate and this acid react in accordance with the equa- tion
CH3O.COCI + NaO.C6H4-COONa = ^'cXnate™" = CH3O -CO .OC6H4 -COONa + NaCl.
The phenolic hydroxyl of the 2>-hydroxybenzoic acid being thus rendered inactive, the acid can be converted into its chloride by means of phosphorus pentachloride, and the product caused to react in alkaline solution with a second molecule of the acid:
CH30.C0.0.C6H4-C0CI + NaO.C6H4-COONa =
= CH30.CO.OC6H4.CO.OC6H4-COONa + NaCL
Saponification replaces the carbomethoxy-group CHsO-CO — by hydrogen, forming the didepside,
HO .C6H4 -CO .OC 6H4 .COOH.
347. The tannins, or tannic addsj are very widely distributed throughout the vegetable kingdom. They are soluble in water, have a bitter, astringent taste, yield a dark-blue or green precipi- tate with ferric salts, convert animal hides into leather, and precipitate proteins from their solutions.
Three groups of tannins are recognized. Most of these sub- stances are related to the tannin obtained from oak-bark. They are also connected with catechin, a white, crystalline substance of known structure, the principal constituent of gawlbier, a tannin material found in Sumatra. These tannins give a red colora- tion with acids.
A second group of tannins comprises those converted by
492 ORGANIC CHEMISTRY, I| 347
the action of wann, dilute acids into ellagic acid. This substance has the constitution
and is therefore a depside.
The constitution of the tannins of these two groups is im- perfectly understood. The small proportion of tannins belong- ing to the third group includes an important compound, the tannin of gall-nuts. The constitution of this substance has been almost completely established by analysis and synthesis. On warming with dilute sulphuric acid, it takes up the elements of water, decomposing into gallic acid and dextrose. From these two compounds Emil Fischer has synthesized pentadigaUoylglucosey
C6H706[C6H2(OH)3.CO.OC6H2(OH)2-CO]5 or C76H52O46,
Dextrose DigaIloyl>resadue
reeidue
a substance displa3ring very great analogy to tannin. The first step in the process is the conversion of gallic acic) into a didepside, gaUaylgallic acid, _j
yOH
XJOOH
the chloride of this acid then reacting wi^ dextrose to form pentadigalloylglucose.
Tannin imparts its characteristic bitter /taste to many beverage — to tea which has been too long infused, fot instance. The addition of milk removes this bitter taste, because the tannin forms an insol- uble compound with the proteins present in the milk.
Tannin is a white (sometimes yellowish), amorphous powder, readily soluble in water, only slightly in alcohol, and insoluble in ether. It forms salts with two equivalents of the metals, and percipitates many alkaloids, such as strychnine and quinine, from their aqueous solutions (407).
§ 347] AMINOBENZOiC ACIDS 493
The tannins find application in medicine and in the tanning of hides.
In making leather, the hide is saturated with the tannin, because without this treatment it cannot be employed in the manufacture of shoes and other articles, since it soon drie^ to a hard, horn-like substance, or in the moist condition becomes rotten. When satu- rated with tannin it remains pliant, and does not decompose.
The skin of an animal consists of three layers, the epidermis, the cuticle, and the fatty layer. The cuticle being the part made into leather, the two other layers are removed by suspending the hides in running water, when the epidermis and fatty layer begin to decom- pose, and are removed by means of a blunt knife. Alternate hori- zontal layers of the hides thus prepared and oak-bark or some other material containing tannin are placed in large troughs or vats, which are then filled with water. At the end of six or eight weeks the hides are taken out and placed in a second vat containing fresh bark of stronger quality. This is continued with increasingly concen- trated tannin solutions until the hides are perfectly tanned, the proc- ess lasting as long as two or three years, according to the thickness of the hide. Whether a hide is thoroughly saturated or tanned can be judged from the appearance of its cross-section, or by treatment with dilute acetic acid: if this treatment makes it swell up intemallyi it shows that the conversion into leather is incomplete.
The process of tanning probably involves a mutual precipitation of coUoids. The hide contains proteins in the form of gels {" Inor- ganic Chemistry," 192), and the tanning material dissolves similarly as a colloid in water. Among the reasons for this assumption is the fact that the freezing-point of the solvent remains unaltered. At first the tanning material is simply absorbed by the hide, since it can be extracted by water. After the tanning process has continued for some time, there is a diminution in the quantity extracted.
Aminobenzoic Acids.
The most important of the aminobenzoic acids is o-amino- benzoic acid, called anthranilic acid, first obtained by the oxidation of indigo (404). It has the character of an amino-acid, yielding salts with both acids and bases. It possesses a sweet taste and slightly antiseptic properties. It is obtained by the method of HooGEWERPP and van Dorp (259), by treating phthalimide with bromine and potassium hydroxide. The potassium salt of phthal- aminic acid is first formed, and then changes into anthranilic acid:
494 ORGANIC CHEMISTRY. [§348
/COv /CONH2 /NH2
CeHK >NH -» C6H4C -♦ C6H4<
XJCK N300K Ndooh
. Phthalimide Potftssium phthalaminato Anthraoilic acid
By a very intel^esting intramolecular rearrangement^ o-nitro- toluene is transformed into anthranilic acid by a boiling alkaline solution:
C6H4V — ♦ CqBl4\^ •
\iHz XJOOH
Anthranilic acid melts at 14<5^, and by careful heating can be sublimed without decomposition. When strongly heated, it decomposes to a considerable extent into carbon dioxide and aniline. It dissolves in water and readily in alcohol. By the method' indicated it is prepared technically for the synthesis of indigo, bleaching-powder being substituted for the potassium hydroxide and bromine. Its methyl ester causes the fragrance of many flowers. It has a powerful, but agreeable, odour, and finds application in the perfume-industry.
Phtfaalic Add.
348. Phthalic acid is the or^Ao-dicarboxylic acid of benzene, and
OOOH 1 has the formula C6H4 <nQQ}j o- ^^ ^^ obtained by the oxidation
of aromatic hydrocarbons with two side-chains in the ortJuh position, or their derivatives with substituents in the side-chains. It is worthy of note that chromic acid cannot be employed in this oxidation, since it decomposes ortAo-derivatives completely into carbon dioxide and water. Phthalic acid is employed in the preparation of artificial indigo (405), and is manufactured by oxi- dizing naphthalene (377), CiqHs, by heating with very concen- trated sulphuric acid.
Phthalic acid is crystalline, and dissolves readily in hot water, alcohol, and ether. It has no definite melting-point, since on heating it loses water, yielding phthalic anhydride, which sublimes in beautiful, long needles:
S 3481 PHTHALIC ACID. 496
/\
V
COOIH CO'OH
/\co
>0. CO
Phthalio anhydride
Phthalyl chloride is formed by the interaction of phosphorus
pentachloride and phthalic acid. It exists in two tautomeric forms,
/COCl /CCI2
C6H4C and CeHK >0 .
XJOCl X!0
I. 11.
The first form is produced by direct interaction of the chloride and acid, and is converted into the second modification by warming with aluminium chloride. Form II. is very readily converted into I. There is a marked divergence in melting-point, I. melting at 16^; and II. at 89*^. With ammonia and aniline I. reacts much more rapidly than II., although in these and various other reac* tions identical substances are produced from the two tautomerides. An example is the formation of cyanobenzoic acid under the influence of ammonia, as indicated in the scheme
/COCI+NH3 yC^Ha
C6H4< -► CoHZ \oH - 2HC1 ->
XJOCl \coci
/C=NH >CN
^ CoHZ >0 -> C6H4< ,
N:0 X300H
while the tso-cUoride reacts thus:
>CCl2+H2NH -► >C=NH.
This similarity in behaviour has made it extremely difficult to solve by purely chemical methods the problem of the correct constitutional formula of each isomeride.
The results of optical research indicate the great probabiUty of the product directly produced having formula I. Chlorine atoms in immediate union with a carbonyl-group, >C0, have a higher atomic refraction than chlorine atoms otherwise linked to carbbn. The atomic refraction of O'' is also greater than that of <0. A compound with constitution I. must therefore have a higher
496 ORGANIC CHEMISTRY, [5348
molecular refraction than one with structure II., and the value found experimentally for the direct product melting at 16^ is actually higher than that of the substance melting at 89^.
The oxygen of the carbonyl-group in phthalic anhydride can also participate in other reactions. Thus, when the sub- staAce is heated with phenols and sulphuric acid, phthal^ns are formed: .
I win TT nw /C6H4OH
C6H4<Ql— Mi^££^ - H^O+CeH/ >0
Phthalic anhydride Phenolphthaleln
Phenolphthakin, the simplest member of the phthalein series, is a yellow powder. On account of its phenolic character it dis- solves in alkaline solutions, with formation of a fine red colour, and is a sensitive indicator for alkalimetry.
Resorcinolphthalein or fluorescein is characterized by the display
of an intense yellowish-green fluorescence in alkaline solution. It
owes its name to this property, which affords a delicate test for
phthalic anhydride, phthalic acid, and resorcinol, since fluorescence
is exhibited by mere traces of fluorescein. It is prepared by heating
together resorcinol and phthalic anhydride at 210®, in presence of
zinc chloride as a dehydrating agent. On treatment with bromine,
fluorescein yields ietrabrovwjluorescein:
XeHBrzCOH) ^^C< > O.
C6H4<(^ I X)6HBr2(OH)
Its potassium derivative, C2oH605Br4K2, is the beautiful dye eosin.
The constitution of the phthaleins is inferred from their being convertible into derivatives of triphenylmethane (373).
In the preparation of phenolphthaleln a by-product, Jfiioron,
insoluble in alkalis is formed. This substance has the formula
CO
000
0
n.
$349] PHTHAUMIDE. 497
in which the two phenol-residues are united at the orf^positions to the phthalic-anhydride-residue, and not at the paro-positions, as in phenolphthaleln. Fluoran contains the pyrone-nucleus.
c c
\/
Many derivatives containing this nucleus fluoresce. Fluorescein is dihydrox3rfluoran, with the formula
.COv
OH
.CO 349. Phthalimide, C6H4^ > NH, is of importance on account
\:o
of its application to the synthesis of primary amines with sub- stituted alkyl-groups. It is obtained by passing dry ammonia over heated phthalic anhydride. The imino-hydrogen is replace- able by metals : thus, the potassium compound is precipitated by the action of potassium hydroxide on the alcoholic solution of the imide. When potassium phthalimide is treated with an alkyl halide, the metal is replaced by alkyl: on heating with acids or alkalis, a primary amine, free from secondary and tertiary amines, is produced :
XO /CO
CftHK >N[KTBf3C^H2„+i-*C6H4< >N.CnH2n+i-* \C0 XJO
PMaaaium phthalimide
-* C6H4<QQQj^^+NH2-CnH2n+l.
Alkyl halides with various substituents can be employed in this reaction: thus, from ethylene bromide, CH2Br«CH2Br, is obtained bromoethylamine, NH2«CH2«CH2Br ; from ethylenebromohydrin, CHaBr-CHzOH, hydroxyethylamine, NH2-CH2-CH20H; etc.
498 ' ORGANIC CHEMISTRY. [§ 350
Another example is Emil Fischer's S3mthesis of amiihtne (243). Potassium phthalimide is brought into contact with tri- methylene bromide:
CO
C6H4<go >N[KJ-JBr|.CH2*CH2-CH2Br
— ► C6H4<p^> N»CH2»CH2»CH2Br.
The compound obtained is treated with diethyl monosodiomaionate,
and yields C6H4<cq>N.CH2-CH2-CH2-CH(COOC2H6)2, the ter- tiary hydrogen atom of which can be substituted by bromine. Saponification and elimination of CO2 give
C6H4<^2>N.CH2-CH2-CH2-CHBr.COOH.
By heating with aqueous ammonia, Br is then replaced by NH2. Subsequent heating with concentrated hydrochloric acid yields ornithine:
C6H4<co>N-CH2-CH2-CH2-CH(NH2)-COOH -
+20HH
= C6H4 < ™5 +H2N .CH2 •CH2 -CHa .CH(NH2) -COOH.
I^VAJn Ornithine
These examples make it evident that this method can be ap- plied to the preparation of the most variously substituted primary amines.
MoPhthalic and Terephthalic Acids, C6H4(COOH)2(l:3)
and (1:4).
350. iaoPhthalic acid can be obtained by the oxidation of com- pounds with two side-chains in the tn^to-position, and also by the oxidation of resin (colophonium) with nitric acid. It dissolves with difficulty in water, and does not 3deld an anhydride.
Terephihalic acid can be prepared by several methods; for example, by the oxidation of turpentine. It is almost insoluble in water, alcohol, and ether. It does not melt at the ordinary pros* sure, but at high temperatures sublimes without decomposition. Like ido-phthalic acid, it does not form an anhydride.
§3511 SUBSTITUTED ALDEHYDES. 499
Higher Polybasic Acids.
Tricarboxylic, tetracarboxylic, pentacarboxylic, and hexacar- boxylic acids are known. The most remarkable is the hexacar- boxy lie meUitic addf a constituent of the mineral honeyrstone, found in brown-coal seams. Honey-stone is the aluminium salt of mellitic acid, and has the formula C13O13AI2 + I8H3O : it forms yellow quad- ratic octahedra. MeUitic acid is produced by the oxidation of wood- charcoal with an alkaline solution of potassium permanganate. It crystallizes in fine needles, and dissolves freely in water and alco- hol. On heating, it loses two molecules of carbon dioxide and two molecules of water, with formation of pyromellitic anhydride,
PTT^C0>"2 C0^^5 which takes up water, and yields pyromelliHe acid, CoHsCCOOHV
Vm. SUBSTITUTED ALDEHYDES.
351. ra-Nitrobenzaldehyde is the main product formed in the nitration of benzaldehyde, o-nitrobenzaldehyde being a by-product in the reaction. The best mode of preparing the aW/w-compound is to oxidize o-nitrotoluene with manganese dioxide and sulphuric acid. In sunlight it is rapidly transformed into o-nitrosobenzoic acid:
.NO2 yNO
X;H0 X!00H
Hydrozyaldehydes*
Hydroxyaldehydea can be obtained artificially by a synthetical method generally applicable to the preparation of aromatic hydroxyaldehydes. It consists in treating the phenols in ethereal solution with anhydrous hydrocyanic acid and hydrochloric-acid gas, it being sometimes an advantage to add a small quantity of zinc chloride as a condensing agent. This mode of synthesis was discovered by Gattermann, whose name it bears. The hydro- chloride of an imide is formed as an intermediate product, and can sometimes be isolated:
CeHsOH+HCN+HCl = C6H4<22.j^jj jjpj.
500 ORGANIC CHEMISTRY, [f 361
On treatment with warm water, the imide-ealt is converted into the hydroxyaldehyde and ammonium chloride:
^«^4<CH:NH.HCl+^20 = C6H4<cuq+NH4CL
p^Hydroxybenzaldehyde is here obtained from phenol.
/OH 1 Salicylaldehyde, ColU\ /H , occurs in volatile oU of spiraa.
It can be prepared artificially by Reimer's synthesis, another reaction generally applicable to the production of aromatic hydroxyaldehydes, and depending on the action of chloroform and potassium hydroxide on phenols:
.OH .OH 1 /
C6H4^ — ♦ C6H4^ pH rt
Nh + CICHCIo ^'^O ^•
-[HTCl|CHCl2
Salicylaldehyde
The 0-hydroxyaldehydes colour the skin deep yellow. To this class o£ substances belongs vanillin,
y ^o
CeHafoCHg 3' \0H 4
the methyl ether of protocatechualdehyde. It is the aromatic prin- ciple of vanilla, and is prepared on the large scale by oxidizing iaoeugend,
/OH CbHs^-OCHs •
XJH:CH.CH8
This substance is obtained by boiling eugenol,
/OH CeHs^OCHs ,
\CH2.CH:CH2
with alcoholic potash, which alters the position of the double linking in the side-chain. Eugenol is the chief constituent of oil of cloves.
f352] HYDROXY'ACIDS, 501
Vanillin has been synthesized by Reimer's method, the action of chloroform and sodium hydroxide on guaiacol (336) :
CHCI2
Intonnediate produots
Piperonal is mentioned in 353.
IX. poltsubshtuted bbnzenb dbrivativbs with subsht-
UENTS IN THE SIDE-CHAIN.
OH 35a. jhHydroxyphmylpropionicacid,C^Tl4<Q^ pjj .qqqjj
is of some importance owing to its relation to tyrosine (M. P. 235^), which derives its name from its presence in old cheese (Greek, rupos), and is produced when proteins, such as white of egg, horn, hair, etc., are boiled with hydrochloric acid or sulphuric acid. Its formula is
CgHnOsN, and its structure HO.C6H4^CH2*C^OOH; itisthe
NNH2
a-amino-acid of p-hydroxyphenylpropionic acid. Being an amino- acid, it yields salts with acids as well as with bases.
The oxidation of tyrosine under the influence of an enzyme called iyrosinase yields very stable red, brown, or black colouring matters, the melanins. These substances are probably the colouring prin- ciples of the hair of the higher animals and of man, and of the dark colour of negroes.
OH o-Hydroxycinnamic add, C6H4<qtt . q^ .COOH' ®^^ ^^ *^^
forms, coumaric add and coumarinic acid,. which are easily con- verted into each other. Coumarinic acid is not known in the free state, but only in the form of salts, since, on liberation, it at once loses a molecule of water, yielding caumarinj the aromatic principle of woodruff {Aspenda odorata). Comnaric acid, on the other hand, does not yield a corresponding anhydride: removal
502 ORGANIC CHEMISTRY. H 353
of water produces coumarin, which is converted into salts of coumarinic acid by treatment with alkalis.
Conmarin can be obtained from salicylaldehyde by Sib William Pbrkin's synthesis (328) : acetylcoumaric acid,
po ^OlCgHaO ^^*^CH:CH.CO|OH'
is first formed, and is converted into coumarin by heating, acetic acid being eliminated.
353. The unsaturated piperic acid, or Si^tnethylenedihydroxy^ cinnarnenylacrylic acid, GX2HX0O4, is a decomposition-product of piperine (390). Oxidation converts pipeiic acid into piperotial or hdiotropin,
>/NcH:CH.CH:CH.COOH
<
Piperio acid Piperonal
The constitution of this substance is established by two reactions. First, on heating with hydrochloric acid it is converted into proto* catechiuildehyde and carbon:
CHO.CeHa <q> CHa « CHO-GeHa <oh+^-
Second, it is regenerated by the action of methylene iodide and alkali upon this aldehyde.
Piperonal melts at 37®, and boils at 263°; its odour exactly resembles that of heliotropes. In presence of caustic soda, piperonal condenses with acetaldehyde to piperonylacraldehyde:
CH2<q>C6H3«Cq H-CH3-Cq =■
= CH2</-v>C6H3«CH»CH«Cq H-HaO. By Pbrkin's synthesis (328), piperonylacraldehyde is con-
^
1353]
PIPERONAL AND ADRENALINE.
503
verted by the action of sodium acetate and acetic anhydride into piperic acid:
CH2<q>C6H3.CH:CH.Cq+CH3.COOH- «CH2<o>C6H3-CH:CH-CH:CH.COOH+H20.
Adrenaline or suprarenine, CqHi^ON, is prepared from the suprarenal capsules of the horse and other animals. It is char- acterized by its powerful hsemostatic properties. On oxidation, it yields protocatechuic acid, and on distillation with sodium hydroxide, methylamine. With benzoyl chloride it forms a tri- benzoyl derivative.
It is prepared by a sjmthetic method. Chloroacetyl chloride reacts with catechol (I.) to form chlaroacetylcatechol (II.). On treatment with methylamine, this substance yields an amino- ketone (III.), reducible to adrenaline (IV.):
HO HO
HO
HOj^CO-CHaCl Ho/NcOtCHa.NH.GHa
II. — ► III. -♦
Ho/\^
IV.
V
AdranaliiiD
HO
HO CHOH.CHa-NH.GHs
Many organic bases of phenolic character have valuable phar- macological properties. Other types of this class are hordenine,
H0-C.H4»CHfCHi«N(CH.)i, present in germinating barley; and p -hydroxyphenykthylamine, HO • CA • NH • CtHi, the active principle of ergot.
ORIElfTATIOlf OF AROMATIC COMPOXTNDS.
354. Orientation is the determination of the relative positions occupied by the side-chains or substituents in the benzene-ring. A description of a number of the most important substitution- derivatives of benzene having been given in the foregoing pages, it becomes necessary to furnish an insight into the methods by which orientation is carried out.
These methods are based on two main principles.
1. Relative determination of position. — ^The compound with sub- stituents in unknown positions is converted into another with known positions, it being inferred that the first compound has its substituents arranged similarly to the second. If, for example, the constitution of one of the three xylenes is required, the hydrocarbon can be oxidized. The particular phthalic acid formed indicates the positions of the methyl-groups in the xylene under examination, provided the positions of the carboxyl-groups in the three phthalic acids are known.
To apply this method, it is necessary to know the positions of the substituents in a small number of compounds, and it is further assumed that the positions of the substituents remain the same during the course of the reactions involved. Usually, this continu- ity holds, although the position of the side-chain does alter in a few reactions (332).
To avoid erroneous conclusions, it is, therefore, desirable in cases of doubt to check the determination of position by convert- ing the substance into another compound.
2. Absolvie deterrnmaixon of position. — ^The positions of the substituents are determined without the aid of other compounds with substituents in known positions. A general method is afforded by Korner's principle, by which it is possible to ascer- tain whether substances G6H4X2, containing two substituents, are
504
1355] ORIENTATION. 506
or/^-compounds, r?i«to-compounds, or para-compounds, effected by determining the number of trisubstitution-products correspond- ing with them.
When a third group, Y, is introduced into an ortAo-compound, C6H4X2, whether Y is the same as or different from X^ only two isomerides can be formed,
and
The introduction of a third grou^ into a meto-compound renders possible the formation of three isomerides.
and
With a para-compound the introduction of a third group yields only one trisubstitution-product,
In addition to this general method, there are other special methods, several of which are described. They substantiate fully the conclusions already arrived at by Korner's method.
z. Absolute Determination of Position for or< Ao-Compoimds.
355. For the or^/w-series, the structure of a dibromobenzene melting at 5»6® is determined by means of Korner's principle: this body yields two isomeric nitrodibromobenzenes. The con- stitution of a xylene boiling at 142^ and melting at — 28° has also been established by this method: it gives rise to two isomeric
506
ORGANIC CHEMISTRY.
[S355
nitroxylenes when treated with nitric acid. This xylene is con- verted into phthalic acid by oxidation, proving that the latter is an ar^(>-compoiind.
The oxidation of naphthalene (377), CioHg, to phthalic acid also proves that the carboxyl-groups of this acid are in the or^feo-posi- tion. This reaction indicates that the structure of naphthalene must be C6H4<C4H4, the group C4H4 being linked to two positions in the benzene-ring. When naphthalene is treated with nitric acid, nitronaphthalene is formed, and is converted by oxidation into nitrophthalic acid. The group G4H4 has, therefore, been converted into two carboxyl-groups:
N02-C6H3<C4H4 -> N02-C6H3<^|.
NitronaphthaleDe Nitrophthalic add
If, however, the nitro-group is reduced, and the jmoinonaphthalene thus obtained oxidized, phthalic acid is formed. Hence, the group C4H4 forms a second benzene-ring with the two carbon atoms of the benzene-ring, so that naphthalene must be represented by the formula
/\y\
The oxidation of nitronaphthalene and aminonaphthalene is expressed by the scheme
NO9
^COOH
and
NHa
HOOC/^ HOOcl.
§356] ORIENTATION, 507
Phthalic acid must, therefore, be an or^fto-compound, because if it be assumed to have the Tneto-structure, for example, naphtha- lene must be represented by the formula
which involves a contradiction, for there could not then be a ben- zene derivative produced by the oxidation of b<^ nitronaphthalene and aminonaphthalene.
2. Absolute Detennination of Position for me^a-Compound&
356. The proof that mesitylene is symmetrical trimethylbenzene (1:3:5) is stated thus by Ladenburg. If this compound has the constitution
H CHa/XCHs
hIJh»
CH3
the three hydrogen atoms directly linked to the benzene-ring must be of equal value. If this can be proved, the structure of mesityl- ene is established.
The proof of the equality is as follows. On nitrating mesitylene a dinitro-compound is obtained. If the hydrocarbon is represented by
I. Ce(CH3),HHH, the dinitro-oompound may be arbitrarily assumed to be
. II. C(CH,),NOaNO,H.
One of the nitro-groups of the dinitro-compound is reduced, and the resulting amino-compound is converted into an acetyl-derivative! sappoee that this acetyl-derivative is
III. Cfl(CHs)sNb,NH(c5H.0)H. This substance can be again nitrated, when there must result
608 ORGANIC CHEMISTRY. U 356
Ce(CH,)jN0aNH(cjH30)N0,.
It is possible to eliminate the acetylamino-group, NHCCsHgO), from this compound by saponification, subsequent diasotisation, etc. A dinitromesitylene with the formula
Ce(CHa),N02HN0,
is obtained, identical with the former dinitro-product, tbe nitro- groups of which are at a and 6. It follows that
Nitromesidine, a:b, the acetyl-compound of which is represented by formula III., furnishes a further proof that H««H«. When the amino-group is eliminated by means of the diazoH:eaction, there is formed
IV. Ce(CH,),NOaHH-
This substance is reduced, and converted into an acetyl-compound^ acetylmesidine,
Ce(CH3)3NH(C2HsO)HH,
which can be again nitrated, 3delding
Cfl(CH3)aNH(C^H30)N02H.
It is immaterial whether the nitro-group of this compound is at 5 or c, since the equality of these positions relative to a has been already proved.
On eliminating the acetylamino-group from the last substance, a mononitromesitylene is produced, identical with the compound IV. Hence, a — &— c, which completes the proof of the equality of the three hydrogen atoms.
From the known constitution of mesitylene it is passible to deduce the structure of many other compounds. For example partial oxidation converts it into mesUylemc acid;
^OOH X!H,
> ...
which is in turn converted into xylene by distillation with lime: this
§357] ORIENTATION. 509
xylene must be the tn^to-compound. Oxidation converts m-xylene into isophthalic acid, indicating that the carboxyl-groups in the latter occupy the meto-position. These determinations of position have been fully substantiated by the application of K^rner's principle. Thus, Nolting has prepared three isomeric nitroxyl- enes, in which the relative positions of the methyl-groups are the same as in the xylene obtained from mesityienic acid.
Among other rr^eto-compounds in which the position of the groups has been independently established, is a dibromobenzene boiling at 220°. Korner proved that corresponding to this sub- stance are three isomeric tribromobenzenes and three nitrodibromo- benzenes. In conclusion, the phenylenediamine melting at 62° can be obtained from three different diominobenzolc acids by elimina^ tion of CO21 so that it also must be a meto-compound.
3* Absolute Determination of Position for para-Compounds.
357. KSrner's principle has been of great service in determin- ing the constitution of some members of the paranseries. For example, from the xylene boiling at 138°, and melting at 13°, it is only possible to obtain one nitroxylene: the phenylenediamine melting at 140° can only be obtained from one diaminobenzoic acid by removing CO2: and so on.
These determinations of position have been confirmed by another method, exemplified by the identification as a para- compound of a hydroxy-benzoic acid melting at 210°. The start- ing-point of the proof is bromobenzoic acid, obtained directly by the bromination of benzoic acid. On nitration, two isomeric nitrobromobenzoic acids are formed, either of which yields on reduction the same aminobenzoic acid, anthranilic acid. This acid can be converted into saUcylic acid by means of the diazo- reaction. It follows that in both the isomerides the nitro-group must be situated symmetrically to the carboxyl-group; at 2 or 6, or at 3 or 5, if the carboxyl-group is at 1. The same reasoning establishes the position of the hydroxyl-group in salicylic acid. The bromine atom cannot be at 4, because two isomeric nitro- compounds which would yield the same aminobenzoic acid on reduction could not be obtained from
510 ORGANIC CHEMISTRY. [{ 358
Bi/^^\C00H.
The bromine atom must, therefore, occupy the m€to-poBition or or/Ao-position to the carboxyl-group. A hydroxybenzoic acid melt- ing at 200**, corresponding with this acid must bs, therefore, meta or ortho. Since the isomeric salicylic acid can a^so be only a meta- compound or an or^Ao-compound, there remains no possibility, except the parcHStructure, for the third hydroxybenzoic acid melt- ing at 210^
Determination of Position for the Trisubstituted and Higher- substituted Derivatives.
358. Thi& orientation can usually be effected by ascertaining the relation in which they stand to the di-derivative6 of known constitution. For example, since a certain chloronitroaniiine, GqH3C1(N02)(NH2), is obtained by nitrating m^hloroaniline.
and yields p-chloronitrobenzene.
CI
by exchange of the amino-group for hydrogen, it must have the constitutional formula
NHa
NOaf
a-
A more complicated example of orientation is afforded by the detemiination of the positions of the groups in picric acid. Careful nitration converts phenol into two mononitrophenols,
iSfiS] ORIENTATION. 511
OH OH
NO. M.P. 45<> M.P. 114**
One of these monooitrophenols must be the orththcompouad and the other the poro-compoundy because the third nitrophenol can be obtained from m-dinitrobenzene — the constitution of which has been proved by its reduction to m-phenylenediamine (339) — ^by reduction to meto-nitroaniline, and subsequent exchange of KH2 for OH by diazotizdng.
When further nitrated, both nitrophenols jrield the same dinitro- phenol, which can therefore only have the formula
OH
Qno..
NO,
The mononitrophenol melting at 114^ is converted by oxidation into benzoquinone (338), and must, therefore, be the parcHXiTDr pound. For the body melting at 45^ there remains only the ortho- structure. On nitration this o-nitrophenol yields, in addition to the 1:2: 4-dimtroi^enol (OH at 1), another dinitrophenol with its groups at 1:2:6,
OH
0
NO.i'^jNO,;
for on conversion of this into its methyl ether, and heating the latter with alcoholic ammonia, the group OCH, is replaced by NHa; and this substance, which has the formula
NH, NO,[^NOi,
is converted by substitution of hydrogen for the NHrgroup into the ordinary meto-dinitrobenzene. Thus, we have two dinitro- phenols of known structure,
512 ORGANIC CHEMISTRY. ($ 350
OH OH
^ and NO,AnO..
NO,
Further nitration converts both into picric acid, which must, there- fore« have the constitution
OH NOai-^NQi
NO,
From the constitution of picric acid may be inferred the posilion of the groups in ordinary trinitrobenzene, since this compound is readily oxidized to picric acid (334). This trinitrobenzene must, accordingly, have the symmetrical structure.
Equivalence of the Six Hydrogen Atoms in Benzene.
359. It is stated in 28a that benzene does not yield isomeric mono-sub^ tution-products, and the inference is drawn that the six hydrogen atoms of this hydrocarbon are of equal value.
There are several direct methods of proving this equivalence, one of them, devised by Nolting, being characterized by its simplicity. If the six hydrogen atoms are denoted by a, h, c, d, e, and /, the amino-group in aniline may be arbitrarily assumed to be at a. When bromobenzene, obtained from aniline by the diazo-reaction (307, 4), 19 treated with methyl iodide, and sodium it yields toluene. On nitration, three isomeric nitrotoluenes are obtained — the proportion of the me/o-compound being very small. In these compounds the CHt group is at a, so that the nitro-^roups may be arbitrarily assumed to be at 6, c, and d respectively. On reduction, the three corre- sponding toluidines result:
C6H,-CH,(a) -♦CH,-C6H4*NO,(&:c:cO -^ COOH*CiH4-NH,(6:c:d).
After protection of the amino-group in each of these compounds by acetylation, the three aminobcnzoic acids are obtained by oxidation. These acids yield, by elimination of COs, the same aniline, identical with the original substance. It foUows that
§ 3601 EQUIVALENCE OF BENZENE HYDROGEN ATOMS. 513
CiHjra. -* C.H.Br -* C.B[.-CH,^-^C,H4<§§; ^ -* a a a >^
r« TT ^ COiH a
^ XT ^ COiH a
The starting-point of the proof of the equivalence of e and / to a, &, c, and d is o-toluidine, in which the CH<-group may be assumed to be at a, and the NHr-group at h. Nitration of its acetyl-deriva- tive, followed by elimination of the acetyl-group, produces simul- taneously four nitro-o-toluidines. Since a and h are occupied, the nitro-groups must be at cfd, e, and / respectively. Replacement of the amino-group by hydrogen yields four nitrotoluenes, aiCfO: d a : e, and a : /. The first two are m^-nitrotoluene and p-nitrotoluene; they are also obtained by direct nitration of toluene, as described in the previous paragraph. The nitrotoluene a : 6 is identical with a : c, and a :/ with a : b, which indicates the equivalence of c to e and of 6 to/, thus completing the proof:
yCH, a
C JI,f NH, b
^NO, c
/CH, a
CeH^NH, b
^NO, e
Influence of the Substituents on Each Other.
360. On introduction of a second substituent into a monosub- stituted benzene derivative, CeHsX, the three theoretically possible di-derivatives are formed in very unequal proportion. There
514
ORGANIC CHEMISTRY,
[{360
are two main types of substitution: either the pora-derivative and the ortAo-derivative predominate; or the meto-derivative constitutes the chief product. The table summarizes the most important types of substitution, the numbers in brackets indicat- ing the by-products, and being arranged in order of diminishing proportion.
Element or Group'already present (in Position 1).
CI.... Br.. .
I
OH... SO,H. NOj.. NH,.. CH,.. COOH CN...
Poaition entered by Substituents.
|
a |
Br |
I |
SOiH |
NOi |
|
4(2) (3) 4(2)(3) |
4(2)(3) |
4 |
4 |
4(2) |
|
4(2)(3) |
— |
4 |
4(2) |
|
|
4 |
4 |
4 |
4 |
4(2) |
|
4(2) |
4(2) |
4(2) |
4(2) |
4(2) |
|
3 |
— |
3(4) |
3(2)(4) |
|
|
3 |
3 |
— |
3(2)(4) |
3(2)(4) |
|
m |
4 |
4 |
4(2) |
4(2) |
|
4(2) |
4(2) |
4C2)(3) 3(4) |
2(4)(3) |
|
|
3 |
3 |
3 |
3(2)(4) |
|
|
3 |
The table indicates that a second substituent is directed into the para-position and the or^Ao-position by the presence of halogens and the groups hydroxyl, amino, and methyl; but into the meta- position by the groups sulpho, nitro, carboxyl, and cyano. In both instances the influence is exerted independently of the nature of the substituent introduced. This rule is of general appUcation, and is known as the rvle of the constancy of substitu- tion-type.
The relative proportions in which the isomerides are formed vary greatly even for the same type of substitution, and depend on three factors: (1) the substituent already present; (2) the substituent introduced; (3) the experimental conditions. These three factors are powerless to modify the substitution- type, which is almost invariable; but they cause important changes in the proportions of the isomerides formed in each type. A few examples illustrating this influence are subjoined.
1. Nitration at O*' of fluorobenzene yields 12-4 per cent, of the or^Ao-nitro-product, and 87*6 per cent, of the pora-nitro-
{ 361] INFLUENCE OF SUBSTITUENTS ON EACH OTHER, 515
product. Nitration at the same temperature of chlorobenzene produces 30 •! per cent, of o-chloronitrobenzene, and 69-9 per cent, of p-chloronitrobenzene.
2. The chlorination at 90° of phenol gives 50-2 per cent, of p-chlorophenol, and 49*8 per cent, of o-chlorophenol. Bromina- tion under the same conditions yields 90-7 per cent, of p-bromo- phenol, and 9-3 per cent, of o-bromophenol. These percentages indicate the great influence exerted by the substituent introduced on the proportion of the isomerides formed, even when these substituents are as similar as chlorine and bromine.
3. Temperature is one of the important factors in the experi- mental conditions. In nitration-processes it exerts no great influence on the proportion of the isomerides. At —30°, nitra- tion of benzoic acid gives 14-4 per cent, of o-nitrobenzoic acid, 85-0 per cent, of m-nitrobenzolc acid, 0-6 per cent of p-nitro- benzoTc acid; at 30°, the corresponding percentages are 22-3, 76*5, and 1-2. The temperature can exert a very important influence on the course of sulphonation-processes. Sulphonation of toluene at 0° \yiih excess of sulphuric acid gives 53 -5 per cent, of p-toluenesul phonic acid, 3*8 per cent, of m-toluenesulphonic acid, and 42 -7 per cent, of o-toluenesulphonic acid; for sul- phonation at 100° the corresponding percentages are 72-5, 10-1, and 17 •4.
In halogenation-processes the nature of the catalyst influences the proportion of the isomerides formed. The chlorination of chlorobenzene with 0*5 per cent, of aluminium chloride as catalyst yields 65 • 7 per cent, of p-dichlorobenzene, 29*6 per cent, of o-dichlorobenzene, and 4«7 per cent, of m-dichlorobenzene; with an equivalent proportion of ferric chloride as catalyst the cor- responding percentages are 55*5, 39*2, and 5*3.
361. The introduction of a third substituent C into a benzene derivative CtHiAB raises an interesting problem: knowing the isomerides formed by the introduction of C into CeHsA and CtHiB respectively, and the proportion of each, is it possible to predict . the isomerides CeHsABC formed by the introduction of Cinto CiHiAB, and the proportion of each?
In a qualitative sense prediction is possible, but the problem is much more complex than a superficial consideration indicates. For a benzene derivative CeHiAB with formula I.,
i
516
ORGANIC CHEMISTRY.
IS 361
Apo
6 3 6 81
I.
Apo
6 3
n.
Bm
in which both A and B direct substitution to the ort^position and para^positiony the entrance of the third substituent would be expected to take place at 4 and 6 under the influence of A, and at 3 and 5 imder the influence of B; that is, the formation of the four possible isomerides would be anticipated. Similarly, in combination II., in which Bm indicates direction by B of a new substituent to the me(a-position, A would be expected to direct a new substituent to positions 2, 4, and 6, and B to direct it to position 5. In actual practice, the relations are much more complex, although there are instances of the formation of the four isomerides, exemplified by o-chlorotoluene, corresponding with formula I. In other examples such as that of o-creso),
CH,,
substitution takes place at positions 4 and 6 only; while with compounds of type II. substitution at position 5 has never been observed.
The explanation must be that the velocities of the substitution induced by the substituents already present have very divergent values. Assuming the velocity of substitution due to the hydroxyl- group in o-cresol to be a hundred times as great as that due to the methyl-group, the extent of substitution at positions 3 and 5 would be so small as to render detection of the products impossible. The conclusion is also inevitable that in compounds of type II. sub- stitution is much more rapid at the para-position and the ortho- position than at the meto-position.
A study of the different examples of substitution in compounds CeHfAB, and a quantitative estimation of the isomerides formed, enable the velocities induced by the various substituents to be arranged in order, although in almost all instances the attainment of such an arrangement by direct determination is precluded. The
§ 3621 INFLUENCE OF SUBSTITUENTS ON EACH OTHER. 517
groups causing substitution at the paro-position and the ortho- position exert their influence in the order
0H> NH,> halogens> CH,;
and the much less powerful groups causing substitution at the meto-position in the order
COOH>SO,H>NO,.
Inversely, knowing these orders of velocity, it is possible to predict the isomerides obtainable in a givien reaction; thus, in chloro- phenol the substitucnt would be introduced mainly at the orlho- position and the paro-position to hydroxyl; but in chlorobenzoic acid chiefly in the or^Ao-position and para-position to chlorine.
362. This opposition between ori/io-derivatives and para- derivatives on the one hand, and m^to-derivatives on the other, is not only observed in their preparation, but also in many of their properties. As a class, the ?w6to-compounds are more stable towards reagents than the oriAo-derivatives and para-derivative3. An example is given in 331.
Ori/io-groups sometimes exert a remarkable influence in retarding or partially preventing reactions which take place readily in their absence. The following reactions exemplify this phenomenon.
When an acid is dissolved In excess of absolute alcohol it can be almost quantitatively converted into an ester by passing a current of hydrochloric-acid gas through the mixture (93, 1). Victor Meyer and his students found, however, that esterification of acid s containing two groups in the ortho-position relative to carboxyl,
COOH
xQx,
could not be thus effected. On the other hand, when the acid has been converted into an ester (by means of the silver salt and an alkyl halide) the ester so formed can only be saponified with diflSculty. When the two substituents occupy any of the other positions, these peculiarities do not manifest themselves, or at least
518 ORGANIC CHEMISTRY. (| 982
not to the same extent. Ketones substituted in the two oriho- poeitions,
CH3
CHs
where R k an alkyl-radical, cannot be converted into oxiines, wberdn they differ from all other ketones. o-o-Dimethylaniline,
<(3nh>,
CHa
is not converted by treatment with an alkyl iodide into a quater- nary salt. Pentamethylbenzonitrile, Gg(CH3)5CN, cannot be hy- drolyzed to the corresponding acid. The methyl-hydrogen in 0-0- dinitrotoluene,
/NO32
CgHa^-CHs I,
\NO36
cannot be replaced by halogens even at a high temperature (200^, as is also true of l:2:4-dinitrotoluene. In spite of numerous attempts, the hydrolysis of o-nitrosalicylonitril^
OH X/NOa
to the corresponding ackl,
OH
/NCOOH
has not been effected.
i 3621 INFLUENCE OF SUBSTITUENTS ON EACH OTHER. 619
Groups occupying positions further separated sometimes exert a similar effect. One of the NO^-groups of symmetrical trinitro- benzene is replaced by OCH3 through the action of sodium methozide: for trinitrotoluene,
NO2
NO2
this substitution is not foimd possible, the methyl-group preventing exchange of the nitro-group even in the ponohposition.
Instances are, however, known of or^Ao-substituents increas- ing the reactivity of a group situated between them.
HTDROCTCLIC OR HTDROAROMATIC COMPOUNDS.
363. A number of compounds occur in nature containing pro- portions of hydrogen intermediate between those in the aromatic derivatives with saturated side-chains and those in the saturated aliphatic derivatfves. These hydrocydic or hydroaromatic com- pounds are readily converted into aromatic bodies. Caucasian petroleum contains naphthenea, with the formula CnH2n, which 'have two hydrogen atoms less than the corresponding saturated hydrocarbons, CnH2n+2> but nevertheless display all the properties characteristic of saturated compounds. The explanation is that they lack multiple bonds, but have a closed carbon chain; thus,
CjHo CH
cyeioHezaoe
The ierpenes, CioHie, are vegetable-products, and are the prin- cipal constituents of the '' essential oils.'' These oils also contain compounds of the formulse CioHieO, CioHigO, and C10H20O, among them the camphors. Like the naphthenes, the t^rpenes and cam- phors are readily converted into aromatic compounds, and therefore belong to the hydrocydic series. The progress recently made in this division of organic chemistry has rendereda systematic classi* fication of these compounds possible.
Two principal I methods are employed in their preparation: by one they are obtained from compounds of the aliphatic series, and by the other from those of the aromatic series. Several examples of each method will be cited.
On dry distillation, calcium adipate yields cycZopentanone (277). By the same treatment calcium pimelate is converted into cyclohexanone:
CH2<gi::gl::gg8> Ca= CH.<gH2.CH.^cO+CaC03.
Calcium pimelate cyc/oUezaDone
This structural formula is established by the ketonic character of
the compound, and by the fact that dilute nitric acid oxidizes it
almost quantitatively to adipic acid:
£20
S 363] HYDROCYCLIC COMPOUNDS. 521
CH2.CH2-CO CH2.CH2.COOH
CH2.CH2.CH2 CH2.CH2.COOH
cyeloHezuioiM Adipio add
Diethyl succinate constitutes an important basis for the syn- thesis of other cyciohexane derivatives. In presence of sodium, two molecules of it condense to diethyl succinylsuccinate, which melts at 127° :
XIOOCzHb /COOCzHb
+ I
JOH2 /CHa
CaHeOOC/ CzHsOCXX
Diethyl succinate
HzC CH.COOCaHj
I +2C2H6OH.
CzHbOOC.HC CHa
Diethyl succinylauooinate
The free acid, obtained by saponification, is decomposed at 200^, with elimination of two molecules of carbon dioxide, yielding
yCH2 CH2V
p-dikeiocyclohexanef CO^ /CO.
XJHz CHa^
The structural formula of this substance is indicated by this 83mthesis, and also by its reduction to c^cZohexanone.
The second method of obtaining hydrocyclic compounds depends on the reduction of aromatic derivatives. The proce- dure devised by Sabatier and Senderens involves passing a mix- ture of the vapour and hydrogen over finely-divided nickel at tem- peratures between 150° and 200°. In Willstatter's process hydrogen is passed at ordinary temperature through the undiluted liquid compound, or through its solution in ether or glacial acetic acid, platimun-black formed by reduction of a solution of platinum chloride with formaldehyde and sodium hydroxide being em- ployed as catalyst:
CeHe + 3H2 — CoHia.
Benxene cycZoHexane
522 ORGANIC CHEMISTRY. [§364
In describing the hydrocycUc compounds, it is convenient to treat the cymene derivatives, or terpenes, separately, for they exhibit many characteristic properties. The other hydrocyclic compounds will first be briefly reviewed.
364. cycloHexane is the simplest member of this group. It is best obtained by the method of SABATiER^and Senderens (363). Like its homologues, it is a colourless liquid. Its boiling-point, 80°, is very near that of benzene, 80-4®: as the crude hydrogenation- product always contains benzene, the isolation of pure cydohexBjie from it by fractional distillation is therefore impracticable. In its separation, advantage is taken of its stability at ordinary tem- peratures towards fuming sulphuric acid and concentrated nitric acid, which respectively convert benzene into benzenesulphonic acid and nitrobenzene. Since each of these compounds is soluble in the corresponding acid, and cycZohexane insoluble, the sep- aration of the latter can be readily effected. The melting-point (82) affords the best criterion of the purity of cydohexBue. It is 6 •4°, and therefore approximates closely to that of benzene, 5 •4®.
Zelinsky has found that at 300^ palladium-black can eliminate six hydrogen atoms from q/dohexane, with formation of benzene; while at 100^-110^ this catalyst transforms a mixture of benzene and hydrogen into q^dohexane. He has also observed the remark- able fact that at 300^ palladium-black is incapable of abstracting hydrogen from either c^cJopentane or cycZoheptane. This phenomenon affords a veiy valuable method of ascertaining whether a cyclic hydrocarbon is a derivative of cychhexBLae or not, previously a veiy difficult matter. The application of this reaction is exemplified by a hydrocarbon of the formula CeHu, which might be either cydohexane, (CHs)e, or methylq^c^opentane, (CHs)4> CH*CH^.
Chlorine reacts very energetically with cydohexane in dif- fused sunlight, and with explosive violence in direct sunlight. A mixture of substitution-products is formed, from which mono- chlorocyclohexane can be obtained by fractional distillation. Replacement of the Cl-atom in this compoimd by hydroxyl is not readily effected : treatment with alcoholic potash converts it into tetrahydrobemene, a liquid boiling at 83®-84°, and possessing all the properties characteristic of unsaturated compounds.
When a mixture of phenol-vapour and hydrogen is passed over finely-divided nickel, cyclohexand is formed. It is a colourless
J3641
HYDROCYCLIC COMPOUNDS.
523
somewhat thick liquid : it boils at 160 • 5^, and at a low temperature solidifies to a camphor-like mass, which melts at 20^.
P'Diketocyclohexane (363) melts at 78°. Careful reduction with sodium-amalgam in an atmosphere of carbon dioxide converts it into the dihydric alcohol quinitd:
yCH2»CH2v X!H2»GH2v
C0< >C0+4H-H0.CH< >CH.OH,
X3H2 • CH2^ XJHz • CHa^
p-Diketoeye2ohezane QuiniUd
Two modifications of quinitol are known, distinguished by the prefixes cis and trans. They are best prepared from quinol by the reduction-method of Sabatier and Sexderens (363). They can be separated by means of their acetyl-derivatives. The stereochemical character of their isomerism is indicated by a consideration of Fig. 31 (167), in which a cycZopentyl-ring is repre- sented. If the pentagon is supposed to lie in the plane of the paper, one of the free Unkings of each carbon atom will lie above, and the other below, this plane. If a ct/cZohexyl-ring is simi- larly constructed, there is obtained the perspective figure
in which the aflSnities not forming part of the ring are represented by vertical lines. The isomerism of the quinitols is explained by the assumption that the hydroxyl-groups of the cts-modification are situated on the same, and of the tont-modification on the opposite, side of the hexagon:
OH H
s
|
H |
|
|
H H |
H H |
H
\ OH
H
/
OH H
i\
H
'H H
<<M)uiiiitol (U P. 101*)
H
H
H H
H OH
H HI
(ratw-QuinitolMf P.180>)
Inositol, C6Hi206, is a hexahydric alcohol derived from cyclo- hexane. Its molecular formula is the same as that of the hexoses:
624 ORGANIC CHEMISTRY, [§ 364
on account of its sweet taste and its occurrence in many legumi- nous plants, it was formerly classed with the sugars. Its relation to q/cZohexane is proved by its reduction with hydriodic acid to benzene, phenol, and tri-iodophenol, and by its conversion by phosphorus pentachloride into quinone and substituted quinones. The presence of six hydroxyl-groups is indicated by the formation of a^hexa-acetate. Inositol is also a constituent of the heart- muscle, the liver, and the brain.
An important derivative of q/cZo-hexane is l-^methylcyclO' hexylidene-ArOcetic add,
CHsv •CH2»CH2v /H
h/ \ch2-ch2^ Njooh
This substance affords a striking example of optical activity occasioned by '' Dissymmetric mol^ulaire '' (196), since it lacks an asymmetric carbon atom, and can be resolved into its optically active components. It is one of the substances of the type
a c
NctCiC/,
b d
one of the double bonds being replaced by a ring of six carbon atoms. The mirror-images of such substances cannot be super- imposed, and in 1874 van 't Hofp predicted the discovery of their optical activity.
cycloHexanone can be prepared from pimelic acid (363), but is more readily obtained by the oxidation of hexahydrophenol with chromic acid. It boils at 155^. Its alkaline solution reacts with benzaldehyde to form a well-crystallized condensation-product:
<H2-CH2v +OCH.C6H6 Ha-Cng/ +OCH.C6H5
cycZoHexanone
CH2 • C==CH • GeHs
-2H20+Cn2<f >co
\CIl2-C=CH.C8H5
DibensalcydohexanoQe
This reaction furnishes a good test for ci/cZohexanone.
§ 366] TERPEN ES. 526
The properties of the hydrocyclic acids are analogous to those of the aliphatic acids. Thus, hexahydrobemolc acid has a rancid odour, like that of capric acid. It meltaat 92^, almost 30^ lower than benzoic acid, which melts at 121 -4°. The hydrophthalic acids exhibit isomerism which admits of the same explanation as that of quinitol.
TERPENES.
365. The terpenes are hydrogenated derivatives of cymene and its sut)stitution-products. Many of them ar^ vegetable products. They are readily volatile with steam, and this property facilitates the isolation of the natural terpenes. The distillate separates into two parts, an aqueous layer below, and a mixture of terpenes above. After drying, the terpene-layer is fractionated several times in vacuo to isolate its constituents. Complete purification has some- times to be effected by conversion of the terpenes into derivatives which can be freed from impurities by crystallization: from the crystalline compounds thus obtained the terpenes can be regen- erated.
VoN Baeyer has devised a rational nomenclature for the numerous derivatives of hydrogenated cymene. He numbers the carbon atoms of this hydrocarbon as in the scheme
C(8)
C(9) C(iO)
A double linking between two carbon atoms, such as 3 and 4, is denoted by J^.
The saturated cyclic hydrocarbon hexahydrocymene, C10H20, is called menthane. It is not a natiu'al product, but can be obtained by the interaction of cymene and hydrogen with nickel as a cata- lyst. It boils at 168*^.
526 ORGANIC CHEMISTRY. [{ 366
The saturated alcohols and ketones derivable from menthane are very important. Among them is menthol or S-mentlianol, C]oH2oO, the principal constituent of oil of peppermint, frpm which it crystallizes on cooling. It forms colourless prisms of characteristic peppermint-like odour. It melts at 43^.
Menthol has the constitution
CHa H
i
H2C CH2
H2C CHOH.
\/ CH
CH
CH3 CH3
Menthol
It is a secondary alcohol, since oxidation with chromic acid elimi- nates two atoms of hydrogen, yielding a substance of ketonic charac- ter, called menthonef a constituent of oil of peppermint. Since there are several processes for the conversion of menthol into cymene or its derivatives, it must contain a cymene-residue. One of these methods also proves that the hydroxyl-group is attached to carbon atom 3: when a solution of menthone in chloroform is treated with bromine, there results a dibromomerUhone, from which quinoline eliminates 2HBr, forming thymol (294),
CH3
CH(CH3)2
Thymol
When thymol is heated with phosphoric oxide, it yields propyl- ene and m-cresol (294), so that its methyl-group and hydroxj'l- group must be in the meto-position.
366. Terpin, CioHi8(OH)2, a dihydric alcohol, is also a derivative of menthane. Its hydrate, C10H20O2 +H2O, is obtained by keeping oil of tulpentine in contact with dilute nitric acid and a small pro-
§ 366] TERPEN ES. 627
portion of alcohol in shallow dishes for several days. During the process the turpentine takes up the elements of three molecules of water. Terpin hydrate forms well-defined crystals, melting at 117^. On heating, it loses one molecule of water, anhydrous terpin distilling at 258"".
Terpin can be synthesized from geraniol,
CH3V
^G=CH •CH2 •CH2 'C^:^!! •CH20H*
^^« CHg
Geraiiiol
When agitated for a prolonged time with sulphuric acid of five per cent, strength, geraniol takes up two molecules of water, being almost quantitatively converted into terpin hydrate:
CH3 CH3
C C-OH
/ \ / \
H2C CH H2C CH2
HaC CH2OH + 2HaO - HaC CH2OH - HaO-^
CH CHj'
C C-OH
CH3 CH3 CH3 CH3
Geraniol Terpin hydrate
CHa
C-OH / \
H2C GH2
~* H3C CH2*
\ / CH
C-OH
CH3 CH3
Terpin
528 ORGANIC CHEMISTRY. [066
This mode of qmthesis indicates that terpin is 1 : 8-dihydroxy- menthane, and there is other evidence in favour of this view. Hydriodic acid reduces it to menthane, proving the presence of a C3nnene-nucleus.
The constitutional formula indicated for terpin is confirmed by the synthesis of this compound effected by W. H. Pebkin, jun. Ethyl sodiocyanoacetate and ethyl jS-iodopropionate react thus:
2GN.CHNa.COOC2H:6+ 2I.CH2-CH2-COOC2H6=2NaI +
CNv XH2 • CH2 • COOC2H6 + >C< +CN.CH2-COOC2H5.
C2H600(r X5H2-CH2-COOC2H5
I.
Hydrolysis of compound I. simultaneously eliminatee carbon dioxide with formation of the acid
.CH2-CH2-COOH HOOC-CH<
XJH2-CH2-COOH
from which water and carbon dioxide are eliminated by heating with acetic anhydride^ with formation of the ketonic acid
<CH2 • CH2V >co. CH2-CH2^
The carbethoxyl-group and the carbonyl-group of the ester of this acid react readily with methyl magnesium iodide (91 and 102)1 forming a compound of the formula
.CH2-CH^ yOMg.I \lH2-CH2^ XJHa
converted by dilute mineral acids into the product
CHgv yCH2^CH2v yOH
identical with terpin.
t367]
TERPENES.
529
Elimination of water from terpin yields, among other pro* ductd (367); a substance of the formula CioHigO, which is neither an alcohol nor a ketone, and is identical with cineolf a constituent of many essential oils. Oil of eucalyptus and oil of wormseed (Oleum cincB) contain a large proportion of this compound. ltd mode of formation and properties indicate that cineol has the constitutional formula
CH,
c-
H2C . CH2 M2C GM2
CH3 CHs
o
CUieol
367. Some of the unsaturated derivatives of menthane are also very important. The menthenes, C10H18, hydrocarbons with one double linking in their molecule, need not be considered, but the alcohol terpined and the ketone pulegone, derived from them, merit description.
Terpineolf CioHigO, is a constituent of some essential oils. It has an odour resembling that of lilacs: it melts at 35^, and boils at 218^. Terpineol is closely related to terpin, since agitation with dilute sulphuric acid converts it into terpin hydrate: inversely, boiling with dilute sulphuric acid regenerates terpineol from terpin hydrate, with elimination of water.
The constitution of terpineol must therefore be very similar to that of terpin, the only question being which of the hydroxyl- groups of the latter compound has been eliminated fiom the molecule along with one hydrogen atom. Since an optically active terpineol is known, it must be hydroxyl-group 1 of terpin, so that terpineol has the constitution indicated in the scheme
530 ORGANIC CHEMISTRY. [( 367
CHs CELz
C C-OH
/\ /\
HaC CH -» HaC (M,
T I J, i •
ri^o CH2 <~ H2O CH2
\/ V
CH CH
C.OH C-OH
CH3 CH3 CH3 CHs
Terpineol Terpin
Carbon atom 4 in the formula giwen is asymmetric, whereas removal
of water from C-atoms 4:8, 8:9 (=8:10), or 1:7 could not produce
an asymmetric carbon atom.
Pvlegone, CioHiqO, is the principal constituent of the cheap
oil of polei. It boils at 222^, and has a peppermint-like odour.
The formation of an oxime indicates that it is a ketone. On
reduction with sodium and alcohol, it takes up four hydrogen
atoms, yielding menthol, which proves that the carbonyl-group is
at position 3:
CHs CHs
CH CH
H2C CH2 H2C CH2
H2C CO H2C CHOH
Y ^
h
C CH
/\ /\
CH3 CH3 CH3 CHj
Puleffone Menthol
Both oxidation and heating with water decompose pulegone with formation of acetone, so that the double linking is between C-atoms 4 and 8.
Among the unsaturated menthane derivatives with two double Unkings are the hydrocarbons terpindene, ddinwnene, and l4imonene, and their racemic form, dipentene. Each has the formula CioHie.
Terpinolene boils at 185^. It is formed when terpineol is boiled
§367] TERPENES. 531
"with oxalic-acid solution, one molecule of water being eliminated. Theoretically, two reactions are possible:
CH3 CH3 CHs
• • •
c c c
H2C CH HjC CH HiC CH
I T -H:iO- I I or 1 1 [ . MgC GH2 H^ CH2 H^ CHs
\/ \/ \/
CH C CH
COH C C
TMpineol TBipinofene d" and I- Limoneiie
TU IL IIL
Since terpinolene is optically inactive; and is derived from the opti- cally active terpineol, the asymmetry of the carbon atom must have vanished, as in formula II. Oatom 4 of formula III. is asym- metric, as in terpineol itself, formula I.
Formula III. is that of the optically active limonene, which occurs in many essentia] oils and varieties of turpentine. It has an agreeable, lemon-like odour. Its constitution is inferred from two facts: first, it is also obtained from terpineol by ^ elimination of water, effected by heating with potassium hydrogen sulphate; second, addition of 2HBr yields the same dibromomenthane as is obtained from terpin by exchange of the hydroxyl-groups for bromine:
CH3 CI13 C113
C-OH C-Br C +^'
/\ /\ /\ H
D.*fj CH2 H2C CH2 H2C CH
H2G CH2 H2C CH2 H2C CH2
CH CH
C-OH C-Br .J+ C
/\ /\ H /\
GH3 CH3 CH3 CH3 CH2 CHj
Tsrpin DibromomenthAna Limonene
CH
532 OBGANIC CHEMISTRY. (§388
Dipentene, a constituent of oil of turpentine, is also obtained by mixing d-limonene and Mimonene in equal proportions by weight. Like the limonenes, it yields a well-crystallized tetrabro- mide, indicating the presence of two double Unkings in its mol- ecule. Isoprene (127) can be prepared from limonene.
368. Carvane, C10H14O, is an important ketone belonging to this group. It is the principal constituent of oil of caraway, and has its characteristic odoiu*. It boils at 228°. Related to carvone is carvacrolf which is obtained from it by heating with potassiimi- hydroxide solution :
CH3 9^
C c
Hc/Nc-OH HC 00
HC" JCH HaC Ce,*
Y ^
Ah J,
CHs CH, jjg^ -^jj^
Oftrraerol Orvooe
The hydroxyl-group in carvacrol is linked to C-atom 2, since, on heating with phosphoric oxide, propylene is evolved, and a-cresol (294) formed. The carbonyl-group in carvone is assumed, there- fore, to be at position 2. Carvone is proved to be a ketone by the formation of an oxime, called carvoxime.
When nitrosyl chloride is added to limonene, subsequent elim- nation of HCl yields carvoxime :
CH3 CHs CHs
G c.a C
H2C CH H2C C:NOH HC C:NOH
I I +Noa =11 ; -Ha -11 H20 CH2 H2C CH2 H2C CH2
\/ \/ \/
CH CH CH
• • •
c
GHaCHa
.Canrozima
|
c |
c |
|
/\ |
r\ |
|
CH2 CH3 |
CH2 CHs |
|
Limonene |
Limonene nitroso-cUoride |
3601
TERPBNES
633
This reaction proves that carvone contains one double linking d^'^f but leaves it doubtful whether the other double linking is J6 Qp ji : 7^ jn ^\^Q production of terpineol from terpin the double linking is formed between two C-atoms of the nucleus, and by analogy this should also hold for carvone. Further evidence in favour of the formula indicated is afforded by the decomposition- products of the carvone molecule^ but the details are beyond the scope of this work.
Polycydic Terpene Derivatiyes.
369* There exist hydrocarbons of the formula CioHie which contain but one double linking, for they take up only two univalent atoms or groups. As they contain foiur hydrogen atoms less than the saturated cyclic menthane^ CioH20y they must have a second closed chain in the molecule. Moreover, these compounds and their derivatives are closely related to cymene, most of them being convertible into it or kindred substances. Investigation has shown that the formation of the second ring can take place in three different ways, as the formulse indicate:
CH3 CHs
CH CH
HaC
CHs G CHs
CH
CH,
HaC
CH
H2C
CHg'C'CHs
CH
Camphane
534
ORGANIC CHEMISTRY.
[§3G9
The tertiary carbon atom takes part in the formation of the ring, or "bridge-formation." Carane has a trimethylene-ring, pinane a tetramethylene-ring, and camphane a pentamethylenc- ring. Several members of these three groups will be considered.
Carane itself is miknown, but there is a synthetic derivative, carone, which is not a natural product. It has the structural formula
CHa
CH HaC CO
CH3 CHs
H2C CH
CH_^C<
Oarone
for opening of the trimethylene-ring at 3:8 yields derivatives of p-cymene, and at 4:8 derivatives of m-c}Tnene.
Pinene is the typical member of the pinane-group. It is the principal constituent of the various oils of turpentine, and is, therefore, also of technical importance. It is optically active, a dextro-rotatory, a laevo-rotatory, and an inactive modification being known. It boib at 156®. The presence of a double bond is proved by addition of one molecule of hydrochloric acid, the dry gas pre- cipitating from cooled oil of turpentine a compound of the formula CioHie-HCl, called "artificial camphor," which resembles camphor both in appearance and odour. Pinene also readily forms an addition-product with nitrosyl chloride. Pinene has the formula
CH3
HC^ H,C CH, >CH
\/ C
§ 3701 CAMPHORS. 536
The presence of a tetramethylene-ring is assumed in order to ex- plain the constitution of oxidation-products of pinene, such as pincmic acid and pinic acid, and for other reasons. Under the influence of benzenesulphonic acid, pinene in acetic-acid solution combines with one molecule of water to form terpineol, the tetramethylene-ring being opened. This transformation indi- cates the position of the double bond.
CAMPHORS.
370. Ordinary camphor, CioHieO, is the most important mem- ber of the camphane-group. No other organic compound has been so much investigated, or from such widely different points of view. Ordinary, dextro-rotatory, "Japan camphor '' is obtained by the steam-distillation of the bark of the camphor-tree. It forms a white, soft, crystalline mass of characteristic odour, and sublimes even at the ordinary temperature. It melts at 175- 7°, and boils at 209. l^
The camphor-odour is characteristic of many compounds in which all the hydrogen atoms attached to one carbon atom have been replaced. Very few of the relations between odour and chemical constitution have been discovered. Compounds of widely divergent chemical structure often have a very similar odour, as with artificial and natural musk. Other substances closely related from the chem- ical standpoint exhibit complete dissimilarity in smell. This phe- nomenon is exemplified by the chlorophenols, the ortho^ompound in a very dUute condition having a powerful odour like that of iodoform; the smell of the meto-compound and the paro-compound is much less pronounced, and resembles that of unsubstituted phenol.
Camphor is a saturated ketone — ^saturated because it does not yield addition-products, and a ketone because it forms an oxime. Reduction converts it into a secondary alcohol, bomeol or " Borneo camphor ":
C9Hi6-CO+2H = CoHie-CHOH.
Camphor Borneol
In addition to the carbonyl-group, the camphor molecule con- tains a methylene-group, for it has the properties of compounds with the group — CH2-C0 — . As explained in 199, the hydrogen
536 ORGANIC CHEMISTRY. (i 370
> of such a methy lene-group can be replaced by the oxime group by the action of amyl nitrite and hydrochloric acid. Camphor reacts Similarly, these reagents converting it into.isonftrosooainpAar, which melts at 153^:
XJH2 yC=NOH
Ounphor MoNitrovoeamphor
Elimination of the oxime-group from isonitrosocamphor yields eamphor-qairumef
On treatment with hydrogen peroxide, this compound is oxidized, forming the anhydride of camphoric acid,
which can also be obtained directly from camphor by oxidation with nitric acid. It follows that, given the constitution of cam- phoric acid, that of camphor can be inferred.
Ordinary camphoric acid is dextro-rotatory, and melts at 187®. Four optically active camphoric acids are known: dextro-rotatory and Isevo-rotatory camphoric acid, and dextro-rotatory and Isevo- rotatory iaocamphoric acid, with the same constitution as camphoric acid. These facts indicate that the molecule of camphoric acid must contain two dissimilar asymmetric Oatoms (z88).
Energetic oxidation converts camphoric acid into the tribasic, optically active camphoronic acid, the constitution of which follows from its synthesis, and from its decomposition-products when sub- mitted to dry distillation. This process decomposes it into tri- methylsuccinic acid, iaobutyric acid, carbon dioxide, and carbon:
(CH3)2C.C500H (CH3)2C.COOH
CHa-C-COOH - CH3-CH.C00H +
CH2-C00H H-C+H2+C02
OMnphoroDio Mid
S370]
CAMPHORS.
537
and
(CH3)2CH.COOH + + §|^CH.COOH +
+ COa.
From theee facts it is possible to deduce a formula for camphoric acid, which also accounts for its other properties:
OOOH COOH CHa CH COOH
CH3 C CH;
3
CH
CH3 — C — CH3
2"
A,
<XX)H CH
2-
!H3
Ounphoronio aoid
CHa-
k
<X)OR
■ca-
CH;
I — C — CH3
Camphorie add
<3H2
CH,
A
00
;h3
Cunphor
This structural formula for camphor was originally proposed by Bredt. His view has been confirmed by the synthesis of camphor^ effected by W. H. Pbrkin, jun. and Thorpe, and by Komppa, but the details of the processes involved are beyond the scope of this work. The formula of camphor contains two dissimilar, asymmetric C-atoms, represented in italic.
The position of the carbonyl-group in camphor follows from its conversion into carvacrol by the action of iodine : in this compound the hydroxyl-group is in the ortAo-position to the methyl-group
(368).
Bomeol contains a CHOH-group instead of the CO-group present in camphor. By replacement of the hydroxyl-group by iodine, it yields bomyl iodide, which can be reduced to camphane:
CH2 CH CH2
CH,
CH3 — C — CH3
—I—
(Mi
I CHa
OMnpbane
638 ORGANIC CHEMISTRY. (§ 870
According to the formula, the conversion of CO into CH2 should destroy the asymmetry of both the as3rmmetric C-atoms of cam- phor, and camphane is, in fact, optically inactive.
The formula of camphor contains an isopropyl-group and therefore accounts for the conversion of camphor into cymene by heating with phosphorus pentasulphide. The complete synthesis of camphoric acid previously mentioned has definitely settled the constitution of this acid, and that of camphor itself.
In the chemistry of the terpenes and camphors molecular refrac- tion has been an important aid in coniirming structural formulae based on purely chemical methods, and also in iadicating the correct formulae in cases to which chemical processes are inapplicable.
Example. — ^A camphor derivative, thujone or tanacetone, CioHnO, has the molecular refraction iK/>=44*78; while that calculated for a saturated ketone CioHuO is 44*11; and for a ketone CioHi«0 with one double carbon bond 45*82. The fact of the observed molecular refraction being intermediate between these two values indicates the presence of a trimethylene-ring.
POLTTERPENES.
The polyterpenes include a number of compounds of the for- mula (C5H8)n, n being greater than 2.
The most important member of the class is caoulchoix or india-rvbberj the latex or coagulated milky juice of various tropical plants, chief among them Hevea brasiliensis. Caoutchouc is purified by dissolving in it chloroform or another solvent, and precipitating it with alcohol in a white, amorphous form. It is vrdcanized by the action of sulphur or sulphur monochloride, S2CI2, a process considerably augmenting its elasticity and durability. Unvulcanized caoutchouc becomes sticky at 30*^, and loses its elastic! 1^ at 0°. Over-vulcanization yields eixmite or vulcanite.
Ozonized air reacts with a solution of caoutchouc in chloroform, with production of an ozonide in the form of a vitreous mass. This substance has the empirical formula CsHsOs, but its molecu- lar weight must be much higher than that indicated by this formula. The ozonide is quantitatively converted by water into
H
laetruMdehyde, CH3*CO*CH2*CH2«Cq, and a peroxide of this
substance.
§ 370] POLYTERPENES, 539
On addition of a molecule of hydrogen chloride to caoutchouc, followed by elimination of the chloride, a compound of the formula (C5H8)n is formed. Ozonization of this substance and decomposi- tion of the ozonide yields not only laevulaldehyde, but diacetyl- propane, CH3«CO-(CH2)3*CO*CH3, and small proportions of a triketone and a tetraketone. On the basis of these facts and others observed by him. Harries assumes caoutchouc to have a ring of twenty carbon atoms, formed by regular repetition of the group CHa .C .CH2 -CHz .CH=.
The great technical importance of caoutchouc has led in recent years to many attempts to prepare it synthetically. Although polymerization of isoprene (127) readily yields a product capable of undergoing vulcanization and characterized by a great resem- blance to caoutchouc, the synthetic derivative lacks the funda- mental properties constituting the basis of the great practical importance of natural caoutchouc. Despite numerous attempts, and the possibility of preparing isoprene on the large scale, no technically applicable method for the production of caoutchouc has hitherto been discovered.
BENZENE-NUCLBI LINKED TOGETHER DIRECTLT^ OR
INDIRECTLY BY CARBON.
371. The simplest possible compound of this nature is one con- taining two benzene-nuclei directly linked together. In addition, there are compounds with the benzene-nuclei indirectly connected by a carbon atom, or by a chain of carbon atoms. A few typical examples will be cited.
Diphenyl, CeHs-CeHs. Diphenyl can be prepared by heating iodobenzene with finely- divided copper at 220^. A better procedure is to pass benzene- vapour through a red-hot iron tube: ^•
2C6H6 = C12H10 + H2.
Another method for the preparation of the derivatives of diphenyl, the conversion of hydrazobenzene into benzidine, is mentioned in 301. On removal of the amino-groups from benzidine by means of the diazo-reaction, diphenyl remains. This method of formation also afifords a proof of the constitution of benzidine.
Oxidation converts diphenyl into benzoic acid. This reaction and its synthesis prove its constitution.
Diphenyl forms large, tabular, colourless crystals, readily soluble in alcohol and ether. It melts at 71^, and boils at 254^.
The isomeric substitution-products of diphenyl are much more numerous than those of benzene, as the scheme indicates:
A
Diphenyl
A monosubstitution-product can exist in three isomeric forms, the substituent being in the or/Ao-position, mdo-position, or para-pcsi- tion to the bond between the benzene-nuclei. In a disubstitution-
540
§3721 DIPHENYLMETHANB. 541
lion to the bond between the benzene-nuclei. In a disubstitution- product, both substituents may be linked to the same benzene- nucleus, or to different benzene-nuclei, and so on.
Benzidine b of technical importance, because many of the azo- dyes are derived from it.
Diphenyhnefliana, CoH6*CH2-C6H5.
372, Diphenylmeihane can be obtained from benzyl chloride, Cf(H6*CH2Cl, or from methylene chloride, CH2CI2, by means of benzene and aluminium chloride. Its homologues are obtained by the action of benzene and concentrated sulphuric acid upon alde- hydes. Thus, acetaldehyde yields unsymrn^iical diphenyldhane:
H
^^5 fxrr fXTT^CfiH.1
CHa-CH O+g^U - CH,.CH<^+HjO,
When derivatives of benzene are substituted for benzene itself, many derivatives of diphenylmethane can be obtained by the application of these syntheses.
Diphenylmethane is crystalline. It melts at 26^, boils at 262^, and has an odour resembling that of orange-peel. Oxidation with chromic acid converts into benzophenone (3x6).
«
A derivative of diphenylmethane, in which the benzene-nuclei
are directly linked, lafltwrene, J /CHj. It is formed by leading
the vapour of diphenylmethane through a red-hot tube. From alcohol it crystallizes in leaflets: the ^rystal8 are fluorescent, a cir- cumstance which gave this compound its name. It melts at 113^, and boils at 295°. It yields red needles with picric acid.
The constitution of fluorene is thus established. It is converted by the action of oxidizing agents into diphenylenekeUme, the formula
CeH4v of which, I ^C0| is established by its formation when the cal
dum salt of diphentc acid, \ ( ^Ca, is distilled. Diphenic
CeH^-lcOO^
add, for its part, is obtained from tn-hydrazobenzoic acid by the
542 ORGANIC CHEMISTRY. [§ 373
b^izidine-transformation (301), and subsequent elimination of the ' amino-groups:
COOH HOOC HOOC COOH
It follows that the carbonyl-group in diphenyleneketone is linked at the or^Ao-position in both the bensene-nuclei : it has/ therefore, the structure
^ \ vy» ^^^ fluorene itself ^ \ ^ \
/ \/
00 CH,
This view receives confirmation from the fact that phthahc acid is the only product obtained by its oxidation.
The hydrogen of the CHr-group in fluorene can be replaced by potassium. Oxidation of fluorene with lead oxide at 310^-330^ yields di-diphenylene-ethylene,
which melts at 188^. It is characterized by its deep-red colour, most hydrocarbons being colourless, at least in thin layers (388).
Triphenylmethane and its Deiivatiyes.
373. Triphenylmethane, CH(C6H6)3, is formed from benzal chlor- ide, C6H5«CHCl2, by the action of benzene and aluminium chloride; from benzaldehyde and benzene in presence of a dehydrating agent, such as zinc chloride; and from the interaction of chloroform and benzene in presence of aluminium chloride. It crystallizes in beau- tiful, colourless prisms melting at 93*^. Its boiling-point is 359**.
A series of important dyes, the rosanilines, is derived from this hydrocarbon. Triphenylmethane itself is not employed as a basis for their preparation, but simpler substances which are converted into its derivatives. The formation of the dye takes place in three stages: malachite^een furnishes an example.
S 3731 QUINONOID STRUCTURE, 643
When benzaldehyde and dimethylaniline are heated with zinc chloride, tetramethyldiaminotriphenylTnethane is formed:
CeHfi-C:
Ih] <(^^N(CH3)2 ^ .C6H4N(CH3).
>=C « H20+C6H5-C<
< >N(CH8)2 X^e
T«1^_^N(CH8)2 \C6H4N(CH3).
The carbon atom of the aldehyde group, therefore, furnishes the "methane carbon atom " of triphenylmethane.
This substance is also called leucomalachite-green. It is con- verted by oxidation with Pb02, in hydrochloric-acid solution, into
,, ,. ,. , CeH5C[C6H4N(CH3)2]2 , ,
the correspondmg carbmol, • , a colourless,
OH
crystalline substance, like the leuco-compound from which it is
derived. Being an amino-base, it is capable of yielding salts: thus,
it dissolves in acids with the formation of colourless salts. When
such a solution is warmed, water is eliminated, and the deep-green
dye produced. The dye, either as a double salt with zinc chloride,
or as an oxalate, is known as malachite-green. The elimination of
water may be representee^ in several ways; it is usually supposed
to take place thiis:
.C6H4N(CH3)2-HC1 Q>H6.C< -H3O -
I X!eH4-N(CH3)2-fH]Cl
(OHl
yC6H4N(CH3)2-HC!r
XJ>=N(CHg)2.
I CI
Quinoiurfd form
This '* quinonoid reaction '' is analogous to the formation of quinone from quinol, in which the colourless quinol is converted into the deep-yellow quinone.
The conversion into a quinonoid form also explains many other instances of the formation of coloured substances; for example, the
544 ORGANIC CHBMI8TBY. [|873
conversion of the colouriess phenolphthalein (34S) into its red metal- lic derivative.
Bbrnthsbn has proved that this indicator in the colourieas
state is a lactone, '
C(C.H40H)t
CA<^0 ;
CO
bat that its red salts are derivatives of a carbozylie add containing a quinonoid-group,
9\
C,H, ^Me*
0001
When the phenolphthalein is regenerated from this salt by the action of an acid, it changes, like the pseudo-acids (aaa), into the colour- less lactone-form, the transformation in this case being instantaneous.
The distinguishing characteristic of the group >C«H«< is its strongly marked chromophore character.
The nitrophenols constitute one of the many examples of this
phenomenon. In the pure state both they and their ethers are
quite colourless, but their salts are highly coloured. It has, however
been possible to prepare highly coloured ethers of the nitrophenols,
and by various reactions to transform them into colourless ethers
with the same molecular weight. The isomerism of these compounds
is explicable on the assumption for the colourless derivatives of the
/NO, normal structure C«H«< , and for the coloured products of the
OR
Ino-or
quinonoid structure CJB^ , the nitrophenols being regarded
as pseudo-acids with a quinonoid act-form.
VoN Baxter has pointed out that the development of colour is not always due to transformation into a quinonoid form. The intensely coloured acid salts of trianisyUxtrbinol, (CH^*C«H«)iC«OH, and of similar compounds undoubtedly are not quinonoids. Their colour is probably caused by intramolecular rearrangement of an ob- scure type. VoN Babter has named this phenomenon halochromy,
^ Me represents one equivalent of a metaL
1 3741 TRIPHENYLMETHANE DYES. 645
374. The three stages necessary to the formation of the dye, may, therefore, be defined as follows.
1. Formation of a leuco^xise (colourless), a derivative of
HC(C6H4NH2)3,
2. Formation of a colour-base (colourless), a derivative of
HO.C(C6H4NH2)3.
3. Formation of the dye, a derivative of
p(C6H4NH2,HCl)2 ^C6H4NH2.C1
Reduction reconverts the dyes into their leuco-bases, two hydrogen atoms being taken up during the reaction.
CrytUal-viold (hezamethyltriaminotriphenylmethane) furnishes an excellent example of a phenomenon also exhibited by other ana- logous basic substances. When an equivalent quantity of an alkali is added to a salt of crystal-violet, the liquid still remains coloured, has a strong alkaline reaction, and conducts an electric current. On standing, the solution slowly becomes colourless, when it is no longer alkaline, and its electric conductivity has fallen to that of the alkali-metal salt present in the liquid. The liquid now contains a colour-base. These phenomena are analogous to the conversion of acids into p&eudo-&6ida (333). For this reason the colour-base may be looked upon as a pseudo-6a«e. Thus, on addition of the equiva- lent quantity of NaOH to crystal-violet, the true base,
■o^
is at first present in the solution : after standing for several hours a^
25^, however, this true base changes into the colour-base {pseudo-
base),
(CHs),N.Q,H4. p ^CH4-N(CH,),. (CH8)2N-CeH4>^<OH
Hantzsch has been able to identify as pseudoAyasea substances other than those mentioned.
546 ORGANIC CHEMISTRY. I|374
Pararosamline is obtained by the oxidation of a mixture of p-toluidine (1 molecule) and aniline (2 "molecules) by means of arsenic acid or nitrobenzene. The methyl-group of toluidine thus furnishes the '' methane carbon atom " of triphenylmethane:
yC6H4.NH2 /C6H4NH2
CHa'^^CeHfi-NHz+SO = HO— CeC6H4NH2+2H20. CgHs-NHg ^H4NH2
This colour-base dissolves in acids, forming a red dye: it can be reprecipitated by alkalis. It is transformed by reduction with zinc- dust and hydrochloric acid into paraleucaniliney HC(C6H4NH2)3, a colourless, crystalline substance which melts at 148^, and is recon- verted into the colour-base by oxidation. The constitution of paraleucaniline is indicated by the formation of triphenylmethane on elimination of its amino-groups by diazotization. On the other hand, paraleucaniline can be obtained by the nitration of triphenylmethane, and subsequent reduction of the trinitro- derivative thus formed. Paraleucaniline is converted by oxidation into triaminotriphenylcarbinoly which, like malachite-green, loses water under the influence of acids, forming the dye:
/C6H4NH2 /C6H4NH2
CfC6H4NH2 -H2O - CA)6H4NH2 ( \C6H4NH2.HCl ^C6H4:NH2.a
Another important dye related to triphenylmethane iBrosaniline. Its preparation is similarly effected by oxidizing a mixture of ani- line, o-toluidine, and p-toluidine in equimolecular proportions with arsenic acid, mercuric nitrate, or nitrobenzene. In this reaction the methane carbon atom is obtained from p-toluidine as follows:
• NH2-C6H4.CH8+C6H4(CH8)NH2+C6H5.NH2 +
p-Toluidin. o-ToIuiaiii«
+ 30 - 2H20+HO.C^-CbH4NH2 -» C^eH^NHa
\C6H4NH2 x;6H4:NH2.a.
Colour>baae Magenta
The chloride obtained from the rosaniline colour-base, by combination with one equivalent of hydrochloric acid and elimina-
§3741 TRIPHENYLMETHANE DYES. 547
tion of one molecule of water, is called magenta. This substance forms beautiful green crystals with a metallic lustre, which dis- solve in water, yielding a solution of an intense deep-red colour. The colour of the magenta solution is due to the univalent cation, (C20H20N3), because such solutions are almost completely ionized, as the slight increase of their molecular conductivity on further dilution shows. Moreover, the solutions of all the magenta ^ts — chloride, bromide, sulphate, etc. — exhibit the same absorption-spectrum for solutions of equimolecular con- centration, an indication of the presence of a constituent common to all of them (the cation).
The salts containing three equivalents of acid are yellow, the red, univalent cation having been converted into the yellow, tervalent cation: in consequence, magenta dissolved in excess of hydrochloric acid yields a nearly colourless solution. These salts are, however, very readily hydrolyzed: the red colour reappears when this solution
in hydrochloric acid is poured into water.
t
Many derivatives of pararosaniline and ros^niline are known in which the hydrogen atoms of the amino-group have been replaced by alkyl-radicals. They are all dyes. The violet colour becomes deeper as the number of methyl-groups present increases (341). Pentamethylpararosaniline has the trade-name "methyl-violet." When one hydrogen atom in each of the amino-groups of rosaniline is replaced by phenyl, a blue dye is formed, called "aniline-blue."
Methyl-\dolet is obtained by the oxidation of dimethylanlline with potassium chlorate and cupric chloride, the methane carbon atom being obtained from one of the methyl-groups.
Aniline-blue, or triphenytrosaniline hydrochloride, is formed by heat- ing rosaniline with aniline and a weak acid, such as benzoic acid, whereby the amino-groups in the rosaniline are replaced by anilino- groups, the ammonia set free entering into combination with the acid. This process in analogous to the formation of diphenylamine from aniline hydrochloride and aniline (298).
Dyes formed from hydroxyl-derivatives of triphenylmethane are also known, but are much less valuable than those just described, on account of the difficulty of fixing them. Rosalie add,
5 48 ORGANIC CHEMISTRY. (§ 376
CH C^3<oH CA36H4OH
obtained from rosaniline by diazotization, is an example of such dyes.
Malachite-green and the pararosaniline and rosaniline dyes colour wool and silk directly, and calico after it has been mordanted.
The phthalelnSy dyes related to triphenylmethane, have been mentioned (348).
375* GoMBERG has investigated the action of zinc upon a benzene solution of triphenylchloromethane : zinc chloride separates and the solution contains a compound which can be precipitated by addition of acetone or ethyl formate. This compound he regards as triphenylmethyl, (C8H5)8C — , with one free linking. Its power of forming addition-products is remarkable. It is at once oxidized by atmospheric oxygen to a peroxide,
(G6H5)8C^O— 0-C(C6H5)3.
It decolorizes iodine-solution instantaneously, funning triphenyl- methyl iodide. It yields addition-products with ether and many other compounds.
A close investigation of triphenylmethyl has revealed the existence of two foims, one being colourless and the other yellow. The solid, colourless hydrocarbon is converted by solution into the yellow isomeride, the only highly reactive form. In solu- tion, the two modifications attain an equilibrium dependent on the temperature and the nature of the solvent. Since the mo- lecular weight indicated by the cryoscopic method corresponds with nearly twice the empirical formula, the equilibrium
2(C6H6)30 T± (C6H5)3C.C(C6H6)s Triphenylmethyl Hexaphenylethane
requires the presence of only a small percentage of the yellow modification.
The colourless form consists of hezaphenylethane, and the yellow isomeride of triphenylmethyl. In tridiphenylmetkyl, (C(jH5-C«H4)3C, the unimolecular form predominates strongly, the solution having an intense violet colour. These compounds recall the parallel instance of nitrogen peroxide, known in a
§ 376] TRIPHENYLMBTH7L. 540
colourless form, N2O4, and in a yellowish-brown modification, NO2. like triphenylmethyl, the simpler form of nitrogen per- oxide is characterized by its abnormal condition of unsaturation. In two respects these compounds are very remarkable: first, triphenylmethyl contains a tervalent carbon atom; second, the carbon linking in hexaphenylethane can be severed with extraor- dinary ease, even by mere solution in benzene or other solvents. Among the reasons for assuming the colourless compound to be hexaphenylethane is its analogy to perUaphenylelhane, a sub- stance readily decomposed at high temperature, but proved hf its synthesis to have the structure (C6H5)3C-CH(C6H6)2.
Since the existence of a compound with a free carbon linking was revealed by this research, a number of other compounds of similar character has been discovered. In contact with potassium, an ethereal solution of an aromatic ketone, such as benzophenone, develops a very intense colour, the change being probably occasioned
:>c
by the formation of a compound of the formula yC\ . The
R'
unchanged boiling-point of the liquid after complete solution of the potassium points to the presence of the same number of molecules, and is an argument against the double formula. Such compotmds are also instantly oxidized on contact with air.
Compounds containing a bivalent nitrogen atom with a free linking have also been prepared. Oxidation of diphenylamine yields tetraphenylhydrazine :
CeHiv •C«Hi C«Hfv yCtEU
'>NH + 0 + HN<^ - H,0 + ^N— N<^
CfHt CeHi CeHi CeE[»
In solution in toluene at QO*', this compound dissociates, although only
CJIjv
to a slight extent. The free diphenylnitrogeny yN — , is much
c.h/
less stable than triphenylmethyl. Its hot solution combines quanti- tatively with nitric oxide to form dtphenylnitrosoamine, and with triphenylmethyl it yields a compound of the formula
(C.H*),C-N(C.H»),.
like triphenylmethyl, the. free compounds RtN — are intensely coloiued. The solution of tetrcHinisylhydrazine,
(CHiO •C.H4)»N— N(CsH4 •OCH,),,
550 ORGANIC CHEMISTRY, [J 376
illustrates this characteristic. At ordinary temperature it is almost colourless; on warming, it becomes deep green; on cooling, the colour vanishes.
According to the law of Beer, solutions containing the same quantity of colouring matter in different amounts of the solvent exhibit the same light absorption when the thickness of the liquid layer is inversely proportional to the concentration, since under these conditions the light in transit encounters the same number of molecules of colouring matter. For dissociated substances the law does not hold, for the degree of dissociation varies with the dilution. On this fact is based a method of determining dissociation. Its application to tetra-anisylhydrazine has proved a 0*05 per cent. solution in benzene to be 3*2 times as much dissociated as a 0*3 per cent, solution in the same solvent.
Although this compound undergoes only slight dissociation, ietra (j^iinethylainino)'tetraphenylhydr<mne,
[(CHa),N .CeHJ,N-N[CeH4 .N(CH,) J„
in nitrobenzene solution is dissociated to the extent of 21 per cent.
Dibenzyl and its Derivatives.
376. Dibenzyl f C6H6-CH2-CH2-C6H5, can be obtained by the action of sodium upon benzyl chloride:
CeHfi-CHgp+Naa+CnCHa-CeHfi - C6H6-CH2-CH2-C6H5+2Naa.
This method of formation shows it to be symmetrical diphenyl^ ethane. It melts at 52^.
Symmetrical diphenylethylene, CoHi-CHiCH-CbHj, M.P. 125^ is called atHbene. It can be obtained by various methods : for ezampley by heating an aqueous solution of phenylsodionltromethane, which is thereby decomposed into stilbene and sodium nitrite:
2CSeH,-CH:N0.0Na - Q,H5*CH:CH.CeH5+2NaNO,.
Stilbene forms an addition-product with bromine, from whidi tdan, G0H5 • C iB C • C0H5, is produced by elimination of 2HBr. Tolan can be reconverted into stilbene by careful reduction.
p-Diaminostilbene, NH2-CoH4-CH:CH-C8H4-NH3, can be ob- tuned by treatment of p-nitrobenzyl chloride, ClHaC'CtH^^NOj, with alcoholic potash, and subsequent reduction of the p-dinitn>-
S 376] BENZILIC ACID. 551
ftxCbene thus formed. It is used as a bams for the preparation of oertun dyes.
DerivativeB of dibenzyl are got by the condensation of benzal- dehyde in presence of potassium cyanide. For example, benzoin is thus formed:
CsHfi.cST^ScCjHB - CeHfi.CO.CHOH.CsH^
\J "T a. Benaoln
It has the character of a keto-alcohol, since it takes up two hydrogen atoms, with formation of a dihydric alcohol, hydro- benzoin, CeHfi.CHOH.CHOH.CoHfi. On oxidation it yields a diketone, benzU, CeHs^CO-CO^CeHs. Benzoin contains the group — CHOH*CO — , which is present in the sugars (202). It also pos- sesses properties characteristic of the sugars: thus, it reduces an alkaline copper solution, and yields an osazone.
Benzil is a yellow, crystalline substance. As a diketone it unites with two molecules of hydroxylamine to form a dioxime.
When heated with alcoholic potash, benzil takes up one mole- cule of water, imdergoing an intramolecular transformation, with production of benzilic acid, a reaction analogous to the formation of pinacolin from pinacone (150):
C^.CO.CO.CeHfi+HaO - q^J>C<cooH-
Bensilic acid
CONDENSED BENZENE-NUCLEI.
377. Condensed-ring compounds contain two or more closed chains, with Oatoms common to both. Such compounds are pres- ent in the higher-boiling fractions of coal-tar (286). Next to the phenols, naphthalene is the principal constituent of the second fraction, carboUc oil, and of the third fraction, creoeote-oil. The anthracene-oil contains anthracene and phenanthrene, and other hydrocarbons. These three compounds and some of their deriva- tives will be described.
L HAPHTHALBHEy CipHe.
Naphthalene is present in considerable proportion in coal- tar, from which it is readily obtained pure. On cooling, the crude crystals of naphthalene precipitate from the fraction distilling between 170^ and 230°. The liquid impurities are pressed out, and are further eliminated by conversion into non-volatile suiphonic acids on warming the crude product with small quantities of con- centrated sulphuric acid, and distilling with steam or subliming. The process yields pure naphthalene.
Naphthalene crystallizes in shining plates, melting at 80^, and boiling at 218°. It is insoluble in water, but readily soluble in hoK alcohol and ether: it dissolves to a very small extent in cold alcohol. It has a characteristic odour, and is very volatile. It is always present in coal-gas, the illuminating power of which is to a large extent due to its presence. It is extensively employed in the manufacture of dyes.
The formation of naphthalene on passing the vapours of many compounds through a red-hot tube, a process somewhat similar to that which takes place in the retorts of the gas-works (286), ex- plains its occurrence in coal-tar.
552
§ 377] NAPHTHALENE. 553
The constitution of naphthalene is proved in 355 to be
This view is confirmed by two ssmtheses.
1. o-Xylyleae bromide is converted by treatment with tetraethyl disodioethanetetracarboxylate into tetraethyl hydranaphthalenetetrijh earboxf^ate:
/CHjBr NaC(COOCH,), .CH,-C(0OOCH.),
XJHjBr NaC((X)OCH,), ^CH,-<J(0OOCH,),
•-Xylyleiia bromide
On saponification^ this compound loses two molecules of carbon diozidey forming kydranaphthalenedicarboxylic add:
XH,-OH-000H
chZ I
^CHa— CH-OOOH
The diver salt of this acid readily gives up two molecules of carbon dioxide and two atoms of hydrogen, yielding naphthalene.
2. On heating, phenylvinylacetic add is converted into a-naph^ ihol, a hydrozy-derivative of naphthalene:
H CH
=0^r -H/> - CO
H\/H XH, \/\/
HOC^ OH
HO
PheDyhrinyUoetio aoid o-Naphthol
Naphthalene behaves in all respects as an aromatic hydrocarbon, ^th nitric acid it yields a nitro-derivative; with sulphuric acid a sulphonic acid: its hydroxy i-derivatives have the phenolic charac* ter: the amino-compounds undergo the diazo-reaction: etc.
For naphthalene, as for benzene (283)1 ^^ formula indicating its internal structure and satisfactorily accounting for its properties has been proposed.
554
ORGANIC CHEMISTRY.
({378
Fonnula I. (Fig. 85) is analogous to the centric fonnula for ben- sene: it is difficult to represent its configuration in space.
L
.^
I. Fig. 85.
II.
vV
Flo. 86.
III. Fig. 87.
Fig. 85. — Centric Naphthalbne-fobmula. F?G. 86. — ^Thiele's Naphthalene-formula. Fig. 87. — Simplb Naphthalene-formula.
Thiele has suggested formula II. (Fig. 86), with inactive double linkings (283), and of those put forward it seems to give the best expression to the properties of naphthalene. The question of what formula most accurately represents the internal structure of the naphthalene molecule is, however, of no practical importance, for, the simple scheme III. (Fig. 87), which leaves the problem unsolved, fully accounts for the isomerism of the derivatives of naphthalene.
As with benzene, partial hydrogenation of naphthalene changes its characteristic aromatic character; for naphthalene dihydridef CioHio, adds bromine as readily as compounds with double linkings.
378. Naphthalene yields a much greater number of substitu- tion-products than benzene, the number obtained corresponding with those theoretically possible for a compound with the for- mula in 377. This fact supports the constitution indicated.
A compound of the formula
H
H
i|H
8
s5 H
H
must yield two isomeric monosubstitution-products. Substitution can take place at a carbon atom directly linked to one of the two C-atoms common to both rings (1, 4, 5, or 8), or at one of the others (2, 3, 6, or 7), which are also similar to one another. Two aeries of moncsubstitution-products are in fact known: thooe in which
§3781 NAPHTHALENE. 556
tjie hydrogen at 1,4, 5, or 8 has been replaced are called a-deriva- tives; when hydrogen is substituted at 2, 3, 6, or 7, the products are termed /?-derivatives.
A great number of disubstitution-products is possible: for two similar substituents it is iO, and for two dissimilar substituents 14. Many of them have been obtained. The ten isomerides are denoted by the numbers
1:2, 1:3, 1:4, 1:5,1:6, 1:7, 1:8, 2:3, 2:6, 2:7.
In any other arrangement the grouping is identical with one of these: thus, 2:5=1:6, and 3:6=2:7, etc. For three similar sub- stituents the number of possible isomerides is much greater, and stillgreater for three dissimilar ones. The disubstitution-products with the substituents in the same ring are called or/Ao, meta, and 'para. When they are in different rings, the compounds are usually distinguished by numbers, or sometimes by letters: thus, a com- pound 4 : 5 is also denoted by aa', and one 3 : 6 by ^^'. The positions 1:8 and 4:5 are also called the pen-positions: in certain respects they resemble the or^Ao-positions. For example, peri-naphthaknedi'
carboxylic acid,
*
/~\-COOH
resembles o->phthalic acid in its ability to form an anhydride.
On account of the great number of isomerides, the orienta- tion of naphthalene derivatives is sometimes diflficult, and the positions occupied by the substituents in many compounds are still uncertain. The same method of orientation is employed as for the benzene derivatives, the conversion of compounds with side-chains in unknown positions into others with substituents in positions that have been determined.
Oxidation is another important aid in their orientation, and is employed to determine whether the substituents are attached to the same ring, or to different rings, as well as their position relative to one another. Thus, suppose the position of the nitro-groups in a dinitronaphthalene has to be determined. If it yields phthalic
556 " ORGANIC CHEMISTRY. [|379
acid on oxidation, the two nitro-groups must be in union with the same ring, that one which' has been removed by oxidation. If a dinitrophthalic acid is formed, this also proves that the two nitro- groups are linked to iijffSAme ring, and the orientation of these groups in this acid should indicate their* relative position in the naphthalene derivative. Lastly, if oxidation yields a monomtro- phthalic acid, one nitro-group is attached to each ring, and orienta- tion of the mononitrophthalic acid obtained will determine the position of one of the nitro-groups.
Substitution-products.
379. The homologues of naphthalene — methyt-derivatives, ethyl-derivatives, etc. — are unimportant. They can be prepared by Frmo's method, or that of Friedel and Crafps (287, 1 and 2).
a-Afe<Ay2napA(Aa2ene is a liquid, and boils at 240^-242^: p-methyU naphthalene is a solid, and melts at 32^. Both are present in coal- tar. Ou oxidation, they yield a-naphlhatc acid and fi^naphihoie acid respectively, which resemble benzoic acid in their properties. The naphthoic acids are converted into naphthalene by distillation with lime.
orChloronaphthalene and ot-bromonaphihalene are respectively formed by the action of chlorine and bromine upon boiling naph- thalene. Although their halogen atom is not so firmly linked as that in monochlorobenzene or monobromobenzene (289), they are not decomposed by boiling with alkalis. A similar stability characterizes the corresponding ^-compounds, which are not obtained by the direct action of halogens upon naphthalene, but can be prepared from other |3-compoiInds, such as amino-deriva- tives, sulpho-derivatives, etc., by the methods described under benzene (307, 4).
The product obtained by the action of concentrated nitric acid upon naphthalene is very important for the orientation of the naphthalene derivatives. It is a^itronaphthalene, M.P. 61^ which IS proved to belong to the a-series by its conversion into the same naphthol as is obtained from phenylvinylaoetic acid (377) .
The position of the substituents in a great number of mono- iubstitution-products can be determined from a knowledge of that ^f the nitro-Kroup in this nitronaphthalene, for the nitro-group
S 379] NAPHTHALEN3 SUBSTITUTION-PRODUCTS, 557
can be reduced to an amino-group, which is replaceable by numer- ous atoms or groups by means of the diazo-reaction. If a mono- substituted naphthalene is known to be an a-compound, its iso- meride must belong to the /?-series.
a-Nitronaphthalene is a yellow, crystalline compound, and melts at 61°. The corresponding /?-compound is similar, and melts at 79°. It is obtained by diazotizing 2-mYro-a-napfc<Ai/i- atnine.
On heating naphthalene with concentrated sulphuric acid at a temperature not exceeding 80°, a-naphthalenemonosidphonic acid is chiefly formed : at 160° the /?-acid is the principal product, owing to the conversion of the a-compound into its fl-isomeride. Both are crystalline and very hygroscopic.
On fusion with caustic potash, the naphthalenesulphonic acids are converted into naphihols, CioHy-OH, with properties very simi- lar to those of phenol. They are present in coal-tar. a-Naphthol melts at 95°, and boils at 282°: p-naphihol melts at 122°, and boils at 288°. The hydroxyl-group in these compounds can be replaced much more readily than that in phenol. They dissolve in alkalis. With ferric chloride a-naphthol yields a flocculent, violet precipi- tate: /?-naphthol gives a green coloration, and a precipitate of fi-dinapfUhol, HO-CioHe-CioHe-OH. The violet precipitate obtained with a-naphthol is po3sibly an iron derivative of a-dinaphthol.
a-Naphthylamine and ^-naphthylnmine, CioTIr-NHg, can be obtained by the reduction of the corresponding nitro-derivatives, but are usually prepared by heating a-naphthol and ^-naphthol respectively with the ammonia compound of zinc chloride or of calcium chloride. a-Naphthylamine is a solid and is also formed by heating naphthalene with sodamide, NH2Na, above 200°, hydrogen being evolved. It melts at 50°, and has a fsecal-like odour: ^-naphthylamine melts at 112°, and is nearly odourless. A mode of distinguishing between the isomerides is afforded by the fact that the salts of the a-compound, but not the ^-compound, give a blue precipitate with ferric chloride and other oxidizing agents.
These bases are of technical importance, since the dyes of the congo-group and the bemopurpurins are derived from them, and pos- sess the important property of dyeing unmordanted cotton.
Congo-red is formed by diazotizing benzidine, and treating the
558 ORGANIC CHEMISTRY. [§380
product with a sulphonic acid of naphthylamine. The dye is the sodium salt of the acid thus formed :
HaN-C6H4-CoH4-NHa ->a-N,-CBH4-CeH4-N2a +2C,oH, <^^ -»
B«osidine BenBidinediasooium chloride NaphthsrlaiDincmil-
phonic acid
-^^^^>C„H,.N:N-CH,.CH4.N:N-C„H.<^^*.
OoDgo-red
The acid itself is blue.
The benzopurpurins differ from congo-red only in having a methyl-group attached to each benzene-nucleus of the benzidine- group.
380. Among the poIysubBtituted naphthalene derivatives is 2'A'dinitrO'a-maph(hol, obtained by the action of nitric acid upon the monosulphonic or disulphonic acid of ce-naphthol. Its sodium salt is Martins' 8 yellow: it dyes wool and silk directly a golden- yellow. Nitration of a-naphtholtrisulphonic acid )delds dinitro- naphtholsulphonic acid, the potassium salt of which is napkthoh yellow: it resists the action of light better than Martius's yellow.
Naphthionic acid is one of the longest-known naphthalene derivatives. It is 1 i^naphihylaminesulphonic acid,
SOoH
NH2
and results from the interaction of a-naphthylamine and sulphuric acid. It is crystalline, and only slightly soluble in water. It is manufactured for the preparation of congo-red and other dyes. Solutions of its salts display an intense reddish-blue fluorescence. Three quinones of naphthalene are known:
CO' o5- ..CO- d
•• ••
o o
a fi amphi Bensoquinone
/
S 381] NAPHTHAQUINONES. 559
a-Naphthaquinone, C10H6O2, is formed by the oxidation of many a-derivatives, and of some di-derivatives, of naphthalene. It is usually prepared from naphthalene itself by oxidation with a boiling solution of chromic acid in glacial acetic acid, a method of formation which has no parallel among those lor the prepara- tion of the corresponding benzene derivatives. It crystallizes from alcohol in deep-yellow needles, melting at 125°. On oxi- dation, it yields phthalic acid, proving both oxygen atoms to be attached to the same ring. With hydroxylamine it yields an oxime. Knowing the structure of a-naphthaquinone, it is possible to determine that of other di-derivatives. If, on oxida- tion, they yield this quinone by elimination of the substituents, they must be l:4-derivatives.
^-Naphthoquinone, C10H6O2, is formed by oxidation of 1:2- aminonaphthol.
ajupin-Naphthaquinone, or 2:6'naphthaquinone, is obtained by oxidation of a benzene-solution of the corresponding dihydroxy- naphthalene with lead peroxide.
The structural formulae indicate that only in the amphi" isomeride is the arrangement of the CO-groups relative to the double bonds similar to that in benzoquinone; and these two quinones are very similar in chemical character. Both oxidize at once a cold, dilute solution of hydriodio acid, turn ferrous ferrocyanide blue, and oxidize sulphurous acid. a-Naphtha- quinone exhibits none of these characteristics, but resembles benzoquinone in odour and volatility. ^-Naphthaquinone does not oxidize dilute hydriodic acid, but turns ferrous ferrocyanide blue, and oxidizes sulphurous acid. Like the ampAi-derivative it is non-volatile, and therefore odourless. Each of the naphtha- quinones has a red colour.
Addition-products;
381. Naphthalene and its derivatives yield addition-products somewhat more readily than the benzene derivatives.
All the intermediate hydrogenation-products of naphthalene from dihydronapkihalene, CioHio, to decahydronapkthalenef CioHw, are known, each member having two hydrogen atoms more than its immediate predecessor. The first-named is obtained by the action of
560 ORGANIC CHEMISTRY. I§381
sodium and alcohol upon naphthalene. Oxidation converts it into o-phenylenediaceHe acid:
H H H H.
h/\/\H Hj^\/\H /\CH..COOH h'^ A > "h^/'I i'H-^^'cH..COOH-
H H H H,
Naphthalene Dihydride o-FbenyleDediacetic acid
Assuming that the formula given represents naphthalene, the hydro- gen is added to the conjugated double linking at the positions 1 :4.
When reduced with sodium and boiling amyl alcohol, /9-naph- thylamine yields a tetrahydride, C10H11NH2, a compound with most of the properties characteristic of the aliphatic amines: it is strongly alkaline, absorbs carbon dioxide from the air, has an ammoniacal odour, and cannot be diazotized. All four hydrogen atoms are in union with the same ring as the amino-group,
H H2
H H2
since, on oxidation with potassum permanganate, the compound is converted into the o-carboxylic acid of dihydrocinnamic acid.
fi TT ^CH2*Cxi2»COOH
which must evidently result from a tetrahydride with the above structure if the oxidation takes place at the C-atom linked to the NH2-group. Moreover, the hydrogen addition-product does not take up bromine, another proof that the four H-atoms are attached to the same benzene-nucleus. The entrance of two hydrogen atoms into each ring would produce a compound with double bonds, capable of yielding an addition-product with bromine.
The reduction-product may, therefore, be regarded as benzene
§381] NAPHTHYLAMINES. 561
with a saturated side-chain, — CH2*CH2-CH(NH2)'CH2 — , linked to two ortho-C'&toms.
a-Naphthylamine can also be reduced by amyl alcohol and sodium, but the tetrahydride formed is different in character from that obtained from ^-naphthylamine, for it possesses all the proper- ties characteristic of the aromatic amines: it can be diazotized, and has no ammoniacal odour. Since, like ^-naphthylamine, it forms no addition-product with bromine, its constitution is
which proves that the four hydrogen atoms in it likewise are in union with the same nucleus, but not the one linked to the amino- group. In support of this view are its completely aromatic character, and the fact that, on oxidation with potassium per- manganate, the ring containing the amino-group is removed, with formation of adipic acid (i6i},
CH2
/\ CH2 COOH
A
H2 COOH
\/ CH2
a-Naphthylamine tetrahydride must, therefore, be looked upon as aniline containing a saturated side-chain, — CH2*CH2*CH2*CHj linked to two or^Ao-C-atoms.
The molecular refraction of benzylamine is 34*12, the calculated value being 34-30; the corresponding values for aniline are 30*27 and 29-72. These facts prove the refraction of benzylamine to be normal; but that of aniline to be abnormal, with an exaltation of 0»55. A similar discrepancy characterizes the reduction-products of a-naphthylamine and j8-naphthylamine. The molecular refraction
562 ORGANIC CHEMISTRY, [( 382
calculated for both is 45*80: the experimental value for the a-com- pound containing an aromatic amino-group, is 46 '66; and that for the i3-compound, with an aliphatic amino-group, is 45-88. Only the amine of aromatic character exhibits an exalted molecular refrac- tion. This example furnishes further evidence of the value of molecular refraction in deciding questions of structure.
n. ANTHRACENE, CuHio.
382. Anthracene is present only in small proportions in coal- tar, varying between 0-25 and 0-45 per cent.; nevertheless, it is the basis of the manufacture of the important dyestufT, alizarin
(385).
The so-called " 50 per cent, anthracene," obtained by distilling
anthracene-oil (286), is distilled with one-third of its weight of
potassium carbonate from an iron retort. Certain impurities are
C H
thereby removed, among them carbazole, • >NH, which is
C6H4
present in considerable proportion in the crude anthracene, and
is thus converted into a non-volatile potassium derivative,
(C6H4)2N-K. The distillate consists almost entirely of anthracene
and phenanthrene: it is treated with carbon disulpbide, which
dissolves out the phenanthrene. By crystallization from benzene,
the anthracene is obtained pure.
It crystallizes in colourless, glistening leaflets, with a fine blue
fluorescence. It melts at 213^ and boils at 351^ It dissolves
readily in boiling benzene, but with difficulty in alcohol and ether.
With picric acid it yields a compound Ci4Hio''C6H2(N02)30H,
melting at 138^
On exposure to light, anthracene is transformed into dtantkracenef which in the dark becomes depolymerized to anthracene, one of the rare instances of a reversible photochemical reaction:
Light ^
2Ci4Hio ^ CjbHjo*
^ Dark
Several modes of preparing anthracene are known which give an insight into its constitution. One of these is its synthesis by
§ 383] ANTHRACENE, 563
Anschutz's method from benzene, aluminium chloride, and tetra- bromoethane:
BrCHBr XHv
C6H«+ I +C6H6 = CeH^C I >C6H4+4HBr. BrCHBr N^H^
Thia synthesis proves that anthracene contains two benzene- nuclei united by the group C2H2, linked to two oWAa-C-atoms of each, as proved for anthraquinone in 383. Its constitutional formula is
7 2
Anthracene
It follows that it must yield a very large number of isomerio substitution-products. Three monosubstitution-products are possible. Numbering the carbon atoms as in the formula, then 1 - 4 « 5 « 8, 2 = 3 «= 6 = 7, and 9 = 10. Fifteen disubstitution- products with similar groups are possible. A very considerable number of anthracene derivatives is known, although it is small in comparison with the enormous number theoretically possible.
The orientation, of the anthracene derivatives is effected simi- larly to those of naphthalene (377), oxidation and a study of the resulting products being an important aid.
Substitution-products.
383. Anthraquinone, Ci4H802, is one of the most important derivatives of anthracene, from which it is obtained by oxidation with such agents as nitric acid and chromic acid. Anthracene is so readily converted into anthraquinone by nitric acid that it is not possible to nitrate it.
Anthraquinone is proved to have the structure
564 ORGANIC CHEMISTRY. [J 383
since it is formed by the interaction of phthalic anhydride and benzene in presence of a dehydrating agent such as aluminium chloride:
C6H4<gg>[OTH7|C6H4 = CeH4<go>C6H4+H20.
Phthalio anhydride
The reaction takes place in two stages: o-benzoylbenzoic acid, C6H4<pQQi| ^ is first formed, and then loses one molecule of water, forming anthraquinone;
CO
C5H4^ NU5H5 — H2O = C6H4<p^>C6H4.
X)OOH ^^
The constitutional formula of anthraquinone indicates that only two isomeric monosubstitution-products are possible. This has been verified by experiment — a further proof that the formula is correct.
The central groups in an,thraquinone, and hence those in anthra- cene, can be proved to be in union with two o-C-atoms in each benzene-nucleus. The method is similar to thatt employed in prov- ing the coastitution of naphthalene (355), the marking of one of the nuclei by the introduction oi a substituent affording a means of identifying the nucleus eliminated by oxidation.
On treatment with benzene and aluminium chloride, hromo- phthalic anhydride reacts analogously to phthalic anhydride, yield- ing bromoanthraquinone by elimination of water from the hromo- hemoylbemolc add first formed:
yCOv r. /C0\ II.
Br.C,H< >0 -* Br.C.H,< X:»H, -♦
\C0/ \C00H
Bromophthalio anhydride Bromobenioylboniolo j yCOv 11.
— ► Br«CeHi^ ^CtH4.
Bromoanthraquinone
Since bromoanthraquinone is a derivative of phthalic acid, its two carbonyl-groups must be united to two o-C-atoms of nucleus I.
§ 384] ANTHRAQUINONE, 565
Its Br-atom can be replaced by a hydroxyl-group by heating with potassium carbonate at 160^, and the hydroxyanlhraquinone thus formed can be oxidized to phthalic acid by the action of nitric acid. These transformations prove nucleus II. to be unattacked, and to have the two carbonyl-groups attached to o-C-atoms:
HO-CJI,'^
COv 11. HO-COv 11.
\co/ HO-CO^"
k 11. HO-COv
>CeH4 -* >
yC«H4.
Hydroxyanthraquinone Phthallo aoid
384. Anthraquinone crystallizes from glacial acetic acid in light-yellow needles, melting at 277°. At higher temperatures it sublimes very readily, forming long, sulphur-yellow prisms. It is very stable, and is not easily attacked by oxidizing agents, or by concentrated nitric acid or sulphuric acid.
The name anthraguirione is in some measure incorrect, for this substance lacks som? of ths properties characteristic of quinones, such as being easily reduced, great volatility, pungent odour, etc., and has much more the character of a diketone. With fused potassium hydroxide it yields benzoic acid, and with hydroxyl- amine an oximc. On warming with zinc-dust and sodium- hydroxide solution, it forms the diso.lium-dcrivative of anthra-
quiiujl,
COH
C6H4<J>C
6H4. COH
Antfaraquinol forms brown crystals melting at 180**, its solutions exhibiting an intense green fluorescence. Its alkaline solution has a deep blood-red colour, and in this condition it is converted into anthraquinone by atmospheric oxidation.
This property of anthraquinol makes its formation a delicate test for anthraquinone. It is effected by warming the substance to be tested with zinc-dust and sodium-hydroxide solution: if anthra- quinone is present, a blood-red coloration is developed, and is destroyed by agitating the mixture with air.
Isomeric with anthraquinol is a ketonic compound, oxarUkrone,
CO H OH
536 ORGANIC CHEMISTRY. [§ 385
It is converted by a cold alcoholic solution of hydrogen chloride into anthraquinol to the extent of 97 per cent., the same reagent effecting the inverse transformation of anthraquinol into oxanthrone to the extent of 3 per cent. Oxanthrone melts at 167*', is colour- less, and does not exhibit fluorescence in solution. Anthraquinol and oxanthrone exemplify a type of desmotropy characterized by the great stability of both forms.
On reduction with tin and hydrochloric acid, anthraquinone is converted into antkrone,
CO
CH2
a substance converted by boiling with alkalis into the tautomeric anthranol,
C-OH
C6H4^ ^C6H4.
CH
In solution, anthranol exhibits a bright-blue fluorescence. It is readily reconverted into anthrone, and anthranol is also produced to some extent by boiling anthrone with dilute acetic acid. -Vnthrone is to be regarded as a pseiuJo-acid, anthranol being its oci-form.
When anthraquinone is more strongly reduced, by heating with zinc-dust, it yields anthracene.
385. Alizarin, or dihydroxyanthraquinone, Ci4H602(OH)2, is the most important derivative of anthraquinone, and is a dye of a splendid red colour. It was formerly manufactured from mad- der-root, which contains a glucoside, rvberytkric acid, C26H280i4. When boiled with dilute sulphuric acid or hydrochloric acid, this glucoside yields dextrose and alizarin:
C26H280i4-h2H20=2C6Hi206 + Ci4H602(OH)2. Rttbersrthrio acid Dextrose Aliiarin
The dye is now prepared almost wholly by a synthetical method. It is one of the organic dyestuffs known in antiquity.
§ 3851 ALIZARIN. 667
In preparing alizarin, the anthracene is first oxidized to anthra- quinone with sodium dichromate and sulphuric acid. Heating with concentrated sulphuric acid at 100** converts various impur- ities into sulphonic acids, the anthraquinone remaining unchanged: on dilution, these sulphonic acids dissolve, so that pure anthra- quinone is left after filtering. This is then heated to 160® with fuming sulphuric acid containing 50 per cent, of sulphur trioxide, the main product being the monosulphonic acid.
It is remarkable that the a-sulphonic acid is formed in presence of a mercury salt, but that otherwise the Sulphonic acid is the product. Catalysts very rarely exert an influence of this type.
The sodium salt of the sulphonic acid is only slightly soluble in water, and separates out when the acid is neutralized with sodium carbonate. On fusing with sodium hydroxide, the sulpho- group is replaced by hydroxyl. A second hydroxyl-group is simultaneously formed, its production being considerably facil- itated by the addition to the reaction-mixture of potassium chlorate as an oxidizing agent :
C6H4<^>C6H3.S03Na-|-3NaOH+0 =
Sodium anthraquinon*- moDoeulphonate
C6H4 < CO >C6H2(ONa)2 +2H2O +Na2S03.
The dye is liberated from the sodimn salt by addition of an acid.
Anthraquinone can be directly oxidized to alizarin by heating it with very concentrated aqueous alkali in presence of certain oxidizers, such as mercuric oxide, potassium chlorate, and so on.
Alizarin crystallizes in red prisms, and sublimes in orange needles, melting at 289^-290®. It is almost insoluble in water, and slightly soluble in alcohol. On accoimt of its phenolic character, it dissolves in alkalis. It yields a diacetate. On distillation with zinc-dust, it is converted into anthracene, a reaction which gave the first insight into the constitution of alizarin.
The value of alizarin as a dye depends upon its power of forming with metallic oxides fine-coloured, insoluble compounds, called
668 ORGANIC CHEMISTRY. [f 385
lakes. When a fabric is mordanted with one of these oxides, it can be dyed with alizarin, the colour depending on the oxide used. The ferric-oxide compound of alizarin is violet-black, the chromium- oxide compound claret-colour, the calcium-oxide compound blue, the aluminium-oxide and tin-oxide compounds various shades of red (Turkey-red), and so on.
The method by which alizarin is prepared proves it to be a derivative of anthraquinone, but the positions of the hydroxyl- groups have still to be determined. The formation of alizarin when phthalic anhydride is heated at 150® with catechol and sulphuric acid proves that both are in the same benzene-nucleus; and, since the hydroxyl-groups in catechol occupy the o-position, the same must be true of alizarin:
CftH4<QQ>0-|-C6H4<Qjj2 '^ C6H4<QQ>C6H2<Qjj2+H20.
Phihalio anhydride Catechol AlUarin
It follows that the choice lies between the two structural formute
O OH
OH I. I I 1 I and II.
The result of nitration proves that formula I. is correct. Two isomeric mononitro-derivatives are obtained, each with the nitro- group in the same nucleus as the hydroxyl-groups, since both can be oxidized to phthalic acid. Formula I. alone admits of the for- mation of two such mononitro-derivatives, and must therefore be correct.
Other hydroxy-derivatives of anthraquinone are also dyes, an example being purpurin or 5:(yiS4rihydroxyarUhraquinoriey
C,H4<(C0),>CeH(0H)„
a constituent of madder-root. The power of the hydroxyanthraqui- nones to form dyes with mordants is conditioned by the presence of two hydroxyl-groups in the orfAo-position to -one another. Other
S 3861 PHENANTHRENE. 569
anthraquinone derivatives with hydroxy 1-groups and amlDo-groups, or with amino-groups only, are also valuable dyes.
The very fast, brilliant colours of the indanihrenrgrcup are derivatives of 2-<iminoanihraquinonet
CO
NH,
000
CO
being obtained by its oxidation. IndarUhrenMue is supposed to have the structural formula
m. PHENANTHRENE, CuHio.
386. Phenanthrene is isomeric with anthracene, and is present with it in " anthracene-oil." They are separated by the method already described (382). It crystallizes in colourless, lustrous plates, which dissolve in alcohol more readily than anthracene, 3aelding a blue fluorescent solution. It melts at 93°, and boils at 340°.
On oxidation with chromic acid, it yields first phenantkra^ guirume, and then diphenic acid (372),
[OOC
COOH
This reaction proves that phenanthrene possesses two benzene- nuclei directly linked to one another, and is therefore a diphenyl- derivative, and also a di-or^Ao-compound. Diphenyl with two hydrogen atoms substituted, — CeH4 -00114—, or — CiaHg — , diflfeni
570 ORGANIC CHEMISTRY, [§386
from phenanthrene by C2H2. This must link together two o-posi- tioDS, so that phenanthrene has the constitution
or
8 7. 6
\5/
1
Phenanthrene
This structure finds support in the conversion of stilbene into phenanthrene, on passing its vapour through a red-hot tube, a method of formation analogous to that of diphenyl from benzene (371) :
CH — G0X15 CH — G0H4
II -Ha -II I .
CH — GgHs CH — C0H4
Stilbene Phenanthrene
In the formula of phenanthrene the group — CH=CH —
and the four carbon atoms of diphenyl yield a third ring of six
carbon atoms. This ring is distinguished from a true benzene*
ring by the facts that the C2H2-group readily takes up brominei
and that on oxidation it behaves as an ordinary side-chain.
C6H4-CO Phenanthraquinone, \ I , is an orange, crystalline sub-
C6H4— CO
stance, melting at 200^, and boiling without decomposition above
360°. Its diketonic character follows from its yielding di-deriva-
tives with sodium hydrogen sulphite and with hydroxylamine. It
is odourless, and non-volatile with steam.
PscHORR has discovered an important synthesis of phenan-'
threne and its derivatives, the condensation of o-nitrobenzalde-
hyde with phenylacetic acid by the Perkin reaction (328) :
CH /^°" /NO,
^O+BsCY \CH:C5<
\COOH X!OOH
o-Nitro- Phenylacetic add c-Phenyl-^nitroeinnamic acid
bensaldehyde
§3S6] PHENANTHRENE. 571
On diazotization of the corresponding amino-acid obtained by reduction, and treatment in sulphuric-acid solution with copper- dust (307), nitrogen and water are eliminated; and an almost quantitative yield of p-phenanthrenecarboxylic acid obtained:
CH CH CH
DUio-deriTataye of o-phenyl* • PhenAnthren*- Phenanthrene
o-aminodimamic acid carbozylio acid
On distillation, this acid loses carbon dioxide, forming phenan- threne.
When the methyl ether of o-nitrovanillin is substituted for o-nitrobenzaldehyde, there results a dimethoxyphenanthrene, dimethylmorphol, also formed by the breaking down of morphine
(413) :
CH
GH3OI Jn02 + J -> CH30'^. >v^
>fcH3 A «^«^
Methyl ether of o-nitrovuiillin PTT
0CH3I J
Dimethylmorphol
B. HETEROCYCLIC COMPOUNDS.
NUCLEI CONTAINING NITROGEN, OXYGEN, AND
SULPHUR.
L PTRIDINE, CiH,N.
387. Pyridine and some of its homologues are constituents of coal-tar. On mixing the " light oil '' (286) with sulphuric acid, they are absorbed by the latter, and separate on addition of sodium car- bonate in the form of a dark-brown, basic oil, from which pyridine and its homologues are obtained by fractional distillation. Pre- pared by this method, pyridine is never quite pure, always con- taining small proportions of its homologues.
Another source of pyridine is " Dippel's oil," a liquid of ex- tremely disagreeable odour, obtained by the dry distillation of bones which have not been deprived of their fat. It is a very complicated substance, containing, in addition to the pyridine bases and quinoline, many other substances, such as nitriles, amines, and hydrocarbons.
Pyridine is a colourless liquid boiling at 115®, and with a specific gravity of 1-0033 at 0®. It is miscible with water in all propor- tions, and has a weak alkaline reaction, colouring aqueous solutions of litmus only purple. It has a very characteristic odour, reminis- cent of tobacco-smoke, and is a constituent of crude ammonia. It is very stable, being unattacked by boiling nitric acid or chromic acid. It reacts with sulphuric acid only at high temperatures, yielding a sulphonic acid. The halogens have very slight action on it. On very energetic reduction with hydriodic acid at 300°, it yields normal pentane and ammonia.
Being a base it forms salts with acids, mostly readily soluble in water.
Pyridine ferroq/anide dissolves with difficulty, and is employed in the purification of the base. With platinum chloride, the hydro-
672
§ 388] PYRIDINE. 573
chloride yields a double salt, (CiHiN)sHsPtCl6, freely soluble in water. When the solution is boiled, two molecules of hydrochloric acid are eliminated, with production of a yellow compound, (CiHtN)iPtCU, which is only slightly soluble in water: the reaction affords a delicate test for pyridine.
The following test is also very delicate. On warming the base with methyl iodide, an energetic reaction takes place, with forma- tion of an addition-product, CJItN •CHJ. When warmed with solid potash, this compound gives off a very pungent and disagreeable odour.
3f88. Many methods for the synthesis of pyridine and its homo- logues are known, although but few of them afford insight into its constitution. Among them is the formation of pyridine from quinoline (400) ; that of piperidiTie from pentamethylenedlamine is mentioned in 159. Piperidine can be oxidized to pyridine by heating with sulphuric acid :
H
<CH2 — CH2V /C'CH
>NH-*HQC >N. CH2— ch/ \c.ch
Piperidine J]
Pyridine
The formation of ^-chloropyridine from pyrrole is described in 395-
The converse of these syntheses is the decomposition of piperi- dine, discovered by von Braun. On treatment of bemaylpiperidine, CsH,oN-COCi,Hs, with phosphorus pentabromide, PBrs, the oxygen is replaced by two bromine atoms. Distillation converts this dibromo-derivati ve into pentameihylene dibromide and benzonitrile :
XH,-CHjv XHj.CHj.Br
CH2C >N-CBr,-CeH5 - CH,^ +NC-CbH5.
^CHj.CH/ ^CH2-CH,.Br
A practical method is thus afforded of preparing pentamethylene dibromide, a substance of importance in various syntheses.
Since pyridine is reduced to piperidine by sodium and alco- hol, and piperidine can be oxidized to pyridine, it may be assumed that pyridine has the same closed chain as piperidine; thai is, one of five C-atoms and one N-atom. Moreover, it can be proved that
574 ORGANIC CHEMISTRY. [§388
the N-atom in pyridine is not linked to hydrogen; for, while piperi- dine possesses the character of a secondary amine, yielding a nitroso- derivative, for example, pyridine has that of a tertiary amine; thus, it yields an addition-product with methyl iodide (387), and the iodine atom in this substance, like that in other ammonium iodides, can be exchanged for hydroxyl by means of moist silver oxide.
The number of isomeric substitution-products, like that of ben- zene (282), indicates that each carbon atom is in union with one hydrogen atom. A substance of the formula
|
N |
N |
|
|
0 2 |
«'A |
|
|
or |
||
|
6 8 V |
^v |
|
|
r |
a
Fhould yield three monosubstitution-products, 2(a)=6(a0f 3(^)=5(^), and 4(/-). Moreover, for similar substituents, six disubstitution*product8 are possible: 2:3 « 6:5; 3:4 « 5:4; 2:4 = 6:4; 2:6, 3:5, and 2:5 = 6:3. This view agrees with the results of experiment. The mode of linking of three out of the four valencies of each carbon atom is thus established, and that of two of the three nitrogen valencies: it remains only to determine how the fourth valency of each carbon atom and the third valency of the nitrogen atom are distributed in the molecule.
The marked analogy between benzene and pyridine leads to the assumption of analogous formulae for both (283). The great stabil- ity of pyridine towards energetic chemical reagents proves that it does not possess double Unkings. Only the side-chains of both compounds are attacked by oxidizing agents: with sulphuric acid, both yield sulphonic acids, which are converted by fusion with caustic potash into hydroxyl-derivatives, and by heating with potassium cyanide into cyanides. At 330°, pyridine is converted by a mixture of fuming sulphuric acid and nitric acid into )3- nitropyridine, colourless needles melting at 41**, and boiling at 216®. The hydroxyl-derivatives of pyridine have a phenolic character: they yield characteristic colorations with ferric chloride. Pyridine must, therefore, be regarded as benzene with one of its CH- groups replaced by a N-atom.
The principle of the orientation of p3rridine is the same as that
§ 389] HOMOLOGUES OF PYRIDINE. 675
of benzene — conversion of a compound of unknown structure into one with its side-chains in known positions. The monocarboxylic acids and dicarboxylic acids have served as the main basis for its orientation. The method of ascertaining the positions occupied by the carboxyl-groups in these compounds is described in 391.
Homoiogues of Pyridine.
389. The homoiogues of pyridine are the methylpyridines or picolines, dimethylpyridines or liUidines, and trimethylpyridines or coUidines. Many of them can be obtained by more or less complex methods: thus, /?-picoline is formed by the distillation of acralde- hyde-ammonia (141), and coUidine by the distillation of crotonalde- hyde-ammonia. The formation of pyridine and its homoiogues by the dry distillation of bones depends upon these reactions: under the influence of heat, the fat present yields acraldehyde, which reacts with the ammonia resulting from the heating of the proteins, forming pyridine bases.
When a mixture of acetylene and ammonia is passed over oxide of aluminium, ferric oxide, or chromimn sesquioxide at 300^„ a-picoline, 7-picoline, and some higher homoiogues are produced. Owing to the presence of a trace of moisture, acetaldehyde is first formed, and imites with ammonia, yielding acetaldehydeanmionia.
Hantzsch has discovered an important synthesis of pyridine derivatives - the condensation of one molecule of aldehyde-ammonia with two molecules of ethyl acetoacetate :
CH,
OCH CiH,0-OC-CHj CHj-00-OC,H,
CH,-CO CO-CH,
HNHj
CH,
CaH,OOC-C C-COOCH,
11 II + 3HA
CHjC C-CH,
\N/ • H
DitthTl dihydrocoIlidiiiedioarboxyUto
576 ORGANIC CHEMISTRY. [| 390
On oxidation with nitrous acid, this substance loses two H-atoms, one from the CH-group and one from the NH-group, with formar tion of ethyl coUidinedicarbaxylate. On saponification with caustic potash, and subsequent heating of the potassium salt with quick- lime, the carboxyl-groups are eliminated, and ooUidinei
CH,
O
N distils.
In this synthesis acetaldehyde may be replaced by other alde- hydes, and ethyl acetoacetate by the esters of other P-ketordc acids, so that it affords a method of preparing numerous pyridine deriva- tives.
Some of the homologues of pyridine can be obtained from it by the action of an alkyl iodide, an addition-product being formed. On heating this compound to 300**, the alkyl-group be- comes detached from the nitrogen atom and linked to a carbon atom, a reaction analogous to the formation of p-toluidine by heating methylaniline hydrochloride to a high temperature (399).
390. a-Propenylpyridine is of theoretical importance. Laden- burg obtained it by the condensation of a-picoline with acetalde- hyde:
NC5H4-CH3+OCH.CH8=NC6H4-CH:CH.CH8+H20.
ct-Piooline Acetaldehyde o-Propenylpyridine
By its aid he effected the first synthesis of a natural alkaloid, that of coniine, CsHijN (409). a -Propenylpyridine was reduced with sodium and boiling alcohol, yielding a-propylpiperidine,
rlHa 'H •CH2 •CH2 •uH8' H
optically inactive, like all synthetical substances prepared from inactive material. This substance was resolved into a dextro- rotatory and a laevo-rotatory modification by fractional cr3ratal- lization of its tartrate, the dextro-rotatory isomeride being named iaoconiine because heating at 300^ transforms it into an
5391]
PYRIDINECARBOXYLIC ACIDS.
577
isomeride identical with natural conilne. Ladenburg attributes the difference between coniine and Moooniine to asynunetry of the nitrogen atom.
The constitutional formula of a-propylpiperidine indicates that the carbon atom in union with the propyl-group is asjrmmetric. 7-Propy]piperidine does not contain an asynmietric carbon atom, and should therefore be optically inactive. The side-chain can- not be at the jS-position, for conilne jrields ammonia and normal octane when strongly heated with hydriodic acid. Thus treated, a ^propylpiperidine or 7-propylpiperidine must yield an octane with a branched carbon-chain, which proves that conilne is an o-compoimd
Piperidine is present in pepper in combination as piperine, CitHiiOiN. On boiling with alkalis, it yields piperic acid (353), C11H10O4, and piperidine, by addition of one molecule of water. Piperine must, therefore, be a substituted amide of piperic acid, containing the piperidine-residue, C»HioN — , instead of the NHi. group:
CH:
<
/\
CH:CH.CH:CH.C0.N
V
Pipeline
HtCl JCHt CH,
Piperidine is a colourless liquid, boiling at 106®, with a charac- teristic pepper-like odour and strongly-marked basic properties (159). It is best obtained by the electro-reduction of pyridine.
, lie Adds. pyridi
N
'^COOH
1
Picolinie .dd (a) M.P. 136*
N
COOH
and
Nieotinio avid (ff) M.P. 331*
N
"%
OOH
itoNiootinic add (y) M.P. dOQ^'
The orientation of the carboxyl-groups in these acids can be carried out as follows. It is stated in 3Q0 that the side-chain in conilne occupies the cr-position. On oxidation, this substance yields pico-
578
ORGANIC CHEMISTRY,
[|391
linic acid, by conversion of the propyl-group into a carboxyl-group, and elimination of the six added hydrogen atoms. Picolinic acid is therefore the a-carboxylic acid.
Nicotinic acid is proved to have the ^-constitution thus. Quino- line (400) haj3 the formula
It is naphthalene with one of the a-CH-groups replaced by N. On oxidation, quinoline yields a p3rridinedicarboxylic acid, quinolinic acid, which must therefore have the structure
N /\C00H
fi
COOH
\/
On heating this acid, one molecule of carbon dioxide is eliminated, with formation* of nicotinic acid. Since the carboxyl-group in picolinic acid has been proved to occupy the a-position, nicotinic acid must be the /?-acid. There remains only the ^'-fltructure for isonicotinic acid.
The pyridinemonocarboxylic acids are formed by the oxidation of the homologues of pyridine containing a dide-chain. Nicotinic acid derives its name from its formation by the oxidation of nico- tine. The monocarboxylic acids are crjrstalline, and possess both a basic and an acidic character. As bases, they yield salts with acids, and double salts with platinum chloride and mercuric chloride, etc. As acids, they form salts with bases, the copper salts being often employed in their separation.
Picolinic acid can be distinguished from its isomerides by two properties: on heating, it loses CO2 more readily, with formation of pyridine; and it gives a yellowish-red coloration with ferrous sulphate. Quinolinic acid answers to the same tests: it may, there- fore, be concluded that they are applicable to acids with a carboxyl- group in the a-position.
S 3921 FURAN. 579
n. [FURAN,* C4H4O. 392. Furan, C4H4O, B.P. 36*^, is of little importance, but two of its substitution-products must be considered in some detail. To furan is assigned the ring-formula
0 0 0
HC CH [» ^ a
4 3
hU> °'
;h
or
This formula is supported by the resemblance in properties between some of its derivatives, such as furfuraldekyde (furfural or furfvroU),
C4H30*Cq, and the corresponding benzene derivatives. More- over, the O-atom can be proved to be linked similarly to that of ethylene oxide (150), for on treatment with sodium, furan does not evolve hydrogen, proving the absence of a hydroxyl-group; and it does not react with hydroxylamine or phenylhydrazine, indicating that it has no carbonyl-group.
Furan derivatives can be obtained from the l:4-diketoneB, R 'CO -0112 -0112 'CO -R, by treatment with dehydrating agents, such as acetyl chloride. This reaction may be regarded as the restilt of the conversion of the diketone into an unstable, tauto*
. , R-C:CH-CH:C-R ^. ^ , menc form, • • , which loses water:
OH OH
* The Chemical Society of London adopts the name furan for the O
simple ring [ ] , the corresponding radical being fvryl. The double syl-
^f).
hblefurfiar ... is reserved for derivatives with a side-chain, oontainins the O
ringQ"^
530
ORGANIC CHEMISTRY.
[§ 393
This method yielis 2t5-furan derivatives, the C-atoms in furan being denoted as in the scheme previously indicated.
This synthesis of furan derivatives is likewise a proof of their constitution.
393. The most important derivatives of furan are /i*r/uraWe-
AycfeC4H30»CQ, and pyrormicic acid, C^HaO-COOH: both have
long been known.
Furfuraldehyde is prepared from pentoses by the method men- tioned in 207. It has the character of an aromatic aldehyde: like benzaldehyde (314), it is converted by alcoholic potash into the corresponding acid, pyromucic acid, and the corresponding alcohol, furfuryl alcohol, C4H3O.CH2OH:
'0
ForfimldeliycU
V
V jCOOH
o
Pyxomacie acid
n
, 'CHjOH.
\/
O
Furfuryl aleohbl
With ammonia it jrields furfuramide, (C5H40)3N2, analogous in composition to hydrobenzamide (315) . Just as benzaldehyde con- denses in presence of potassium cyanide to benzoin (376), furfur- aldehyde under the same conditions yields the similarly constituted
H
furfuroin, C4H80-C- CO -041180. The resemblance in properties
OH between the two compounds is, therefore, very striking.
Furfuraldehyde is proved to have the 2-Btructure by various means: for example, by its formation from pentoses (207), a reac- tion which may be represented by the scheme:
JH-(V10H I I \
B11
Pantoie
^
Ah=c>,
o
IViTfunldehyds
§ 3931 FURFURALDEHYDB, 581
Furfunddehyde thus results from the elimination of three molecules of water under the influence of hydrochloric acid or sulphuric acid. It is a colourless, oily liquid of agreeable colour, and boils at 162°. A test for it is described in 207.
Analogous to the conversion of pentoses into furfuraldehyde is that of ketohexoses into hydroxymethylfurfuraldehyde,
HC — CH HO-CH,-C C.C^,
o
effected by heating with dilute acids. The structure of this sub- stance is proved by its oxidation to the dibasic dehydromucic acid,
HC — CH
II II HOOC-C C-COOH.
\/
o
Heating with hydrochloric acid or dilute sulphuric acid converts hydroxymethylfurfunddehyde ahnost quantitatively into formic acid and Ifevulic acid:
C*HeO,+2H,0 »H*COOH+C»HaO,.
Sydroxymethvl- L«vulio
furfuraldehycle add
The formation of hydroxymethylfurfurafdehyde is the cause of certain reactions exhibited by the hexoses. When heated with resorcinol and concentrated hydrochloric acid, it yields a dark-red precipitate. This reaction serves to distinguish the artificial honey made from invert-sugar (309) from the natural product, since in the inversion of the sucrose by heating with dilute acid a small proportion of hydrox3rmethylJriLrfuraldehyde is formed.
As its name indicates, pyromucic acid is formed by the dry dis- tillation of mucic acid 210). It can also be obtained by oxidiz- ing furfuraldehyde with silver oxide. It is crystalline, melts at 132°, can be readily sublimed, and dissolves freely in hot water. When heated at 275° in a sealed tube, it yields carbon dioxide and furan.
682 OBOANIC CHEMISTRY. [f 394
In physical properties pyromucic acid resembles benzoic acid, being readily sublimed, and cr3rstallizing in similar colourless leaflets. In chemical character it resembles the aromatic com- pounds in a few reactions only, an example being its conversion into a sulphonic acid by means of fuming sulphuric acid. In most of its chemical properties its behaviour approximates more closely to that of an unsaturated aliphatic acid. Thus, it easily undergoes oxidation: it almost instantaneously decolorizes von Baeter's reagent (113), and readily adds four bromine atoms. Hence, the distinguishing characteristics of the benzene-nucleus are absent, so that the formula
HC=CH
I >0 HC=C
i
JOOH with two double bonds, must be assigned to it.
in. PYRROLE, C4H5N.
3g4, P3rrrole is the most important of the heterocyclic com- pounds With a ring of five atoms. Several natural products con- taining the pyrrole-nucleus are known: examples are the colouring- matter of blood; chlorophyll; and certain alkaloids, among them nicotine. Pyrrole derivatives have also been found among the decomposition-prod^icts of proteins. Pyrrole is a constituent of " Dippel's oil" (387). The fraction of this oil which distUs between 120® and 130® is employed in the preparation of pyrrole. After removal of the pyridine bases by treatment with dilute sulphuric acid, and of the nitriles by boiling with sodium carbonate, the frac- tion is dried, and treated with potassium. Potassiopyrrole, C4ll4NKy b formed, and can be purified by washing with ether. It is recon- verted into pyrrole by the action of water.
Pyrrole is a colourless liquid, specifically somewhat lighter than water, and boiling at 131®. On exposure to light, it soon acquires a brown colour. The vapours of pyrrole and its derivatives impart a carmine-red colour to a wood-shaving moistened with hydro- chloric acid, due to the formation of an amorphous substance.
S3d5]
PYRROLE.
583
** pyrrole-red." This reaction furnishes a delicate test for pyrrole and its derivatives.
Pyrrole can be 83mthe8ized by several methods: for example, by the interaction of succindialdehyde and ammonia:
i
CHa— C^+NHa CHj— CH<25 Ha-C^ + NHa "° CH2-CH<2h'
-I >NH + NH3+2HaO.
:CH PycTola
Inversely, siuxinald-dioxime is obtained from pyrrole by the action of hydroxylamine, ammonia being evolved.
The homologues of pyrrole are produced by the interaction of ammonia and i:4-diketone3:
.R
^9=^|0U , H
NH
\r
1 : 4-Diketone (tautomeric form)
/R
Hc=c<:
I >NH+2H80.
HC=C<
\R
oa'-Pyrrole
The nomenclature of the pyrrole derivatives is indicated in the scheme
NH NH
■^
or
/\
^
a.
fi
This structure is inferred from the foregoing S3mthese8 and other- wise. The basic properties which should be characteristic of a substance with the formula of pyrrole are masked by the resinifying action of acids. As a result of this influence, no sulpho-acids have been obtained, and nitro-derivatives only by an indirect method.
395. Among the properties of pyrrole indicating its relation to the aromatic compounds is its behaviour with halogens: unlike an aUphatic unsaturated compound, it yields substitution-products, but not addition-products. The analogy in properties between pyrrole and aniline, and especially phenol, is very marked. The transformation of l-methylpyrrole into 2'methylpyrrole under
584 ORGANIC CHEMISTRY. [f 395
the influence of heat resembles the conversion of methylaniline into p-toluidine (299) :
C4H4N-CH3 -> C4H3(CH3)-NH.
l-Methylpyrrole S-Metbylpjrrroto
Just as sodium phenoxide is converted by carbon dioxide into
salicylic acid (344), so potassiopyrrole and carbon dioxide yield 2-pyrrolecarboxylic acid. Like phenol, pyrrole unites with ben- zenediazonium chloride, with elimination of hydrochloric acid (309). When pyrrole is treated with chloroform in presence of sodium alkoxide, a notable reaction ensues. The C-atom of the chloroform takes up a position between two of the C-atoms of the pyrrole- nucleus, forming ^^Moropi^ridine:
NH N
/\
+ CHa8-»
Pyrrole /S-ChloropyridiDe
On reduction with zinc-dust and cold hydrochloric acid, pyrrole takes up two hydrogen atoms, forming 2i3'dihydrapyrr6le, C4H7N1 which boils at 91^. Like the partial reduction-products of aromatic compounds, dihydropyrrole behaves as an xmsaturated compound, another indication of the aromatic character of pyrrole.
Very important researches have been carried out in recent years by WiLLSTATTBB and Stoll on chlorophyU. This substance is indis- pensable for the assimilation process, and constitutes 0*6 to 1 •2 per cent, of the weight of the dried leaves. Its molecule contains mag- nesium in complex combination. Towards alkalis the magnesium- complex is very stable, but the metal is readily eliminated from the molecule by means of acids.
Chlorophyll is saponified by caustic alkahs, with formation of an unsaturated alcohol named phytol, CmHi«OH. During the reaction the alkali combines with polybasic acids, the chlorophylUnSf sub- stances convertible into an oxygen-free product, o/diophyUin, CjiH«4N4Mg, by elimination of the carboxyl-groups. Acids replace the magnesium atom in this compound by two hydrogen atoms, forming aetioporphorifif CsiHmN4. This derivative can also be ob- tained from haemin (350), an indication of the relationship of chlorophyll to haemoglobin, the colouring matter of blood.
Reduction of aetioporphorin yields a mixture of pyrrole homo- logues, each nitrogen atom being associated with a pyrrole-nucleus.
S 3961 THIOPHEN. 585
The chlorophyll of all plants ifi identical, and consists of a mixture of two related compounds, chlorophyll-a and chlorophyll-6, there being about one molecule of & to three molecules of a. Their form- uhe are
, and GioHsi
<OOCH, • OOCtoHit
IV. THIOPHEN, CaH^S.
396. Thiophen has a more aromatic character than furan or pyr- role. It is present in the crude benzene obtained from coal-tar (286) to the extent of about 0*5 per cent.: its homologues, thiotolen or methyl thiophen, and thioxen or dimethyl thiophen, are contained in toluene and xylene from the same source.
Thiophen was first obtained by Victor Meyer by agitating coal-tar benzene with small amounts of concentrated sulphuric acid till it ceased to give the indophenvnrreacHon^ a blue coloration with isatin (403) and concentrated sulphuric acid. By this treat- ment the thiophen is converted into a sulphonic acid, from which it can be regenerated by the action of superheated steam.
A better method for the separation of benzene and thiophen is to boil the crude benzene with mercuric oxide and acetic acid. The thiophen is precipitated as thiophen mercury oxyacetate, C4HfS(HgOOC-CH,)-HgOH, which is reconverted into thiophen by distillation with moderately concentrated hydrochloric acid. It is formed by passing acetylene over pyrites at 300°.
Thiophen can be synthesized by various methods. The interaction of acetylene and iron pyrites, FeS2, at about 300° yields a liquid containing 50 per cent, of thiophen:
CH CH HC— CH
III III -^ II II
CH-fS + CH HC CH.
\/
8
When sodium succinate is heated with phosphorus pentasulphide, a vigorous reaction ensues, carbon disulphide is evolved, and a liquid, consisting chiefly of thiophen, distils.
586 ORGANIC CHEMISTRY. [f 396
It L9 a colourless liquid, boiling at 84^, a temperature which differs little from the boiling-point of benzene (80*4^. It has a faint, non-characteristic odour. It is heavier than water, its specific gravity being 1-062 at 23''.
Bromine reacts energetically with thiophen, forming chiefly dibromothiojAen, C4H2Br2S, along with a small proportion of the monobromo-derivative.
The notation of thiophen derivatives is indicated by the sch^nes
S S
and
The homologues of thiophen can be obtained by Fimo's syn- theeis (387) and by other methods: for instance, by heating 1:4- diketones with phosphorus pentasulphide, a mode of synthesis which proves the constitution of the thiophen homologues. Thus, acetonylacetone yields dimethyUhiophen:
, , , a'/\a
fi
I \0H ^?=^
1/
^
HC=C^ Xprr
\CH3 ^»
Aoetonylaoetone 2 : 6-Dtmethylthiophen (tautomeric fonn)
2:5-Dialkylthiophens are obtained from l:4-diketone6: the 3:4-alkyl-compounds can be prepared by another method. As stated, thiophen results from the interaction of succinic acid and phosphorus pentasulphide:
H H2C— COOH HC=Cv
H2C-COOH "^ HC=C-^*
H
Sueotnie aotd Thiopliea
Similarly, a monoalkylsuccinic and synmietrical diaUcylsao- cinic acid respectively yield a 3-alkylthiophen and a 3 : 4-alkyl- thiophen:
iS 397, 3981 PYRAZOLB. 687
CHa-CH— COOH CHa-C— CH
I - I >S.
CH3.CH-COOH CH3C-CH
Symmetrical dimethyl- 8:4*I>imethyl-
suocinio acid thiophAo
Tho known structure of these compounds can be employed as a basis for the orientation of the derivatives of thiophen.
397* When a cold aqueous solution of the two monocarboxylie acids, 2-4hiophencarboxylic acid and 34hiaphencarboxylic acid,
S S
Hi
is crystallized slowly, there is formed a mixture wliich cannot be resolved into its components. This phenomenon is due to the formation of mixed crystals, and is of rare occurrence with posi- tion-isomerides.
A thiophensidphonic acid is also known : it is more easily formed than benzenesulphonic acid, which is the basis of Victor Meyer's method of separating thiophen and benzene.
When a mixture of acetic anhydride and concentrated nitric acid is added to thiophen, mononitrothiophen is formed. It is a solid, melting at 44^, and boiling at 224^: it has an odour like that of nitrobenzene. On reduction, it yields aminothiophen, or thiophenine, which differs from aniline in being very unstable : it changes quickly to a varnish-like mass, but its hydrochloride is stable. It does not yield diazo-compounds, but reacts with benzenediazonium chloride, forming a crystalline, orange dye.
V. PTRAZOLB, C3H4N2.
398. Pyrazole derivatives are produced by the interaction of the esters of unsaturated acids and ethyl diazoacetate. An example is the union with explosive energy of diethyl acetylenedicarboxylate and ethyl diazoacetate to form trieihyl pyrazoletricarboxylate:
C2H600C-C CH*COOC2H6 C2H600C*C C*C00C2H5
C2H5OOC • C + •N = C2H6OOC • C N
Diethyl acetylene- ^ -u
diearboxylate Triethyl pyrasoletrioarbozyUte
588
ORGANIC CHEMISTRY.
[fad9
Pyrazde is formed in several reactions, one of them being the combination of hydrazine with propiolaldehydeacetal (142) :
CH^C.CH(OC2H5)2+n2N.NH2 «
Propiolaldehydeacetal
- CH=CCH=N-NH2+2C2HsOH;
Intermediate product (not isolated)
C— CH
H /^ NH2
Intermediate product
i!
CH— CH CH. /^''
\nh
Pyrasole
or
NH
4 3
This synthesis proves that p3rrazole has the formula indicated, so that it may be regarded as pyrrole in which one of the CH-groups has been replaced by N.
It is crystalline, melts at 70®, and is very stable. It is only a weak base, for its aqueous solution has a neutral reaction.
Pyrazole has a much more aromatic character than pyrrole. It is very stable towards oxidation, and can be sulphonated and nitrated like benzene. The halogen atom in its monohalogen derivatives can be eliminated only with great difficulty.
The identity of the 3-derivatives and the ^-derivatives of pyrazole is of theoretical interest, since the structural formula given indicates that they should be dissimilar. On replacing the hydrogen atom of the imino-group by alkyl or phenyl, the deriv- atives with substituents at positions 3 and 5 are no longer identical. Since migration of the hydrogen atom from one nitrogen atom to the other, with a simultaneous migration of the double bonds, makes position 3 equivalent to position 5, it must be assumed that free pyrazole readily undergoes this type of tautomerization:
NH
6 2
4 8
N
R
NH
rAn
4 3
399* The derivatives of pyrazole are not important, but there are valuable products related to its dihydrlde, vyrazoline^ C3H6N2. Substances of this type are prepared by condensing ethyl diaxo- acetate with esters containing a double linking:
{ 399] PYRAZOLINE DERIVATIVES. 589
CaHjOOC-CH CH.COOCjHs CsHsOOCCH— C-COOCsHs
C2H8OOC.CH+ l^N -C2H5OOC.CH N
^ \/
NH
Diethyl f umanta Triethyl pyruolinetrioarboiylate
Pyrazoline (I.) is fonned^ by the interaction of hydrazine hydrate and acraldehyde. Bromine cont^erts it into pyrazole. Pyrazolone (II.) is a ketonic derivative of pyrazoline:
NH NH
H2C N OG N
H2C— CH H2C— CH
I. It
Substitution-products of pyrazolone are obtained by the interac- tion of ethyl acetoacetate and phenylhydrazine:
CHa— C O H2 N CHs • C=K
C— CO.fOC^lS HlNCeHs HaC—CCr
GeHft.
Methylphenylpyrazolone is thus formed. Methylphenylhydrazine, CeHs'NH^NH'CHa, condenses similarly with ethyl acetoacetate, yielding a dimethylphenylpyrazolone of the formula
CHs-C— N(CH8)
11 >r
HC— CO
jl >N.C6H6. C— (
This substance is called " antipyrine," and was discovered by Kkorr; it is extensively employed in medicine as a febrifuge. It crystallizes in white leaflets melting at 113^. It cannot be distilled without undergoing decomposition. It is readily soluble in water and alcohol: the aqueous solution gives a red coloration with ferric chloride, and a bluidh-green coloration with nitrous acid. '' Salip3rrine " is a compound of antipyrine and salicylic acid.
CONDENSATION-PRODUCTS OF BENZENE AND
HETEROCYCUC NUCLEI.
L QUINOLINB, C1H7N.
400. Quinoline is present in coal-tar and bone-oil,but is difficult to obtain pure from these sources. It is prepared by Skraup's synthesis, described below. It is a colourless, highly refractive liquid of characteristic odour: it boils at 236^, and has a specific gravity of 1 • 1081 at OP. It has the character of a tertiary base, so that it possesses no hydrogen linked to nitrogen. It yields salts with acids: the dichromate, (C9H7N)2H2Cr207, dissolves with diflS- culty in water.
Quinoline can be synthesized by various methods which prove its constitution. Its synthesis was first effected by Konigs, by passing allylaniline-vapour over red-hot oxide of lead:
H NH H N
H dks H H
AUylaniline
Skraup's synthesis consists in heating together aniline, glycerol, sulphuric acid, and nitrobenzene. In presence of sulphuric acid as a dehydrating agent, the glycerol loses water, forming acraldehyde, which unites with the aniline to an addition-product,
C6H5 • NH • CH2 • CH2 • C/-W .
In KoNio's S3mthesis the oxidizing agent is the lead oxide; in this reaction it is the nitrobenzene, which is reduced to aniline. Arsenic acid can be substituted for nitrobenzene.
Von Baeter and Drewsen have discovered another method of synthesis which proves the constitution of quinoline: it involves
590
S 4011 QVINOUNE. 591
the reduction of o-nitrocinnamaldehyde. This compound is first converted into an intermediate product, the corresponding amino- derivative, the H-atoms of the NH2-group of this substance being subsequently eliminated along with the 0-atom of the aldehyde- group:
t^Aminoeiimainaldehyde QaiDc^ne
The last synthesis proves quinoline to be an or^Ao-substituted benzene: the constitution of the ring containing the N-atom has now to be determined. The method employed is based upon oxi* dation, which produces a dibasic acid, quinolinic acid,
N
hooc/\h hooc^Jh*
On distillation with quicklime, quinolinic acid yields pyridine. From these facts it must be concluded that quinoline contains a benzene-nucleus and a pyridine-nucleus, with two or^Ao-C-atoms common to both. It may be regarded as naphthalene* with one of the CH-groups, 1-4-5-8, replaced by N.
The number of isomeric substitution-products is very large. The seven hydrogen atoms occupy dissimilar positions relative to the nitrogen atom, and consequently seven monosubstitution- products are possible. Twenty-one disubstitution-products are possible for similar substituents, while the number of tri-derivatives possible is much greater, and so on.
40X. There are three methods for the orientation of quinoline derivatives.
First, the relative method (354, 1) .
Second, oxidation. This process usually removes the benzene- nucleus, leaving the pyridine-nucleus intact, and thus furnishes a means of determining which substituents are present in each.
592
ORGANIC CHEMISTRY.
nm
Third, Skraup's synthesis — ^an important aid to orientation. It can bo carried out not only with aniline, but with many of its substitution-products, such as homologues of aniline, nitroanilineB, aminophenols, and other derivatives. The quinoline compx>unds thus obtained have their substituents in the benzene-nucleus. But this synthesis also indicates the positions of the side-chains when an ortiio-Bubstituted or a para-substituted aniline is used: thus.
X N
can only yield
waQQ.
and
N
only
00
can yield
N
00
or
All four possible quinoline derivatives with substituents in the benzene-nucleus can, therefore, be prepared by Skraup's syn- thesis.
The nomenclature of the quinoline derivatives is indicated in the scheme
Many of the known quinoline derivatives are obtained by Skraup's method, a smaller number directly from quinoline. The sulphonic acids are best prepared by the latter method. On fusion with caustic potash, they are converted into hydroxyquinolines; when heated with potassium cyanide, they yield cyanoquinolines, which on hydrolysis give carboxylic acids.
IS 402, 403] iaoQUINOLINB AND INDOLE. 693
Carhoatyril, or 2-hydroxyqiiinolme, can be synthesised by the elimination of water from o-aminocinnamic acid:
, N NH
/N|HaO|C-OH
C6H4< I - H2O =
X3H=CH
tf-Amipocinnamio acid I. ' Carbostyril
Formula II. must be ascribed to the free compound, since its absorption-curve in the ultraviolet region almost coincides with that of a derivative methylated at the nitrogen atom (337). Since carbostyril also has phenolic properties, being soluble in alkalis, and reprecipitated from alkaline solution by carbon dioxide, it is susceptible of transformation into the tautomeric form I.
II. tsoQUraOLINE, CtHrN.
403. is/oOvinoline is present in coal-tar, from which Hoogewebff and VAN Dorp isolated it in the form of its sparingly soluble sulphate. It is a colourless substance with an odour like that of quinoline. It melts at 21^, and boils at 237^. It has the formula
^/^N
0
3
MoQuinoline
This constitution is Indicated by its oxidation to cinchomeronic acid and phthalic acid, in accordance with the scheme
Cinchomeronic acid Phthalic add
The synthesis of isoquinoline furnishes additional confirmation of the structure indicated.
m. niDOLs, C1H7N.
403. The relation between indigo and indole is made evident by the following series of transformations, chiefly the discoveries of VON Baeter.
594 ORGANIC CHEMISTRY. [§ 403
On treatment with nitric acid, indigo, CieHio02N2, yields an oxidation-product, isatin, C8H5O2N, which can also be S3aithe- sized by treating o-nitrobenzoyl chloride with silver cyanide. When hydrolyzed, the resulting nitrile yields o-nitrobenzoyl- formic acid:
NO2 1 _ nxT ^N02 _ n TT ^N02
CflH4 <co.Cl 2 ^ ^^^^ "^CO-CN ~* ^®^* ^CO-COOH.
o-NHrobenioyl o-Nitrobenxoyl o-Nitrobenzovl-
chloride cyanide formic acid
On reduction, the nitro-group in this acid is converted into an amino-group, and water eliminated simultaneously with the for- mation of isatin, which has, therefore, the constitution indicated by the equation
yNHa yNv /NHv
XXX X!0/
o-Aminobenioylformio acid Intin
When reduced with zinc-dust and hydrochloric acid, isatin takes up two hydrogen atoms, forming dioxindoU, C8H7O2N. This com- pound also results on the elimination of water from the unstable o-aminomandelic acid, which determines its constitution:
m
o^Axninomandelic acid
OH
Dioxindole
When reduced with tin and hydrochloric acid, dioxindole yields oxindole, CgHjON, which is also obtained by reduction of o-nitro- phenylacetic acid and subsequent elimination of water:
NHIH yNH
o-AmiDophenylaoetio add Oxindole
Distillation with zinc-dust converts oxindole into indole, CsHjN, which must, therefore, have the structure
§ 403] INDOLE. 595
|
C<|H4< >CH; |
or |
|
NH • |
|
|
v-^ |
Indole
Indole, therefore, possesses a benzene-nucleus condensed with a pyrrole-nucleus. It does, in fact, display some of the properties characteristic of pyrrole: thus, it is a very weak base, and gives a red coloration with hydrochloric acid.
Indole is present in small proportion in coal-tar and in oil of jessamine. It can be isolated as potassium derivative with the metal in union with nitrogen by heating with potassium hy- droxide the coal-tar fraction boiling between 240^ and 260*^. In ' spite of its characteristic, disagreeable odour, it is employed in the manufacture of perfumes. It forms white leaflets, melting at 52^, and is readily volatile with steam. Its picrate crystallizes in well-developed, red needles.
^Metkylindokf or scatohf
NH
CJI,^^H, CCH,
is present in fseces, and occasion;:* the unpleasant odour. It is also found in a species of wood grown in India, and is formed in the putrefactive decay of proteins, or by fusing proteins with caustic potash.
Tryptophan or indolealanine, C11H12O2NS, is an important decom- position-product of proteins (252, 5) and an indole derivative. It is synthesized by treating indole with chloroform and potassium hydroxide in alcoholic solution. 3-Indolealdehyde (I.) is formed as an intermediate product, and condenses with hippuric acid to indolyl- benzaylaminoacrylic acid (II.). On treatment with sodium and alcohol, the double bond of this compound adds two hydrogen atoms and the benzoyl-group is simultaneously eliminated, with formation of racemic tryptophan (III.):
596 ORGANIC CHEMISTRY, l| 404
|
j'^'^l |CHO _, (^ |CH:C-CXX)H \/\/ \/\/ NH-COCH, NH NH L II. |
|
|
- |
/\ |CH..CH-CXX)H \/\/ NH, xrxT |
|
Din. TryptopluiD ni. |
Indigo.
404. The constitution of indigo is inferred from its formation from isaiin chloride, obtained by the interaction of isatin and phosphorus pentachloride. On reduction with zine-dust and acetic acid, it is transformed into indigo:
C6H4^^^>|crTCi]C^ '^ -
+ H
CO H
Since on treatment with sulphuric acid, and subsequent reduc-
tion, di^(o^itrophenyl)-diacetylenej • • , is
converted into indigo, the two isatin-residues in the latter must be united by a carbon linking.
Indigo has long been known as one of the most beautiful blue dyes, and is very permanent, being unaffected by light, acids, alkalis, or washing. It can be prepared from certain plants, among them Indigofera sumatrana and /. arrecia. Formerly these plants were cultivated on a large scale in Bengal in India — whence the dyestuff derived its name — as well as in Java, China, Japan, and South America; but sinc6 its introduction, synthetic indigo (405) has to a very great eictent displaced the natural product, even in the countries mentioned, and the com- petition has become so keen as to lead to the abandonment of many indigo-plantations, and the financial ruin of their proprietors.
§ 406) INDIGO. 697
Indigo is not present in the plant as such, but in combination as the glucoside indican, which occurs chiefly in the leaves, and can be extracted with hot water. It is crystalline, and has the formula Ci4Hi706X,3H20. • In addition to the glucoside, the leaves contain an enzyme, the activity of which, like that of all enzymes, is destroyed by boiling water: hence, when indican itself is to be prepared, hot water must be employed in the extrac- tion. With cold water, both indican and the unchanged enzyme dissolve, and the glucoside decomposes into dextrose and indoxyl, CgHrON, or j^jj
X!(OH)^
a substance which is moderately stable in acid solution, but in dilute alkaline solution is quickly oxidized to indigo by atmospheric oxygen.
The manufacture of indigo from the plants containing it is carried out by the method indicated. The leaves of the indigo- plant are allowed to remain immersed in lukewarm water for some hours: the aqueous extract is "churned " by a revolving water- wheel with wooden paddles, which aerates it, and thus oxidizes the indoxyl to indigo. The oxidation-process is facilitated by the addition of slaked lime to make the liquid faintly alkaline. The indigo formed sinks to the bottom, is removed by filtration, and dried. It is put on the market in the form of small cubes.
In addition to the blue dye, indigotin, commercial indigo con- tains indiglucin, indigo-brown, and indirubin; these substances can be extracted by water, alcohol, and alkalis, in which indigotin is insoluble. Ind'go' in is a dark-blue powder, which, when rubbed, has a copper-like lustre. It can be sublimed in vacuo, so that it is possible to determine its vapour-density. It is insoluble in most solvents, but can be crystallized from nitrobenzene or aniline. It dissolves in fuming sulphuric acid, with formation of sulphonic acids.
405. On account of the great industrial importance of indigo, many attempts have been made to synthesize it. One method is commercially successful, enabling the artificial product to be sold at a much lower price than that formerly obtained for natural indigo. It yields pure indigotin, which is also an advantage.
Anthranilic acid, or o-aminobenzoic acid (347), C6H4<pJ?^TT,
5S8 ORGANIC CHEMISTRY. [f 406
combines with monochloroacetic acid to form phenylglycine-iy' carboxylic add:
^ „ /NHfH+Cl]H2C-C02H ^ „ yNH|H^C'lCO^H
\COOH \C|0j0H
[Phenyl^ydne-o-earboxylio aoid
Fusion with sodium hydroxide transforms this compoimd into
/ HN V indoxyl, C6H4^ .^H, which in alkaline solution is con-
X;(OH)^
verted by atmospheric oxidation into indigo.
Another process involves the interaction of aniline and mono- chloroacetic acid to form phenylglydnef C6H6*NH-CH2'COOH, convertible into indoxyl by fusion with sedamide, NH2Na :
\ NH
^CH2 — > C6H4^ yCH2.
wmpcy CO
y NH
Nh HO|C(y
Tautomerio form of iDdozyl
On reduction in alkaline solution, indigo takes up two hydrogen atoms, with formation of indigo-white, C16H12O2N2, a white, crystalline substance, the phenolic character of which is proved by its solubility in alkah's. In alkaline solution it is speedily reconverted into indigo by atmospheric oxidation, a reaction employed in dyeing with this substance. The dye is first reduced to indigo-white, and the fabric thoroughly soaked in an alkaline solution of this compound: on exposure to the air, the indigo- blue formed is fixed on the fibres. The process is technically known as " indigo vat-dyeing."
The reduction of indigo to indigo-white is variously carried out in the dyeing-industry according to whether wool, silk, or cotton is to be dyed. Reduction is best effected with a salt of hyposul- phurous acid, H2S2O4 (" Inorganic Chemistry," 83), for the two first named. The solution is mixed with zinc hyposulphite, and treated with excess of milk of lime, which precipitates zinc hydrox- ide. The indigo is mixed with water, and warmed to about 60° with the solution of calcium hyposulphite, a concentrated alkaline solution of indigo-white being obtained in a short time. On adding
§ 405] INDIGO. 599
sufficient water to it in the dyeing-vat, the bath is ready for use.
The hyposulphite reduction-process possesses the advantage that the reduction stops at the formation of indigo-white, so that ahnost none of the indigo is lost.
Indigo is the longest-known and most important member of the series of vatrdyestuffs. They include pigments insoluble in water, but characterized by their ready reduction to a form soluble in dilute alkali, their attraction in this condition by vegetable and animal fibres, and their subsequent reoxidation on the fibre to the original insoluble condition.
The vat-method of dyeing has great advantages over other processes, since the fabric requires no previous treatment by mor- danting or otherwise, and both the prep^uration of the vat and the operation of dyeing are usually carried out at the ordinary tem- perature. A further advantage is the very fast nature of the colours imparted by these dyestuffs.
Vat-dyestuffs derived from indigo, and others related to anthra- quinone, are known. Those of the first class are called indigoids, and contain the chromophore-group, — CO-CJC-CO — .
Substitution by halogen of the hydrogen atoms in the benzene- nuclei of indigo produces a marked change in colour only when the hydrogen atoms occupying the para-positions to the carbonyl-groups are replaced. Symmetrical dibromoindigo,
NH NH
is the celebrated "Purple of the ancients'' employed in antiquity for dyeing Tynan purple. It was formerly obtained from the colour-yielding glands of the mollusc Murex brandaris in the form of a colourless substance converted into the dye by the action of light.
Thioindigo is a reddish-blue derivative in which two sulphur atoms replace the two imino-groups. The tint of the dyestuff can be so much altered by substitution as to render possible the pro- duction of almost every colour. ^
ALKALOIDS.
406. Plantd of certain families contain substanceB, usually of complex composition and basic character, called alkaloids. Their classification in one group is of old standing, and had its origin in an idea similar to that which prevailed concerning the v^etable acids (i) prior to the determination of their constitution. Just as the latter have been subdivided into different classes, such as monobasic, polybasic, aliphatic, and aromatic acids, so it has become apparent that the individual alkaloids can be arranged in different classes. Most of the alkaloids are related to pyridine, quinoline, or isoquinoline, while a smaller nimiber belongs to the aliphatic series. Some of the latter class are described along with the compounds of similar chemical character: among them arebetalne (242), mus- carine (22<)), choline (160), caffeine, and theobromine (272). Only alkaloids which are derivatives of P3aidine are described in this chapter: to them the name alkaloids, in its more restricted sense, is applied, the other substances being known as vegetable bases.
PROPERTIES.
407. It is seldom that an alkaloid is present in more dian one family of plants: many families do not contain them. The occur- rence of alkaloids is almost entirely confined to dicotyledonous plants. Only a few, such as coniine and nicotine, are liquids: most of them are crystalline. Many are optically active and l«vo-rota- tory: it is very exceptional for them to exhibit dextro-rotation. They have an alkaline reaction and a bitter taste: most of them are insoluble in water, more or less soluble in ether, and readily soluble in alcohol. Most are insoluble in alkalis, but dissolve in acids, forming salts which are sometimes well-defined, crystalline sub- stances.
Some substances precipitate many of the alkaloids from their aqueous or acid solution: such general alkaloid^eagenls are tannin (347), phosphomolybdic acid, mercuric potassium iodide,
600
i 407] ALKALOIDS 601
KI*Hgl2 (" Inorganic Chemistry/' 273), and others. Some alka- loids are excessively poisonous.
Strong tea is sometimes employed as an antidote, the tanmn present precipitating the alkaloid, and rendering it innocuous.
Some of the alkaloids, such as quinine and strychnine, give very characteristic colour-reactions. Despite the obscure nature of these processes, they afford a certain means of detecting even small quantities of these alkaloids.
The complex structure of many alkaloids renders their investi- gation a matter of extreme difficulty, and despite a century of unremitting toil the elucidation of the constitution of all tiiese substances is far from attainment. The research involves the identification of the better known groups present in the molecule, such as OH, OCH3, C=C, CO, CH3, and so on; and also includes the determination of the particular ring of the carbon-nitrogen nucleus in imion with these groups.
As regards the first problem, most alkaloids have been proved to be tertiary amines, yielding addition-products with methyl iodide. Many alkaloids contain acid-residues or methoxyl- groups, — OCH3. The acid-residues can be eliminated by saponi- fication with hot bases or acids; and the methoxyl-groups can be removed ad methyl iodide by heating with hydriodic acid. Hydroxyl-groups can be detected in the ordinary way by means of acid chlorides or acetic anhydride.
In the investigation of the nucleus, it is necessary to try to break it down, good results having been sometimes obtained by the use of powerful oxidizers such as potassium permanganate, chromic anhydride, and nitric acid; and distillation with zinc- dust and fusion with potassium hydroxide have also been of service.
In the extraction of the alkaloids from plants the latter are cut up into fine pieces and lixiviated with acidified water in a conical vat tapering towards the bottom, where there is a layer of some material such as glass-wool or lint. The effect is that the acidified water gradually sinks through a thick layer of the sub- stance under extraction, a process technically known as " percola- tion." Dyes, carbohydrates, inorganic salts, etc., are dissolved along with the alkaloids. When the alkaloid is volatile with steam, it can be separated by this means from the liquid, after
602 ORGANIC CHEMISTRY. Hi 40&-ilO
making the mixtiire alkaline: when it is comparatively insoluble, it can be obtained by filtration. Further purification is always necessary, and is effected by crystallizing the free alkaloid or one of its salts several times.
408. Constitution furnishes the best basis for the classification of the alkaloids. Pictet recognizes eleven groups:
I. Aliphatic Bases. Methylamine, choline, betalne, and muscarine.
II. Tetrahydropyrrole Bases (395). Tetrahydropyrrole itself has been detected in tobacco and opium.
III. Pyridine Derivatives. Piperine (390), and coniine (409).
IV. Iminazole Derivatives. Iminazole has the formula HC==CH
HN N . This class includes allantoine (269), a constituent
Yh
of sugar-beet and other substances.
V. Alkaloids with Condensed Tetrahydropyrrole and Piper- idine Chains. Atropine, and cocaine.
VI. Purine Derivatives. Xanthine, caffeine, and theobromine.
VII. Aromatic Amines. Hordenine, and tyramine.
VIII. Indole Derivatives. Strychnine.
IX. Quinoline Derivatives. Quinine.
X. mQuinoline Derivatives. Morphine, and narcotine.
XI. Alkaloids of Unknown Structim. Aconitine, colchicine, cytisine, and so on.
niDIVIDnAL ALKALOIDS.
Coniine, CsHitN.
409. The synthesis of coniine is described in 390. It is present in spotted hemlock {Conium macvlatum), and is a colourless liquid of stupefying odour. It boils at 167^, is but slightly soluble in water, and is very poisonous.
Nicotine, C10H14N2.
410. Nicotine is present in combination with malic acid and citric acid in the leaves of the tobacco-plant (Nicotiana t€Lbacum).
1 410] ALKALOIDS. 603
It is a colourless, oily liquid, which is laevo-rotatory, and readily soluble in water. It has a tobacco-like odour, which is not so marked in a freshly-distilled sample as in one which has stood for some time. It boils at 246*7^, and is excessively poisonous. It quickly turns brown on exposure to air. It is a ditertiary base: on oxidation with potassium permanganate, it is converted into nicotinic acid (39i)» proving it to be a /^-derivative of pyridine. The constitutional formula of nicotine is
CH2 — CH2
0-CH CHj; \/- N N.CH3
with a hydrogenated pyrrole-nucleus methylated at the nitrogen atom, and a /^-substituted pyridine-nucleus. The formula also ex- presses the facts that nicotine is a ditertiary basis and that it yields nicotinic acid on oxidation. This formula is proved by the syn- thesis of nicotine; which yields an optically inactive modification resolvable into components. The laevo-rotatory isomeride is iden- tical with natural nicotine. The dextro-rotatory form is much less poisonous than the laevo-rotatory, and also differs from it in other respects in its physiological action.
Nicotine dissolves in its own volume of water to form a stisky, viscous liquid resembling glycerol. On warming, this liquid becomes turbid, and separates into two liquid layers, the upper being a satu* rated solution of nicotine in water, and the lower a saturated solution of water in nicotine.
Systematic investigation of mixtures of nicotine and water in various proportions and at various temperatures has proved the two liquids to be miscible in all proportions below 60^ and above 208^. For this range of temperature the mutual solubility is limited. A graphic representation of the solubilities (Fig. 88) gives a closed curve. The region inside this curve corresponds with two liquid layers; that outside with nuscibility in all proportions.
On addition of nicotine to water at 90^ there is at first complete solution. At a concentration of about 6 per cent., the liquid sepa- rates into two layers, but again becomes homogeneous when the proportion of nicotine has risen to 82 per cent. When a solution containing 60 per cent, of nicotine and 40 per cent, of water is warmed,
604
ORGANIC CHEMISTRY.
K411
900
180
&100{- &
0 liOl-
i
B ItO-
100
two layers form at 60^, but heating the mixture in a sealed tube
restores homogeneity at 200°.
Other bases, such as ^-piooline and methylpiperidine, exhibit similar behaviour towards water. In most instances a com- pletely closed curve is not obtained. The system phenol — ^water gives only the upper part of the cur\'e, for at low temperature the component phenol separates in the solid state before homogeneity is attained. For the system triethylamine — water it is possible to plot only the bottom part of the curve, the critical temperature of one of the components being reached before the liquid becomes homogeneous.
Atropine, C17H28O3N.
411. Atropine is present in the NiootiM berry of the deadly nightshade (Atropa
Water PkrwnUgv b> Weight • i *
belladonna) and in the thorn-apple, the Fig. 88.-THE System Jj^j^. ^f Datura stramonium. It is
NiOOTINE-WATER. . „. ,, a i i c cO • •
crystalline, melts at 115 • 5 , and is very poisonous. It exercises a " mydriatic '' action — ^that is, when dropped in dilute solution on the eye, it expands the pupQ: for this reason it is employed in ophthalmic surgery. It is optically inactive. On heating with hydrochloric acid or caustic soda at 120°, it takes up water and yields tropine and tropic acid:
C17H23O3N + H2O = CsHisON + CfiHioOa.
Atropine Tropine Tropic add
It can be regenerated from these two substances by the action of hydrochloric acid. Atropine is, therefore, the tropine ester of tropic acid (324). The constitutions of atropine and tropine are:
H2O-CH CH2
H.
I.
11.
H2C — CH C112
N-CHa CHO.CO.CH.CH2OH
N-CHa CHOH.
I
H2C — CH CII2
Tropine
i 412] ALKALOIDS. 605
This formula for tropine was proposed by Willstattbr and is based on the decomposition-products of this substance. They are
1. Meihylsucdnimide, (I.) indicating the presence of a tetra- hydropyrrole-nucleus.*
2. Tropidine, obtained through elimination of water by heat- ing with potassium hydroxide or dilute sulphuric acid:
CsHisON-HaO = CgHisN.
Tropine Tropidine
Tropidine can be converted into a-ethylpyridine (II.), proving that tropine contains a pyridine-ring.
Ecgonine (412) is a carboxylated tropine: it breaks down to suberone (Ill.)y indicating the presence of a ring of seven carbon atoms in the tropine molecule. It has also been estab- lished by the usual methods that tropine is a tertiary base, and contains a hydroxyl-group:
CH2— CO
L I >N-
CHa— CCK
CHa : II.
fcH.-C0/^^ ^"^ ' ^^•kyC.H,;
CH2^"CH2^"CH2\^
»H2^^H2^^H2^
Cocaine, C17H21O4N.
m. I NCO.
412. On account of its use as a local anaesthetic, cocaine is the best known of the alkaloids present in coca-leaves {Erythroxylon coca). It is crystalline, is readily soluble in alcohol, and melts at 98°. On heating with strong acids, a benzoyl-group and a methyl- group are eliminated, with formation of ecgonine, (I.), so that the constitution of cocaine is represented by II. :
CH2 • CH CH . COOH CH2 • CH CH . COOCH3
N.CH3 CHOH
N.CH3 CHO.COCeHfi.
CH2 • CH CH2 GH2 • CH CH2
L II.
By benzoylating and methylating ecgonine, cocaine is regenerated. Ecgonine is a tropinecarboxylic acid.
606 ORGANIC CHEMISTRY. \\ 413
Morphinei C17H10O3N.
413. Morphine is the longest-known alkaloid : it was obtained from opium in 1806 by Serturner. Opium is the dried juice of the seed-capsules of Palaver somniferutn, a variety of poppy. It is a very complex mixture, containing caoutchouc, fats, resins, gums, sugars, proteins, mineral salts, meconinic acid,
(CH30)2C6H2(CH20H)(COOH),
some more organic acids, and other substances, together with numerous alkaloids. Twenty of the last-nampd have been identi- fied : of these morphine is present in largest proportion, and con- stitutes about 10 per cent, of opium.
Morphine is crystalline, and melts with decomposition at 230°. It is slightly soluble in water, is without odour, and is employed as an anodyne and narcotic.
The reactions of morphine indicate that one of its three oxygen atoms is linked as phenolic hydroxyl, proved by its solubility in alkalis; the second is present as alcoholic hydroxyl; and the third has an ether-linking. On distillation with zinc- dust it yields phenanthrene, C14H10, so that the empirical formula may be expanded to
C17H19O3N = C3Hi6N[Ci4][0][OH][HOH].
Treatment with methyl iodide in alkaline solution methylates the phenolic hydroxyl; the simultaneous addition of methyl iodide at the nitrogen (I.) proves morphine to be a tertiary base. The product formed is identical with the methyl-iodide derivative of codeine. On treatment of this substance with aqueous sodium hydroxide, hydriodic acid is eliminated, and another tertiary base containing a like number of carbon atoms formed. It is called a-methylmorphimethine (II.). On heating with acetic anhydride, methylmorphimethine yields a product free from nitrogen (III.), aiid one containing nitrogen (IV.) The first is methylmorphol or irhydroxy-S-methoxy-phenanthrene, convert- ible by further methylation into a synthetic product, dimethyl- morphol (386), a reaction indicating its structure. The second is dimethylhydroxyethylamine, CH20H«CH2*N(CH3)2:
{414] ALKALOIDS. 607
CHaO-CsHa— CH2 CHgO-CeHa— CH
HO-CeH— dHv /I HO-CeH — CH
CH2 — CH/ XJHa CH2 — CH2.N(CH3)3
I. U.
TT/-\> C6H2 CH
-* i il
-♦ CeH4— CH
III.
HO . CHz^Hj • NCCHa) % IV.
By combining these facts with others it has been possible to assign provisionally to morphine the structural formula
H
ho/Nh
,H,
n.ch.
Ha
2 "2
It represents morphine as a combination of a partially hydro- genated dihydroxyphenanthrene containing an ether-linked oxygen atom with a hydrogenated pyridine-nucleus having the nitrogen atom linked to methyl.
Heroin is the diacetyl-derivative of morphine.
Narcotine, C22H23O7N.
414. Narcotine is present in opium to the extent of about 6 per cent., its percentage being next to that of morphine. It is crystal- line, melts at 176°, and is slightly poisonous. It is a weak tertiary base, its salts readily imdergoing hydrolytic dissociation. It con- tains three methoxyl-groups, and has formula I. Namarcotine has the formula Ci9Hi404N(OH)3. On hydrolysis, narcotine yields cotamine (II.), a derivative of isoquinoline, and the anhy- dride of meconinic acid, or meconin (III.) :
608
ORGANIC CHEMISTRY
IS 416
CHa<^
OCH3
C CH CH C
oc.c
J
CH2
CH CH2
CH3O.C
I.
Nmrootine
G 6CH3
OCH3
C CHOH
0 CHa
I C
OC.c/\/\ CH oc-c/NcH
^'^K/\/ CH,O.C
CH CHa
CH
II.
Cotamine
c
OCHs III.
Meeonin
Bromine converts narcotine into dibromopyridine.
Quinine, C20H24O2N2.
415. The barks of certain trees of the Cinchona and Remya families contain a great nmnber of alkaloids. 'The most important of them, on account of its anti-febrile effect, is quinine, Cincho- nine, C19H22ON2, is the next best-known: its physiological action is similar to that of quinine, but is less pronounced.
In addition to alkaloids, these barks contain various acids, such as quinic acid, quinovic acid, and quino tannic acid: neutral sub- stances, such as quinovin, quina-red, etc., are also present.
Quinine is very slightly soluble in water, and is laevo-rotatory. In the anhydrous state it melts at 177®, and at 57® when it con- tains three molecules of water of crystallization. It is a strong base, and both N-atoms are tertiary. It unites with two equiva- lents of an acid. In dilute solution the salts of quinine exhibit a splendid blue fluorescence, which serves as a test for the base.
The constitution of quinine has been elucidated, chiefly through
S416]
ALKALOIDS.
609
the researches of Skraup and of KOniqs, the latter aasigning to it the formula
n.
HaC
CH
d-H^^CH-CHtCHa CH,
CHj
CH C CH-OH
CH80.C/''^^CH
I.
HC
^^
/
CH
which expresses the following properties of quinine. On fusion with potassium hydroxide quinine yields quinoline, "p-meihyU quinoline or lepidine, and p-^methoxyguinoUne from the part of the molecule numbered I. in the structural formula; and p- ethylpyridine from part II. On oxidation, aj37-pyridinetri- carboxylic acid is obtained, also from part I. In addition, quinine is a ditertiary base, and contains a hydroxyl-group and a methoxyl-group. Its additive power indicates the presence of a double carbon bond.
The formula of cinchonine differs from that of quinine in having methoxyl replaced by hydrogen.
The synthesis of the quinine alkaloids from derivatives of quinoline and piperidine has been attained.
Strychnine, C21H22O2N2.
4x6. Three extremely poisonous alkaloids, strychnine, brucine, and curarine, are present in the seeds of Strychnos nuz vomica, &s well as in others of the Strychnos family. Little is known of the chemical nature of curarine, although it has been much studied from a physiological standpoint: when administered in small doses, it produces total paralysis. Strychnine and brucine cause death,
610
ORGANIC CHEMISTRY.
II416
preceded by tetanic spasms — ^that is, contraction of the muscles; curarine is, therefore, employed as an antidote.
Strychnine is crystalline, and melts at 285**; it is almost insoluble in water. It is a monohydric, tertiary base, only one of its X- atoms exhibiting basic properties. On fusion with potassium hydroxide, it yields quinoline and indole; and when distilled with slaked lime, it is converted into /?-picoline (389). Heating with zinc-dust produces carbazole (382) and other substances.
W. H. Perkin, jun., and Robinson consider the chemical
properties of strychnine to be represented most completely by
the formula
CH2 CH
CH CH CH2* CH CHj
N
CO
I
CH2
<3H CHa CH.OH
Brucine differs from strychnine in having methoxyl-groups as Bubstituents in positions 1 and 4.
INDEX
The baaaa of the arrangement of this index is three-fold:
(1) The numbers refer to pages.
(2) In all instances of possible ambiguity as to the identity of the principal references, they are given in old-style figures.
(3) Where a reference is a sub-division of a principal heading, it is indented one em space for each word of the principal heading not repeated. Portions of words followed by a hyphen are treated as words for the purposes of this arrangement.
A.
Abbreviated thermometers, 32. Abderhalden, 344. Abel, Sir Frederick, 39. Absolute alcohol, 58, 59. Acetal, 258, 259.
Chloro-, 303. Aeetaldehyde, 69, 132, 133, 137-141, 144-145, 163, 167, 177, 179, 181, 184, 191, 196, 230, 232, 258, 259, 273, 305, 320, 429, 502, 541, 575, 576. -ammonia, 137, 575. Sjrnthesis of, 191. Acetals, 137-138, 187, 284, 285. Acetamide, 127, 128. hydrochloride, 128. Acetaminohydrazobenzene, 7>-, 422. Acetates, 111, 112. Acetic acid, 2, 16, 56, 61, 62, 94, 104, 105, 107, 109-112, 117-125, 132, 146, 163, 173, 190, 191, 204, 222, 223, 227, 256, 305, 307, 403, 420, 433, 441, 456, 502, 585, 596. Glacial, 16, 31, no, 414, 559. Chloro-, 203, 04, 222, 223, 228,
320, 323, 598. Synth sis of, 191. anhydride, 120, 136, 138, 264, 282, 300, 443, 456, 489, 503, 587, 601, 606. fermentation, 291. Acetoacetic acia, 306.
ester. See elhijl acetoacetate. synthesis, 306-309. %
Acetoanilide, 414, 417, 475. Acetobromodextrose, 282. Acetoferric acetate, 112.
Acetone, 16, 56, 61-63, 88, 132, 135, 146, 147, 154, 155, 161, 162, 164, 166, 167, 179, 181, 183, 184, 188, 191, 250, 257, 258, 302, 307, 316, 398, 530, 548.
Sjmthesis of, 191. Acetonitrile, 102. Acetonuria, 146. Acetonvlacetone, 25S, 309, 586. Acetophenone, 441, 455. Acetoxime, 13^, 316.
hydrochloriae, 135. Acetyl-acetone, 257, 258, 312.
chloride, 119, 120, 121, 136, 253, 257, 305, 311, 357, 437, 441, 579.
-coumaric acid, 502.
-group, 107.
-mesidine, 508.
-phenetidine, 477.
-salicylic acid, 487./ Acetylene, 159-163, 178, 185, 186, 191, 348, 398, 455, 575, 586.
bromide, 167.
-dicarboxylic acid, 218. Acid-albumins. See Tneta-proletna.
anhydrides, 120, 208, 209.
azides, 129, 367.
chlorides, 119, 120, 127, 133.
decomposition, 306, 307, 308.
hydrazides, 129.
-ureides. See urdldes. Acids, CnHsnOt, I 4-1x8, 130, 170, 192.
CnHsn-jOj, 170-176.
C«H2-40,, 175, 176.
C4Hfl02, 172, 173. Acidylglycollic acid esters, 330. Aci-modifications, 451. Aconitic acid, 220. Aconitine, 602.
611
612
INDEX
Acraldehyae, 168, 177, 178, 191, 192, 267. 675, 689, 690.
-acetal, 178.
-anunonia, 177, 675.
-aniline, 690. Acroldn. See acraldehyde. Acroee, 267.
AcryUc acid, 168, 170, 171, 177, 321. AdditionB-reactions, 231. Adipic acid, 199, 521, 661.
anhydride, 386. Adjacent compounds, 396. Adrenaline, 603. Actio-phylUn, 684.
-porphorin, 684. Afaricus muscarius, 303. Air-condenser, 21. Alanine, 320, 323, 340, 342.
ci-, 326.
^,326.
nitrile, 320.
Albumin, 334f 339, 345. Albuminates. See metorprolelns. Albuminoids. See Mclero-proieina. Albumins, 332, 334, 336, 336, 337,
338. Albumose, 335. Alcohol. See ethyl alcohol. Alcoholates. See aUcoxides. Alcoholic fermentation, 56, 57, 272,
273, 290-2193, 324. Alcohols, Aromatic, 463. CiJI«fi+iOH, 51-69, 80, 81, 83, 86, 89, 119-121, 128, 129, 148, 286. Higher, 69. Aldehyde. See acetaldehyde. -resm, 139, 140. sulphite compounds, 134. Aldehydes, 130-145, 149, 160, 161, 185, 187-189, 198, 226, 263, 315,
382,438-441. Aldehydo-acids, 304.
-alcohols. See auQors. .
Aldohexoees, 261, 263, 278.
Aldol, 139, 140, 178.
Aldopentoses, 278, 279.
Aldoses, 261, 262, 271, 277.
Aldoximes, 136, 136.
Alicyclic compounds, 158, 159, 381,
383-388. Ah'phatic compounds, 36, 36-380. Alisarin, 662, 566-568.
diacetate, 667. Alkali-albumins. See metOfproUrins. Alkaloid-reagents, 600. Alkaloids, 293, 492, 600-610. Alkoxides, 61, 6^^ 70, 77, 81, 106, 108,
148.
Alkyl-anilines, 418.
-glucosides, 286.
-groups, 38.
halides, 73^5, 77, 81, 86, 87, 97, 148, 164, 166, 181. .
-hydrazines, 91.
magnesium halides, 100, 104, 122, 136, 318.
nitrites, 92.
-nitrolic acids, 94.
-sulphinic acids, 83.
-sulphonic acids, 83.
sulphonyl chlorides, 83.
•sulphuric acids, 75, 76, 82, 150.
-ureas, 363, 364. Alkylenes. See olefines. Allantolne, 372, 373, 602. iiUocinnamic acid, 467. Allotropy of carbon, 19. Alloxan, 371-373, 376. AUoxantine, 372.
AUyl alcohol, 166, 167, 168, 169, 177. 186, 190, 196, 202, 203.
-aniline, 690.
bromide, 167, 185, 186.
chloride, 166, 167, 168.
cyanide, 172.
iodide, 167, 169, 170, 172.
MOthiocyanate, 355.
magnesium bromide, 172.
sulphide, 169. Allylene, 169, 160. Aluminium acetate, x 12, 481.
aeetylacetone, 258.
mellitate, 499. Amber, 207. Amic acids, 202. Amidines, 129. Amidoximes, 129. Amine hydrohalides, 87. Amines, 85-91 » 96^ 136, 406, 412-425,
497, 601. Amino-acetal, 303.
-acetaldehyde, 303.
-acetic acid. See glycine.
-acids, 291, 320-325, 326, 327, 340.
Di-, 340.
Dibasic mono-, 340, 342.
Hydroxy-, 340.
Monobasic mono-, 34 .
-alcohols, 197.
-aldehydes, 303.
-anthraquinone, 2-, 6C9.
-azo-dyes, 481, 482. -ben ene, 432, .78, 480, 482, 483.
barbituric acid, 373.
-benzenesulphonic acid, p-. See siUphaniUc acid.
INDEX
613
Amino-benxolc acid, o-. See arUhra- nilic acid. acids, 493, 494, 512. -benzo^lformic acid, o-, 594. -butync acid, 7-, 321 .
Lactam of 7-, 321 . •K»iproic acid, at-. See lysine. -chlorides, 128. -cinnamaldehyde, o-, 591. -cinnamic acid, o-, 593. -glutaric acid, a-, 325. -guanidine, 369. -5-giianino^n^valeric acid, a-. See
arginine. -««o-butylacetic acid. See leucine. -ketones, 303. -mandelic acid, o-, 594. -^thyl valeric acid, a-. See iso^
leucine, -naphthalene, 506, 507. -naphthol, 1 : 2-, 559. -nonolc acid, 9-, 176. -phenol, 0-, 477.
;>-, 423, 465, 473, 476, 477. -phenols, 476, 477. -phenyl-acetic acid, o-, 594. -arsinic acid, p-, 477. -p-acetaminophenylamine, p-, 422. -propionic, acid, a-. See alanine.
^-, 321. -succinamic acid. See aaparagine. -succinic acid. See aspartic acid. -thiophen, 587.
hycrochloride, 587. -valeric acid, or-, 340. Ammonium carbamate, 366. formate, 348, 349. i«ocyanate, 362, 363. oxalate, 202, 347. picrate, 464. succinate, 209. thiocyanate, 368, 369. Amygdalic nitrileglucoside, 349. Amygdalin, 266, 349. 439. Amvl acetate, i«o-, 121 alcohol. Normal, 53, 54, 81, 148,
314, 560. alcohols, 53, 57, 64, 65, 66, 401. bromide. Normal primary, 74. chloride, Normal primary, 74. iodide. Normal primary, 74.
Optically active, 66, 67. isovalerate, wm>-, 121. nitrite, 256, 536. -sulphuric acids, 152. Anylene, Normal, 149. Amylenes, 148, 149, 15a, 154. Amylocellulose, 296.
Amyloid, 300, 301. Anaesthetics, 182. Analysis, Example of, 10, 11. Angelic acid, 170. Anhydro-bases, 477.
-formaldehydeaniline, 415, 416. AniUdes, 414.
Aniline, 263, 270, 301, 407, 415, 416, 417, 424-426, 431, 433, 435, 440, 446, 473, 474^76, 479, 512, 646, 547, 561, 590, 697.
-black, 479.
-blue, 547.
-dyes. See coot-tor coUmrs,
hydroarsenate, 477.
hydrochloride, 416, 418, 432, 547. Aniline hydrogen sulphate, 477.
nitrate, 426.
-yellow, 482. Animal fats, 35, xia-115. Anisanilide, 445. Anisole, 412. AnschCtz, 563. Anthocyanidins, 490. Anthocyanins, 319, 490. Anthracene, 552, 562-564, 666, 567,
-oil, 400, 552, 562, 569. Anthranilic acid, 493, 494, 509, 697. Anthranol, 566. Anthraquinol. 56s, 566.
DiBodium derivative of, 565. Anthraquinone, 563-56^, 567, 568, 599.
oxime, 565.
-sulphonic acids, 567. Anthrone, 566.
Antifebrine. See aceloanxLide, Antipyrine, 589. Antiseptics, 184, 411, 487. Apiose, 269, 282. Apricot-stones, 269. Arabinosazone, 269. Arabinose, 266, 268. 269, 277, 278, 279-281, 293, 303.
-methylphenylhydrazone, 277. Arabitol, 193 266, 269. Arabonic acid, 269. Arginine, 340, 342, 369. Argol, 240. Armstbono, 408. Aromatic compounds, 35, 381, 389-
571. "Arsacetin," 478.
Arsenobenzene, 446.
Arsines, 96, 97.
Arsinobenzene, 446.
Artificial camphor, 534.
Asparagine, 247, 292, 324, 325.
Aspartic acid, 325, 337, 342.
614
INDEX
Aapenda odorcUaf 501. Asphalt, 40. Artificial, 40.
" Aspirin /' See acetylsalicylic acid . Asymmetric carbon atoms, 66-68, 326, 327.
nitro.en atoms, 250, 251.
phosphorous atoms, 250.
selen am atoms, 250.
silicon atoms, 250.
sulphur atoms, 250.
synthesis, 293, 294.
tm atoms, 250. Asymmetry, molecular. See moleciir
lar asymmetry. Atoms, Law of the even number of,
47. "Atoxyl," 478. Alropa belladonna J 604. Atropine, 453, 602, 604, 603. Autogenous welding, 16^3. Auxochromeic groups, 480. Axial-Substitution, 251. Azelaic acid, 174, 199. Azo-benzene, 420, 421, 422, 424, 425, 446, 480.
-dyes, 476, 479-484. Azoxy-benzene, 420, 421, 424, 425.
-phenetole, p- 421. Azulminic acid, 348.
B.
Bacillus acidi Icevclaclici^ 248. Baeyer, von, 149, 157, 209, 2LS, 318, 329, 395, 441, 469, 525, 544, 582, 590, 593. Balsam of Peru, 436.
Tolu, 389, 436. Balt, 480. Barbituric acid, 373. Barium acetate, 173.
carbine, 350.
cyanide, 350.
ethoxide, 70.
ethylsulphate, 76.
stearate, 173.
thiocyanate, 354.
trithiocarbonate, 360, 361. Baumann-Schotten reaction, 437. Baumhauer, VON, 59. Beckmann, 136.
-transformation, 136, 176, 353, 445. Beer, 550. Beer, 58, 109. Beeswax, 122. Behenolic acid, 224. Beilstein'b test, 5. Benzyl-aniline, 415. J
Benzyl-chloride, 438, 450, 456, 542. Benzaldehyde, 281, 349, 415, 423, 435, 437, 43^44X1 452, 453, 455, 456, 524, 543, 551, 580. -ammonia, 440. -phenylhydrazone, 440. Benzaldoximes, 443. Bcnzamide, 435, 437, 438. Benzaniside, 445. Benzan/taldoxime (a), 443, 444. Benzene, 16, 30, 100, 161, 339, 359, 381, 386, 38^403, 404, 406, 441,.448, 458-464, 473, 478, 494, 512, 513, 621, 622, 624, 540-542, 550, 553, 563, 564, 570, 575, 585- 587 Constitution of, 389-395. -diazohydroxide, 432. -diazomum chloride, 428-433, 481, 482, 484, 487. Benzene-diazonium hydroxide, 423, 427, 428, 432. nitrate, 426. sulphate, 429. -sulphonic acid, 476. xanthate, 430. -disulphonic acid, m-, 462, 4G4. 0-, 462. P-, 462. Molecular weight of, 11, 12. -sulphonamide, 409. -sulphonic acid, 397, 408, 430, 522,
5:35, 587. -sulphonyl chloride, 408, 409. -syndiazo-chloride, 430. -hydroxide, 428, 430. Benzhvdrol, 441.
Benzidine, 421, 422, 540, 541, 557, 558. -diazoniimi chloride, 558. sulphate, 422. -transformation, 421, 542. Benzil, 551.
dioxime, 551. Benzilic acid, 551. Benzine, 39.
Benzoic acid, 29, 322, 339, 389, 434- 437, 438, 441, 449, 452. 453. 456, 484, 485, 515, 525, 540, 547, 556, 582. anhydride, 437. iminoether, 438.
sulphinide, 0-. See ^* saccharin,** Benzoin, 551, 580.
Benzo-nitrile, 43^, 438, 443, 454, 573, -o-sulphonamide, 485. -phenone, 441, 442, 541, 549.
-oximes, 443. -purpurins, 557, 558.
INDEX
615
Benzo-quinone, 466, 473, 474, 476, 479, 511, 524, 543, 558, 559. dioxime, 474. mono-oxime, 465, 471.
-trichloride, 434, 450. Benzoyl-benzoic acid, o-, 564.
cUoride, 435-437, 438, 441, 450, 503.
-formic acid, 294.
-hydrogen peroxide, 441.
-pil>eriaine, 573.
-serine, 341. Benzpinacone, 441. Benz92^naldoxime (/3 or iso), 443, 444. Benzyl alcohol, 435, 438, 440, 453.
-amine. 450, 454, 561.
bromide, 448, 449.
chloride, 4481 449i ^^i 452^53, 541,550.
cyanide, 452.
halidee, 448-450.
iodide, 440, 450.
-idene-anilme, 440.
-phenylhydroxylamine, 423. Bernthben, 544. Berthblot, 2, 28, 122. Berzeuus, 1. Be tame, 323, 600, 602. Bctalnes, 323. Beyerinck, 291. Bimolecular reactions, 88, 125, 126,
260. Bioses. See diosea. BioT, 66.
Bismarck-brown, 482, 483. Bismuth mercaptides, 82. "Bisulphite" process, 403. Bitter almonds, 286, 349, 407, 439. Biuret, 333, 364, 365.
-reaction, 333, 335, 336, 339, 314, 365. Blasting gelatine, 193. B5EBEKEN, 401, 467, 468. Boiling-point apparatus, Eykman's, 17, 18. Determination of, 2. BONDT, 186.
Borneo camphor. See bomeol. Bomeol. 535, 587. Bomyl fumarate, 294.
pyroracemate, In, 294. Bourquelot, 286. Brain-substance, 197. Bran, 269.
Branched chains, 47. Brandy, 58.
Brassidic acid, 174, 175, 224, 225. Brassy lie acid, 199. Braun, von, 573.
Brediq, 330.
Bredt, 537.
Brigham, 110.
Brisant effect, 193, 301, 356.
Bromination - method of Victor
Meyer, 185. Bromo-acetaldehyde, 266.
-acetic acid, 222.
-acetylidene, 167.
-anthraquinone, 564.
-benzene, 11, 390, 397, 400, 404, 405, 416, 417, 429, 435, 447, 461, 512, 556. -sulphonic acids, 461.
-benzoic acid, m-, 484. P-, 484, 509, 510.
-benzophenone, 443.
-benzoylbenzolc acid, 564.
-butylene, Mono-, 155.
-camphorsulphonic acids, 250.
-erucic acid, 224.
-ethylamine, 497. Bromo-fumaric acid, 216.
-iaohuiync acid, 173.
-maleic acid, 215, 216. anhydride, 216.
-malonic acid, 234.
-naphthalene, a-, 556.
-phenol, 0-, 462, 515. 0-. 462, 515,
-phtnalic anhydride, 564.
-propionic acid, at-, 231, 328.
-propylene, ^, 167.
-succinic acid, 212.
-thiophen, 586.
-toluenes, 449. Bromoform, 183. Brucine, 609, 610. Bruyn Lobry de, 69. BucHi^R, Eduard, 290, 291. BuNSEN, 98, 365. Butane, 37, 38, 42, 43, 48.
cydo-, 383, 384, Butanol, q/cla-y 384. Butanone; q/cuy-f 384. Bdtlerow, 155. Butter, 112, 113.
of antimony, 389. Butyl-acetylene, 159.
alcohol. MO-, 53, 54, 63.
Normal, 53, 54, 63.
Secondary, 53, 54, 63, 125.
-amine, n-, 90. q/do-, 384.
bromide, cycla-y 384. Normal primary, 74.
bromopropionate, iso-t 231.
-carbinol, i«o-, 53, 64, 324. Secondary, 53, 64, 324.
616
INDEX
Butyl-carbinol, Tertiary, 53. -carboxylic acid, qfclo-t 3S4. chloride, Normal primary, 74. derivatives, q^cUn, 383, 384. -dicarboxylic acid, q/do-, 383. -group, 38. iodide, 190-, 154. Normal primary, 74.
seconoary, 193. Tertiary, 150, 154. -sulphuric add. Tertiary, 150. Butylene, cudo-, 384. iso-, 150, 154, 155. Normal, 149. pseudo-j 223. Butyraldehyde, Normal, 131. Butyric acid, tso-, 112, X13, 227, 536. Normal, 106, 107, 112, 113, 117, 139, 171, 173, 222, 264, 273, 339. fermentation, 273. Butyrolacetone, 22S, 233. Butyryl chloride, Normal, 131. -group, 107.
C.
Cacodyl, 98.
chloride, 98.
oxide, 98.
-test for acetates, 98, 112. Cadaverine. See penlamethyUriedia-
mine. Cafeine, 374, 375, 376-378, 600, 602. Calcium acetate, 56, 109, 132, 146, 191.
acetylene. See calcium C€urblde.
adipate, 384, 385, 520.
bensoate, 389.
carbamate, 366.
carbide, 162, 356.
citrate, 252.
cyanamide, 356.
diphenate, 541.
etnylsulphate, 75.
glyooUate, 228.
-i^obutyrate, 113.
-n^butyrate, 113.
oxalate, 207.
pimelate, 520.
salicylate, Basic, 487.
suberate, 386.
succinate, 207.
tartrate, 240. Calculation of formulae, 9-19.
percentage-composition, 9-11. Calico-printing, 112, 253. Camphane, 533, 534, 537, 538.
-group, 535.
Camphor, 535-538. -odour, 535. -quinone, 536. Synthesis of, 537. Camphoric acids, 536-538/
annvdride, 536. Camphoronic acid, 536, 537. Camphors, 386, 403, 520, 535-538. Cane-sugar. See sucrose. Caoutchouc, 163, 186, 360, 538, 539,
606. Capric acid, 107, 146, 174, 308, 525. Caprolc acid. 107, 113. Caprylic acid, 107. Caprylonitrile, 103. Caramel, 284. Carane, 533, 534. Carbamic acid, 366. ' Carbamyl chloride, 435. ' Carbamide. See urea. Carbasole, 562, 610. Carbides, Metallic. See metallic aoeir
ylenes. Carbinol. See methyl alcohol. Carbinols, 54. Carbocyclic compounds, 381, 383-
571. Carbohydrates. See sugars. Carbolic acid. See phenol.
oil, 400, 409, 552. Carbon chains, 47. disulphide, 28, 183, 314, 360, 361,
562,585. oxy-chloride. See carbonyl chloride,
-sulphide, 354, 355, 361. suboxide, 206. tetra-bromide, 37, 181. -chloride, 37, 181, 183. -fluoride, 404. Carbonic acid, 359.
esters, 360. Carbonyl chloride, 182, 316, 359, 362» 419, 435, 441. -luemoi^obin, 338. Carbostyril, 593. Carbylamines. See iaonitriles, Carbylamine-test, 102, 415. Cariub, 8. Carone, 534. Carvacrol, 532, 537. Carvone, 532, 533. Carvoxime, ^2. Casein, 334, 341, 342. Caselnogen, 334. Castor-seed, 114.
Catalytic action of aluminium halidee, 401; 441, 449, 489. antimony pentachloride, 186. calcium chloride, 145.
INDEX
617
Catalytic action of copper, 133.
ferric haUdes, 185, 404, 449,
458, 484, 515. h3rdrogen ions, 330. mineral acids, 125, 138, 144,
145. nickel, 36, 134, 152, 521. palladium, 522. rhodium and other platinum-
gproup metals, 109. sulphuric acid, 138, 144, 145. Catechol, 465, 466, 467, 473, 488, 503,
568. Catechu, 491. Cayley, 49. Cellose, 300. CeUuloid, 301. Cellulose, 299-302, 403. Centric formula for benzene, 394, 395.
naphthalene, 554. Cetyl alcohol, 69. Chattawat, 358. Chemical reduction-products, 423. Chemistry of silicon, 98. Cherry-gum, 268. Chevreul, 115. Chitin, 303. Chitonic acid, 303. Chitose, 303.
Chloral, 60, 181, 223, 258-260, 304. alcoholate, 259.
hydrate, 258, 2<9, 260, 304, 310. Chloro-aoetic acids, 223. -acetone, 15^, 160, 165. -acetyl chloride, 503.
-catechol, 508. -aniline, m-, 510.
P-, 431, 479. -benzene, 397, 405, 429, 430, 459, 461, 515, 556. -sulphonic acid, p-, 461, ijfi. -«2^mliazocvaniae, p-, 341. -benzoic acia, m^, 484. 0-, 484. p., 435, 484. -benzonitrile, p-, 431. -benzophenone, 443. -)>utync acid, a-, 222. ^-, 222. 7-, 222. -buWronitrile, y-, 325. -caffeine, 377. -carbon J 459. -carbomc esters, 360. -<^c2ohexaBe, 522. -ether, 195. -ethers, 194.
•formic esters. See ehhrocarhonic esters.
Chk>ro*metliyleiie, 182.
-naphthalene, a-, 556.
-nitro-amline, 510. -benzene, m-, 459. 0-, 459i 516. p.. 459, 510, 515.
-phenol, m-, 535. 0-, 402, 515, 535. P-, 462, 515, 535.
-propionic acid, a-, 323.
-propylene, ct-, 165, 166. /S-, 165, 166.
-pyridine, ^, 573, 584.
-succinic acid, 234. d-, 326. ^-,326.
-toluene, 0-, 448, 516. p-, 448. Chloro'formi 16, 28, 60, 102, 181-X83,
223, 259, 260, 349, 368, 500, 501,
538, 542. 584, 595. Chlorophyll, 582, 584, 585.
-a, 585.
-6,585. Chlorophyll-grains, 294. Chlorophyllins, 584. Chloropicrin, 368. Choline, 196, 197, 600, 602. Chondrm, 334. 336, 337. Chondroitinsulphuric acid, 387. Chondrosin, 337. Chromogens, 480. Chromophore-groups, 480, 599. Chromoproteins, 335, 338. Chrysoidine, 482. Chrysin, 490. Cinchomeronic acid, 593. Cinchonine, 608, 609.
malate. 235.
mandefates, 452, 453.
d-tartrate, 248.
^tartrate, 248. Cineol, 529. Cinnamaldehyde, 456. Cinnamic acio, 456, 457. AUo-, 457.
acids, iao-, 457. Cinnamyl alcohol, 455, 456. Citral. See geranial. Citric acid, 252, 2S3, 287, 602. Cilromycee giaber^ 252.
pfefferianue, 252. Claisen, 256, 257, 306. Classification of organic compounds,
35. Clupelne, 342. Coagulated proteins, 335. Coagulation, 332, 333. Coal, 159, 399.
618
INDEX
Coal-gas, 36, 148, 159, 350, 399, 402, 552.
-mine-exploeions, 37.
-tar. See tar. colours, 399, 416. Cocaine, 602, 605. Cocoa, 375. Cod^ne, 606.
methyl-iodide derivative, 606. Coefficient of distribution, 29. Coflfee, 375. Cognac, 58. Coke, 399. Colchicine, 602. CoUagens, 336, 337. CoUicEne, 575, 576. CoUidines, 575, 576. Collie, 317. Collodion, 301. CoUoids, 332, 493. Colophonium, 498. Colour-bases, 545, 546. Combustion-furnace, 5.
of peat. 142. wooa, 142. Combustions, 5-8. Compound ethers. See esters. Condensation, 140. Condensed rings, 381, 55a. Confectionery, 272. Conglomerate, 249. Congo-dyes, 557, 558.
-red, 557, 558. Conilne, 576, 577, 600, 602.
iso-, 576, 577. Conium maculatum, 602. Conjugated proteins, 335, 337, 338.
linkmg, 392, 395.
system, 164. Constancy of substitution-type. Rule
of, 514. Constitutional formula, 46, 53. Constitution of alcohols,
CnHw+i-OH, 51-53. Contact-difference of potential, 380,
422,423. Copper aoetylacetone, 258.
acetylene, 160, i6a.
disodium tartrate, 240, 241.
mercaptides, 82.
-oxide test. 4.
-zinc couple, 151. Coral, 337. Comeiln, 337. Corn-flower, 490. Cotamine, 607, 608. Cotton, 299.
-seed, 269.
-wool, 300, 301.
Coumaric acid, 501. CoumariUj 501, 502. Coumarinic acid, 501, 502. Crafts, 400, 401. "Cream of tartar," 240. Creatine, 370. Creatinine, 370. Creosote-oil, 400, 409, 552. Cresol, m-, 626. 0-, 486, 516, 532. P-, 339, 411. Cresols, 409, 411.
Critical temperature of saturated hy- drocarbons, 43. Croconic acid, 385, 386. Crotonaldehyde, 140, 178.
-ammonia, 575. Crotonic acid, 170, 171, 172, 175, 178, 212, 213, 223, 228. MO-, 172, 173. Solid. See crotonic acid. Cryoscopic methods, 14-18, 345.
solvents. 14, 15, 16, 402, 403. Crystalloids, 332. Crystal-violet, 545. Cumene, 402. Cupric cvanide, 347.
phenylpropiolate, 455. Cupric xanthate, 361. Cuprous cyanide, 347.
xanthate, 361. Curarine, 609, 610. CuRTius, 329. Cyamelide, 352, 358, 362. Cyanamide, 340, 356, 364, 368-
370. Cyanic acid, 351, 352, 353, 354. 180-, 352, 362, 363. esters, 353. Mo-i 353, 354, 361, 363, 367. Cyanides, 347, 348, 349-351. Cyano-acetic acid, 203, 204. -benzoic acid, o-, 495. -hydrin-synthesis, 134, 135, 226, 230, 262, 267-269, 274, 280, 281, 293, 308. -propane, a-, 186. -quinolines, 592. Cyanogen, 200, 347, 348. chloride, 352, 353. derivatives. 347-358. Cyanuric acid, 351, 352, 357, 358, 362, 365. Insoluble, See cyamdide, iso-, 357, 368. bromide, 357. chloride, 353, 357. esters, 357, 358. ^«>-, 353, 357» 358.
INDEX
619
Cyclic compounds, 36, 158, 159, 258, 381-610. hydrocarbons, CnHzti, 383-388, 520-522. Cymene, 389, 402, 403, 525, 526, 533, 538. WI-, 534.
p-. See cymene. Cysteine, 341. Cystine, 341, 342. Cytisine, 602.
D.
Datura atromoniumf 604. Decamethylenedicarboxylio acid,
199. Davy, J., 359. Decane, 42.
Defunition of organic chemistry, 1. Dehydromucic acid, 581. Deocan, 186. Denaturation of albumins, 332.
ethyl alcohol, 56, 60, 61. Dennstedt, 7. Density, 32. Deoxy-cafFeine, 378. -compounds, 378. Depressimeter, Eykman's, 17, 18. Depression of the freezing-point, 14- 18.
Molecular, 14, 15, 16. Depsides, 491, 492. Desmotropy. See tautomerism. Detection of carbon, 3, 4.
carbonyl-group, 136.
halogens, 4, 5.
hydrogen, 3, 4.,
nitrogen, 4.
oxygen, 5,
phosphorus, 4.
sulphur, 4, 5.
water in acetone and alcohols, 59. Determination of boilins-point, 32.
melting-point, 31, 32.
molecular weight, 11-19.
specific gravity, 32.
vapour-density, 12-14. Developers, 201, 467, 477. Dextrin, 296, 298, 299. Dextrins, 296. Dextrose, 56, 67, 229, 252, 270-273,
274, 276, 278, 280-286, 289, 291-
296, 300, 344, 349, 468, 469, 486,
492, 566, 597. a, 271, 272, 286, 468, 469. ^, 271, 272, 286, 468, 469. •-, 271, 272.
Diabetes mellitus^ 146, 270. Diacetoneamine, 146.
-propane, 539. Diacetyl, 256, 305, 306. Diacetylen^carboxylic acid, 218. Dialdehydes, 254, 255. Dialkyl-phosphines, 96.
-phosphinic acids, 97. DiaUyl, 255. Diamines, 196, 209. Diamino-azobenzene. See chryscndine.
-dihydroxyarsenobenzene, 478. dmydiochloride, See ialvarsan.
-stilbene, p-, 550.
-trihydroT^dodecanic acid, 341. Diamylene, 152. Dianthracene, 562. Diastase, 57, 282, 296. Diazo-acetic ester. See ethyl diazo-' acetate.
-aminobenzene, 431, 432.
-compounds, 329» 330, 425-433. anti-f 426, 431. 82^, 426, 430, 431.
-hydrat^, antU. See diazohy- droxides, anti-. Diazonium compounds, 410, 415,
^je— '^tk) 434.
Dibasic acids,* 198-220, 234-246,
494-499. Dibenzalc^cZohexanone, 524. Dibenzhydroxamic acid, 450. Dibenzyl, 550, 551.
-amine, 454. Dibromo-acetic acid, 304.
-benzene, m-, 390, 458, 509. 0-, 390, 505. P-, 390.
-brassidic acid, 224, 225.
-butyric acid, 175.
-erucic acid, 224, 226.
-indigo. Symmetrical, 599.
-menthane, 531.
-menthone, 626.
-nitroethane, 94.
-propane, aa'-. See irimethylene bromide.
-propane, a/8-, 186. .
-pyridine, 608.
-succinic acid, 214, 215, 235. ISO-, 214, 215, 216, 235.
-thiophen, 586. Dicarbonyl-bond, 284. Dichloro-acetal, 358, 259.
-acetic acid, 222, 223.
-acetone, 252.
-benzene, m-, 458, 551. 0-, 515. p., 479, 515.
620
INDEX
Dichloro-ethylene, 186.
-hydrin, Svmmetrical. See glycerol dichlorohydrin. Didiphenylene-ethylene, 542. Dietnoxy-8-chloropurine, 2 : 6-, 377. Diethyl. See also ethyl.
-aoetonedicarboxylate, 469.
-acetylenedicarboxylate, 587.
-carbinol, 53.
carbonate, ^6o, 362, 366.
c^cfobutyldicarboxylate, 383.
dlacetylsuccinate, 309.
dibromomalonate^ 310.
dihydroooUidinedicarboxylate, 575.
dLsodiomalonate, 204, 219, 383.
disulphide, 82.
ether. See ether.
inalate 234.
malonate, 204-206, 210, 211, 3H, 469.
monosodio malonate, 204, 205, 207, 219, 311, 314, 325, 469, 498.
oxalate, 202.
phloroglucinoldicarboxylate, 469.
succinate, 521.
succinylsuccinate, 521.
sulphate, 75, 76.
sulphonedimethylmcthane. See sulphoncd. Dihydric alcohols. See glycols.
phenols, 465-467. Dinydro-cinnamic acid o-carboxylic
acid, 560. Dihydro-naphthalene. See naphtha- lene dihydride.
-pyrrole, 2 : 3-, 584. Dihydroxy-acetone. See glycerose.
-acids, 235-246, 487, 488.
-anthraquinone. See alizarin.
-azobenzenesulphonic acid. See resorcir^yeUow.
-benzene, m^. See resorcinol. 0-. See catechol, jh. See quinol.
-flavone, 1:3-. See chrysin.
-fluoran. See flvoreaceHn.
-naphthalene, 2 : 6-, 559.
-phenanthrene, 607.
-xanthone, 1 : 2'-. See euxanlhone. Di-iodopurine, 376. Diwopropyl, 46. Diketens, 206. Diketo-cyc^ohexane, i>-, 521, 623.
-piperazine. See glycine ar^ydride. Diketones, 255-258. Dimethoxyphenanthrene. See di-
melhylmorphol. Dimethyl-acetylene, 161.
-allene, 163, 164.
Dimethyl-alloxan, 375. -amine, 87, 90, 143, 419. -aminoazobenzene, 432, 481.
-sulphonic acid. See helianlhine. -aniline, 4181 4i9» 432, 440, 481. 543,547. hydrochloride, 483. O'Chj 518. -arsinic acid, 97. -benzenes. See xylenes. -diethylmercaptole, 147. -ethylcarbinol, 53, 163. -ethylene, Symmetrical, 149.
Unsjrmmetrical, 149. -hexane, 2 : &-, 50. -hydroxyethylamine, 606, 607. -ketone, 132. -morphol, 571, 606. -A>^^-octadiene-8-al, 2:6-. See
geranial. oxalate. 202. -phenylpyrazolone. See antipy^
rine. -phosphinic acid, 97. -pyridines. See lutidines. -pyronc, 316-318.
hydrochloride, 317. sulphate, 76, 90, 93. -sulphoneaimethylmethane, 147. -thiophen. See thioxen. Dinaphthol, a-, 557.
/3-, 557. Dinitriles, 198.
Dinitro-benzene, m-, 458, 460, 511. 0-, 460, 461. P-, 460. -cellulose, 301, 302. Dinitro-compounds, 195, 196, 460, 461. •ethane, 451, 452.
aci-y 451. -tit-naphthol, 558.
-sulphonic add, 558. -phenol, 2 : 6-, 460. -stilb^ie, p-, 550, 551. -toluene, 1:2:4-, 518. (M>-^ 518. Di- (o-nitrophenyl)-d]aoetylene, 596. Dioses, 261, 281-294. Dioxindole, 594. Diozonides, 255. Dipentene, 530, 532. tetrabromide, 532. Dipeptides, 343, 345. Diphenic acid, 541, 542, 569. Diphenyl, 400, 422, 447, 540, 54i, 569. 570. -amine, 413, 416, 4x7, 422, 547, 549.
INDEX
621
Diphenyl picrate, 413.
-ethane, Symmetrical. See dt- henzyl. Unsyimnetrical, 541.
ether. 412.
-ethylene, Symmetrical. See siil- bene.
-methane, 541.
-nitrogen, 549.
-nitroeoamine, 549. Diphenyleneketone, 541, 542. Dippers oil, 57a, 582. Dipropyl, 46, 47. Direct ayes, 481. Dispersion, 34. Dissociation, 550. DiseymnUirie molecular . See molecu'
lor asymmetry. Distillation, 21-28.
-apparatus, 21-24, 26, 27.
-flask, 21.
of wood, 56. Divi-divi, 488. Dodecarhvdronaphthalene, 559.
-methylenedicarboxylic acid, 199. Dodecane, 38, 4a. Dodecyl-group, 38. Dorp, van, 268, 353, 493, 593. Double bonds, 152, 153, 155-158. Drewsen, 590. Dry-cleaning process, 39. Dulcitol, I93i 194, 277, 468. Dumas. 2, 7. Dutch liquid, 186. Duty on alcohol, 61. J)^fiiaLsedd,49Q^ Dynamile, l93.
E.
Earth-wax. See ozokerite. Ebonite. See mdcanite. Ebullioscopic methods, 14, 16-19.
solvents, 16. Ecgonine, 605. Edbb's solution, 202. Edge-substitution, 251, 252. Egg-albumin, 333, 334, 345.
-yolk, 197. Ehrlich, 324, 478. Eicosane, 42. Elaldic acid, 174, 175.
transfonnation, 174. Elastin, 334, 336^ 337, 342. Electric conductivity. Molecular, 35,
116, 117. Electrol3rtic dissociation, 116-118.
methods, 377-380, 422-425. . reduction-products, 423.
Elements in carbon compounds, 3. Elevation of the boiling-point, 14,
16-19. Ellagic acid, 492. Emulsin, 286, 295, 349, 452. Enantiomorphism, 248, 249. Enantiotropy, 442. Engler, 40. Enolic form, 313-315. Ensilage, 229. Ensymes, 57, 192, 249, 266, 273, 282,
286, 290, 501. Eosin, 202, 406. Epichlorohyarin, 195. Equilibrium, 122-125. Ergot, 503. Errors in carbon-estimations, 9, 10.
hydrosen-estimations, 9, 10. Erucic acid, 170, 174, 175, 224. Erythritol, 193, 468. Erythrose. 281. Erythroxylon coca, 605. Esterification, 120-125. Ester-method, Fischer's, 340, 341. Esters, 71:1:76, 92, 120-127, 210, 211. Estimation of carbon, 5-7, 9-11. halogens, 8, 9. hydrogens, 5-7, 9-11.
ions, 330. nitrogen, 7, 8, 10, 11. oxygen, 9-11. phosphorus, 8. sulphur, 8. Ethane, 37, 38, 42-45, 96, 99, 152, 162, 185. -tricarbojcylic acid. 207. Ethenylaminophenol, 477. Ether, 16, 28-30, 76, 77-79, 100, 151, 182, 194, 314, 318. Chloro-, 194, 195. -synthesis, Williausgn's, 77. Ethers, 72, 77-79, 80, 81-83, 148, 412.
Chloro-, 194. Ethyl. See a^^ diethyl. Ethyl acetate, 106, 120, 121, 122-125, 127, 257, 302, 306, 469. acetoacetate, 306-315, 575, 576,
589. -acetylene, 159. (i-alanine, 326.
alcohol, 16, 31, 51-53, 54, 56-61, 69, 72, 75, 77-79, 81, 92, 109, 120-127, 137, 144, 151, 163, 181-184, 189, 190, 195, 205, 254, 258, 259, 270, 272, 273, 282, 304, 306, 309, 312, 314, 324, 356, 428, 429, 437, 438, 527. Test for. See iodoformrtest.
622
INDEX
Ethyl-amine, go, 101, 102, 197,420, 438. -aminoacetate hydrochloride, 323. -benzene, 400, 402. benzoate, 436, 437. bromide, 72-74, 76, 84, 400. n^butylacetoacetate, 308. butyrate, 121. carbonate, 469. -carbylamine, 101, 102. chlonde, 72, 182, 185. chloro-carbonate, 219, 311, 359, 366,436.
-formate. See elhyl chlorocar- honate.
-oxalate, 439. ooUidinedicarboxylate, 575. copper-acetoacetate, 316. cyanide, 101, 102. 7-cyanopropylmalonate, 325. cyanurate, 353.
diazoacetate, 329, 330, 386, 587. di-iodoacetate, 330. ether. See ether. formate, 453, 548. fumarate, 219, 330, 589. glycollate 227, 330. glycollic acid, 227. -group, 38.
hydrogen sulphate. See elhylsul- jmuric acid.
malonate, 210, 211. iodide, 51, 67, 74, 75, 77, 83, 88,
92, 97, 106, 412. -/S-iodopropionate, 528. isocyanate, 353. magnesium bromide, 100. maleate, 216. -mercaptan, 146. mesoxalate, 310.
methanetricarboxylate, 218, 219. methy!-?i-butylacetoacetate, 308. monochloroaoetate, 207, 219, 309,
330. nitrate, 75. nitrite, 92. -nitrolic acid, 94. n-octy?a"etoacetate, 308. orthoformate, 182. phenylacetate, 453. phosphate, Normal, 75. pseu^phenylacetate, 386. -pyridine, at-, 605.
^,609. sodio-aoetoacetate, 306-309, 310- 313, 315.
-cyanoacetate, 528. sulphate, 75, 76. sulphide, 82.
Ethyl-sulphonic acid, 83.
-sulphuric acid, 75, 76, 78, 151, 152, 408. Ethylene, 91, 149, 150, 151, 152, 153, 154, 185, 186, 188.
-bromohydrin, 497.
bromide, 151, 153, 159, 165, 168, 186, 207, 383, 497.
chloride, 153, 185, 186, 189, 190.
cyanide, 207.
-diamine, 196, 252:
oxide, 189, 190, 196, 197, 209, 579. Ethylidene chloride, 133, 153, 159. Eugenol, 500.
iso-, 500. Euxanthone, 489. Exaltation of refraction, 164, 395,
561, 621. Extraction with solvents, 28-30. Eykman, 15, 17, 18, 34, 35, 43, 158,
172, 388.
F. Fseces, 595. Faraday, 402. Fats, 2, 40, 113, 114, 115, 173, 186,
191, 192, 331, 606. Fatty acids, 104-106, io>7, 108-118.
compounds. See cdiphalic com- pounds. Fehlinq's solution, 240, 241, 242,
262, 337, 434. Fermentation, 56, 57, 290-293.
butyric acid. See butyric acid, Normal. Ferric acetate, Aceto-, 112. Basic, 112.
succinate, 207.
thiocyanate, 354. Fibrin, 334. Fibrinog^, 334. Fibroin, 337, 342, 344. Filtering-flask, 30. Filtration, 30. Fire-damp, 36, 37. Fischer, Emil, 236, 276, 282, 284.
292, 293, 303, 326, 340-344, 374,
376, 377, 491, 492, 498. FiTTiG, 228, 400; 405. Ftttig's sjmtheas, 400, 405, 556, 586. Flash-point, 39.
apparatus of Abel, 39. Flavone, 489.
dyes, 489. Flax, 300. Fluidity, 110. Fluoran, 496, 497. Fluorene, 541, 542. Fluorescan, 496, 497.
INDEX
623
Fluoro-benzene, 614.
-nitrobenzene, o-, 514. p-, 514. 515. Force, Vital, 1. Formaldehyde, 56, 91, 132, 142-144,
267, 277, 294, 322, 333, 415, 416,
521. Formaldoxime, 143. "Formalin." See formaldehyde. Formamide, 127. Formates, 108. Formic acid, 101, 107-109, 112, 117,
142, 143, 146, 178, 182, 200, 202,
203, 259, 273, 351, 357, 403, 581. Formonitrile, See hydrocyanic acid. Formose, 267.
Formuke, Calculation of, 9-11. Formyl chloride, 439.
-group, 107. Fortified wines, 58. Fractional crystallization, 30, 31.
distillation, 22-26. curves, 25. Fractionating-apparatus, 21.
-oolunms, 23, 24, 57, 58. Franchimont, 363, 417. Friedel, 191, 400, 401.
and Craft's synthesis, 400, 401, 441,556. Fructosazone, d-. See d-glucoaazone.
i-. See inglucosazone. Fructose, d^. See UemUase.
dt-, 278. Fruit-essences, 121.
-sugar. See Icevulose. "Fulminating mercury," 336. Fulminic acid, 356, 357. Fumaric acid, 211-217, 219, 235, 244,
245 327. Furan, 382, 579, 580, 585. Furfural. See furfuraldehyde. Furfuraldehyde, 270, 580, 581. Furfuramide, 580. Furfuran. Bee furan Furfuroln, 580.
Furfurole. See furfuraldehyde, Furfuryl alcohol, 580. Furs, 467.
FURTH, VON, 334.
Fusel-oil, 58, 60, 63, 64, 152, 324.
G.
Galactonic acid, d-, 277, 278. Galactose, d-, 193, 269, 277, 283, 292,
295 Gallic' acid, 467, 488> 490, 492. Gall-nuts, 488, 492.
-stones, 341.
GaUovl-«allic acid, 492.
-gallylchloride, 492. Gambier, 491. Gas, Coal-, 36, 148, 150, 309, 402,
552. Gas-manufacture, 399. Gastric juice, 339. Gattermann, 429, 499. Gaidtheria procumbens, 486. Gelatin, 143, 334, 336, 337, 342. Gelatose, 335. Gentianose, 286. Gentiobiose, 286. Geranial, 178, 179. Geranic acid, 178. Geraniol, 178, 527. Geranium, 490. Gerhakdt, 2. Germanium alkides, 98. Gernez, 66. Gin, 58.
Glacial acetic acid, 31, zzo, xzz. Gladstone, 151. Gliadin, 334. Gliadins, 334. Globin, 338.
Globulins, 334, 335, 336. Globulose, 335. Gluconamide. 268. Gluconic acid, d-, 268, 271, 276, 282,
283. Gluco-proteins, 334, 335, 338. Glucosamic acid, d-, 303. Glucosamine, 303.
hydrochloride, 303. Glucosazone, d-, 271, 274, 275, 277.
i-, 277. Glucose, dr. See dextrose.
i-, 270.
Ir, 270, 292. Gluoosides, 266, 281, 284-286, 349, 486, 566, 597.
Artificial, 284-286. Glucosone, d-, 275.
i-, 278. Glue, 322.
Glutamic acid. See glulamine. Glutamine, 325, 337, 340, 342. Glutaric acid, 199, 208, 269, 385.
anhydride, 208. Glutelms. 341.
Glyceraldehyde, 27, 276, 277. Glyceric acid, 190, 305. Glycerol, 57, 113-115, 177, 190-193, 194, 195, 202, 203, 266, 272, 468, 590, 603. Glycerol dichlorohydrin, 195, 252. Glycerophosphoric acid, 197. Glycerosazone, 266.
624
INDEX
Glycerose, 266.
Glyceryl monof«jrmate. See maruH formin.
oxalate, 203.
trinitrate. See nitroglycerine. -fltearate. See tristearin. Glycine, 226, 320, 321, 322, 323, 324, 337. 340, 342, 344.
anhyoride. 343.
Copper salt of, 323.
ethvl ester, 329, 343.
hyarochloride ethyl ester, 322. GlyoocoU. See glycine. Glycogen, 299. Glycol, 167, 188, 189, 190, 468.
-chlorohydrin, 150, 189.
diaoetate, 210.
diethyl ether, 189.
mono-aoetate, 210. -ethyl ether, 189. Glycollaldehyde, 266, 267, 277. 340. Glycollic acid, 226, 227-229, 234, 254,
274 304. Glycollide, 229, 234. Glycollose. See glycoUaldehyde. Glycols, 187-190, 198, 209. Glycyl-iJanine, 345.
-glycine, 342, 343. Glyoxal. 235, 254, 255, 304. Glyoxalic acid, 304, 310, 330, 372.
GOLDSCHMIDT, 432. GOMBEBQ, 548.
Gout, 374.
Granulose, 296.
Grapes, 270.
Grape-sugar. See dextrose.
Graphic method, Eykman'b, 15.
Green oil. See anthracene'oil.
CtRtbss 42^
Griqnard, ioO, 104, 122, 135, 318.
Guaiacol, 465, 466, 501.
Guanidine, 368, 369.
thiocyanate, 369. Guanine, 338. 374. Guanylic acid, 335. Gum-arabic, 268.
-benzoin, 389, 436.
Cherry-, 268. Guncotton, 193, 301, 302, 356.
H.
Haber, 424, 425. Hfematin. 338.
hydrochloride, 338. Haemin, 338, 584.
Hsemoglobin, 335, 338, 342, 345, 584. HsBmoglobins. See chromo-prot^ns. Halochroniy, 544.
Halogen-benzenes, 404, 405, 449.
-benzoic acids, 449, 484.
-carriers, 440, 449, 458.
derivatives of methane, 181-184. homologues, 184-187.
-hvdrins, 195.
-phenols, 462.
-substituted acids, 221-225.
-sulphonic acids, 461.
-toluenes, 448, 449. Hamblt, 362.
Hantzsch, 425, 428, 431, 545, 575. Hardening of oils, 174. Hard water, 116. Harries, 255, 539. Hartley, 470-472. Hata, 478.
Heating substances, 20, 21. Heavy oil. See creosote oil. Helianthine, 476, 483. Heliotropin. See piperonal. Hempbl, Fractionating column of, 23. Heneioosane, 42. Hentriaoontane, 38, 42. Heptachloropropane, 183. Heptane, 42, 67.
cydo-j 522. Heptonic acids, 268, 274. Ileptoses. 261, 268. Heptyl alcohol. Normal, 54. Heptyhc acid, 107, 274, 308. Heroine, 607. Herring-brine, 90. Heterocyclic compounds, 381, 572-
610. Hevea brainlienaisy 538. Hexa-bromobenzene, 404.
-chloro-bensene, 404. -ethane, 183, 185, 186.
-contane, 37, 42.
-decane, 42.
-diene, cydo^y 392.
-dione, cydo-, 472.
-hydric alcohols, 262, 264, 265, 275.
-hydro-benzoic acid, 525. -cvmene. See methane. -phenol. See hexatwl^ cyclo-.
-hydroxvbenzene, 385, 472, 473.
-methylbenzene, 161.
-methylene. See hexane^ cyclo-. ^ ' -tetramine, 143.
-methyltriaminotriphenylmethane. See crystal-violet.
-phenylethane, 448, 549.
-triene, 395. cydor 392, 394. Hexane, 37, 42, 46, 47, 48, 88, 314.
cydo-, 386, 388, 470, S30-Sa2, S23, 524.
INDEX
625
Hexane, derivative, cyclo-f 386, 520-
Hexanol, cyda-, 392, 523, 523. Hexanone, cycu)-, 620, 521, 524. Hexene, q^do-, 392.
bromide, cyclo-, 392. HexodioeeSj 261. Hexonic acids, 262, 275, 276. Hexoses, 261, 263-265, 267-269, 270-
281, 291, 295, 309, 523, 581. Hexotrioses, 261, 294. Hexyl alcohol, Normal, 54.
-amine, cydo-^ 392.
iodide, Normal secondary, 264.
-methylamine, cydo-, 387. Hexylene, 149. 388. «^
Higher alcohols, C»Htn+i • OH, 69. Hippuric acid, 322, 436. Histidine, 341, 342. Histones, 334.
HoPF, VAX ^T, 16, 66, 68, 524. Hoffmann, 86, 90. Homologous series, 41. Honey, 273.
Artificial, 851.
-stone, 499. HooQEWEBFF, 268, 353, 493, 593. Hops, 58.
Hordenine, 503, 602. Hormathic compounds. SeealipftcUic
compounds. How ABO, 356. Humic substances, 277. Hydrazines, 433, 434. Hydrazinoacetic acid, 330. Hydrazo-benzene, 420-422, 424, 425, 540.
benzoic acid, m-, 541. Hydrazones, 1^6, 137, 262, 263. Hydro-aromatio compounds, 38(), 398, 520-539.
-benzamide, 439, 440, 556, 580.
-benzoin, 551.
-carbons, CiJItfi, 79, 148-159, 165, 383-388, 520-525. CnH«+,, 36-50, 149, 387.
CnUtn-ty 159-164, 166.
-cinnamide. 456.
-cyanic acid, 226, 230, 231, 2G3, 281, 291, 303, 324, 339, 348, 349i 350, 351, 355, 439, 499.
-cyclic compounds. See hydro- aromatic compounds,
-ferrocyanic acid, 318 .
-naphthalenedicarboxylic acid, 553.
-phthalic acids, 525.
-quinone. See quinol. Hydrolysis, 103. Hydrolytic dissociation, 115.
Hydroxamic acids. 94, 95. Hydroxy-acetic fdd. See glycollic acid. -acids. Dibasic, 234^252.
Monabasic, 226-234, 305. -aldehydes, 499-501. -anthraquinones, 565-569. Hydroxy-azo-benzene, o-, 421, P-, 420, 433, 481. -dyes, 481, 482. -benzaldehyde, p-, 500. -benzoic acid, m-, 487.
0-. See salicyiic acid. P-, 487, 490, 491, 509. didepside, p-, 491. -butyric acid, a-, 139. /?-, 170, 228. 7-, 228, 233. -cinnamic acid, o-, 501. -cymene, p-. See thymol. -ethylamine, 497. -isobutyrio acid, a-, 227. -methylfurfuraldehyde, 581. -3-methoxyphenanthrene, 4-. See
methylmorphol, -phenyl-arsinic acid, p-, 478. -ethylamine, ^, 603. -propionic acid, p-, 501. -proline, 341. -propionic acid, ot-. See lactic acid.
/3-, 227,229. -propylene, /3-, 167. -quinoline, 2-. See carbostyril. -quinolines, 592, 593. -stearic acid, 175. -succinic acid. See malic acid. -tetrahydropyrrolecarboxylic acid.
See hydroxyproline. -toluenes. See cresols. Hyoscyamine, dl. See atropine. "Hypnone,"441. Hypoxanthine, 338, 374.
I.
Iminazole, 602. Imino-chlorides, 128.
-ethers, 128, 129. Immiscible liquids. Separation of,
28-30. Increment of the double bond, 158. Indanthren-blue, 569.
dyes, 569. ** Indian yellow." See euxanthone. India-rubber. See caoutchouc. Indican, 597. Indigo, 415, 441, 463, 493, 494, 593,
596-599.
-brown, 597.
626
INDEX
Indigo-eulphonic acids, 440, 441, 597.
-vatpdyeing, 598, 599.
-white, 598, 599. Indigofera arrectat 596.
sumatrana, 596. , Indiglucin, 597. Indigoids, 599. Indigotin, 597. Indirubm, 597. Indole, 593-S95i 610.
-alanine. See tryptophan.
-aldehyde, 3-, 595.
picrate, 595. Indolylbenzoylaminoacrylic acid, 595. Indophenin-reaction, 585. Indoxyl, 597, 598. Industrial spirit, 61. Infusorial earth. See kieselguhr. Ink, 488. Inoculation, 247. Inositol, 523, 524.
hexa-acetate, 524. Introduction, 1-35. Inulin, 273.
Inversion, 370, 284, 289, 300. Invertase, 291. Invertrsugar, 229, 270, 373, 284, 289,
581 lodol, 183. lodo-acetic acid, 222.
-aniline, p-, 477.
-benzene, ^04, 405, 540. dichloride, 405.
-butane, ce-, 186.
-phenol, 462.
-propionic acid, ^, 171, 321. Iodoform, 60, 61, 183, 184, 535.
-test. 60, 184. lodosooenzene, 405. lodoxy benzene, 405. lonization-constant, 117. lonone, 179, 180. Iron, Catalytic action of, 185, 404,
458. Irone, 180. Isatin, 504, 596.
chloride, 596. /so-amyl acetate, 121 . wovalerate, 121.
-butyl alcohol, 53, 54, 63. bromopropionate, 231. -carbinol, 53, 64, 324. iodide, 154.
-butylene, 150, 154, 155.
-but3rric acid, Z12, 113, 227, 536.
-camphoric acids, 536.
-cinnamic acids, 457.
-crotonic acid, 172, 173.
-cyanic acid, 353, 362, 363.
/«o-cyania esters, 353, 361, 363, 367. -cyanuric acid, 358.
esters, 353, 357, 358. -dibromosuccinic acid, 2x4, 215,
216. -eugenol, 500. -leucine, 324. -maltose, 296. -nicotinic acid, 577, 578. -nitriles, 101-103, 182, 183. -nitroso-camphor, 536.
-ketones, 256. -phenylacetic aoid, 386. -phthalic acid, 498, 509. -propyl alcohol, 53, 61-63, 125, 146, 188, 191. -amine, 86, 87. -benzene. See cumene. -carbinol. See mobtUyl alcohol. iodide, 46, 112, 154. -purone, 378. -quinoline, 593, 600, 607.
sulphate, 593. Hsaccharic acid, 303. -thiocyanic esters, 355, 361. -urea, 364.
-valeraldehydeammonia, 324. -valeric acid, 282. Isomeric compounds. Physical prop- erties of, 49, 50. Isomerides, 43.
Number of possible, 48, 49. Isomerism. 3, 43-46. of the alcohols, CmHm+i'OH, 53, 54. amines, 86. paraffins J 43-49. Optical, spacial, or stereochemical. See stereoisomerism. Isoprene, 163, 532, 539.
Japan camphor. See ramphar.
JORISSEN, 55.
JuLiN, 459.
K.
Kekule, 389, 392, 394, 395. Keratin, 334i 336, 342. Ketens. 206. Keto-aloohols. See sugars.
-aldehydes, 256.
-hexamethylene. See hexaiume^ cyclo-.
-hexoses, 251, 581.
-pentamethylene. See pentanane^ cyclo-.
-stearic acid, 175.
INDEX
62Z
Ketone deoompoeition, 306, 307, 309. Ketones, 63, 130-137, 145, 146, 156, 160, 161, 185, 188, 193, 194, 226, 315, 441, 442, 443.
isonitrocK)-, 256.
Mixed, 133. Ketones, Unsaturated, 179, 180. Ketonic acids, 305-310.
form, 313-315. Ketoses, 261, 262. Ketoximes, 135. ''Kieselguhr," 193. Kjeldahl, 8. Klason, 358. Knop, 365. Knorr, 313, 589. KoLBE, 2, 54, 486. KoMppA, 537. KdNiGS, 590, 609. KdRNER's principle, 504, 505, 509. K0S8ELL, 334, 342. kostanecki, von, 489. Krapft, 173. Kreubsler, 7. KOSTER, 241.
L.
Laboratory-methods, 19-35. Lachrymatory shells, 450. Lact-fiubumin, 334. Lactams, 321.
Lactic acid, 226-228, 239, 230, 231, 273. dr, 230, 248. U, 230, 248, 294. Racemic, 230, 248.
fermentation, 229, 291. Lactide, 227, 228. Lactobionic acid, 283. Lactones, 223, 228, 232-234, 268, 269,
275, 285, 286, 544. Lactonitrile, 230, 320. Lactose, 229, 283. Ladenburg, 507, 576, 577. Lsevulaldehyde, 538, 539.
peroxide, 538. Laevulic acid, 179, 277, 309, 310, 581. Leevulose, 193, 270, 271, 273-275, 278,
284, 285, 292, 295, 308. Lakes, 568. Lassaiqne's test, 4. LaUx, 538. Laurent, 2.
Polarimeter of, 33, 34. Lauwerenburqh, 186. Law of Beer, 550.
of Berthelot, 28. dilution, 117. the even number of atoms, 47, 48.
Lead acetate, xi2,I288. Basic, 112.
mercaptides, 82.
oleate, 173.
palmitate, 173. L^d stearate, 173. Lecithin, 197. Lecithins, 197. Lecitho-protdfns. See conjtiQQUd
protons. Lemonade, 253. Lemon-grsbss, Oil of, 178. Lepidine, 609.
Leucine, 324, 337, 339, 340, 342, 344.
wo-,324. Leuckart, 430. Leuoo-bases, 545.
-malachite-green, 543. Leuconic acid, 385, 386.
pentoxime, 386. Lichens, 490. L?EBiQ, 2, 5, 8, 20, 290, 351, 365.
Condenserof, 20, 21. Libbermann's reaction, 417.
LlEBREICH, 260. Light oil, 460, 572.
petroleum. See pelrolemretker, Lignin, 269, 299, 301. Ligroln^ 39. Lime-nitrgoen, 356.
-water-test, 4. Limonene nitrosochloride, 532. Limonenes, 530-532. Linen, 299, 300. LiNNEMAN, Fractionating-column of,
23. Liqueurs, 272. Liquidambar orierUaliSy 455. Liquid crystals, 421. Liquids, Separation of solids and, 30. Lister, 411. Lithium urate, 374. LORENTZ, 34, 35. Lorenz, 34. Low wines, 58. Lubricating oil, 39. LuMiisRE, 477. Lupine seeds, 324. Luteolin, 490. Lutidines, 575. Lyddite, 464. Lysine, 325, 340. Lyxonic acid, 278. Lyxose, 278.
M.
Madder-root, 666. Madeira, 58.
INDEX
Magenta, 142, sa6, 517. MagDesium hafides, Alkyl, 100, 104,
122, 135, 318. Maiachite-jKreen, 543, 543, 546. Maleic acid, azi-217, 235, 244, 245,
327 474. anhy(iride,'2ix, 213, 214, 217. Malic acid 211, 234, 235, 325, 602.
(i», 326.
^326. Malonic acid, 199, 203-206, 208, 219,
310. 373, 456. anhydride, 206, 208. -ester synthesis, 205, 206. Malonylurea. See barbituric add. Malt, 57, 58. Maltase, 286, 291, 349. Maltobionic acid, 282. Maltosazone, 282. Maltose, 57, 282, 383, 285, 291, 296,
300. i80-.296. Mandelic add, 452, 453. •
dr, 452, 453.
Ir, 248, 4Sa.
r-, 248, 294, 45a, 453. Mandelonitrile, 452.
Manneotetrose, 295.
Mannitol, 193, 194, 266, 275, 376,
301.
Manno-heptonic acid, 293.
-nonoee, 293.
Hsaocharic acid, dr, 276, 280. Mannonic acid, d-, 276, 278.
^, 276, 278. MannosaaoncL d-. See d-glucosazone.
v-. See i-glucosazone. Mannose, d-, 193, 266, 275, 276, 278, 280, 292, 293, 300.
i-, 276,278. -
hydraione, d-, 277. Marckwald, 248« Margaric acid, 107. Margarine, 113. Margskrylmethylketone, 173. Marsn-gas. See methane. Martius's yellow, 558. McKenzie, 294. Meconin, 607, 608. Meconinic acid, 606, 607. Melanins, 501. Melediose, 295. Melissyl palmitate, 122. MelUtic acid, 499. Mendel^eff, 32, 59, 98. Mendius's reaction, 103. Menschutkin, 88, 414. Menthane, 525, 528, 583. Menthanol, 3-. See menthol.
Menthenes, 529.
Menthol, 248, 294, 526, 530.
Menthone, 52^.
Mercaptans, 80-S2, 83, 120, 355,
368. Mercaptides, 81, 82. Mercurialis perewiia, 90. Mercuric C3ranide, 258, 347, 350.
formate, 108. Mercuric fulminate, 301, 356, 3G0,
460. Mercurous formate, 108. Mercury acetate, 447.
alkides, 100.
mercaptides, 81.
phenide, 446, 447.
thiocyanate, 354. Mesityfene, 398. 402, 507, 506. Mesitylenic acid, 508. Mesoxalic acid, 310, 372. Mesoxalylurea. See aUoxan. Metaoetaldehyde, 144, 145. A/eto-oompounds, 396. Metallic acetylenes, 40, x6o.
alkides, 99, 100. Meta-proteins, 332, 335, 338.
-st3rrene, 455. Metnacrylic acid, 173. Methane, 35, 36-38, 41, 42, 43, 44, 99, 112, 133, 142, 162, 181, 389, 448.
homologues. Halogen derivatives of, 184-187.
-tricarbox]^lic acid, 219. Methoxy-lutidine, 317.
-quinoline, p-, 609. Methyl acetate, 126.
-acetic add. See prapwnic acid.
-aoetoanilide, 417.
alcohol, 54, 56, 70, 81, 88, 91, 108. 125, 142, 143, 202, 299, 314, 364, 385, 418.
-alloxan, 375.
-amine, 87, 90, 143, 316, 349, 355. 364, 503, 602.
-aniline, 417, 434, 584. hvdrochloride, 576.
anthranilate, 494.
-arsinic acid, 97.
-benzene. See toluene.
bromide, 74.
-n-butylacetic acid, 308.
-carbylamine, 102.
chloride, 37, 74, 151, 400, 418.
chlorocarbonate, 491.
cyanide, 102. -q^c2a-butane, 384.
-hexylidene-4-acetic acid, 1*, 5 : : pentane, 522.
INDEX
629
Methyl-ethyl-acetic acid. See valeric acidf Active.
-acetylene, 161, 162.
-amine, 86, 90.
-carbinol . See butyl akohal^ <Seo- ondary.
ether, 77.
-ketone, 133, 134, 146, 256.
-malonic acid, 205, 231. Methyl-glucoside, 284-286.
Of-, 286.
/3-, 286. -glycine, 370. -glyoxal, 272, 273.
oaazone, 272. -sroup, 38. -Heptane, 2-, 60.
3-, 60.
4-, 60. -heptenone, 179. -indole, 3-. See scaioU. iodide, 44, 45, 74, 205, 316, 384,
417, 434, 464, 466, 612, 573, 574,
601,606. -ifiopropyl-benEene, p-. See cy-
tnene.
-carbinol, 53, 163.
-ketone, 164. -ketones, 134, 160, 307. magnesium iodide, 528. -malonic acid, 205. mercaptan, 81. -morpnimethine, op-, 606, 607. -morphol, 606. -naphthalene, ot-, 566.
^,566. nitrite, 93.
-nonylketone, 145, 146, 308. ^
-o-nitrovanillin, 571. -orange, 483.
-phenyl-hydrazine, 276, 277, 434, 589:
hydrazones, 277.
-propiolate, 489.
-pyrazolone, 589. -phosphine, 97. -phosphinic acid, 97. picrate. 464. -piperidine, 604. -propyl-carbinol, 63.
-ketone, 132. -pyridines. See vicciinee. -pyrrole, 1- (or iV-). 583, 584.
2-(ora-), 683, 684. -quinoline, 'p-. See lepidine. -succinic acid, 210. -succinimide, 605. sulphate. See dimethyl sulphate, -thiophen. See thiotcien.
Methyl-ureas, 364, 375.
-violet, 547. Meth^^lated ether, 78.
spirit, 60, 61, 78. Methsdene, 150, 151.
-aminoacetonitrile, 322.
chloride, 183, 641.
-diphenyldiamine, 416.
ioaide, 184, 602. Meter, K. H., 313.
Victor, 12, 185, 517, 585, 687. Michael, 126. Michler's ketone, 419. Microplanktanf 40. Middle oil. see carbolic oil. Milk, a83, 334, 492.
-sugar. See lactose. Millon's reagent, 333. Mineral acids, Catalytic action of,
125. 138, 144, 146. Mixed crystals, 249, 687.
ketones 133. Mobile equilibrium, Principle of, 113,
125.
MOISSAN, 108. Molasses, 323.
Molecular association, 42, 66, 402, 403.
asymmetry, 67, 260, 524.
depression of the freezing-point, 14, 15, 16.
dispersion, 168.
electric conductivity, 35, 116, 117.
elevation of the boiling-point, 14, 16.
refraction. See refractumf Molecur lar,
volume, 33, 388.
weight of carbon, 19. MonoHalkyl-phosphines, 96. -phosphmic acids. 97.
-basic hydroxy-ocids, 226-234.
-bromo-. See bromo-,
-carbonyl-bond, 283.
-chloro-. See cfdoro-.
-ethyl. See ethyl.
-formin, 203.
-halogen compounds, 404, 405.
-hydroxy-acias, 486, 487.
-iodo-. See iodo-.
-methyl. See methyl.
-nitro-. See niiro-.
-sulphonic acids, 408, 409. Monoses, 261-281, 282, 283, 286, 291,
292, 295, 340. Monotropy, 442. Mordants, 112, 481, 668, 699. Morin, 499. Morphine, 571, 602, 606, 607.
630
INDEX
Moras tinctorial 490. Motor-spirit, 39. Mucic acid, 277, 581. Mucins, 335, 338. Mulberry. See Morua tindoria. Mvrex firandariSf 599. Murexide, 372.
-test, 372. Muscarine, 303. 600, 602. Musk, Artificial, 451, 535.
Natural, 535. Mustard-oils, 355, 367. .
Mutatotation, 271, 468, 469, Myosin, 334.
Soluble, 334. Myosinnogen, 334. Myricyl alcohol, 69.
N.
Naphtha. 39, 61.
Naphthalene, 16, 381, 399, 494, 506, 507, 552-562, 563, 564.
Constitution of, 553, 554.
-dicarboxylic acid, Peri-y 555.
dihydride, 554, 559.
-st^urosylphonic acid, 114.
-sulphonic acid, a-, 557. /?-, 557. Naphthaquinone, ot-, 558, 559.
fi-y 558, 559
am^pkir (or 2:6), 558, 559.
-oxune, a-, 559. Naphthenes, 520. Naphthionic acid, 558. Naphthoic acid, op-, 556.
/3-. 556. Naphthol, Of, 553, 556, 557.
^, 557. - -disulphonic acid, a-, 558.
-monosulphonic acid, or-, 558.
-trisulphonic acid, a-, 558.
-yellow, 558. NaphthyLamine, ot-, 557, 558, 561.
^, 557, 560, 561.
-sulphonic acid, 1 : 4-. See naph- thionic add.
tetrahydride, or-, 561. ^, 560, 561. Narcotine, 602, 607, 608. Nbf, 102, 167, 357. Nernbt, 380. Neurine, 168. Nicotiano tabacuniy 602. Nicotine, 578, 582, 600, 603-604. Nicotinic acid, 577, 578, 603.
M0-, 577. Nitriles, 101-103, 127-129, 136, 156.
wo-, 101-103, 182, 183.
I Nitro^mine, 367.
-amines, 363, 364, 417, 419. -aniline, m-, 459, 463, 475, 476, 511.
0-, 461, 475, 476.
P-, 475, 476, 480. -anilines, 475, 476. -anisole, p-, 471, 472. -benzaldehyde, m^, 499.
0-, 499, 570, 571. -bensene, 16, 27, 397, 406, 407, 411, 415, 420, 421, 423, 424, 429, 446, 459, 460, 463, 477, 480, 522, 546, 550, 587,'590.
-diazonium chloride, p-, 429.
-sulphonic acid, m-, 461. 0-, 461. P-, 461. -benzoic acid, m-, 484, 485, 515. 0-, 484, 485, 515. P-, 484, 485, 515. -benzo]rl chloride, 0-, 594.
cyanide, o-, 594.
-formic acid. 594. -benzyl chloriae, p-, 550. -butane. Tertiary, 93. -cellulose, 301, 302. -celluloses, 30X, 302. -cinnamaldehyde, o-, 591. -compounds, 92-95, 406-408.
Pnmary, 94.
Secondary, 94.
Tertiary, 94. -dimethylaniline, p-, 419. -ethane, 92-94. -glycerine, 192, 193. -gaimidine, 369. -4-hydroxyphenylarsinic acid, 3-,
478. -mannitol, 301. -mesidine, 508. -mesitylene, 506. -methane, 93, 455. -naphthalene, ot-, 506, 556, 557.
/?-, 557. oe-naphthylamine, 2-, 557. -paraffins, 92-95, 451. -phenol, m-, 463, 466.
0-, 461, 463, 511.
©., 463, 471, 472, 480, 511, -pnenols, 411, 451, 463-464, 544. -phenyl-acetic acid, o-, 594.
-nitromethane, m^, 451. -phthalic acid, 506. -propane. Secondary, 93. -prusside-test, 5. -pyridine, /3-, 574. -salicylonitrile, o-, 518. •stryrene, 455. -thiophen, 587.
INDEX
631
Nitro-toluene, ntr, 407, 512, 513.
0-, 407, 408, 416, 484, 494, 499,
512, 513. P-, 407, 408, 416, 512, 513. -urethane, 367. •vanillin, a-, 571. Nitrogen, Quinquivalency of, 350,
251. Nitroso^mines, 89, 91, 4x7. -benzene, 423, 424. -benzoic acid, o-, 499. -camphor, uo-, 536. -dimethylaniline, 418, 419, 425, 465.
hydrochloride, 418. -ketones, iso-, 256. -phenol, p-. See hemoquinone
mono-oxime. -piperidine, 574. Nitrowhacid test for amines, 89.
nitro-compounds, 94. NoLTiNO, 509, 512. Nomenclature of the alcohols,
CHw+rOH, 53, 54. Nonane, 42.
-dicarboxylic acid, 199. Nonoses. 268, 291. Nonyl alcohol, Normal, 54. Nonylic acid, 107. Normal chains, 47. Nomarcotine, 607. Notation, 47. of Chemical Society of London, 185, 186. the monoses, 271. Nucleic acids, 338. Nucleo-protdfns, 335, 338. Nucleus, Benzene-, 396. Number of carbon compounds, a, 47, 382. possible isomerides, 48, 49.
O.
Oak-tannin, 491. Octa-decapeptides, 344.
-peptides, 345.
-tetraene, qiclo^ 394, 395. Octane, n-, 38, 43, 50.
cycio-, 387. Octoses. 266. Octyl alcohol, Normal, 54.
-amine. Normal, 90, 103.
bromide, 88.
iodide. Normal, 308. Odour, 535. Oil, Fusel-, 58, 60, 63, 64, 152, 324.
Lubricating, 39.
of bitter almonda, 389, 439. caraway, 389, 403. 532.
Oil of castor-seed, 114. cinnamon, 456. citron, 178. cloves, 500. cumin, 389. eucalyptus, 403, 529. ^lic, 169. jessamine, 595. lemon-grass, 178. orange-rind, 178. peppermint, 526. polei, 530. rue, 308. spirse, 500.
tne Dutch chemists, 186. thyme, 503. turpentine, 33, 498, 526, 527,
533»534-
wintergreen. 486.
wonnseed, 529.
Olive, 32.
Paraffin-. See naphtha.
Train-, 40. OQs, 115, 173, 186, 192.
Hardening of, 174. Olefines, 14^158, 188, 387. Oellc acid, 114, 170, 173-175, 176, 192, 197.
series of acids, 170-175. Oleum cina, 529. Olive oil, 32. Opium, 602, 606.
Optical inactivity, 33, 34, 65, 250- 252, 524.
isomerism. See stereoisomerism. Organic analysis, 5-11.
chemistry. Definition of, 1.
compoimas. Classification of, 35. Orientation, 396, 504-519, 555, 556,
563. 574, 575, 591, 592. Ornithine, 335, 340, 369, 498- Ortho-acetic acid, 110.
-carbonic esters; 368.
-oompoimds, 396.
-esters, 105. 182, 187, 194, 368.
-formic acid, 182. Osazones, 262, 263. Osmotic pressure, 12, 14, 15, 345. Osones, 275.
OSTROMISSLENSKY, VON, 247.
Ost's solution, 243, 262.
OSTWALD, 117.
Over-proof spirit, 60. Oxalacetic acid, 272. Oxalic acid, 172, 199-203, 208, 252,
254, 287, 304, 317, 347. Oxalis, 200. Oxaluric acid, 371. Oxalyl chloride, 202.
632
INDEX
OxalyUurea. See parabanic add. Oxamic acid, 202. Oxamide, 202, 203. Oxanthrone, 565, 566. Oximes, X35i 136, 315, 316, 443-445, 451
Tautomensm of, 315, 316. Oxindole, 594.
Oxonium salts, 317-3191 490. Oxy-cellulose, 301.
-2:6-dichloropurme, 8-» 376.
-bjemoglobin, 338.
-methylenes, 142. Osn^gen-carriers, 8.
Detection of, 5.
Estimation of, 9. Osokerite, 40. Ozonides, 255, 538.
Palmitic acid, X07, 113, 114, 173, 174,
197. Pancreas, 192. Pancreatic juice, 344. Papaver somniferum^ 606. Paper, 299, 300, 301. Parabanic acid. 371, 372, Paracetaldehyde, 138, 139, 144, 145. Para-compounds, 396.
-cyanogen, 347.
-formaldehyde, 142.
-leucaniline, 546.
-mandelic acid, 453.
-myosinogen, 334.
-rosaniline, 546. Paraffin, Liquid, 32, 40.
-oil. See naphtha.
-wax, 39, 40, 106, 114. Paraffins, 38, 39> 159, 402. See also saturated hydrocarbons.
Isomerism of the, 43-50.
Structure of the, 43-49. Parchment-paper, 301. Parsley, 281. Partial valencies, 394. Paotbur, 66, 67, 243, 247, 248, 250,
290. Peat, Combustion of, 142. Pelargonic acid, 146, 174, 176. PeniciUium glaucunif 248, 452. Penta-chlorethane, 183, 185.
-digalloylglucose, 492.
-hydric alcohols, 262.
-methyl-aminobenzene, 418. -benzonitrile, 518. -pararosaniline. See methyl . violet.
Penta-methylene. See pentone, cyclo-. -diamine, 15^, 255, 573. hydrochloride, 196.
dibromide, 573.
-phenylethaney 549.
-triacontane, 37, 42. Pcntane, 37, 42, 48, 66, 73, 152, 158, 184 572
cvdo-l 158, 384, 385, 522.
oerivatives, cydo-, 384-386. Pentanone, cifdo-y 384, 385, 520. Pentonic acids, 262, 268. Pentosans, 268. Pentoses, 261, 268-270, 281, 282, 295,
580,581. Penloiwria, 269. iPentyl iodide, 154. Pepper, 577.
Peptones, 335» 338, 339, 343-345. Percentage-composition, &-1 1 . Perchloroethane. See hexachloro-'
ethane. Percolation, 601. Percu8sion-cai>s, 356. Perfumes, Artificial, 180. Peri-compounds, 555. Perkin, W. H., jun., 528, 537, 610.
Sir William, 456, 502, 570. Petrol, 39. Petroleum, 39, 40.
American, 39, 40.
Caucasian, 385, 520.
-ether, 28, 39, 100, 463.
-fires, 39.
Formation of, 40, 41. . Java, 40.
-jelly. See vaseline. Pharaoh's serpents, 354. Phenacetin, 477. Phenanthraquinone, 569, 570. Phenanthrene, 552, 562, 569-571, 606.
-carboxylic acid, ^, 571. Phenetole, 412, 428, 431, 477. Phenol, 14-16, 399, 400, 409-412, 428, 430, 433, 462-465, 481, 487, 499, 500, 522, 524, 535, 557, 584, 604.
-phthaldfn, 496, 544.
-sulphonic acid, m-, 464. 0-, 464, 465. P-, 464, 473. acids, 464. Phenolates. See phenoxides. Phenols, 409-412, 413, 433, 440, 481,
499, 500, 552. Phenoxides, 410, 412, 490. Phenyl-acetic acid, 452, 570. t«>-386. pseudo-, 386.
INDEX
633
Phenyl-acetylene, 455. -alaDine, 340. -amine. See anUine. -aminopropionaldebyde, ^, 500. -anisyl-ketone, 443.
-ketoxime, 445. -arsine oxide, 446. -arsinic acid, 446. -chlorotfmine, 416. ether. See dipkenyl ether. -ethylene. See slyrene. glucosazone. See glncasazone, d-. -glycine, 598.
-o-carboxylic acid, 598. -hydrazine, 136, 137, 262, 263, 277, 283, 298, 433, 434, 440, 579, 589. hydrochloride, 433. -hydrazones. See hydrazanes. -hydroxy lamine^ 423, 42^, 425. -jtf-hydrox3T>ropionic acicl, a-. See
tropic acid. -iodide chloride. See iodobemene
dichloride. isocyanate, 450. magnesium bromide, 405. mercury acetate, 447.
hydroxide, 447. -nitromethane, 450, 454. -o-aminocinnamic acid, cr-, 571. -diasocinnamic acid, ct-^ 571 . -nitrocinnamic acid, ce-,570. -phosphine, 445. 446. -phosphinic acid, 445. -phoephinyl chloride, 445. -propiolic acid, 455, 457. salicylate, 487. -salicylic acid, 489. -sodionitromethane, 550. -tolylketone, 443. -vinylacetic acid, 553, 556. xanthate, 430. Phenylene-diacetic acid, o-, 560. -diamine, m-, 458, 460, 478, 479, 482, 483, 509, 511. 0-, 479.
P-, 478, 479, 609. -diiBulphonic acid, m^, 466. Phloroglucinol, 301, 469-472.
triacetate, 470. Phosgene. See carbonyl chloride, Phosphenyl chloride, 445, 446. Phosphenylous acid, 446. Phosphines, 96, 97. Phosphinobenzene, 445, 446. Phospho-benzene, 446.
-proteins, 331, 334, 336. Phosphonium bases. Quaternary, 96. Photo-chemical reactions, 562.
Photographic 61m, 302. Phthalelns, 496, 548. PhthaUc acid, 4^-496, 506, 507, 555, 559, 564, 565, 503. M0-, 498, 509. ^
Tere-, 389, 498.
acids, 452, 494-498, 504.
anhydride, 494, 495, 496, 497, 564, 568. Phthaliniide, 493, 494, 497. Phthalvl chloride 495.
iso-chloride, 495. Ph3rsical properties of isomeric 00m-
poimds, 49, 50. Phytol, 584. Picoline, »-, 575, 576.
^, 575, 604, 610.
T-, 575. Pioolines, 575. Pioolinic acid, 577, 578. Picramide, 460, 464, 476. Picric acid, 333, 413, 460, 463, 464,
510-512, 541, 562. Piciyl chloride, 459, 464. PiCTBT, 602. Pimelic acid, 199, 524. Pincaolin, 180, 551. Pinacone, 188, 189, 551. Pinaoones, 188. Pinane, 533. Pinene, 534, 535. Pinic acid, 535. "Pink salt," 481. Pinonic acid, 535. Pip>eric acid, 502, 503, 577. Piperidine, 74, 196, 573, 577, 609. Piperine, 502, 577, 602. Piperonal, 501, 502. Piperonylacraldehyde, 502. Pitch, 400.
lake, 40. Plankton, 40. Platinotypes, 202. Polarimeter, Laurent's, 33, 34. Polarimetry, 33, 34, 288, 289. Poly-amino-compounds, 478^-484.
-basic acids, 198-220, 494>490. hydroxy-acids, 252, 253.
-halogen derivatives, 181-187, 458, 459.
-hydric alcohols, 187-194. phenols, 465-473.
-methylene compounds. See aU- cyclic compounds.
-nitro-derivatives, 460, 461.
-oxymethylene, a-, 142. /3-, 142. 7-, 142. IT-, 142.
634
INDEX
Poly-peptides, 291, 343-345-
Hsulphonic acids, 462.
-terpenes, 538, 539. Polymerization, 138, 139, 142-145.
of aldehydes, 138-145. Polyoees, 261, 266, 268, 270, 294-302,
340. Port, 68.
Potash-bulbs, 6, 7. Potassiopyrrole, 582, 584. Potassium acetate, 271, 311, 453.
anilide, 416.
antimonyl d-tartrate, 240.
bensenesulphomite, 409, 435.
benzoate, 440, 441.
carbazole, 562.
carbonyl, 472, 473.
oopper-propiolate, 218.
cuprous cyanide, 429.
cyanate, 347, 353, 362, 365, 374.
cyanide, 101, 103, 134. 170, 172, 182, 196, 203, 207, 219, 252, 322, 347, 350, 351, 435, 452, 551, 580, 592.
diacetylenedicarboxylate, 218.
ethoxide. 70, 361.
eth^^sulphate, 76, 81, 82, 101.
ferric oxalate, 201, 202.
ferricyanide, 218.
ferrocyanide, 101, 103, 348, 351.
ferrous oxalate, 201. ' formate, 200, 351.
sly collate, 222.
Hydrogen diacetylenedicarboxylate, 218.
mesotartrate, 244.
saccharate. 271 . o-sulphooenzoate, 485. (i-tartrate, 240.
monochloroacetate, 203.
nitrophenoxides, 476.
oxalate, 200.
phthalaminate, 493, 494.
phthalimide, 497.
propiolate, 218.
d-tartrate, 240.
tetra-aoetylenedicarboxylate, 218.
thiocyanate, 354.
trithiocarbonate, 361.
xanthate, 361, 430. Potato-starch, 296, 298, 299.
POTONiA, 40.
Primary alcohols, 54, 62, 64, 105, 125, 130, 133, 141, 147. amines, 86, 87, 89, 90, 92, 103, 136,
183, 363, 412-416, arsines, 97. carbon atoms, 47. oompoimds, 54,
Primary nitro-compounds 94. phosphines, 97. reduction-productfi, 423. Principle of mobile equilibrium, 113, 125. the counter-current, 287. Prino, 37. Producer-gas, 56. Proline, 341, 342. Proof-spirit, 59, 60, 61. Propanal, cydo-^ 384. Propane, 37, 38, 42, 43, 45, 46, 185. cycUh, 383, 387.
-tricarboxylic acid, o^'-. See trv- carballylic acid. Propargyl alcohol, 167, 169.
compounds, 167. Propenylpyridine, a-. 576. Properties of alcohols, CnUsn+fOH,
54-56. Propiolaldehyde, 178.
-acetal, 178, 588. Propiolic acid, 169.
series of acids, 175, 176. Propionaldehyde, 61, 62, 132, 134,
154, 166. Propionic acid, 61, 62, 101, 102, 107, 112, 117, 132, 146, 161, 171, 222, 227, 231; 305. Propionitnle, 102. Propionyl-group, 107, Propyl-ace^ylene, 161. Propyl alcohol, iso-f 53, 61-63, 125, 146, 188, 191. Normal, 53, 54, 61-63, 77, 125, 166, 169. -amine, mo-, 86, 87.
Normal, 86, 87, 90. -benzene, iso-. See cumene. bromide, Normal, 74, 88. -carbinol, tso-. See iaobuiyl alco- hol. Normal. See butyl alcohol^ Nor- mal. -carboxylic acid, cyclo-t 172, 173,
383. chloride. Normal, 74.
cyanide, 172.
derivatives, cydo, 383.
-dicarboxylic acid, cyclo-, 383.
-group, 38.
iodide, tso-, 46, 112, 154.
Normal, 46, 74, 112, 154. -piperidine, oe-, 576, 578.
/3-, 577.
7-, 577. -p«eudonitrole, 94. Propylene, 149, 153, 154, 186, 191, 383, 526, 532.
INDEX
635
Propylene chloride, 154, 166, 191.
-glycol, 226. 230. Propylidene cnloride, 154, 165. Prosthetic group, 334, 335. Protamines, 334. Proteans, 335. Protein-derivatives, 335, 336, 338,
339 Proteins, 2, 57, 58, 143, 287, 288, 291-
293, 320, 322^24, 331-346, 369,
412, 492, 493, 501, 575, 582, 595,
606. Proteoses, 335. 339. Protocatechualdehyde, 500, 502. Protocatechuic acid, 487, 488, 490,
503. Protoplasm, 287, 290, 292. Prussian-blue test, 4. Prussic acid. See hydrocyanic acid. PSCHORR, 570.
PsetMio-acids, 450-452, 544, 566.
-bases. See cotour-iases.
-ionene, 179.
-nitroles, 94.
-racemic mixed crystals, 249, 250.
-uric acid, 374. Ptomaines, 196, 339. Pulegone, 529, 530. Purine, 374, 376. Purone, 378.
180-, 378. "Purple of the ancients," 599. Purpurin, 568. Putrescine. See tetramethylene'
diamine. Pyknometer, 32. Pyrazole, 330, 382, 587-589 Pyrazoline, 588, 589. Pyrazolone, 451, 589. Pyridine, 263, 276, 312, 381, 399, 400,
. 572-578, 591. 600, 603, 605, 607.
-carboxylic acios, 577, 678.
ferrocyanide, 572.
-sulphonic acid, 572.
-tricarboxylic acid, a/Sy-, 609. Pyro-catechm or pyrocatechol. See catechol.
-gallic acid. See pyrogaUol.
-gallol, 467, 488.
-mellitic acid, 499. anhydride, 499.
-mucic acid, 580-582.
-racemic acid, 226, 240, 272, 305, 306.
-tartaric acid, 240.
Pyrone derivatives, 316-319, 497. Pyrrole, 382, 573, 582-584, 595.
-carboxylic acid, 2-, 584.
-red, 583.
* ' Py rrolidin . ' ' See tetrahydropyrrole . "Pyrrolin." See dihydropyrrole. Pyruvic acid. See pyroracemic acid.
Q-
Quadrivalent oxygen, 317. Quadroxalates, ^1. Qualitative analysis, 3-5. Quantitative anal3rsis, 5-11. Quaternary ammonium bases, 86, 87, 420.
arsonium bases, 97.
carbon atoms, 47.
phosphonium bases, 96. Quick process for vinegar, 109. Quina-red, 608. Quinhydrone, 473. Quinic acid, 608.
Quinine, 452, 492, 601, 602, 608, 609. Quinitbl, 523.
cia-, 523.
trans- 1 523. Quinol, 466, 467, 473, 479, 543. Quinoline, 276, 382, 400, 526, 572, 573, 578, 590-593i 600, 609, 610.
dichromate, 590.
MO-, 593, 600, 607.
sulphate, iso-^ 593.
H9Uiphonic acids, 592. Quinolinic acid, 578, 591. Quinone. See benzoquinone.
di-imide, 479. Quinones, 473, 474, 563-566.
0-, 473. Quinonoid forms, 472, 543, 544. Quinotannic acid, 608. Quinovic acid, 608. Quinovin^ 608. Quinoxalmes, 479.
R.
Racemic acid. See tartaric acidf r-.
substances, 230, 243. Resolution of, 246-252. Racemisation, 327, 328. Racemoids, 249. Raflinose, 294, 295. Raphides, 200. Reactions. Bimolecular, 88, 125, 126.
Reversible, 122, 138.
Unimolecular, 126. Reagent, Schifp's, 142. Reduction-products, Chemical or sec- ondary, 423. Electrolytic or primary, 423. Reflux-condenser, 20.
X
636
INDEX
Refraction, 34, 35, 113, 149, 157, 158, 313, 388, 305, 452, 495, 538, 561, 562. Atomic, 495. Index of, 34.
Molecular, 35, 43, 158, 164, 172, 388, 395, 452, 496, 538, 561, 562.
Refractive power. See refraction.
Reimer's S3mthe8is, 500, 501.
Rebisen, 485.
Rennet, 334.
Reseda hUeola, See dyer^s loeld.
Residual affinity, 394.
Resinification, 139, 140.
Resorcin. Seie reaorcinol. -yellow, 483
Resorcinol, 461, 466, 467, 473, 483, 496, 581. -phthaleln. See fluorescein.
Reversible reactions, 123, 138.
Rhodium, Catalytic action of, 109.
Rice-starch, 297.
Ricintis communis, 114.
Rigor mortis, 334.
Ring compounds. See cyclic com- pounds.
Robinson, 610.
"Rodinal," 477.
ROMBURGH, VAN, 395.
RoozEBOOM, Bakhuis, 249.
Rosaniline, 546, 547, 548.
Rosanilines, 542-548.
Rose, 490.
Rosenheim. 334.
Rosolic acia, 547, 548.
Rotation of plane of polarization, 33,
34, 65. Rotatory power, Specific, 34. Ruberythric acid, 566. Rum, 58.
Rutci ffraveolens, 308. RyeHstarch, 297.
S.
Sabatier, 36, 152, 521-523. Saccharates, 265, 287. Saccharic acid, d^, 371, 280.
i80-^ 303. Saccharides. See sugars. Saccharification, 57. "Saccharin," 485. Saccharose. See sucrose. Saint Giles, P6an db, 122. Salicin, 486. Salicylaldehyde, 500. Salicylic acid, 486, 487, 489, 509, 510,
584, 589. Saligenin, 486.
;
''SalipyrineX* 589.
Salmine, 334> j^3.
''Salol," 487. V
"Salt of sorrel," 201.
"Salting-out," 114, 115, 332, 336,
482. "Salvarsan," 478. Sandmeter, 429. Saponification, 135-137, 210, 211.
of fats, 113, 114, 126. Saproproj^ium, 40. Sarcokctic acid, 230. Saroosine. See methylglycine. Saturated hydrocarbons, CwHsm+i,
36-50,99,149, 181,187,387. See
also paraffins. Sawdust, 200. Scatole. 339, 341, 595. ScHiFF^s reagent, 143, 259, 286. Schizomycetes, 290. Schizosaccharomyces octosporus, 291.
SCHORLEBOCER, 73.
Sclero-protelns, 334, 336, 337. Schmidt, 486.
SCHtiTZENBERGER, 339-341.
Schweitzer's reagent, 300, 302. Scutching, 300. Sebacic acid. 199.
Secondary alcohols, 54, 62, 64, 125, 130-133, 135, 148.
amines, 86, 87, 89, 90, 103.
arsines, 97.
carbon atoms, 47.
oompoirnds, 54.
nitro-compounds, 94.
phosphines, 97.
reduction-products, 423. Selenium compounds, 84. Semi-carbazide, 365, 366.
-carbazones, 366. Semidine-transformation, 422. Senderens, 36, 79, 151, 521-523. Senier, 191, 352, 358. Senter, 326. Separatmg-funnd, 28. Separation of amines. 89.
immiscible liquids, 28-30. solids and liquids, 30. from one another, 30, 31, gericin, 337. »jerico!n, 344. Serine, 340. SertCrner, 606. Serum-albumin, 332, 334.
-globulin, 334. Sherry, 58. Side-chain, 49, 396. Silicanes, 99. Silicoheptane, 99.
INDEX
637
Silicon alkides. See sUicanes.
atoms, Asymmetric, 250.
Chemistry of, 98.
tetraethide, 99. Silk, Artificial, 302.
-gum. See aericin. SiLVA, 191.
Silver acetate, 106, 187, 188.
acetylene. 160.
cyanamide, 356.
cyanate, 353.
cyanide, 348, 594.
cyanurate, 357, 358.
formate, 108.
fulminate, 356.
Isvulate, 277.
-mirror-test, 141.
picrate, 464.
thiocyanate, 354. Simpson, 182. Skraup, 590, 592, 609. Sleeping sickness. See trypanosomia-
818.
Smokeless powder, 302. Soap, Green, 114.
Hard, 114.
Potassium-, 114.
Sodium-, 114.
Soft, 114. Soaps, 114-116. Soda-lime-test, 4. Sodamide, 257, 557. Sodio-acetylacetone, 311.
-n-amylacetylene, 257.
-dinitroethane, 451, 452.
-nitro-ethane, 93. -propane, Secondary, 93.
-phenyl-nitromethane, 450. -Monitromethane, 450. Sodium acetate, 112, 264, 456, 503.
acetylene, 175.
alkides, 100.
ammonium racemate, 247, 249. d-tartrate, 247, 248. (-tartrate, 247, 248.
anthraquinonesulphonate, 567.
benzoate, 435, 437.
cyanamide, 350.
cyanide, 350.
diazobenzenesulphonate, 423.
theoxide, 69, 70, 93, 182, 187, 205, 206, 256, 257, 307, 325, 376, 453, 460,469.
formate, 200.
hydrogen urate, 374.
methide, 100.
methoxide, 69, 70, 77, 93, 105, 316, 405, 459, 460.
-nitroprusside-test, 5.
Sodium oxalate, 200.
-p^cetylaminophenylarsinate . arsacelin. -aminophenylarsinate. See atoxyl.
-nitrophenoxide, 471, 472.
phenoxide, 410, 412, 486, 489, 584.
phenyi-carbonate, 486. -hydrazinesulphonate, 433. -salicylate, 487.
propiolate, 175.
salicylate, 487.
stearate, 105.
succinate, 585.
sulphanilate, 476.
urate, 374. Soluble myogen-fibrin. See myosinf
Soluble. Solvents, Cryoscopic, 14, 15, 16
EbullioscopiCj 16.
Extraction with, 28. Soporifics, 146, 147, 258, 260, 441. Sorbitol, d-, 271, 468. Sorbose-bacteria, 266. Spacial isomerism. See stereoisomer- ism. Specific gravity, Determinatoin of, 32,33.
rotatory power, 34. Spent lees, 58.
wash, 58, 350. Spermaceti, 69. Spirits, 58.
of wine, 58. Sponging, 337.
Starch, 57, 270, 273, 282, 296-299, 300.
Manufacture of, 299. Starck's hypothesis, 328, 329. Steam-distillation, 26-28. Stearic acid, 16, 107, 113, 114, 173, 192. Structure of, 173. "Stearine," 114.
candles, 114. Stearolic acid, 175. Stearyl, alcohol, 105. Stereochemical isomerisn. See stereo- isomerism. Stereochemistiy of the monoses, 278-
281. Stereoisomerism 66, 67, 68, 211-217, 223-225, 230-232, 235-239, 278- 281, 326-329, 346, 443-445, 456, 457.
of nitrogen, 443-445.
VAN 't Hoff's theory of, 66-69. Stilbene, 550, 570. Stoll, 584. Storax, 455.
638
INDEX
Strain-theory, von Baeter's, 157,
209. Straw, 270, 300. Strecker, 320. Strength of acids, 117, 118. Strong hydrolysis, 306. Structural or constitutional formula,
46,53. Structure of the paraffins, 43-50. Strychnine, 248, 492, 601, 602, 609, 610.
i-mannonate, 276. Strychnos nux vomicaf 609. Sturine, 334. Styphnic acid, 466. Styrene, 455.
Suberanecarboxylic acid, 386, 387. Suberic acid, 199. Suberone, 386, 387, 605. Substitution, 37, 231. Succindialdehyde, 255, 583.
Oxime of, 583. Succinic acid, 29, 30, 57, 199, 206, 207, 208, 209, 212, 217, 232, 234, 240 586.
anhj^uride, 208. Succinimide. 209.
Succinonitrile. See ethylene cyanide.
Sucrose, 33, 112, 200, 229, 252, 269,
270, 284-289. 290, 291, 295, 581.
Manufacture ot, 287, 288.
Quantitative estimation of, 288, 289.
Velocity of inversion of, 289. Sugar-beet, 268, 269, 284, 287, 288, 323, 602.
-cane, 284.
Cane-. See siLcrose.
of lead. See lead acetale. Sugars, 261-302, 324, 331, 334, 338,
606. Sulphaminobenzoic acid, 485. Sulphanilic acid, 473, 476, 477. Sulphinic acids, Alkyl-, 83. Sulphite-method, 300, 301. Sulpho-benzenediasonium chloride, p-,483.
-benzoic acid, m-, 485. 0-, 485. acids, 485.
-cyanic acid. See thiocyanic add.
-pyromucic acid, 582. Sulphonal, 146, 147. Sulphonamides, 409. Sulphones, 83, 84. Sulphonic acids, 83, 408, 409, 461,
462, 464, 476, 485. Sulphonium halides, 82.
hydroxides, 82.
Sulphonium iodides, 82. Sulphonyl chlorides, Alkyl-, 83.
Aromatic, 408, 409. Sulphoxides, 83. Sulphur, Estimation of, 8. Supertension, 380. Suprarenine. See adrenaline. Symmetrical compounds, 396. Sjmtonins. See metorproteins.
T.
Tafel, 377, 379. Tanacetone. See thujaiie. Tannic acids. See tannins. Tannin, 296, 333, 337, 491-493) 600,
601. Tanning, 493. Tannins, 491-493. Tanret, 271, 272.
Tar, 399, 400, 403, 409, 552, 562, 572, 585, 590, 593, 595. Wood-, 56. "Tartar-emetic," 240. Tartaric acid, d-j 235-239, 240-242, 243, 246, 248, 272, 294, 305. /-, 235-239, 242, 246, 248, 294. Meso-, 235-237, 239, 242, 243,
244i 245, 281. r-, 235-237, 239, 242, 243, 244, 248, 305. acids, 235-246, 293. Tartronic acid, 190, 234. Tautomerism, 310-316, 346, 470-472,
495, 566, 579, 588, 593, 598. Tea, 375, 488, 492, 601. Tellurium compounds, 84. Terephthalic acid, 389, 498. Terminal carbon atoms, 47. Terpenes, 386, 403, 520, 525-535, 538,
539- Terpin, 526-529, 530, 531.
hydrate, 526, 527, 529. Terpineol, 529, 530, 531, 535. Terpinolene, 530, 531. Tertiary alcohols, 54, 62. 122, 125, 135, 148.
amines, 86, 87, 89, 90, 103, 601.
arsines, 97.
carbon atoms, 47.
compounds, 54.
nitro-compounds, 94.
phosphines, 97. Tervalency of cargon, 549. Test, Beilstein's, 5.
Carbylamine-, 90, 102, 103, 415.
CoppeiK)xide-, 4.
Iodoform, 61, 184.
Lassaigne's, 4. *
INDEX
639
\
Test, Lime-water-, 4. Pnifisian-blue-, 4. Silver-mirror-, 141. Soda-lime-, 4. Sodium-nitroprusside-. 5. Test for absolute alcohol, 59. acetates, Caoodyl-, 98, 112. Ferric-chloride, 111, 112. amines. Nitrous-acid-, 89. anthraquinone, 565. blood, 338. cellulose, 300. c^c/o-hexanone, 524. dextrose, 271. double bonds, von Baeyer's,
149. formaldehyde, 415, 416. glycerol, 191. hexoses, 277.
identity of substances, 31. ketoses, 275. lignin, 299, 301. nitric acid, 416, 417. nitro-compounds, Nitrous-acid-,
94. nitrous acid, 479, 483. pentoses, 270. phenols, 411. phthalic acid, 496. anhydride, 496. primary amines, Hofmann's, 90,
102, 103, 415. pyrrole, 582, 583. resorcinol, 496. starch, 296. xylose, 270. Tests for aldehydes, 141, 142. amines, 89, 90, 102, 103, 415. aniline, 415, 416. /
ethyl alcohol, 61, 184, 437. hydroxyl-group, 51, 52, 119, 120. monoses, 262, 263. primary, secondary, and tertiary
alcohols, 64. proteins, 333. ' tautomeric forms, 313-315. Tetra-acetylenedicarboxyUc acid, 218. -alkvlammonium iodides. Velocity
of fonnation of, 88. -anisylhydrazine, 5^9, 550. -bromo-ethane, 563. -fluorescein, 496. -methane. See carbon tetrabro- mide. -chloro-ethane, 185, 186. -ethylene, 183, 185. -methane. See carbon tetrachlo- ride. -decane, 42.
Tetra-ethyl-ammonium hydroxide,91 . disodioethanetetracarboxylate,
553. hydronaphthalenetetracarbox-
ylate, 553. •^methane, 99. orthocarbonate, 368. -hydro-benzene, 522. -pyrrole, 602, 605. -carboxylic acid. See proline. -hydroxyflavone, 1 : 3 : 2' : 4'-. See morin. 1 : 3 : 3' : 4' :-. See luteolin. -methyl-ammonium hydroxide, 91. -butone, 2 : 2 : '3 : 3'-, 50. -diamino-benzophenone, 419. -triphenyl-carbinol, 543. -methane, 543. -succinic acid, 221. -uric acid, 377. -methylene. See bulanef cyclo-. bromide, 384. -diamine, 196, 325. -nitrophenol, 2:3:4:6-, 466. - (p-dimethy Lamino) -tetraphenylhy-
drazine, 550. -peptides, 343. -phenylhydrazine, 549 Tetrolic acid, 175. Tetronal, 147. Tetroses, 295. Thelne. See caffeine. Theobromine, 374-376, 600, 602. Theory of stereoisomerism, van 't
HoFP's, 66-^. Thermometers, Abbreviated, 32. Thiele, 31, 164, 393, 394, 395,
554. Thienylmethylketone, 2-. See cuxtO'
tkiinone. Thio-cyanic acid, 354, 355. esters, 355.
«<>-» 355, 361.
-ethers, 80-82, 83.
-indigo, 599.
-methylene, 355.
-phenol, 397, 409.
-tolen, 585.
-urea, 367, 368. Thiophen, 382, 585-587.
-carboxylic acid, 2-, 587. 3-. 587.
Dimetnyl-. See tkioxen.
mercury oxyacetate, 585.
Methyl-. See thiotolen.
-sulphonic acid. 587. Thioxen, 585, 586.
Thorpe, 637. '
Thuione, 538.
640
INDEX
Thymol, 4x1, 526.
Tickle, 317.
Tiglic acid, 170.
Tin atoms, Asymmetric, 250.
ethide, 100. T. N. T. See trinitrctolitene, Sym-
metrical. Toadstool, 303. Tobacco, 602. Tolan, 550.
Tolaene, 389, 399, 400, 401, 403, 407, 411, 434, 448-450, 460, 485, 512, 585.
-«ulptionamide, a-, 485.
-fiulphonic acid, m-, 515. 0-, 515.
»-, 515. >ho
-sulphonyl chloride, o-, 485. P-, 485. Toluic acid, 438, 452. Toluidine, m^, 512.
0-, 416, 512, 546.
p., 16, 416, 512, 546, 576, 584.
hydrochloride, p-, 418. Train-oil, 40. Triacetoneamine, 146. Trialkyl-phosphines, 96.
-phospnine oxides, 97. Triamino-azobenzene, 482.
-benzenes, 478.
-triphenyl-carbinol, 546. Triamylene, 152. Trianisylcarbinol, 544. Tribasic acids, 218-220, 252, 253,
499. Tribe. See Gladstone. Tribenzoyladrenaline, 503. Tribenzylamine, 454. Tribromo-aniline, 2:4:6-, 414, 475.
-hydrin, 169, 185, 191, 219.
-phenol, 2:4: 6-, 411, 462.
-resorcinol, 2:4:6-, 466. Tricalcium saccharate, 287. TricarbaUylic acid, 219, 220. Trichloronacetal, 258, 259.
-aoetaldehyde. See chloral.
-acetic acid, 125, 222, 223, 259. -ethylene, 185, 186.
-hydrin, 191.
-phenol, 462.
-purine, 2:6:8-, 376. Tricosane, 42. Tridiphenylmethyl, 548. Trietnyl-amine, 88, 91.
-arsine, 97.
citrate, 249.
-methane, 99.
-phosphine, 97. oxide, 96.
Triethyl pyrazpletricarboxylate, 687.
pyrazolinetricarboxylate, 589. Trinalogenbenzenes, 1:2:4-, 458. Trihydric alcohols, 190-193.
phenols, 467^72. Trihydroxy-acids, 488. -anthraquinone, 5:6:8-. See pttr-
purin -glutaric acid, 269, 274, 279, 280. ^ Tri-iodophenol, 524, " Triketohexamethylene. See phloro* glucinol. Trimethyl-acetic acid, 221. -acetyl chloride, 189. -amine, 86, 90, 91, 143, 168, 196,
323, 384, 392. -carbinol, 53, 63, 125, 135. -ethylene, 163 -glycine, 323. -oxonium iodide, 318. -phloroglucinol, 472. -phosphine oxide, 97. -P3rridines. See coUidines. HBUccinic acid, 536. Trimethylene. See yropane, cyclo-. bromide, 186, 187, 196, 383, 498. cyanide, 196. -diamine, 196. -glycol, 187. diacetate, 187. Trinitro-aniline, 2:4:6-. See 711c- ramide. -benzene, S3anmetrical, 460, 512,
519. -butybcylene, 461 . -cellulose, 301, 302. -oxy cellulose, 301. -phenol, 2:4:6-. See picric acid. -phenylnitroamine, 419. -toluene, symmetrical, 460. Trional, 147. Trioses, 261, 266, 291. Tripeptides, 343. Triphenyl-amine, 413, 416, 417. -chloromethane, 548. -methane, 419, 440, 496, 543.
dyes. See rosanilinea. -methyl, 548, 549. iodide, 548. peroxide, 548. -rosaniline hydrochloride. See ani- Une^ue. Tristearin, 192, 344. Trithio-carbomc acid, 361?
-methylene, 355. Troostwyk, Paets van, 186. Tropic acid, 453, 604 Tropidine, 605. Tropine, 604, 605.