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tJ
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WOB3E6 OF nor. A. F. BO:
rvBUBUO) mr
JOHN WILEY & SONS, INC.
ijisued it: Jb^ig^Joii iu of»-<ipermtioD witb HntMOji CiuJUUE* Coormtu Fourtb Ftttg}mh edition, oom- pkrf :!/ rerJMcL &ro. viii -t- S05 pp.. 7y £(»»■- Cloth.
AT
ICdiltd br A. JAMinow Wauuhu Ph.D. CHcsdel' becf; • hJL., Uend <if Um- Depakrimeut of Gheinisbr>'. Terbuif^ CoU«f:«'. iMsrby, EucUuid. assisted by Ov'SN K. M</TT. J'b.D. 'Heidelberc. . with the oo- op«sr»tioo of the author. Fourth £ucliiL Edition, partljr revntUm. Svo, xviij -rC19 pp. 82 ficunw. Ckitiu 12^.
A eonpiiuioo roiume to the preeedinc* auud forminc vitli it s «OB«pc«faefaittv« treatise on pure Chetuistnr.
An Appendix to the author's Text-book c^ ODsanie Chctfustr . Edited by A. JAJUisaav Wjxxxa. Fh.D. (JHeidelberK;. B A.. Head U the Department ot Cheiuisuy, Technical College, Derby, v^^^a Witii tb« oo-operatiow ot tb« author. Seoood EucUsh Edition, partly rewritten. 12iiio, zvii+WS pp.
A TEXT-BOOK
09
ORGANIC CHEMISTRY.
A. F. HOLLEMAN, Ph.D., P.R.A.Amst.,
Profeuor Ordlnariua in the VnivenUy of AnuUrdanu
EDITED BY
A- JAMIESON WALKER, Ph.D. (Heidelberg), B.A..
Mtad of th€ Devartment of Chemigtry^ Technical CoUege^ Dtrh\h Enffiand-
ASSISTED BY
OWEN E. MOTT. Ph.D. (Heidelberg).'
WITH THE CO-OPERATION OF THE AUTHOB.
FOURTH ENGLISH EDITION, PARTLY REWRITTEN.
TOTAL ISSUE, THIRTEEN THOUSAND.
NEW YORK
JOHN WILEY & SONS, Inc.
London: CHAPMAN & HALL, Limited
1914
Copyright. 1903. 1907. 1910. 1913,
BT
A. JAMIESON WALKER. {Entered at Stationer** Hall.)
CHRONOLOGICAL SUMMARY.
ENOi^iBH Editions.
Firtt EdUion: AprU. 1903. Second Edition: August, 1907. Third Edition: August, 1910. Fourth Edition: August. 1913.
Editions in Other Lanquaobs. Original Dutch: Five Editions. German: Ten Editions. Italian: Two Editions. French: One Edition. Ru9»ian: Two Editions. Polith: One Edition. Japanese: One Edition.
TMC-SCltNTinC
IMIUIMKHIO AMO COMXWy •nOOKLVN, N. V.
• •
• •
• «
• •• •
• • • • •
AUTHOR'S PREFACE TO THE FOURTH 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.
The section on tautomerism has been cntirclv rewritten: and the chapters on the benzene derivatives have been com- pletely rearranged, because I have found it possible to treat this subject more systematically than formerly.
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.
Amsterdam, July, 1913.
• • •
lU
74395
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 formulse frequently leave much to be desired. However useful these books may be for reference, they are often illnsuited for text-books, as many students have learned from their own experience.
In this book I have endeavoured to keep the ntmiber 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-chemical 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. Groningen, Netherlands, November, 1902.
iv
EDITOR'S PREFACE TO THE FOURTH EDITION.
About one-eighth of the matter included in the fourth edition is new, and many minor alterations have also been made. I have again to thank Professor Holleman for devoting much time and energy to this work. It has been found neces- sary to renumber the paragraphs from § 17 onwards, a fact to be borne in mind when comparing the present issue with previous editions.
References in the text to " Inorganic Chemistry '' allude to Professor Holleman's " Text-Book of Inorganic Chemistry/' edited by Dr. Hermon C. Cooper, and published by Messrs. John Wiley & Sons, Inc. The " Laboratory Manual '' referred to is Professor Holleman's " Laboratory Manual of Orgam'c 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. Derby, England, July, 1913.
V
CONTENTS.
Light 6gure8 refer to pages, old style figures to paragntpha.
PAor
Introduction (1-27) 1
Qualitative and quantitative analysis (3-9) 3
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 formuLe, 10.
Determination of molecular weight (10-15) 11
Victor Meyer's method, 12. Cryoscopic methods, 14. EbuUio- scopic methods, 14.
The element carbon (16) 19
Laboratory-meihods (17-26) 19
Heating siibstances 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, 31. Determination of specific gravity, 32. Polarimetry, 32. Determination of refraction, 33.
Classification of organic compounds (27) 34
FIRST PART.
ALIPHATIC COMPOUNDS (2a-273) 35
Saturated Hydrocarbons (2&-38) 35
Occurrence, 35. Preparation, 35. Physical and chemical proi)ertics, 36. Nomenclature, 37. Petroleum, 38. Homologous series, 40. Isomerism and st ructure, 42. Carbon chains, 45. Law of the even number of atoms, 40. Number of ix)Ksible isomerides, 46. Physi- cal properties of isomeric compounds, 48.
Alcohols, CnHjn+ aO (39-50) 49
Methods of formation and constitution, 49. Nomenclature and iso- merism, 51. General properties of the alcohols, 52. Methyl alco- hol, 5S. Ethyl alcohol, 54. Propyl alcohols, 59. Butyl alcohols, 60. Amyl alcohols, 62. Van 't Hoff's theory of stereoisomerism, 64. Higher alcohols, 66. Alkoxides, 66.
Alktl Halides, Esters, and Etuers (51-56) oti
Alkyl halides, 69. Eatera of other mineral acids, 72. Ethers, 74.
vu
Viii CONTENTS.
PAGB
Alktl-radicals Linked to Sulphur (57-60) 77
Mercaptans, 78. Thioethere, 79. Sulphonic acids, 80.
Alkyl-radicals Linked to Nitrogen (61-70) 82
Amines (61-67) 82
Nomenclature and isomerism, 83. Methods of formation, 83. Properties, 86. Individual members, 87.
Nitro-compaunds (68-70) 91
Preparation, 91. Properties, 92. Derivatives, 93.
Alkyl-radicals Linked to other Elements (71-75) 95
Alkyl-radicals linked to elements of the nitrogen group (71-73) 95
Phosphines, 95. Arsines, 96. Stibines and Bismuthines, 97.
Alkyl-radicals linked to the elements of the carbon group (74) 97
Optically active compounds with asymmetric atoms other than carbon, 98. Metallic alkides (75) 100
NiTRILES AND i^oNlTRILES (76-78) 102
Carbylamines, 103. Nitriles, 104.
Acids, CnHmOa (79-88) 105
Constitution, 105. Syntheses, 105. General properties, 107. Formic acid, 109. Acetic acid, 110. Butyric acids, 113. Higher fatty acids, 114. Soaps, 115. Electrolytic dissociation, 116.
Derivatives of the Fatty Acids Obtained by Modifying the
Carboxyl-group (89-97) 11^
Acid chlorides, 119. Acid anhydrides, 120. Esters, 120. Thio- acids and acid amides, 127. Other derivatives, 128.
Aldehydes and Ketones (98-111) 130
General properties (98-193) 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. Tests, 141. Formaldehyde, 141. Acetaldehyde, 143. Paracetaldehyde, 143. Met acetaldehyde, 143.
Ketones (no, in) 145
Special properties, 145. Acetone, 146.
Unsaturated Hydrocarbons (112-127) 147
Alkylenes or ole/ineSy CnHjn (i la-iao) 147
Methods of formation, 147. Properties, 148. Ethylene, 150. Amylenes, 151. The nature of the double carbon bond, 151.
Alicydic compounds (lai) 157
Hydrocarbons unth triple bondsy CnHjn-i (122-126) 158
Nomenclature, 158. Methods of formation, 158. Properties. 159. Acetylene, 160.
Hydrocarbons with two double bonds, CnHin- j (127) i62
Isoprene, 162. Dimethylallene, 162. Conjugated system, 163.
CONTENTS. IX
PA OB
SUBSTITUTTON-PRODTTCTS OP THE UnSATTTRATED HYDROCARBONS (X28-
133) ' 164
Unsaluraled halogen compounds (128-130) 164
Preparation, 164. Properties, 165. Allyl chloride, 165. Vinyl chloride and bromide, 165. Allyl bromide and iodide, 166. Propargyl compounds, 166. Bromoacetylidene, 166.
Unsaturated alcohols (131-133) 166
Vinyl alcohol, 167. Neurine, 167. Allyl alcohol, 167. Prop- argyl alcohol, 168.
Monobasic Unsaturated Acids (134-140) 169
Acids of the oleic series (134-138) 169
Preparation, 169. Nomenclature, 169. Properties, 170. Acrylic acid, 170. Acidsof the formula C4H6O2, 171. Oleic acid, 172.
Acids of the propiolic series (139, 140) 173
Preparation, 173. Properties, 174.
Unsaturated Aldehydes and Ketones (141-143) 175
Acraldehj'de, 175. Crotonaldehyde, 176. Propiolaldehyde, 176. Geranial, 176. Derivatives of geranial, 177.
Compounds Containing more than one Substituent (144-160) 179
Halogen derivatit'es of methane (144-146) 179
Chloroform, 179. Methylene chloride, 181. Tetrachloro- methane, 181. Bromoform, 181. lodofonn, 181. Methyl- ene iodide, 182.
Halogen derivatives of the homologues of methane (147, 148) 182
Preparation, 182. Xomenclaturo, 183. Tetrachloroethane, 184. Ethylene chloride, 184. Hexachloroethane, 184. Ethylene bromide, 184. Trimethylene bromide, 184.
Polyhydrie alcohols (149-157) 185
Glycoln, 185. Trihydric alcohols, 188. Tetrahydric and higher alcohoi.s, 193. DeriiHitives containing halogen atoms^ hydroiyl-growps^ nilro-groupSy
or amino^roups (158-160) 194
Chlon)ether8, 195. Halogen-hydrins, 195. Dinitro-compounds, 195. Diamim^s, 196. Chohne, 196. Lecithin, 197.
P0LYBA.SIC Acids (161-174) 198
Saturattd diahasic acitis (161-168) 198
Physical and chemical i)rop<»rti<v, 198. Oxalic acid, 2(K). Malonic acid, 202. Carbon suboxide. 205. Succinic acid, 205. Elect ro-synthesLs of dibasic and other acids, 207. Formation of anhydrides, 208.
Unsaturated dibasic acvls (169-173) 210
Fumaric acid and maleic acid, 210. Af!inity-<*onstants of the unsaturates! acids, 215. Dibasic acids with more than one ^ triple bond, 21().
Higher jxtlybasic acids (174) 217
Tricarballylic acid, 217. Aconitic acid, 218.
X CONTENTS.
PAOB
Substituted Acids (175-197) 219
Halogen-substituted acids (175-178) 219
Formation, 219. Properties, 219. Chloroacetic acids, 221. Acids with more than one halogen atom in the molecule, 221.
Monobasic hydroxy-acids (179-186) 223
Formation, 223. Properties, 224. GlycoUic acid, 226. Hydroxy- propionic acids, 226. Lactones, 230.
DiJbasiq hydroxy-acids (187-196) 232
Tartronic acid, 232. Malic acid, 232. Tartaric acids, 233. (/-Tartaric acid, 238. /-Tartaric acid, 240. r-Tartaric acid, 240. Mesotartaric acid, 241. Racemic substances, and their resolution into optically active constituents, 245.
Polybasic hydroxy-acids (197) 248
Citric acid, 248.
DiALDEHYDES AND DiKETONES: HaLOGEN-SuBSTITUTED AlDEHYDES
AND Ketones (198-301) 250
Dialdehydes (198) 2i:0
Glyoxal, 250. Succindialdehyde, 251.
Diketones (199, 200) 251
Diacetyl, 252. Acetylacetone, 253. Acetonylacetone, 254.
Halogen-substituted aldehydes (aoi) 254
Chloral, 254. Chloral hydrate, 254.
Aldehydo-alcohols and Keto-alcouols or Sugars (302-228) 257
Nomenclature and general properties of the monoses and their derivatives
(303, 203) 257
Constitution of the monoses (204, 305) 259
Methods of formation of the monoses (306) 262
Monoses (307-313) 264
Pentoses, 264. Hexoses, 266. Stereochemistry, 273.
Dioses (313-223) 276
Constitution, 276. Maltose, 277. Lactose, 278. Sucrose, 279. Manufacture of sucrose from sugar-beet, 282. Quan- titative estimation of sucrose, 283. Velocity of inversion of sucrose, 284. Fermentation and the action of enzymes, 285. AsjTnmetric synthesis, 288.
Polyoses (224-228) 289
RaflTihcse, 289. Starch, 291. Glycogen, 294. Manufacture of starch, 294. Cellulose, 294. Technical applications of cellulose; Nitrocelluloses; Artificial silk, 295.
Amino-aldehydes and Amino-ketones (229) 298
Aminoacetaldehyde, 298. Muscarine, 298. Chitin, 298.
Aldehydo-acids and Ketonic Acids (230-239) 299
Aldehydo-acids (230) 299
Glyoxyhc acid, 299.
Ketonic acids (231-234) 3(X)
Pyroracemic acid, 300. Acetoacetic acid, 301. Acetoacetic-
CONTENTS. XI
PAOB
ester synthesis, 302. Lscvulic acid, 304. Mesoxalic acid, 305.
Tauiomerism (235-237) 305
Ethyl acetoacetate, 305. Oximes, 310.
Pyrone derivatives (238, 239) 311
Chelidonic acid, 311. Dimethylpyrone, 312. Oxonium salts, 314.
Amino-acids (240-245) 316
Formation (240) 316
General properties (240, 241) 316
Individual members (242, 243) 318
Glycine, 318. Betainc, 318. Alanine, 319. Leucine, 319. MoLeucine, 319. Asparagine, 320. Glutamine, 320. Lysine, 320. Ornithine, 321.
The Walden inversion (244) 321
Examples, 321. Werner's theory, 322.
Ethyl diazoacetate (245) 323
Formation, 323. Properties, 323.
Proteins (246-254) 325
Composition, 325. Properties, 326. Tests, 327. Nomenclature, 327. Classification, 328. Structure of the molecule, 333. Syn- thesis, 336. Molecular weight, 338.
Cyanogen Derivatives (255-262) 340
Cyanogen, 340. Hydrocyanic acid, 341. Cyanides, 342. Cyanic acid, 344. Thiocyanic acid, 340. Fulminic acid, 349. Cyanuric acid and wocyanuric acid, 349.
Derivatives of Carbonic Acid (263-270) 351
Carbonyl chloride, 351. Carbon disulphide, 352. Carbon oxysul- phide, 353. l-rea, 353. Derivatives of carbamic acid, 358. Thiourea, 359. (Uianidine, 360.
Uric-acid Group (271-273) 362
Parabanic acid, 362. Oxaluric acid, 362, Alloxan, 362. Alloxantine, 363. Allantoine, 363. Uric acid, 364. Purine, 365. Xanthine, 366. Theobromine, 366. Caffeine, 366. Electro-reduction of purine de- rivatives, 368.
SECOND PART. CYCLIC COMPOUNDS (274-416) 373
Introduction (274) 373
Classification of cyclic compounds 373
A. caruocyclic compounds (275-386) 375
1. ALICYCLIC COMPOUNDS (275-280) 375
cyc/oPropaiK* derivatives, 375. ci/r^Butane derivatives, 375. cyr^Pentane derivative, 376. Higher alicyclic derivatives, 378.
2. AROMATIC COMPOUNDS (281-386) 380
xii CONTENTS.
PAOB
Constitution of Benzene (281-284) 380
Relation to the aromatic compounds^ 380. Structure of the mole- cule, 381. Formula of KekulI: and Thiele, 384. Nomenclature and isomerism of the benzene derivatives, 384. Properties Characteristic of the Aromatic Compounds: Syntheses
FROM Aliphatic Compounds (285) 386
Benzene and the Aromatic Hydrocarbons with Saturated Side- chains (286-288) 388
Gas-manufacture and its by-products: Tar, 388. Benzene and its homologues, 389. M0NOSUB8TITUTI0N-PRODUCT8 OF THE Aromatic Hydrocarbons
(28^320) 393
Monohalogen compounds (289) 393
Mononilro-derivatives (290) 395
Preparation, 395. Nitrobenzene, 395. Nitrotoluenes, 396.
Monosidphonic acids (291) 397
Formation, 397. Properties, 397. Sulphonyl chlorides, 397. Sulphonamides. 398.
Monohydric phenols (292-295) 398
Formation, 398. Properties, 399. Phenol, 400. Cresols, 400. Thymol, 400. Ethers, 400.
Monoamino-compounda(2g6-29g) 401
Formation, 401. Properties, 401. Aniline, 403. Homologues of aniline, 404. Secondary amines, 404. Tertiary amines, 405. Quaternary bases, 407. Intermediate products in the reduction of aromatic nitrocompounds
(300-304) 407
Azoxybenzene, 408. Azobenzene, 408. Hydrazobenzene, 409. Benzidine, 409. Electro-reduction of nitro-com- pounds, 409.
Diazocompounds (305-309) 413
Classification, 413. Constitution of the diazonium salts, 414. Reactions of the diazonium compounds, 415. Diazoamino- compounds, 419. Aminoazo-compounds, 419. Hydroxy azo- compounds, 420.
Hydrazines (3x0) 420
Phenylhydrazine, 420. Methylphenylhydrazine, 421. Aromatic moru)basic acids: Benzoic acid and its hornoloffiies (^11-^1^).. 421 Formation, 422. Benzoic acid, 423. Benzoyl chloride, 424. Benzoic anhydride, 425. Ethyl benzoate, 425. Benzamide, 425. Benzonitrile, 426. Toluic acids, 426. Xylic acids, 426.
Aromatic aldehydes and ketones (314-318) 426
Aldehydes, 426. Autoxidation, 428. Ketones, 429. Oximes, 431.
Aromatic phosphorus and arsenic derivatives (3x9) 433
Phosphinobenzene, 433. Phenylphosphinic acid, 434. Phenyl-
CONTENTS. xiii
PAGB
phosphine, 434. Phosphenyl chloride, 434. Phosphobenzene, 434. Phosphenylous acid, 434. Arsinobenzenc, 434. Phenyl- arsinic acid, 434. Arsenobenzene, 434. Phony larsine oxide, 434. Aromatic metallic compounds (320) 435
Benzene Homologues with Substituted Side-chains (321-326) 436
Compounds with halogen in the side-chain (321) 436
Formation, 436. Benzyl chloride, 437. Benzyl bromide, 437. Benzyl iodide, 437. Benzal chloride, 438. Benzotrichloride, 438.
Phenylnitromethane and the pseudoacu/8 (322, 323) 438
Acids with carboxyl in the side-chain (324) 440
Phcnylacetic acid, 440. Mandelic acid, 440.
Aromatic alcohols (325) 441
Benzyl alcohol, 441.
Compounds with the amino-group in the side-chain (326) 441
Benzylamine, 441. Dibenzylamine, 441. Tribenzylamine, 441.
Compounds Containing an Unsaturated Side-chain (327, 328) 443
Hydrocarbons (327) 443
Styrole, 443. Phenylacetylene, 443.
Alcohols and aldehydes (327) 443
Cinnamyl alcohol, 443. Cinnamaldehyde, 444.
Acids (328) 443
Cinnainic acid, 444. AUocinnojnic acid, 445. isoCinnamic acids, 445.
Polysubstituted Benzene Derivatives (329-353) 446
Polyhalogen derivatives (329) 446
Halogen-nitro^ompounds (330) 447
Polynitro-derivatives (331) 448
Dinitrobenzenes, 448. Trinitrobenzenes, 448. Trinitrobutyl- xylene, 449.
Substituted benzenesulphonic acids (332) 449
Substituted phenols and polyhydric phenols (333-338) 450
Halogenphenols, 450. Nitrophcnols, 450. Phenolsulphonic acids, 452. Nitrosophenol, 453. Dihydric phenols, 453. Trihydric phenols, 455. Higher phenols, 457. Quinones, 457.
Substitution-products of aniline (339-341) 459
Nitroanilines, 459. p-Aminobenzcnesulphonic acid, 4(30. Amino- phenols, 461. Polyamino-compounds, 462. Azo-dyes, 404. Substituted benzoic acids; Polybasic acids and their derivatives (342-
350) 468
Halogenbenzolc acids, 468. Nitrobenzoic acids, 469. Sulpho- benzoic acids, 469. Monohydroxy-acids, 470. Xanthone- dyes,472. Flavone-dyes, 472. Dihydroxy-acids, 472. Trihy- droxy-acids, 4Z3. Aminobcnzolc acids, 475. Phthalic acid,
XIV CONTENTS.
PAOB
476. MoPhthalic and Terephthalic acids, 480. Higher poly- basic acids, 481.
SubslUiUed aldehydes (351) 481
Nitrobenzaldehydes, 481. Hydroxyaldehydes, 481. PolysubsiiitUed benzene derivatives with svbstUuenls in the side-chain
(353,353) 483
p-Hydroxyphenylpropionic acid, 483. o-Hydroxycinnamic acid, 483. Coumarin, 484. Piperic acid, 484. Piperonal, 484. Adrenaline, 485. Hordenine, 486. p-Hydroxyphenylthyl- amine, 486.
Orientation of Aromatic Compounds (354-363) 487
General principles, 487. Absolute determination of position for or/Zio-compounds, 488. Absolute determination of position for 7ncto-compounds, 490. Absolute determination of p)Osition for para-compounds, 492. Determination of position for the trisub- stituted and higher-substituted derivatives, 493. Equivalence of the six hydrogen atoms in benzene, 495. Influence of the sub- stituents on each other, 496 .
Hydrqcycuc or Hydroaromatic Compounds (363-370) 503
Hydrocydic compounds (363, 364) 503
Preparation, 503. cyc/oHexane, 505. p-DiketocycZohexane, 506. Quinitols, 506. Inositol, 507. cyc/oHexanone, 507. Hydro- cyclic acids, 507.
Terpenes (365-369) 508
Isolation, 508. Nomenclature, 508. Menthol, 508. Terpin, 509. Terpineol, 512. Pulegone, 513. Terpinolene, 513. Limonenes, 514. Carvone, 514. Carvacrol, 514. Polycyclic terpene derivatives, 516.
Camphors (370) 518
Camphor, 518. Borneol, 518. Camphoric acid, 519. Cam- phoronic acid, 519. Synthesis of camphor, 520. Camphane, 520. Thujone, 521 .
Folyterpenes (370) 521
Caoutchouc, 521. 1 : 5-Dimethylf yc/ooctadiene, 522.
Bei^zene-nuclei Linked Together Directly or Indirectly by
Carbon (371-376) 523
Diphenyl (371) 523
r : : Diphenylmeihane Xs7^) 524
Triphenylmelhane and its derivatives (373-375) 525
. Triphenylmethane, 525. Leucomalachite-green, 526. Mala- -:;^ chite-green, 526. Quinonoid reaction, 526. Halochromy,
cl: 527.. Stages in the formation .of the triphenylmethane dyes,
528. Crystal-violet, 528. Pararosaniline, 529. Paraleucan- - . iline, 529. Rosaniline, 529. Magenta, 530. Methyl-violet, . . 530. Aniline-blue, 530. Rosolic acid, 530. Triphenyl- .L,.-- .methyl, 531.
CONTENTS. XV
• PAGE
Dibemyl and its derivalives (376) 532
Dibenzyl, 532. Stilbene, 532. Benzoin, 533. Hydrobenzoin, 533. Benzil, 533. Benzilic acid. 533.
Condensed Benzene-nuclei (377-386) 534
Naphthalene (377-381) 534
Preparation from coal-tar, 534. Properties, 534. Constitu- tion, 535. Number of substitution-products, 536. Orienta- tion, 537. Substitution-products, 538. Addition-products, 541.
Anthracene (382-385) 544
Preparation from coal-tar, 544. Properties, 544. Constitu- tion, 544. Number of substitution-products, 545. Orienta- tion, 545. Anthraquinone, 545. Anthraquinol, 547. Oxan- throne, 547. Anthrone, 548. Anthranol, 548. Alizarin, 548. Lakes, 550. Purpurin, 550. Indanthren-group, 551.
Phenanlhrene (386) 551
Preparation from anthracene-oil, 551. Properties, 551. Con- stitution, 551 . Phenanthraquinone, 552. Dimethylmorphol, 553.
b. heterocyclic compounds (387-416) 554
Nuclei Containing Nitrogen, Oxygen, and Sulphur (387-399) 554
Pyridine (387-391) 554
Preparation from coal-tar, 554. Properties, 554. Constitu- tion, 555. Number of substitution-products, 556. Orienta- tion, 556. Homologues, 557. a-Propenylpyridine, 558. Piperidine, 559. Piperine, 559. Piperic acid, 559. Pyridine- carboxylic at^ids, 559.
Furan (392, 393) 561
Constitution, 561. Preparation of derivatives, 561. Furfur- aldehyde, 562. Furfuramide, 562. Furfuroin; 562. Hydroxy- methylfurfuraldehyde, 563. Dehydromucic acid, 563. Pyro- mucic acid, 563.
Pyrrole (394, 395) 564
Preparation, 564. Properties, 564. Synthesis, 564. Constitu- tion, 565. Derivatives, 565.
Thiophen (396, 397) 566
Preparation, 566. Synthesis, 567. Properties, 567. Homo- lof^ies, 567. Derivatives, 568.
Pyrazole (398, 399) 568
Formation of derivatives, 568. Synthesis and constitution, 569. Identity of derivatives with substituents at positions 3 and 5, 569. Pyrazoline, 570. Pyrazolone, 570. Methyl- phenylpyrazolone, 570. *' Antip>Tine," 570. " Salipyrine," 571.
XVI CONTENTS.
PAOB
Condensation-products op Benzene and Heterocyclic Nuclei (400-
405) 572
Quinoline (400, 401) 572
Properties, 572. Synthesis, 572. Constitution, 573. Orienta- tion, 573. Nomenclature, 574. Derivatives, 574.
isoQuinoline (402) 575
Properties, 575. Constitution and synthesis, 575.
Indole (403-405) 575
Relation to indigo, 575. Constitution, 576. Scatole, 577. Tryptophan, 577. 3-Indolealdehyde, 577. Indigo, 578. Indoxyl,578. Indigo-white, 580. Vat-dyestuffs, 580. Indig- oids, 581. " Purple of the ancients," 581. Thioindigo, 581.
Alkaloids (406-416) 582
Classification (406) 582
Properties (407) 582
Extraction from plants (408) 583
Indii-idual alkaloids (409-4x6) , 583
Coniinc, 583. Nicotine, 584. Atropine, 584. Cocaine, 586. Morphine, 586. Heroin, 588. Narcotine, 588. Nornarcotine, 588. Cotarnine, 588. Quinine, 589. Cinchonine, 589. , Strychnine, 590. Brucine, 590. Curarine, 590.
INDEX 591
FIGURES.
FIRST PART.
riOVRE PAOB
1. Organic analysis '. . 5
2. Potash-bulbs 6
3. Tube-furnace 9
4. Victor Meyer's vapour-density ap])aratus 12
5. Eykman's graphic nxethod 15
6. Eykman's dcpressimeter 17
7. Eykman'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. Fractional-distillation curves 25
17. Steam-distillation 27
18. Separating-funnel 28
19. Filtering-flask 30
20. Thiele's melting-point apparatus 31
21. Pyknometer 32
22. Laurent's polarimeter 33
23. Fractionating-column 55
24. Carbon tetrahedron 65
25. 26. Asynmietric C-atoms 65
27. Solubility-curves for triethylamine and water 89
28. Usual form of solubility-curve for two liquids 89
29. Asynmietric molecular structure 99
30. Melting-point curve of the fatty acids 107
31. Preparation of vinegar by the " quick " or German process 110
32. Graphic representation of the melting-poinU of the acids CnUsn-204. 199
33. Spacial representation of the bonds between 2-5 C-atoms 208
34. 35. Single bond between two carbon atoms 211
36, 37, 38. Graphic spacial representation of the double bond between
two carbon atoms 211
39. Fumaric add 213
xvil
xviii FIGURES.
riQURB PAGS
40. Dibromosuccinic acid 213
41. Maleic acid 213
42. isoDibromosuccinic acid 213
43. Dibromosuccinic acid 214
44. Bromomaleic acid 214
45. woDibromosuccinic acid 214
46. Bromofumaric acid 214
47. Erucic acid 222
48. 49. Dibromoerucic acid 222
50. Brafisidic acid 223
51, 52. Dibromobrassidic acid 223
53. Acetaldehyde 228
54, 55. Lactonitrilc 228
56, 57. Conversion of an optically active substance into its optical iso-
meride 229
58, 59. Emil Fischer's spacial representation of two C-atoms in union. . 235
60. Electrolysis of an alkaline copper solution 239
61. Maleic acid 242
62. 63. Mesotartaric acid 242
64. Fumaric acid 243
65. Racemic acid 243
66. Crystal forms of the sodium ammonium tartrates 246
67. Rye-starch 292
68. Rice-starch 292
69. Potato-starch 293
70. Werner's theory of the Walden Inversion 322
71 . Normal reduction-curve 370
72. Abnormal reduction-curve 370
SECOND PART.
73. Kekul^'s benzene-formula 384
74. Thiele's benzene-formula 384
75. Fusion-curve of mixtures of o-nitrotoluene and p-nitrotoluene 396
76. Haber's electro-reduction scheme 412
77. Solubility-curve of benzoic acid in water 424
78. Enantiotropic 8ubsta.nce 430
79. Monotropic substance 430
80. Centric naphthalene-formula 536
81. Thiele's naphthalene-formula 536
82. Simple naphthalene-formula 536
ORGANIC CHEMISTRY.
INTRODUCTION.
I. 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 was thought that the substances which occur in organized nature, in the animal and vegetable 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 chemistr>' 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 com|X)und body from its decomposition-products, or to obtain an organic com|)ound from its elements.
In the year 1828, Wohler had indeed obtained from inorganic sources the organic compound urea^ a product of the animal economy. This discovery was at first regarded as of small im- portance, for it was thought that this sulwtance 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 Kolbb 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 chem- 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 degrees 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 inorganic chemistry now exists, and numerous syntheses 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 compoundi 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 compounds 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 com pound j^ 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
§ 3] QUALITATIVE ANALYSIS. 3
chemical change, whereas the carbon compounds, almost 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 CioHiaO^N have been discovered. This phenomenon is called isomerism, and is almost unknown in inorganic chemistr>', 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 is 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, which can be
4 ORGANIC CHEMISTRY. [§ 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 oxidise 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 l>e 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 Prussiaa blue (*' Laboratory Manual,'* I, 3, a).
II 5, 4 QUANTITATIVE ANALYSIS. 5
S- The halogens can be recognized by heating the substance vith 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 volatilizes, 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 sul- 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 analysis.
6. Following on qualitative, must come quanlUatire, 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 often 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 liydrogen are always estimated together. The principle of the method of organic analysis chiefly used was worked out by LiEBiG (1803-1873). It is usually carried out as follows. In the combustion-fumsce, k (Pig. 1], is a hard glass tube, ab.
Fia. 1. — OnoANic Analvsis.
open at both ends. A complete drawing of it is shown in the figure above the furnace. It contains granulated copper oxide.
6 ORGANIC CHEMISTRY. [§«
//, and a spiral of copper-gauze, c, oxidized by heating to redness in the air or in a stream of oxj'gen. About one-third of the length of the tube is left emptyi 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, h, /, in which the air or oxygen is freed from water- vapour and carbon dioxide: g contains concentrated caustic potash, h soda-lime, and / calcium chloride. To the end of the tube furthest from the boat is attached a weighed calcium-chloride tube, /, 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 b on the right, pass Fig. 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 amoimt 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 absorption-apparatus I and m. The hot copper decom- poses any nitrogen oxides formed, which would otherwise be absorbed in the potash-bulbs: it also combines with and retains the halogens.
§7J 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 circimi- 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 copper 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, PbOj, 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.
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 eflfect com- plete expulsion of the air from the tube before the combustion is begun. The absorption-apparatus /, ni, 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 combustion is over, all the nitrogen remaining in the tube is swept into the graduated tube by a stream of carbon dioxide from the Kreussler generator. The tube, along with the mercury, potash, and gas which it contains, is then placed in a wide cylinder filled with water. The mercur>' and potash are displaced by the water, and
8 ORGANIC CHEMISTRY. [§8
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 Kjeldahl 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 LiEBiG 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- phur, phosphorus, and other elements. Non-volatile 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 peroxide, the final product being a chlo-
S^ QUANTITATIVE ANALYSIS. 9
rate, bromat«, or iodate. On reducUon with sulphurous acid, this is converted into a halJde, which can be precipLtat«d with silver nitrate in the usual manner.
9. The results of a quantitative analysis are expressed jn pet^ centage-numbers. If the total of these percentage-numbers is very nearly 100. then no other element is present in the compound; 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. TUBB-PCRNACB.
100. This has the disadvantage that all experimental errors are included in the percentage-number of the oxygen.
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 arc 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
10 ORGANIC CHEMISTRY. [{9
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. HjO.
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 CO2, and 2 parts by weight of H in 18 parts by weight of H2O, the number obtained for CO, must be multiplied by tt=A to find the weight of C, and the number found for H2O by A =4 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 la saturated with water-vapour, the tension of this expressed in mm. 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 7-0 mm. The actual pressure of the nitrogen is therefore 762 — 7 — 755 mm. Since 1 c.c. of nitrogen at 0° and 760 mm. weighs 1 -2562 mg., at 755 mm. and 6° C. the weight of this volume expressed in milligrammes is
1.2562 xPI-1.2211.
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- centage of oxygen in the substance analyzed is 21 -9. The percentage- composition given by the analysis is therefore
C 65.0 H 3.5 N 9.6'
o 21.9
On dividing these values by the numbers representing the atomic weights of the corresponding elements, there results
C H N O
5.4 3.5 0.7 1.4. These numbers divided by 0-7 give
C H N 0
7-7 5-0 1.0 2-0.
1 10] DETERMINATION OF MOLECULAR WEIGHT. 11
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 MOLECULAR WEIGHT.
10. An analysis only gives the empirical formula of a com- pound, and not its molecular formula, because CaHbOo has the same percentage-composition as (CftHbOo)n. When the empirical formula has been ascertained by analysis, the molecular weight has still to be determined.
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, CeHsBr, 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, (C6H6)n; the bromine com- pound would then have the formula (C6H5Br)n. Assuming the formula to be C12H12, that of the bromine compound would be Ci2HioBr2. It is evident that the formation of a compound of this formula would involve direct replacement of two hj^drogen 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 CeHsBr would be increased. This would not, however, be decisive, because the experimental conditions necessary to the formation 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 C^Hg, 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 state, or of cer- tain values depending on the osmotic pressure of the substance in dilute solution. The theory of these methods is fully ex- plained in "Inorganic Chemistry." 31-35 and 40-43. Here it
12
ORGANIC CHEMISTRY.
nil
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 volimie is meas- ured, and the barometric pressure — must be known.
II. Vapour-density is usually determined by a method sug- gested by Victor Meyer. The apparatus (Fig. 4) consists of a glass tube B with an internal diam- eter of about 4 mm. This tube is closed at the top with a stopper, and underneath has a wider cylindrical portion of about 200 c.c. capacity, closed at the lower end. Near the top of the tube is sealed on a de- livery-tube A for the gas, which is collected over water in a graduated tube E, The apparatus is partly sur- rounded by a wide glass (or metal) jacket C This contains a liquid boil- mg higher than the substance the vapour-density of which is being de- termined. This liquid is heated to boiling, some of the air in B being in consequence expelled. A point is soon reached 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 substance under examination enclosed in a small glass tube is dropped into the appa- ratus, and the stopper replaced, care
FiQ. 4. — Victor Meter's Vapour- DENSITY Appa- ratus.
i
r
9 11] DETERMINATION OF MOLECULAR WEIGHT. 13
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 remam constant during the short time occupied by the experiment.
The result is 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 //, the temj)era- ture /, and the tension of aqueous vapour 6, then, at a pressure of H — b mm. and at /°, 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 —b mm. of pressure, and at <°, weiglis in milligrammes
1-429 ^H-b 1-hb- 00367/^ 760'
from which it follows that the vapour-density D referred to oxygen = 16 is
F"" 1-429 ^H-b' The molecular weight M being twice the density,
M = 2D.
14 ORGANIC CHEMISTRY. [§ 12
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 ("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
-AM = 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 molecular depression of the freezing^ point or the molecular elevation of the boiling-point of the solvent.
Example. — Numerous determinations have proved that when phenol is used as the solvent the molecular depression of its freezing-point is equal to 75. We have then for phenol
AM =75.
A solution of 2-75 per cent, concentration was prepared by dis- solving 0«3943 g. of a substance of empirical formula C7H7ON2 in 14-34 g. of phenol. The depression of this solution was 0-712°. For
a one per cent, solution the depression would have been -z-^- —
J«7o
J 13]
DETERMINATION OF MOLECULAR WEIGHT.
15
0*258, therefore A — 0>25S. It follows that the molecular weight is
-^^-291 0.258 '^^^•
Since CyH^Nj corresponds with the molecular weight 135, and
CuHj^OaN^ 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 i4M = 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. ^1 should be derived from a solution of infinite dilution; but as this is not possible,
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- tions are the abscissae. Eykman states that very often the line drawn through the tops of the 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 freezing^ point of a numl)er of solvents are given in the following table:
Si
?
o z
e
PEACENTAOEa
Fig, 5. — Eykman's GRAPmo Method.
Solvent.
Water.......
Acetic acid. .
Benzene
Nitrobenzene.
Phenol
Naphthalene. Urethane. . . . Stearic acid. . j>-Toluidine. .
Melting-point.
0° 16. S**
6^
5^ 39.0° 80° 48.7° 5:^° 42.5°
|
Molecular Deprefvion. |
|
|
Obi»erved. |
Calculated. |
|
19 |
18. 9 |
|
39 |
38.8 |
|
53 |
53 |
|
70 |
69.5 |
|
75 |
77 |
|
69 |
69.4 |
|
51.4 |
— |
|
45 |
|
|
52.4 |
16
ORGANIC CHEMISTRY.
[§14
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.
|
Boiling-poiDt. |
Molecular |
Elevation. |
|
|
Solvent. |
Obaerved. |
Calculated. |
|
|
Water |
100° 35.6° 78.0° 80.4° 61.0° 56.3° |
5.1 22.1 11.3 26-0 35. G 17.3 |
5.2 |
|
Ether |
21.1 |
||
|
Ethvl alcohol |
11.5 |
||
|
Benzene |
26-7 |
||
|
Chloroform |
36.6 |
||
|
Acetone |
16.7 |
||
The numbers in the last column of the tables are cal- culated from VAN^T Hoff's formula
is: =
0.02X^2 W '
K being the molecular depression or elevation, T the freez- ing-point or boiling-point on the absolute scale, and W the latent heat of fusion or of evaporation per kilogramme of the solvent.
14. Eykman has constructed convenient apparatuses for the determination of the depression of the freezing-point and the elevation of the boihng-point. The first (Fig. 6) comprises a small thermometer divided into twentieths of a degree with a small flask attached as shown in the figure, this being contained in a glass cylinder: it is held at the top by a stopper, and supported underneath by cotton-wool. The latter has the effect of making
(151
DETERMINATION OF MOLECULAR WEIGHT.
the cooling take place slowly. Being a poor conductor of heat, the cotton-wool retards cooling. A weighed quantity of the solvent is placed in the Hask, and its freezing-point determined. Then a known weight of the substance is introduced, and the freezing- point again observed. From the depression of the freezing-point thus obtained A can be calculated as in the example given (12).
15. Eykhan's apparatus (Fig. 7) for determining the eleva- 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. vide, and serves both as a heating jacket for the pure solvent, and as an air-condenser. Into B, which is only a few millimetres
18 ORGANIC CHEMISTRY. [5 15
narrower than ^4, there is fused the boiling-tube C, with a narrow side-tube D, C is suspended from the clamp K hy & platinum wire, Pf 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 (7. 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 .1. 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 A", and the volume accurately determined by reading with a lens the height of the solution-meniscus on the thermomctcr-scale.
A second determination is made with a solution of greater concentration by introducing a further quantity of the substance 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 con- tents, a series of determinations at diff'erent concentrations can be quickly made, and the results plotted on squared paj)er. From the curve thus obtained the value of A for infinite dilution can be readily calculated (12).
i§ 16, 17] THE ELEMENT CARBON. 19
THE ELEMENT CARBON.
i6. Carbon occurs in three allotropic forms: diamond y 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 CnH2n-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 treated of in '' Inorganic Chem- istry/' 76. With univalent demerits 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.
The compound CO2 is also an instance of the quadrivalency of carbon. In carbon monoxide, CO, on the other hand, the carbon atom must be looked upon as bivalent, at least if the bi valency of oxygen is retained. Other compounds are well known in which carbon may be looked upon as bivalent, but their number is very small in comparison with those, numbering many thousands, in which carbon must be regarded as quadrivalent. \ ,
LABORATORY-METHODS. ^ ^
17. To prevent repetition, it is doslrable, boforo 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 vctv 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.
HIT
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 Pig. 8. The flask is iminerse<l in an air-bath formed of a vertical iron cylinder closed at the lower end, a piece of stove- pipe being very suitable. The upper end is closed with a sheet of asbestos mill-board, with an opening for the neck 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
Fia. 8.-
SOBSTAKCES lA
Open Flask.
Fw. 9. — FiASE WITH Reflox-
CONDENBER.
attributed to Liebio, although it was first constructed by Weioei. in 1771. It consists of a glass tube aa, enclosed in a jacket b of glass or metal, through which a stream of coUi water can pass. For substances of high boiling-point a plain vertical glass tube may
$181
LABORA TORY- METHODS.
21
be substituted: it is called an "air-condenser," being sufficiently cooled by the air alone. The effect of the condenser is evident: the boiling liquid is condensed in it and drops back into the flask.
Fio. 10. — ^Distillation-apparatus.
When substances have to be heated above their boiling-points, 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-furnace <9, Kig. 3).
i8. Distillation. — ^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 (Fig. 11) is substituted, and, if its neck is sufficiently loag, contact of the vapour with the stopper during distillation is prevented.
At the ordinary pressure many substances decompose oa heating to their boiling-points, but distil unchanged under di- minished pressure, because the Pio. H.—Fractionating-flask. boiling-point is then much lower.
The apparatus shown in Fig. 12 can be used for vacuum-dis- tillation.
22
ORGANIC CHEMISTRY.
HX»
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 is 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 flask. The receiver b is kept cool by a stream of water from c. m is a mercury manometer: a is a two-way
Fia. 12. — Distillation in Vacuum.
stop-cock which permits access of air to the apparatus after the distillation, and also serves to cut off the connection between the air-pump and the rest of the apparatus when the pump "strikes back "; that is, when the water rises through the tube s into the apparatus.
19. The separation of a mixture of volatile substances is effected by fractional distillation. 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-
§20]
FRACTIONAL DISTILLATION.
23
tion as complete as possible, the fraction IQOP-llQP 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-
YoUDf.
Bbmpkl. Wuktz. Linnemam.
Fig. 13. — Fractignatinq-columns.
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- colunm (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.
21. 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 -4 and Bj and the line AB the values of these constants for mixtures. The curve thus obtained usually varies more or less from a straight line.
The boiling-points of mixtures will be lower (line c) or higher (line 6) than those calculated by the proportion-rule. Sometimes, these boiling-point curves 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 always 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 fra(;tion with this highest, or lowest, boiling-point will always be obtained, and at constant pressure further separation will be impossible.
Comprehension 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 i>ortion 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 6'. The vapour-tension
§21)
FRACTIONAL DISTILLATION.
25
cwrve AVB throughout the complete trajectory AB lies higher than the boiling-point curve.
If the boiling-point curve has a maximum b (Fig.. 16), along the trajectory Ab the vapour will be richer in A than the liquid from
Fig. 14.
Percentages
Fig. 15.
Percentages
Fig. 16. Fraction ALrDisTiLLATioN Curves.
which it is evolved: along the trajectory bB 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 an
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-distUlation. — In the preparation of many organic substances a crude reaction-product is often 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 6, 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 b. 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, l^ecause the water in the receiver Ls mixed with fine, oily drops. There is also an oily layer above or below the water.
In steam-distillations two li(iui(ls take part — water and the sub- stance to be distilled. Usually these licpiiils are not miscible in all proportions. In the limiting ease, when each li(niid is wholly insoluble in the other, the vapour-pressure of each is unaffeoted by the presence of the other. At the boiling-point of the mixture, the sum of the vapour-pressures of the two constituents must \x^ ecjual 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 n( cessarily smaller than
STEAM-DISTI LLA TION.
27
the totai pressure, which is equal to that of the atmosphere. The same result is therefore attained as by distillatJon at diminished pressure; that is, the volatilization of the substance at a tem- perature lower than its 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 with
FlO. 17. STEAM-DTSTtLLATfOK.
the values of these physical constants for water. If the pressures are p, and p;, and the vapour-densities rf, and (4, the quantities dia- tillinu simultaneously are p.rf, (substanre) and pA (water). If the ratio pirf, :pjrf, is larRe, the substance distils with a small quantity of water, the distillation being quickly completed. The reverse takes place when the ratio pid, :p,d, is small.
At a pressure of 760 mm, a mixture of nitrobenzene and water bnils at 99°. The steam exerts a pressure of 733 mm., so that the tension of the nitroljcnzcne- vapour is 27 mm. Since the vapour- denailies of wat<T and nitrobenzene are in the ratio of their rcsprrtive molecular weights, 18 and 123, the proportion of wafer to nitrobenzene in the distillite should be a.-) 733x18 : 27x123; that is, approximately as 4 : 1. Notwithstanding its small vapour- tension at the Iwiling-point of the mixture, the quantity of nitro- l)enzene which passes over is about one-fifth of the total distillate, the rapid volatilization of the nitrobenzene beinR due to the fact that it has a large, and water a small, molecular weight. Evea
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, separaHng-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 ether, light petroleumy chloroform^ carbon disiUphide, 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 are 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 'ratinq-fun- ^^ ^*^® 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 ethier is distilled ofif. 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 distribut<is itself so that the ratio of the concentrations reached in both solvents is constant (law of Berth ei.ot). If a quantity A'u of the su])stance is dis- solved in a quantity I 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^i —Xi has passed into the second solvent.
The value of the quantity Xi is, in accordance with the above law, given by the equation
or X-X
A7
m
'!»
m + X/
523] EXTRACTION WITH SOLVENTS. 2^
X X ^x
for -r and ""^ are the two concentrations after agitation with
I m
the solvents, and K is the number expressing the constant ratio, or
the coefficient of distribution (German, Teilungskoeffizient).
A second extraction with the same quantity m of the second
solvent gives
Xi V^^ — "^2
I m '
OTy substituting the value of Xi from the first equation,
and for the nth extraction,
Thus Xn, the quantity remaining in the first solvent (water)^ diminishes as n increases, and as rn and K are respectively greater and less. Complete extraction is impossible, because although-
^) can approach zero very closely, it can never become
m+Kl/
equal to it.
Examples will facilitate comprehension of this formula. Sup«
pose the problem is to determine how often 1000 c.c. of an aqucou9
solution of benzoTc acid must l)e 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 u'o; that is, if the concentration of the
benzoic acid in the ethereal solution is represented by 80, that in
the acjueous solution is exfM'essed by 1. On substituting these
values for /, rw, and K res[x*ctivoly, the formula becomes
X _ Kl 1000Xft\) _ 1
A'o~m + A7~200 + 1000X]Ai~17'
wluch means that a single extraction with 200 c.c. of ether leaves iV of tlie benzoic acid in the aqueous solution. ^Vfter three extrac- tions with 200 c.c. of ether, there remains only Itz) ■^TJTT^ of the
acid, so that the extraction of the acid is [)ractically complete. For succinic acid K'=Q, A single extraction of 1000 c.c. of an.
ORGANIC CHEMISTRY. ISS24.25
squeoua solutioa of this acid with 200 c.c. of ether leaves
extraction is necessary to remove all the succinic acid from the
aqueous solution.
It can be further shown from the equa- tion by the use o( the diflerential calculiia that with a given quantity of the secoDd solvent (ether) a more complete separa- tion is effected by extracting frequently with small quantities than by urang larger quantities a correspondingly fewer number of times.
Separation of Solids and Lipids. — This is effected by filtration, a process materially accelerated by attaching the funnel with a rubber stopper to a flask a (Fig. 19), connected through b to a water air-pump. To prevent rupture of the point of the filter-paper, it must be supported by a hollow platinum cone c.
24. Se/Hiration of Solids from one Another. — This process de- pends on difference in solubility. For a soluble and an insoluble substance l!ie operation is very simple. If both substances are soluble, the nielhod of fractional cri/stailtzation must be used. The mixture is dissolvetl in the minimum quantity of a boiling liquid: on cooling the solution the less .soluble sulwtancecry.stallizea first. The mother-liquor is poured off just as cr\'stals of the second body l>egin to separate, and the second compound crystallized either by further cooling or by concentrating the liquid by evaporation. Several repetitions of these processes are essential to the separa- tion. Even when the pure compounds have very different solu- bilities, the method is not free from difficulty, because the solu- bility of one subsfance may be very considerably modified by the presence of another. Water, alcohol, ether, glacial acetic acid, benzene, and other substances are employed jis solvents.
25. From the foregoing it is seen that solid substances are usually purified by crystallization, and liquids by distillation. It is an indication of pur it :i when the physical constants remain un- changed after the substance has been purified anew. Although
i25]
MELTING-POINTS AND BOILING-POINTS.
31
every physical constant could serve this purpose, the melting^ point and the boUing-paint are those most used, because 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 tUe substance coincide with those of the compound with which it is supposed to Ix; 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 approximately equal proportions and detennine the melting-point of the mixture. When iden- tity exists, the melting-point of the mixture will
coincide with that of the two individual sub- p,(j 20. Thielf's
stances; when it does not, the mixture molts Meltinu -point at a much lower temperature, which Is not Apparatus. sharply defined.
Thiele has devised a very convenient apparatus for deter- mining the melting-point (Fig. 20). A small quantity of the substance is placed in a thin-walled capillary tulx^ sealed at one end. This tube is attached to a thennometer, T, with its bulb dipping into a liquid of high boiling-point, sucrh as concentrated sulphuric acid, olive oil, or liquid paraffui (31), the \iscosity causing the tulx» to adh(»re to the thennometer. The liquid is contained in the apparatus ABC. Heating with a small flame at B induces circulation of the licjuid, ensuring uniform heat- ing of the thermometer and capillary tulx*. When the sub- stance fus(»s, the thermometer is n^ad.
The boUiug-point is d(»t(»nnined by heating the liquid to boil- ing in a fractionation-flask with a high side-tube. Short ther- mometers art* us(»d, so that the whole of the; mercury column is surr()und(Ml by th(» vapour of the boiling lifjuid. To avoid in- conveniently small graduations, t\mm thermometers are con- structed so that they can only Iw employed for a comparatively
32
ORGANIC CHEMISTRY.
[§26
\J
Fig. 21.— Pyk-
NOMKTER.
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- termined with the pyknomeieTf the most useful form of which is shown in Fig. 21. It consists of two thick-walled capillaries a and b, termi- nating in a wider tube c. The parts a and b 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 observ-ed; from the data thus obtained the spi^cific gravity can be calculated.
2. The rotation of the plane of polarizaiion is another constant of importance.
Some substances, such as turix?ntine, a solution of sugar, etc., have the proi)erty of rotatinq out of its original fK)sition the plane of a ray of polarized light i)assing through them. This phenomenon is called the rotation of the plane of polarizaiion^ and substances pos- sessing this proixjrty are said to l)e optically active, Polarimetcrs have lxM?n constructed for measuring the angle through which the plane of ])()larizati()n has Ixhmi rotated by an optically active sub- stance: of these LAniENT's (Fig. 22) is one of the lH»st known. The yellow sodium-light of the burner TT is ])olarize(l in the part of the apparatus marked IW, and then passes through a tuln? of known length (2(K)-.")()0 mm.) placed in the channel L. This tul)e contains the liquid or solution under examination. The [)art C)C of the appa- ratus serves to measure the rotation of the plane of polarization.
The extent to which the plane of jKilarization is rotated is pro- portional to the length of the tul)e, and is variously expressed. The rotation of a substance can be stated, for example, in terms of the efTect produced by a given length of the tul)e (l(\s(Til)ed. The angle of rotation is read off directly from the inst'ument, and is usually d(Mi()ted by a. By convention, the Hpecific rotalory power is defined as the quotient obtained by dividing a by t^H^ product of
§2C]
FOLARIMETRY.
33
the length of the tube into the specific gravity of the liquid. This value is denoted by [a] so that
» -u
where I is the length of the tube, and d the specific gravity of the liquid. Under these conditions, [a] expresses the rotatory 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.
Fig. 22. — Laurent's Polarimeter.
The extent of the rotation is dependent on the colour of the light. The measurement is often carried out with sodium-light, which gives a yellow line in the spectroscope, denoted by D. This is expressed by the symbol [a]p.
When the rotatory power of a substance is small, or when, on account of its slight solubility, it can only be obtained in dilute solu- tion, 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 apparatus employed is given in text-books of physics. The index of refraction^ n, depends on the colour of the light
34 ORGANIC CHEMISTRY, [§ 27
employed, and is generally determined for the three principal lines of the hydrogen spectrum, or for the yellow sodium line. The difference in refraction for the various colours is called dispersiarif and also finds application in organic investigation.
The refraction also depends on the temperature, and on the specific gravity of the liquid. On theoretical grounds, Lorentz, of Leyden, and Lorenz, of Copenhagen, have proved the expression
n«-l 1^ n«+2 ' d
to be independent of the temperature, d representing the specific gravity, a result fully supported by numerous experimental deter- minations. The product of this expression by the molecular
weight Mj
n=-J M
^ n2+2 ' d'
is called the molecular refraction. Reference will be made sub- sequently to the great importance of this constant. The molecular electric condvctivily is considered in 87.
CLASSIFICATION OF ORGANIC COMPOUNDS.
27. The organic compounds are usually classed in two maia divisions. One of these includes the fatty or aliphatic com- pounds (aXcK^ap, f at) , and the other the cyclic or rin{/ compounds. The first class owes its name to the fact that the animal and vegetable fats Ix^long 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 l)e 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 ho shown later that there are important differences between the general properties of these two classes of compounds.
FIRST PART.
THE ALIPHATIC COMPOUNDS.
SATURATED HYDROCARBONS.
28. The aliphatic compounds are defined in 27 as those derived irom methane, 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 rharsh-gas, 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:
C04-3H2 = CH4 + H20.
The nickel undergoes no apparent change, and can be used re- peatedly. At a temperature of 230^-300°, carl)on dioxide reacts similarly with hydrogen in presence of finely-divided nickel:
C02 + 4H2=CIl4-f2H20.
2. Methane can also be synthesized directly from its elements by passing hydrogen through a heated tulx* containing nHhiciNl nickel mixed with very finely-divided carbon obtained by previously decomposing methane. An ecjuilibrium is attained, corn\sponding at 475° and one atmosphei-e with 51 per cent, of methane:
Cll4^C-f2II..
35
36 ORGANIC CHEMISTRY. [§29
Prixg 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 met ham*.
3. By the action of water on aluminium carbide:
C3AI4 -f r2H2() = 3CH4-f 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 shghtly 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 burns 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 ecjuation
CH4 + 202 = C02 + 2H20.
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 + 2Cl=CH3Cl-fHCI.
The replacement of one atom by another is called sitbstiiiUwn. If chlorine or bromine is present in excess, the final product is ecu 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 CsHg, butane C4H10, pen- tane C5H12, hexane C6H14, etc., pevtatriacontane C35H72, and A^xa- contane C60H122. These formula* can be summed up in the general expression CnH2n+2' for methane, n = l. The hydrocarbons CnH2n+2 resemble methane in their power of rosiating oxidation,
f 3pJ PARAFFINS, 3T
and are unacted on by concentrated sulphuric acid, while halogens act on them with substitution of hydrogen and formation of compounds CbHsb+iCI, CnH2nCl2i 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 + Na2 = C2He+ 2NaI.
Propane can be prepared in accordance with tne following equa* tion:
CH3I + C2H5I + Naa = C3H8 4- 2NaI :
and, in general, CnH2n+2 is obtained by the action of sodium upon' CBiH2Bi+iI-f CpH2p+iI, when m+p=^n.
In addition to propane, butane, C«H,o, is formed from 2C,H5l, and ethane, C^Hc, from 2CH,I, 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 the number of carbon atom i. Thus CgHig is called octane, C12H26 dodecane, C31H64 hentriacontancy 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 aUcyl-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 butyl, CiaH25 dodecyl, etc.
The hydrocarbons CnH2n+2 have the general name saturated hydrocarbons, because they are saturated with hydrogen; that is, are unable to take up any more hydrogen atoms into the molecule. They are also called paraffins ^ because paraffin- wax consists of a
38 ORGANIC CHEMISTRY. [§31
mixture of the higher members. The word paraflSn is derived from parum affinis, and indicates the stability of this substance towards chemical reagents.
31. Occurrence in Nature, — The hydrocarbons CnH2n+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 fractional distillation, after treatment with acids and al kalis tofree itfromsubstances other than hydrocarbons of the formula CaH2n4-2. The most volatile por- tion is called light petroleum, petroleum-ether ^ benzine, naphtha, or ligroin: it distils between 40° and 150°, and contains lower mem- bers, chiefly C6H14, C7H16, and CgHig. It is extensively employed as motor-spirit, as a solvent for fats, oils, and rosins, 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 danger involved in its use is by no means small, a large num- ber of accidents by fire being attributable to this source. The fact that fires are often caused by the overturning of petroleum-lampa is traceable to the presence in the petroleum of a part of the more volatile products, and to their vapour producing an inflammable mixture with air. When a lamp filled with petroleum freed by careful fractionation from constituents of low boiling-point, is upset^ the flame is extinguished. Petroleum thus purified is a commercial product.
To ascertain whether a sample of petroleum contains these more volatile products, its flash-point is determined by heating it slowly in a specially constructed apparatus, devised by Sir Frederick Abel, and observing the temperature 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 flash-ix>int of 40° C. (104° F.). Large quantities of petroleum come into the market with a flash-point of 22°-24° C. (72°-75° F.): thev are the cheaper kinds, are used by the largest proportion of the population, and constitute a great source of danger from fire. It would be very advantageous if the law insisted ujwn a flash-point of about 40° C. or 104° F., as haa already been done in some countries.
Further distillation above 300^ yields lubricating oil, and then wax-like products, the residue in the still ultimately carboniz- ing. The residual product from th^ evaporation of Amcricaa
S 32] PETROLEUM. 39
petroleum in the air is called " vaseline " or petroleum-jelly. It is semi-solid at ordinary temperatures, white when pure, and and finds application 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 series CnH2n4-2, among them the hydrocarbons C22H46, C24H50, C26H64, C28H58.
Some kinds of crude petroleum, 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 Gralicia, and consists chiefly of paraffin-wax. This substance is also obtained in the dry distillation of the brown coal found in Saxony.
Asphalt is an oxidation-product of the higher-boiling con- stituents of petroleum. On prolonged heating at a high tem- perature in the air, paraffin -wax also absorbs oxygen and becomes dark in colour.
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 ver>' similar to natural petroleum. The parent fats may have had either a vegetable or an animal origin.
There appears to be no genetic interdependence between the occurrence of the enormous deposits of fossilized vegetable remains constituting coal, brown coal, and so on, and that of petroleum, since coal-fields and petroleum-wells are found in districts far apart. This fact constitutes a powerful argument in favour pf the theory of the animal origin of the fats from which petroleum has been formed; although a possible explanation is the formation of petro- leum and coal during different geological periods.
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 (»ver>' variety of petroleum is optically active, an indication of its dcTivation from optically active organic material (223); (2) petroleum is never
40 ORGANIC CHEMISTRY, [5 3S
found in the oldest geological formations, but only in those in which, the presence of vegetable and animal remains has been demonstrat^ed*
Homologous Series.
33. Each of the hydrocarbons CnH2n+2 differs in compositioa 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 arc said to be homologous (6fU)Xoyo«^ corresponding), the name homologous 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 properties^ 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 increas3S. 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 physical constants of a number of normal (36) members of the paraffin series is given on p. 41.
An inspection of this table reveals that the first four members are gases at the ordinary temperature, those from C5 to Cie 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 band, 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-
5C31
HOMOLOGOUS SERIES.
41
bers of the series become smaller with increase in the number of carbon atoms. This phenomenon is usually found in homologous series.
Por- mtda.
Name.
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
Undecane
Dodecane
Tetradecane
Hexadecane
Eicosane
Heneicosane
Tricosane
Hentriacontane
Pentatriacontanc
Hexacontane
Melting- point.
-186* -172-1°
135**
130. S** 94.03 97. r 56. 5**
- 51*
- 31*
- 26*
- 12*
4* 18* 36.5° 40.1° 47-4* 68-4° 74* 101*
Obrarved Boiling- point.
Calculat'd
Boiling*
point.
-160*
- 93*
- 45*
- o.r
36.3** 68.9* 98.4 125-6* 149.5 173* 194* 214.5° 252.5* 287.5* 205* * 215* 234* 302* 331*
166
95
43 0
36
68
98 125 149.8* 172.8* 194.3 214.6 252.0* 285.9*
3* 3* 1*
4*
4*
9*
3
I
Specific Gravity.
tt
tt
if
0.415 (at -160*)
0.446 (at 0*)
0.536 (atO*)
0.600 (at 0*)
0.627 (at 14*)
0.658 (at 20*)
0.683
0.702
0.718
0.730
0.774 at melting-point
0.773 *' '^
0.775 "
0.775 "
0-7775"
07778"
07799"
0-7799"
0-7813"
tt tt
» ft tt tt tt »
* At 15 mm. pressure, and the same for those following.
For the boiling-points these difTcrences afe functions of the ab- solute temperature. Sydney Young has induced the empirical formula
144.86 " yi0.oi4Sv/r'
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.
42 ORGANIC CHEMISTRY. [§34
Young's formula holds for normal pressure, 760 mm. For the absolute boiling-points of two substances a and 6 the simple relatioii
Ta Ta
n ■" n
often obtains, T and T' being the absolute boiling-points of the substances at the sanie arbitrary pressure. Otherwise expressed, this equation means that the ratio of the boiling-points at different
pressures is oft«n constant.
Isomerism and Structure.
34. Only one substance with the formula CH4 is known: it is 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 C5H12, five with the formula CeH^, and so on. The phenomenon of two or more copfipoi^nda hftinp; r^prp^nt-fi^ hy nnA fprmula is called isomerism (2), and compounds having the same formula are called xsomerides. 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 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 millimetre, 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.
k definite and unchanging arrangement of the atoms in a mole- cule does not involve their Ixjing immovable with respect to one another. For cxam[)le, they might revolve round a point of equilibrium without alteration in their order of succession.
S35] ISOMERISM AND STRUCTURE 43
35. Since the phenomenon of isomerism leads to the assump- tion of a definite arrangement of the atoms in the molecule, it is necessary to solve the problem of how the atoms ij^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 linkings 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 boimd 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, C'^Hg, must now be investigated. This substance can be obtained by the action of sodium upon methyl iodide, CH3I (53), with a quadrivalent 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-^C— .
Since the formula of ethane is CaHg, it is evident that the only possible arrangement of its atoms is that having the two free linkings of the methyl-groups united to one anotlier:
44 ORGANIC CHEMISTRY. [§35
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
H -^C C;-— H ,
•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/ I \H H
or shortly HaCCHg-CHs.
Such an arrangement of symbols expressing the configuration •of a molecule, and indicating the form or structure, is called a structural or constitutional 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 58°, and has a specific gravity of 0-6701 at 17-5°. The first is obtained by the action of sodium on normal propyl iodide f CH3 '0112 -01121. From the foregoing 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 union of two propyl-groups.
In addition to this normal propyl iodide, an isomeride called isopropyl iodide is known. Both compounds can be readily converted into propane, CH3 -0112-0113. Assuming that the isomerism is due to a different arrangement of the atoms Jn the molecule, it follows that the isomerism of the two compounds •C3H7I can only be explained by a difference in the position occu-
1361 CARBON CHAINS. 46
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. woPropyl iodide must therefore have
the structure
H
CHs'C'CHs,
•
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 isopropyl iodide, and consequently must have the structure
CH.3-CH.CH3 PH, PHo
A or Xo^>CH.CH<J^iJ\
CH3.CH.CH3 CH3 CHa
Hence it is called diisopropyL
Carbon Chains.
36. The foregoing 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 bncy 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 chainf 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 is so enormous is due to this property, in conjunction with the quadri- valency 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 diisopropyl. 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 iso.
46 OBGANIC CHEMISTRY. [{37
A few other definitions may find a {dace beve. A carbon atom
linked to only ftn^ niYwr far^ At/wn k r^Hfi^ primnni^- if Gnked to two Ca^iy^ at/im^ it M fiamAH ^^ywi/lffry; if tO thiee^ fertigyj^^
il^ to ^^"r, qtin/jnm/irjf _ A carbon atom situated at the aid of a chain is called terminal. The carbon atoms of a chain are dis- tinguished by nombers, the terminal one being denoted by 1, the one next it by 2, and so on; for examine,
CH3 •CH2 •CHj •CH3.
13 3 4
Sometimes the terminal atom b d^ioted by a, the one linked to it by ^, and the succeeding one by ^^^ etc., but a terminal C-atom in a CX-group, CHO-group. or OOOH-group, is distinguished by Wf the next by a, and so on.
Law of the Even Htunber <rf Atoms. — ^The number of hydrogen atoms in the saturated hydrocarbons is even, since their formula is CnHtn^3- All other organic compounds may be regarded as derived by exchange of these hydrogen atoms for other elements or groups of atoms, or by the removal of an even number of hydrrjgen 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 (\U/)S must be at least twice as great as this, because 2H + 1N is uneven.
Number of Possible Isomerides.
37. The quaclrivalenoy 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 pre<liction of the existence of unknown compounds. Thus for a compound C4H10 either the structure CH3«CH2-CH2-CH3 or
ppl^>CH-CH3 may be assumed, and there are no further possi- bilities. Pentane may have the following structural formulae: (1) CH3-CH2-CH2.CH2-CH3; (2) CH3.CH2.CH<^JJ3.
CH3 p .CH3 CH3^^^CH3'
[§37 NUMBER OF POSSIBLE IS0MERIDE8. 47
For hexane the following five are possible:
'(1) CH3.CH2.CH2.CH2.CH2.CH3;T2) CH3.CHa.CH2-CH<g^3; •^(3) CH3.CH2.CH.CH2CH3; "(4) CH3.CH.CH.CH3;
CH3 CH3 CH3
/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 synthesis 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 confirmation 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 man)' 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. Cay ley has calculated that there are nine possible isomerides for C7H16, eighteen for CgHig, thirty-five for C9H2o» seventy-five for CioH22» one hundred and fifty-nine for C11H24, three hundred and fifty-four for C12H2Q, eight hundred and two for Ci3H28» and so on. Chemists have not tried to prepare, for example, every one of the eight hundred and two possible isomerides of the formula Ci8H28» 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 difficulties in the way of these experiments, though there might be hindrances of an experimental nature.
48
ORGANIC CHEMISTRY,
[S38
Physical Properties of Isomeric Compotinds.
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 isomeridc with two side-chains linked to the penultimate carbon atom has the lowest boiling-point. The sub- joined table affords confirmation of these statement's.
|
Name. |
Formula. 1 |
Boilins- , point. |
|
n43ctane S^Mcthylheptanc |
CH3(CIl2)6CH3 CIIaCH.CCH2)4CH, CH3 |
124. T'' 1160'' |
|
3-Methylheptanc |
cn3cn2CH.(CH2)3cn3 CH3 |
117-6^ |
|
4-Methylheptane |
CII3 . (CH2)2 • CH • ^CHj). . CH3 CH3 |
IISO" |
|
2 : 5-Dimcthylhexane |
CH3Cn.(CH2)2cn.CH3 CH3 CH3 |
108-3^ |
|
2 : 2' : 3 : 3'-Tctraincthylbutanc |
CH3C C CH3 |
104* |
|
(Ha CII3 1 |
ALCOHOLS, C„H2n+20.
Methods of Formation and Constitution.
39. The alcohols of this homologous series can be obtained by the action of silver hydroxide on the alkyl halides:
C„H2o+iI + AgOH = C„H2„+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 = CzHfiO + HI.
When sodium reacts with an alcohol CnH2n+20, one gramme- atom of free hydrogen is liberated from each gramme-molecule of the alcohol, and a compound called sodium alkoxide {alcoholate) , CBH2n+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 is replaceable by sodium.
When an alcohol is treated with trichloride or pentachloride of phosphorus, an alkyl chloride is formed:
3CnH2n+20 + PCI3 = 3C„H2n+l CI -|- 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 sot free from thealkyl- group, and on the other hand the silver atom from the hydroxyl-
49
50 ORGASIC CHEMISTRY. [§39
*
group. The alkyl-group and the hydroxyl-group are thus afiforded the opportunity of uniting by means of the linking set free in each:
CnH2B+1 ff + A^IOH -> C„H2n+,— 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 imited through its second linking to a carlx>n 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 alkvl chlorides
by the action of the chlorides of phosphorus is additional proof
that they contain a hydroxyl-group. The empirical formulae
CnH2n+20 and CnHon+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: y^ ^>^
3(CnH2„+,-OH)-fCl3P.
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 formulas thus, the compound C2H6O could be either
1. CH3.CH2-OH, or II. CHg-O-CHa.
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, wi^uld accord equally ill with this formula, wh?rc:is for- mula I. explains these reactions fully. It must therefore be adopted*
•• ••••• • •••
• • *•• •* :'
• •• • • \ • • • ••
«
§40]
ALCOHOLS, CoH2n+i OH.
51
The constitutional formulae of the alcohols have thus been induced from their properties. Inversely, the constiiiUional for-^ miUce represent all the chemical properties of the cojnpotinds, 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 many instances been established by experiment.
Nomenclature and Isomerism.
40. The alcohols of this series are named after 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 hydroxy l-group; or through both these causes simultaneously.
This is seen from the following table of the isomeric alcohols Ca to Cfi.
|
1 |
1 |
Specific |
||
|
Name. |
Formula. |
' Melting- point. |
BoiliiiR- ' point. |
Gravity at 20* |
|
Propyl alcohols CjHbO |
1 |
1 |
||
|
1. Normal |
CHsCHjCHsOH |
Glass- like |
.97° |
0-804 |
|
2. 180 |
CHsCHOHCH, |
-85-8° |
81° |
0789 |
|
Butyl alcohols C4H,oO |
||||
|
1 . Normal primary |
CH,CHj.CH2.CH20H |
-79-6° |
117° |
0810 |
|
2. , , secondary ' CH, • CH, • CHOH • CH, |
Glmvs- like |
100° |
||
|
3. iso |
(CHa),CH.CH20H |
do. |
107° |
0-806 |
|
4. Trimethylcarbinol |
(CHa),COH |
25-5° |
83° |
0786 |
|
Amyl alcohols CtHijO |
||||
|
1. Normal primary |
CHafCHOsCHaOH |
138° |
0-815 |
|
|
^^. woBiit vlcarbinol (CH3),CH • CH, • CHjOH - |
-134° |
131° |
0810 |
|
|
-^3. Secondary butvl- |
||||
|
carbinol CH, • CH (C2H5) • CH2OH |
128° |
|||
|
4. Methyl propylcar- |
I |
|||
|
binol |
CH3(CH2),CHOH.CH, |
119° |
||
|
5. Methyltsopropyl- |
||||
|
carbinol |
(CH,)2CH.CH0HCH, |
112. 5° |
||
|
6. Diethylcarbinol |
CtHsCHOHCaH* |
117° |
||
|
7. Dimethylethylcar- |
||||
|
binol |
(CH,)2C(OH).C,H6 |
102° |
||
|
8. Tertiary butylcar- |
||||
|
binol |
(CH,),C.CH,OH |
112° |
52
ORGANIC CHEMISTRY.
[5 41
The alcohols with names ending in '' carbinol '^ are so eaHed because all alcohols may be looked upon as methyl akohd {car- binol), 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, isobutyl 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 hydrogea linked to a primary, secondary, or tertiary atom are called primary^ secondary, or tertiary compounds. Primary alcohols are repre- sented by the general formula CnH2n+i — CH2OH, secondary by
CnH2n+I — C^-CmH2ni+I» \0H
and tertiary by
CnH2n+l V CmH2m+l--7C — OH.
CpH2p+i /
General Properties of the Alcohols.
• 41. Some of the physical properties of the alcohols are given in this table, which includes only normal primary compounds.
Name.
Formula.
|
Methyl alcohol |
CHaOH |
|
Ethyl |
CjHsOH |
|
Propyl ." |
CJItOH |
|
Butyl " |
C4II9OH |
|
Amyl " |
CHnOH |
|
Hoxvl |
CcHuOH |
|
Hcptyl '♦ |
CtH.^OH |
|
Octvl " |
CkH.tOH |
|
Nonyl " |
CHlOH |
Melting- point.
971° 114. 15°
- 79-6*
36- 5° 17-9°
Boiling- point.
674°
78°
96-5° 116-7° 137° 157° 175° 194-5° 213°
Difference of the Boiling- points.
13-3°
18-5°
20-2°
20-3°
20°
18°
19-5°
18-5°
Speci6c Gravity.
0-812 0-806 0-817 0-823 0-829 0-833 0-836 0-839 0-842
Tliis tabl(», with that in 40, shows that the normal compounds have the highest boiling-points (38).
:§42l METHYL ALCOHOL. 53
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 three ways: (1) The vapour-densities of the alcohols at temperatures slightly above their boiling-points are greater than indicated by their formulae; (2) the degree of association can be inferred from measurements of the capillarity and viscosity of the liquids; (3) there subsists between the boiling-point and the molecular weight a relationship of the type
— = + 1000-— = C<m«^, VM T
T being the absolute boiling-pwint, 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. This formula also affords a means of detecting asso- ciation.
The lower alcohols (Ci — C4) are mobile liquids, the middle members (C5— Cn) are of a more oily nature, while the higher 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 large 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 producer-gas, ^hich is a mixture of carbon monoxide and nitrogen, obtained by passing air over coke at a white heat. To this method of
54 ORGANIC CHEMISTRY. I§ 4S
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 accompanied by contraction and the development of heat. It is poisonous.
Ethyl Alcohol, C2H5-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 C6H12O6, of decomposing into carbon dioxide and alcohol in presence of yeast-cells:
CeHiaOe =2C2H60 + 2CO2.
About 95 per cent, of the dextrose decomposes 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 (242).
On account of its cost, dextrose itself is not employed in the manufacture of alcohol, some substance rich in starch (225), (C6Hio05)n, such as potatoes, grain, etc., being used instead. By the action of enzymes (222), the starch is almost completely transformed into maltose (214), C12H22O11, one molecule of this compound being thon converted into two molecules of dextrose by the action of one molecule of water:
C12H22O1 1 + H2O =2CttHi20ti.
Maltose Dextrose
ETHYL ALCOHOL.
The enzyme employed in the technical manufacture of maltose from starch is called diastase, and ia present in malt. The reaction it induces is called sac- charificaiion. When po- tatoes arc used, they are first made into a thin, homogeneous pulp by treatment with steam under pressure at 140° to I'lff', malt being added aft*'r cooling. At a tem- perature of 60° to 62°, the tlecom position into maltose is completed in twenty minutes.
Yeast is then added to the maltose solution, anil the fermentation car- rietl on bctwe<'n 23° and 2o°. To separate the re- sulting alcohol from the other substances present, the product is submitted to distillation; and by using a fraclion- atiny-column {Kig. 2;i), alcohol of 90 per cent, strength can be obtained, although the concentration of the alcohol in the fermented liquid does not exceed IS per cent.
The thin liquid residue remaining in the still is called sptiit toosA. and ia used for feeding cattle. It contains, amongst other products, jilnidst all the proteins present in the :;i:',t;^niil frjni which the spirit has been manufactured.
The crude spirit {low wines) so prepared is again carefully fractionated, when alcohol of 96 per cent, by volume (spirits) is obtained. The fractions of higher boiling-point consist of an oily liquid of unpleasant odour, culled fusel-oil: it contains chiefly amyl alcohols and other homologues. The residue Is called si>ent Uea.
Atcobnlic bevera|;c9 are classified into those that have been die- tilled, and those thiit have not.
Fio. 23.— Fraction,
56
ORGANIC CHEMISTRY,
[§44
Distilled (about 50 percent, of alcohol).
Brandy or cognac^ from wine.
Whisky, frcm fermented solution of malt.
Rum, from fermented solution of sugar.
Gin, Hive whisky, but flavoured with juniper.
Not distilled.
Beer, from fermented malt and hops
(3-6 per cent, of alcohol). Wine, fermented prope-juice (8-10
per cent, of alcohol). ^'Fortified*' wines, such as port^ sherry, and madeira. They are wines with added alcohol. (Nat- ural wine never contains more than about 10 per cent, of alcohol.)
44. The alcohol of commerce C spirits of wine ") always con- tains water. To obtain anhydrous or absoltUe alcohol from this, lumps of quicklime are added to spirit containing a high per- centage of alcohol, imtil 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 100° in a water-bath. The spirit is then distilled. To 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 woight is thus obtained.
Absolute alcohol is a mobile, colourless liquid of character- istic odour, and Ijums with a pale-blue, non-luminous flame. Cooling with liquid air renders it very viscid, and ultimately causes crystallization. It is very hygroscopic, being iniscible with water in all proportions with contraction and rise in tempera- ture. The maximum contraction is obtained by mixing 52 volumes of alcohol with 4S volumes of water, the volume of the resulting mixture at 20° being 9G*3 instead of 100.
Tho pn^sence of w^ater in alcohol can l)c detected by anhydrous copper sulphate, which remains perfectly colourless when in con- tact vrith absolute alcohol, whereas if a trace of water is present.
§44] ETHYL ALCOHOL. 57
the copper sulphate develops a light-blue colour after several hours. The specific gravity, a physical constant often employed to ascertain the purity of liquid compounds, can also be employed for the same purpose. A method of detecting and estimating very slight traces of water in alcohol is described in 67.
A simple arid 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 vox Baumhader, Mendeleeff, 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 commerce and in the arts, the amount of alcohol is usually expressed on the Contment of Europe in volume-percenlage, or the number of litres of absolute alcohol contained in 100 litres of the aqueous solution. In Great Britam the standard is proof-spiriL This name is derived from the old method of testing spirit by moisten- ing gunpowder wUh it, and then bringing the mixture into contact 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 he orer proof; for example, a spirit 5® under proof would contain in each 100 volumes the same quantity of alcohol as 05 volumes of proof-spirit, and a spirit 5° over proof would need 5 vohiin(\s of water added to each 100 volumes to con- vert it into proof-spirit. Hy Act of Pariiamcnt "proof-spirit" is defined as "such a spirit as shall at a tem|)erature of 51° F. weiph exactly { J of an c(|ual measure of distilled water," corR»sf)ondinK with a spirit containinp; 57.1 per cent, of alcohol by volume, or 49.3 per cent bv weight.
For tciditific purposes the amount of alcohol i.s usually ex- pressed in jxTccntage by weight, or the number of grammes of
58 ORGANIC CHEMISTRY. [5 4^
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 preserva- tion of anatomical specimens. Alcohol is a good solvent for many organic compounds, and finds wide application in laborator}'- 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 unfit 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 Britain this is supplemented by the addition of a small quantity of paraffin-oil. The sale of denatured alcohol is also permitted in the United States.
In the United States the tax on alcohol is $1.10 per proof gallon (50 per cent, alcohol by volume), or S2.07 per standard gallon (231 cubic inches of 94 per cent, alcohol by volume). The duty is much higher in Great Britain, l)eiiig 14s. Orf. per gallon of proof-spirit (British standard, p. 57). Besides permitting the sale of methyU ated spirit containing naphtha, the British Government allows the sale for manufacturers' use of alcohol denatured with wood- spirit only, under the name " Industrial si)irit." It has the import- ant 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 gn the addition of iodine and caustic potash (146).
5 45J PROPYL ALCOHOL. 59
i
Propyl Alcohols, CsHy^OH.
45. Two propyl alcohols are known, one boiling at 97° and liaving 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-CHg-CHgOH, and CH3-CH(OH).CH3.
Normal propyl alcohol itoPropyl 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 C3H5O, but these oxidation-products are not identical. On further oxidation, the compound CaHgO (propionaldehyde), obtained from the alcohol of higher boiling-point, yields an acid
«
C3H6O2, called propionic acid; whereas the substance C3H6O (acetone), formed from the alcohol of lower boiling-point, is con- verted into carbon dioxide and acetic acid, C2H4O2:
C3H8O (propyl alcohol, B.P. 97°) -^CaHeO (propionaldehyde) -♦
— ^ C3H6O2 (propionic acid) ;
CaHgO (wopropyl alcohol, B.P. 81°) -> C3H6O (acetone) ->
— > CO2 + C2H4O2 (acetic acid).
Propionic acid has the constitution CH3«CH2-(X)OH, and acetone CH3«CO*CH3, 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 C3H8O 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 iso- propyl alcohol.
Oxidation affords a general method for distinguishing primary from secondary alcohols. By referring to the formulae given in
60 ORGANIC CHEMISTRY. [§ 46
40, it is seen that all primary alcohols contain the group — CH20H'^ which is converted by oxidation into the carboxyl-group — C^^tjj
the characteristic group of organic acids. Further, all secondary
I alcohols contain the group H'C«OH: removal of the two hydro-
I I
gen atoms from this yields the group C:0, characteristic of the
ketones (no), the homologues of acetone. The oxidaiionjof a prir mary alcohol and that of a secondary alcohol 'produce respectively an acid and a ketone tuith 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 submitted to oxidationy the molecule is attacked at the 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, tso Propyl alcohol is also a liquid: it is not present in fusel-oil, but can be obtained by the reduction of acetone (in and 150).
Butyl Alcohols, C4H9-OII.
46. Four butyl 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 boiling at 117® and 107® respectively yield acids with the same number of carbon atoms. They must therefore have the structures 1 and 3 (Ibid.), since each contains the group — GH2OH. For reasons referred to later, the alcohol boiling at 117° is considered to have the normal structure (1), and that boil- intr 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 corresf>onding with structure (2). Lastly, for the fourth, which is
§ 461 BUTYL ALCOHOLS. 61
solid at ordinary temperatures, melting at 25*5° and boiling at 83°, since three of the theoretically possible structural formulae 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,
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.
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 yrimaru alcohol yields rrp. nTiAafinn an acid with the same number of carbon atoms: a secondary alcohol yields on oxidation a ketone loith 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 boiling-point of naphthalene. At the last temperature tertiary alcohols are decomposed, yielding similar products to those formed from secondary alcohols at 300°. 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 ba.sed on the normal or abnormal character of the results obtained.
62 ORGANIC CHEMISTRY. [§47
Amyl Alcohols, CgHn-OH.
47. The alcohols containing five carbon atoms are called amyl akohols. There are eight possible isomerides, and all are known (c/. Table, 40). They are liquids with a disagreeable odour, like that of fusel-oil. isoButylcarbinol, (CH3)2CH.CH2-CH20H, and secondary butylcarbinol, CH3*CH(C2H6)«CH20H, are the prin- cipal constituents of fusel-oil (43).
Secondary butylcarbinol furnishes a very remarkable exampb 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 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^^ H C2H5 CH2OH.
That they have this constitution is proved by the fact that on oxidation they yield valeric acid with the structure
CH3 p 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 optically active (26, 2).
Since the difference between optically active compounds de- pends only upon a physical property, while their chemical proper-
5 47] AMYL ALCOHOLS. C3
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 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 optic- ally active substances.
Hence it follows that an explanation of the rotation of the plane of polarization by liquids and dissolved substances must be sowjht for in the internal structure of the molecules.
It is now necessary to determine what peculiarity. in the struc- ture of the molecules causes this phenomenon. The following considerations will furnish an insight into this. The kevo-rotatary nmyl alcohol, with the constitution
CH3 p H C2H5^^^CH20H,
is converted by the action of gaseous hydriodic acid into amyl iodide, with the structural formula
^'Ha p II Calls^ ^^CIl2l. This compound is optically active. On treatment with nascont hydrogen, the iodine atom is replaced by hydrogen, with forma- tion of pentane,
CH3 ,,^ H
CzHs^^^^CIIa. This compound is optically inactive.
64 ORGANIC CHEMISTRY, [§48
If amyl iodide is subjected to the action of ethyl iodide in the presence of sodium, there results a heptane,
C2H 5 CH2 • C2H5 ,
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 dif- ferent.
48. Van 't Hoff has shown that most oplicnUy active compounds tontain at least one carbon atom linked to jour different aioms or groups; and he has designated a carbon atom so linked an asymmetric carbon atom.
As stated above, there are three amyl alcohols with the same constitutional formula, of which one is dextro-rotatory, the second lievo-rotatory, and the third optically inactive. Three such isom- erides always exist when there is one asymmetric carbon atom in the molecule, and of the two optically active substances one causes exactly the same amount of dextro-rotatiori as the other of tevo- rotation. Van 't Hoff has shown that the existence of this num- l>er of isomerides is a necessary consequence of the presence of one asymmetric carbon atom in a molecule, provided certain as- sumptions are made regarding the relative positions of the atoms in space. These assumptions are as follows.
The quadri valency of the carbon atom has its origin in four points of attraction, situated on its outer surface, so that it is able to link itself to atoms or groups of atoms in four directions. The only supposition about th(*se directions in agreemont with the facts is that the carbon (itom in ftitiiatrfl at the centre of a regular four-mird fiijarv (tctrchedron) irith it.s Unkings directed toward the angles (Fig. 24). By putting the groups R, P, and Q of com- pounds CR2Q2, CRoPQ, or CR3P in different positions in two atom models,* it is always possible by rotating the models to
* Tho compn.'hcnsion of wluit follows will be c.'onsidorably facilitated by the const nirtion of srvcral models of carbon atoms with their linkinj»?5. This is easilj' tlone by cutting out a sphere from a cork to represent the carbon atom, the linkinRs beinj^ represented by moderately tliick wires about ten centimetres Ion;:, with ends filed to a point. Thes(» wires are fixed in the
§ 48] VAN T HOFFS THEORY OF STEREOISOMERISM,
65
a
Fio. 24. — Carbon Tetrahedron.
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 asymmetric carbgn atom, the possibility of the existence of two isomeric forms is indicated. It is seen from Figs. 25 and 26 (and still better from models) that for these four groups two arrange- ments are possible, which cannot be made to 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 symmetr}', hence the name " asymmetric carbon atom.'*
It is thus possible to understand how one isomeride causes as much dextro -rotation as the other laevo-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. 26.
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 Isevo-rotatory compound. Since these rotations are equal
<jork sphere in the manner shown in Fig. 24. To show the linking of the atoms or groups of atoms, cork spheres of dilTe .cni colours aie fastened to the ends cf the wires, the different colours ii.diciiting dissimilar groups.
66 ORGANIC CHEMISTRY. [§§49,60
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 ran be shown to be untenable. Thus, the tour linkings of the carbon atom might be supposed unequal in value; so that such a compound as CPsQ could exist in isomeric forms. Experience contradicts this assumption.
This phenomenon might also be supposed to be due to a differ- ence in till* motion of the atoms in the molecule. Then isomerism could no longer exist at absolute zero, sinc^ 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.
Higher Alcohols, CnHon+i-OH.
49. The prop(Tti('s of the higher nlcohds ai*c rnontioned in 41. Here may be cited cdifl alcohol, Ci6H33«OH, obtained from sper- maceti, and myricyl alcohol, C^Uqi'OH, obtained from wax. The number 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.
Alkoxides.
50. Alkoxides (alcoholatos) are compounds obtained from alco- hols by exchange of the hydroxy l-hydrogen atom for metals (39). The best known are sodium methoxidc (methylate), CH^'ONa, and Bodium ethoxide (ethylate), C2H5-ONa. Both are white powders, and yield cr>'stalline compounds with the corresponding alcohol.
S 50] ALKOXIDES, 67
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 Lobry de Bruyn has shown this to be only partly true, an equilibrium being reached in the reaction:
C2H60Na + H.^0 ^ CaHgOH + 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 alkoxide.
The alcoholic solution of sodium cthoxide, usually obtained by dissolving pieces of sodium in absolute ethyl alcohol, gradually becomes brown in consequence of oxidation to aldehyde (106). On the other hand, the solution of sodium methoxide in methvl alcohol remains unaltered, and therefore is employed in syntheses more than that of sodium cthoxide.
Only the alkali-metals mact directly with alcohols to produce alkoxides. Those of other mentals 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 cthoxide by the combination of potassium cthoxide and barium nitrate:
2C2H*OK -hBa(NO,), = (C2H50).Ba -f 2KN0,.
The alkoxides of calcium, strontium, and lead have been prepared similarly.
ALKYL HALIDES, ESTERS, AND 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 wat^r:
m.[oHTh].ii=m.r+hoh.
Alcohol Acul K-stcr
The substances formed are comparable with the salts of inor- ganic chemistry, and are called com]>ound 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 instantaneoaslv: it is a reaction of the ions, because the hydrogen ion of the acid unites with the hydroxyl ion of tlie base (*' Inorganic Chemistry,'' 66):
[B + OH']4-[FI+7/] = [H+7/] + H20.
Ba.se AckI Salt
The formation of esters, on the other hand, takes place very slowly, especially at ordinary temperatures, the reaction lx*ing between the non-ionized alcohol and the acid:
R.0H+[II+Z'] = R-Z+H20.
Aleohol Acid t^ter
68
§ 52] ALKYL HAL2DES. 69
Reactions between ions usually take place instantaneously,, those between molecules slowly.
Many bases can lose water, with formation 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 — O — CnH2n+i are formed. By elimination of water from two different alcohols, com- pounds called mixed ethers with the general formula
CnH2n +1 — O — CmH2m +1
are produced.
Alkyl Halides.
52. 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:
CnHg^^ipThHlX = C„H2„+,X+H20.
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 = C2H5Br-hKHS04 + H20.
Two other methods of formation for alkyl halides are men- tioned in 28 and 39: they arc 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 temperature 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:
PBra -h 3C2H6OH = PO3H3 -h 3C2H6Br.
The careful addition of bromine is continued until a quantity cor- responding to that required by the equation has been used. The
70 ORGANIC CHEMISTRY. § 53j
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 tliat whenever one molecule of a hydro- carbon CnH2n+2 is brought into contact with one molecule of chlo- rine or bromi!ie, the reaction does not take place merely as indi- cated by the equation
C^nH2n^-2+Cl2 = CnH2n+lCl-hHCl,
but that compounds CnH2nCl2, CnH2„_iCl3, etc., are simultaneously fomied, a portion of the hydrocarbon remaining unacted on.
ScHORLEMMER ()l)sorvo(l tho possibility of avoiding the formation of those hiRluT substitution-products by bringing the halogens into contact wi\\\ tho wpour of the boiling hydrocarbons.
The other caase 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,
CH3.CH2-CH2-CH2-CH2C1 and CH3-CH2-CH2.CHCl.CH3,
as can be proved by converting these chlorides into the corre- sponding alcohols and oxidizing tho latter (45).
53. The following table gives some of the physical properties of the alkyl halides.
$53]
ALKYL HALIDES.
71
|
• a 9 8 |
Name. |
Chloride. |
Bromide. |
Iodide. |
||
|
Alkyl- |
Boiling- point |
Specific Gravity |
Boiling- point. |
Specific Gravity. |
Boiling- point. 45° 72.3° 102.5° 130° 156° |
Specific Gravity. |
|
CH, C.H, C,H, C^Hu |
Methyl Ethyl n-Propyl n-Prim. butyl /i-Prim. amyl |
-23.7° 12.2° 46.5° 78° 107° |
0.952(0°) 0.918(8°) 0.912(0°) 0.C07(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°) |
2.293(18°) 1.944(14°) 1.786(0°) 1.643(0°) 1.543(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, CaHr |
Methvl Ethyf n-Propyl |
-140.85° |
Below -75° -119.0° |
- 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
72 ORGANIC CHEMISTRY, [f54
ions present in an alkyl halide solution, or at least that their number is verv small.
The alkvl 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.IOH-hHI.ONO2 = HaO-hCgHfi.ONOj.
Alcohol Nitric acid Ethyl nitrate
2. By the action of an alkyl halide on a silver salt:
S04[Ag24:2riC2H6 = S04(C2H6)2-h2Agl.
Kthvl sulphate
3. By the action of mineral-acid chlorides on alcohols or alkox- ides:
PO
Cl3-h3Na|OC2H5 = PO(OC2H6)3+3Naa.
Phojiphorus Normal ethyl
oxycoloride phoHphate
The acid esters of sulphuric acid, called alkylsul'phuric acids,. are of some importance. EtlnjlsiUphuric acidj or ethyl hydrogen sulphate, C2H50.S02-OH, is obtained by mixing alcohol with con- centrated sulphuric acid. The formation of this compound is never quantitative, Iwcause 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 Ixjing readily soluble in water, while the sulphates are insoluble, or nearly so. It is only necessary tc^ neutralize the mixture of sulphuric acid and alkylsulphuric acid
i 64] ETHYLSULPHURIC ACID, 73
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 sulphuric 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* eium 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:
K0>S02'0'[C^^TB?1K = KO-SOz-OK+CzHfiBr.
Potasnium ethyl- Potaivttum Ethyl
sulphate sulphate bromide
When free ethylsulphuric acid is heated, the neutral ethyl ester irf sulphuric acid and free sulphuric acid are formed:
SO.<ggH»+SO,<gHjj^ = S03<gH+SO,<gC2H..
Simultaneously, free sulphuric acid and ethylene are produced (115):
The conversion of ethylsulphuric acid into ether is described in 5^-
Dimetfiyl sulphate, (CHa)2S04, is obtained by the vacuum-dis- tillation of methylsulphuric acid:
2CH,HS0, = (CH,)2S04-hH:S04.
It is an oily liquid, boiling at 188°, and is often employed in the introduction of methyl-groups into organic compounds.
* ba = JBa.
74 ORGANIC CHEMISTRY, [§§55,56
Ethers.
55. The ethers are isomeric with the alcohols. Their coiv* stitution is proved by Williamson's synthesis, the action of an alkoxide on an alky I halide:
CnH2„+,.0. Na+I .C„H2„,^i - C„H2„+i.O.C„H2„,+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 3'ield propyl alcohol:
CaHfi. I+Na .CH2OH - C2H5.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 preseiity the reaction is almost quantitative. It follows that the greater part of the sodium alkoxide must be present as such, and is therefore not decom[X)sed 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, C2H5.0-C2H5, 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 ISO*'- 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 adde<l as was in the first instance mixed with the sulpluiric acid, the distillate becomes richer and richer in alcohol, and finally
56] ETHER, 75
the formation of ether stops altogether. Methylated spirit 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'lOSOaHTHJOH = C2H5.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'lO'SOaHTHl'O'CgHs = C2H5.O.C2H5+H^04.
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+HSO4H - C2H5-S04H+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, tlius putting an end to the pro- ducticm 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 :
C2H5. S04H-hHJ.O.C6Hn - C2H5.0.C5Hn +H2SO4.
76 ORGANIC CHEMISTRY. [{56
This reaction proves that the formation of ether takes place in the two stages mentioned above.
Senderens found that addition to the liquid of five per cent, of its weight of sulphate of aluminium or lead causes the forma- tion of ether smoothl}" at 120*^.
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 unsaturat^Kl hydrocarbons of the series CnH2ii being protluced. Ethyl ether is also formed by passing alcohol-vapour over aluminium oxide at 240°-260*^.
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- tiUation, first over calcium chloride and finally over sodium.
Diethyl ether is a colourless, very mobile liquid of agreeable oilour, boiling at 35-4®, and solidifjnng at — 117-6°. Pro- longeil bR^athing of it produces unconsciousness, followed by but slightly disagreeable const»quences on awakening. Ether is there- foa^ useil in surgery as an anaesthetic. It is slightly soluble in water, one volume dissohing in II- 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 liiglily combustible, burning with a luminous flame, and protlucing an explosive mixture with air, it is a substance requiring ver}- careful handling. Intense cold is pnxluceil by its evaporation, the outside of a tlask containing it bt^coming coated with ice when the evaporation of the ether is promotetl by the introduction of a rapid stream of air.
In the laboratory*, ether is an invalual>le solvent and cr\'stal- lizing-me^lium for many compounds, and is used for extracting aqueous s«>lutions ^,23"^. It is also of great utility in many manu- facturing processes.
ALKTL-RADICALS LINKED TO SULPHXTR.
57. The elements grouped in the same column of the periodic system ("Inorganic Chemistry/'2i3-22i) yield 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 difiference 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:
CiiH2n+l*SH and CnH2n+l*S«C„H2in+i.
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:
QiH2ii+i- X+K •SH = CnH2n+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 to sulphur, the other hydrogen atoms being linked to carbon.
77
78 ORGANIC CHEMISTRY. [| »
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 mercaptideSy with alkyl halides:
CnH2n + l'S» Na-fl •CmH2ni+l = CnH2n+l •S«CmH2ni+l "HNal.
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:
5CnH2n+l -OH -hP2S6 — ► 5CnH2n+l 'SH;
or by distilling a solution of potassium alkylsulphate with potas- sium hydrogen sulphide:
CaHs'fO^SO^K-hK.lSH = C2H6.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 l^eing much less volatile than oxygen. It may he explained by assuming non-association of the mercaptan. molecules, and association of the alcohol molecules. The mercap- tans are chanictorized by their exceedingly disagreeable odour, a property characteristic of almost all volatile sulphur compounds. 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-cr}^st alii 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 aptum to mer^
S 59] THIOETHERS, 79
•
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, K^S, upon the salts of alkylsulphuric acids may be employed:
2C,H Jo • SO3K -f K^IS = (CHJ^S -h2K2S04.
Potassium othylHulphate
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)2S-HgCl2.
With one molecule of an alkyl iodide the thioethers form remark- able crystalline compounds of the type (€2115)381. These com- pounds, called sulphonium iodides j are readily soluble in water. Moist silver oxide replaces the I-atom by hydroxyl:
(CjH5)3SI + AgOH = (C2H5)3SOn+AgL
The sidphanium 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 halidcs, such as (C2H5)o8«Cl, sulphur is the only element to which the univalent alkyl-groups and univalent Cl-atom can be united, so that these substances must have constitutional formula of the type
S
Cjll/ \ci
The mercaptans resemble 8ul[)hurettcd hydrogen in being slowly oxidized by contact with air, whereby they are converted into disul- phides like diethyl disulphidef
The hydrogen linked to sulphur has Ix^en removed by oxidation, m>
80 ORGANIC CHEMISTRY. ' l§ 60
that the disulphides have the constitution given above. A further proof is their formation when potassium ethylsulphate is heated with potassium disulphide, K2S2.
Numerous inorganic compounds containing oxygen and sulphur exist. Similar substances are also known in organic chemistry.
C H
The sulphoxides, ^,"ij-"'"^>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, be- cause neither alcohols nor ethers lose their oxygen by gen tie reduction.
The sulphones are compounds with the constitution i^u**^* > S0„
as shown in 60. They are formed by energetic oxidation of the thio- ethers, and also by oxidizing sulphoxides. Nascent hydrogen is unable to effect their reduction.
Sulphonic Acids.
60. The sulphonic acids result when mercaptans undergo vigorous oxidation (with nitric acid). They have the formula CnHtn+i -80,11. During this oxidation the alkyl-group remains intact, for the salts of these sulphonic acids are also formed by interaction of an alkyl iodide and a sulphite:
C,H,pTKlSO,K - KI + CjH^O.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 yield mercaptans. The struc- ture of ethyloulphonic acid is therefore CIIj-CHj -80,11.
The group 80,11 must contain a hydroxyl-group, because PClj yields with a sulphonic acid a sulphonyl chloride, CnH2n + i -80,01, from which the sulphonic add may Ix^ 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, crystiilliiie substances, and are very soluble in water.
In the sulphonyl chlorides, clilorine can be rej)laced by hydrogen in the nascent state. The bodies thus obtaine<l have the formula CnH-jn + i-SOiH, and arc called sulphinic acids. When an alkyl halide reacts with the sodium salt of a sulphinic acid, a sulphone (59) ^ formed :
f 601 SULPHONIC ACIDS, 81
C,H,SO,|N^TbF|C,H, = ^'^•> so, + NaBr.
This mode of preparation is a proof of the constitution of the sulphones.
Selenium and tellurium compounds corresponding to most of these sulphur compounds are known, and have also a most offensive odour.
ALKYL-RADICALS LINKED TO NITROGEN.
I. AMINES.
6i. At the beginning of the last chapter (57) it was stated that the properties pcxssessed 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 scries, better conductors of electricity for the same molecular concentration of their aqueous solutions, and are therefore more strongly basic than ammonia itself C* 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 is very unstable, being com- pletely decomposed 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 ver}' 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 NIL-group, and experi- ence has shown that these compounds possess great stability. Since the nitrogen cannot revert to the tervalent condition, their
82
5§ 62,63] AMINES. 83
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-J^-normal solutions.
The amines yield complex salts fully analogous to the ])latinum salt, (NH4)2PtCl6, 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 propj'lamine or ?sopropylamine, CH3-CH2'CH2'NH2 or
^TT^>CH-NH2, primary; methylcthylamine, q t? >NH, sccond-
CH3\ ary; ortrimethylamine, CH3-/N, tertiary.
CH3/.
Methods of Formation.
63. HoFMANN discovered that when an alcoholic or aqueous solution of ammonia is heated with an alkyl halido, the following reactions take place:
I. CnH2n+l-Cl + 7>NH3 = CoH2n4-l-NH2,HCl+(p-l)NH3.
The alkyl halide 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
84 ORGANIC CHEMISTRY. [§ 6»
primary amine, the free base reacting with the alkyl halide in accordance with equation 11. :
11. CnH2n+l-Cl-hCnH2n+l-NH2=(CnH2n+i)2NH,HCl.
Part of the secondary amine thus produced is also set free, and reacts according to equation III.:
HI. CnH2n+l-Cl+(CnH2o4-l)2NH=(CnH2n+l)3N,HCl.
The tertiary amine is also partly liberated, and reacts with the alkyl halide to yield the halide of a quaternary ammonium base :
IV. (CnH2n+2)3N-hCnH2n+l-Gl = (CnH2n+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 so on. The propylamines and those succeeding can be sepa- rated bv fractional distillation.
Various methods of preparing primary amines unmixed with secondary or tertiary are known (78, 96, 258, 268, and 349).
J 64] AMINES. 85
64. The velocity of the formation of tetraalkylammoniuvi iodides from triethylamine and an alkyl iodide or bromide has been investigated by Menschutkix. It is apparently a bimolecular reaction (" Inorganic Chemistry/' 50) and therefore takes place according to the equation
dx s=^=A;(a-x)(6-x),
where s is the velocity, k the constant of the reaction, a and h 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
t(a-by^a{b-xy
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 knowTi intervals of time t. The value of A; is found to 1x5 constant for ever}' reaction: that is, if corresponding sots 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 kj although the decrease is not vary marked : for example, when the amine reacts with propyl bromide, fc =0-00165; with octyl bromide fc =0-00110 (with acetone as solvent). The equation is always applicable, l^eing 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.
86
ORGANIC CHEMISTRY.
[§65
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+l-OH+N2 + H20.
The reaction is fully analogous to the decomposition of ammonium nitrite into water and nitrogen:
NH3-H0N0 =
[HT IHO
N N
H2 O
-2H2O+N2.
Secondary amines yield nitrosoaynines:
(CnH2n^l)2N[H+HO[NO = (C„H2„H.02N.NO+H2O.
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 nitrosoaminc into a secondary amine.
Tertiary amines are either unacted 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 separoting-funnol. The tertiar>' 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.
§661
AMINES.
87
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
(CH>I = C6H:6NI:
C H or if C3H9N = QTT^>NH, the same treatment should yield
/Pw^^NI = C5H14NI : or lastly, if C^aHgN = (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-Butyl
n-Octyl
|
Secondary. |
Tertiary. |
|
7° |
3-5° |
|
56° |
90° |
|
98° |
156° |
|
160° |
215° |
|
297° |
366° |
Methylamine occurs in Mercitrialis pcrenms: it is readily pre- pared by the interaction of ammonia and dimethyl sulphate. Di- methylamine (2^) and trimethylamine are constituents of herring- brine.
88 ORGANIC CHEMISTRY. I§ 67
Trimethylamine, (CH3)3N, can be readily prepared by heating ammonium chloride with formaldehyde (*' Formalin," io8) in an autoclave at 120^-160°:
2NHs + 9CH,0 = 2(CH3)3N +3C0, + 3Hp.
Tetramethylammonium hydroxide ^ (CH3)4N.OH, is obtained by treating a solution of the corresponding chloride in methyl alcohol v»rith 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+CH30H.
The higher ammonium bases are converted by dry distillation into a tertiary amine, water, and a hydrocarbon (^nH2n:
(C2H5)4N.OH = (C2H5)3N+C2H4+H20.
Triet hylainine £t hylene
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
^nH2n-f-l\ p TT
_\\r^^rAl2r+l>
CmH2nH-l~>N < p5rT
2p+l
n, m, p, and r being similar or dissimilar.
Alkyl-dorivatives of hydrazine or diamide^ HzN-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 copf>er solution, for example, at the ordinary temperature.
67. Tricthylamine is soluble in water, although at about 20^ this solution separates into two layers. The upper consists of a solu- tion of water in the amine, and the lower of a solution of the amine
5 67]
AMINES.
89
in water. In the neighbourhood of 20° a slight rise in temperature effects this separation into two layers, merely holding the tube for a short time in the warm hand being sufficient.
This separation at a definite temperature is best understood from a consideration of the solubility-curve of the system amine + toater. This amine (Fig. 27) is less soluble in warm water than in
. p.ip.y .ap.ip.y.iy.^. go.y
TEMPE8ATU3E
Fio. 27. — Solubility-curves for Trietuylamine and Water.
TEMPERATURfi
Fio. 28. — Usual Form of Solubility-curve for Two Liquids.
cold, and below 20® is miscible with water in all proportions. If, for example, increasing quantities of the amine be added to water at 30°, it dissolves until the amount of amine reaches about 5 per cent. (c/. Fig. 27). The solution is then saturated, and addition of more of the amine produces a second layer of licjuid. On the other hand, when water is added to triethylaminc at 25°, it dissolves until the amount of water reaches about 5 per cent, (cf. Fig. 27). Beyond this point two layers are formed. The line DC is the solu- bility-curve for water dissolved in triethylaminc, and the line AB that for triethylaminc in water. When the temperature falls, on the one hand the solubility of the water in the amine increases, and
90 ORGANIC CHEMISTRY. (5 67
on the other that of the amine in the water, so that the solubility- curves meet between B and C. The whole area is divided into two part5 by the solubilityn'urves. All points within ABCD correspond with two layers of liquid, and all points outside it with a homoge- neous mixture.
If, for example, the abscissa PQ is drawn for a mixture of 20 per cent, of amine and 80 per cent, of water, the mixture is homogeneous for all temperatures up to the point ft, and heterogeneous above that temperature. Along the very stef^p jjortion of the curve, repre- sented in this special case by the part BC, a slight rise in tempera- ture must evidently result in si^paration of the liquid; because al- though at about 20° (the point /?) an 80 per cent, amine solution of water and a 20 per cent, aqueous solution of amine are just about to form, al /?' (less than 1° higher) the separation would proiluce an 80 per cent. a(iueous solution of amine and a 20 per cent, amine solution of water. It follows that in this part of the curve a small rise of temperature must cause a sei)aration of water suHlicient to alter the composition ot one of the layers from 20 |kt cent, to 80 per cent, of amine.
It has iM^en alreadv mentioned that the relative sol ubilitv -curve for th(? system irnt^r -^ tnvtinjaminc has an abnormal path in the portion B(\ Moreover, the whole curve diflers from those ordi- narily obtained. The solubility of licjuids partially miscible with one another usually increases with the tem[)crature, just as in the ca.se of solids and lK]ui(ls, so that the ordinary curve is iherelore the converse of that in Fig. 27, and is usually as represented in Fig. 28. Ver>' many piperidine (159) derivatives belong to the same type as triethylamine, and give a similar curve of diminishing solubility in wat( r.
The highest temperature, C (Fig. 27), at which two liquid layers can exist without being homogeneous is called the critical tempera- ture of solution. At this point a rise of temperature renders the entire liquid h(miogeneous; a fall is accompanied by the fonnation of minute drops in the iK-mogeneous liquid, due to the reappear- ance of the second li(|ui(l layer. The point of inception of turbidity caased by the separation of the drops often admits of very accurate obscrv-ation. Since the part ACB of the curve is frecpiently con- siderably flattened, in many instances a slight percentage-change in the ratio of the amount of the two licjuids alters the critical temperatun* of solution by less than 0.1°.
Addition of a third substance in small proi)ortion, however, has a great effect on the critical temperature of solution. For a mixture
S 68] NITRO-COMPOUNDS. 91
of equal volumes of absolute alcohol and petroleum Crismer found the critical temperature of solution to be 15 -0°; 0*14 per cent, of water raised it to 17-5°, and 1-04 per cent, to 30-9°. It is evident that the detennination of the critical temperature of solu- tion furnishes a very sensitive process for the detection and estima- tion of traces of water in ethyl alcohol; the same method can be applied to methyl alcohol, acetone, and other substances.
U. NITRO-COMPOUNDS.
68. When silv(»r nitrite reacts with an alkyl iodide, two com- pounds are formed, both with the empirical formula CnH2n4.iN02, but having different boiling-points. From ethyl iodide, for ex- ample, a substance C2H6NO2, boiling at 17°, and another boiling at 113^-1 14°. 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„H2„^,|TTA^|.0N0 = C„H2n+i-0N0 + AgI.
When these esters, or alkyl nitrites ^ are reduced, they are con- verted into an alcohol and ammonia.
The compound boiling at the liigher 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.
^'nH2n+lN02 ->.CnH2n + lNH2.
The last reaction shows that the nitrogen in this class ot compounds is diiectly linked to carbon, l)ec:ause 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. Tliis leads to the conclusion that these substances, called nitrocompounds f liave the constitution CnH2n+i — NOo.
Nitrocompounds therefore contain a group NO-^y the nitrogen atom being directly linked to carbon; this group is called the nitrocp-oup.
92 ORGANIC CHEMISTRY. [(( 6^
The generation of nitrite and nitro-compoimd may be explained by assuming the production of the nitrite to be a regulat ionic reaction, and that of the nitro-compound to be preceded by the
Ag-O-N-0 formation of an addition-product, /\ , subsequently
I CjHs decomposed with fission of silver iodide.
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 nitromethanfe.
The names of these compounds are formed from those of the saturated hydrocarbons by means of the prefix nitro. The com- pound CH3NO2 is thus nilromethanc; 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-clerivatives 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 nitroparafTins 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,
CH3. 2
CH3-CH< VQ but tertiary nitrobutane,
CH3V
CHs^.NOg,
CH3/
does not yield any corresponding metallic dorivativo. The stnic-
ture of these metallic compounds is considered in 291.
When an alkaline solution of a nitro-compound is brcugl.t into
§ 70] NI TRO-COMPO UNDS. 93^^
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^CHa
\N02.
70. The behaviour of nitro-compounds with nitrous acid is very characteristic, aud affords a method of distmguishing between pri- mary, secondary, and tertiary ihtro-derivatives. 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 alkylmtrolic acid is formed:
CH3>C|H» + 0iN0H = CH3-G^ ^'^^^^ + H,0.
N0« Ethylnitrolic acid
The constitution of these compounds is indicated by their produc- tion from a dibromonitro-com pound by the action of hydroxylamine, HJ^OH:
CH3>C|Br. + H7|i\OH - CHa-C^ ^:Q" + 2HBr.
The 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, the secondary nitro-compounds jneld
NO
pseudonV/ro/es. They contain the group =C<vTf) *.
CHwp^ H + HONO CH3. p^NO . „^ CH,>^<N(^ "CH3>^<N0, + ^'0.
TropylpxeudomtTole,
When solid, the pseucionitroles 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 cm by nitrous acid.
Among the other properties of nitro-compounds is their decom-w position into the acid with the same number of carbon atoms and hydroxylamine, by heating with hydrochloric acid:
CH,.CH,.NO,4-H20 = CHa.COOH + HAOH.
NitroethaiM Acetic acid Hydroxylamine
94 ORGANIC CHEMISTRY. [i 70
The mechanism of this reaction is explicable on the assumption that the nitro-compound is first transformed into a hydroxamic acid:
R.CH,NO, -^ R.C ^oH^-
Hydroxamic acid
The hydroxamic acid is then converted by the water present into the acid and hydroxylamine:
R.C^ OH^ ^ ^>^ -R-C< OH +^2N0H.
Acid Hydroxylamine
ALKYL-RADICALS LINKED TO OTHER ELEMENTS.
I. 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 plios- phonium salts, PH4X, are decomposed even by water into an acid and phosphine.
The basic character has wholly disappeared in arsine, ASH3, and stibine, SbH^. Bismuth does not yield a hydride, and possesses only very slight traces of the characteristics of metalloids.
Ammonia cannot be easily oxidized, and is unacted on by the oxygen of the atmosphere at ordinary teniperutures. 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 rases this property becomes more marked as the number of alkyl-groups replacing hydrogen atoms increases. The salts of the monoalkyl* phosphines, for example, are decomposj^d by water, whereas those of the dialkyl phosphines and trial kylpho8i)hinos are not. TTie quaternary phosphomum bnsrSf PR,OH, an* as strongly basic as the ammonium haws. When a phosphonium base is heated, it does not, like an ammonium base (66), decompose into an alcohol (orCnHtn +H1O) and a trialkyl base, but into a hydrocarbon GoHtB^t and an oxygen compound :
(C,H,),P .OH -C,H. + (C A)tPO.
95
96 ORGANIC CHEMISTRY. l§ 73
This substance is called triethylphosphine oxide. In this reaction the great affinity between phosphorus and oxygen plays an impor- 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, PH3, to phosphoric acid, 0P(0H)3: 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:
jjr gives (H0)2^'^' j^ r gives hq^*^'
Monomethylphosphinic Dimethylphosphiiuo
acid acid
and (CH3),P gives (CH,),P:0.
Trimethylphoaphine oxide
The constitution of these compounds is established by a variety of considerations: for instance, by the fact that the monoalkylphoa-- 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, CHjPHj, is a gas: in very small quan- tities triethylphosphine has an odour of hyacinths.
Methods of Formation. — Only tertiary phosphines and phospho- nium compounds are formed by the action of alkyl halides upon phosphiiic, PII3. Primary and secondary phosphines are obtained by heating phosphonium iodide, PH4I, with an alkyl iodide and zinc oxide.
Arsines.
73. The primary and secondary arsines, HjAsCHj and HAsCCHs),^ are obtained by reduction of monomethylarsinic acid and dimethyl- arsinic acid, (CH3)HAsOOH and (CH3)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, AsCls, and from sodium arsenide and an alkyl iodide:
AsNa,4-3C,Ha = As(C,H5),H-3NaI.
Quaternary arsonium bases, however, have strongly marked basic properties. They are prepared by the addition of alkyl halides to
i 74J STIBINES A^D BISMUTHINES. 97
tertiary arsines, and treatment of the resulting halide with silver
hydroxide.
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
OH
r^u'>As — . Cacodyl oxide^ [(CH3)2As1jO, is formed by distiUing
arsenious oxide with the acetate of an alkali-metal. All the other cacodyl compounds are obtained from cacodyl oxide; thus, cacodyl chloridey (CH3)2AsCl, is prepared by heating the oxide with hydro- chloric acid, and cacodyl^ (CH3)2As-As(CH3).^, by heating the chlo- ride with zinc in an atmosphere of carbon dioxide. When brought into contact with air, both ignite spontaneously.
Stibines and Bismuthines.
The tertiary stibines and the quaternary stibonium bases have been obtained from antimony. The first-named are very readily oxidized, taking fire spontaneously m the air. The stibonium bases are as basic in character as the corrcspcn.ling nitrogen, phosphorus, and ar- senic derivatives. The pentamethy -d?riv:itiv3 Sb (CHa)^ is also known. '
Bismuth does not yield a hydride, but tertiary bismuthines, such as (€2^15)361, have been prepared. They are very unstable, and explode when heated. They do not form addition-products with alkyl halides, so that the **bismuthonium " bases are unknown.
IL ALKYL-RADICALS LINKED TO THE ELEMENTS OF THE CARBON
GROUP.
74. The elements in each group or column 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," 213). 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 sub-groups are capable of yielding alkyl-compounds, this being true not only of the carbon group of elements, but also of the elements of the other groups. In 1870, Mendeleeff for this reason predicted that the then unknown element germanium would, in accordance with its position in the periodic system, yield jdkyl-derivatives; this prediction was confirmed by the researches of Winkler, to whom science is indebted for the discovery of this
98 ORGANIC CHEMISTRY. I§74
element. Titanium belongs to the electro-positive sub-group, and though in many respects it resembles sihcon, 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 form- ing 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 silicon alkides, or silicaneSf have a character analogous to that of the similarly constituted alkyl-derivatives of carbon. For example, silicon tetraeihidey SiCCjHs)^, and teiraethylmethane^ C(CjH6)4, are known. Both are liquids, and are not acted upon by cither fuming nitric acid or fuming sulphuric acid at ordinary tempera- tures, but yield substitution-products with chlorine. Silicohep- tane, (( -2H5)3iSiH, has a petroleum-like odour, a resemblance to tri- eihylmeihnne, (C2H6)jCH.
Optically Active Compounds with Asymmetric Atoms Other Than
Carbon.
The existence of optical activity occasioned by the presence of asyniinetric atoms of elements other than carbon has been established by several researches. Asymmetric sulphonium compounds of the type
S 112^ ^OH
are known, with optical activity caused by the presence of an asymmetric, quadrivalent sulphur atom.
Pope has re'solv(»d into optically active components nitrogen compounds of the type
N Ri R2R3R4X,
in which X n^presc^nts an acid-radical, the activity being due to an asymmetric nitrogen atom.
§741
ASYMMETRIC MOLECULAR STRUCTURE.
99
He prepared the salt of the strongly optically active rf-cani- phorsulphonic acid with the base methylallylphenylbenzylammo- nium hydroxide,
HO • N (CH,) (CH5) (CeH,) (CeHs • CHt) ,
and crystallized it fractionally from acetone, a solvent less likely to cause decomposition than those with a hydrox>'l-group. By this means he succeeded in resolving the base into its dextro- rotatory and laevo-rotatory components. Pope has resolved simi- larly the sulphonium compound (195),
HO . S (CH3) (C2H5) (CHo • COOH) .
Although the tetrahedron-grouping is assigned to compounds with a quadrivalent, asymmetric atom such as carbon, there is
B
B
Fio. 29. — Asymmetric Molecular Structure.
HO general agreement as to the position and the direction of the linkings of the quinquivalent, asymmetric nitrogen atom.
Werner's researches also support the hypothesis that any asymmetric molecular structure occasions optical activity. He assumes (" Inorganic Chemistry,'' 323) in the complex cobalt derivatives direct union of six atoms or groups to the metallic atom, and regards them as situat(Hl at the angles of a regular octahedron, with the metallic atom at its centre. Various groupings giving mirror-images incapable of being superimposed are possible; he succeeded in preparing such compounds, and by combination with an optically active acid, such as bromocamphor- fiulphonic acid, in resolving them into their optically active components.
100 ORGANIC CHEMISTRY, [§ 75
Organic compounds of tin containing a tin atom linked to four dissimilar groups, and therefore possessing an asymmetric tin atom, have been prepared by Pope. He has also succeeded in resolving these derivatives into their optically active components, and Kippinq has effected the resolution of asymmetric silicon compounds, proofs that optical activity does not depend on the nature of the carbon atom, but is inherent in every asymmetric arrangement of groups round a central atom.
III. METALLIC ALKIDES.
75. When excess of ethyl iodide is warmed with zinc, a white txrystalline compound, G2H5ZnI, is formed, and on stronger heat- ing it yields zinc cthide, Zn(C2H5)2, and zinc iodide:
2C2H5ZnI = Zn(C2H5)2+Znl2.
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:
;^Jj3^Znl2+2CH3.CH3.
Water converts zinc alkides into saturated hydrocarbons and ^inc oxide:
Zn(CH3)2 + H20 = 2CH4+ZnO.
The halogens react very energetically with zinc alkides, yielding Alkyl halides.
Sodium alkides and pot<i8sium alkides are formed by the action of sodium and potassium respectively upon zinc alkides. These metals dissolve in zinc alkides, precipitating an equivalent •quantity of zinc. Sodium alkides and potassium alkides have not been obtained in the pure state, but only in solution in zinc alkides.
Very remarkable compounds of magnesium have been obtained by Grignard. When magnesium-turnings are brought into con-
§ 75J MRTALLIC ALKJDES. 101
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 , Cn H 2n + 1 • Mg • I . This is combined with one molecule of ether, because on evap- oration to dryness the residue still contains equi molecular 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 ignite 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:
CnH2„+i .Mg.Cl+HzO = C„H2n+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 CiHs-Hg-OH arc 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: f
SnBr4 -f 4C,H6 . Mg . Br - SnCCH.)* +4MgBr,.
NITRILES 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 + 2H2O = CH2O2 + C2H5NH2.
Ethylcarbylamine Formic acid Ethylamine
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, C3H6O2, 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 cannot, therefore, be in direct union with the ethyl-group:
C3H5N+2H2O = C3H6O2 + NH8.
Eihyl cyanide Propionic add
102
§ 771 NITRILES AND isoNITRILES. 103
These facts indicate that the nitrogeft atom in ethylcarbylamine is in direct union with the ethyl-group, and that the three carbon 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 (So), and the nitrogen cannot be directly linked to the ethyl-group. These facts are expressed by the constitutional formate
I. C2H5— NC, II. C2H5— CN.
Carbylamine Cyanide
On account of their method of formation, each must contain the group CN.
Compounds with a structural formula like I. are named carbyl- amines OTisonitriles; those with a structural formula like 1 1. are called cyanides or nitriles. The names of the former are derived from the alkyl-radical they contain, thus viethylcarbylamine, ethylcar- bylamine, etc. The latter can be designated analogously methyl cyanide, ethyl cyanide , etc., but are usually called nitriles and are named after the acid from which they are derived. Thus CH3.GN is acetoniirile, and CoHs'CN propionitrilc, Sind so on.
The constitution of the groups — CX and — NC requires further consideration. They are roprcsent(Ml as — C~N and — X^rC, the first with a triple, and the second with a double, bond l)etween C and X (c/. 119).
In Xef's view, the carbylamincs furnish one of the few examples of compounds with a bivalent carbon atom. He proved the formula R.N:(y to represent the constitution of the carbylamincs 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.NCX«, 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 unmixed with nitriles by the action of caustic potash and chloro- form, CHCI3, upon primary amimjs:
C2H6N|H^+C|HCI^ + 3K0II =3KC1 + 31120 -h CgHg. NC.
104 ORGANIC CHEMISTRY [§ 7g.
On account of the disagreeable and characteristic odour of the carbylamines, this reaction affords an exceedingly delicate test for primary amines. Secondary and tertiary amines are not converted into carbylamines by this reaction, since they lack ttoo 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. Xitriles are the chief product obtained when potassium cyanide reacts with alkyl iodides (c/. 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 hy the action of an alkaline bromine solution (German, Brorrdduge) on the higher primary amines:
C7H15CH, . NH, -f 2Brt -h2NaOH = GHuCH, . NBr, +2NaBr +2H,0; CrHuClHTlNjBi^ -h2NaOH ^CrHiuCN -f 2NaBr -h2H,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):
C2H5.CN+4H = CsHfi.CHa-NHj.
This produces a primary amine (63) with the same number of carbon atoms as the nitrile, the yield being very 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.
ACmS, C,|H2nQ2.
79. A solution of a sodium alkide in zinc alkidc is obtained by the interaction of sodium and a zinc alkidc (75). When a stream of dry carbon dioxide is passed into this solution, the sodium salt of an acid' with one carbon atom more in the molecule tlian the alkyl-group is formed. Thus, sodium methide, CHaNa, yields sodium acetate, C2H302Na. This reaction may be explained by assuming that the sodium atom is released from the alkyl-group, and reacts with CO2, becoming linked to an oxygen atom, an element
for which it possesses great affinity: C\^ is thus converted into
— ^^ONa* Since this group, and also the alkyl-radical from
which the sodium atom has been separated, have one free carbon bond apiece, it may be assumed that the two groups unite, forming a compound
Analogous to this is tho formation of acids by the interaction of Grignard's alkyl magnasiuni hnlulos (75) and carbon dioxide:
Cn,.Mg.Br+CO, = CH,.C().().Mg.Br.
Acl(iitioii-pr(Mluct
The addition-product is decomposed by water, with production of the acid :
CHa-CO.O.Mg.Br + Hp = CH3-C0.0H+Mg(0H)Br.
In accordance with these reactions the acids CnH2n02 contain
the group — ^^qu ^^ union with an alkyl-radical. This view is
supported by the formation of these compounds by other methods.
Among them is their synthesis by the intoniction of an alkyl iodide and potassium cyanide, followed by hydrolysis of the resulting nitrile. This hydrolysis consists in the addition of the elements of water.
lOG ORGANIC CHEMISTRY. [§ 79
and entails breaking the bonds between carbon and nitrogen in the group — C = N. If any other bond in a nitriie 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 nitriie. The hydrolysis of the nitriie, in which an acid and ammonia are formed, may therefore be explained by assummg 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 nitrogen is converted into ammonia, the three bonds between car- bon and nitrogen, in the nitriie, being severed:
/OH H\ CHa-C^OH H^N. \0H H/
The formula of the acid formed is not CHs-COsHs, but CHs-CO^H, containing one molecule of water less. When one molecule of water is eliminated from CHs-COaHa, there results
0|" o
CH3-C|0H -- CHs-C^QTT, a substance containing the carboxyl-
OiT
group.
In this explanation of the formation of acids, the existence of
an iiit(Tniediate compound contiiining three hydroxyl-groups is
assumed. Such substances are not known, but the assumption
seems by no means improbable, because compounds containing
/OC2H5 three alkoxyl-g roups exist; for example, CHa-C— OC'2H5.
\OC2H5
They are called ortho-esters (149).
The acids CnH.>^02 can be formed by the action of carbon monoxide on metallic alkoxiilfig under the influence of heat:
CHa-OxNa+CO = CHg-COONa.
The formation of an addition-product between CHa-ONa and CO can be explained by the as.sumption that the alk oxide first decom- poses into CUii and ONa.
It is montioned in 45 and 46 that oxidation converts the primary' alcohols into acids of the general formula CnH2n02. with the same
§801
ACIDS, CnllinO,.
107
number of C-atoms in the molecule. In this reaction the group — CH2OH is oxidized to — COOH.
The higher primar>' alcohols can also be transformed into the corresponding acids by heating them with soda-lime, free hydrogen being evolved:
Ci7H35.CH,OH-fNaOH=C,7H«.COONa-h2H,.
Stoaryl alcohol 8odiuni stearatc
Other methods are descrilx^d in 98, 145, 164, 232, and 233.
The presence of hydroxy! in the carboxyl-group is proved by 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, CHaAg.COOH.
80. The lower members of this series of acids are liquid at ordinary temperatures. They can be distilled without decomposi-
90
to
JO
40
•to •so
•<o -00
9 10 11 18
> NUMBER OF CARBON ATOMt
Fio. 30. — Melting- POINT Curvf or the Fatty Acids.
tion, and have a very irritating and strongly acid odour in the concentrated state. They are inisciblc in all proportions with
108
ORGANIC CHEMISTRY.
[§80
yrskter. The middle members (C4 — Co) 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.
The acids of the series CnH2n02 are called faity 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, formuke, and certain physical constants of the normal-chain acids of the series
Name
Formula.
Formic acid . . Acetic acid. . . Propionic acid But>Tic acid . . Valeric acid. . Caproic acid . . Heptylic acid. Caprylic acid . Nonylic acid. . Capric acid . . . Palmitic acid . Margaric acid. Stearic acid . .
C2H402
CjHcOj
C4H.O2
C5H10O1
CfiHioOj
CtHmOj
CsHieOj
CjHisOj
CieHj202 Ci7Hj40s CiHHa602
Melting-point. Boiling-point.
8-3° 16. 671°*
3. 12"
15'' 10-5°
les**
12. 5° 31.4** 62-618° 60" 69- 32"
101"
118"
141"
162"
186"
205"
223"
237. 5"
254"
269"
269" t
277" t 287" t
Specific Gravity.
1 1 0 0 0 0 0 0 0
0
2310 •0532 •9985 •9599 9560 9450 •9186 •9100 •9110 •930
(10")
(16^;
(14")
(191")
(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. 30). 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 " into ''yl"; thus.
i 81] FORMIC ACID. 109
H-CO Formyl,
CHa-CO Acetyl,
CgHs-CO Propionyl,
CsHt-CO Butyryl,
C4H9-CO Valer>i, etc.
Formic Acid, H-COOH.
8i. Formic acid derives its name from its presence in ants (Latin, /ormica). It can be obtained by passing carbon monoxide over soda-lime at 210°, the yield being good (79), but is usually prepared by another method (153) . It can also be obtained by oxi- dizing^ mf>t.hy] ftlpohnl. A peculiar method of synthesis is to pass a silent electric discharge through a mixture of carbon monoxide and steam, or carbon dioxide and hydrogen. Moissax discovered a mode of synthesis from carbon dioxide and potassium hydride:
KH-hC02 = H.C00K.
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 wanned, mercurous formate is precipitated with evolution of car- bon dioxide, and on further warming, metallic mercury is liberated: OOCH H COO Hg |OOCH-fH|COQ|Hg - 2HgOOCH+C02+HCOOH;
i 1 ! • Mercurous
Mercuric formate formate
Hg|OOCH + H|COQ|Hg = 2Hg +CO2 +HCOOH.
Mercurous 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 lilx^rated.
When formic acid is warmed with concentrated sulphuric acid, water and carbon monoxide are formed:
fH|C0[0H| = H20+C0.
(Ho
ORGANIC CHEMISTRY.
IS 82
The introduction of finely powdered metallic rhodium, or other mcfals of the platinum group, into an aqueous solution of the acid cffcfta its decomposition into carbon dioxide 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 homolt^ous series in which it b the lowest member. A similar phenomenon is of frequent occurrence.
Acetic Acji CHa-COOH. 82. Acetic 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 regulated 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 " or German process for the preparation of vinegar (Fig. 31), dilute alcohol (6-10 per cent.) is allowed to drop on beeth-wocd shavings contained in a vat with a perforated false 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 shavings of bceth wood distribute the liquid over a \try large surface thus facihtatmg the oxidizing action of the air whilt at the same time the^ serve us a feeding ground for the bacteria
b Acetic acid is obtamed m the distillation of wood (42) By treat mcnt with quicklime the acid is converted into cahium auetite which is freed from tarry im puiiiu i>\ lirilin^ (o 2(X>° in the air TIm. acetic acid is then hiii'raii'd !>y distilliiij; with an equivalent quantity of concentrated
82] ACETIC ACID. Ill
hydrochloric acid. It can be purified by distillation from potas- sium dichromate, Ixnng vcr>' stable towards oxidizing agents.
At tcmperaturc»s below 16*671°/760 mm., anhydrous acetic acid is solid and has much the appearance of ice; hence the name glacud 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 soUdified acid, again allowing it to crystallize, and so on, these operations being repeated until the melting-point is constant. A rise of temperature and contraction of volume occur when glacial acetic acid is mixed with water, the maximum rise and contraction being produced by mixing in the proportion of one gramme-molecule of acetic acid to one gramme-molecule of water. This fact indicates the existence of a compound called ortho-acetic acid (79), with the formula CH3-COOH-H20=CH3-C(OH)3.
The existence of a compound of the formula, C2H402,H20, is also indicated by other physical properties, such as viscosity, a constant measured by determining the rate of efflux of a known volume of the liquid through a capillary tube at constant temperature, since changes of temperature greatly affect its value. The rate of efflux is proportional to the viscosity. With mixtures of acetic acid and water the viscosity attains a fairly distinct maximum for the molecular ratio 1:1. In a number of other instances there are breaks corresponding with molecular proportions in the curves plotted with the compositions of the liquid mixture as abscissse, and the viscosities as ordiuates. An example is furnished by mixtures of methyl alcohol and water corresponding with the formula, CH,0H,2H,0 and C-H30H,3H,0.
A fifty-five p(*r 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 risers: further addition of water causes it to fall. This circumstance makes it impossible to determine the amount of acid present in such mixtures by the simple use of the hydrometer.
The strength of verj*^ concentrated acetic aciil is best determined by an observation of its meltiiig-ix)int, a thennomet<jr graduated in tenths of a degree l)eing used. In accordance with the formula given in 12,
i43f= Constant,
112 ORGANIC CHEMISTRY. [§83
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—r i — r-, or 0*025 per c^it.
2-16x2' ^
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 203"^, 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 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 ])eing simultaneously lilx?rated. .
The drv' distillation of anhydrous sodium acetate with soda- lime produces methane:
CHa-COONa-hXaOH =CH4-hXa2C03.
A ver>" delicate t<*st for acetic acid is the formation of cacodyl oxide (73). Owing to the extremely poisonous nature of tliis sub- stance, great care must be exercised in applying tho test. Among the acetates of technical importance are lead acetate (" sugar of lead '0> basic lead acetate, and aluminium acetate. The first two are used in the manufacture of white lead, and the third as a mordant in calico-printing (340).
I 841 BUTYRIC ACIDS. 113
Butyric Acids, C4H8O2. 84. Two Isomeric acids with the formula C4H8O2 are known.
They are normal butyric add, CH3.CH2«CH2-COOH, and vsobviy-
CH ric add, ^it^>CH«COOH. The constitution of these acids is
proved by their synthesis, the normal compound being obtained from n-propyi iodide, and the iso-acid from fsopropyl iodide:
CHg-CHz-CHgl -^CHa.CHz.CHg.CN -^CH3.CH2.CH2.COOH.
S2^>CHI -> ^J5^>CH.CN ^ ^5^ >CH.COOH. 1^x13 v>ii3 L^ris
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-butyric acid, along with smaller quantities of other volatile acids of the fatty series, such as 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 to determine that a sample of butter has been adulterated with margarine by estimating these adds. By the application of other tests, however, it is sometimes possible to decide in such doubtful cases.
iBoButyric acid 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 isa-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.
114 ORGANIC CHEMISTRY, [§86
In accordance with the principle of mobile expiilihrium ("In- organic Chemistry," 235), calcium n-butyrate should dissolve ia water with slight evolution of heat, and calcium isobutyrate with slifrht absorption of heat. This view is fully supported by the results of experiment.
Higher Fatty Acids, CnH2n02.
85. Many of the higher members of the series of fatty acids are natural products, chief among them being palmitic acid, C16H32O2, and stcoric acidy C1SH30O2, 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 (222) present in castor-seed (Latin, ricinus communis). After removal of the oil, the powdered seeds are intimat<?ly 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 temj>erature of SO^'—IO® 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 lower of an aqueous solu- tion containing 40-50 per cent, of glycerol.
Saponification of fats yields a mixture of acids, semi-solid at ordinary temperatures. This mixture contains the two acids men- tioned above, meltins: at 62^ and 69° respectively, when pure; but when mixeil, each lowers the melting-point of the other (25). More- over, liquid oleic acid, belonging to another homologous series, is also present : it can be pressed out of the mixture, leaving 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 parafhn-wax, to prevent crystallization of the fatty acids, which would make the candles brittle, the molten sub- stance is j)oured into moulds, in the axes of which wicks are fas- tened.
5 861 SOAP, 115
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 ].)y 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 ^ concentrated solution of sodium chloride, the soap separates out in the molten state, forming a layer on the surface of the brine, in which the glycerol remuina 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 [or^ matioQ_of free alkali, a fact that was pointed out by Chkvhkul as early as at the beginning of the nineteenth century. The acid thus liberated unites wfth a second molecule of the salt^to form an in- soluble substance, which with the water produces tlie 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 rcxl 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 oxido, or clay. An insight into the mechanism of the removal of the fatty substances is afforded by the following oxporimt^nt. When a drop of oil or a small piece of fat is plac(Ml in water, the two substances do not mix. On additicm 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
116 ORGANIC CHEMISTRY. [§87
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 emulsifying 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 effect 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.
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., i6.
Water containing a certain percentage of calcium salts is called a **hard" water C' 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
5 87]
ELECTROLYTIC DISSOCIATION.
117
ion, and a negatively charged OH'-ion; salts a positively charged metallic ion, and a negatively charged acid-radical ion.
It is further stated {Ibid., 66) that in the solution of a partly ionized substance there is an equilibrium which for a monobasic Acid can be expressed by
ZH?i*Z'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
V
non-ionized portion is
V
The equation representing the equi-
librium in the above example of a monobasic acid is, therefore (Ibid., 49) I
l-a fay
~ W '
or
a'
= *.
v{l — a)
In this equation A: is constant, and is called the ionization-constant. 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 — , the latter was always found to have the same value,
V(l-tt)
as it must if k is constant.
The accuracy of this law is evident from the examples in the following table.
|
Acetic Acid. |
Propionic Acid. |
n-Butyric Acid. |
||||||
|
V |
lOOa |
lO^k |
V |
lOOa |
lO^ib |
V |
100a |
lO^I; |
|
8 16 32 64 128 1024 |
1*193 1*673 2380 3*33 4-68 12*66 |
0180 0179 0182 0179 0*179 0177 |
8 16 32 64 128 1024 |
1-016 1-452 2-050 2- 895 404 10-79 |
0-130 0134 0-134 0135 0133 0128 |
8 16 32 64 128 1024 |
1068 1-536 2-165 3053 4* 292 11-41 |
0 144 0*150 0-149 0150 0-150 0144 |
118 ORGANIC CHEMISTRY. [{88
88. The "strength" of acids depends upon their degree of ionization; strong acids undergoing considerable, and weak acids but slight; ionization. Since the constant A; 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, 018, 0.13, 0-15, 0-16.
It is noteworthy that formic acid has a greater ionization-constant^ and is therefore stronger, than its homologues, another example of 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 r=16, then for hydro- chloric acid 100a = 95'55, and for acetic acid only 1-673. It is obvious that 100 a is the amount ionized, expressed in percentage.
The weak organic acids follow the law of dilution : the strong mineral acids do not. No perfectly satisfactory explanation of this phenomenon has been suggested hitherto.
DERIVATIVES OF THE FATTY ACIDS OBTAINED BY MODIFYING THE CARBOXYL-GROUP.
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.
Acid 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 PCI3, or of phosphorus oxy- chloride, POCI3:
3C„H2„+i.COOH + 2PCl3 = SC^Hsn+i-COCl + PoOa + SHCl.
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 effected 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 cMonde, 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.OlHj-CgOC.CHa = RO.OC.CH3+HCI.
119
120 ORGAMC CHEMISTRY. (1190,91
'Iho compoaud to be tested is allowed to remain for scMiie time in coaruot with ai-etyl chloride, either at the ordinary temperature or with gentle warming. To ascertain whether an acetyl-compoimd h;is I'een fonned. the purified product is analyzed or saponified. If si4jK>nitication yields acetic acid, an acetyl-derivative was present. Tlie homologues of acetyl chloride are also sometimes employed iu the detection of hydroxyl-groups.
The acid chlorides also react with the merci^ytans, fonnii^ sob** stances of the type of acetyl-compounds.
n. Acid Anhydrides.
90. Acid anhydrides are fonned by interaction d the alkali- metal salts of acids and acid chlorides:
CH3-C01Cl + Na'0>OC.CH3 = 0<^;^Jj3+Naa.
Acetic anhydride
Higher anhydrides are best obtained by heating the sodium saltB 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 decomix)se into the anhydrides 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 Dr^ = 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 n^spcct 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:
CH3-CO|Cl+H|OC2H5=CH3-COOC2H5+Ha
i 911 ESTERS. 121
They are also formed by direct treatment of the alcohol with the acid, although extremely slowly at ordinary temperatures:
CHa-COOH+HOCzHfi = CHa-COOCzHg+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 = CHa-COCl-hHaO.
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 should be dissolved in a large excess of alcohol. The formation of esters is called esterification.
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 l>etween 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 fruit-essences. For example, isoa???/// m)r(iler(ite (b.p. 196*^) has an odour of apples, ethyl bntffrate (l).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, CisHai-COOCsoHoi.
Tertiary alcohols can be synthesized from the esters by means of Grignard's alkyl magnesium halides (75) :
R.C^Q^ jj +R'MgBr - R-C^OCA .
Addition-product
The addition-product thus obtained reacts with a second molecule of the alkyl magnesium halide .
/OMgBr /OMgBr
R.C^OC^H. -f R"MgBr - R-Cf R" +C2H,0MflrPr. \R' \R'
On decomposition with water the tertiar}' alcohol is formed:
/OMgBr /OH
R .Cf R" + HaO - R -C^R" + MgBrOH. ^R' \R'
R, R', and R" represent alkyl-groups
92. The formation of esters has been carefully investigated by several chemists, first of whom were Berth elot and Pean db St. Gilles. Their researches have shown that the reaction between the acid :.nd the alcohol is never complete, some of both remaining uncomhined no matter how long the process has been carried on. With equivalent quantities of acetic acid and ethyl alcohvol, 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 forn^.ed, while ore- 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 rcversibUiiy of the reaction (** Inorganic Chemistry," 49). It may be represented as follows:
CgHfi-OH + CH3 .CO .OH ?:> CH3 -CO .OC2H6+ H2O.
§ 931 ESTERS, 123
The equation of equilibrium deduced in Ibid., 49-51, may be applied to the formation and decomposition of esters. It is
k(p—x)(q—x) =A;'a:2, q^ (^p-x)(q—x) =Kx^,
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. All these are expressed in gramme-molecules, and K is a constant. There are here two opposing reactions taking place simultaneously, so that all the statements referred to above (loc. cit.) 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. When one gramme-molecule of alcohol (46 g.) and one gramme-molecule of acetic acid (60 g.) arc brought into contact, both p and q are equal to 1, and the equa- tion is
(l-a;)*-0-25x», or x'-Jx + J-O,
80 that
X =• 3.
It follows that this system in equilibrium contains ) gramme-molecule €Ucohol-\-i gramme-molecule acetic aad + J gramm^-Tnolecule vjater-^r J gramme-molecule ester,
93. Several deductions can be drawn from the equation
(p—x)(q—x) = Kx^.
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
p— X _
= K
X q—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.
^24 ORGANIC CHEMISTRY. I§ 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 cf 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. Ai can be readily deduced from the equa- tion, this holds for the formation of ethyl acetate when one gramme- molecule of acid reacts with ten gramme-molecules of alcohol, or,, inversely, when one gramme-molecule of alcohol reacts with tea gramme-molecules of acid.
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
2Lzf = K- ^
np—x
Inversely, when np gramme-molecules of alcohol are added to p gramme-molecules of acid, we have
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—x)(q—x) = Kx(x-{-r). It follows that the equilibrium is influenced to the same ex-
i§ 04, 95] ESTERS. 125
tent 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 effect 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 ver}'- small. That it actually is so has been established by experiment.
In the esterification of primary, secondary, and tertiary alcohols with trichloroacotic acid, CCh-COOH, Michael proved the velocity- constant k to have a much higher value for primary alcohols than ^ for secondary and tertiary. For n-propyl alcohol ^X 10^=725, for isopropyl alcohol 98. For secondary and tertiar>' alcohols the value of the constant is of the same order; for s(?condary butyl alcohol, CH3 • CHOH • C2H&, k X 1 0' = 90, for trimcthylcarbinol, (CH3)3C«OH, 118. For methyl alcohol the constant has a much higher value than for other primary alcohols, since A' X 10* =3690. All these determinations were made at a temperature of 25°.
95. The conversion of an ester into an acid and an alcohol by a mineral acid or an alkali is called mponificcUiorif from analogy to the formation of soap from alkali and fat (85) . It is represented by an equation of the type
CH3 . COOC2 H5 -h II2O = CH3 • COOH + CoHsOH.
The action of the mineral acid is then'foro catalytic. Its presence only accelerates the saponification: the same result would be attained without it, though the time required would be incom- parably longer (81). If the concentration of the ester be Ci, that of the water is C2, and x the quantity of ester saptmified during the
dx time <, then the velocity of saponification 5=-^- for each mo- ment can be represented by the equation for bimolecular reac- tions (''Inorganic Chemistr>'," 50):
S-^-kiCi-x){C2-x) (1):
126 ORGANIC CHEMISTRY. [{05
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:
^ = *i(Ci-x) (2)
The saponification of esters by bases can be represented by ao equation of the type
CHa-COOCgHs + NaOH = CHa-COONa+CgHsOH.
It b a bimolecular reaction, and consequently equation (1) is applicable to it.
The velocity of saponification of esters by acids dep)endfi 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 methyl 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
5 965 THIO-ACIDS AND ACID AMIDES. 127
very weak, so that their salts undergo partial hydrolytic dissocia- tion. Thus, notwithstanding the excess of acid, there is always enough of the free base (hydroxyl-ions) present to effect the saponification.
IV. Thio-acids/R-CO.SH, and Acid Amides, CnH2n+i-CONH2.
96. The ihio-acida are obtained by the interaction of acid chlo- rides and potassium hydrogen sulphide, KSH, this method of formation proving their constitution. They are liquids with a most disagreeable odour, and when heated with salts of heavy metals yield a fatty acid and the corresponding metallic sulphide.
Acid amides are formed by the action of ammonia on acid chlorides or anhydrides, a circumstance which affords a proof of their constitution:
CnH2n+l -CO Cl-f H NH2 = C„H2„+i •CONH2 + HCI;
CnH2n+l*C0 CnH2n+l 'CO
O+H
552=' = 2C„H2„+i-CONH2 + H20.
XI. i>ixi2
Acid amides are also formed when the ammonium salt^ 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:
C„H2n ^i -C0[0]NH2[H^ = CnH2„ M .CONH2 -f 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 tlie nitrile in concentrated sulphuric acid — that only one molecule of water is added, when amides are obtained:
C„H2„+i .CN + HoO = C„H2„+i .CONH2.
The acid amides are therefore intermediate products in the con- version of nitriles into acids. Distillation with such a dehydrathig 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.
128 ORGANIC CHEMISTRY. [§97
The acid amides arc also formed by the action of ammonia upon esters:
CH3'CO|OC^H7nJiXH2=CH8>CONH24C2H50H.
The acid amides are solid, crystalline compounds, with the exception of the liquid formamide, H-C0NH2. The lower members are soluble in water, and odourless when pure. Acetamide, CH3.GONH2, 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^ ^-tt -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 by water. Acetamide hydrochloride, CH3 -CO' NHo • 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 tlio formula ((^II:j.(X)XH)2ng.
Tlio Ir^Iiaviour of the amides and amines towards nitrous acid is analog< us, the corresponding acids and alcohols respectively b(»ing produccMi by exchange of XH2 for OH (65).
Amides can Ik? cnivorteil into primary amines by a method dos('ribe<l in 259.
97. SoHK* further derivatives, obtainable from the acids by substitution in the carboxyl-group, are described below.
Amino-rhhn'drfi are [)r()ducL»d by the action of phosphorus penta- chloride on the acid amides:
R.CONH^ + PCl, = R.CC1,.XH, + P0C1,.
These com[)ounds are r.n\y stable when one or Iwth of the hydrogen atoms of the ami no-group, XH^, are replaced by alkyl-radicals.
597] IMINO-COMPOUNDS, HYDRAZIDES, AND AZIDES. 129
They 5rield imino-chloridesj R-CClrNH, by the elimination of one molecule of HCl, the same compounds being formed by the addition of HCl to nitrihs.
NH Imino-^thers have the constitution R'^^qd , and may be re- garded as the product of the replacement of the doublv-linked oxy- gen of the carboxyl-group by the imino-group, NH. They are ob- tained by combination of alcohols and nitriles under the iofiuence of dry hydrochloric-acid gas:
The well-crystallized hydrochlorides of the imino-ethers are con- ^ verted by treatment with ammonia into the hydrochlorides of the amidines:
R.C < oc,h"^' +NH. - R.C 1 515;"^' +C,H..OH.
The amidines are unstable !n the free state, but are strongly mono- basiCy and form stable salts.
Amidoximes are addition-products of the nitriles and hydroxyl* amine, NH2OH:
R .CN + H^^OH « R .C < ^^.
They yield salts with both acids and bases, and give a flocculent, muddy-brown or green precipitate when treated with an alkaUne solution of a copper salt, a reaction which affords a characteristic test for them
Acid hydroxides are produced by the action of hydrazine, HiN — NH2, on acid chlorides or esters, and therefore have the con- stitution R.CONH-NHi. Nitrous acid converts them into acid azides:
R.C0NH.NH,+HN0,=R.C0N,+2H,0.
f The acid azides are volatile, explosive substances, and some yidd well-developed crystals.
ALDEHYDES AND EXTONES.
98. Rotii the aldehydes and ketones have the general formula CnH2nO. 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 ^toms.
On further oxidation, an aldehyde takes up one oxygen atom, forming the corresponding acid with the same number of carbon atoms; thus CnH2nO is converted into CnH2n02. It follows that an aldehyde is an intermediate product in the oxidation of an alcohol to an acid (45) :
CnH2n+20 -^ CnH2nO -* CnH2n02.
Primary alcohol Aldehyde Add
A primary alcohol has the constitutional formula CnHin+i •CH2OH, and on oxidation yields an acid CnH2n^.i-C00H. Since in this reaction the alkyl-gtoup, CnH^n^.!, 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 — CHvsOH.
Two structural formulae are, therelore, possible,
R.C^g and R-C— OH.
The improbability of the existence of free bonds or bivalent carbon atoms in compounds (16) 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
599] 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 aldehydes, it follows that the first is the correct one. Tliis view is supported by the fact that aldehydes are formed when acid chlorides dissolved in moist ether react with sodium, the chlorine atom being replaced by a hydrogen atom:
CaHy-Cv^Q — >C3H7«C>$Cq.
fi-Butyryl chloride n-Butyraldehyde
The aldehydes therefore contain the group — ^ "^tt*
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-compounds, 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 arc represented below, R and R' being alkyl-groups:
I. 11.
CH2R CH2R CH2R CHR
I I l>0
)HOH -> CO or CHOH -> CH •
i,
CHoR'
CH2R' CH2R' CHzir CHoR'
For reasons analogous to those for aldehydes, formula I. is more probable than formula II. Tlie 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-Clls-Cfcila-R'.
From such an alcohol two acids, R-CIIz-COOH and R'.CH2-C00H, are obttuned by strong oxidation, the carbon chain 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 iilcohols 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 aldehvuc is derived from a/(cohol) dehydijogQTidXws)^ that is, "dehydrogenated alcohol." The word ketone has its origin in the name of the first member of the series, acetone, CHa-CO.CHa (iii).
The aldehydes are named after the corresponding acids: for- maldehyde y H-CHO; acetaldehydCj CHa-CHO; propionaldehydef C2H5.CHO; valeraldehyde, C4H9-CHO; etc.
The ketones derive their names from the alkyl-groups which they contain: dirnethylketone, CHa-CO-CHa; methylpropylketone, CHs-CO.CsHt; etc.
Methods of Formation.
100. 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:
^J5'3;^^>Ca|=CH3.CO.CH3-fCaC08.
The conversion of acetic acid and propiomc acid into the cor- responding ketones is readily effected by passing the vaporized acida over aluminium oxide heated to a temperature above 400'.
When an equivalent quantity of a formate is mixed with the salt of the other fatty acid, an aldehyde is produced by the dis- tillation:
CaHy.COON^ H COONa
=C3H7-C<2+Na2C08.
i 101) ALDEHYDES AND KETONES. r'l 133^
When a mixture of the salts of two different fatty acids, excluding formates, is distilled, mixed ketones are obtained:
CHa-COONa
CaHs- COONa
= CHg-CO-CzHs+NazCOa.
Methylethylketone
^2. Aldehydes or ketones can be obtained from compounds containing two halogen atoms linked to a single carbon atom, by heating them with water:
CHa-CH CI2 + H.2 0 = CH3-CH04-2HCL
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:
4. An important method for the preparation of ketones, but not of aldehydes, is the interaction of acid chlorides and zinc alkides (75)> 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, /OZnCHa
When this addition-product is treated with water a ketone is
formed:
^0|Zn|CH3 H]0] C„H2„+, -cAlHa + = C„H2n+i .CO.CH3+ZnO+CH4 +
^|(1 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. (§ 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 sulphite, — When aldehydes or ketones are agitated with a very concentrated aqueous solution of this com- pound, a crystalline addition-product is obtained:
CgHfi-C^^ + NaHSOa = CgHs-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). The 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 raethylkctones.
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 aijueous solution of potassium carbonate, potassium cyanide, or a similar substance, combination takes place:
On addition of a small proportion of acid, the catalyst is rendered inopemtive. and the cyarwhydrins or hydroxynitrUes formed can l)e obtaintnl in a pure state by vacuumnlistillation. This layn-
(§ 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.cJJ + R'.Mg.I = R.C^Q.Mg.I, ^ \R'
Aldehyde Addition-product
H
2R.CO.Mg.I+2H20 = 2R.CriOH.R'+Mgl2+Mg(OH)8;
^ f Secondary ttlcohol
g;;>C0+CH3.Mg.Br = ?Sj>C<^jMi-Br,
Acetone Addition-product
2p?'>C< po^'^*^^+2H20=2(CH:0..(^()H 4 M-Br2 + Mg(0H)2.
^^113 L.n.3 Trimethylcarhinol
103. Other reactions common to aldehydes and ketones depend upon exchange of the doubly-linked oxygen atom for other atoms or groups.
1. Phosphorus pentachloridc replaces the oxygen atom by two chlorine atoms.
2. Hydronjlamine reacts in accordance with the equation
(.„ /v.^w^rw^..^,.. - p„
3>CO + H2NOH = >;"-^>C:N0H+H20.
3
OximcB are thus produced, and are called aldoximes when derived from aldehydes, and ketoxivws 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, addition- products are formed, the reaction being sunilar to the production of ammonium salts:
(CH3)2C^^N()H.nCl.
Amtoxiine hydrochloride
136 ORGANIC CHEMISTRY. [§ 10^
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 237.
Energetic reduction converts the oximes into amines:
RjC^NOH + 4H = R2CNH2 + H2O.
H
The aldoximes are readily transformed into the corresponding nitriles by the action of dehydrating agents, such as acetic anhy* dride:
CnH2„+i •C=N|OH -> C„H2„+i .CsN.
ri
Ketoximes undergo a remarkable rearrangement of the atoms in the molecule or intramolecular transformation, called after its dis- coverer the "Beckmann transformation." It takes place, for exam[)lc, under the influence of acetyl chloride. The ketoximes thus yield acid amides, with substituents in union with the nitrogen atom ;
R.C.R'
I -> R.CO.NHR'.
Ozime Amide
The behaviour of aldehydes and ketones with phenylhydrazine^ C6H5NH-NH2 (310), is exactly analogous to that with hydroxy !• amine:
Iv ^ f^\r\ . TT IXT XTTT /I TT R
g,>ClO + H2lN.NH.C6H5 = JJ;,>C=N.NH.C6H5+H80.
Phenylhydrarine Phenylliydrasone
The substances formed, called hydrazones, are either well-defined crystalline compounds, or liquids. When heated with hydrochloric Bcid, 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 phenylhydrasine itself, so
JIM] ALDEHYDES. 137
NH that the structure R^< • is excluded. This is rendered even
more evident by the fact tliat 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. Aldehydeamnumia. — Acetaldehydeammonia is produced from anmionia and acetaldehyde:
C2H4O + NH3 = C2H4ONH3.
Acetaldehyde Aoetaldebydeatntnoni*
It is precipitated in the form of white crystals when dry ammonia- gas is passed into a solution of acetaldehyde in anhydrous ether, and is very soluble in water. Acids decompose the aldehyde- ammonias into an aldehyde and ammonia; caustic potash 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, \t loses water and is converted into (CH,«CHNH)|, (105) a polymeride of ethylideiie-imine.
2. Acetals. — An aldehyde combines with two molecules of an alcohol, with elimination of water, and production of an acetal:
CH3.CJ + JJ
OC2H5 ^ CH3 . CH < Q^^jj__ + H2O.
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 powerful 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
they were produced, a fact which supports the view expressed in the above structural formula, that the aikyl-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 acid anhydrides. — Addition-products are ob- tained with acid anhydrides:
CHs-Cq +0(C0CH3)2 *■ ^^'^^^ OCOCH •
Aoetio anhydride
These compounds are analogous to the acetals. They are easily 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 acctaldehyde, C2H4O, but its vapour-density is three times as great, so that it has the molecular formula C6H12O3. This substance, paracetaldehjfde, is readily converted into acctal- dehyde by distillation with dilute sulphuric acid, another example of a reaction limited by the reverse one:
C6Hi2034=^3C2H40.
The equilibrium reached must be independent of the nature of the acid, that is, of the catalyst C' Inorganic Chemistry," 49), as has been proved for this reaction by experiment. The same equilib- 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 paracetaUehyde is improbable, and the existence of an indirect Unking through the oxygen atoms must be assumed, becpuse it accounts for the ease with which the molecule of paracetaldehyde can be resolved. The compound is not attacked by sodium, and therefore cannot contain hydroxyi-groups. It
§1061 ALDEHYDES. 139
lacks all the characteristics of aldehydes, proving the absence of the group — C ^ tt. These properties are best expressed by the ocxistitutional formula
H/^\H
i i •
CHa
The union of two or more molecules of a substance to form a body from which the original compound can be regenerated is called polymerizcUion.
io6. Under the influence of dilute alkali-solutions aldehyde molecules combine with production of compounds of a different kind. When an aqueous solution of acetaldehydc is warmed with concentrated caustic potash, the liquid becomes yellow; after a short time, reddish-yellow, amorphous masses are precipitated. The aldehyde has resiniji d, and the reddish-yellow substance formed is called aldehyde-rcftin. When, however, dilute caustic potash (or sodium acetate, zinc chloride, etc.) is addend to acetalde- hydc, a substance is formed having the same empirical composition as acetaldehyde, but with double the molecular formula, C4lls0j. This compound is called cUdol: it Is a liquid, distilling without de- composition under diminished pressure, and readily undergoin^j poly- merization. It possesses the pro|x>rties characteristic of aldehydes, yielding on oxidation, for example, an acid with the same number of carbon atoms. The acid thus obtained has the formula C4H.vt03, and is a n-hydroxybutyric acid; that is, /^-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 m')lecules has bc»en effected through the carbon bonds, a view supported by the fact tliat aldol cannot be reconverted into aldehyde. The combination (f tiic aldehyde molecules to form aldol may be represented by the equa- tion
140 . ORGANIC CHEMISTRY. [§ 107
H H / H
CH3»Cq + HCH2»C>^ = CH3»C~CH2*Cy^.
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<^" ^ rMj
•' |OH + H|CH,.CHO « CH3.C <gj .cuo+^fi.
'2
Aldol
Reactions are often explained by assuming the formation of such addition-products and the subsequent elimination of water. In a few instances this view has been ex|>erimentally verified.
Aldol is both an alcohol and an aldehyde, hence its name, aW(ehyde-alcoh)o/. The union of molecules through carbon bonds, as in the formation of aldol, with the production of compounds from which the ori«!:inal 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 whea heated, with formation of crotonaldehyde {142) :
H H
CHj'CHOH •CH2«C/'% — H2O =CHi«CHr CH«Ca%.
Aldol Crotonaldehyde
The mechanism of the condensation of the higher aldehydes always involves transposition of a hydrogen atom linked to the carbon atom carr}*ing the aldehyde-group of one molecule, this hydrogen combining with the carbonyl-oxygen of another molecule
S§ 107, 108] FORMALDEHYDE. 141
to form hydroxyl, the liberated carbon valencies being simulta- neously saturated:
I ^^*^*i^0 * ^"^Hjm+i — CnHai+i • CH • CHOH • CmHan+i.
/
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.
3. When an aldehyde is added to a solution of magenta <l3Colorized by sulphurous acid — Schiff's reagent — the red colour is restored.
■^onnaldehyde, H • C ^ q .
108. Formic acid, the first member of the homologous series of fatty acids, has certain properties not possessed by the higher members (81). Formaldehyde affords another strikin;^: example of this phenomenon of disparity between the first and sucTe^ding 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
142 ORGANIC CHEMISTRY, [§ 108
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. Atordinar}' 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, parq/brwaWeA?/de, a crystalline poly meride of unknown molecular weight, is produced. It melts at G3°. 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'polyoxymethylene. The molecular weights of these polymerides are not known: on heating, they arc reconverted into formalde- hyde, proving them true polymerides. Prolonged heating of the /•-variety with water yields another polymeride, d-po!yoxy methylene. On treatment with ammonia at the ordinary temperature, formal- dehyde does not yield an aldehydeammonia, but a complicated compound, G6H12N4, hexamethylenetetramine, (CH2)6^^4, a crys- talline, very hygroscopic, basic substance, employed as a medicine under the name '* urotropinc.'' At 120°-1G0° and increased pressun*, mcthylamines are formed:
3XH3 + 3CH20=2NH2-CH3 + C02-fH20, 2XH3 + 6CH20=2XH(CH3)2 + 2C02 + 2H20; 2XH3 + 9CH20=2X(CH3)3 + 3C02 + 3H20.
When treated with potassium hydroxide, formaldehyde does not resinify, hut is converted into methyl alcohol and formic arid:
2CH2O + II2O ^CHgOH + HCOOH.
When a fifte(?n per cent, solution of formaldehyde is mixed with an ecjual volume of a solution of stnlium hydroxide, and a small proporti(m of cuprous oxide added, formic acid is produced, with evolution of hydrogen:
n.cH04-ii20=n.cooH-f H2.
§ 109) ACETALDEHYDE, . 143
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 formalin for half-an- hour; brain-substance attains the consistency of india-rubber; and a solution of gelatin is converted into a hard, transparent, in- soluble, odourless mass, reducible to a fine powder. Before development, photopjraphic films with a basis of g.^latin 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.
The concentration of a formalin solution is determined by adding excess of a solution of twice normal .wdium hydroxide, and then hydrogen peroxide, the formaldehyde Mug 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.
Acetaldehyde, CHg-C^Q.
•
109. Acetaldehyde is the typical aldehyde of this series, since *it has all the properties chal-acteristic of aldehydes as a class. It is obtained by the oxidation of ethyl alcohol by means of potassium diohromate and sulphuric acid, and is a liquid with a disagreeable odour, at lea.st in the dilute state: it boils at 22®, and solidifies at — 120-C**. It readily pjiymerizes to paracetaldetivde. C6H12O8 (105), or to Tnetacetaldehyde, The molecular weight of this product is not known with certainty, but crj-oscopic determina- tions point to the formula (C2H40)4, or a pol>Tneric multiple of it. Metacetaldehydc forms well-developed, acicular crystals,
144 . ORGANIC CHEMISTRY, [§ 109
which begin to sublime at 160*^. Neither it nor paracetaldehyde exhibits the aldehyde reactions; for example, neither is rcsinified 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 IxMng also produced in small proportion. If the liquid is strongly cooled immediately after addition of the catalyst, metacetaldehyde is the main product, and cr>'stallizes out in well- develojK*d needles, but paracetaldehyde is also formed. If the temperature ri^es, metacetaldehyde is decomposed under the influence of the catalyst, with production of acetaldehyde and par- acetaldehyde. Xo direct transformation of metacetaldehyde into paracetaldehyde has been observed, the mechanism of the trans- formation probably involving a preliminar>' complete depolymeriza- 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- dehyde is formed. Calcium chloride, a much less energetic catalyst, also induces the formation of metacetaldehyde, paracetaldehyde being produced only in traces. The equilibrium between acetal- dehyd(» and metacetaldehyde is, therefore, much more readily attained than that between acetaldehyde and paracetaldehyde. The predominance of paracetaldehyde or metacetaldehyde in the temar\' system
Paracetaldehyde ^ Acetaldehyde <=^ Metacetaldehyde
is dependent on the experimental conditions, temperature being a ver>' 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 paracctaldc^hyde 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 equilibrium, causing the catalyst to decom- pose a fresh portion of paracetaldehyde. The acetaldehyde thus
no] KETONES, 145
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.
1 10. 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'.
I n
Thus, methylnonyl ketone, CHa-ICO-lCgHio, can yield formic
I II
acid, CH2O2, and capric acid, C10H20O2; or acetic acid, C2H4O2, and pelargonic acid, C9H18O2; 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 -02115, produces acetic acid and acetic acid by decom- position at point II., and formic acid and propionic acid by decom- position at I. Usually 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, CeHiaXO or (2C3H6O + NH3 — H2O) , triacetone- amine, C9H17NO or (3C3H6()-fNH3-2H20), and so on.
143 ORGANIC CHEMISTRY. [§ 111
The ketones do not yield polymerides, but are capable of form- ing condensation -products.
Acetone, CH3.CO.CH3.
III. Acetone is prepared on the manufacturing scale from crude wood-spirit (42), and by the dry distillation of calcium ace- tate. It i.s present in very small quantities in normal urine, but in much greater proportion in pathological cases, such as diabetes vidliim and acetonuria. It is a liquid of peculiar, peppermint-like odour, boils at o6*3**, solidifies at —94-9®, and has a specific gravity of 0*812 at 0°. It is an excellent solvent for many organic com- pounds, and is miscible in all proportions with water; on addition of certain salts, such as potassium carbonate, the liquid separates into two layers. It is converted by reduction into isopropyl alcohol (150), and >nelds a crystalline oxime melting at 69^. Condensation-products derived from acetone are considered in 143 and 285.
Sulphonalf an important soporific, is prepared from acetone. In presence of hydrochloric acid, acetone unites with ethylmercaptan with elimination of water:
(CH.),C0 + 2IIS.C,H. - (CH,),C(SC.H.), + H,0.
Dimetbyldiethyl- mercaptole
Oxidation with potassium permanganate converts the two sulphur atoms of this compound into SO,-groups, forming diethylsulphonedi- mcthylmethane, (CH,)2C(S02C2H5)2, or sulphonal. It crystallizes in colourless prisms, soluble with difficulty in cold water, and melting at 126°.
UNSATURATED HYDROCARBONS.
I. ALKYLENES OR OLEFINES, CnHan.
Methods of Formation.
112. 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
CfiHu-OH^CfiHio + HzO.
This can sometimes be effected by heat alone, as with tertiary alcohols, but it is usuallv necessary to warm the alcohol with a dehydrating agent, such as concentrated sulphuric acid (54 and lis) o^* zinc chloride. Water is more readily eli mi natetl from the secondare and tertiary alcoliols than from the corresponding pri- mary compounils.
3. By abstraction of hydrogen halide from alkyl halides, effected by heating with alcoholic potash, a solution of caustic potash in alcohol :
CnHan+il + KOCsHs =- CnHan + Kl + CgHfiOH. An ether is also formed (55) :
CnH2n+lI + KOC2H5 = CnHzn+lOCsHsH- 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.
147
148
OROANJC CHEMISTRY.
[§11?
|
Name. |
Fonnula. |
Boiling- point. |
Name. |
fiot]ii«. point. |
|
|
Ethylene. . . . Propylene. . . fi^Butylene. . 11- Am vlene. . . Hexylene. . . . |
CA CA C,H,o QHiv |
-103^ - 48** 39** 68** |
Heptylene . . Octylene. . . . Nonylene. . . Decgrlene Undecylene. |
CiiHit |
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 alkylenes or olefines.
To indicate the position of the double bond in the molecule, the alkylenes are sometimes regarded as substituted ethylenes: thus, CHs-CHrCH'CHa is called symmetrical dimethylethylene; and (CH3)2C:CH2, utisymmetricdl dimethylethylene.
Properties.
113. The lowest members of this homologous series are gases, and arc 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 arc 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 unsaturated. 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- gane'je dioxide. Compounds of other classes, such as aldehydes.
§ 114) OLEFIN ES, 149
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, pTj^>C:CH2, treated with sulphuric or hydriodic acid
yields
ChJ>^-"^^3 or cH3>^-^"3. isOaH i
This reaction may be otherwise expressed by stating that there is a tendency for the number of methyl-groups to increase in such addition-reactions.
Hyp)ochlorous acid, CI -OH, can also form addition-products which are chloro-alcohols:
CH2=CH2+C1.0H = CHgCLCHgOH.
Ethylene Glycolchlorohydrin
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 \yQ 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:
riTT (CH3)2C — CH3
J^{}3>C:CH2-> J
OS03H+H|HC:C(CH3)a'
(CH3)2C-CH3
~* H(';=C(CH3)2. The simplest member of this series, CH2, methylene, has not
150 ORGANIC CHEMISTRY, [§ 115
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 CH2-groups uniting to form a single molecule.
Ethylene, C2H4.
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-f H2SO4.
In the preparation of ether (56) the temperature is maintained below a certain limit, and fresh alcohol is continually added, but in tliis 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 liquid. 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 practically 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 fonned. 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
§§116,1171 THE NATURE OF THE DOUBLE CARBON BOND. 151
bromide, C2H4Br2 (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° (28).
AxnyleneS) C5H10.
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 dvaviylene and triamylene. The other mode of separation depends upon the different velocities with which the isomeric amylenes form addition-products with hydriodic acid.
The Nature of the Double Carbon Bond.
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:
II mm
CH3 — C — CH3, CH2 — CH — CHs*
2. Existence of free bonds:
a. On one carbon atom only:
CH3 — C — CHs,
6. On different carbon atoms:
CH3 — CH — CH2*
152 ORGANIC CHEMISTRY. [§ 117
3. Existence of a double carbon bond:
CH3 — CH=CH2.
4. Existence of a closed chain or ring:
CH2 — CH2.
\/
CH2
It is stated in 113 that unsaturated compounds are convertible into ^atu^ated 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 CHs-C-CHa or
CH3«(/-CH3, the addition of bromine produf^es the same substance,
A
CH3-CBr2«CH3. Similarly, the assumption of tervalent carbon atoms, or of free lx)nds on different carbon atoms, leads to the
III in
same result; CH2*CH2 with two tervalent carbon atoms, and CH2-CH2 with free bonds, yielding with bromine the same addi-
tion-produd, CH2Br.CH2Br. 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, C2H4CI2, would have the constitution CH3.CHC12, and ethylene itself, CH3-CH. Ethylene chloride would then be iden- tical with the product obtained by the action of phosphorus penta- chloride upon acctaldehyde, CH3«CH0, since the exchange of the oxygen atom in the latter for two chlorine atoms yields a com- pound of the formula CIl3«CHCl2. But ethylene chloride is differ- ent from the compound C2H4CI2 (ethylidene chloride) got from aide-
§ 1181 THE NATURE OF THE DOUBLE CARBON BOND, 153
hyde. Similarly, propylene chloride, C3H6CI2, formed by the addition of chlorine to propylene, is not identical with the reaction- product obtained by treating acetone with phosphorus penta- chloride, CH3«(Xl2'CH3 (chloroaceUyne) , nor with that from pro- pionaldehyde, CH3.CH2 '011012 (propylidene chloride). Ethylene
n
therefore cannot have either the formula CHa-CH or CHa-CH.
nor propylene an}'^ of the formulae CHa-C-CHa, CHa«CH2«CH,
A A
n u
Cria'O'CHa, or CH3»CH2*CH.
118. 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 iso- propyl iodide, CHa*CHI-CHa. Hence, it follows that propylene
CH2 — CH2 cannot have either the formula CH2-CH2*CH2 or \^^ , and
I I CH2
therefore the remaining possibilities are CHa«CH«CH2,
m in
CH3-CH.CH2, and CHa-CH:CH2.
is^oButijlenej C4H8, is similarly formed by the elimination of HI from both isobutyl iodide, (CH3)2C[H|CH2jT], and tertiary butyl
iodide f (CHa)2C[T[ «CH2|h1. Thus, isohutylene can only have one of
III ni
the formula (CHa)2C.CH2, (CHa)2C.CH2, and (CHa)2C:CH2.
Both these examples indicate that the removal of hydrogen halide from an alkyl halide necessitates the elimination of a halogen atoni and a hydrogen atom respectively m union wUh two carbon atoms directly linked together.
Other examplesserve as further illustrations of this principle. If
CH HI be removed from a pentyl iodide, p TT^>CH«CH2r, the result- ing amylen€f CsHjo* should, in accordance with the principle, have
CH the constitution ^ ir^ >C-CH2. That it actually has is proved bv
the f:ict that the addition-product obtained by the action of hydri- odio acid on this amylene is not the original pentyl iodide, but one
154 ORGANIC CHEMISTRY, [§ 119
with the formula ^t,^^>CI-CH3, as is established by replacement
of 1 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)2CH-CH2«CH2l, which yields C5H10 on elimination of III, 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 tsobutylene, (CH3)2C:CH„ by addition of two bromine atoms into (CH3)2CBr«Cn2Br. Elimination of HBr from this di- bromidc produced (CH3)tC:CHBr, the constitution of which is in- ferred from its oxidation to acetone:
(CH3),C|:CHBr -> (CH,),CO.
It was not possible again to eliminate HBr from the compound (CH3)2C:CHBr, monobromohutijlcnc ^ there being no hydrogen at- tached to the carbon atom in direct union with the CHBr-group.
119. From the foregoing considerations it is evident that only three possible constitutional formuhe remain for the unsaturated hydrocarbons.
1. Two free bonds on two carbon atoms directly linked to one another: R-CH-CH-R'.
ni ra
' 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 te 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 hvdrocarbons
§ 1201 THE NATURE OF THE DOUBLE CARBON BOND. 155
CoH2n^2» come in order of the number of hydrogen atoms, CuH^n, CuH2u-2? etc. Hydrocarbons, CnH2u+i, CnH2n_i, etc., with oive or three free bonds, or tervalent carbon atoms, are unknown, all attempts to isolate methyl CH3, ethyl C2H5, etc., having failed. Tlie facts afford no support for the assumption of either free bonrls or of tervalent carbon atoms. On the other hand, in forming a double linking hydrogen halide must be eliminated from adjoining carbon iitoms in direct union, thus excluding the possibility of the forma- tion of such compounds as CnH2n-ri- 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 Irom 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 possessed 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 l>ond, but that an addi- tion-product is first formed by the taking up of two OH-groups:
^CH N^HOH
II becomes | Jen XHOH
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 occuj)ied by the double bond. The breaking of the unsaturated chain by oxidation therefore depends on the formation of an intermediate addition-
1^6 ORGANIC CHEMISTRY, [§ 120
product, and it is only necessary to find an explanation 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 closely as posf^ible.
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 ta 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 Baeyer'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 h:is been demonstrated, but its effect on physical properties is no less marked. This phenomenon has iK^en most fully investigated in connection with refraction.
J§ 121, 1221 THE NATURE OF THE DOUBLE CARBON BOND. 157
The members of a homologous series exhibit a constant dif- ference in molecular refraction (26) for each additional CH2- group, and this difference can be regarded as the refraction of this group. Multiplying this difference by n, and subtracting
the product from the molecular refraction of a compound CnH2in-2» give the refraction for 2H, and therefore also for C and H separately. The atomic refraction of ox^'gen and other elements can be similarly ascertained. Inversely, knowing the molecular formula, simple addition of the atomic refractions gives the molecular refraction, the values calculated agreeing well with those deter- mined experimentally. For an unsaturated compound, however, the molecular refraction thus calculated is always less by a con- stant amount than that determined experimentally. Bruhl calls this difference the increment for the double bond. On these facts is based an optical method of detecting the presence of a double carbon linking in a compound.
II. ALICYCLIC COMPOUNDS, CnH,n.
121. Isomeric with the olefines is a series of compounds, CnH2n, chiefly distinguished from the former by the absence of, or at l^ast a diminution in, the power of forming addition-products. Most of these compounds are yary stable: thus cydopentane, CsHio, closely resembles n-pentane, C5H12. The methods for the formation of these compounds make it evident that there is a ring or closed carbon chain in the molecule (275-280).
III. HYDROCARBONS, CnHai-j.
122. Two structures are possible for these compounds, which contain four hydrogen atoms less than the corresponding paraffins. Hydrocarbons with two double bonds have the general formula CnH2n-2; for example,
CHo • CH • CH • CH2.
Vinylethylcno
Further, substances with a triple bond have the same general for- mula; for example,
CH3 -0=011.
Allyleno
158 ORGANIC CHEMISTRY [§ 123
The triple linking here is assumed for reasons similar to thoee applicable to the double bond in the olefines (119).
A. HYDROCARBONS WITH TRIPLE BONDS.
Nomenclature.
123. The first meml)er, C2H2, is called acetylene: the second, C3H4, allylene: the higher members are regarded as substituted acetylenes; thus C4H6 is called ethylacetylene; CeHio, butylacetylene; 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 halogen to alkylenes:
CHaBr— CHaBr - 2HBr = CH^CH.
Ethylene bromide Acetyleoe
The elimination of hydrogen halide is effected by heating with alcoholic potash.
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 CnH2nT 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- product with bromine, and so on.
3. By the elimination of 2HX from compounds of the formula Cnn2nX2, prcviously formed by the action of phosphorus penta- halide upon aldehydes or ketones:
CH3.CHCI2 - 2Ha = CH=CH.
Ethylidene chloride Acetylene
CH3-CCl2-C^Il3 - 2HCI = CH3-C3:H.
Chloroacetone AUylene
({ 124, 125J HYDROCARBONS WITH TRIPLE BONDS. 159
124. Some of the hydrocarbons prepared by the foregoing methods exhibit a characteristic behaviour towards an ammoiiiacal 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 solution or in water, which separate out as a voluminous precipitate. These compounds are explosive, the copper yellow or red, and the silver white. Acetylene, and of its higher homologues, those derived from the dihrflogen compounds of the aldehydes, yield these metallic compounds. The method of formation of these homologues shows that they contain the group =CH :
CnH2n+l •CH2 -CHO — » CnH2n-Hl '0112 '011012 — ► OnH2n + l '0=011.
From this it may be concluded that the -presence of the group ^OH is essential to the yielding oj melallw denvativcs: it io the hydrogen of this group which is replaced by metals. In supix)rt of this view IS the fact that only the dichloro-derivatives of the methylketones (loi) can be transformed into hydrocarbons yielding metallic compounds:
CnH2n^i-CO'CH3 -*0„H2n^i -OOl^'OHg -^ 0„H2„^i •0=0H;
Yields metallic derivatives
C2H8-CO.C2H6 - C2H6.CCI2.CH2.CH3 -» CHvC^CCHa.
Does not yield metallic derivativeit
The isomeric hydrocarbons containing two double bonds (127) are also incapable of forming metaUic compounds.
The hydrocarbons are readily lilx»rated from their metallic derivatives by the action of dilute hydrochloric acid. • This affords a means of isolating from mixtures the members of th(» scries C11H2B-2 which yield such derivatives, and of obtaining them in the pure state.
125. The hydrocarbons of this series can add on four halogen 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 = OH., -OHO. CH3-C=0H + H2O =0H3-0O-0H3.
Mercury compounds are first formed by addition: thus, when aUylene, C8H4, b passed into a solution of mercuric chloride, there
160 ORGANIC CHEMISTRY. [§ 126.
is first formed a precipitate of the composition 3HgCl2,3HgO,2C3H4y which is converted into acetone by the action of hydrochloric acid.
The hydrocarbons of the acetylene series also yield condensa- tion-products. The condensation sometimes takes place between three molecules: thus, acetylene, C2H2, condenses to benzene, CeHo; dimethylacetylene, C4II6, 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:
C2H5-CH2-C^CH is converted into C2H5-C=C.CH3.
Propylaoetylene Methyiethylaoetylene
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 jx)sition of the triple bond, since, for reasons similar to 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 given above, and be methylethylacetylene.
Acetylene, C2H2.
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 Ix; detected bv means of an anmioniacal solution of cuprous chloride^
? 1261 Hf-DBOCARBOXS WITH TRIPLE BOXDS. 161
iKrhich yields a red precipitate of copper acetylene even from traces of acetylene mixed ii-ith other gases. Acet^'lene 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, CaC^:
CaC2+2H20 = Ca(OH)2-hC2H2.
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 iiith quicklime, CaO, in an electric furnace. Under the influence of the high temperature, the calcium lil^rated by the action of the carbon on the quicklime enters into combina- tion with the excess of carbon, forming calcium carl)ide: 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 this 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- riages, motor-car lamps, gas-buoys, and so on. Another important application is exemplified by autogenous welding, sufficient heat being generated by an oxy-acetylene blowpipe to melt iron readil3\ Steel plates for safes, rails for railway or tramway use, and other iron or steel material can be readily welded l)y it5 aid.
Acetylene must be handled carefully, since a mixture with air explodes with extreme violence, and is much more dangerous than a mixture of ordinar\' coal-gas and air. This is due to the fact that much heat is taken up in the formation of acetylene: it is strongly endotherniic (''Inorganic Chemistr>','' 97). Moreover, the limits of explosion are much wider than for any other gas, an explosive mixture being formed with air by the admixture of ^82 per cent, of acetyU ne, while for coal-gas the limits are only 5-28 per cent. The velocity of propagation of combustion is also much greater for acetylene, and this augments considerably the force of the explosion.
102 ORGANIC CHEMISTRY. [§ 127
Acetylene prepared from calcium carbide sometimes contains small quantities of hydrogen sulphide and phosphiue, to which it owes its disagreeable odour. It can be freed from the former by a solution of caustic alkali, and from the latter by a solution of mercuric chloride in hydrochloric acid. The removal of phosphine is of special importance, since its presence may lead to the spon- taneous ignition of the gas.
B. HYDROCARBONS WITH TWO DOUBLE BONDS.
127. A hydrocarbon of this series of great importance is isoprene, CfcHj,, on account of its close relationship to caoutchouc (370). In recent years many attempts to prepare isoprene have been made, but hitherto without technical success. A very good laboratory- method for its preparation is described in 367. A poor yield of the hydrocarbon is obtained by the dry distillation of caoutcliouc. It is a liquid boiling at 37°, and has the specific gravity D4** =0»6793.
CH Isoprene is proved to have the constitution pTT*^C*CH=CHi by the
addition of 2HBr, which yields a dibromide, ^^'>CBi— CH,--CH,Br,
CH
identical with that obtained from dimethylallene, pTT*>0=C=CH2.
DimethylaUene is thus obtained. Two carbinol-derivatives,
PH dimethylethylcarbinol, pu'>C(0H).CH2CHs, and methylisopro-
pylcarbinol, ^JJ'>CH.CH0H.CI1„ are prepared by the method
described in loa, and converted into the corresponding iodides. On elimination of HI, each iodide yields trimethylethylene^
CH
£^TT*>C— CH-CHa, its formation from both iodides admitting of no
other position for the double bond. Trimethylethylene takes up 2Br, forming ^[J'>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,
^Tj -^ v-' — C/ •— C- H J.
This mode of formation does not wholly preclude another arrangement of the double bonds, but other evidence proves that dimethylallene has the structural formula indicated:
1. On oxidation it yields acetone, proving the presence of the group (CH3).C---.
i 127] HYDROCARBOXS WITH TWO DOUBLE BONDS, 103
2. Treatment with sulphuric acid of 50 per cent, strength con- verts it into methyhsopropylketone:
^g«>C=C=CH,+2H,0 - ^2»>CH-C(0H),.CH,-»
Intermediate product
— ^}|*>cn.cocH,.
Ck>mpound8 like this intermediate product are referred to in 149.
When forming an addition-product with two univalent atoms, organic compounds containing the group C=C — C=:C, called by Thiele 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.CHaBr. The subject of conjugated bonds is further discussed in 283.
SUBSTITUTION-PRODUCTS OF THE UNSATURATED
HYDROCARBONS.
I. UNSATURATED HALOGEN COMPOUNDS.
128. Since the saturated hydrocarbons do not themselves poe- Bess 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 descril)ed. 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 unsaturated kcdogen cam pounds.
Halogen derivatives of the type CnH2n-iX are obtained by the addition of halogen to the hydrocarbons CnH2nf and subsequent elimination of one molecule of hydrogen halide:
CH2=CH2 + Br2 = CH2Br-CH2Br. CH2Hr-CH2Br-HBr = CH2=CHBr.
Ethylene bromide Vinyl bromide
They are also formed by removal of one molecule of hydrogen halide from comix)unds containing two halogen atoms in union with the same carbon atom:
cn3.cH2-rKCi2-Hci = ch3-chz=chci.
Propyiidene chloride a-Chloropropylene
CilsCCia-CHa-HCl = CH3-CC1=CH2.
CbioruaoetODe A-Chloropropylene
164
§ 1291 UNSA TURA TED HALOGEN COMPOUNDS. 165
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 atom^ 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 ^-chloropropylenCf 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, prepared by a method described in 153. 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 ])c at the end of the chain, since it takes the place of the hydroxyl-group. Given the constitutions of a-propylene chloride and /9-propylene chloride, which are deduced from those of propionaldehyde and acetone, the allyl halides can only have the constitutional formula
CHa^^CII-CHzX.
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 meml>ers of the series. Vinyl chloride CHjiCHCl is a gas, vinyl bromide ClIaiCHBr a
166 ORGANIC CHEMISTRY. (55130,131
liquid of ethereal odour. Both these compounds polymerize readily.
130. AUyl chloride, aUyl bromide, and allyl iodide, boil respec- tively at 46°, 70°, and 103°. They are often employed in 83mtheses 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-jn-aX. Their constitution is inferred from the facts that they yield metallic derivatives, indicating the presence of the group 3CH, and that their halogen atoms are capable of taking part 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.
Bromoacetyliden€y CHBriC, which is assumed by Nbp to contain a bivalent carbon atom, can be obtained from acetylene bromide, CHBriCHBr, 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.
131I The hydroxyl-group of the unsaturated alcohols may be attached to a singly-linked or to a doubly-linked carbon atom:
CHzrCH.CHzOH, CHgrCH.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, CH20H«CH20H, there results, not vinyl
XT
alcohol, CH2^=CH0H, but an isomeride, acetaldehyde, CH3 — C^ q.
When /?-bromopropylene, CH3*CBr:CH2, is heated with water, there is formed not /^-hydroxy propylene, CH3*C(OH):CH2, but the isomeric acetone, CHa-CO-CHs. 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
§1321 UNSATURATED ALCOHOLS. 167
atom are unstable, they have a tendency to become transfonned into isomerides. Compounds do exist, however, in which the group — CH:C(OH)— is stable (235-236).
The following compounds either cont^n hydroxyl in union with a doubly-linked carbon atom, or are related to substances of that type.
Vinyl alcoholf CHjiCHOH, so called because it contains the vinyl-group f CH,:CH — , 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 HgaCljOgCaHj is formed, and on treatment with hydrogen halide yields vinyl-compounds.
A vinyl-derivative of great physiological importance, called weu-
rinCf is formed in the putrefactive decay of flesh, and in other fer-
CH'CH mentation-processes. Its constitution is (CH3)8N<qtt" *, as is
indicated by synthesis. When trimethylamine reacts with ethy- lene bromide, a substituted ammonium bromide of the formula
(CH3),N<o '* " is obtained. HBr* is eliminated from the
group — CIIa'CHxBr by the action of moist silver oxide, the bromine atom attached to nitrogen being simultaneously replaced by hy- droxyl. A substance of the constitution indicated is thus obtained, and IS in all respects similar to neurine.
AUyl Alcohol, CHa-.CH.CHjOH.
132. Many unsaturated alcohols containing hydroxyl attached to a singly-linked carbon atom are known. The most important is alli/l alcohol, the preparation of which is described in 153. Its constitution is inferred from that of the chlorine derivative formed by the aption of phosphorus pcntachloride (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-^CIl2:CH.C^^->CH2:CH.C00a
Allyl alcohol Acraldehyde ^ Acrylic acid
AUyl alcohol mast therefore contain the group — CH2OH, charao- teristic of primary alcohols.
1G8 ORGANIC CHEMISTRY. [§ 133
Ally I alcohol is a liquid of irritating odour, solidifying at —50®^ 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, among them allyl sulphide (CH,:CH*CHjf)^, the prin« cipal constituent of oil of garlic. It is synthetically obtained by the action of potassium sulphide, K^S, on allyl 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 hydroxyl, but that otherwise its influence is much less marked. When two groups are situated in immediate proximity to one another in the same molecule, each group exercises a strong influence upon the properties oj Oie other,
Propargyl Alcohol, CH=C.CH20H.
133. Propargyl alcohol contains a triple bond, and is prepared from tribromohydrin, CHoBr-CHBr-CHxBr (147). Potassium hydroxide converts this substance into CHalCBr-CHjBr, which on treatment with potassium acetate and saponification yields CH2rCBr-CH20H, sinoo only th(^ terminal Br-atom is capable of taking part in a double deconi|)osition (128). When this alcohol is again brought into con- tact with caustic potash, HBr is eliminated, with formation of pro- pargyl alcohol, the constitution of which is indicated by this method of formation and also by its proi>erties. The presence of the group =CH is indicated by the formation of metallic derivatives: on oxidation it yields propiolic acidy CH=C«COOH, with the same number of carbon atoms, proving that it is a primary alcohol.
Propargyl alcohol is a li(]uid of agreeable odour, soluble in water, and boiling at 114°-115°: its specific gravity at 21° is 0-963. Its metallic derivatives are explosive.
MONOBASIC UNSATURATED ACIDS.
I. ACIDS OF THE OLEIC SERIES, CnHa^^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:
CH3-CHOH.CH2-COOH-H20 = CH3-CH:CH.COOH.
)?-Hydroxy butyric acid Crotonic acid
The acids of this series can also be prepared from uasaturated compounds by
3. Oxidation of the unsaturated alcohols and aldehvdes.
4. The action of potassium cyanide on imsaturated halogen compounds, such as ally I 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 numl)er of carl)on aton:s in the molecule. The first member, CIl2:Cll-C0()H, is called acrylic acid: others are crotonic acid, C4H(i02; angelic acid end tiglic add, C6H8O2; undenjlenic acid, C11H20O2; oleic acid, C18H84O2; erucic add, €22114202; etc.
109
170 ORGANIC CHEMISTRY. [§§135,136
Properties.
135. In common with all compounds containing a double bond,t 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 : thu3, the vahi? of the constant lO^A; (87) for propionic acid, C3H6O2, isO«134; for acr>1ic acid, 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'CHOIl — 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 0
CH-COOH 0|H
{{ =CnH2n+i-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 Acid, CH2:CH-C00H.
136. Acrylic acid is obtained by the elimination of HI from ^-fodopropionic acid, CH2l'CH2-COOH. It is a liquid of pungent odour, boiling at 140°, and is reduced by nascent hydrogen to pro- pionic acid.
§ 136 ' ACIDS OF THE OLEIC SERIES. 171
Acids of the formula C4H6O2. The theoretically possible acids of the formula C4He02 are 1. CHarCH.CHz.COOH; 2. CHa-CHiCH-COOH;
3. CH2:C<^Q^^^jj; 4. | >CH.COOH;
but five acids of the formula C4H0O2 are known.
An acid of the constitution indicated in formula 1, vinylacetic acid, 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 + CO2 = CH2 : CH • CH2 • C02MgBr ;
CH2 :CH .CH2 • C»2MgBr -f-HoO =
=CH2:CH.Cn2-COOH+MgBr.OH.
Its fonnation 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-^CH2:CH.CH2-COOH.
AUyl iodide
Actually, however, an acid of formula 2 is ol^tained, solul crotonic acidf which melts at 71° and boils at 1S()°: careful oxidation with permanganate converts it into oxalic acid,HOOC — CXJOH, a proof of its coastitution. It follows that during the reaction the position of the double bond must have changed.
isoCroionicacid, melting at l.j«5° and boilmg at 172°, has also constitution 2, because, on the one hand, like solid crotonic acid it can be reduced to /i-bu*yric acid, j)roving that it too contains a normal carbon chain; on the other, it is converted by careful oxidation into oxalic acid. Ordinarv constitutional formuUe are incapable, therefore, of accounting for the isomerisni of tlu'se acids, which is explained in 169.
An acid with formula 3 is obtained bv the elimination of HBr from bromou'obutyric acid; it is called vivUiacrylic acid:
^Jj3>(MJr.C0()H^[.JJ'^>C.C00H.
The acid of formula 4 is described in 275.
372 ORGANIC CHEMISTRY. [\ 137
Oleic Acid, C18H34O2.
137. Oleic add is obtained by the saponification of oils and soft fats (8$). 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, CiyHaj-CO-CHji
CnHsj. (COOba* 4- baO .JOC -CH, -> CtHss.CO.CH,.
Barium stearate Barium acetate Blargarylmethylketone
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 CjeHa •CH2 -CO -CHj, for only from such a compound could oxidation produce an acid with seventeen carbon atoms. This acid, C^^W^fi^ {margaric acid), is similarly transformed into a ketone, CjoHjj.CO-CHa, which on oxidation yields an acid CnHsaOi. The formula of margaric acid must therefore be CjsHji-CHj.COOH. and that of stearic acid, CijHj, .CHj-CHjCOOH. The acid CieHjjOj, palmitic acidy is in its turn converted into a ketone, and the process continued until capric acidy CjoHjoOj, is obtained. This acid has been proved by synthesis (233i 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
♦ba-JBa.
a 138, 1391 ACIDS OF THE PROPIOLIC SERIES. 173
bond is situated at the centre of the chain, the constitution of oleic acid being
CH3-(CH2)7-CH:CH.(CH2)7-C»OH.
This constitution is inferred from the products of careful oxida- tion, which yields pelargonic add, CsHjr-COOH, and azelaic acid, HOOC-(CH2)7-COOH.
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 acid. The reaction is called the "elaidic trans- formation." Other acids of this series are similarly transformed: thus, erucic acid, C22H42O2, is converted by a trace of nitrous acid into brassidic acid,
Elaidic acid has the same structural formula as oleic acid, the double bond occupying a similar position in the molecule of each, since each acid readily forms a bromine addition-product from which eUmination of 2HBr yields stearolic acid, C18H32O2:
C18H34O2 -^ Ci8H34Br202 — * C18H32O2. Oleic and ^aldio Bromine addition- Stearolic acid acids product
Oleic acid and elaidic acid yield the same hydroxystearic acid by the addition of one molecule of water, a reaction effected 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. ACroS OF THE PROPIOLIC SERIES, CnH^i-A.
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 +CO2 = CH=C • COONa.
Sodium propiolate
174 ORGANIC CHEMISTRY, I§ 140
The a-carbon atx)m of these acids has a triple bond, and such acids are very readily decomposed into an acetylene hydrocarbon and 002; 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:
•
CH3 . CH : CH . COOH -^ CH3 • CHBr • CHBr • COOH ->
Crotonio acid Dibromobutyrio acid
-^CHg-CrC-COOH. TetroUc acid
140. In presence of concentrated sulphuric acid, substances with a triple bond take up water with formation of ketones (125) :
— C=C > — CH2-C0— .
In this manner stearolic acid is converted into a ketostearic acid of the formula
C8Hi7-CO-CH2-(CH2)7-COOH,
and treatment with hydroxylamine transforms this into the corre- sponding oxime:
CgH 1 7 • C • CH2 • (0112)7 • COOH .
II NOH
Under the influence of concentrated sulphuric acid, this oxime undergoes the Beckmann transformation (103), among the pro- ducts being the substituted acid amide
C8H,7-CO
NH-(CH2)8-COOH,
which is proved to have this formula by its decomposition into pelargonic acid, C8Hi7«COOH, and the 9-aminononoic * acid, NH2 -(0112)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 thev can be converted into stearolic acid in the manner already described.
♦ If the carboxyl-carbon atom is denoted by 1, the amino-group is ia unioQ with the ninth carbon atom of the chain.
UNSATURATED ALDEHYDES AND KETONES
141. The lowest unsaturated aldehyde is acraldehyde or acrolein, 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 (acer, 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 polymerization-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 aldchydic character. This is exhibited in its behaviour towards ammonia, with which it does not com- bine like acetaldchyde (104), but in accordance with the equation
2C3H4O -h NH3 = C0H9ON -h H2O.
Acraldehyde-ammonia is an amorphous, basic substance, is soluble in water, and in its appearance and l^ehaviour towards water bears a close resemblance to glue.
Acraldehyde docs 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
175
176 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.
14a. Crotonaldehyde, CH,*CH:CH*CHO, results on elimination of water from aldol, CH,.CHpH[^CHJhj -Cq (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
Propiolaidehyde. CH=C«C<!^, can be obtained from acrolein-
acetal by the addition of two bromine atoms, and subsequent removal by means of caustic potash of 2 H Br from the addition- product thus formed:
CH, :CH -C^oc J, j^ -^ CH,Br -CHBr-C^^jp j,^)^ -
Acrolelnacetal Dibromo-coni pound
Propiolaldchydeacctal
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 propiolaidehyde towards alkalis is remark- able. It decomposes into acetylene and formic acid:
CH^CCHO +NaOH =CH:^CH +Cf-ONa.
143. An important unsaturated aldehyde is gcranial {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°-H2° under a pressure of 12 mm. Its aldehydic nature is shown by its reduction to an alcohol, gcraniol, and its oxidation to an acid with the same number of carbon atoms, geranic add.
Geranial has the structural formula
pTj > C=CH»CH2«CIl2*C(CH3)-^:^CH«C>-.,
S 143] UNSATURATED ALDEHYDES AND KETONES. 177
since on oxidation it yields acetone, lajvulic acid (234), and carbon dioxide, the molecule breaking down at the double bonds:
^•^ >Cz=CH.CH2-CH:,.C(CH3)=CH.c2 ^
Geranial
-^ ^>C0 +HOOC-CH2-CH2.CO.CH3+C02+C»2.
Acetone ' Lsevulic acid Carbon dioxide
When boiled with a solution of potassium carbonate, geranial takes up one molecule of water, forming methylheptenone and acetal- dehyde :
CH3 >c==:CH.CH2-CH2-C(CH3)=CH.c5->
Geranial
— ^g*>C=CH-CH2-CH2-CO-CH3+CH3.cf .
Methylheptenone Aoetaldehyde
On oxidation, methylheptenone also yields acetone and laevulic acid. Ihis reaction indicates its constitution, which is further proved by synthesis.
Baryta-water converts a mixture of geranial and acetone into a condensation-product, pseudowian^;
(CH3)2C=CH.CH2-CH2-C(CH3)=CH.CHO-fH2CH.CO-CH3 =
Geranial Acetone
= HiO + iCHs) 2C=CH • ( Ha • iHi ■ C(CH3)=tB • CH=CH • CX) • C H3.
pscudolononc
When boiled with dilute sulphuric acid, psei/^oionone yields ionone:
CH3 CH.{ CH3 CH3
\/ \/
c c
/ /\
HC CH-CH:CH«(X)«CH3— H2C CH-CHrCH-CO'CHa.
H2C C'CHs H2C C'CHa
\/ \y
CH2 (^H
pnetuiolonone Ionone
178 OnOANlC CHEMISTRY. J143I
The structure of ionone is proved by its decomposition-productB. It is manufactured as an artificial perfume, as it has a powerful, violet-like odour, and is closely related to irane, the active principle of violets. The formula of irone is
CH3 CH3
c
/\
HC CH.CH:CH-00-CH8,
II i
HC CH'CHa
CH2
which differs from that of ionone only in the position occupied by the double bond in the carbon ring.
COMPODNDS CONTAINING MORE THAN ONE
SUBSTITUENT.
I. HALOGEN DERIVATIVES OF METHANE.
144. The halogen 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 compounds formed by exchange of more than one hydrogen atom for halogen.
It is possible to replace all four hydrogen atoms in methane, ia 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 tetrabromo methane ; on reduction they are con- verted into dihalogen-substituted methanes. On account of their important therapeutic properties, the compounds CHX3 are pre- pared on the large scale.
Chloroform, CHCI3.
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 trichloroaldehyde, or chloral, CCia-CHO.
179
180 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 soh'difying at —70**. Its specific gravity at 15° is 1*498: it is very shghtly 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. Ordinary 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 vcr>' dangerous. The decomposition of the h'quid 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:
CHICI3 -H3Nal >OC2H5= CH(OC2H5)3 +3NaCL
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, CCla, 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-
i 1461 IODOFORM, 181
triles frotn 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, C'jCIq, C3HCI7, and others of similar type.
Methylene chloride, CHjCl,, is obtained from chloroform by reduc- tion with zinc and hydrochloric acid in alcoholic solution. It is a liquid, lioils at 40°, and has a specific gravity of 1 -337.
Tetrachloromethan€f or carbon tetrachloride, CCI4, produced by 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 COj. Its specific gravity is 1-593 at 20°: the high specific gravities of these polychloro-com pounds is noteworthy. The bromine and iodine compounds are specifically much heavier than the corresponding chlorine compounds.
Bromoform, CHBrj, 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 <;hloral, has not been isolated. On the manufacturing scale acetone, ibeing 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 4)y the slow evaporation of a solution in anhydrous acetone. • It
182 ORGANIC CHEMISTRY. (8 147
has a peculiar, saffron-like odour, sublimes very readily, and ir.elts 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 CHa-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 in surgery as an antiseptic. It is note- worthy that it does not kill the bacteria directly, its action on the micro-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^ CH2I2, 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.
n. HALOGEN DERIVATIVES OF THE HOMOLOGUES OF METHANE.
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 compounds: 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 already been described, the compounds CnH2n+i*CHX2 and CpH2p^.l•CX2•CqH2q^.l being obtained by the
§ 148] HALOGEN DERIVATIVES OF PARAFFINS. 183
action of phosphorus pentahalide on aldehydes and ketones respect- ively (98). 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
GpH2p+l • CH X • CHX • CrH2r • CHX • CHX • CTnH2m+l
result on addition of halogen to the hydrocarbons CnH2n-4> 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 halide by means of alco- holic potash, halogenation of the hydrocarbon CnH2n thus obtained, removal of HX, renewed halogenation of the product, and so on.
CH3-CH3 ->CH3-CH2CI-HC1 -^CH2:CH2 +2C1 ->
Ethane Ethyl chloride Ethylene
^ CH2CI • CH2CI - 2HC1 -^ CH=CH + 4C1 -*
Ethylene chloride Acetylene
-<;HCl2 • CHCI2- HCl -^ CHCl : CCI2 +2C1 -♦
Tetrachloroethane Trichloroethylene
-♦ CHCI2 • CCI3 - HCl -» CCI2 : CCI2 + 2C1 — CCI3 • CCI3.
Pentachloroethane Tetrachloroethylene Hexachloroethjtne'
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 CnH2in.2 i^ 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 iri6romo/i//d/'in, 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 is that " In open-chain compounds Greek letters must be used to
184 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 CO2H/' Thus, CHa-CHa-CHa-CHal is a-iodobutane ; CH3.CH2-CH2-CN a-cyanopropane; CH2Br.CH2 -011261 aa'- dibromopropane; CH2Br«CHBr«CH3 a^-dibromopropane.
Only a few of the numerous compounds of this group will be described.
Teirachlmoethane, CHCU'CHCh, is prepared technically by the interaction of chlorine and acetylene, with antimony pentachloride as catalyst. It is a liquid boiling at 147**. When it is boiled with milk of lime, hydrochloric acid is eliminated, with formation of trichloroethyleney CCU^CHCl, a liquid boiling at 88®. On addition of zinc-dust to an aqueous suspension of tetrachloroethane, heat is developed, and pure dichhroethylene, CHCl: CHCl, distils. It is a liquid boihng at 55°. All these substances are excellent solvents for fats and oils; they also dissolve sulphur readily, and are emploj'ed in vulcanizing caoutchouc.
Ethylene chloride, CHjCl-CH^Cl, is called "Dutch Liquid," or the "Oil of the Dutch Chemists," it having been first prepared at the end of the eighteenth centurj' by four Dutch chemists, Deiman, BoNDT, Paets van Troostwyk, and Lauwerenburgh, 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°.
Ilexachlorocthane (porchloroethane), CjCl«, is formed by the direct imion 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 lic^uid of agreeable odour, solidifies at 8°, boils at 131°, and has a specific gravity of 2- 189 at 15°.
Trimethylene bromidey CH2Hr-CHj*CH2Br, a « '-dibromopropane, also plays an important part in syntheses, and is obtained by addi- tion of HBr to allyl bromide, CHj: CH«CHjBr, produced from allyl alcohol. This method of formation suggests the constitution CHs'CHBr-CHsBr, that of the addition-product obtained by the action of bromine upon propylene, CHa'CHrCHj. Since the two compounds arc not identical, trimethylene bromide must have the
§§ 149, 150]
POLYHYDRIC ALCOHOLS,
185
aa'-formiila. It is a liquid, boiling at 165®, and has a specific gravity of 1-974 at 17^
Pentamethylene dibroniide is mentioned in 388. % \^«5^*
-.\
vV
a.
m. POLYHYDRIC ALCOHOLS. ^ c>(\
149. 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 l-group 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 hydroxy! in the halogen derivatives R -011X2, R-CX3, and R-CX2*R'. Silver acetate converts halogen compounds of this
OP« H O type into stable acetates, such as CH2<qp^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 orlho- esters f are obtained. On saponification R-C(0H)3 does not result, the corresponding acid being formed instead, through loss of water.
OP H Ethers of dihydric alcohols, such as CH3 • CH < ^^^tt^ are known,
and are called acetcUs (104, 2). The saponification of these sub- stances does not yield R-CH(0H)2, but an aldehyde. It follows from these facts that compounds with more than one hydroxyl-group aUached to the same carbon atom are unstable, although it is some- times possible to obtain such compounds (201, 230, and 234).
Many compounds are known containmg several hydroxyl- groups, of which not more than one is in union with each carbon atom.
I. Glycols or Dihydric Alcohols.
150. The glycols arc obtained from the corresponding halogen compounds analogously to the monohydric alcohols (39) :
O.OC.CH3
0.0C-CH3
|
CHz- |
O-OC-CHs+H |
|
CH2 |
|
|
CH2. |
OOC-CHs+H |
OH CHj-OH
I
CH,
OH CHj-OH
Trimetbylene bron.ide
Trimet h vleneglycol diacetate
Trimet hylene* glycol
186 ORGANIC CHEMISTRY, [§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 oiefines 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:
CHgiCHo+HcO-fO^CHoOH-CHoOH.
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 a(]ucous solution, or by electrolysis. Acetone yields pirzo- conc and ?.sopropyl alcohol. Glycols of the type of pinaconc — called pinacones — 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:
2CH3.CJJ +Mg=CHa.CH CH.CH,
O.Mg.O or 2Cn,.C().CH, + Mg=^U«>C C<^|J\
O.Mg.O
Water decomposes the addition-product, with formation of the •"»inacone:
CH,>y ]"<CH,+2H,0-^|J«>C(0H)-C<^(0H) + Mg0.
O.Mg.O ' ^^'
The constitution of pinacone is indicated by its synthesis:
CH,.CO.CH, H CH,.C(OH).CH,
+ - I
CH,.a3.CH, H CH,.C(0H).CI1,
Acetone PiDscone
#
§1501 GLYCOLS, ' 187
When distilled with dilute sulphuric acid, pinacone undei^oes a remarkable intramolecular transformation, explicable on the assump- tion that a hydroxyl-group changes place with a methyl-group:
yOR /0|H
(CH,),C(OH).C^CH,-» (CH,),C-C^[OH ~H,0 -(CH,),C-CO.CH,.
Pinaoone ^CH. P H Pinacolin
The constitution of pinacolin may be deduced from its synthesis by the action of zinc methide on trimethylacetyl chloride, (CH,),C-COCI, 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
•I
ethers,, esters, and alkoxides, and the oxidation of primary glycols to aki^hydes and acids, may take place in connection with one or both of the hydroxyl-groups. For instance, the compounds CH2OH.CH2CI, glycolchlorohydrin; CH2OC2H5.CH2OH, glycol- fHonoethyl ether; CH20C2H5.CH20C2H5, 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:
CH2CI CH2V
I -HCl = I >0.
CH2OH CHa^
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 phosphorus pentachloride, the oxygen atom being replaced by two chlorine
1S8 ORGANIC CHEMISTRY. [§151
CH2
atoms. If the compound had the constitution || , which ia
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 four
or five carbon atoms between the hydroxy 1-groups yield anhydrides
with a constitution analogous to that of ethylene oxide. The}'
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," C3H5(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.CKOH.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 -> CH2OH.CHOH.CH2OH.
2. When glycerol, CaHgOa, is carefully oxidized, glyceric acid, C3H6O4, is first formed, corresponding to the formation of acetic acid, C2H4O2, from ethyl alcohol, C2H6O, by exchange of two hydrogen atoms for one oxygen atom : this indicates that glycerol contains one — CH20H-group. Further oxidation converts gly- ceric acid into iartronic acid^ C3H4O5, two hydrogen atoms being replaced by one oxygen atom, with formation of a new carboxyl- group. Hence, glycerol contains two — CH20H-groups in the molecule, so that its couotitution is CH2OH -01120 -012011. Since tartronic acid, COOH«CH20'COOH, still possesses alcoholic properties, the group CH2O must have the constitution >CHOH^
ii 152, 1531 GLYCEROL. 189'
and since it must have the same constitution in the molecule of glycerol, the structure of the latter is proved to be CH2OH.CHOH.CH2OH.
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 hydroxy l-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 ta t for glycerol.
Since glycerol is a substance which plays a very important part in the economy of nature as a constituent of the fats (154), its synthesis from its elements is of great interest. This was effected by Friedel and SiLVA, the starting-point being acetic acid. This substance can. be synthesized from its elements in seveVal ways, for example by the oxidation of acetaldehyde obtained by the action of water on acetylene (125). The dry distillation of calcium acetate gave ace- tone, which was reduced to isopropyl alcohol. On elimination of water frpm 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, -*
Acetic acid Acetone uoPropyl alcohol Propylene
-♦ CH,.CHC1 .CH,a -» CH,C1 -CHCl .CH,C1 -» CH,OH .CHOH .CH,OH.
Propylene chloride Trichlorohydrin Glycerol
153. Several compounds, difficult to prepare otherwise, can be obtained from glycerol. Among them are allyl alcohol, allyl iodide, acraldchydc, and isopropyl iodide.
AUyl (dcoholy CH2 2CH'CH20H, can bo prepared from glycerol.
190
OSGANJC CHEMISTRY.
»!»
by beating it witb oxalic acid, (X)OH*(XX)H. Glyceryl monO' JortncUe or monojormin,
CHaOH-CHOH.CHz-OCO CHaOH-CH.CHiOH
H
b first produced, as under these conditions oxalic acid loses one molecule of carbon dioxide, yielding formic acid, |COO|H — COOH, which combines with the glycerol to produce monoformin. When heated more strongly, this decomposes into allyl alcohol, water, and carbon dioxide:
CHjjOH-CH
H
CHaOH-CH— CH2pa
or
0-CO|H
Allyl iodide is obtained by the action of phosphorus and iodine on anhydrous glycerol:
CH2I
CHI+PO3H3;
CH2I
CH2
CH
CH2I
-21
CHa II CH ,
CHoI
The tri-iodohyilriii.CsHsIa, jvrobably formed as an intermediate product in this reaction is uastablc, and at once loses two atoms of iodine, yielding allyl iodide.
Acraldehyde (141) results by elimination of water from glycerol:
[oTIh]
CHs-C— CHOH.
• •
|OH"ll] CH2:C:CH0H should be obtained, but immediately changes to acraldehyde, CH.rCH.cJJ (131).
Large quantities of acraldehyde can be prepared by passing glycerol-vapour over anhydrous magnesium sulphate at 330°-340**, 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, KStOj.
§ IMl GLYCEROL. 191
•
iaoPropyl iodide is formed by the addition of water to a mix- ture of glycerol with iodine and phosphorus. In this reaction propylene, CH3*CH:CH2, is an intermediate product, and is evolved in the free state if insufficient hydriodic acid is present. By the addition of HI, produced by the interaction of iodine, phosphorus, and water, zsopropyl iodide is formed from the pro- pylene thus generated :
CHa'CH 2CH2 + HI = CHa'CHI'CHa.
Propylene i«oPropyl iodide
Formic acid (81) is usually prepared by the action of glycerol on oxalic acid. As, previously mentioned, when these substances are heated together, carbon dioxide is evolved, and glyceryl monoformate produced. Formic acid is obtained from the latter by saponification, the glycerol being simultaneously regenerated by the addition of a fresh quantity of oxalic acid, C2H204,2H20, the water of crystallization saponifying the ester, and the formic acid distilling over. The glycerol thus regenerated is again converted into monoformin by the freshly-added oxalic acid, and the ester once more decomposed by the addition of a further quantity of oxalic acid, and so on. It is thus possible to convert unlimited quantities of oxalic acid into formic acid by means of a given quantity of glycerol.
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.
Saponification of the esters of polyhydric alcohols. — The saponi- fication of the tri-esters of glycerol with caustic soda or lime takes place in stages, the di-esters and mono-esters being formed as intermediate products, as can be readily proved. On complete saponification, pure tristearin, or glyceryl tristearate yields only stearic acid and glycerol, so that if no intermediate products are formed, a partially-saponified portion, in which the soap produced has been decomposed by hydrochloric acid, and the glycerol removed by washing with water, should contain only unchanged tristearin and stearic acid. Neither tristearin nor stearic acid can yield acetyl- derivatives with acetic anhydride. If the saponification takes place
192 ORGANIC CHEMISTRY.] [§ 155
in stages, nionostearin and distearin should be formed, and the free hydroxyl-groups of the glyceryl-residue in these compounds should react with acetic anhydride to form acetyl-compounds. On treat- ment with this anhydride, and subsequent complete saponification, acetic acid should be among the products, and it has been proved by experiment that this is so.
When glycol diacetate and glyceryl diacetate are saponified with very dilute hydrochloric acid, the velocity of saponification for each compound differs at the various stages. It has been stated that the ratio of the velocity-constant of glycol diacetate to that of the monoacetate is as 2 : 1, the corresponding ratio for the glyceryl tri-esters, di-estcrs, and mono-esters being as 3:2:1. It is obvious that during saponification a molecule containing n acid-radicals will encounter the hydroxyl-ions or hydrogen ions n times as often as if only one were present. It follows that in the saponification of poly-esters, the ratio of the velocity-constants of the individual stages must correspond with that of the acid-radicals present in each stage.
Inversely, the fats can be synthesized from glycerol and the fatty acidb: for instance, tristearin is obtained by heating glycerol with 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 dipcestion of fats is attended by decomposition into glycerol and fatty acid, effected by an enzyme present in the pancn^ar.
155. (Jlycorol is extensively employed in the arts and in n)edi- 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 glycer>'l trinitrate,
CH2O.NO2
CHO.NO2,
CIi20-N02
and not a nitro-compound (68) ; for on saponification with aikalis it yields glycerol, and the nitrate of th(» corresponding alkali-metal.
3 1561 TETRAHYDRIC AND POLYHYDRIC ALCOHOLS. 193
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- tion-mixture is poured into water, whereupon the nitrate separates in the form of an oily, very explosive Uquid 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 m'troglycerine is 1-6. Its metastable form sohdifies 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 (228), 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 crythritol,
CH2OH .CHOH.CHOH.CH2OH,
which is a natural product. It contains a normal carbon chain, since reduction with hydriodic acid converts it into n-secondary butyl iodide, CHs-CHI-CHa-CHa.
Examples of pentahydric alcohols are arabitol and xylitolj C5H12O5, which are stereo isomerides, as are also the hexahydric alcohols dvlcitol and mannilol, C6H14O6, 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.
194 [ORGANIC CHEMISTRY, ' (§§ 167, 158
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 lavulose. The reason for assuming their stereoisomerism is explained in 205, but here it may be pointed out that the polyhydric alcohols contain asymmetric carbon atoms, indicated in the formulae by- asterisks:
CH2OH . CHOH . CHOH . CHOH • CH2OH ;
Arabitol and Xylitol
CH2OH. CHOH • CHOH . CHOH . CHOH . CH2OH.
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 (igi).
IV. DERIVATIVES CONTAINING HALOGEN ATOMS, HYDROXYL- GROUPS, NITRO-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: wlien 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
instance, for while compounds of the type R-CH < ^tt are unknown.
§ 158J CHLOROETHERS AND CHLOROHYDRINS, 195
CI derivatives of the formula R-CH<^ ^ tj are known. These
substances are called chloroethers. When chlorine is passed into ethyl ether, kept cool and in the dark to avoid explosion, the hydrogen atoms are replaced by chlorine. The monosubstitution- product has the constitution
CH3 • CH2 • O • CHCl • CH3,
Monochloroetber
as is proved by the action of sulphuric acid, under the influence of which it takes up one molecule of water, forming ethyl alcohol, acetaldehyde, and hydrochloric acid:
CzHj H CaHfiOH
>0+ ; = + „, CHa-CHCl OH CH3-CH<X' = CHs-CHO+Ha.
Ifonoobloroether KJil
Compounds containing halogen and hydroxy 1 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-hydrins, GUjcvrol dichloruhydrin, CaliaCOIDCl^, is formed when a solution of glycerol in glacial acetic acid is taturated with hydrochloric-acid gas. It has the symmetrical formula
CH2C1.CH0H.CH2C^
since it differs from the dichlorohydrin obtained by addition of chlorine to ally I alcohol, this having the constitution
CH2()H.CHC1-CH2C1.
On treatment of both dichlorohydrins with caustic potash, ejrir
chlorohijdrin,
CH2-CH.CH2C1,
\/ O
is obtained.
DinUr<xompounds with both nitro-groups in union with the
same carbon atom are formed from primary bromo-nitro-com-
pounds by the action of potassium nitrite:
CH3-CHBrN02+KN02 = CH3.CH(N02)2+KBr.
196 ORGANIC CHEMISTRY. [§§159,160
The hydrogen atom belonging to the carbon atom carrying the nitro-groups can be readily replaced by metals, so that 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 compounds 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)j NH2-CH2- (CH2)2'CH2-XH2. The constitution of these substances has been proved by synthesis, pentamethylenediamine being thus obtained. Trimethylene bromide, Br -0112 -0112 -0112 -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 OH2NH2-tiroups (78), with formation of the diamine:
CN CH2NH2
(CH2)3 — > (CH2)3
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:
yCH2'CH2NH2 yCH2*CH2
CHz -NH3 = CHa ^NH.
^CHa-CHjNHa ^CH^-CHj
Pentamethylenediamine Piijeridine
When heated, tetramethylenediamine and trimethylenediamine yield analogous cyclic compounds, but less readily, whereas ethylene- diamine does not.
i6o. A substance, partly amine and partly alcohol, should be mentioned on account of its physiological importance: it is choline^ C6II15O2N, which is widely distributed in the vegetable kingdom. Its constitution is inferred from its synthesis by the
i 1601 CHOLINE AND LECITHIN, 197
interaction of trimethylamine and ethylene oxide in aqueous solution:
(CHs)3N +CH2 -CHz /CHij . CHjjOH
+ \/ -(CH3)3N OHH O \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^ lecithinf present in brain-substance, yolk of egg, many seeds, and* elsewhere. It is glycerophosphoric acid in which the aJcohoJie hydroxyl-groups are esterified by palmitic# stearic, and oleic acid; and the acidic hydroxyl-groups are combined with choline. Various, lecithins are known: some of them probably contain more than one kind of acid-residue in the molecule. The native lecithins are always mixtures.
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-€— OH
I CH,.0-PO(OH)«
the central C-atom being asymmetric.
Lecithin, likewise, is optically active, and may have the formula
CH,OR
CHOR'
I xOH
CHa.O~P:0
^0— CH,.CH,.N(CH,),.0H,
R and R^ being similar or dissimilar acid-radicals.
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 ACIDS.
I. SATURATED* DIBASIC ACIDS, CnHtn-sOi.
i6i. Many isomerides of the acids CnH2n(COOH)2 are theoretic- ally possible, and difTep 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 immediately succeeding thf^m, with an uneven number of carbon atoms, as is seen from the table on next page.
This relation is graphically represented in Fig. 32, which indi- cates that the melting-points of the even and uneven series approxi- mate 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 161]
SATURATED DIBASIC ACIDS, CnH„-/)*
199
colunm of the table. The solubility of the acids with an uneven 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.
|
Nume. |
Formola |
Mclllna- point. |
wHV |
|
COOH.COOH COOH.CH.COOH COOH-{CH,),.COOH COOH.lCH,).-COOH COOH.(CH,)«-COOH COOH.(CH,)>.COOH COOH.(CH,).-aK)H COOH-(CH,>.-COOH COOH.(CH,),.Ct)OH COOH.(CH,),.COOH COOH.{CH,).o.COOH COOH.(CH,)„.COOH COOH.(CH,).,.COOH |
133" 183° 97-5° ISS" 105-5° 140° 108° 134.5° 110° 126' 112° 124° |
||
|
Makmic Bcid |
73.5 |
||
|
Suberic acid |
|||
|
Decamethylpnevficarboxylic acid Dodersmel hy Icned icai^ boxylic acid |
Oxalic acid is a very much stronger acid than its homologuee, as the diasociation-constanta indicate. For oxalic acid I0*jt b
|
im |
J_ |
|
, |
|
|
||||||||
|
— |
h- |
■ — |
— ' |
^rrr |
— |
— |
|||||||
|
L-^ |
|||||||||||||
|
•> |
1 |
— , |
— 1 |
— 1 |
-I |
— |
Pro. 32. -<iitAPHic Rbprbbentation op the Mbltino-pointh or ram Acids C;iH«,-iO,.
about 1000, for malonic acid 16-3, and for succinic acid 0-65: for (he lematning acids it has values which diminish with increase in
203 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).
Oxalic Acid, C2H204,2H20.
162. Between oxalic acid and formic acid there exists a. genetic interdependence: it is possible to prepare formic acid from oxalic, or conversely, oxalic 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 :
KOOC KOOC
H H
KOOC
I +H2. KOOC
The reverse transformation of oxalic acid into formic acid haa already been described (153), 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 calciu.n oxalate by the addition of milk of lime, and finally obtained in the free state by the action of sulphuric acid.
The pnKluction 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 specicis of oxalisj in the form of potassium hydrogen, or calcium, salt. It is sometimes found as a crystalline deposit of calcium oxalate, called raphidesy in plant-colls. It crystallizes with two molecules of water of crj^staUization, which it begins to lose at 30°. On careful heating the anhydrous acid sublimes, but when strongly heated, either alone or with concentrated sulphuric acid, it decomposes into COo, CO, and H2O. The velocity of this decomposition is largely dependent on small di£ferences in the
5 1621 OXALIC ACID. 201
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 :
C2H2O4+O = 2CO2 + H2O.
The oxidation with permanganate accords with the equation
2KMnO, 4-5CaH204 4-3H2SO, =IC^O, +2MnS0, 4- lOCO, -f 8HA
The manganese sulphate formed has a catalytic accelerating action on the process, so that, although the first few drops of permanganate solution are very slovv.y 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 quadroxalates 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 alkali-metals, and are soluble in water. They Are employed in electro-analysis.
A t)rpe of these complex salts is potassium ferrous oxalate, K,Fe(C,OJ„ 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.
PoUusium ferric n?:alat^j^K^FeAC^O^\j yields a green solution, whicE^^ust, therefore, also contain a complex ion, possibly {Te{Cj04\Y'\ Its solution is rapidly reduced by sunlight, in accord- ance with the equation
2K,Fe(CA)s - 2K,Fe(C,04)a+K,a04+ 200,.
202 ORGANIC CHEMISTRY. [SS 163, 164
This property is made use of in the preparation of platinotypes. 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 ammonium oxalate, and one volume 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:
2HgCU H-(NH4)2C,04 =2HgCl +200, +2NH4CI.
The decomposition is much accelerated by the presence of certain fluorescent substances, such as eosin (348).
163. Dimethxjl oxidate is solid, and melts at 54°: it is employed in the preparation of pure methyl alcohol. Diethyl oxalate is a liquid. Both an^ prepared by distilling a solution of anhydrous oxalic acid in the absolute alcohol.
Oxalijl cfUoridcj COCl-COO, 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.
Oxamidcy CONH2-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 acidSj that of oxalic acid being oxamic acid, C0NH2'C00H. It is a crystal- line compound, readily soluble in cold water, and insoluble in alcohol.
Malonic Acid, C00H-CH2-C00H.
164. The constitution of vmlonlc acid is proved by its synthesis from monochloroaoetic acid. When an aqueous solution of potas- sium monociiloroacetatc is boiled with potassium cyanide, cyano-
i 1641 MAWNIC ACID, 203
acetic acid is formed , and can be converted into malonic acid by hydrolysis of the nitrile-group :
fxri ^ CI ^ p-rr ^ C/N ^ pry ^ COOH
^"2 < COOH ^"2 < COOH "* ^"2 < COOH'
Monochloroaoetic 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 monoxide, being converted into acetic acid :
C00H.CH2-iC00|H = 002+ COOH.CHs.
It is found that when a compound with two carboxylrgroups in umon with one carbon atom is heated above its melting-pointf 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 198°, 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- Modiomalonate, a compound of the structure
COOCzHfi CIINa .
COOC2H5
This is proved by treating it with an alkyl halide (iodide), a sodium halide and an ester being obtained :
CzHfill +Na|CH(COOC2H5)2 = C^2H6-CH(COOC2H5)2-f Nal.
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 methylenc-^roup, because, on treatment of the disodio-compound with two molecules of an alkyl iodide, the two sodium atoms are replaced by alkyl, with
204 ORGANIC CHEMISTRY, [{ 164
production of a substance which on saponification is converted into a homologue of maionic acid :
COOC2H6 COOC2H5
C Na2-f2l C2H5 = 2NaI +C(C2H5)2 .
COOC2H6 COOC2H5
It is also possible to introduce two different alkyl-groups into diethyl malonate. Thus, when diethyl monosodiomalonate is treated with methyl iodide, the diethyl ester of methylmalonic acid is formed: on treatment with sodmm this again yields a sodio-com- pound, which is converted by ethyl iodide into the diethyl ester of mcthylcthylmalonic 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, nnd have in common with maionic 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 COo on heating, yielding methyl- ethylacetic acid, identical in constitution with active valeric acid (51), and resoluble into two active components:
COOH COOH
CH3-C»C2H6 = CH3-C»C2H5.
■ •
itOOlH H
MethyleihylnialoDic Valeric acid
acid
The malonic-ester synthesis 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) m 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 licjuid is no longer alkaline. After the alcohol has been distilled off, the residue is treated with
SS 1G5, 1661 CARBON SUBOXIDE AND SUCCISrC ACID. 205
water to dissoh^e 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
CO
It is a gas of very pungent odour, which can be condensed to a liquid boiling at 7*^. With water, it regenerates malonic acid, and may, therefore, be regarded as an anhydride of this acid. The true anhydride,
CH2<^g>0,
analogous to the anhydrides of the higher homologues of malonio .acid, is unknown.
Succinic Acid, COOH.CH2-CH2-COOH.
166. Succinic acid is a crystalline substance, melting at 182^, and dissolving with difficulty in cold water. It is present in amber, in fossilized wood, and in many plants, and can be syn* thetically prepared by the following nietlKxls.
206 ORGANIC CHEMISTRY. [§ 166
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:
(C(XX)2H6)2CH[NaTci]H2C-COOC2H6
- NaCl + (COOC2H6)2CH-CH2-COOC2H6.
In this reaction an ester of ethanetricarboxylic acid is formed; and when heated above its melting-point, the corresponding acid loses CO2, yield'mg succinic acid:
CHg-COOH CHa-COOH [COOlH.CH.COOH ~* CHa-COOH
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 COOC2H6 COOC2H6 COOC2H5
A-CNa -fl2 + NaC.A' =A-C CA' +2NaI.
COOC2H5 COOC2H6 COOC2H5 COOC2H6
A — Hydroceo or alkvl Tetracarboxylic ester
By saponification, and elimination of CO^^ the ester formed is con- verted into the dibasic acid:
COOH COOH
• ,, A.CH.COOH
' , • , A'.CH.COOH ^
fCOOlHfCOOjH
I'nliko calcium oxalate, calcium succinate is soluble in water. A characteristic salt is ferric succinate, deposited as an amorphous, flocculent, brownish-red precipitate by mixing solutions of ferric chloride and an alkali-metal succinate.
§ 1671 ELECTRO-SYNTHESIS OF DIBASIC ACIDS. 207
Electro-synthesis of Dibasic and Other Acids.
167. When the aqueous solution of an ester-salt of a dibasic acid is eiectrolyzed, the metallic ion goes to the cathode, the anion to the anode:
Anion Cation
CaHfiO.OC-CHj.COO K .
Ethyl potasnum malonata
This anion, however, is not stable; after being discharged at the anode, it decomposes into carbon dioxide and C2H600C-CH2 — , and two of these residues unite to form diethyl succinate:
C2H5OOC • CH2 — CH2 • COOC2H5.
By this method it is possible to synthesize the higher dibasic acids from the lower. A high current-dermty is necessary; that is, the number of amperes entering or leaving the electrode per square centimetre of surface. This is attained by employing a very small anode. The concentration of the anions discharged at the anrxle is proportional to the current-strength — the numh>er of amperes — 80 that with a high current-density there is a great numl^er of dis- charged anions at the anode, and these can interact readily.
This synthesis of dibasic acids is an extension of an electro- synthesis carried out long ago by Kolbe. He showed that on electrolysis a solution of potassium acetate yields ethane:
CHa-WO K CH3
CHa-'rOO K ~*. CH3'
Anion Cation
Many other extensions are known: thas, a mixture of a salt of r. monobasic fatty acid and an ester-fsalt yields at the anode the ester of a monobasic acid :
CH3.!CXX)Tv ^ivCKX;. CHj.rHz-aXX'zHs —
state Etnyl potA*nium »uecutate
-^ CHa.CH.rHs.CrxXjH^
208
ORGANIC CHEMISTRY.
[§ 168
Fonnation of Anhydrides.
i68. Oxalic acid and malonic acid do not yield anhydrides (165), while succinic acid, C4H6O4, and glutaric acid, C6H8O4, 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 Ls proved by a determination of the molecular weights of the anhydrides:
CH2— COOlH CH2— COOH
/CH2— COOjH CH2 ,— — H2O
\CH2— colon
CH2— CO.
I >0;
CH2— co^
Succinic aohyclride
/CH2— C0\ CH2 o.
\CH2— CO/
Glutaiic anhydride
Fig. 33. — Spacial Representation of the Bonds between 2-5
C-ATOMS.
S 168) 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, succimmide, \ /NH, lias
CHa-CO'^ 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 readily: 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 ammonia 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 compoimds, 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. 33). The position in space of the C-atoms in a chain of three or more members, and the direction of their affinities, arc represented in the figure.
It is evident that in a normal chain of four C-atoms the affinities at the extremities approach one 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.
0
The figure indicates that for two C-atoms the direction of the affin- ities must undergo a considerable change to render tlie 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 Baeyer (120).
210 ORGANIC CHEMISTRY. [§ 169
n. UNSATURATED DIBASIC ACIDS.
Fumaric Acid and MaleIc Acid, C4H4O4.
i6g. The most important members of the group of unsaturated dibasic acids are fumaric acid and maletc acid, 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 diu'ation of the reac- tion. Fumaric acid is the principal product when the temperature 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 methcxl for the preparation of these acids, and it indicates that both have the same structural formula:
COOH.CH.CH-COOH-H2O = COOH.CH:CH.C(X)H.
OH II
This view of their constitution is support^ 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.CII:CH.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.
$169]
FUMARIC ACID AND MALEIC ACID.
211
A single bond between two carbon atoms may be represented as in Fig. 34 (i68). If the tetrahedra are drawn in full, then the
Fio. 34. Fig. 35.
Single Bond between two Carbon Atoms.
single bond will be as in Fig. 35. If the tetrahedra are free to rotate roimd their conmion axis, isomerism cannot be expected for com- poimds Cafec — Cde/, nor has it ever been observed.
or
Fig. 36. Fio. 37. Fig. 38.
Graphic Spacial Representation of the Double Bond between
TWO Carbon Atoms.
When a double bond is present, then two affinities of each carbon atom come into play, as graphically represented in Figs. 36, 37, and 38. Free rotation of the tetrahedra relative to one another is then no longer possible.
The figures indicate that difference of grouping depends on the poeition of the groups a and b of one tetrahedron with reference to
212 ORGANIC CHEMISTRY. [§170
the similar groups a and b of the other, a may be over a, and b over b, as in Fig. 37 : or a may be over 6, and b over a, as in Fig. 38. This can be represented by the formulae
a—C—b a—C—b
II and II .
a—C—b b—C—a
Thus, the two crotonic acids would be
CH3 — C — H H — C — CIi8
II and II
H— C— COOH H— C— COOH
Traru Cit
and fumaric and maleic acids would have the formulae
COOH— C— H H— C— COOH
I. II and II. II
H— C— COOH H— C— COOH
Tran* Cia
It must now be proved which of these two formulae 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 as possible. Only in the acid with the cis-formula are the carboxyl- groups represented in a position to interact readily:
H— C— COOIH H— C— CO
>0.
H— C— CO
OH H— C— CO
Maleic acid Maleic anhydride
From this it is inferred that fumaric add has the constitution indi" caied in formula I., and makic acid thai in formula II.
170. Further consideration indicates that this view also accounts for the other kno\Mi 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 asymmetric carbon atom, is to be expected. Fumaric acid and maleic acid do, in fact, display great differences in these physical properties.
51701
FUMARIC ACID AND MALElC ACID,
213
Both fumaric acid and maieic acid combine with bromine, but the dibromo-addition-products thus obtained are different. Fu- maric acid yields dibromosuccinic acidy soluble with difficulty in water; and maleic acid laodibromosiuxnnic acid, much more readily soluble in water. Figs. 39 to 42 indicate that different acids must result from this reaction. Figs. 40 and 42, representing^ dibromo-
HOOC
H
HOOC
+ aBrss
CO-OH
CO*OH
Fia. 39. — Fumaric Acid.
CO-OH
Fia. 40. — Dibromosuccinic Acid.
COOH
+ .2Br
COOH
Fia. 41. — Maleic Acid.
j^:^^^ CO-OH
Fig. 42. — isoDibromosuccinic Acid.
fluccinic acid and isodibromosuccinic acid respectively, cannot be made to coincide by rotation; and this is made more evident by •comparing Figs. 42 and 43. The latter is obtained from Fig. 40 by 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 iso-acid 18 H, Br, COOH from left to right: for the lower carbon atom of
214
ORGANIC CHEMISTRY.
[§170
dibromosuccinic acid (Fig. 40) the order is similar, but for the upper carbon atom it is from right to left.
When HBr is removed from dibromosuccinic acid (Fig. 43), 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
— HBr =
CO.OH
Fig. 43. — Dibromosuccinic Acid.
CO-OH
COOH
Fig. 44. — BromomaleIc Aciow
HO-OC
— HBr =
CO-OH
CO OH Br Br
Fig. 45. — ?soI)inRoMosuc'aNic Acid. Fig. 46. — Bromofumaric Acid.
in the position shown in Fig. 40: rotation roimd the vertical axis is essential to bring H and Br into ** corresponding" positions, as in Fig. 43: elimination of HBr produces the acid represented in Fig. 44. This acid readily yields an anhydride, since the COOH- groups are in the corresponding positions: it is therefore bromo* makic acid.
if in, 172] FUMARIC ACID ASD MALtlC ACID. 2l"»
When HBr is removed from iikxiibromi^succir.x* ioii. n?pre- sen ted in Fig. 45 (obtainable from Fi^. 42 by n>tat:oi: in rh^ same way as Fig. 43 from Fig. 40). an acid resuks which doe? noc yield a corresponding anhydride, but is convened by ellni:nj.::>;:; of water into the anhvdride of bromomaleic acid. This beha\~iv»ur resembles that of fumaric acid, which under the same conditioR5 yields maleic anhydride. This acid musi therefore be 6ri>»nt>- Jumarie acid (Fig. 46).
It follows that the constitution assumed for these acids on stereochemical grounds accounts for their chemical propenies. Another example which also supports this explanation is men- tioned in 194.
171. Maleic acid can be convertcnl into fumaric acid by keopini! it for some time at a temperature above its melting-point; by bringing it into contact with hydrogen haliiles at on.linary 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 bv other means. The facilitv of all these decom- positions indicates that maleic acid is the unstable, and fumaric acid the stable, modification. Inversely, fumaric acid is con- verted by distillation into maleic anhydride. Fumaric acid is also converted into maleic acid by the action of ultraxnolet light.
AflSnity-constants of the Unsaturated Acids.
172. Like the monobasic unsaturated acids (135), the dibasic unsaturated acids have grcat(?r affinity-constants than the corn^- sponding saturated acids. For succinic acid, 10*fc=0*665, and for fumaric acid, 10*fc=9-3. The strength of acetylenedicar- boxyh'c acid, COOH-ClEC-COOH (obtained by the interaction of alcoholic potash and dibromosuccinic acid,
COOH-CHBr— (^HHr.COC)H),
is about equal to that of sulphuric acid. Thus the presence of a double bond, and even more of 11 triple bond, intensifies theacidir character. For maleic acid \0*k = \l7, or about twelve times :is
216 ORGANIC CHEMISTRY. [5173
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 H,A first yields 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 id 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 vice-versa.
This phenomenon is readily 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 close together. Other negative groups produce a similar effect (178 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'-residuc. 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 less resistance, and therefore takes place more readily.
Dibasic Acids with more than one Triple Bond.
173. Von Baeyer 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 CO,:
KOOC.C^C.fCO^lH = CO,-hKOOC.C=CH.
174J POLYBASIC ACIDS. 217
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 diacetylencdicarboxylic acid^
KOOC -C^C--C^C .COOK.
The potassium hydrogen salt of this acid also loses CO2 readily, and the copper derivative of the monobasic acid thus formed is converted by similar oxidation into CuO and the potassium salt of tetrorocetylenedicarboxylic acid :
2K00C.C^C.C=Ccu* -> KOOC.C=C.(SC.C^C.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 unknowTi, except as esters. The triethyl ester of methanetricarhoxylic acid is obtained by the action of ethyl chloro- carbonate (263) on diethyl monosodiomalonate:
C2H5OOCICI -f Na|CH(COOC2H5)2 = C2H500C.CH(COOC2H6)2.
Kkhyl chlorooarbonate
Whea this ester is saponified, CO2 is simultaneously eliminated, malonic acid being 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 synthesc^s of a few of the polybasic acids will afford examples of the methods adopted for the preparation of compounds of tliis class.
A type of the tribasic acids is apa'-propanetricarboxylic acid, or tricarballylic acid, obtainable by several methods.
1. From tribromohydrin by treatment with potassium cyanide, and hydrolysis of the tricyanohydrin thus formed:
CH2— CH— CH2 CH2— CH— C:H2 CII2 CII 0112
Br Br Br "" CN CN CN "^ COOII COOH COOH.
* cu = JCu.
218 ORGANIC CHEMISTRY. U 174
2. From diethyl disodiomalonate and ethyl monochloroacetate:
(C2H600C)2C[Na2+2Cl CH2 • COOC2H5 =
_ C2H500C^p^CH2'COOC2H5 rtXT^pi " C2H600C^^^CH2.COOC2H5'^'^^^^*-
On saponification of this ester, an acid is obtained which on beating loses CO2, with formation of tricarballylic acid:
CH2-C00H CH2-C00H
' ' CH2-C00H CH2-C00H
A synthesis p?:*uliar to the polybasic acids consists in the addition of ethyl monosodiomalonate to the esters of unsaturated acids, such as fumaric acid:
NaCH.COOCzHfi Na CH.COOC2H5 I
I +11 = CH.COOC2H5
HC(COO02H6)2 CH.COOC2H5 I
CH(COOC2H5)2
Saponification, with subsequent elimination of CO2, yields tricar* ballylic acid. It melts at 1G6°, and dissolves readily in water.
Aronitic acid, melts at 191°: it is a type of the unsaturated tribasic acida. It is obtained from citric acid (197) through removal of water by heating. The constitution of aconitic acid is
CH=C CH2
COOH COOH COOh'
for on reduction it is converted into tricarballylic acid.
SUBSTITUTED ACIDS.
I. HALOGEN-SUBSTITUTED ACIDS.
175. The halogen'SubstUuted 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 directly 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 hydn^en halide or halogen to the unsaturated acids, or by the action of phosphorus halides on the hydroxy-acids. The iodo- ackls can sometimes be advantageously obtained from the corre- sponding chloro-derivatives by heating them w ith potassium iodide.
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 on next page of dissociation-constants, lO^k. This table indicates that the strength of an acid is increased to a greater extent by chlorine than by bromine, and by bromine than
219
220
ORGANIC CHEMISTRY.
[8176
|
• Name. |
Formula. |
10«ib. |
|
Acetic acid |
CH,.CO,H CH,Cl.CO,H CH2Br.C0,H CH,I.C(),H CHCU.COjH CCla.COaH CH5.CH2.CH,.CO,H CHr..CH,-CHCl.a),H CHs-CHCn-CHt-COtH CHiCl-CIU-CIIt.COjH |
0.18 |
|
Monochloroacetic acid |
15.5 |
|
|
Monobromuacetic acid |
13.8 |
|
|
Monoiodoacetic acid |
7-5 |
|
|
Dichloroacetic acid |
514 |
|
|
Trichloroacetic acid |
12100 |
|
|
But vric acid |
0*152 |
|
|
a-Chlorobutvric acid .' |
13*9 |
|
|
6-Chlorobut vric acid |
0*89 |
|
|
Y-Chlorobutvric acid |
0-3 (CO.) |
|
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 /3-iodopropionic acid lO^fc is only 7 times as gR^at as for propionic acid.
The influ(*nce of the carboxyl-groups upon the halogen atoms is such tliat the properties of tJie nionoJuilogen-subsiUiUed acids depend ch'wjhj upon the relative 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 hvdroxvl:
CH,,('IOOOH+KOH = KCI+CH2OH.COOK.
Monochloroacetic acid Potaiwium gly collate
On similar treatment, the /?-halogen -substituted, acids loee hydrogen halide, with formation of unsaturated acids:
CIl3.(^H(1.('H2-COOH = CH3-CH:rH.rOOH + HCl.
,?-(''hl'»roljutyric acid (Yotonic acid
The lK»haviour of the ;?-halogen-suhstituted acids with sodium carhoiiiit:? is vcrv characteristic. Wlu^ii thov are warmed with it.s a'iii.'M)i> s:)hiti(?n, hydrogen halide and CO.. are simultaneously eliminated from tiie molecule, with formation of an unsaturated hvdrocarlyon :
CHj.CH.CHiCOjNa = CH,.rn:CH.CH,+ NaBr + CO,.
• I ptetM^Uutyleue
Hi--. J (
H 177, 1781 HALOGEN-SUBSTITUTED ACIDS. 221
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 • ^O
I
Br H-0
i
Valerolaotone
Chloroacetic Acids.
177. MonocfUoroacetic acid, CH2C1-C00H, is obtained by the action of chlorine upon acetic acid, in presence of sulphur as a chlorine-carrier. It is a crystalh'ne solid, melting at 63°. Di- chloroacetic acid, CHC12-C00H, a liquid boiling at 191°, and trichloroacetic acid, CCla-COOH, 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-|C02|H = CCI3H + CO2.
This is another example of the fact that " loading '' a carbon atom with negative elements and groups ren(l(»rs 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 halogen atoms in the molecule. Addition of halogen to an unsaturated acid produces a compound with the halogen atoms linked to adjoining carbon atoms.
The elimination of hydrogen halidc from acids of this class affords a striking example of the value of stereochemistry in explaining phenomena for which the ordinarj' constitutional formula? are unable to account. Among them is the fact that in the series of unsaturated acids the dibromide of one modification loses 2HBr v(?r>' readily, yielding an acid with a triple bond, while the dibromide of the other modification either does not react thus, or only with difficulty. An example of this is afTordod l)y (*nicic and brassidic acids, which have been proved, by the method indicated in 140, to have the constitution
C\Hw-CH:(^H.Cnn,,.COOH.
When heated with alcoholic potash at 150°- 170**, dibromoerucic acid, obtained by addition of bromine to erucic acid, readily loses 2HBr,
222
ORGANIC CHEMISTRY.
18 178
yielding befienoUc acid, CgHiT-C^C'CnHjrGOOH; 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 trdns-foTmula. to erucic acid and the m-formula to brassidic acid, as indicated in Figs. 47 to 52.
CfHiT
+ Br,
CiiHa-OOtH
Fig. 47. — Erucic Acid, Trans-formula.,
CtHiT
Rotated
CnH„O0,H
Fig. 48. — Dibrjmoerucic Acid.
CaHji
CiiHsfCO,H
Fig. 49. — Dibromoerucic Acid.
Each H-atom in corresponding position to a Br-atom.
In the formula for dibromoerucic acid, the tetrahedra may be rotated so as to bring each Br-atom alx^ve a 11-atom (170), making the elimination of 2HBr possible (Figs. 4S and 40): in that for dibromobrassidic acid, only one Br-atom and one H-atom can be brought into the ** corresponding positions *' to one another (Figs. 51 and 52).
1791
MONOBASIC HYDROXY 'AC IDS
223
CtH„
+ Br, =
CnHaCO,H
Fia. 50. — Brassidic Acid. Ci«-formula.
C.II„
Uotuted
CnHjjCOaH
FlQ. 61. DlBROMOBR.\SMlDIC AciO.
CuH^COiH
Fig. 52. — Dibromobrassidic Acid.
Only one H-atoni in corresponding position to one Br-atom.
II. MONOBASIC HYDROXY-ACIDS.
179, The hydroxy-acids are sul)stances witli one or more hydroxyl-groups and carboxyl-gronps in the molecule. The general methods for their formation dei>end upon the introduction of hydroxyl-groups and carboxyl-groups. Tliey are pnxluced in the following reactions.
1. By the careful oxidation of polyhydric alcohols:
CHa-CHOH-CH^OII -♦CHa.rHOH.rOOH.
Propyleneiclycol Luct ic acid
2. By replacement of tlie halogen in halogen-Hubstituted acids by hydroxyl, as already described (150).
224 ORGANIC CHEMISTRY. [§ 180
3. By reduction of the aldehydic acids and ketonic acids, which, contain both a carboxyl-group and a'carbonyl-group:
CH3-CO.COOH+2H = CHs-CHOH-COOH.
Pyroracemic acid Lactic acid
4. By the action of nitrous acid upon acids with an amino-group- in the aikyl-residue:
NH2-CH2-COOH+HN02 = CH2OH.COOH + N2 + H2O.
Glycine Glycollic acid
5. By addition of hydrocyanic acid to aldehydes or ketones,, and hydrolysis of the nitriie thus obtained (loi.. 3), a method yield-^ ing only a^hydroxy-acids:
C„H2„+i.CH0+HCN = C„H2b+i-C^CN;
Aldehyde \0H
CyaDohydrin
/H /H
CnH2„+i.Ct-€N+2H20 = C„H2„+i-C^C00H+NH3.
\0H \0H
Cyanohydrin a-Hydroxy-acid
By exchange of Br for OH, acids brominated by the method de- scribed in 175 yield hydroxy-acids identical with those obtained hy this cyf I nohydrin'Sifntfiesis. . It follows that in these acids the bromine is in union with the a-carbon atom.
6. Oxidation with potassium permanganate effects the direct replacement of hydrogen by hydroxyl in acids with a hydrogen atom linked to a tertiary carbon atom:
^Jj3>cH.C00H+0 = ^23>c(OH).COOH.
isoButyric acid a-Hydroxyt«obutyric acid
Properties.
180. Different compounds are obtained from the hydroxy-acids* by substitution in the hydroxyl-group and carboxyl-group respect- ively. When the H-atoin of the hydroxyl-group is replaced by alkyl, an acid ether is obtained :
ciioOii .cooH -> cn20c^H5.rooH.
Glycollic acid EthylglycoUic acid
1801
MOSOBASIC HTDROXYACIDS
2^2,">
Like an ordinary ether, CnHsn+i-O-CmHini-i. ethylglycollio aokl cannot be saponified. When, on the other hand, the H-atom of the carboxyl-group is exchanged for alkyl. an ester is produced:
CH2OH -COOH — CH2OH . axx\>H5.
Like other esters, these compounds can be saponified.
The introduction of hydroxyl strengthens the fatty acids to an extait 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 dis^sociat ion- constant, 10*A:, for several acids.
|
Name. |
Formula. |
|
Acetic acid |
CHs-CCX>H |
|
Olycollic acid (Hydroxyacetic acid) Prooionic acid |
CH,OH.aX)H CH,.CH.-CXX)H |
|
Lactic acid (a-Hydroxypropionic acid). . jS'-HvdroxvDroDionic acid |
CH,.GHOH.a)OH CH20H.CH..(XK)H |
10*4.
0.180
1.52
ihVM
1.38
0.311
On heating, the a-hydroxy-ncids readily lose water, two mole- cules being simultaneously eliminated irom two molecules of acid: this reaction takes place between the hydmxyl-group of one mole- cule and the carboxyl-group of the other. Lactic acid yields lactide:
CH3-CH|0HH|00C
COOHHO— CH.CH3
= 2H2O +
CHa.C'II.OOr
COO— rn-nia.
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 asters, itis sajxmified, yielding lactic acid. P-Hydroxy-acids readily give up water, with formation of un- fiaturated acids:
CH3-CH.CH.COOH
[oIThI
^-Hydroxybutyrio acid
= H20+CH3.rn:CH-rOOIL
C^^r>torlio acid
226 ORGANIC CHEMISTRY. [55181,182
When a i9-hydroxy-acid is boiled with excess of a 10 per cent, solution of caustic soda, it is partly converted into an aj9-unsaturated acid, and partly into a /^T-unsaturated acid, while a portion remains unchanged. An equilibrium is thus reached:
R.CH:CH.CH,.CXX)H ^ R.CHa.CHOH.CHj.COOH ^
^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-acids and o-hydroxy-actds lose water, with formation of inner anhydrides, called lactones (176 and 185-186) :
CH2*CH2*Cxi2*CO CH2*Cxi2*CH2*CO.
I ^1 =H20+! I
p! HJO 0
r-Hydroxybutyrie acid Butyrolactone
Glycollic Acid, C2H4O3.
181. Glycollic acid is present in unripe grapes. It is usually pre- pared by treating monochloroacetic acid with caustic potash:
COOH.CH.ICI + KJOH -= C00H.CH,0H + KC1.
Glycollic acid is a crystalline solid, melting at 80°. It is very readily soluble in water, alcohol, and ether: the calcium salt dissolves with difficulty in water. When distilled in vacuOf glycollic acid loses water, with formation of glycoUide :
CH,0|H HO CO CH,O.CO
I , ^1 -2H,0+| I
COO|H HO|CHa a)-0.CH,
GlycoUide
Hydrozypropionic Acids, C3U6O3.
182. Two hydroxypropionic acids are known, differing in the position occupied by the hydroxyl-group: they are a-hydroxypro^ pionic acid J CHa-CHOH-COOH, and ^-hydroxypropionic acid, CH20H.CH2-COOH. The first is ordinary lactic acid,
a-Hydroxy propionic acid can be obtained synthetically by the methods described in 179, although it is usually prepared by other
{ 1821 LACTIC ACID. 227
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, such as ** Sauerkraut "; 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 mm.), 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 (i8o) 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- crvstals with three molecules of water.
The constitution of lactic acid is deduced from its formation from acetaldehyde by the cyanohydrin-syn thesis (i7Q, 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
CH3>CH0[H>C00H ->CH3.Cq+H.C(X)H
This decomposition may be regarded as a reversal of thecyanohydrin- synthesis, and is characteristic of many a-hydroxy-acids.
H
Lactic acid, CHs'C-COOH, contains one asymmetric carbon
OH
228
ORGANIC CHEMISTRY.
[8 183
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- lactic 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 synthetic 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 afforded 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. 53:
CH,
CHs
or
OH
FiQ. 53.
ACETALDKHYDE.
FlQ. 54.
Lactonitrile.
Fig. 55. Lactonitrile.
The addition of H-CN can take place in two ways, the oxygen doubly linked to the central carbon atom of the figure becoming Bevered either from the bond c or from d. In the first case the group CN becomes linked to c (Fig. 54), and a hydroxy 1-group is formed at d: in the second case this is reversed (Fig. 55). The -confiirurations thus obtained are mirror-images, and cannot be made to coincide: they represent asymmetric C-atoms.
Tlie 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
184] LACTIC ACID, 229
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 oddfi^iow-reaction. An example of the formation by subsiiitdioii of a compound containing such an atom is that of a-bromopro-
pionic acid, ^ ^^'^COOH' "^ propionic acid, jh^ COOH
By replacement of He and Hd respective!}, 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 cf methyl-
CH H
ethylacetic acid,p t? ^^^rooH' ^^^^ niethylethylmalonic acid,
c
?H ^^^COOH' ^y '^^^ ^^ ^^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 other optically active substances arc strongly heated, they are converted into the corresponding optically inactive form, containing equal propor- tions of the dextro-modification and la^vo-modification. This necessitates the conversion of one-half of the optically active sub- stance into its optical isomeridc, it lx?ing sufficient that two of the groups or atoms linked to the asymmetric C-atom should change places. To convert Fig. 56 into its mirror-image. Fig. 57, it is only
Fig. 60. Kk;. 57.
necessary, for example, for B and D to exchange positions. This can only happ>en through a soveniiu*" of the bonds l)etwoen B and I) and the carbon atom, for a peri ex I how(»ver brief, followed by a n'union,
230 OROANIC CHEMISTRY. [§ 186
either as at first B to 6 and D to d, or in the reverse order D to 6 and B to d. The similarity of the positions occupied by b and d with respect to a and c makes the probability of the union of B with b and D with d equal to that' of the union of D with b and B with d, so that dextro-rotatory and laevo-rotatory molecules are formed in equal numbers, and after heating the substance is optically inactive.
Optical inactivity is sometimes attained without the aid of heat. Walden found that the dextro-rotatory i^obutyl bromo propionate, CHa-CHBr-C00C4Hu, and other compounds with a Br-atom in union with an asymmetric C-atom, became optically inactive through being kepc 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 ver}' readily, with forma- tion of lactones (176 and 180). So great is this tendency that some ;'-hydroxy-acids, when lil)erated 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 (168). Many ^'-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 r-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 /Opposition or ;'J-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.CH:CH.CH2-C0 -> R-CH-CHj-CHz-CO.
H
•i I A
§186] LACTONES. 231
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,.Cq+h,c.cooh ch,.c5hc.cooh
H,C.COOH " f^ ^r mofHl
Aldehyde Succinic acid | n^K;»KAJKJ\ n | .
By elhnination of one molecule of water, there results a iactonic acid,
CHa.CH.CH.CO,H
I
O— CO On dry distillation, this loses CO,, yielding the unsaturated acid:
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 £-lactonos are also known.
186. On boiling with water, the lactones aro 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 iieid and lactone -h water:
CH20H.CH2-CH2-COOH?±CH2-CH2.CH2.CO-fH20.
T-Hydrozybutyric acid I
Butyroiactone
If the molecular concentration per litre of the ^--hydroxy- butyric acid is A, and if, after the lapse of a time /, -r molecules have been converted into lactone, t^e velocity of lactone-forma- tion at that instant, s, is given by the equation.
2:J2 ORGANIC CHEMISTRY. [§187
k ho'\ni\ the reaction-constant. But the reverse also takes place, the acid being regenerated from the lactone and water. If the lactone is dissolveil in a large excess of water, no appreciable error is in- tHxiucwl by assuming the quantity of the latter to be^ constant. The velocity s' of this reverse reaction is then represented by the equation
hi which k' is again the reaction-constant. The total velocity of tho laotoiu^formation for each instant is, therefore, equal to the dilTorence between these velocities:
s-s'==^=A:(A-a:)-A:'a: (1)
When equilibrium is reached, s=s'; and if the value of x at this point has become equal to xi, then
A:(A-a:i)-A;'a:i=0, or ^^-J^^-. ... (2)
At A—Xi
Equations 1 and 2 can be solved for k and k'. 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 well as with water, yielding ;'-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 HTDROXT-ACmS.
187. The simplest dibasic hydroxy-acid is Uxiironic acidj COOH.CHOH.COOH. It can be obtained by tho action of moist oxide of silver upon bromomalonic acid, and is a cr>'8talline solid, melting at IST** with evolution of COa. Tho glycollic acid, CHjOH .COOH, thus formed, at once loses water, jielding a poly- nioridoof glycollido (181).
A substance of gn»ater importance is malic ocirf, C4H605^ which is present in various unripe* fruits, and is best prepared from unripe mountain-ash U^rries. It is a crj'stalline solid, melting at
$1881 MAUC ACID ASD TARTARIC ACIDS. 233
100^, and is readily soluble in water and in alcohol. Natural malic acid is optically active.
It b possible to prove in several waj-s 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 b)*^ the formation of an acetate when its diethvl ester is treated with acetyl chloride.
The conversion of malic acid under the influence of heat into fumaric acid and malelc acid has been already mentioned (169). In addition to the natural laevo-rotator}- acid, both a dextro-rota- tory and an inactive modification are known. The latter can be ' resolved by fractional cr}'stallization 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, C^HeOg.
188. Four acids of the composition C4He06 are known, all with the constitutional formula
COOH.CHOH.CHOH.COOH.
They are called dextro-rotatory tartaric acidy keve-rotaiory tartaric acid, raceniic acid, and mesotartaric acid: the last two are optically inactive. Their constitution is proved by their formation from the dibromosuccinic acids — obtained from fumaric acid or malcic acid by the action of bromine — by lx)iling their silver salts with water, as well as by their production from glyoxal (198) by the cyan o- hydrin synthesis. The inactive modifications are proilucod 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 sten^oisomeridcs are theoretically possible.
With a single asymmetric C-atom then* are two optical isomerides, which can l)e denoted by r^ and l\ (I.). Addition of a second asvmmetric C-atom, which mav 1h» dcxtro-rotatorv or Iffivo-rotatory, produces the combinations II. of the subjoined scheme. Increase in the numl)er of (*-atoms to three gives
234 ORGANIC CHEMISTRY. (§189
similarly eight isonicrides (III.)- It is evident that for n asym- metric C-atoms the number of possible isomerides is 2":
I. r, h
II. rir2 riZa l\r2 hk
III. rir2r3 rjr^^ ril2r3 riWa hr2r3 lir2h hhrs IMs. 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 group3, lir2 and ^2^1 become identical, leaving so far three isomerides possible. rir2 and Z1/2 lx»ing able to unite to form a racemic compound, the total numlx»r of possible isomerides is raised to four:
12 3 4
CH(OH)(COOH) Dextro Dextro Laevo jj^^^j^j^^ ^^^^^^
CH(OH)(COOH) Dextro Lavo Lavo tion of rir2 and /iJjj
The four tartaric acids, C4H6O0, correspond in properties with the four theoretically possible isomerides. Dextro-tartaric acid and laevo-tartaric acid must be represented respectively by 1 and 3, since in these lK)th 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 resolvwl 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 hevo-acid.
189. Emil FiscHKit has mtroduced a simple mode of writing the spacial formula? of optically active compounds, of which frequent
1 1891
TARTARIC ACIDS.
235
use will be made later. The representation in space of two C-atoms
Cabc iti union , in a compound | , is shown in Fig. 58 (i68) .
Cabc
0
b Fig. 58. Fig. 59.
If the tw^o bonds uniting the two carbon atoms are supposed to He in the plane of the paper, then the positions of a and c are to the back, and of b to the front. If a, 6, 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:
b
a c
a c
a
c 6
c 6
b I.
a
II.
If Fig. 58 is rotated round its vertical axis, so that a, for example^ lies in front of the plane of the paf)er, Fig. 59 results, its projection lx?ing repre- sented by II. These apparently different configurations are identical.
For a chain of four carbon atoms there is obtained analogously the projection-figure
236
ORGANIC CHEMISTRY.
IJ190
This will be understood if it is imagined that the figures in i68 (Fig. 33) art* so placed that the plane in which the carbon bonds lie is at right angles to that of the paper, and the figures in thiB position are projected in the manner just described.
190. Tlie 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 ISO^ in the plane of the paper, the similar grouping of HO, H, and COOH about the asymmetric C-atoms in both halves,
Ha
-H and Ha
■H,
COOH COOH
indicates that both C-atoms rotate the plane of polarization in the same direction. We shall arbitrarily assume that this grouping Decisions 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-
OH
-H
COOH •results, and is therefore the projection-formula for the dextro- rotatory acid.
The grouping with respect to the two C-atoms in the tevo- rotatory acid must be the mirror-imaie of that in the dextro- j-otatorj' (48) : thus.
n-
-OH ami H-
■OH.
COOH
COOH
5 1901
TARTARIC ACIDS.
237
The combination of these two gives the projection-formula
Ha
H-
COOH
-H -OH
COOH
for the laevo-rotatory acid.
These representations of the constitutions of dextro-tartaric acid and laevo-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 tevo-rotatory C-atom, as in mesotartaric acid, the arrangement of the groups will be
Dextro
Ha
■H
COOH
Ljevo
H-
■OH,
COOH
and their projection-formula
Ha
COOH
Ha
■H ■H
COOH
♦ These projection-formuliB can he 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 formulae cannot be made to coincide by this treat- ment. To determine by means of projection-forniu'a; whether this is possible for spacial formuls, it is only admissible to trans[K>se them in the plane of the paper.
23S
ORGANIC CHEMISTRY.
191{
The projection-formula for racemic acid is
Dextro
COOH
H- HO-
OH
■H
COOH
LflBVO
COOH
HO
H-
-H
OH
COOH
Dextro-tartaric Acid.
191 • Fotassium hydrogen d'iartrate, C4H5O6K, 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 dextrc tartaric acid, the crude argol is boiled with hydrochloric acid, and the acid precipitated as calcium tartrate, CaC4H406, 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 bro\vn, with production of a caramel-like odour, and at a still higher t^m* perature chars, with formation of pyroracomic acid (231) and pyrotartaric acid, C00H.CII(CH3).CH.j.C()()H. It can 1>- converted into succinic acid by the action of certain bacteria.
In addition to the potassium hydrogen tartrate may be men- tioned the rwrmal potassium salt, C4II4OGK2; which is readily soluble in water, and potassium antimotiijl tartrate,
2[C00K . CHOI I'Vl lOH • COO (8bO)] + H2O.
On account of its medicinal properties, the latter is known as "tar- tar (»inctic." It is obtained by boiling potassium hydrogen tartrate with antimony oxide and water, and is readily soliil)le in water.
J 1911
TARTARIC ACIDS.
239
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 compoimds, since reducing agents precipitate yellowish-red cuprous oxide, or its hydroxide, from the dark-blue solution. In this alkaline copper solution the hydroxyl- groups of the central C-atoms have reacted with the copper hydroxide, since one gramme-molecule of normal alkali tartrate can dissolve one gramme-molecule of copper hydroxide. These copper alkaU 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.
0-CH.COONa
Experiment has proved that in aqueous solution this compound
is ionized to Na* and the complex anion Cu < • . First,
O.CH.COO'
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.
60. One U-tube contains copper-sulphate solution at 6; the other.
Fig. 60. — Electrolysis of an Alkaline Copper Solution.
Pehling's solution at d: 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 copper-sulphate solutions in the two U-tubes lie in the same horizontiil plane. When an electric current is passed through the tubes, preferably arranged in parallel.
240 ORGANIC CHEMISTRY. § 1921
and not in series, a different effect is produced on the level erf the surfaces pi tha copper solutions in each tube. In the copper-sulphate solution a rise takes place at the cathode, since the Cu-ions are cathions, 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- pared as required. Ost has discovered a much more stable alkaline copper solution, applicable to the same purposes as that of Fehling. 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.
Lcovo4artar{c acid is obtained from racemic acid. With two exceptions, the properties of the IsBVO-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 Acid.
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-morlification ani laevo-modification in equal proportions. This change is often facilitated by the presence of certain substances: thus, dextro- tartaric acid is readily converted into racemic acid by l)oiling 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 la^vo-modification. If formula I. represents the dextro-acid, then formula II. will correspond ^\'ith the la»vo-acid; and the formulae indicate that the exchange of groups, by which an
S193]
TARTARIC ACIDS.
241
active compound is converted into its optical isomeride (184), must in this instance take place at both asymmetric Oatoms, in order that the dextro-acid may jrield its laevo-isomeride.
H- HO
COOH
-OH H
COOH I.
HO-
H-
COOH
•H -OH
COOH 11.
Racemic add is not so soluble in water as the two optically active acids, and differs in crystalline form from them: the crystals have the composition 2C4H6O6+2H2O. 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 C4H6O6; and the vapour-density of its ester \vith single, instead of with double, molecules.
The term ^^ racemic *' is applied to substances which consist of isomerides of equal and opposite rotatory power in equi molecular proportions, and are therefore optically inactive. This phenom- enon was first observed by Pasteur in his researches on racemic acid (195).
Mesotartaric Acid.
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).
242
ORGANIC CHEMISTRY.
[§193
If formula I. is assigned to dextro-tartaric acid, it is evident that to convert it into mcsotartaric acid, formula II.. it is only necessary
COOH COOH
H-
HO
OH
-H
CCX)H I.
HO-
HO-
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
COOH
20 H
CO'OH
Fig. 61. — MaleIc Acid.
COOH H
or
CO-OH
CO*OH
CO-OH
OH
Fia. 62.— Mesotautaric Acid. Fig. 6.'^. — Mesotartaric Acid.
groups linked to both C-atoms. This affords an explanation of the fact that when dextro-tartaric acid is heated with dilute hydrochloric
§194]
TARTARIC ACIDS,
243
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 maleic acid (169), which, on treatment with a dilute aqueous solution of potassium perman- ganate, yield respectively racemic acid and mesotartaric acid by addi-
HO-OC
+ 2 (OH),
CO-OH
Fig. 64. — Fumaric Acid.
H HOOO
CO-OH H^- — -i- ':\CO'OE,
h"^ oh
Fig. 60. — Racemic Acid.
tion of two hydroxyl-groups. Addition of 20H to maleic acid may result from the severance of the bond 1:P or 2:2' in Fig. 61, with production of the configurations represented in Figs. 62 and 63* The projection-formulae corresponding with Figs. 62 and 03 arc
244
ORGANIC CHEMISTRY.
l§194
H
OH
HO
HO
■COOH H-
and ■COOH H-
H I.
-COOH
<X)OH
OH II.
These apparently difTerent configurations are ideniicaly as becomes evident on rearranging I. (p. 235) :
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 11. 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 hydroxyl-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. 64 and 65.
Severance of the bonds 1:1' or 2:2' by addition yields two con* figurations which cannot be made to coincide by rotation. This i made clearer by the projection-formulae
COOH
COOH
Ha
H
HO-
HO-
■COOH
H-
H OH
H
■OH
COOH COOH
OOOH- H-
-H COOH
H- HO-
OH •H
OH
COOH
3 195] RESOLUTION OF RACEMIC SUBSTANCES. 245
These projcction-formulap are identical with the configurations repre- senting dextro-tartaric and la?vo-tartaric acid (p. 238).
I^cemic Substances, and their Resolution into Optically Active
Constituents.
195. Optically active isomerides 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- 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 laevo-salt: these can be mechanically sep- .arated. Pasteur effected this for sodium ammonium racemate, 'C8H80i2Na2(XIl4)2;2H20. Crystals of the dextro-tartrate and laevo-tartratc are only obtained from this solution at temperatures below 2S°, the transition-point for these salts C' Inorganic Chemistry/' 70) :
2Na(NH4)C4H406 • 4H2O ^ CgHgOi 2Na2(NH4)2 • 2H2O +6H2O.
Dextro- + lffiVO- Na-NH4-tartrat« Na-NH4-raoemate
Fig. 66 represents the crystal-forms of the two tartrates, the •difference between them being due to the positions of the planes ■a and b. 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 cr>'stal of another substance isomorphous with only one of the components. By thus inoculating a supersaturated solution of sodium ammonium racemate with ^-asparagine (243), von Ostromisslensky isolated sodium anmionium dextro-tartrate in crystalline form.
246
ORGANIC CHBMJUTRY.
HIM
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 & Iffivo- acicf 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 configxirations which are mirror-imagea. But it is otherwise when the dextro-acid and the lievo-acid are united with an optically active (for example, a dextro-rotatory) base: the configurations of the sait-molecules are then no longer mirror- images, and identity of physical properties must of necessity cease.
Racemic acid can be thus resolved by means of its cinchonine salt, since cinchonine Ifevo-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.
|
/ |
^ ^ |
>
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 arc not esterified at the same rate, since the compounds formed arc no longer mirror-images of one another. Marckwald found thai whoii ran-mic miindelic aciil (324), is heated for one hour lit |.V»° with nii-nthol (365}, an active alcohol, the non- PHt^'rificd ;ic)<l is l;i'v<Hn>t!itor\-.
The third method of fission doviscd l.y Pastei-k depends on
§ 196] RESOLUTION OF RACEMIC SUBSTANCES. 247
the action of mould-fungi {PeniciUium glaucum), or of bacteria. Thus, when racemic lactic acid in very dilute solution is treated with the Bacillus acidi Icevoladici, after addition of the necessary nutriment for the bacteria, the optically inactive solution becomes laevo-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-fungus PeniciUium glaucum have been introduced, becomes tevo-rotatory, the fungus propagating itself with decomposition of the dextro-rotatory acid.
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.
196. 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 lajvo- 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 under certain conditions.
The third possibility is also analogous to the crystallization of salt-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 crya- tola; and optical isomerides produce pseudoracemic 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
248 ORGANIC CHEMISTRY, [§197
is afforded by sodium ammonium racemate (195). 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 laevo-rotatory body. If now the solid dextro-compound or laevo- 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, although the solution was saturated in the first instance with regard to this, it is unsaturated with re- spect to the two optically active modifications: addition of the solid dextro-rotatory or IsBvo-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 pseudoracemic mixed crystals.
IV. POLYBASIC HYDROXY-ACIDS.
197, Of these acids it will be sufficient to describe the tribasic citric acid J CqHsOj, 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 s}Tithetically by a method prov- ing its constitution. On oxidation, symmetrical dichlorohydrin, CH2C1«CH0H.CH2C1 (158), is transformed into symmetrical di- chloroacetone, CH2CI • CO • CH2CI. The cyanohydrin-synthesis con-
§197] CITRIC ACID. 249
/OH verts this into CH2C1«C^CH2C1, and hydrolysis yields the hydroxy-
\CN
yOR acid, CH2C1-C;— CH2CI. On treatment of this compound with
\COOH
potassium cyanide, a dicyanide is formed, which can be hydro-
lyzed to citric acid:
CH2-CN CH2.COOH ' .OH _A^OH V^COOH"*V COOH • CH2-CN CH2-C00H
The alcoholic character of citric acid is indicated by the forma- tion of an acetyl-compound from triethyl 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.
DIALDEH YDES AND DIKETONES : HALOGEN-SUBSTITUTED
ALDEHYDES AND KETONES.
Dialdehydes.
loS* Tlio simplest member of the series of dialdehydes, glyoxal,
W « ^HMubination of two aldehydo-groups, q^C — C^q. It is best
l^vj^utnl by carefully floating a layer of water on the surface of .nH\u»H »»itrlc acid contained in a tall glass cylinder, and pouring i^l^\l nirohol on the surface of the water, care being taken that I ho h^yiTs do not mix. The nitric acid and alcohol diffuse intj i\\v wntor; and the alcohol is slowly oxidized to glyoxal, glycollic Hvivl, oxalic acid, and other substances.
Tlnm prepared, glyoxal is a colourless, amorphous substance: wht^u moist, it dissolves readily in water, but very slowly after fompK^te drying in vacuo at 110°-120^. It is a polymeride of un- known molecular weight , although its aqueous solution reacts as lliouK*^ Jit contained only simple molecules. Distillation of this' polymeride with phosphoric anhydride evolves an emerald-coloured gtw, <'ondensable by cooling to beautiful yellow crystals, which at u low(T temperature become colourless. They molt 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, yielding oxalic acid, of which it is the dial-
250
5ld9j DIKETONES. 251
dehyde. Treatment with caustic potash converts glyoxal into 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
cS.cS + HaO = CH2OH.COOH,
^ ^ . GlycoUic acid
H H
Succindialdehydef qC«CH2-CH2*Cq, hhs 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 diozonide — is formed,
CH2 • CH • CH2 — CH2 • CH • CH2y
O3 O3
each double linking uniting with one molecule of ozone. 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< + H2O = >CO+OC< +H2O2.
\/ O3
The formation of 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. The diketones contain two carbonyl-groups: their proper- ties and the methods employed in their preparation depend upon the relative position of these groups. 1 : 2-Diketones with the
12 12 3
group — CO • CO — are known : 1:3-d iketones with — CO • CH2 • CO—:
12 3 4
1 :4-d iketones with — CO«CH2'CH2*CO — : and so on.
1 \2'Diketone8 cannot be obtained by the elimination of chlorine
252 ORGANIC CHEMISTRY, [J 20a
from the acid chlorides by the action of a metal, in accordance with the scheme
R.COCl-fNaz+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 CHj- groups being converted into C=NOIL:
R.CO.C
H2 O
.R' R.CO.C. R'
NOH NOH
These compounds are called \sonitrosoketones. When boiled with dilute sulphuric acid, the oxime-group is eliminated as hydroxyl- amine, with formation of the diketone. The ketooMehydes are both
ketones and aldehydes, and contain the group — CO.C<^ : they,
too, can be obtained by this method.
Diacetylj CH3.CO.CO.CH3, 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 chljrinc. Diacetyl boils at 88°, and has a specific gravity of 0.973 at 20°. Its behaviour points to the presence of two car- bony K'^roups in the molecule: thus, it adds on 2HCN, yields a mono-oxime and a dioxime, and so on. The adjacency of the two carbonyl-';roups in diacetyl is proved by its quantitative con- version into acetic acid under the influence of hydrogen peroxide:
CH3.CO— + OH
CO.CH3_^2CH3.CO.OH.
200. 1 '3-Diketones can bo prepared by a condensation-method of general application discovered by Claisex and Wislicenhs. Sodium ethoxide is the condensing agent. An addition-product is formed by the* interaction of this substance and an ester:
The addition-product is th?n brought into contact witii a ketone R'.CO-CHs, two molecules of alcohol being eliminated wrlh forma- tion of a condensation-product:
S 200] DIKETONES. 253.
^ONa
Il«C^
OC2H5 H
CH.CO.R'=R.C<' +2C2H6OH.
On treatment of this compound with a dilute acid, the sodium> atom is replaced by hydrogen. This might produce a compound with a hydroxyl-group attached to a doublyrlinked carbon atom; but usually compounds of this type are unstable, the group OH
— C=±CH — changing to — CO — CH2 — . The principle applies ia
OH the present instance, • yielding a l:3-diketone,
xi • C^i^CH • CO • R
R.CO-CH2— CO.R'.
Claisen has found 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 : 3-diketones is the action of acid chlorides on the sodium compounds of acetylene homologues:
CH3. (CH2\.C^C(NaTci]OC-CH3 -> CHs. (CHj^.C^C-CO.CH,.
Sodio-n-amylacetylene Acetyl chloride
By treating this ketone with concentrated sulphuric acid, water ia- added, and the desired diketone obtained:
CH,-(CH2),.C:^C-CO-CH3-CH3.(CH2\.CO.CH3.CO-CH,. + O Hj
These diketones have a weak acidic character, their dissocia- tion-constants being very small. Among others, that of acetyl-- acetone, CH3-CO«CH2-CO-CH3, has been determined. They con- tain two H-atoms replaceable by metals. These must belong to the methylene-group between two negative carbonyl-groups; for if the other hydrogen atoms could be thus exchanged for metals, there is no reason, since they are of equal value, that two, and only two, should be replaceable.
Acetylacetone is obtmned 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, it decomposes into acetone and acetic acid, a reaction affording,
254 ORGANIC CHEMISTRY, [J 201
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, (CJ^'fi^ij<^f which is sparingly soluble in water; and the volatile aluminium salt, (C5H702)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 acetonylacdonef
CH3 • CO • CH2 • CH2 • CO • CH3,
the preparation of which is described in 233, 4. It is a colour- loss liquid of agrooahle oilour: it boils at 193°, and has a specific gravity of 0« 970 at 21°. Acetonylacetone and other lU-cHke- tones yield cyclic compounds, which are dealt with in 392-396.
Halogen-substituted Aldehydes.
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 60®, and finally to 100°.
The reaction may be explained by assuming that the alcohol is first converted mto aldehyde, which is then transformed into acetal, dichloroacetal, and trichloroacetal: the last compound is
§ 201] CHLORAL. 255
converted, by the hydrochloric acid produced, into chloral alcohol^ ate, CC13'CH<qJ^ ^ Dichloroacetal and other intermediate products of this reaction have been isolated:
CH3.CH2OH+CI2 = CH3-CH<^^jj+HCl - CH3.CQ+2HCI;
Alcohol Aldehyde
cH..cg.|;
SS'"» - CH,.CH<9J;'I'»+HA-
Ut^2ll6 V^2"6
CH3.CH<ggg^^ - CHCl..CH<g^jH5_^
Aoetal Dichloroacetal
Triohloroacetal Chloral alcohoiate
The final product of chlorination is a crystalline mixture of chloral alcohoiate, 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 restoni 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 (230 and 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 :
CCl3-
-h H
^O =CCl3H-hHC\^ . HO ^OH
256 ORGANIC CHEMISTRY. [§201
In dilute sohitions of about centinormal strength, and at low
temperature, this reaction has a measurable velocity. Experiment
has proved it to be unimolecular, and not bimolecular as indicated
by the eciuation. This phenomenon is explicable by assuming
preliminary combination of the base and chloral hydrate to form a
OH salt of the type CCh*CH<Qj^' subsequently decomposed into
chloroform and formate. The electric conductivity of a mixture of solutions of chloral h^^drate and a base also indicates a union of the molecules.
On account of its purity, chloroform prepared in this manner is preferred for anae-sthetization.
The formation of chloroform from chloral by the action of alkaline li(}uids originally suggest(Kl the use of chloral as a soporific: it was cxi>ected that the alkaline constituents of the blood would decompose it with the formation of chloroform in the body itself. LiEBREicii 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, urochloralic acid.
ALDEHYDO-ALCOHOLS AND EETO-ALCOHOLS OR
' SUGARS.
202. Aldehydoalcohols and keto-alcohols are natural products, end are very widely distributed. They are called carbohydrates, sugars, or saccharides. They contain one carbonyl-group and •several hydroxyl-groups. One of the hydroxyl-groups must be linked directly to a carbon atom in union vdth the carbonyl-^oup, 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.
Nomenclature and General Properties of the Monoses and their
Derivatives.
When the monoses are aldehydes they arc called aldoses, and when ketones, ketoses. The number of carbon atoms in the molecule is indicated by their names: thus, pentose y hexose, heptose, etc. To distinguish between aldoses and ketoses the prefixes "aldo-*' and "keto-'' respectively are used; as aldohexose, keto- hexosCy 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
trioses; as hexotriose, etc.
257
258 ORGANIC CHEMISTRY. [§203
Like other aldehydes, the aldoses are converted by oxidation into monobasic acids containing the same number of carbon atoms, the pentoses yielding the monobasic pentonic acidsy the hexoses the hexonic acids , etc. The oxidation can be carried further; for the
/H
general formula of an aldose is CH20H- (CHOH)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 yield acids containing a smaller number of carbon atoms.
On reduction, the aldoses and kotoses take up two hydrogen atoms, with formation of the corresponding alcohols: thus, hexose yields a hexahydric alcohol y and pentose a pentahydric alcohol (204 and 207).
203. Four reactions are known which are characteristic of all monoscs: 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 (Fehling or Ost, 191) is heated with a solution of a mono.se, reduction takes place, with formation of y(»llow-re(l suV)()xi(l(» of copper.
4. When a nionose is heated with excess of phenylhydrazine, CeHs-Nli-XHi), in dilute sulphurous-acid solution, a yellow com- pound, crystallizing in fine needles, is fonntnl: substances of this type an* insohibU^ in wat(T, and an* called osazones. Their for- mation may be explained as follows.
It is nientioniul in 202 that the sugars are characterized by containing the group — CHOH — CO — . The action of phenyl- hydrazine on a carbonyl-group has alrea ly been explained (103) ; water is eliminated, and a hvdrazone formed:
Cki+HlX-XHCtiUs = rrX-XHCoHs+HaO.
I I
A scM-ond molecule of phenylhydrazine then reacts with the group - -CHOIi — , from which two hydrogen atoms are eliminated, the
§ 204] MONOSES. 259
molecule of phenylhydrazine bein^ decomposed into ammonia and aniline:
CflH5.NH.NH2 = CflHs-NHa+NHg.
Pheuylhvdrazine Aniline
+ 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 phenvlhvdrazine reacts, forming a hydrazone, so that
CHOH C^N.NHCflHs
the group | is converted into | . This group
CO C=N.NHC6H5
18 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 Monoses.
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 into nn 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.
260 ORGANIC CHEMISTRY. [§205
on further reduction at a high temperature with hydriodic acid, yields w-secondary hexyl iodide, CH3-CH2«CHI-CH2-CH2*CH3.
The constitution of this iodide is inferred ffom the fact that it can be converted into an alcohol, which on oxidation yields
CH3.CH2.CO-CH2.CH2.CH3;
for on further oxidation this is converted into n-butyric acid and acetic acid.
4. The hexoses have five hydroxy l-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;
• TT
an aldehydo-group, C — C — C — C — C — C^ ; and
H
five hydroxyi-groups, I I I I I ^
OHOHOHOHOH
There are six other hydrogen atoms in the formula C6H12O6, 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
CH2— CH— CH— €H— CH~€^|^
OH OH OH OH OH
205. In these fomuila? a somewhat arbitrary assumption has been made as to the distribution of th(» hydroxy l-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 usually have linked to it more than one hydroxy 1-grou p. 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, CoHioOo, is reduced to a hexahydric alcohol, CeHuOe, only two hydrogen atoms are added, and this addition
S 205] MONOSES. 261
must take place at the doubly-linked oxygen atom, since the carbon chain remains unbroken. If the hexose contains two hydroxyl- groups attached to one carbon atom, so must also the hexahydric alcohol derived from it. Compoimds containing a C-atom 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 saccharateSf which are, there- fore, to be looked upon as alkoxides (50).
It follows from these considerations that the constitution of the aldohexoses cannot be other than that given above, and, since the name method of proof is applicable to each member, they must all have the same constitutional formula, and are therefore stereoiso- merides. This is due to the presence in the molecule of asymmetric carbon atoms: an aldohexose has four such atoms, indicated by asterisks in the formula
CH2OH . CHOH . CHOH . CHOH • CHOH • Cq.
2G2 ORGANIC CHEMISTRY. [{206
Methods of Formation of the Monoses.
206. 1. From the polyoscs, by hydrolysis; that is, decomposi- tion with addition of water.
2. From the corresponding alcohols, by the action of oxidizing agents, such as nitric acid. Arabitol, C5H12O5, fields arabinose, C5H10O5; 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 oi^tained, 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**:
CH2OH CH,OH CH2OH
CHOH CO C^N-NH-C,H*
'h CH2OH C=N-NH-C.H4
^O H
I. II. III.
In accordance with the nomenclature already indicated, glycerose is a triose.
When sorbosc-bacteria are cultivated in a solution of glycerol, tiic final product obtained by the action of the atmospheric oxygen is dihvdroxvacetono. Tliese bacteria can also oxidize other poly- hydric alcohols to kotoses.
3. From bromo-compounds of aldehydes, by exchange of bromine for hydroxyl, which can \)e effected by cold baryta-water.
In this manner the simplest member of the sugars, glycolose or
glycoUaldehyde, CHjOII-C q, is obtained from monobromoaldehyde,
CHjBr*(^..: it shows all the reactions of the monoses. Glycolose
crystallizes well, and melts with decomposition at about 97°. It polymerizes readily, and is volatile with steam.
Tiie addition of bromine to acraldehyde (141) yields
(:H.Br-C'HHr-c|J, which is converted by the action of baryta- water into glyceraldehyde.
S206) MONOSES. 263
4. Prom formaldehyde, by the action of lime-water (aldol- condensation). The crude condensation-product, called /ormose, is a sweet, syrup-like substance: it consists of a mixture of com- pounds of the formula C6H12O6. In this reaction, six molecules of formaldehyde undergo the aldol-condensation (106) :
-H ^ — H ^ H ^ ^H ^ — H
H2CO + HCO -h HCO + HCO + HCO + HCO =
= H,COH • Cqjj • Cqjj . Cqjj . Cqjj . Cq.
By the aid of sunlight and moisture, plants are able to converfe the carbon dioxide of the atmosphere into starch, a polyose of the formula (CsHioOs)!- The reaction may be represented empirically, thus:
6C0, +5H,0 = C«Hio04 -h 60,.
The botanical term for this reaction is photosynthesis^ and the process is of the highest importance for every form of life, since without it the existence of life would be impossible. Von Baeyer explains the mechanism of the synthesis by assuming preliminary reduction of carbon dioxide to formaldehyde, CH,0, followed by condensation of the aldehyde to form a monose, and the ultimate conversion of the monose into a polyose.
Under the influence of ultraviolet light, moist carbon dioxide is reduced to formaldehyde. Since photosynthesis is promoted prin- cipally by yellow light, but not by blue or ultraviolet light, the formation of aldehyde in the process must be due to a different cause.
CuRTius has demonstrated the presence of small quantities of formaldehyde in fresh leaves.
A hexose can also be obtained from glyceraldchydc, two mole- cules of which yield, by the aldol-condensation, one molecule of the hexose. This hexose is called acrosc, on account of its relation to acraldehydc, from which glyceraldehyde can be obtained by method 3. Acrosc is a constituent of formosc, and, like ail compounds prepared by purely chemical synthesis, is optically
inactive.
5. A very important general method for the conversion of an aldose into another containing one more carbon atom in the mole- cule is the formation of an addition-product with hydrocyanic
264 ORG ASIC CHEMISTRY. [§207
add. An aldohexoee yields a cyanohydrin which is converted on hydrolysis into a monobaac add containing seven C-atoms,
J ^ a
CH2OH.CHOH.CHOH.CHOH.CHOH.CHOH.COOH. 1 2 3 4 5 6 7
The /^-hydroxyl-group reacts easily with the carboxyl-group, form- ing a lactone,
CH2OH CHOH -CHOH CH -CHOH • CHOH -CO.
I h
In aqueous soliUum, these lactones can be reduced by sodium-amat" gam to tfie corresponding aldehydes, the aldoses.
The great importance of this synthesis consists in the theore- tical fxissibility of obtaining from the lower members, step by step, a\/lfmiH with any desired number of C-atoms in the molecule, by repeiiterl application of the cyanohydrin-synthesis, and reduction of the lactone thus obtained. It has thus been possible to prepare nonoses, with nine C-atoms, by conversion of an aldohexose into a heptonic acid, the lactone of which can then be reduced to a heplose. This compound can be converted into an octose, and the latter into a nonose, by the same process.
I. MONOSES.
Pentoses.
207. Reference has already been made to the dioses and trioses (202). Tetrosej? can be obtained by the oxidation of pentonic acid, in the form of its calcium salt, by means of hydrogen peroxide, a smull fiuantity of ferric acetate bein^ used as a catalyst:
CH20H.CH0H.CH0H.CH0H.C00H+0=
Pentonic acid
= CHgOH-CHOH-CHOH-C^+COz+HaO.
Tetrone ^
Also pentoses can be obtained from hexoses by this method.
A numlx^r of different pentoses have been identified, among them arahinoHc and xylose, both of which are present in many plants as polyoses, called jycntosans.
1 2071 MONOSES. 265
Arabinose can be prepared by boiling gum-arabic or cherry-gum with dilute acids, but the best method is to hydrolyze sliced sugar- beet after extraction of the sugaj^ the resulting mixture of galac- tose and arabinose being freed from galactose by fermentation. Xylose, or wood-sugar, can be obtained similarly from bran, wood, straw, and other substances, especially the shells of apricot- stones. Arabinose and xylose can be prepared from any plant- cells which have been converted into wood, and which show the reactions 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 • C^ .
This constitution is proved by their conversion, on gentle oxidation with bromine-water, into arabonic acid and xylonic acid respectively, both of which have the formula CHgOH. (CH0H)3.C00H, and are therefore stereoisomeric. On stronger oxidation, both arabinose and xylose yield trihydroxyglutaric acid^ 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 arabitol and xylitolj which are stereoisomeric pentahydric alcohols. Arabinose and xylose can be converted into hcxoses by the cyanohydrin- synthesis, a proof that neither contains a C-atom in union with more than one OH-group (205), and that each has a normal carbon chain:
CH20H.(CHOH)3.C? -> CH20H.(CHOH)3.CH<pJ->
Pentose ^ ^ ^^
-> CH20H.(CHOH)3.CHOH.COOH.
Hexonic acid
This hexonic acid yields a lactone which, on reduction, gives the hexose. Arabinose and xylose contain three asymmetric C-atoms, and are optically active.
266 ORGANIC CHEMISTRY, [§208
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)1 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 phenylhydrazine yields a phenyl- hydrazone very sparingly soluble in water. Both these reactions indicate the presence of furfuraldehyde.
Hexoses.
208. The hexoses are colourless compounds of sweet taste, which are difficult 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, arc also stereoisomerides.
1. Dextrose (d-glucose or grape-^ugar) 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 lajvulosc (209), called invert-sugar. The technical preparation of dextrose from starch, by boiling with dilute acids, is likewise a case of hydrolysis.
Dextrose crystallizes from water, or alcohol, with some diffi- culty; the crystals obtained from methyl alcohol contain no water of cr\'stallization, 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 la^vo- rotatory and an optically inactive mcKlifiration have been arti- ficially I ropared. The dextro-rotatory, hevo-rotatory, and optically inactive isomeride.T are resncctively distinguished by the prefixes d {(hxtcr), I {l(€vus), and i {inactive^', thus. <i^-gl\icose, Z-glucose, i-gluoose.
5208]. MONOSES. 267
By convention, all other monoses derived from a rf-hexose, 2-hexose, or t-hexose are also distinguished by the letters d, /, or i, even when they possess a rotatory power opposite in sign to that indicated by these letters. Thus, loevulose or ordinary fructose, which can be obtained from dextrose or d-glucose, and is laevo- rotatory, is also called d-fructose on account of its genetic relation to d-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-gluconic acid, CH20H-(CHOH)4-COOH: further oxidation produces the dibasic d-saccharic acid,
COOH . (CH0H)4 -COOH.
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 potassium acetate.
On reduction, dextrose yields a hexahydric alcohol, d-sorbitol: it also gives an Osazone, A-glucosazone, 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 mutarokUion, When freshlv dissolved, such substances have a rotatory power other than that possessed by thorn after the lapse of a comparatively short interval of time. Thus, iv\ aqueous solution of dextrose at first produces a rotation [orj^ = 110^: after some hours it produces a constant rotation [a]/j=52-5°. Tho 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 ammoriia.
The explanation of this phenomenon must be sought in the par- tial conversion of the dextrose or other sugar into another modifica- tion of d'lTerent rotatory power. When the rotation has become constnm. there is equilibrium between the two modifications.
Tanrkt has prepared three different crj'stalline modifications of dextrose, denoted by «, P, and €. Ordinary dextrose is the a-modi- fication : it crvstallizcs with one molecule of water. When dissolved
^t>8 ORGAMC CHEMISTRY. U 2C8
quickly in cold water, the solution produces a rotation [a]|> — 110^. When the solid a-form is heated for some days at 105^, it is cbangied to the ^form. In aqueous solution the ^modification at first only rotates the plane through [a]ry = l^: when allowed to remain for some time, or boiled, or mixed with a trace of alkali, the rotation rises to [a]o=52-5°. When dissolved in water, the e-modification at once causes a rotation [«]{>= 52 -5°, indicating that it b not an independent form, but a mixture in equilibrium of the a-modifica- tion and .^-modification.
Taxret has proved by experiment that this surmise is correct. A very concentrated solution of the c-modification wa« made, and cr>'8tallized 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, pro\nng that the crj'stals l)elongo'l to tlie a-modification. If the £-form is a mixture of ths a-modification and the ;5-n:odification. the latter must have remained in solution in the mother-liquor, and addition of alkali should increase tlie rotation of this residual solution. Experiment has proved that alkali has this effect.
The results of these researches, in conjunction v^ith other facts, have led to the adoption of a somewliat modified tj'pe of constitu- tional formula for the monoses (217).
With a small quantity of water, dextrose yields a colourless :8yrup 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, l)eing followed by the migration of oiic hydrogen atom. These changes involve the transformation of the group — CHOH-CHOH — by abstraction of water into — f;H-:C(OH)— , which then changes to — CH,-CO— . The result is the same as that produced by an exchange of position between hydrogen and hydr(»\yl. followed by elinnnation of water:
-rnoiLCHOFi — »— CMK.rcoH), — > -ciij-co— .
Analogous j>henomena are known, among them the formation of acralclehy<lo from glycorol Cisi). of pyroracomir* from tartaric acid (231), and of oxalacetic aciJ, COOH-CO-CH.-C^OOH, from tartaric acid.
Methylglyoxal, which was isolated as osazone, is an inter-
§ 2091 MONOSES. 269
mediate decomposition-product in the interaction of dextrose and dilute alkalis, as indicated in the following scheme :
CH^OH.CHOH.CHOH.CHOH.CHOH.Cq -^
(Migration of H and OH)
-♦ CH3.C(OH)2.C(OH)j.CH2.CHOH.c5 -^
H OH ^
(Decomposition with addition of IH2O)
-♦ CHj.CO.Cq and CHjOH-CHOH -C^ — H2O -♦ CHs-CO-Cq.
MethylHiyoxai Methylgiyoxai
Lactic acid has been identified as an intermediate product in alcoholic fermentation, and may h>e regarded as derived from methylglyoxal in accordance with the scheme
CM3.C(0H),.Cq -^ CHs-CHOH-Cq^,
Methylglyoxal Lactic acid
resulting from a change of position between hydroxyl and hydrogen. The lactic acid then loses carbon dioxide, yielding ethyl alcohol:
CHa.CHOH.CO.H = CH3.CH2OH +CO2.
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 the decomposition of the lactic acid into alcohol and carbon dioxide.
The conversion of dextrose into butyric acid by the butjTic fermentation can also be explained by assuming the intermediate formation of lactic acid, and its subsequent transformation into formic acid and acctaldehyde. Condensation of acetaldehyde pro- duces aldol, which yields 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. Lcevulose (d-frxictose 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 polyene contained in dahlia-tubers, yields only Iffivulose, just as starch yields dextrose. Isevulose crystal- lizes with difficulty, being readily soluble in water, although less so than dextrose. It is Isevo-rotatory, and can be fermented.
270 ORGANIC CHEMISTRY, [§209
Laevulose is a type of the ketoses, but few of which are known. Its formula, CH20H.(CHOH)3-CO.CH20H, is inferred from the following considerations. First, when oxidized with mercuric oxide in presence of baryta-water, it is converted into glycollic acid, CHaOH'COOH, and trihydroxyglutaric acid,
COOH. (CH0H)3-C00H.
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-svnthesis to a compound of this constitution would yield a heptonic acid with
the formula
CH2OH. (CH0H)3-C(0H) .CH2OH.
COOH
That the heptonic acid obtained from laevulose has this consti- tution, is proved by heating it at a high temperature with hydriodic acid, whereby all the hydroxy l-groups are replaced by hydrogen, and a heptylic acid is formed. This acid is identical with the synthetic methyl-n-butylacetic acid (233, 2), ,
CH3 • (CH2)3 • CH • CH3
i
OOH
The osazone of laevulose Ls identical with that of dextrose. A comparison of the formula of dextrose,
CH20H.(CHOH)3.CHOH.Cq,
with that of tevulose, CH20H.(CH0H)3-C0.CHo0H, shows that the two osazones can only be identical if the a-C-atom of dextrose, and the terminal C-atom of licvulose, respectively unite, after for- mation of the liydrazone. with the scn'ond phenylhydrazine-residue: that is, when in both cases this reaction takes place at a C-atom directly linked to a carbonyl-rroup. For this reason, it is assumed that tlie formation of an osazone always results in the union of two plienylhydrazine-residues with neighbouring C-atoms. i\-Clncosazofu\ or d-fi^ucioaazofic, has therefore the constitution
S 2101 MO NOSES. 271
CH2OH (CH0H)3 C^NNH-CbHs C=N.NH.CaH6
•
H
Methylphenylhydrazine, Q Tj >NNH2, 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, osoneSf containing two carbonyl-groups. For example, d-glucosaZone yields d-gltLCosoney
CHvOH.(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 C-atom. d-Glucosone yields la;vulos(f
CH^H.(CH0H)3-C0.CH.0H.
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 in the vegetable-ivory nut: it is also obtained by the careful oxidation of the hexahydric alcohol mann^lol, found in several plants. d-Mannosc, 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 hydrazones
272 ORGANIC CHEMISTRY, [§210
of the other monoses, dissolves with difficulty in water. On oxi- dation, d-mannose is first converted into the monobasic d-mannanir acid, CH20H-(CHOH)4-COOH, and then into the dibasic d-manno- saccharic acidy 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 stereo isomeric 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 synthesis of dextrose. He converted glyceraldehyde into acrose (206, 4), and this into i-mannitol, by reduction with sodium- amalgam. On oxidation, i-mannitol yields first t-mannose, and then i-mannonic acid, which can be resolved, by means of its strychnine salt, into its optically active modificatipns. When the d-mannonic acid thus obtained is heated with pyridine, it is converted into d-gluconic acid, the lactone of which, on reduction with sodium- amalgam, yields dextrose.
The stareoisomorism 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-CeHs these osazones can only be identical when the residue
CH2OH. (CH0H)2-CH0H—
in d-mannose and dextrose is also identical: their stereoisomensrx? 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
§S 211, 2121 MONOSES. 273
always been found that the alteration takes place, as in the above instance, at only one C-atom, and this the one adjoining the aldehydo-group, the a-C-atom.
211. d-Galactose can be obtained by the hydrolysis of lactose, or by tiie oxidation of the hexahydric alcohol dulcitol, which occurs in certain plants. (i-Galactose is crystalline, melting at 168°; it is strongly dextro-rotatory, is capable of undergoing fermentation, znd exhibits mutarotation. Galactose is proved to be an aldose by its conversion, on oxidation, into the monobasic A-galactonic acid, C6H12O7. Further oxidation yields the sparingly soluble dibasic mucic acidy C00H-(CH0H)4-C00H, which is optically in- active, and cannot be resolved into optically active components: its formation serves as a test for c?-galactose. This is carried out by oxidizing the hexose under examination with nitric acid.
Their conversion into ItvuUc acid (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 difficulty, 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 unsymmetrical methylphenylhydrazine, C8H5N(CH3)-NH2, dissolved in acetic acid precipitates arabinose- methylphenylhydrazone. If this is filtered off and the liquid warmed after addition of an acetic-acid solution of phenylhydra- mne,'phenylglucosazone cr>'stallizes out.
Stereochemistry of the Monoses.
212. It wa.s stated (205) that all the aldohcxoses 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 pentoses and hexoses mentioned here, it is desirable to indicate how this is determined for such compoimds; that is, for those containing several asynunetric carbon atoirs in the molecule.
274
ORGANIC CHEMISTRY.
[5212
It was mentioned (i88) 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 number of asymmetric C-atoms in the molecule. The projection-form uke for two aldopentoses,
CH2OH CH2OH
HO-
Ha
HO
H H -H
and
H- H- H-
iH
-OH
OH,
OH
U
H
O O
cannot be made to coincide by rotation in the plane of the paper (190): the aldopentoses, therefore, are not identical. The corre- sponding trihydroxyglutaric acids
GOOH
* H H-
-H and H—
H-
Ha
HO- HO
H
COOH
COOH
OH
OH
OH
COOH
are, however, identical, since their projection-formulae can be made to coincide. In these compounds the asymmetric C-atoms 1 and 3 are similar, while in the pentoses they arc dissimilar.
Assuming that the determination of the configuration of a tri- hydroxyglutaric acid is possible, and that it leads to the projection- formula given alx)ve, it follows that thc^ pentose from which this acid is obtained by oxidation must have one of the above configurations, and that all 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 detemiine that of the corresponding trihydroxyglutaric acid. The optical bt^haviour 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 raeeniic 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 l)eing made to coincide
J 2121
STEREOCHEMISTRY OF THE MONOSES.
275
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- iii;uration is possible.
The above reasoning may be applied to the determination of the stereochemical structure of arabinose. Eight stereoisomeric for- muIjB 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:
H- H- H-
CH2OH —OH —OH —OH
H — H- HO-
CH2OH —OH —OH
C
H 0
H
H- HO-
Ha
CH2OH —OH — H
I.
^O II.
— H H ^0
III.
H-
Ha
H-
CH2OH —OH — H , —OH
'-O
IV.
The mirror-image of I. is represented on p. 274.
Arabinose is converted by oxidation into an optically active tri- hydroxyglutaric acid. This excludes the trihydroxyglutarlc 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 mirror-image,
HO- HO
Ha
COOH COOH
H H. H
COOH COOH
IV.
H-
HO-
H-
OH
H
OH
identical with its mirror-image,
Ha
H- HO-
COOH
H
OH.
H
COOH
The fact that by the aid of the eyanohydrin-synthesis arabinose can be converted into a mixture of dextrose and mannose. which on oxidation yields the optically active saccharic acid and mannosac- charic acid, enables a choice between types II. and III. to be made.
H H
Since in the eyanohydrin-synthesis onlv the group 0^ in CHOH -05;
276
ORGANIC CHEMISTRY.
(§213
is altered, the configuration of the rest of the C-atoms remaining unchanged, saccharic acid and mannosaccharic acid must have tha stereochemical structure
COOH
COOH
H-
H-
HO-
-OH ■OH -H H
or
H- H
Ha
H-
OH -OH -H -OH
COOH COOH
if arabinose is represented by formula H. Neither of these can be 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 HO HO-
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 buildintr-up and the breaking-down of the monose molecules. Thu.-*, oxidation of crythrosc yields mesotartaric acid, and this fact establishes the grouping round the central C-atoms of this tetrose. Since erythrosc Ls a decomposition-product of rf-arabinose, this reaction affords a partial insight into the configuration of that pentose. As already indicated, synthesis 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 (Hoses (or biases) known arc exclusively derived from hexoses, and therefore, have the formula
Ci2H220ii = 2C8Hi20ti— H2O.
§ 214] DIOSES. 277
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, incianosey built up from dextrose and Z-arabinose, as is proved by its hydrolysis:
Cn H20O10 -I- H2O =C6Hi206 + C5H10O5.
Vicianoae Dextrose /-Arabinose
Ajnin, a glucoside present in parsley, is converted by the action of acids into a diose, transformed by further hydrolysis into 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 enzymes (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 synthesize natural dioses have failed.
Emil Fischer has, however, prepared artificial dioses synthet- ically from monoses, such as dextrose. Acetic anhydride and hydrobromic acid convert this sugar into acetohromodexirosey probably with the formula
CH20A"c* • CHOAc • CH • CHOaS • CHO Ai • CHBr.
I O I
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 (217).
Maltose. 214. Maltose in the crystallized state has the formula
Ci2H220n,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.
•Ac=CH,-CO— .
278 ORGANIC CHEMISTRY. [5 215
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 monoeesr thus, it reduces an alkaline copper solution; yields an osazone,. maUosazone (Ci 2H22O1 1 - 2H2O - 2H + 2C6H6NH • NH2) ; and it can be oxidized to the monobasic maUohionic acid, C12H22O12, which, on hydrolysis, splits up into dextrose and d-gluconic acid^ CH2OH . (CH0H)4 -COOH.
These properties show that maltose contains only one of the two carbonyl-groups present in two molecules of dextrose: thus, it forms an osazone with two, instead of four, molecules of phenyU 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.C6Hn05<.
Dextrose Dextroee
Lactose.
215. Lactose (milk-sugar) is present in milk, and is prepared from it.
Whey is usually employed for this purpose: it is the liquid which 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 constituent* of the milk. The lactose is obtained by evaporation, and purified by recrystallization.
Lactose crystallizes in well-defined, large, hard crystals. 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 J-galactose and dextrose. It shows the reactions of the monoses, and can be proved, by a method analogoits to that employed for maltose, to contain one free carbonyl-<rroup in the molecule: it is, therof'.re, made up of dextrose and rZ-jr a lactose, linked bv a monocarbonyl-bond. The
§S 216, 2171 DIOSES. 279
r
free carbonyl-group belongs to the dextrose molecule, since lactose is converted by oxidation with bromine-water into lactobionic acid, which is converted by hydrolysis into d-galactose and d-gluco»i5c acid. Lactose is, therefore, represented by
C6Hn06<O.C6Hn05<.
d-Galactose Dextrose
Sucrose.
2i6. Sucrose {cane-sugar 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 cooling 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 laevulose in equal propor- tions. This mixture is called invert-sugar, and is laevo-rotatory, since laevulose 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 solution, is not turned brown by caustic potash, and does not yield an osazone. Hence, it is evident that there are no free carbon yl-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 dicarbonyl-bondj and is represented by the sign <0>; so that sucrose has the formula
C6Hn05<0>C6Hn06.
l>extrcK« Lcpvuloae
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 glucoa- 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-
280
ORGANIC CHEMISTRY,
I J 217
ficial glucosides are obtained by the action of one molecule of an alcohol upon a monose:
CHisOe+CHaOH = C«H„Oo-CH,+H^.
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):
|
H |
H |
|
R.C |
^ H OCH3 p A^OCH, |
|
Aldehy |
de Alcohol 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 rCHOH iSCHOH aCHOH
cfo
H
+ H
OCH.
CH2OH
CHOH
rCHO —
^HOH oCHOH
C-OCHa H
The grounds for the assumption of this constitution are: first, these glucosides are readily resolved into their components, which argues against the existence of a carbon bond between the latter; second, the hydroxyl of the r-C-atom is assumed to be the one which reacts, since other compounds containing the group — CHOH -CO — do not yield glucosides; the «-hydroxyl-group, therefore, does not react. The r-hydroxyl, being attached to the fourth C-atom of the chain, is, moreover, the most likely to enter into reaction, since a number of instances of similar behaviour are known, such as that of the acids yielding lactones (185).
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:
§2181
DIOSES.
281
CHvOH CHOH
|
rCHOH ^HOH aCHOH |
|
|
cp |
+H |
(CHOHX
OCHa
CH2OH CHOH CHO— , H2O+CHOH CHOH C^==
pH
r
(CHOH)^
CH,
/
I
H
H
O
By analogy the constitution of sucrose, in which Icevulose and dex- trose are united by a dicarbonyl-bond, will be
CH2OH
CHOH
CHO-^
CHOH
CHOH
•
C=-
CH,OH eCHO- aCHOH rCHOH
^c.
-0 aCHjOH
H
The methylglucoside previously mentioned exists in two isomeric forms, denoted by a and /5, and closely related to a -dextrose and /5-dextrose. Hydrolysisof 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 :
CH2OH . CHOH . CH . CHOH . CHOH . CHOH.
L
O
I
The stereoisomerism of a-dextrose and /9-dextrose therefore depends on variation in grouping at the carbon atom indicated by an asterisk (*). Similar rea^soning is applicable to the other monoses. The absence of an aldohydo-group from the constitu- tutional formula; of dextrose and the other monoses accords with their inability to restore the colour to Schiff's reagent (107).
Sucrose forms compounds with bases, called saccharates: among them arc Ci2H220ii,CaO/2H20 and Ci2H220n,2CaO, which are readily soluble in water. When the solution is boiled,
282 OBGAXIC CHEMISTRY. [{218
the neariy indduble tric^Jcium saccharate C12H22Ou.3CaO.3H2O is precijMtated.
Sbonfttctiirc of Sncxose from Sagsr-bcct.
218. Sucrose is present in solution in the cell-fluid of the sugar- beet. The ceU-wails aie lined with a thin, ccntinuous lay^* of protoplasm, constituting a semi-penneable membrane, which pie- \&its the diffusion of the sugar from the ce^ls at ordinar\' tempera- tures. WTi«i placed in water at S0°-90°, the protoplasm b killed, coagulates, and develops minute ruptures, through which the cell- fluid can diffuse. The process is facilitate! by cutting up 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 amount of water, the slices are placed in vats through which water circulates in such a manner that the nearlv exhausted material is acted on by fresh water, while that which is only partly exhausted comes into contact with the solution alreadv obtained, so that the material richest in sugar is treated with the strongest extract, and vice versa (principle of the counter-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 attaineil. First, the free acids in the juice, such as oxalic acid and citric acid, are preeipitateil, 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. 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
i 2191 DIOSES. 283
neutral. After filtration, the S3aiip is concentrated until crystals of sugar begin to separate. It is then allowed to cool, when more crystals are obtained, mixed with a syrupy liquid, which is removed in a centrifugal machine. This syrup is further crystallized by €low 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 9 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]D= +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 is 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 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 will become laevo-rotatory, since invert-sugai' is Isevo-
2S4 ORGANIC CHEMISTRY, (5 220
rotatory. The rotatory power of an invert-sugar solution obtained from a sucrose solution of given strength being known, these two observations furnish the data by which the percentage of dextrose in cane-sugar 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 s in the fraction of time immediately following can be expressed by the equation
in which fc is a constant. The inversion can be eflFected by means of different acids of the same molecular concentration: the velocity of the reaction is dependent upon the nature of the acid employed, so that different values are obtained for the velocity- constant fc. 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 slip;htly 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 concludal 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 a( i J salts, for example, may be determined by measuring the velocity of inversion.
For an inversion effected by the action of an enzyme, the equa- tion does not hold. Tiiis is explained by the fact that the reactivity of an enzyme drponds on both the concentration of the sucrose and that of its own invcrsion-prcxlucts, whereavS the inverting power of an acid is independent of tlic concentration of the latter.
§2211 FERMENTATION AND THE ACTION OF ENZYMES. 285
Fermentation and the Action of Enzymes.
221. The alcoholic fermentation oMiquids 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. Liebio 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-ccUs, a theory which was imivcrsally accepted, Ltebig's supposition that the part played by the cells is only a secondary one being 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. Eduard Cuv'^HXRR has effectal this. He triturated fresh yeast with sand, whereby t,he cell-walls were destroyed. The dough-like mass was submitted to great pressure, which expressed a liquid (German, Presssaft): this expressed yeast -juice was separated by filtration from the cells still floating in it. Buchver proved in various ways that this yeast-juice contains neither living cells nor living proto- plasm: for instance, the veast niav be first killed bv the action of acetone; tlie extract from it can nevertiieless set up active fermen- tation 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
286 ORGANIC CHEMISTRY, . 15 222
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 zymase.
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 wholly unknown. Most of them have not been obtained in the pure stato. 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 heating, they are decomposed. Second, they are sometimes rendered in- active empoisoned") 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,
C3H603 = r2H50H+C02.
Only the monoses are capable of being fermented by enzymes: dioses must first be converted into monoses. Yeast contains an enzyme, invertasc, which first decomposes sucrose into a mixture of Itevulbse and dextrose. Tins is proved by the fact that certain varieties of yeast, wliich do not contain invertase, are incapable of fermenting sucrose: thus, Sch iz')saccharomi/ces octosporuSy discov- ered by Bkyerinck, can ferment maltose, but not sucrose. This variety of yeast contains no invertase, hut only maltase, the enzvme bv which maltose is hvdrolvzed.
The aptitude for decomposition by enzymes, possesseti by the monoses, has been proved by Emil Fischkr to be intimately con- nected with their stereochemical configuration. The three naturally
§2221 FERMENTATION AND THE ACTION OF ENZYMES. 287
occurring sugars, dextrose, d-mannose, and laevulose, 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 :
HO H- H-
.H ■'6
— OH HO— — 'li HO— — CM —OH CHjtOig;
C^ (
H— H—
,H O
H -H
—OH —OH CHaOH
Ha
H
CH2OH
H OH
CO
Dextrose
<f-Manaose
H— I— OH CH2OH
Lasvulose
H- HO- HO
H-
.H O
-OH -H -H -OH
CH2OH
(/-Galactose
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, /-glucose, etc., are not capable of undergoing fermentation.
The cause of these phenomena is probably the asymmetric 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 : tiie sweet taste possessed by one cf the optically active asparagines, and the absence of taste in the other; the different amounts to which the three stereoisomcric tartaric acids are oxidized in the body of a dog fed with them; the fact that, on subcutaneous injection of a rabbit with /-arabinose or
288 ORGANIC CHEMISTRY. [§ 223
d-arabinose, of the first only 7 per cent., of the latter 36 per cent., is excreted from the body unchanged in the urine; and so on.
Asymmetric Synthesis.
223. Laboratory-syntheses 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 under 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 under 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 isomcrides. An example is furnished by mannosc, convertible by the cyanohydrin-synthesis into mannoheptonic acid. From analogy with other cyanohydrin-syntheses, the formation of two Btereoisomeric 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 application 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.
J 224) POLYOSES. 289
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 syntheses of this type have been effected, particularly by McKenzie and his coadjutors.
Reduction of benzoylformic dcidf 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 liEvo-rotatory menthol, produces a mixture of the ester of the dextro-acid with a small excess of that of the kevo-acid. On saponification, active mandelic acid is obtained, despite the elimination of the asymmetric structure occasioned by the menthol-residue. The formation of Mactic acid by the reduction of Z-bomyl pyroracemate with aluminium-amalgam is a similar reaction:
CH3.CO.COOC10H17 — CH3.CHOH.COOH.
/-Bornyl pyroracemate /-Lactic acid
Another example is the formation of excess of /-tartaric acid by treating monobomyl fumarate with permanganates (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 fauna, 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.
in. POLYOSES.
RaflSnose, C,8H320i6,5H20.
324. Raffinose is the most important of the hexotrioses, of which but few are known. Their formula is CwHmOu; that is,
3C6H,,Oe-2H:0.
290 ORGANIC CHEMISTRY, (§225
Raffinosc is a hexotriose, since, on hydrolysis, it takes up two molecules of water with formation of an equal number of molecules of IsRvulose, dextrose, and (/-galactose. By careful hydrolysis, raf- finosc can l)e split up quantitatively into lapvulose and a diose {mek' diose) : from the latter, dextrose and (f-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 (/-galactose and sucrose. Raffinose exhibits none of the monose reactions: thus, it does not reduce an alkaline copper solution. This proves the absenrre of a free carbonyl-group, so that raffinose must be repre- sented by
Melediose exhibits the sugar reactions, and therefore contains one free carbonyl-group, so that its formula is
CJiuO,<0'CJiuO,<,
which proves that the decomposition of raffinose into monose and diose takes place at the dicarbonyl-bond, as otherwise there would have been obtained a diose, C6HnOft<0> CeHnOj, 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.
M anneotelrosc is a tetrose present in manna. On hydrolysis it yieltls two mohMMiIes of galactose, one molecule of dextrose, and one inole(;ule of Iirvulosc:
C\,H«0„+3H.() = 2C,H„0, + CJI.,0,+CoH„0..
Manneotot rose Cialartone DextroHe Lsvuloee
Higher Polyoses.
225. Most of the higher polyoses arc amorphous, and do not possess a sweet taste: many of them are insoluble in water. On hydrolysis, they yield monoscs, either pentoses or hexoses, so that it may be assumed that the monose-residues are united by the oxygen atom. The molecular weight of tlie polyoses is unknown, but must be very- great. Their formula may be represented as being derived thus:
nCeHiaOe-C/i-DHaO.
i 225] POLYOSES. 291
If n is very great, this constitution approximates to
nC6Hi206-nH20= nCCeHioOg),
which is the formula indicated by the results of analysis. On hydrolysis, nearly all the polyses yield monoses with the same number of C-atoms.
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 tannin 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 amylocellulose; 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, arc formed. Both these methods of treat- ment yi(»ld intennediate 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
ORGANIC CHEMISTRY.
FlO. 68.— niCE-9TAR<
§225]
POLYOSES,
293
does not reduce an alkaline copper solution, nor resinify with alka- lis, and yields no compound with phenylhydrazine. This proves
Fig. 69. — Potato-starch. X 250.
the absence of a free carbonyl-group, so that its molecule must be represented by
C6Hio05<0 .... C6Hio04<0>C6Hio04 .... 0>C6Hio05.
It might be suggested that the molecule of starch contains more , than one dicarbonyl-bond, when the formula would be, for example,
C6Hio05<0 CJIio04<0>C6Hio04-0>C6Hio05 0>
>C6Hio04<0>CeHio04.0>C«IIxo05.0>CeHio05 0>C«Hio06.
It does not, since hydrolysis of a compound of this type must yield, in addition to dextrose, a substance >CoHi20e<, containing 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-j^roup.
Certain dextrins have also been prepared in crystalline form.
294 ORGANIC CHEMISTRY. [§§226,227
Glycogen, (CeHioOs)*.
Glycogen is a substance resembling starch, and is present in the anhnal organism: the other polyoses are vegetable products. It is usually prepared from liver, and is a white, amorphous powder, dissolving in water with formation of an opalescent solution. On hydrolysis, it yields only dextrose. Apparently there are different kinds of glycogen, according to the anhnal 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.
Starcli is employed for many purposes in the arts, as an adhesive paste, and for stiffening linen in laundries. In the latter process, the starcli-paste is converted by the heat of the smoothing-iron into a stiff, shining layer of dextrin, coating the fibres of the linen. Starch is of great importance 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 polyosc of very high molecular weight. The cell-walls of plants consist principally of this substance, together with ligmn, 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 cellulose, 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
§ 228] POLYOSES. 295
acid, and the solution boiled, after dilution with water, it is completely hydrolyzed. Cellulose from cotton-wool, paper, etc., yields exclusively dextrose; from coffee-beans, cocoa-nibs, etc., d-mannose. Cellulose is converted by treatment with sulphuric acid containing half its volume of water into a colloidal modifica- tion, amyloid, which gives a blue coloration with iodine: this reaction furnishes a test for cellulose. The latter is soluble in an ammoniacal solution oX 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 cdlose, obtained by saponification of the acetyl-derivative with alcoholic potash. Inversion converts cellose into dextrose. It is the simplest polyose 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.
228. Linen is prepared from the stalk of the flax-plant. The linen fibres can he 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 unpleasant 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 anns nanie<i "wipers," a process called "scutch- ing." The linen-fibres iiave a grey colour, and an* bleached l)y either lH:ing spread out in tlie opf n or by means of bleaching-powder.
Paper was fomierly pn pannl almost exclusively from linen-rags, but is now largely inanufactunMl from wood and straw, which must be divided into fibres; the fibn\s are then separated as much as possible from the other, so-called inrnistinK, substances present. This is effected either by the sulphite-met/uHi, in which the wood is
296 ORGANIC CHEMISTRY. f§ 228
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, p>ossible to remove all the lignin by these means; in consequence, wood-paper and straw-papcT answer to the tests for lignin, and can be recognized thereby. Lignin gives a jtIIow coloration with salts of aniline (297), and a red coloration with a solution of phloroglucinol (337) in concentrated hydrochloric acid.
Parchment-paper is prepared by converting the outer surface of paper into amyloid (227), a process which imparts toughness to it.
The nitrocelluloses are of great technical importance. When cotton-wool is treated with a mixture of nitric and sulphuric acids, a mixture of mononitroceUidoset dinitrocelhdose, and trinilrocellulose 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 C»HioO&. In the nitration of cellulose the final product is trinitro-oxycellulose. For, on treatment with ferrous chloride, trinitro-oxycellulose yields oxycellulose, 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. Oxycellulose has the formula
(C^H^oO^,), or [(CeH,oO,),4-(CcHioO«)]x;
and its trinitro-derivative is
[C Jl7(N0,),0ja +C Jl7(NO,)30e.
The solution in a mixture of alcohol and ether of mononitrocellu- lose and dinitrocellulose is known as collodion: on evaporation 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 burns 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 brisant (155) action, and without modification is, therefore, unsuitable for use in artillery.
S 2281 NITROCELLU LOSES. 297
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, under the name of ** smokeless powder."
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-compounds in alcohol and ether, the threads being then denitrified by the action of various reducers; (3) by conversion of the cellulose into a xanthatc (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 amount of water; and that formed by the third method into a solution of ammonium sulphate or dilute sulphuric acid.
AMINO-ALDEHYDES AND AMINO-KETONES.
229. Very few amino-aldehydes and amino-ketones are known. Aminoacetaldehyde, CH2NHa-CQ, a very unstable compound, can b©
obtained from aminoacctal, CHvNHy«C,Qp u \ * which can be pre- pared from monochloroacetal, CHz- CI -011(002114)2. Muscarine is possibly the corresponding trimethylammonium base:
0HaN(0H3)»OH O
C5C+H2O
It is a crystalline, excessively poisonous substance, and is present in certain plants — for example, toad-stool {Agancus muscarius).
Apart fronn 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, CeHiaOsNjHCl, 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 chitonic acid: further oxidation with nitric acid converts this substance into the dibasic ]&osaccharic acid.
Bromine converts glucosamine hydrochloride into d-glucosamic acid, CH20H.(CHOH)3.CHNH2-COOH, which Emil Fischer has synthesized by the following method. Ammonia and hydrocyanic acid react with d-arabinose to form a compound (240, 3),
CH20H.(CHOH)3-CHNH2.CN,
and with concentrated hydrochloric acid this yields
CH20H.(CHOH)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.
298
ALDEHYDO-ACmS AND EETQNIC ACIDS.
GlyoxyUc Acid, COOH.CQ+H2O.
230. GlyoxyUc 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, CHBr2-C00H, 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 C149) ; thus, CH(0H)2'C00H, as it is in chloral hydrate (201). In each of
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 aldelivdes: it reduces an annnoniacal 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:
2(W)II.rH0 =-- (W)H.CIl20II +(^0011. COOH.
300 ORGANIC CHEMISTRY. [§231
Pyroraccmic Acid, CH3.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 raeemic 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, CH2OH -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 fciulphate:
CH2OH. CHOH. COOH -H2O =
= CH2=C(0H) -COOH -> CHa-CO-COOH.
Pyroracemic acid can be obtained synthetically by hydrolysis of the nitrile formed by the action of potassium cyanide on acetyl chloride;
CH3 . COCl -► CH3 . CO . CN -► CHa . 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-ICO^H = CHa-C^ -fC02.
At ordinary temperatures pyroracemic 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 IQi^k is 0-134; for pyroracemic acid lO^A; is 56, which must be explained by assuming the presence of a negative 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.
On boiling with a solution of barium hydroxide, pyroracemic acid is readily converted into a condensation-product, uvitic or symmetrical methyTi^ophlhalic acid (350), a reaction analogous to the formation of nicsitylene from acetone (285).
The electrolysis of a xnry concentrated solution of potassium pyroracemate yields acetic acid and diacetyl. The formation of
J 2321 ACETO ACETIC ACID. 301
acetic acid ma}' be looked upon as due to the interaction of the anion of the acid and the hydroxji-ion, after discharge at the anode:
CH,-CO-CO(y+OH' = CHa-COOH+CO,;
and that of diacetyl as resulting from the imion of two acid anions^ with elimination of COj:
CHt'-Co'So' - CH,.C0.C0.CH,+2CX>,.
The potassium salts of other ketonic acids are decompK>sed by electrolysis in an analogous manner.
Acetoacetic Acid, CHa-CO-CHgCOOH.
232. Acetoacetic add is a ^-ketonic acid. It is not of much importance, but its ester, ethyl acetoacetaie, CH3 • CO • CH2 • COOC2H5, is an interesting compound.
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
Ethyl acetate
OC2H5+H
OC2H5 H
C-COOC2H5 =
Addition-product
ONa
= 2C2H5OH + CH3 • C=CH . COOC2H5.
Ethyl Bodioacetoacetate
The foregoing explanation of the condensation was proved to be correct in this instance by Claisex, who found that ethyl aceto- acetate cannot l3e prepared by the action of sodium on ethyl acetate which has been carefully purified from alcohol. The free ester, CHa- CO -CHa -00002115, can be obtained by treatment of the sodium compound with acetic acid, since in the substitu- tion of sodium by hydrogen the group — C(OH):CH — is first formed, and subsequently transposed into — C0*CH2 — (131).
Ethyl acetoacetate is a colourless liquid, shghtly 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 hydrolyzed in two ways, respectively known as the ketone decomposition (weak hydrolysis) and the acid decomposition {strong hydrolysis), on account of the nature of the products.
The ketone decomposition is effected by heating ethyl aceto-
1 - -* 302 ORGANIC CHEMISTRY. l§ 232
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.
Q^Hs =CH3 • CO. CH3+CO2 + CaHsOH.
The acid decomposition takes place when ethyl acetoacetate is heated with a very concentrated solution of alcoholic potash or soda:
CH3.CO +0H
CHz-COO H + H
C2H5_
^2^^5 = CHs . GOGH + CH3 . COOH + C2H6OH.
The great importance of ethyl acetoacetate for syntheses 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 CHa-group replaced by ^ubstituents. Replacement of one or two hydrogen atoms by one or two groups R gives the compound
CHa-CO-CHR-COOCzHfi or CH3.CO.CR2-COOC2H5,
•
converted respectively by the ketone decomposition into the ketone
CHa-CO-CHzR or CHa-CO-CHRz,
a reaction affording a general method of synthesizing methyl- ketones (loi).
The acid decomposition converts the compounds
CHa-CO-CHR.COOCgHs and CHa-CO-CRz-COOCaHs
into acetic acid and an acid with either the formula
CHzR-COOH or CHRz-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 ethoxidc and the ester to form a sodium compound, CH3-C(0Xa) :CH.COOC2H6 (235).
82331 ACETO ACETIC-ESTER SYNTHESIS. 303
Addition of an organic halide, R»X, in which X represents a halogen atom, gives the product
ONa H
CHa-C C.COOC2H5.
X R
Elimination 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. Methylnonylket(m€f the principal constituent of oil of rue (from Ruta graveolens), can be obtained by the action of n-octyl iodide upon ethyl sodioacetoacetate:
CH, • C(ONa) : CH » COOC2H5 CH, • CO • CH • COOCjH*
-f- -. I .
I — CaHi? CgHi7
It yields, by the ketone decomposition, methylnonylketone,
CH3-CO-CH2-C8Hi7.
Ethyl n-octylacetoacetate yields, by the acid decomposition, caprio acid, CioHsoOa, which must therefore have a normal carbon chain
(137).
2. Heptylic acid, which is obtainable from laevulose by the cyano-
hydrin-synthesis (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 meihyl-n-butylacetic acid:
CH, • C(ONa) : CH • COOCH, /COOC2H,
+ -. CH,-CO-CH<^ -♦
I — CiHf C«H»
Ethyl n-butylacetoacetate
CH,-C(ONa) :C <p9?^*^' /COOCA
^ + ^*^* ^ CH,-C0-CfC4H,
I— CH, XH,
Ethyl methyl-n-butylacetoacetate
Ethyl methyl-n-butylacetoacetate yields, by the acid decomposition,
methyl-n-butylacetic acid,
/COOH CH^-C^Hf . ^CH,
304 ORGANIC CHEMISTRY [§ 234
3. Y-Kctonic acids are obtained by the action of ethyl acetoace- tate upon the esters of the a-halogen-substituted fatty acids, followed by the ketone decomposition:^
CH, • C(ONa) : CH • COOC,H» yCOOCH*
+ -> CH,-CO-CH<
X — CHR • COOCHi \CHR • COOCH,
This yields, by the ketone decomposition,
CH, • CO • CH, • CHR • COOH.
t ^ a
4. When iodine acts upon ethyl sodioacetoacetate, two molecules unit€ thus:
CH..C(ONa):CH.COOC.H. ^.-C^'cH-COOCA
21 = )l I
CH.-C(ONa) :CH.COOC.H. CH..Q;— CH-COOCH.
Elimination of two molecules of sodium iodide converts this com- pound into diethyl diacetylsuccinate,
CH, • CO • CH CH • CO • CH,
I I
COOC2H6 COOCHi
When boiled with a 20 per cent, solution of potassium carbonate, diethyl diacetylsuccinate loses carbon dioxide and alcohol, with formation of acetonylacetone (200) :
CH, • CO • CH— CH • CO • CH, H |H
- CH,-CO-CH,-CH,-CO-CH,.
Acetonylacetone
|
C.H. 0,C OH |
CO, |
CH, OH |
LsBvuUcAcid, CHa-CG-CHz-CHz-COOH.
234. Lcevidic acid is the simplest /'-ketonic acid: it can be obtained by the synthetical method described in 233, 3 — from ethyl acetoacetate by the action of ethyl monochloroacetate; in this instance, in the formula given R=H. When hexoses are
§2361 MESOXALIC ACID. 305
boiled with concentrated hydrochloric acid, laevulic acid is pro- duced (211): it is usually prepared by this method, which has not yet been fully explained.
Laevulic acid is crystalline: it melts at 33 • 5®, and boils 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.
Mesozalic 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 + Bal (0H)2 = (C2H500C)2C(OH)2 + BaBr2.
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 hydrate (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(OH)2-COOH.
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
306 ORGANIC CHEMISTRY. [§ 235
to the molecule through oxygen. An example is furnished by the interaction of ethyl sodiocetoacetate and ethyl chloroformate (263), two compounds being formed. The one produced in smaller proportion is the C-deri vati ve :
ONa ONa
CHs-CrCH.COOCaHs -^ CHa-C CH-COOCaHs-
CLCOOCaHi CI COOCgHg
COOC2H5
=CH3-C0-CH +NaCl.
COOC2H5
The identity of this product with that formed by the interaction of acetyl chloride and diethyl sodiomalonate proves its con- stitution:
CH3-CO[CrTN^-CH(COOC2H5)2 -^ CH3-CO.CH(COOC2H6)2.* The main product is an isomeride, the 0-derivative :
CHa-CCONa) :CH.COOC2H5 CHa-CiCH-COOCzHs
+ = I +Naa.
CI— COOC2H5 0 . 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. CH3-CO-CH.
COOC2H5
OK
Cq^CH3=CH3-CO.CH2-COOC2H5 + CH3-COOK.
Ethyl acetoacetate Potaaaium
acetate 1
J 2361 . TA UTOMERISM. 307
The 0-derivative, however, is the principal product :
CH3-C(ONa):CH.CO.CH3 CH3-C:CH.CO.CH3
+ =1 -fNaCl.
CI— COOC2H5 O . COOC2H5
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 •
A.
CO2C2H6I =CH3.C(0H) :CH.CO.CH3+C2H8-OH+C02.
Acetylacetone
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 0- deri vative :
CH3 . CO . CH . COOC2H5 CH3 • C=CH . COOC2H5
CO.
CH3 O.CO.CH3
C-derivative C-derivative
(Gives no addition-product (Gives an addition-product
with bromine) with bromine)
Similar equivocal reactions have been observed for many compounds with the grouping — CO- CH2« CO — . It was formerly believed 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 0-derivative by direct union of the sodium atom with oxygen, — C(ONa):CH«CO — . It was accordingly assimied that in compounds of this type there was continual alternation between the groupings — C0-CH2-C0— and — C(OH) rCH-CO— . The phenomenon received the name taiUomerism or desmotropi/.
308 ORGANIC CHEMISTRY. . I§ 23^
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 cooUng it to a low temperature, Ivnorr isolated the ketonic form, CH3« CO -0112 -00002115, in cr}'^stals melting at —39°. By the action of an equivalent quantity of anhydrous hydrogen chloride on a suspension of ethyl sodioacetoacetate in strongly cooled light petroleum, followed by filtra- tion of the sodium chloride and evaporation of the solvent at a low temperature, Kxorr isolated the enolic farm CH3«0(0H): OH -00002115, 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 and 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 enolic form, and its absence in the ketonic form, making the refraction of the enolic 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 applied by him to determine the proportion of the enolic form present in a tauto- meric mixture.
S236]
TAUTOMERISM.
309
These aids can be applied to the elucidation of the conditions governing the ketonizcUion of an enolic compound, and the inverse enolization 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. |
Solvent. |
Percentage of Enolic Form. |
|
Methyl alcohol Ethyl alcohol |
6.9 12.0 15.3 0.4 |
Methyl alcohol (50 per |
1.5 |
|
Amvl 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. In other instances, rise of temperature has been proved to cause displacement of the equilibrium 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 adding an equivalent amount of hydrochloric acid to a dilute aqueous solution of ethyl sodioacetoacetate. The enolic form separates in 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 1 1 per cent.
310 ORGANIC CHEMISTRY. (§ 23r
EnoUc compounds dissolve instantly in caustic alkali; but ketonic compounds do not, their solution proceeding slowly as they change to the enolic form. On subsequent addition of acid, the enolic modification is first obtained, but not the ketonic component.
Tautomerism of Oximes.
R 237. The structural formula, j^/> C=NOH, has been asagned
to the oximes (103). The action of hydroxylamine on aldehydes and ketones admits of another explanation, indicated in the scheme:
HO. /O
>CO-f >NH=H,0 + >C<| . W ^NH
Experiments directed to proving which of these formul® is rights have shown that the oximes are tautomeric in the sense of the scheme
\NH*
>C=N0H ^ >C
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,),0<f I + 2H = (CH,),CO + NH, • CH,.
\n.ch,
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, NHjOCHj. Heat- ing with hydriodic acid transforms this body into hydroxylamine and methyl iodide, proving that its methyl-group is linked to oxygen.
§2381 PYRONE DERIVATIVES. 311
PYRONE DERIVATIVES. 238, A number of compounds assumed to contain the group
CO
hc/\::h
II II
0
are known: they are called pyrone derivaliveSy and some of them occur naturally.
Chelidontc acid, C7H4O6, so called because it is found in Chelidonium majus (greater celandine), forms colourless salts, C7H2O6M2: it also yields yellow salts, C7H2O7M4, which are de- rived from an acid CyHeOy, xanthochelidonic acid. When set free from its salts, this acid readily loses one molecule of water, and is reconverted into chelidonic acid. By boiling with alkalis, the lat- ter is decomposed almost quantitatively into two molecules of oxalic acid and one molecule of acetone:
C7H406-f 3H2O " 2C2H2O4+C3H6O.
Oxalic acid Acetone
These properties are expressed by the structural formula
CO
„ II II
HOOC-a X^.COOH
o
Chelidonis acid
and conseniiently the acid can be called pyranedicarboxyltc acid* • Xanthochelidonic acid must then have the structural formula
i-.iT.p^COOH
CO
CH:C<^QQjj i
312 ORGANIC CHEMISTRY. [§239
in which the two hydroxyl-hydipgen atoms are also replaceable by metals; or, in its tautomeric form,
yCHz— €0-COOH CO
\::h2— co-cooH
The manner in which it is decomposed by water is evident from
the equation
H2 O yCH:C-COOH JCB. C— COOH
CO \o +3H2O - CO + ^q{J .
\jH:C— COOH \:;H C— COOH
Cbelidonic acid J}^ Q
Moreover, a synthesis of chelidonic acid corroborate this for- mula. The starting-point is acetone, which by Claisen's method (200 and 232) can be condensed with two molecules of diethyl oxalate:
.CH3 C2H5OOC.COOC2H6 /CH:C<^^^2H5 CO + =C0 +2C2H5OH.
\CH3 C2H5OOC.COOC2H5 ^H:C<^Jq^jj
The product is an ester of xanthochelidonic acid. When this is heated with concentrated hydrochloric acid, two objects are simul- taneously attained — the ester is saponified, and one molecule of water eliminated. These reactions yield a compound with the structural formula given above for chelidonic acid, and identical with it.
239. An important pyrono derivative is dimethylpyrone:
yCH=C.CH3 CO ')0 .
v)H=C • CH3
It can be synthesized from ethyl copper-acetoacetate and carbonyl chloride (263) :
§239) PYROSE DERIVATIVES. 313
CHa-CO CO.CH3 CHa-CO CO-CHg
HC-Cu— CH =CuCl2+ HC. /CH
/ \ /\co/\
C2H5OOC + CI2 COOC2H5 CzHjOOC COOCjHft
CO
On saponification with dilute sulphuric acid, two molecules of car- bon dioxide are simultaneously eliminated from the molecule, whereupon
CH3.CO CO-CHa
HoCv XH
^o/^'
dioukl result. The tautomcride,
HO OH
/ \, CH3 • C C • CH3
li '!
11 h i
H-C C-H
o
however, is formed, and loses one molecule of water, yielding di- methylpyrone.
Dimethylpyrone Is characterized by its ability to form addition- products with acids, which must be lo^iked upon as salts. These "salts" are former! by dLss<^>lving dimethylpyrone in an aqueous solution of hydrochloric acid, oxalic acid, etc.: thev are obtained in a crystalline form by the spontaneous evaporation of the solu- tkms. By dissohing them in a large quantity of water, they are completely hydrolyze<J. Collie and Tickle, the disrovomrs of these eomprjund.-?. a*ssume the quadnvfilentr/ of tht^ oj: '/'/<?« ntom closing the carl)on chain, thus attributing to dimdkylp>jrone hydrochloride the structure.
^CH=C.CH, C-OH ^O.CI. ^CH— (V-CII,
ca
314 ORGANIC CHEMISTRY. [§239
This mode of expressing the constitution of dimethylp3nx)ne has
TX
been adopted instead of the earlier formula C0C4H,(CH»)j>0<q,
Vox Baeter having proved the addition-product of dimethylpyrone 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 anunonia into methoxylutidine (389), formulated in III.:
CH, I O-I O N
•C C-CH, CH,-C C-CH, CH,-C C-CH,
11 I II II II I '
HC CH HC CH HC CH
\/ \/ \/
C-OCH, CO C-OCH,
I. II. III.
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 limited to dimethylpyrone and analogous compounds. Vox 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 Grigxard's compounds of alkyl magne- sium iodides and ether (75), such as CH3«Mg«H-(G2H5)20, must be regarded as oxonium derivatives,
C2H5^p.^MgT
2X15 O1I3
i 239] FYEONE DERI V A TIVE8. 315
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 aliphatic alcohols reacting readily with hydrogen halides to form tertiary halogen derivatives. The replacement of the hydroxyl-group by halogen is completely analogous to the production of salts by the interaction of bases and acids. v
AMINO-ACIDS.
240. The amtno-acids contain one or more amino-groups in Jirect union with carbon. They are of physiological import- ance, 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+C1]H2C-C00H= HzN-CHg-COOH-hHCl.
2. By reduction of oximes with sodium amalgam: R.C(N0H).C00H-f4H = R-CHNHg-COOH-f 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) :
CH3-C4 ->CH3-C^0H; H-NHj-* ^O \CN
Aoetaldehyde Lactonitrile
-*CH3-C^NH2-*CH3.C(vNH2 . \CN \COOH
Alanine mtrile Alanine
The amino-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
316
§241] AMINO-ACIDS, 317
ammonia, with acid chlorides they yield an acid amide with one hydrogen atom of the amino-group replaced:
R*C01Ci+H|HN>CH2'C00H = R-CO.NH.CHz.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)2NH-|-C1H2C.C00H = (CH3)2N.CH2-COOH-f HCl.
The amino-acids imdergo 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 or-amino-acids readily yield anhydrides (acid amides) by the elimination of two mole- cules of water from two molecules of acid :
CH2-NH|H HO IOC CHgNH-OC
2H2O+
CO[OH HIHNCH2 CO HNCH2
The /?-amino-acids easily lose ammonia, with formation of %insaturated acids. Thus, ^9-aminopropionic acid, obtained from i^iodopropionic acid, is converted by heat into acrylic acid and ammonia:
{NH^>CH2-CHJH1-C00II - NH3+CH2:CH.COOH.
Like the /'-hvdroxy-acids. the /--amino-acids yield inner anhy- ilridcs. On account of their similr.rity to the lactones, these sub- gtancesare called lactams:
CH2-rn2-rH0.ro CH2-rH2-CH2-CO
I ' =H20+|
NHfH OHl NH
f-Aminobutyric acid lactam of r-a<"i'>o^utyric acid
318 ORGANIC CHEMISTRY. [§242
EMII4 Fischer proved that the eaters of amino-ccids 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 eihyl ester of glycine hydrochloride , C2H600C-CH2'NH2'HC1. The esters are 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'COOH, 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 (7Xukv$, sweet; KoWa^ 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:
C6H5CO. OH
NH.CH2-C00H = C6H6-COOH-fNH2-CH2-C(X)H.
p^ Bensoic acid Glycine
Hippuric acid
Glycine can be synthetically prepared by the action of ammonia on monochloroacetic acid.
Glycine is a crystalline solid, and melts at 232*^ with decom- position: it is ver>- readily soluble in water, and insoluble in abso- lute alcohol. Like many amino-acids, it forms a well-crystallized, blue copper salt, soluble with difficulty in water, and obtained by boiling copper carbonate with a solution of glycine. This derivative crystallizes with one molecule of water of crystallization, and has ^he formula (XH2-CH2-rOO)2Cu-f H2O.
Betaine, 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 ammonium salt,
5 2421 A MIXO'ACIDS. 319
(CH3)3N-CH2-CO
OIH OH
since it is synthetically obtained from trimethylamine by the action of monochloroacetic acid, with elimination of HCl:
(CH3)3N + Cl.CH2-C(X)H=(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).
Betaine 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 trimethylamine.
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 beiaxnes.
Alanine, or a-aminopropionic acid, CH3-CH(NH2)«COOH, is synthetically prepared by the action of ammonia on a-chloropropi- onic acid.
Leucine, or a-aminoisobutylacetic 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 isovaleraldehyde-ammonia by the action of hydrocyanic acid, and hydrolysis of the resulting nitrile:
/"
(CH8)2CH.CH2.C^[OH +H|CN -»
taoValeraldehyde-ammonia
-> (CH3)2CH.CH2-CH(NH2).C02H.
Leucine
isoLeucine, or a-amino-y'J-methylvaleric acid,
^^ >CH.CH(NH2)-C00H, is also a decomposition-product of proteins. Its constitution is
320 ORGANIC CHEMISTRY. [§243
proved by synthesis. The aldehyde formed by oxidation of secondary butylearbinol — the optically active amyl alcohol — yields by the method of 240, 3, an amino-acid identical with isoleucine.
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 i^oleucine formed by decomposition of the proteins present in the fermenting liquid. These proteins are 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 butylearbinol 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
R-CH(NH2)-C00H-f-H,0 = R-CH-OH-f-CO,+NH,. The leucine obtained from proteins is optically active: its for- mula contains an asymmetric 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 aminosucdnamic
acirf,C2H3(NH2) <C00H^' ®^^^^ ^^ hydrolysis it is converted into aminosuccimc acid {aspartic acid), COOH«CH(NH2)*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 Isevo-rotatory. The former h swest, the latter tasteless.
Homologous with asparagine is glutamine, a constituent of the seeds of sprouting plants. It is the amic acid (163) of a-amino- glutaric acid, COOH.CH(NH2)-CH2-CH2-COOH.
In iiddition 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
NH
NH2-CH2«(CH2)3-CH<pQQpr» and is an ae-aminocaproic acid.
S 244] THE WALDEN INVERSION. 321
Emil Fischer has proved this formula by synthesis. On bring- ing ethyl nionosodiomalonate irfto contact with 7-chlorobutyro- nitrile, ethyl y-cyanopropylmaJonate is formed :
(COOC2Hs)2CHNa +C1 • CH, • CH, • CH, • (^N -*
Ethyl monosodiom&lonate 7-Clilorubutyronitrlle
- (COOC,H.),CH.(CH,),-CN.
Ethyl Y-cyanopropylmalonate
Treatment with ethyl nitrite and sodium ethoxide converts this ester by elimination of a carbethoxyl-group into the .sodium salt of an oxime :
NC.(CHA-CH<CgO§H;-NC.(CH,),.C<gOH^H^
Oxime
Reduction of this oxime with sodium and alcohol converts the NOH- group into NHj, and the CN-group into CHjNHj, with formation of inactive lysine,
CH2NH2- (CH2)3»CH < fiQQU*
Ornithine is the next lower homologue of lysine, and has the formula QsHjANa or NHj.CHj-CHj.CHj.CHdXHj) .COOH. Bao- teria convert it into putrescino or tetramothylenediamine (159). Its structure is proved by Emil Fischer's synthesis (349).
THE WALDEN INVERSION.
244. When one group attached to an asymmetric carbon atom is replaced by another, it is impossible to predict the sign of the rotation of the new compound: sometimes it is the same as that of the original substance, and sometimes oj)posite to it. By a series of substitutions, Walden has transformed an optically active compound into its optical antipode. On treatment with moist silver oxide, i-chlorosuccinic acid was converted into /-malic acid, and this substance was transformed by means of phosphorus i>enta- chloride into ri-chlorosuccinnic acid On the other hand, starting from <f-chlorosuccinic acid, the same operation yielded Z-chlorosuc- cinic acid. These transformations are indicated in the cyclic scheme
AgOH WUhlorosuccinic acid ►/-Malic a<:i(J.
I P^'l' AgC)H I I*^'''
d-Malic acid^ d-C'hlorosuccinic acid.
3-2 ORGANIC CHEMISTRY, l§ 244
Obviously, a transposition of the groups attached to the asymmetric
carbon atom is induced eithef by the moist silver oxide or by the
phosphorus pentachloride.
The following is another reaction-cycle, worked out by Emil
Fischer :
NOBr (i-Alanine • — ►^Bromopropionic acid.
NH,
I
NH,
NOBr
(i-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, \vith widely different experimental conditions, the same product with a similar sign of rotation always resulted in the latter operation. Although (i-alanine reacted with nitrosyl bromide to form /-bromopropionic acid, its ester under identical conditions yielded d-bromopro- pionic acid.
S ENTER has discovered many other examples of the Walden inversion, and demonstrated the complex nature of the phenomenon.
3r jj H Br
U I OH Br '^
A«OH
I. II. :ill. IV.
Fig. 70. — Werner's Theory of the Walden Inversion.
Werner has put forward a hypothesis in explanation of this inversion. On treatment of a-bromopropionic acid (I.) with silver hydroxide, the reaction can take place in two different ways. One of them involves direct action on the bromine atom, and its n» placement by the hydroxji-group. The lactic acid thus formed has the same configuration as a-bromopropionic acid, and the reaction does not exemplify the Walden inversion. Replacement of the hydroxyl-group by bromine by means of phosphorus penta- broniide. or otherwise, regenerates the original acid.
In the other type of reaction, the silver hydroxide attacks the ni()l(*rulo as indicated in I. On elimination of silver bromide, the hydroxyl-group does not replace the bromine atom, but takes up a position intermediate between the other groups, causing a rear- rangement of the other three bonds, as indicated in II. On
§245] * ETHYL DIAZOACETATE. 323
replacing the hydroxyl-group by bromine by the aid of phosphorus pentabromide or some other reagent, a substance of formula III. is obtained. It is the optical antipode of I., as is proved by rotating III. through 180°, the resulting configuration being repre- sented by IV. In this instance, a Walden inversion has taken place.
ETHYL 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:
C2H500C.CH2.NH2 + HN02=C2H500C.CH<' || +2H2O.
Glycine ethyl e;»ter ^N
It is ethyl diazoacetaiej and is also called diazoacctic ester.
The structurul 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- tion of the diazo-nitrogen. As an example may be cited the conversion of ethyl diazoacetate into ethyl glycollate by treat- ment with dilute acids:
¥ H H
II +6h = C2H500C.CH< +N2. N X)H
C2H5OOC.CH
/
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 monochloroacetatc, and iodine ethyl di-iodoacetate. Organic acids produce acidylgly collie acid esters:
CH3.COO+||^H.COOC2H5=cH3.cOO>^^*^^^^-'H5+N2.
324 ORGANIC CHEMISTRY. [§246
Near its boiling-point ethyl diazoacetate loses all its nitrogen, with formation of ethyl fumarate:
CH.COOC2H5 2N2CH. COOC2H5 - 2N2 + 1 1
CH.COOC2H6
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 acid, 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.
Hydraiiaoacetic acid Hydrasine Glyoxylie aotd
sulphate
The hydrogen atom of the CHN2-group is replaceable by metals, sodium dissolving in ethyl diazoacetate with evolutioa 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 gvj^at physiological importance is made apparent by the fact that the dry «! material in animal bodies — apart from the mineral constituent^^ and fats — consists almost wholly of pro- teins, by their being ^ essential constituent of each living plant-cell, and by their^jjbrming the most important part of human and animal food. 1 An animal can exist without fats 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 ver\^ 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 0-3-5
Those of one variety, called phospho-proteins, also contain phos- phorus. 325
o2o ORGANIC CHEMISTRY. [§247
The solutions of all proteins are optically active and Iffivo- 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 (Joe, cit.). 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 cr>'stalline substance. When the saltmg-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. I'or each albumin there is a definite coagulation- pomt: 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- txon. They cease to be coagulable by heat, but their composition remains unaltered. The products are called victa-protelns. 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-proteins are
248] PROTEINS, 327
insoluble in water, but soluble in dilute acids and alkalis. They are precipitated by neutralizing their solutions.
Th£ 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 acid, 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 fol- lowing:
1. Millon's reagent y a solution of mercuric nitrate containing nitrous acid, yields a red, coagulated mass on boiling.
2. The xanthoprotetn-reaction consists in the formation of a yellow coloration on treatment with waiin nitric acid.
3. The biuret-reaction depends upon the formation of a fine red to violet coloration when potassium hydroxide is added to a protein, and then a two 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).
Nomenclature.
248. The Chemical Society of London, the English Physiological Society, tho American Physiological Soci- ety, and the American Society of Biological Chemists have adopted the following system of nomenclature for the proteins.
328 ORGANIC CHEMISTRY. [§ 248
1. Protamines. — They are the simplest members of the group. Examples are salmine and sturine, 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, serum-albumin, and lad-albumin 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 serumrglobulin, 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 vitellin, caseinogen (the principal protein of milk), and casein (obtained from caseinogen by the action of rennet).t
8. Sclero-protcins.J — ^This class includes such substances as gelatin, chondrin, elastin, and keratin. The prefix indicates the
* The carbohydrate-radical separable in small quantities from many mem- bers 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 mortis. Von FtJ rth's " soluble myogen-fibrin " should be called soluble myosin. The two chief proteins of the musc'e-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 conju- gated proteins (9). Since the phosphorus-containing radical is not eliminated from the phospho-proteXns like a true prosthetic group, and their cleavage* products contain phosphorus, the English Societies prefer the arrangement indicated.
X This term replaces the word "albuminoid "in the limited sense in which most physiologists have employed it, but the American Societies retain the old name.
5 248] PROTEINS. 329
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 arc
a, NucLEo-pROTEiNS. — An example is guanylic acidy isolated from the pancreas, liver, spleen, and mammary gland. 6. CHROMO-PROTEiNS.t — HcBmoglobiu is a type. c. GLUCO-PROTEiNS. — They are exemplified by the mucins.
10. Protein-derivatives. J — Thoy 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 albumose, globulosCj and gelaiose.
c. Peptones . — Further products of hydrolysis which resemble the proteins in answering the biuret-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 " Iccitho-proteiiis" to this class, but their English confreres object on account of the uncertainty as to whether these substances are mechanical mixtures, adsorption-comi)ound8, or true chemical combinatijns.
t The American Societies employ the term "Haernoglobins" for chromo- prote'fns.
X The American Societios include two additional classes in this group: "proteans," insoluble products apparently resulting from the incipient action of water, very dilate 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 Societie? consider that it is better not to single out for special mention a few of the infinite varieties of insoluble modifications exhibited by proteins.
330 ORGANIC CHEMISTRY. [§ 24^
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-protclns 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.
Tlic sclcro' proteins differ somewhat in character from the albumins. Thov occur i:i tli:^ aniiuiil economy only in tho uiidis- solved state, being the organic constituents of the skeleton and the epidermis. They include various substances, such as keratin, ela^tinf 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
§250] PROTEINS. 331
composition as those obtained from the albumins. It is insol- uble in dilute acids and caustic alkalis.
The collagens 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, chondrosiUy which reduces Feh- ling's solution. Chondrin is a derivative of gelatin and chon- droitinsulphuric acid.
lu the inferior ordcT; of animal life a series of substances has been discover^:! appro:c!.n.itin;5 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. WTien 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 sxlk-gum.
Comexn is the organic constituent of coral. On hydrolysis, it yields leucine and an aromatic substance of unknown com- position.
250. Nearly related to the albumins are the conjugated 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.
332 ORGANIC CHEMISTRY, [§250
*
NucleO'proteins derive their name from the fact that they are the principal constituents of the cell-nuclei. They are com- binations of proteins with phosphoric acid or nucleic acids (Nucleus, important part of the cells of animals or plants). A nucleic acid is phosphoric acid which is partially saturated by union with basic substances, such as hypoxan thine, 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'protelns are compounds of proteins with substances containing iron, hwmoglobin being the dye of red blood-corpuscles. It decomposes into globin and koematin. In the lungs it unites readily with the oxygen of respired air, yielding oxyhoemoglohin. 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 carbonyUhcemoglobin, 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, oxyhaemo- globin yields the hydrochloride of haematin, called hcemin, 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- lated by boiling. Unlike the solutions of the albumins, these solutions arc not precipitated by nitric acid. WTien boiled with acids or caustic alkalis, they yield cither 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. 333
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 Protein 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, scatolo, ptomaines, p-cresol, 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 Schlttzen- 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
334 ORGANIC CHEMISTRY. l§ 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 succced 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,
CeHs-CHz-CHNHz-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 arginine, 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 seriney CH20H-CHNH2-COOH, which is sjTithesized from glycoUaldehyde :
CH20H.CQ-fHCN-^CH20H.CH^^;
-hNH3-^CH20H.CHNH2-COOH (240, 3).
This synthesis indicates the constitution of serine, and further confirmation is afforded by its reduction to a-alanine.
§252] PROTEINS. . 335
To this class also belongs the complicated diaminotrihydroxy- dodecanic acid, C12H28O5N2, a decomposition-product of casein.
5. Compounds with a closed chain containing nitrogen. — a- Tetrahydropyrrolecarboxylic ^ acid or proline j and hydroxytetra- hydro pyrrolecarboxylie acid or hydroxyprolinSy 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 • CHo- CH (NH2) • COOH, in its Isevo-modifi*
cation is a degradation-product of almost all albumins. Its racemic form has been synthesized, 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«CH2SH, 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.
• Cf. foot-note, 395.
336
ORGANIC CHEMISTRY,
l§253
On decomposition, some proteins yield almost exclusively a single amino-acid. Examples of such relatively simple proteins are salmine and clupelne, isolated by Kossel 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, the 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 acid. 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 a:id
Arginine
Histidine. . . . . Tyrosine. . . .
Proline
Cystine
|
Hsemo- giobin. |
Casein. |
Gelatin. |
Keratin (from bair) |
|
0 |
0 |
16-5 |
4.7 |
|
4 |
0-9 |
0-8 |
|
|
27-8 |
10-5 |
2-1 |
7.1 |
|
4-3 |
1-2 |
0-6 |
|
|
1-7 |
10-7 |
0-9 |
3-7 |
|
5.2 |
4-8 |
7.6 |
|
|
10.5 |
2-6 |
0-4 |
|
|
1-3 |
4-5 |
3.2 |
|
|
2.3 |
3-2 |
5-2 |
3-4 |
|
0-3 |
0-1 |
8 |
Fibroin
iilgh 21 1-6
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 boon thought that the amino-acids of the protein molecule are linked by their amino-groups, as in glycylglycine,
NH2.CH2.CO— NH.CH.-COOH,
§2531 PROTEINS. 337
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 ami no-acids are converted into anhydrides, with elimination of two molecules of alcohol, the reaction some- times taking place even at ordinary temperatures :
2NH,.CH,.COOC,H4 = 2C,H»0H+NH <ch^CO^ ^^'
Glycine ethyl ester Diketopiperazine
(Glycine anhydride)
Under the influence of dilute caustic potash, this anhydride takes up one molecule of water, yielding a dipeptide, glycylglycine :
NH<^2"^J5L*>NH + H,0 = NHj.CHvCK)— NH.Cm.COOH.
Una — UU
Glycylglycine
When a dipeptide is treated with phosphorus pentachloride in acetyl. chloride solution, the carboxyl-group is changed to COCl, and the residue of this acid chloride fcan be introduced into other amino-acids :
NH,.CHa.CO— NH.CH,.C0a-hH,N.CH2.C00C,H, = = NH, . CH, . CO— NH . CH J . CO— NH . CH, . COOC.H, -h HCI.
Saponification of this substance yields a tripeptide, and so on.
The polypetides, especially from the tetrapeptides to the octapeptides, arc very like the natural peptones, as a short sum- mary of the characteristics of both classes will indicate. Most of them arc 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
338 ORGANIC CHEMISTRY. [§254
bitter and insipid taste, and are precipitated by phosphotungstic acid. They answer the biuret-test (247, 3) : for the poly- peptides the sensitiveness of the reaction augments with mcrease in the length pf 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 ail the characteristics just enumerated, and had it been first discovered m 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 bemg 891. It is the most complex substance of known structure hitherto obtamed by synthesis. The natural proteins are prob- ably mixtures of various polypeptides 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. When it is treated with concentrated hydrochloric acid, sericoin results, and is converted by further boiling with the same acid into a peptone. Pancreatic juice converts this substance into tyrosine (352), and another fx^ptone, which answers the biuret-test. On warming this second peptone with baryta-water, however, it no longer answers this te.5t, and a dipeptide, glycylalanine, can be isolated from the products of decomposition.
254. Nothirg is known about the molecular weight of the proteins, except that it must be ver}^ great. Attempts to deter- mine it by the cryoscopic method have yielded very small depressions of the freezing-point. It is uncertain whether the observed depressions may have been due to the presence of traces of mineral salts in the albumin employed, since their com- plete removal is a difficult operation. The negative character of the results might also be due to the presence of the albumin in the colloidal state, since colloids produce only a very small molec- ular depression (" Inorganic Chemistry,'' 196).
52541 PROTEINS, 339
The proportion of sulphur m 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 haen^oglobin 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.
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
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*3 X 10^^ = 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.
CYANOGEN 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-f2CuS04 = 2K2S04-fCu2(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- nium 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 th^ 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- fiium cyanate, KCNO, are produced, the process ])eing analogous
340
5256] CYANOGEN AND HYDROCYANIC ACID, 341
to the formation of potassium chloride, KCl, 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 ammonium 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 azulminic acid. Cyanogen is inflammable; burning with a peach-blossom coloured flame.
Hydrocyanic Acid, HCN.
256. 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 effected 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 fcrrocyanide (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.
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,' 374), its toxic effect de*
Z42 ORG ASIC CHEMISTRY. I| 257
pends apoo the degree of iooizatioQ, 90 that it must be the cyanogm ions that exert the poisonous sction. Other evidence leads to the same coodusioQ : thus, pota»um ferrocranide, the aqueous aolutioo of which contains no cyanogen ions, is non-poisonous.
Hydrocyaoic acid must be looked upon as the nitrile of formic acid: HCXX)H -►H-CX. Its formation by the distUlation of amm^^ium formate, and the reverse transformation — rrferred to i.bove — fif hydroc>'anic acid into ammonium formate by addition c;f two molecules of water, favour this \^w. as does also the forma- tion of hvdrocvanic acid when chloroform, H-CCU. is warmed with alcoholic ammonia and caustic potash (145). Methylamine IS obtained by reduction of hydrocyanic acid:
H.C^X+4H = H3C NHa.
Hydrocyanic acid is one of the weakest acids, its aoueous solu- tion having low electric conducti\ity.
Hydrocyanic acid can be obtained from amygdalin, Q^fLgfii^S^ which is a glycoside (217), and is found in bitter ahnonds and other vegetable-products. In contact with water, amygdalin is decom- posed by an enzjTne (222), emulsin, also present in bitter almonds, into IxfHzaldehydc, hydrocyanic acid, and dextrose:
C,«H,70„N +2H,0 = C7H.O+HCN+2CJI„0,.
Amygdalin Beiualdehyde Deztroae
Cyanides.
257. The cyanides, or salts of hydrocyanic acid, are pro- duced when carbon, nitrogen, and a strong base are in contact at red heat; for example, when a mixture of carbon and potassium carbonate is strongly heated in a current of nitrogen. Cyanides ftr(» also formed by heating nitrogenous organic substances with an alkali or alkali-metal (4). Ammonium cyanide, NH4CN, is obtained 1)7 passing ammonia-gas over red-hot carbon.
When barium carbide is heated in nitrogen, it yields barium cyanide:
BaC2-hX2 = Ba(CX)2.
This reaction affords a means of preparing cyano-derivatives from atnio-jplicric nitrogen.
§2571 CYANIDES. 343
A good yield of potassium cyanide, KCN, or sodium cyanide, NaCN, is readily obtained by heating magnesium nitride with potassium or sodium carbonate and carbon:
Mg3X2 -f NaaCOa -f C = 2XaCN -f 3MgO.
The isolation of the nitride can be avoided by passing nitrogen over a mixture of magnesium-powder, sodium carbonate, and carbon at elevated temperature :
3Mg -h NaaCOa -f C -f N2 = 2NaCN -h 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 contaim'ng 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 FeCa + N2.
Potassium cyanide is readily soluble in water, and with difficulty 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-h2H20 = HCOOK-hNHa.
Potassium cyanide always has an odour of hydrocyanic acid, owing 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 afforded 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««ium/erroc2/amd6,K4Fe(CN)6,crystallize8inlarge,8ulphur-
344 ORGANIC CHEMISTRY. IS 258
yellow crystals, with three molecules of water, which can be driven off by the application of gentle heat, leaving a white powder. It is not poisonous (256). Wlien 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 (81). This method is often employed in the preparation of carbon monoxide.
Cyanic Acid, HCNO.
258. Cyanic add 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 Wohler, by whom the product was called ''insoluble cyanuric acid," or cyanielide^ which is a polymeride of cyanic acid, and probably has the formula (HCN0)3. It has, however, been shown by Sexier 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 subsisting 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 cyapic 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 0° the velocity of transformation of cyanic acid is much greater, and the i)olyni(Tic, stable cyamelide is formed, the proces:s, moreover, l)eing considerably accelerated by its own calorific effect. Above 150° cyamelide is converted into the isomerii? cyanuric acid. This
§259] CYANIC ACID. 345
transformation is analogous to that of rhombic sulphur into mono- clinic sulphur, the transition-point being about 150°, although the process is so slow that it could not be determined accurately. A similar slowness prevents observation of the reverse process, 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. la this respect it is comparable with detonating gas ("Inorganic Chemistry," 13).
Above 0° an aqueous solution of cyanic acid changes rapidly into carbon dioxide and ammonia:
HCNO + H2O = H3N -hC02.
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, C^ ja , and from isocyanic acid.
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 acid, and polymerizes readily tj cf/anuric chloride, C3X3CI3. Cyanogen chloride is converted by the action of potassium hydro:^- ide into potassium chloride and potassium cyanate:
CNCl +2K0H =CXOK -f KCl -f 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 cyanuratc (CyOC2H5)3, can readily be separated from the reaction- product (262).
Esters 0/ \socyanic add, on the other hand, are well known, and are obtained by the action of alkyl halides on silver cyanate:
CO:NlAg-fI|C2H5 = CO.NC2H6+AgI.
The isocyanic esters are volatile liquids, with a powerful, stifling odour: they, too, polymerize readily, yielding \socyanuric esters, such as (CONC2H5)3 (262).
The constitution of the isocyanic esters follow^s from their decom-
316 ORGANIC CHEMISTRY. [§260
position into carbon dioxide and an amine, by treatment with water, or better with dilute alkalis:
COiN-CHs+HiO = 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 obtaiDed 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-NH,-*R-CO-NHBr. The hydrogenof theamino- 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 compound, R*CO-NKBr, which is unstable, but can be iso- lated. This p>otassium bromoamide readily undergoes an intra- molecular transformation, similar to the Beckmann transformation
(103):
R.C-OK Br-C-OK
II changes to |
Br-N R.N
Potassium biomuamide
The transformation-product loses KBr, with formation of an i«o-
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-
5 2601 THIOCYANIC ACID. 347
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 oxysulphide, COS, instead of carbon dioxide:
HCNS+H2O = H3N+COS.
Potassium ihiacyanate is obtained by boiling a solution 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 thiocyanatey AgCNS, is deposited in the form of a white, cheese-like precipitate, insoluble in dilute mineral acids. Ferric thiocyanate, FeCCNS),, 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(CNS)„ 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
esters, the thiocyanic esters, C^xr' , and the iaothiocyanic esters,
Thiocyanic esters are obtained by the action of alkyl iodides upon the salts of thiocyanic acid:
CN-S K+I C2H5 = CN.SC2H54-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.C2H5+2H - CNH4-H.S.C2H5.
Alkylsulphonic acids, such as C2H5*S020H (60), are obtained by oxidation.
348 ORGAXIC CHEMISTRY, [§260
Under the influence of heat the thiocyanic esters are trans- formed into isothiocyanic esters: thus, distillation of allyl thio- cyanate, CN-SCsHs, effects this change.
The isothiocyanic 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-
stitution C \, ^ . Wien treated with concentrated sulphuric acid,
they take up water, yielding a primarj' amine and carbon oxy- sulphide:
R.NrCS + HzO = R-NHg+COS.
They are converted by reduction into a primary amine and triihiO' methylene J (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-oib are described in 269 and 270.
Cyanamidey CN-NH2, is obtained in various reactions; for in- stance, by the action of ammonia upon cyanogen chloride. It is a crystalline, hygroscopic solid, and polymerizes readily. Its hydro- gen atoms can be replaced by metals; thus, silver ' yields silver cyanamide, CN«NAg2, which is yellow, and insoluble in dilute ammonium hydroxide, wherein it diflfers from most silver com- pounds.
When calcium carbide is heated to redness in a current of nitrogen, calcium cyanamide is formed:
CaC2 + X2 = CN.NCa+C.
The absorption of nitrogen is much facilitated by addition of 10 per cent, of calcium chloride: This' compound cian also be obtained by heating lime and carbon to a red heat in an atmos- pherc of nitrogen. The crude product is called '' Lime-nitrogen " (German, Kalkstickstoff)^ and finds application as an artificial fertilizer, being decomposed slowly by water at ordinary tempera- tures into ammonia and calcium carbonate;
CaCN2+3H20 = 2NH3-hCaC03.
§§261,262] FULMINIC ACID. 349
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.
261. Salts of fulminic acid are obtained by the interaction of mercury or silver, nitric acid, and alcohol, in certain proportions- The best known of them is ynercuric fulminate, HgC202N2, 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-r;alled "fulminating mercury " plays an important part in their application.
Silver julminaie, 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.
Free fulminic acid is a very unstable, volatile substance: it has an odour resembling that of hydrocyanic acid, and is excessively poisonous.
According to Nef, the formula of fulminic acid is C=:N*OH, con- taining a bivalent carbon atom. When mercuric fulminate is treated with acetyl chloride, a compound of the formula CHa«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, BraC202N2, with the constitu- tional formula
Br— C^X— O
I I.
Br— C=N— O
Cyantiric Acid and isoCyanuric Acid.
262. Cyanuric bromide, CaNsBra, is obtained by heating potas- sium ferricyanide with bromine at 220*^. By heating with water, the bromide is converted into cyanuric 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 \socyanuric esters, the former being called ''0-esters/' and the latter ''N-esters.'*
350 ORGANIC CHEMISTRY. II 262
The normal cyanuric esters are obtained by the action of sodiuhi 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 II ; II 11-
N N R-N N-R O O
\/ \/ v
C CO C:NH
OR I. II. 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 and carbon dioxide, a decomposition accounted for in constitutional formula II. The 0-esters are formed when an alkyl iodide reacts with silver cyanurate at ordinary temperatures, but their conver- sion into the X-esters by heating explains the diflference in the products obtained at ordinary and at elevated temperatures.
Klason has suggested that cyamelide (258) is isocyanuric 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 Sexier 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 bv Chattaway and Wadmore, who have succeeded in replacing the metal in potassium cyanurate by chlorine. They regard the compound formed as (0:CrN«Cl)3.
Formula III., containing imino-groups, possibly represents the structure of cvamelide.
DERIVATIVES OF CARBONIC ACED.]
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+C0 4=iCOCl2, is attained, corresponding at 505*^ with about 67 per cent, of dissociation. It was called phosgene (0«$, light; ^€vvau)j to produce) by J. Davy in 1811, under the impression that its formation by this means can only take place in presence of sunlight, a view since proved to be incorrect. Carbonyl chloride is a gas with a powerful, stifling odour. It dissolves readily in benzene, and the solution is 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:
/CI H OC2H5 /OC2H5
CO + ->co
\:i ^Cl
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 ammonia, the two Cl-atoms in carbonyl chloride can be replaced by amino-groups, with formation of the amide of
351
352 ORGANIC CHEMISTRY [§ 264
carbonic acid, urea^ CO(XH2)2 (266). All these reactions are characteristic of acid chlorides.
The chlorocarbonic esters, also called chloroformic esterSj are col- ourless liquids of strong odour, and distil without decomposition. Thc}^ are employed for the introduction of the group — COOCiH* 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 inflanmiable, it must be handled with 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 triihiocarbonates:
BaS+CS2 = BaCSa.
Barium trithiocarbonate
The barium salt is yellow, and dissolves in cold water with difficult}'. By the addition of dilute acids to its salts, free trUhiocarbonic acidf H2CS3, can be obtained as an unstable oil. The potassium salt is employed in the destruction of vine-lice.
§§ 205, 266] XANTHIC ACID AND CARBON OXY SULPHIDE. 353
The potassium salt of xanthic acid is formed by the action of potassium ethoxide on carbon disulphide:
•OC2H6 CS2+KOC2H5 = CS
This is effected by agitating carbon disulphide with a solution of caustic potash in absolute alcohol, when potassium xanthate sepa- rates in the form of yellow, glittering needles. Free xanthic acid is very unstable: it owes its name {^avdos. 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:
•OC2H5 COS+C2H5-OK = rO
\SK
Urea, C0< 5555^^.
266. Urea owes its name to its occurrence in urine, as the final decomposition-product of the proteins in the body.
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.
.Tit ORGANIC CHEMISTRY. [|265
To obtain urea from urine, the latter is first concentrated by evapora- tion. On addition of nitric acid, urea nitrate , (X)(NH2),-HNO^ (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 is set frea from the solution of the nitrate by treatment with barium carbonate :
2COX2H,.HX05+BaCOs = 2COXjH4+Ba(NO,),+H20+CO,.
Crea 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, earbonyl chloride, COCI2, this reaction proving its constitution (263):
y\C\ HINH2 /^^^
CO -h = CO +2HC1.
\lCl~HlNH2 \nh<
^2
Carhonyl Urea
chloride
A confirmation of this view of the constitution of m-ea is its forma- tion by the action of ammonia on diethyl carbonate.
Urea is formed by addition of ammonia to isocyanic acid:
NH /NH2
Cf^ +NH3 = C0 .
Ammoniu'Ti tsocvanate dissolved in water is transformed into urea on evaporation of the solution. This is the method by which WoHLKit e.Tected his classic svTithesis of urea, by heating a mixture of potiissium 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 Hambly. Their researches have shown that the reverse trans- formation of urea into ammonium isocyanate occurs also, since, on addition of silver nitrate, a solution of pure urea in boiling water yields a precipitate of silver cyanate. An equilibrium is attained:
(XXXHjjj^CON-XH^.
Ij Ammonium
267] UREA, 355
When this equilibrium is reached, the solution only contains a small percentage of wocyanate. It is ahnost independent of the tempera- ture, proving that the transformation of the systems into one another is accompanied by but slight calorific effect (54).
tsoCyanic 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 isocyanic ester, addition takes place, with production of a symmetrical dialkyUurea:
yNHR COrNR+HaNR' = CO
^NHR'
This is a general method for preparing symmetrical dialkylureas.
A monoalkylurea is obtained by the action of ammonia, instead of an amine, upon an taocyanic ester.
^NRR'
Unsymmeirical dialkylureas, CO , are prepared by the action
of tsocyanic acid on secondary amines. The method of procedure is analogous to that employed in Wohler's synthesis of urea, and con- sists in warming 6l solution of the t«ocyanate of a secondary amine:
CONH-NHRR'-CO
The unsymmetrical dialkylureas are converted by treatment with absolute (100 per cent.) nitric acid into nitro-com pounds, which were discovered by Franciiimont, and are called nUroamines:
(CH,),N +N0,
CONHj
-> (CH3)jN.NQ,. 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,
356 ORGANIC CHEMISTRY. [§267
2CON2H4,C2H204, dissolve with difficulty in solutions of the corresponding acids.
In some of its reactions, notably in certain condensation-pio-
cesses, urea behaves as though it had the structure C — OH. An
^NH, ether of this isourea is obtained by addition of methyl alcohol to cyanamide, the reaction being facilitated by the presence of hydro- chloric acid:
^ /OCH3
C +HOCHs-C=NH .
Cyftiuuuide Methyli«ourea
This 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,
"^NHCHs CH,.NH2.
When heated, urea melts; it then begins to evolve a gas, con- Bisting 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 HgNv CO. , >C0 = NH2-CO-NH.CO.NH2+NH^
\|NH2H| HN'^ Bi"«^
Biuret is a crystalline substance which melts at 190°. Whea copper sulphate and caustic potash are added to its aqueous solu- tion, it gives a characteristic red to \'iolet coloration ("biuret- reaction").
§267] UREA. 357
On further heating, biuret unites with a molecule of unaltered urea with, elimination of ammom'a, and formation of cyanuric acid (262):
NH
/\
|g|NH*CO-NH>CO>NH[H] _ ^ ^^+2NH
HgN-ICOFTO HN NH ^'
\/ 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 caustic potash and bromine (German, Bromlauge), in which potassium hyp)obromite is present: the percentage of urea can be calculated from the volume of nitrogen liberated. Liebig's titration-method is based upon the formation of a white precipitate of the composition 200X2114- Hg(N03)2*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, H^N-NHj + HjO, react together, with formation of semicarbazide, NHj'CO-NH-NHj, a base which melts at 96°, and combines with aldehydes and ketones similarly to hydroxylamine :
Rj-CIoTH^N-NH-CO.XHj -* Rj.CiN-NH.CO.NHj.
The compounds thus formed are called scmicarbazones; they some- times crystallize well, and are employed in the identification and separation of aldehydes and ketones.
358 ORGANIC CHEMISTRY. [§268
Derivatives of Carbamic Acid. 263. Carbamic acid, .NH2-C0-0H, which b 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 yOHNHs
C02+NH8-C=0 ; +NH3 = C^0
\NH2 \NH2
Ammonium oarbamAte
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. \NH2 When the salts of carbamic acid are heated in solution, they readily take up water, forming carbonates.
The esters of carbamic acid are called urethanes. They are formed by the action of ammonia or amines upon the esters of carbonic acid or chlorocarbonic acid:
/IOC2H54-H NH2 /NH2
CO^ = CO +C2H60H;
\OC2H5 \OC2H5
Diethyl carbonate Urethane
/[CITHINH2 /NH2
CO ->co
\0C2H5 \0C2H5
Ethyl chlorooarbonate
Urethanes also result in the action of alcohol upon tsocyanic esters:
^0 /OC2H5
Cf +HOC2H5 = C=0
^NCHa \NHCH3
Urethanes are also obtaincfl by lx)iliiig acid azifles(97) with alcohol :
R.CON3 + C,H»OH = R NHC00C,H, + N,
"" ♦ca^H'a.
§2691 URETHANES AND THIOUREA. 359
Since the azides are easily prepared from the corresponding acids, and the urethanes readily yield the corresponding amines, the car- boxy 1-group can be replaced by the ami no-group :
R-COOH — R-COOCjHs -> R-CONHNH, — R-CON, —
Acid Ester Hydraside Aside
-» R-NHCOOCjHj -> R-NH,.
Urethane PrimAiy
amine
Urethanes distil without decomposition: ordinary urethane,
/OC2H5
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 nitr our ethane^ C2H60«CO«NH-N02; and on careful hydrolysis this substance yields nitroamine, NH2-N02.
Thiourea, CS(NH2)2.
269. Ammonium uothiocyanate yields thiourea in a manner analo- gous to the formation of urea from ammonium uocyanate (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 Mothiocyanate. Alkyl-derivatives of thiourea result from addition of ammonia or amines to the mustard-oils (260) the reaction being similar to the formation of alkylnsubstituted ureas from Mocyanic esters (266).
These modes of formation prove that the constitution of thiourea is expressed by the formula CS(NH2)2» 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
>NH
an aikyl iodide, compounds are obtained in accordance with the
equation
/NH2 / /NH, \
C:^8|H -h IIC^Ht - ( C -SCjH, IHL
The alkyl-group in this compound \n linked to sulphur; for it de> composes with formation of mercaptan, and on oxidation yiMm a iulphonic acid.
360 ORGANIC CHEMISTRY. [§270
Thiourea forms well-defined crystals, melting at 172*^, and readily soluble in water, but with difficulty in alcohol. On treatment with mercuric oxide, it loses sulphuretted hydrogen, forming cyanamide:
/
NfiTj .N
Ct +HaS.
C IS
\
k.
Guanidine, CH5N3.
270. Guanidine is formed by the interaction of ammonia and orthocarbonic esters or chloropicrin, (XI3NO2. This prob- ably results from addition of four amino-groups to the carbon atom^ the compound formed then losing one molecule of am- monia:
/NH2 C(OC2H5)4 -> C(NH2)4; - NH3 -> C^NH .
Tetraethyl ortho- \NH«
carbonate M^xi2
Guanidine
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/
Guanidine is generally prepared by heating ammonium 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 + (CH5X3)HCNS.
It is obtained in the form of guanidine thiocyanate , the reaction taking place in the following stages:
SCNH.NH3 -> CS(NH2)2 -> H2N.CN.
Ammooium thiocyanate Thiourea' Cyananlide
5 2701 GU AN WINE DERI VA TI VES 36 1
The cyanamide unites with a molecule of the unaltered ammonium thiocyanate:
Ct +NH3.HCNS = (C^NH HCNS. ^NHa \ XNHz/
Guanidine thiocyanate
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 strengthening of the basic character, occasioned by exchange of carbon yl-oxy gen for an imino-group, is worthy of notice. Guani- dine yields many well-defined, crystalline salts.
/NH.NO2 Nitroguanidiney C=:NH , is obtained in solution by the
\NH2
action of fuming nitric acid upon guanidine: dilution with water
precipitates the nitroguanidine, which is very slightly soluble in
/-NH.NH2 water. On reduction, it yields aminoguanidinef 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 synthesized by the action of cyanamide on ornithine (243) :
COOH.CH(NH2)-(CH2)3-NH2+CN2H2 -
Ornithine Cyanamide
COOH . CHNHa . (CH2)3NH
Nc:NH. NHa
ArginiDe
The cyanamide is added at the ^-NH2-group, as represented in the equation, so that arginine is a-amino-d-guanino-n-vaieric acid.
URIC-ACID GROUP.
271. Uric acid, C6H4O8N4, 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 urMo-acids and the (Edd-^retdes (ureides), which are amino-acids and acid amides, con- taining the urea-residue, NH2-C0-NH — , instead of the NHg-group.
Pardbanic dcid, C3H2O8N2, 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 oxalylurea:
.NH OHH
do\ COOH ^^\
I j>CO+ = I + >C0.
COOH TTX<
Parabanic acid (Oxalylurea)
H2N
NH OHH
On careful treatment with alkalis, it takes up only one molecule of water, yielding oxaluric acid:
.NH C0\ CO— NH-CO-NHa
io/^'-A
;ooH
\ '^-._ Oxaluric acid
-fOHH
Alloxan, C4H204X2,4H20, 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
362
1271] ALLOXAN AND ALLANTOINE, ' 363
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 NH2
ho Ao '- '
CO +00. NH+OHH COOH 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 allozarUine :
2C,HaO,N2+2H - CgHAN,.
Alloxantioe
Alloxantine is also formed directly from uric acid by evaporating it to dryness with dilute nitric acid. When treated with ammonia, it forms a purple-red dye, murexide, QHgOcNs. The formation of murexide is employed as a test for uric acid. Alloxantine dissolves with difficuFty in cold water, and gives a blue colour with baryta- water. There is still doubt as to the constitution of these com- pounds.
AUarUoinef C4H6O3N2, is formed in the oxidation of uric acid with potassium permanganate, a fact which has an important bear- ing on the constitution of this acid. AUantoine has the structure
/NH.CH— NH.CO.NH2 CO I \NH.CO
AUantotne
rince it can be obtained synthetically by heating glyoxylic acid with urea:
H
/NH|H HO]— C— |OH+H|HN.CO«NHa
CO +
\NHiH~HOl-CO
Urea Glyoxylic add
/NH-CH— NH-CO-NHa CO I \NH-CO
AUaQtoIne
364 ORGANIC CHEMISTRY. 15271
The formation of alloxan and allantolne from uric acid gives aa insight into its constitution, the production of the first indicating
C-N
the presence of the complex C yC; and of the second, the pre»-
C-N
ence of two urea-residues, together with the complex C^ I
These are accounted for in the structural formula
NH-CO
I CNHv
I II >X). NH— C-NH^
Uric acid
lo
This formula also gives full expression to the other chemical proper- ties of uric acid.
The folio wiag synthesis affords confirmation of the accuracy of the constitution indicated. Malonic acid and urea combine to form malonylurea or barbituric acid :
NH— CO
I I CO CH,.
I I NH— CO
On treatment with nitrous acid, this substance yields an tsonitroso* compound which can also be obtained from alloxan and hydrozyl* amine, vioLwric acid :
NH— CO
CO C=NOH.
I I NH— CO
On reduction, violuric acid gives nminohnrhituric acid:
NH— CO
CO c<Vi ', I I "
NH— CO
§272) URIC ACID. 365
which, like the amines, adds on one molecule of uocyanic acid on contact with potassium cyanate, forming
NH— CO
CO c< ^co.
I \im I
NH— C|0 HjHN
This substance is pseudourtc add, and differs from uric acid only 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 yielding 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 ^ C6H203N4Na2-f H2O, is much more soluble in water than sodium hydrogen urate y 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 conveniently 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 compoimds 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 hypoxarUhinej C6H4ON4; xanthine, C6H4O2N4; and guanine, C5H5ON6: to the latter belong the vegetable bases i/i€o6romine,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=eCH NH
I I N/«\/7\
HC2 «C.7NH or i « 81
II II \3H
4 9 Jf
9
N
366 ORGANIC CHEMISTRY. [|272
Xanthine, theobromine, and caffeine have the following structural formulae and rational names:
NH— CO NH CO
CO C— NHv CO C— NCCHa).
>H; I II >CH;
NH— C — N^ ' N(CH3)— C N^
Xanthine or 2: 6<lioxypurine Dimethybcanthine, theobromine,
3 : 7-€hmethyl-2 : 6-cUoxypurine
N(CH3)<
N(CH,)— CO
io i-._^ I N \CH.
N (GHs)— C N^
Trimethylxanthine, caffeine, thelne. or 1 :3 :7-trimethyI-2; 6-dioxy purine
Theobromine and caffeine result from the introduction of methyl- groups into xanthine.
Xanthine, €511402X4, is present in all the tissues of the human body. It is a colourle&s powder, soluble with difficulty in water, and possessing a weak basic character. On oxidation, it yields alloxan and urea.
Theobromine f C7H8O2N4, exists in cocoa, and is prepared from this product. It is only slightly soluble in water, and is converted by oxidation into monomethylalloxan and monomethylurea.
Caffeine or thelne, CJH10O2N4, is a constituent of coffee and tea It cryst^llisJ'es with one molecule of water in long, silky needles, and is raodarately soluble in water. It is generally prepared from tea- dust. On careful oxidation it yields dimethylalloxan and mono^ methylurea.
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— C^O NH--CO
CO (^— NHv .; CO C— NHv I II >C0 I II >CIL
NH— C— NH-^ NH— C N^
Uric acid Xanthine
These formulae indicate the possibility of obtaining xanthine by the reduction of uric acid, and up to the year 1897 numerous un-
§2731 VRIC ACID. 367
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 oxy chloride. 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 oxychJoride, the first product is S-oxy-2:^-dichlorojmrine: on further careful treatment with the same reagent, this substance is converted into 2:6:8- trichloropurine:
N=C— OH N=CC1
II 'II
HO-C C— NHv -*C1.C C— NHv
II II >C.OH II II Vj.Cl.
Tautomeric form of 2: 6: 8-TrichloropuriDe
uric acid
The behaviour of uric acid in this reaction accords with the tauto- meric (235) formula of tri hydroxy purine, 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:
C5HN,Cl3 4-4HI - C5H2NJ2+3HCI+2I.
Reduction of the aqueous solution of di-iodopurine with zinc-dust yields purine, a white crystalline substance, melting at 216^-217% and very readily soluble in water. It is a weak base, since it 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-atoms
368 ORGANIC CHEMISTRY. [§273
2 and 6 are exchanged for ethoxyl-groups. On heating the corn* 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.OC2H5 N=C.OH NH~CO
C2H5O.C C— NH ->HO.C C— NH -^CO C NH
N-
>c.ci
>CH
N N— C— N NH— C— N
>h'
2:6-Diethoxy-8-chloropuriDe Xanthine (tautomeric form) Xanthine
When 2:6'diethoxy-S-chloropurin€ is heated with hydrochloric acid, only the ethyl-groups are replaced by hydrogen, with produc- tion of a compound of the formula
HN— CO
i
;0C— 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 Utra^ methyluric acid. On treating this with phosphorus oxychloride POCI3, chlorocaffeine is formed :
3C603N4(CH3)4+POCl3 = 3C502N4(CH3)3Cl+PO(OCH8)8.
It can be converted by nascent hydrogen into caffeine.
Electro-reduction of Purine Derivatives.
Tafp:l has stated that caffeine, xanthine, uric acid, and sim- ilar conipouiuls nMluciblc with difficulty by the ordinary methods rcaJily take up hydrogen' evolved by electrolysis. For this pur-
§273] ELECTRO-REDUCTION OF PURINE DERIVATIVES. 369
pose the compounds are dissolved in sulphuric acid, the strength of which is varied to suit the particular compound, and lies between 50 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 current readily effectjj the reduction of these compounds.
Xanthine and its homologues take up four atoms of hydrogen, becoming transformed into deoxy-derivatives:
C8H10O2N4+4H = C8H12ON4+H2O.
Caffeine Deoxycaffelne
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 purane:
C5H4O3N4+6H = C5H8O2N4+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 SC— 7NHv^ ->C0 CH— NHv^.
3NH— *C— ^NH/^^ NH— CH— NH/^
Uric acid Purone
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 isopwronc, which has acidic properties, and is readily oxidized.
370
ORGANIC CHEMISTRY.
[§273
The application of the electro-reduction 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 describing 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. 71, since the quantity of hydrogen absorbed in the unit of
TIME IN MINUTE8
Fio. 71. — Normal Reduction-
CURVE.
0.04 MQaFT*
Fia. 72. — Abnormal Rbdoo*
TION-CURVE.
time must diminish m the same proportion as the quantity of unre* duced 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.
5273] ELECTRO-REDUCTION OF PURINE DERIVATIVES. 371
The graphic representation in this case for the addition of 0-04 milligrammes of platinum for each 100 square centimetres of cathode surface is shown in Fig. 72. This curve indicates that the slightest contamination of the lead of the cathode by certain other metals 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 ex- ceeds a certain value. This is a minimum when platinum elec- trodes 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 auperiension (German, Uberspannung) is necessary. This supertension has a very large value for lead, but as soon as the least trace of platinum or of certam other metals is brought into con- tact with the surface of the lead cathode, the supertension dis- appears, and with it the power possessed by the evolving hydrogen of reducing purine derivatives.
The explanation is that the contact-difference of potential regu- lates 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 unattainable 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 part 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 j 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, C5H5N, and its derivatives, with a
373
374 ORGANIC CHEMISTRY. [8 274
ring of five carbon atoms and one nitrogen atom; furan, C4H4O, with four carbon atoms and one oxygen atom; pyrrolCj C4H6N, with four carbon atoms and one nitrogen atom; ihiophen, C4H4S, with four carbon atoms and one sulphur atom; pyrazole^ C3H4N2, with three carbon atoms and two nitrogen 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.
* In RicHTER*8 " Lexikon der Kohlenstoffverbindungen,'' 319 ring-«yB- tems are mentioned.
A. CARBOCYCLIC COMPOUNDS.
1. ALICYCLIC COMPOUNDS. I. q/cZoPropane Derivatives.
375. cycloPropan€, C»H6 or | yCHi, is obtained by the action
ch/
of sodium on trimethylene bromide, CH-Br^CHi^CHiBr (148). It is a gas, which liquefies at a pressure of five to six atmospheres. It IS not identical with propylene, CHaiCH-CHj, 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:
/COOC,H» CH,v /COOCH,
CC - 2NaBr+ I )C( -*
\0OOCH, CH,/ \COOCH,
CH,v /COOH CH,v
cooH (inX
\ >CH.COOH.
II. q/cZoButane Derivatives.
376. cycloBtUane derirxUives are obtained when diethyl di- sodiomalonate reacts with trimethylene bromide, the diethyl ester of a cyclobtUyldicarhoxylic acid being formed:
CH,fB? I CH,
/\ + Na, C(COOCH«), - CH,C(C00CH,),+2NaBr.
Br I CH,
375
CH. CHj
376 ORGANIC CHEMISTRY. [{ 277
When heated, the dibasic acid obtained by the saponification of this ester loses one molecule of carbon dioxide (164), yielding cydo- butylcarboxylic acid.
cycXoButane 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 QyaXohxdylamine (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 q/cZobutylene (FV.):
CH,— CH . CONH, CH,— CH . NH,
I. I I -* II. I I -.
CHj — CHj CHj — \/Hj
CH,— CH.N(CH,),OH CH,— CH
I -IV. I II
I — CH] CHj — CH
III. II - IV. I II 4-N(CH,), + H,0.
CH,-
On careful reduction with hydrogen and nickel, cyc^butylene is converted into cyc^butane.
CH,— CHOH
The main product of the oxidation of cyclo6wtono/, | | ,
CHi-CH,
^^K H
is cyclopropanoZ, | >CH«C^, cyclo6ii/anone being also formed.
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 q/cfobutyl-ring to a q/c^pentyl-ring
CH,— CH-CHrOH is exemplified by digesting cyclobutylcarbinoly \ \ ,
CHr-CH, with concentrated hydrobromic acid, the corresponding bromide being formed. This })romide is transformed by nascent hydrogen into cyc/opentane, instead of methylcydobiUnne. -
III. ci/c/oPentane Derivatives.
277. cycloPentan^ derivatives can be obtained by a similar method the action of tetraraethylcne bromide on diethyl disodiomalonate.
When calcium adipate is submitted to drj- distillation, cyclo- j pentanone is formed:
§2781 ALICYCLIC COMPOUNDS. 377
CH, . CH, . CO . |(X CH, . CHjv
I I >Ca - CaC03+ I ^CO.
CH,.CH,|.CO 0/ CH,.CH,/
Calcium adipate cyetoPcDtanoDe
It is also obtained by heating adipic anhydride :
CH,
I CH,
[,.CH,.C(X CH,-CH,v
>0 - COa+ I >C0.
[,.CH,.C(K CH,.CHa/
The structure of this compound is proved by its oxidation to glutario
acid:
CHj-CHjv CH^-CHa-COOH
I >C0 - I
CHa-CH,^ CHj-COOH
Glutaric acid
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 bj' the impossibility of oxidizing it to a monobasic acid with the same number of carbon atoms.
cT/c/oPentanone is a constituent of the residue obtained in the fractionation of methyl alcohol (42). It is a liquid of peppermint- like odour, and boils at 130°.
cyc\oPaita7i€ is obtained by the reduction of this ketonic deriv- ative, the carbonyl-group taking up two H-atoms, ^^ith formation of a CHOH-group. By treatment with hydriodic acid, hydroxyl is first replaced by iodine, and finally by hydrogen:
CH,-Cn,. CH,-CHx
I >C0 - I >CHOH -♦
ch^.ch/ ch,-ch/
J VylA2"V.ll2 K^ll7'K,H2
- I >cni - I >CH,. ^^
CHj.CH/ ch^-ch/
n/r/oPentane is a colourless liquid boiling at 50°. It is a constituent of Caucasian petroleum.
278. Croconic acid, CtHjOs, is a remarkable cycJopentyl-deriv- ativo, 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 fcubstance, oxidizable to croconic acid. On oxidation, croconic acid is transformed into leiLConic acid, C606,4H20. This compound has the constitution
378 ORGANIC CHEMISTRY. [§279
CO. CO OC<f NcO,4H20,
x;o/
since it yields a pentoxime of the formula (CtNOH)i.
IV. Higher Alicyclic Derivatives.
279. cyclo/^cxane and its derivatives form the group of hydro^ aromatic compounds. On account of their relationship io 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 miberone, obtained by the dr>' distillation of calcium suberate:
CH, . CH3 . CH3 • COOv CHa • CH3 • CH, V
I >Ca = CaCO,+ | >C0.
CH.-CH,.CH,.C00^ CHa.CHj.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 suberanecarboxylic acid:
CH^-CHj-On^v yOH CH,-CH,.CH,v
yx -> I >CH-
I >A-x — ' I yi^/xi " COOH.
CH,-CH,.CH,/ \CX CHj.Cnj.GH/
This acid is also obtained by the interaction of ethyl diazoacetate and benzene, ethyl i>seudophenylacetate being formed as an inters mediate product:
CH HCy\CH CeH, + N,HC.COOC,H* = ^CH-COOCH* + N,.
nc\/CH
CH
The acid corresponding with this ester can be transformed into the isomeric iaophenylacetic acid:
CH
HC HC
CH.
)>CH-COOH.
^^CH CH
S280]
ALICYCLIC COMPOUNDS.
379
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 ;nr'ith seven carbon atoms is exemplified by the conversion of q/cZohexylmethylamine (I.) and other similar primary amines into stable nitrites (II.) :
/ CHa — CH J V CH/ > CH.CHj.NH, -^ (CH,),>CH.CH,.NH,.NO,H.
\CH,— CH/
I. II.
On boiling in acetic-acid solution, these nitrites are transformed by elimination of nitrogen into the alcohols of the next higher ring-system :
(CH,)5>CH.CHa.NH,.N0,H -► (CH,),>CHOH.
The conversion into suberone by oxidation of the alcohol formed from ct/c/ohexylmethylamine affords a proof of the course of this reaction. The synthesis of cyclic compounds containing eight carbon atoms is effected similarly.
280. The cyclic hydrocarbons, CnH2n, from cyclopropane to cyclo- octane 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 CnH2n+2, and the unsaturated series, CnH2n.
|
Number |
CnH2n + 2 |
^n^2n' Unsaturated. |
CnH2n. CycUc. • |
|||
|
of Carbon Atoms. |
Boiling- point. |
Specific Gravity. |
BoiUng- point. |
Specific Gravity. |
BoiUng- point. |
Specific Gravity, D4^ |
|
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 boihng-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 olefine^. The correspond- ing members of both series have almost the same boiling-points, but their specific gravities are about 0*02 lower.
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 oU of hitter almonds, oil of carrawayy oil of cumin, balsam of Tolu, gumrbenzoin, 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, GjUs, from balsam of Tolu; and benzoic acid, C7He02, from gum-benzoin. The saturated aliphatic compoimds with the same number of C-atoms have the formulae CioH22» 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," SbCls, were classed together because of their similarity in consistency. This method of classification Is still adopted for compoimds with analogous properties, but of imperfectly understood 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 sal^ of which is converted into benzene by distillation with lime. The dibasic terephthalic acid, C8H6O4, is formed by the oxidation of cymene, and can be similarly transformed into benzene.
The discovery of this relation by Kekule brought into promi- nence the <][uestion of the constitution of benzene, the basis of all
380
§2821 CONSTITUTION OF BENZENE. 331
the aromatic compounds. Its formula, CeHo, contaios eight hydro- gen atoms less than that of the saturated paraffin with six C-atoms, hexane, CeHi 4. Ben zene, 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. Compounds with a multiple carbon bond readily form addition- products with the halogens, are very sensitive to oxidizing agents, and easily react with von Baeyer'3 reagent (113): benzene lacks these properties. It yields halogen addition-products very slowly, whereas compoimds 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.
Other considerations lead to the same conclusion. Von BAEYEii has discovered certain dibasic acids, derivable from cyclo/iexane.
|
CH2 — CH2 |
|
|
/ |
\ |
|
H2C |
CH2, |
|
\ |
/ |
CH2 — CH2
by exchange of hydrogen for carboxyl. Removal of two or four hydrogen atoms from these hexamethylene derivatives yields com- pounds the behaviour of which indicates that they contain a mul- tiple carbon bond. The abstraction of six hydrogen atoms would be expected to produce a compound of an even more unsaturated character, but a benzene derivative lacking all the properties con- ferred by a double bond is formed instead. The elimination of the third pair of hydrogen atoms from the hexamethylene derivative, unlike that of the first and second pair, occasions a sudden and complete change in properties.
282. To understand the manner of linking of the benzene 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 isomerides of the monosubstitiUion" products of benzene. Second, the disubstitution-products exist in three isomeric forms. Hence, there is only one monobromobenzene, CeHftBr; but three dibromobenzenes are known, and are distin- guished by the prefixes ortho, meta, and para.
382 ORGANIC CHEMISTRY. [§282
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 formulae, in which the six hydrogen atoms are of equal value, are possible for benzene:
I. C4(CH3)2; II. C3(CH2)3; III. (CH)6.
It has now to be considered which of these formulae agrees with the second fact stated over-leaf.
A disubstitution-productof a compound with formula I. can be either
p j CH2X ^- p j CHX2
No other isomerides are possible, so that this formula is inadmissible as leading to two, instead of to three, isomerides. With formula II. four isomerides seem possible:
a. (CHX b. rCHX c. ( CX2 d. f CHg
C3 < CHX C3 < CH2 C3 < CH2 C3 < CX2.
(CH2 (CHX (CH2 (CH2
The hydrogen atoms in benzene being equivalent, the CH2-group8 in the benzene molecule must be similarly linked, so that a = 6, 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 Cffl^, 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-
§283]
CONSTITUTION OF BENZENE.
383
valent. The six hydrogen atoms can only be of equal value with a ring of six Oatoms:
HC HC
CH
6 2 5 8
CH
OH OH
This arrangement of the CH-groups also fulfils the second condition» as is evident from the scheme:
|
HO |
ex |
CX |
XO |
ex A |
|
HO |
V CH |
CH |
HO |
V CH |
OH OH
HO HO
CX
CH
OH OX
HO
XO
CX
V
CH
OH
OH
HO
HO
CX
6 2
V
ox
CH
OH
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.
In this scheme, each carbon atom is in union with one hydrogen atom and two other carbon atoms, so that three bonds of each car- bon atom are accounted for: it only remains to ascertain the mode of linking of the fourth carbon bond. The hypothesis suggested by Thiele is described in the next section.
283. Thiele has made a sf)ecial study of substances con- taining a conjugated linking (127), and has found that addition of two univalent atoms to such compounds converts them into others with a double bond r-t the centre:
-CH=CH— CH=CH— -f 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— C— C— C.
384
ORGANIC CHEMISTRY,
[§284
The dotted lines denote 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 benzene-formula proposed by Kekul6 is given in Fig. 73:
CH
|
HC |
^ N |
CH |
|
HC |
V / |
CH |
|
CH |
||
|
Fig. 73. — Kekul^'s Benzene- tX>RMULA. |
Fig. 74. — Thiele's Benzene- formula.
Thiele\s' modification of Kekul£\s benzene-formula has three inactive bonds, but lacks free partial valencies (Fig. 74). This peculiar type of structure explains the difference between the properties of benzene and those of other unsaturated compounds. Such a mode of linking is unknown in the aliphatic series, so that it must 1x5 the cause of the properties peculiar to aromatic compounds, and lacked by those of the aliphatic group. Hence, this structural formula not only accounts for the isomerism of the derivatives of Ix^nzcno, but also explains the " aromatic " character peculiar to thorn.
Nomenclature and Isomerism of the Benzene Derivatiyes.
284. The different isomeric disubstitution-products are distin- guished by the prefixes orthOy metaj and 'para, or the positions of their substituents are denoted by numbers:
A
8
V
1:2 = 1:6 substitution-products are called or/fto-compounds. 1:3 = 1:5 " " " " w/a-compounds.
1:4 " " if tt para-compounds.
The number of isomeric substitution-products is the same for
S284]
SUBSTITUTION-PRODUCTS OF BENZENE,
385
two similar or dissimilar substituents, but not for three. When the three groups are similar, three isomerides exist:
X X X
Adjacent or Vicinal 1:2:3
Symmetrical 1:3:5
X
Unsyomietrical 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 compoimd from that resulting on exchange at 4. For four similar groups the same nmnber (three) of isomerides is pos- sible as for two, since the two remaining hydrogen atoms can be in the orfAo-position, m€(a-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 CeHs-CHa or C6H5-CH2*CH2*CH3, is called a side-chairij the benzene-residue being called the nucleus. 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 substituent relative to those already present, the determination of which is called the determina* Hon of position^ or orientation, of the substituents. The methods erf orientation are given in 354 to 358.
PROPERTIES CHARACTERISTIC OF THE AROMATIC COM- POnin)S: SYNTHESES FROM ALIPHATIC COMPOUlfDS.
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 nitrocompounds:
CeHs-jH-fHOlNOg = CeHs-NOa+HsO.
Nitrobenjene
These substances yield amino-derivatives on reduction, and aie consequently true nitro-compounds.
2. On treatment with concentrated sulphuric acid, the aromatio compounds yield sidphonic acids:
CeHs . [H-hHO| • SO3H = CeHs • SO3H +H2O.
Benieneaulphonio add
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:
C6H5 • SH — > CgHfi • 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, C6H5, that they are almost incapable of taking part in double decompositions with such com« pounds as metallic alkoxides, salts, and so on.
386
S 2851 SYNTHESIS OF AROMATIC COMPOUNDS. 387
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):
BCaHeO — 3H2O = C9H12. Other ketones condense similarly to aromatic hydrocarbons.
BENZENE AND THE AROMATIC HYDROCARBONS WITH
SATURATED SIDE-CHAINS.
Gas-manufacture and its By-products : Tar.
286. The aromatic hydrocarbons are employed in large quanti- ties in the manufacture 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 ammonia 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 5-10 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
388
§287] COAL-TAB. 389
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-products 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 pitch. The dis- tillate is submitted to fractional distillation, four fractions being obtained.
1. Light oil, between 80° and 170°; D 0.910-0-950.
2. Middle oil, or carbolic oil, between 170° and 230°; D 1-01.
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 Fittig, 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 ah alkyl bromide or iodide and sodium (2g) :
+
Br H-Br
Na Na
C2H5 - CeHs— C2H5+2NaBr.
Ethylbenzene
A series of by-products is sometimes obtained, among them par- affip-8 and diphenyl, CoHj-CeH,. 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 alky 1-group :
CeHfi- (fITci]CH3 = CeHfi-CHa -|-Ha
390 ORGANIC CHEMISTRY. (§287
In the synthesis of Frtedbl and Crafts more than one alkyl- group is generally introduced, the inonosubstitution-products and the higher substitution-products being simultaneously formed: the mixture is separated by fractional distillation.
This reaction constitutes a method both for the building-up and breaking-down of a hydrocarbon. When toluene, CeHs-CHs, is treated with aluminium chloride, benzene, CeHe, and xylene, CeH4(CH8)2, 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.
3. By heating an alcohol, an aromatic hydrocarbon, and zinc chloride at 270^-300°. The zinc chloride acts as a dehydrating agent :
CeHs H-f HO •C5H11 =C6H6»C5Hn-f 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.
CeHs- IC02ca»-fcaO] H ^CeHe+CaCOa.
5. Benzene and its homologues can be obtained by heating the sulphonic acids with sulphuric acid or hydrochloric acid, the decom- position being facilitated by the introduction of superheated steam:
C6H3(CH3)2fS03H+HO|H = C6H4(CH3)2-|-H2S04.
This method can be employed in the separation of the aromatic hydrocarbons from the paraffins. When warmed with concentrated sulphuric acid, 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.
^ /»*! s=
ctt = JCa.
$288]
BENZENE AND ITS HOMOLOGUES.
391
288. Benzene and the aromatic hydrocarbons with saturated side-chains are colourless, highly refractive substances, liquid at ordinary temperatures, and possessing a characteristic odour. 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
EthvlbenMiie
ttoPropvl benzene ^Cumene) . .. . p-Methyli«opiopylbenzene I
(Cymene) / * * *
Formula.
Botlinc- point.
C.H, CaHj'CHi
CeHa(CH,), (1:3:6)
C«H..CH(CH,), CH, 1
CA<
CH(caa,), 4
Speeifie Gravity.
0-874 (2Xf) 0-869 (16®)
0-881 iff)
0-865 (14*») 0-883 ((f) 0-866 (16®)
0-856 (20®)
The boiling-points of the isomeric benzene derivatives are usually very close together, but the melting-points display wide divergences. It is an almost invariable rule throughout the entire aromatic series for^ the para-compound to have a higher melting-point than the me/a-compound and the or^Ao-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, are sometimes twice as great as the accepted values, whereas normal results are obtained for other substances not containing a hydroxy]- 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 (82).
Xylene, or dimethylbenzene, exists in three isomeric forms: tnrxylene is the principal constituent of the xylene in tar, forming 70-85 per cent, of the whole.
392 ORGANIC CHEMISTRY. [§ 288
The isomeric xylenes are separable with difficulty: their boiling- points lie vcTv close together, that of o-xylene being 142®, while m-xylene and p-xylene boil at 139® and 138® respectively. This makes their 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^Ao-compound can be separated by fractional crystallization of their sodium salts, the ortho-aalt crys- tallizing first.
Cymene, C10H14, is closely related to the terpenes CioHie, and to the camphors CioHieO, since it can be obtained from them. Qymene is a constituent of certain essential oils, such as oUof carra^ way, oil of thyme, and oil of eucalyptus.
MONOSUBSTmrnON-PRODUCTS OF THE AROMATIC
HYDROCARBONS.
I. MONOHALOGEN 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 tctrafluoride. Chlorine and bromine dissolve in benzene, and convert it slowly into the addition-products hexachlorobemene, CeHeCle, and hexabromohemene, CeHeBre, 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 monobromobenzeney CeHsBr, 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, monobromobcnzenc l)eing then produced with evolution of hydrogen bromide. Monoiodobenzene, C6H5I, 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 Ixmzene 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
393
394 ORGANIC CHEMISTRY. [§289
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 effected 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 all respects analogous to that possessed by halogen attached to a doubly-linked carbon atom in an aliphatic unsaturated halogen derivative (128).
Fittig'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 alkyl halidc (75). It 5aelds a solution of a compound of the formula CeH*.Mg.Br, a substance available for the synthesis of tertiary alcohols with the group CeEU, as described in 102.
Monochlorobenzene is a colourless liquid: it boils without decomposition at 132°, and has a specific gravity of 1-106 at 20°. Monobrojnobenzene, B.P. 157°, sp. gr. 1-491 at 20°. Monoiodo- benzene, B.P. 1SS°, sp. gr., 1-861 at 0°.
lodobcnzenc, and other iodine compounds substituted in the nucleus, can add two atoms of chlorine, with formation of sub- stances such as phcnyliodide chloride or ioddbenzene dicMaride, CJIft'ICl... When digested with alkalis, these derivatives give iodoso-com pounds, such as iodosobenzene, CeHi-IO, which are amor- phous, yellowish solids. When heated, or oxidized with bleaching- powder, these compounds >neld iodoxy-compounds (German, lodover- bindungen) ,
2CjI»- 10 ^CeH*- 1 -hCsH6- 10..
lodoxybemene
lodoxybenzene is cr\'stalline, and explodes when heated.
The constitution of these compounds is inferred from their ready conversion 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.
i 290] MONONITRO'DERIVATIVES. 395
n. MONONTTRO-DERIVATIVES.
390. A point of characteristic difference between the aromatic and aliphatic compounds is that the former are very readily con- verted into nitro-derivatives by the a'^tion of concentrated nitric acid (285, 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 specific gravity 1«52:
CeHfi . |H+HO| . NO2 = CeHfi • 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 nitration-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 arc 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 bo 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 hquids 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.
396
ORGANIC CHEMISTRY.
[§^90
Nitrobenzene is a yellowish liquid : it has an odour resembling that of bitter almonds, and for this reason is employed in per- fumer}'. 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 orf/io-compound and para-compound : only a small percentage
51M
para 100 90 80 70 00 50 40 0
!» 20 10 0
«-4*
FlQ.
10 ^ 90 40 dO tiO 70 83 90 VXiortho
75. — Fusion-curve op Mixtures of o-Nitrotoluene and
p-S itrotolue ne .
of the rw€^a-compound is formed. The proportion of orth(h- derivative is greater than that of the para-isomeride, as is exem- plified by the percentage-yields obtained by nitration at 0°, 58-8 of o-nitrotolueney 36-8 o( p-nitrotolueney and 4-4 of m-nitrotoluene. Usually, when there is simultaneous production of oW/io-com- pounds and /^ara-com pounds, the 7>ara-isomoride is formed in greater proportion. o-Xitrotoluene is liquid at ordinary tem- perature, its melting-point being — 3-4°: p-nitrotoluene is solid, and melts at r)l«4°. These isomerides are separated by a com- bination of repeated solidification by cooling and of fractional distillation. Fig. 75 represents the fusion-curve (" Inorganic Chemistry," 237) of mixtures of o-nitrotoluene and p-nitrotoluene.
{ 291] MONOSULPHONIC ACIDS, 397
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 yield an initial fraction so rich in the <?r^/k)-compound that its composition lies on the or^Ao-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 until 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-SOa-Cl.
The 8ulph4>nyl chlorides are very stable towards cold water, being but slowly reconverted into sulphonic acids. Benzenesulphonyl chloride melts at 14-5°. Like the other sulphonyl chlorides, it has a veiy disagreeable odour.
398 ORGANIC CHEMISTRY, [§§ 292, 295
The svlphonamideSf are formed by the action of excess of con- centrated ammonia on the chlorides:
CeHfi-SOaCl -^ CeHg-SOa-NHa.
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 ammonia.
The sulpho-group can be replaced by the hydroxyl-group and the cyano-group (292 and 311).
IV. MONOHTDRIC PHENOLS.
292. The phenols are compounds derived from the aromatic hydrocarbons by replacement of one or more of the hydrogen atoms of the hucleus by hydroxyl.
Phenol, C(jH5-0H, and some of its homoldgues, 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 bo obtained by other methods.
1. By fusion of the salt of a sulphonic acid with alkali:
C6H5-S03K-h2KOH = CeHs-OK+KaSOs + HgO.
2. By the action of nitrous acid on arbmatic amines, a method analogous to the preparation of alcohols of the aliphatic series from amines (65) . But whereas on treating an aliphatic amine with nitrous acid the alcohol is produced directly, in this reaction very important intermodiato products, the diazonium compounds (305), can bo isolatcMl.
3. By the action of oxygen upon benzene in presence of aluminium chloride, phenol is formed.
293. The phenols are in some respects comparable with the
§ 2931 PHENOLS, 399
tertiary alcohols, since in both the hydroxyl is linked 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 acids 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 ae CftHs-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-metals. This increase in acidic character can only be occasioned by the presence of the phenyl-group; in other words, the phenyl-groujp 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 ordinan' temperatures, but the addition of bromine-water to an a(iueous solution of phenol at once precipitates 2:4 :6-^ri6ro7wo- phenol — a reaction employed in its quantitative estimation. Tie 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-<lust, the phenols are reduced to the corresponding hydrocarbons. They can l)e detected by the
400 ORGANIC CHEMISTRY. [§§ 294, 295
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 (13). It follows from the equation AM =7o, in which M is the molecular weight of water (18), that A J the lowering of the freezing-point occasioned by the presence of 1 per cent, of water, is about 4-2°.
The hydroxytoluenes, CH3 -06114 -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-Cresol, CH3^ /OH, is a decomposi- tion-product of albumin.
Thymol is also used as an antiseptic. It is hydroxycymene,
/CH3 1
C6H3^0H 3.
\CH(CH3)2 4
Acid sulphuric esters of phenol are present in urine: they result from the fermentation (putrefaction) of proteins, siuce 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, CtjHs-O.CH.j, and the true aromatic ethers, like phenyl ether, CeHs-O'CoHs. Compounds of the first
§ 2961 MONOAMINO-COMPOUNDS. 401
class are formed by the interaction of alkyl halides and phen- oxides (293) :
CttHs-O. Na+TlCjHs = CeHs-O-CgHs + 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). Phenyl ether is obtained by heating phenol with a dehydrating agent, such as chloride of zinc or of aluminium:
CeHs-iOHTHlO.CoHs = CeHs-O-CeHs + HgO.
The mixed aromatic-aUphatic ethers are stabh compounds, and resemble the true aliphatic ethers closely in behaviour. Many of their reactions are similar to those of the aromatic hydrocarbons themselves. When heated to a high temperature with a hydrogen halide, they yield a phenol and an alkyl halide :
CtjH5-O.CH3 + HI=C6H5-OH + CH3-I.
Aniaole
The true aromatic ethers, such as phenyl ether, are not decomposed by hydriodic ac'd, even at 250°.
AnisolCj CeHs'O'CHa, is a liquid, and boils at 155®. Phenetole, C6H6-0-C2H5, is also a liquid, and boils at 172°. Each has a characteristic odour.
V. MONOAMINO-COMPOUNDS.
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 is effected by various means.
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 propDrties: 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^
402 ORGANIC CHEMISTRY. [| 296
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.
Substitution of the amino-group for hydrogen produces the same effect 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 readiljp converted bv bromine-water into 2:4:G-tribromoaniline. More- over, the amines are much more readily oxidized than the hydro- carbons.
Hy 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-NHz+CHal = C6H5-NH(CH3).HI.
Secondary and tertiary bases and also quaternary ammonium bases, such as C6H5.N(CH3)3.()H, are kno\\Ti. The last are as strongly basic as the corresponding true aliphatic comp>ounds.
The anilides are derivatives of aniline, C6H5'NH2, and its homo- logues: they are acid amides, in which one amino-hydrogen atom has been replaced bv a phenvl-group. Acrtoanilide, CgHs-NH-COCHs, employed as a febrifuge under the name " antifebrine," is a type ot these compounds. The anilides are produced by boiling aniline with the corresponding acid. Acetoanilide is obtained by heating aniline with glacial acetic acid:
CeHs-NHfHTHOlOC.CHa = C6H5.NH.COCH3+H2O.
Menschutkin found that the velocity of formation of acetoanilide is much less for an excess of aniline than for an excess of glacial acetic acid, although on theoretical grounds the velocity of forma- tion should Ix^ the same in lx)th 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 expressed by
in which k is constant.
HaC
0+H
297) ANILINE. 403
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 :
H HNC6H5 TT p^NHCeHs . TT r\ HNCeHs" "^^^NHCeHs"'' "='"•
Formaldehyde Methylenediphenyldiamine
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, nUa, dark-blue, and nito, 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:
CeHsNOa + SFe + GHCl = C6H5NH2 + 2H20 + 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 (302).
Aniline is a colourless liquid, and, unless perfectly pure, turns l)rown 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, (C6H5X=CH2)3. This sub- stance melts at 4(F, and dissolves with difficulty. It is employed in the identification of both formaldehyde (108) and aniline.
An acjucous solution of frce aniline gives a deep-violet colora- tion with bleaching-powder solution, the primary product in the reaction being probably phenylchloroamine, CeHg-NHCl, analo- gous to the formation of chloroamine, XH2CI, from ammonia. The phenylchloroamine condenses with the aniline to form,
404 ORGANIC CHEMISTRY. [§ 298
coloured substances. An aniline 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-toluidine and para-ioZuirfine, CH3-C6H4«NH2, are formed by the reduction of the corresponding nitro-compounds. The or//io-compound is a liquid, B.P. 199*4°; the para-compound is a sohd, 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 isomorides are possible, due to differences in the relative posi- tions of the methyl groups and the amino-group in the ring. Some of the toluidines and the xylidines are employed in making coal- tar colours, and are, therefore, manufactured in large quantities.
Secondary Amines.
298. Diphenylaininey CeHs-NH-CeHs, melts at 54°, and boils at 310°. It is a type of the true secondary aromatic amines. They are formed by heating the hydroclilorides of the primary amines with the free amines:
( V>H5|NH2 . HCl tHJHN • CeHs = NH4Cl + HN(C6H6)2.
Diphenylamine can also be obtained by the action of bromobenzene on potassium anilide, CgHs-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 id concentrated sulphuric acid. This reaction can only be applied to 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 reagents.
• The method of formation of the mixed aromatic-aliphatic amines, such as tnethylamUne , CeHs^NH^CHa, is indicated in 296. The action of the alkyl iodide upon aniline results in the substitu- tion of m )re than one hydrogen atom of the amino-group by an
5 2991 SECONDARY AND TERTIARY AMINES, 405
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-COCHa, by boiling yvith glacir.l acetic acid. The hydrogen atom linked to nitrogen in this compound can be replaced by sodium, yielding CeHs-NNa-COCHa, which on treatment with methyl iodide yields methylacetoanilidey CeHs* NCCHs) • 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,
NO such as nitrosomethylanilinef C6H5«N<pTT. Liebermann's
reaction for nitroso-compounds is described in " Laboratory- Manual," XXVII, II.
Careful oxidation of the nitrosoamines transforms them into
nitroamineSf CeH6'N<T> '. 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. Triphenylaminey (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 bromobenzone on diphenylaminc, and is a solid, melting at 127°. It does not possess a basic character.
It is true that perchloric acid, HCIO4, can unite with triphcnyl- araine, but this acid displays a special aptitude for combination with many substances, both nitrogenous and non-nitrogenous.
CH
Dimethylaniline, C6H5«N<pTT , 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 arj manufactured by heating aniline hydrochloride with the alcohol, a method in which alkyl halides react in the nascent state. Methyl
406 ORGANIC CHEMISTRY. [§ 299
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. C6H5-NH(C2H5)HC1 = CeHs-NHj+CgHfiCL The reaction indicated in equation II. ensues:
II. C6H5.NH2+C2H5CI - C6H4<52H5^(.j.
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 perUamethylaminobenzeney Ce(CH3)6-NH2.
The jxira-hydrogen atoms of dimethylaniline and other dialkyl- anilines are replaceable by various groups. Thus, dimethylaniline reacts readily with nitrous acid, with formation of nitrosodimethyU aniline,
ON<^N(CH3)2,
effected by the addition of potassium 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- verted into a nitro-group, with formation of p^nitrodimethylaniline,
P„ .N(CH3)2l
On boiling with caustic soda, the amino-group of nitrosodi- methylaniline is removed, with formation of dimethylamine and nitrosophenol:
C6H4 < N^'^' +H2O = C6H4 < gg +HN(CH3)3.
Nitrosophenol
§ 300] REDUCTION OF NITROCOMPOUNDS. '407
This reaction is employed in the preparation of pure dimethyl- amine (66).
The jjara-hydrogen atom of dimethylaniline can react with substances other than nitrous acid: thus, aldehydes readily yield a condensation-product :
QHs .ChIo + i|c^;5J[OT3)a " C8H6-CH[C6H4N(CH3)2]2.
The constitution of this compound is inferred from its relation to triphenylmethane, CH(C6H6)3 (373). With dimethylaniline, car- bonyl chloride yields ap-derivativeof benzophenonejCeHs-CO-CeHs, called Michler's ketone:
/CrTH|C6H4-N(CH3)2 j/C6H4.N(CH8J2
- CO ^ +2HCL
C6H4 • N(CH3)2 \C6H4 . N(CH3)2
CO
XcifH
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. INTERMEDIATE PRODUCTS IN THE REDUCTION OF AROIAATIC
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, ethylaminc 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 aniline will be described here, although numerous substitution-products of the same type are known.
In acid solution the nitro-compounds are directly reduced to
408 ORGANIC CHEMISTRY, l§30'
the corresponding amino-derivatives, but in alkaline solution yield substances containing two benzene-residues. Nitrobenzene yields in succession azoxybenzenef azobenzene, hydrazoberzene, and aniline:
1. Nitro-compound, C6H5-N02 02N«C6H6;
^ , ^ CeHs-N N.CeHs;
2. Azoxy-compound, \ /
3. Azo-compaundf CeHs-N^N-CeHs;
4. Hydrazo-compound, CgHs-NH — NH-CeHs;
5. Amino-corapound, C6H5-NH2 H2N-C6H5.
Azoxyhenzene is obtained by boiling nitrobenzene with alcoholic potash, and is also formed in the oxidation of aniline with potas- sium permanganate in alcoholic solution. If forms light-yellow crystals melting at 36°. When warmed with concentrated sulphuric acid, it is transformed into p-hydroxyazobenzene:
CJi».N N.C»H» -. C6H».N=N.C6H4.0H.
\ y/ Hydroxyazobemene
It is readily attacked by various reducing agents. Under the influ- ence of direct simlight, concentrated sulphuric acid converts azoxy- henzene into o-hydroxyazobemene.
p-Azoxyphenetole, CjHUO.CfiHi.N — N.CftHi.OCjH*, 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 crystaUine structure of the turbid liquid 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 crystals between crossed Nicol prisms in converging light. Turbidity is not an essential characteristic of hquid crystals, as VoRLANDEB has discovered perfectly clear liquids which display phenomena like those of double-refracting crystals.
301. Azobenzene, CeHs- NiN-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 witii 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 i:. water. Its constitution follows from its yielding aniline on reduction.
§3021 ELECTRO-REDUCTION OF N I TRO-COM POUNDS, 409
Hydrazohenzen€y 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 atmosphere oxygen. It is also oxidized to the azo- compound by ferric chloride.
The most characteristic reaction of hydrazobenzene is its con- version into benzidine, whereby the benzene-nuclei are, as it were, turned end for end. This *' benzidine-transformation '* is effected by the action of strong acids:
^7T)nH-Xe(7T) -^ H2N.C6H4— C6H4.NH2.
Hydrasobensene Benzidine
That a diaminodiphenyl is thus formed is proved by the conversion of benzidine into diphenyl, CeHs-CeHs. The amino-groups occupy the para-positions:
H2N<r ^-<r ^NHg.
By reducing azobenzene in acid solution, benzidine is formed directly. It is characterized by the sparing solubility in cold water of its sulphate.
The amino-groups in benzidine are proved in various ways to occupy the 7>ara-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/7~^^' H ->*' H . CeH^N H . COCHs-^HjN <^^
3>-Acctam:nohydra«o'.>on»ene p-Aminophenyl-p-acctaniino-
phenylamine
Electro-reduction of Nitro-compounds.
302. There is reason to believe that in the future electrolytic methods will be used more and more in chemical work, for the elec- tric current affords 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 syntheses or to improve those already
410 ORGANIC CHEMISTRY. [§303
known. An explanation of this mode of altering the pressure and concentration is necessary here.
Alteration in the contact-difiference 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). In reduction-processes the same efifect 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-d ifference 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, 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 current (167). In reactions in which the discharged ions must interact, as in the synthesis of dibasic acids {Jioc, cit.), 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 cur- rent of small density, must be used.
On reduction, nitro-compounds ultimately yield 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 -> CeHs-NO -> CeHs-NHOH ^ CgHs-NHa.
Nitrobenaene Nitrosobeniene Phenylhydroxyl- Aniline
amine
The presence cf nitrcsobenzene 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 diazonium hydroxide, CtH5»N2«OH: on adding a-naphthol, an azo-dye is produced (340).
i 304) ELECTRO-REDUCTION OF NITROCOMPOUNDS. 411
The formation of phenylhydroxylamine can be proved by adding benzaldehyde., with which it yields benzylidenephenylhydroxylamine:
CeH6.N;--^H.CoH5 . CJEls.NHOH+OCH.QHs - 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 converted into p-aminophenol:
CeHfi.NHOH -> HO.C6H4.NH2.
This substance is not further reduced. Since phenylhydroxylamine undergoes the same transformation, though much more slowly, 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 jiitrobcnzene is accompanied by two secondary processes.
1. Nitrosobenzene reacts with phenylhydroxylamine, yielding azoxybenzene: ^^^^^ ^^^^^
CeHfi.NHOH+CeHfi.NO - \/ +H2O.
O In presence of alkali this reaction proceeds much more quickly than 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+2C6H5.NO2 = 3C6H5.N:N.C6H6 +
CeHfi.N N.CeHg
+ \/ +3H2O.
Since hydrazobenzene in alkaline solution is quickly oxidized hy 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
412
ORGANIC CHEMISTRY.
(§304
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 following scheme, the vertical arrows indicating primary, and the oblique arrows secondary, reactions:
CeH;NO, C,H,-N(0H)2
1
CeHs-NO
1
C,H,-NHQH
C.H,.N:N.C,H,
C.H,-N^.C.H. O
C,H,-NH-NH.C,H,
>v.
C, H.-NH, Fig. 76. — Haber's Electro-reduction Scheme.
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 excess of hydrochloric-acid solution indicates that the reaction is bimolecular, and must therefore be represented by the equation
R.NOj+SnClj + nHCl - R-NO-f SnCl^-f HjO+Cn -2)HCl.
This reaction has a measurable velocity. The further reduction of the nitroso-com pound 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 chloride, it is at once reduced.
§ 3051 DIAZO'COM POUNDS. 413
: nA'^'
Vn. DIAZO-COMPOUNDS
305. The diazo-compounds of the aromatic series, discovered by Griess in 1860, are not merely of theoretical importance, but play an important part in the manufacture of dyes. In the aliphatic series only amino-comppunds 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 diazotization 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 || , in which
N Ar represents phenyl, CeHs, and its homologues and derivatives. They are called diazonium salts, and are analogous to the ammonimn salts.
II. Substances with the structural formula Ar • N=N • X. These derivatives are called diazo^ompoundsy and resemble the azo-com- pounds. They are known in two stereoisomeric modifications.
Ar.N
1. Compounds with the stereochemical formula ||. They
XN
are called syndiazo^ompoundSy are unstable, and can be isolated only in certain cases.
Ar.N
2. Compounds with the stereochemical formula
tLUtidiazo^ompoundSy which are stable.
, or N.X
Intrinsically, the diazonium compounds are of slight imports ance, but the numerous transformations which they can undergo, 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:
CeHg.NHg.HNOa-fHNOa = 2H20+C6H5.N2-N03.
Aniline nitrate [Bensenediaxonium nitrate
414 ORGANIC CHEMISTRY. [§306
This is effected by adding a solution of sodium nitrite to a solution containing an equimolecular 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 hemenedia- zonium nitrate , CeHt.Na.NOa, 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 crystalUne form. On ignition or percus- sion, the dry salt explodes with great energy, so that only a few deci- grammes should be isolated in the dry state. Almost all the dry dia- zonium salts are excessively explosive, and must, therefore, be handled with great care. In aqueous solution they are harmless, and as they yield 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 cf the benzene-nucleiLs, 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)2Ptri4, soluble with diffi- culty in water. Other analogous salts, such as (r6H5N2Cl)AuCl3, have also been obtained. Free benzenediazornnm hydroxide^ CeHs'No'OH, is only known in the form of an aqueous solution, which has a strongly alkaline reaction. It is obtained by treating the aqueous solution of the chloride with silver oxide, or by the
J 3071 DIAZO-COMPOUNDS. , 415
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:
CftHgN^N.X or CeHgN^^.
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 caustia potash, a potassium derivative, CeHg-Nj-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 (C6H5N20)' + 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, Hantzsch assumes that an equilibrium exists in the aqueous solution between the diazonium hydroxide and the syndiazohydroxide (308):
CHsN-OH ->C,H»N
II - II
N HON
Diazonium «ynDiaso- hydroxide hydroxide
He suppopes 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 git)up — N2 — as free nitrogen, and its replacement by a substituent linked by a single bond to the benzene-nucleus. Extended research has
416 ORGANIC CHEMISTRY. [{ 307
revealed the conditions best suited for obtaining nearly quantita- tive results in most of these reactions.
1. Replacement of the N2^oup by hydroxyl. — This reaction is effected by allowing the aqueous solution of the diazonium salt to stand, or by warming it:
CeHfi.Na-Cl-hHOH = CeHs-OH-f N2+HCI.
2. Replacement by an aUcoxyl-group, — 0«CnH2n+i- — ^This re- placement is carried out by boiling a diazonium salt with alcohol:
CeHs-Ng- HS04-hHO.C2H5 = C6H6O.C2H5+N2+H2SO4.
In some instances, sunlight exerts an accelerating influence on reactions of the type described in 1 and 2.
3. Replacement of the diazonium-group by hydrogen. — Under certain conditions the diazonium salts do not yield alk3xyl- compounds with alcohols, but produce the corresponding hydrogen compound, the alcohol being converted into aldehyde:
N O2 • CbH* • N2 . CI + C2H5OH = NO2 • CeHs + C2H4O + N2 + HQ.
p-Nitrobcniencdiasonium Nitro- Acetal-
chloride benzene dehyde
Usually reactions 2 and 3 proceed simultaneously; but if the benzene-nucleus is already attached to several negative sub- stitiients, 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 dlazonium-group by chlorine. — ^This reac- tion is effected by treating a solution of diazonium chloride either with cuprous chloride dissolved in concentrated hydrochloric acid (Sandmeykk), or with finely-divided copper (Gattermann) :
CgHs-Xo.CI = CoHs-Cl+No.
Cuprous chloride and finely-divided copper have a catalytic action: it is probable that a copper compound is formed as an inter- mediate |)ro(luct, and afterwards decomposed.
Ke|)lacement by bromine is carried out similarly: thus, in the preparation of bromol)enzene, a solution of potassium bromide is
1308) REACTIONS OF THE DIAZONIUM COMPOUNDS, 417
added to an aqueous solution of benzenediazonium sulphate con- taining 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-grr<mp. — 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-Nz-Cl+KCN = CoHg-CN+Na-f KCl.
This reaction is of great importance for the synthesis of aromatic acids, which can be obtained by hydrolyzing the resulting nitriles.
6. Replacement of the diazonium-group by sulphur. — Addition of a solution of potassium xanthate (264) to one of a diazonium salt usually precipitates the diazonium xanthate :
CeHs-Na-Cl-fKS.CS.OCaHs^CeHs-Ng-S.CS.OCaHs-fKCl.
•
On warnaing the precipitate with its mother-liquor, nitrogen is evolved, and sulphur becomes directly attached to the nucleus, with formation of phenyl xanthate, CoHs-S-CS -002115. The con- stitution of the product is proved bj^ 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 ami no-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 are first converted into syndiazo-com pounds, which then decom-
418 ORGANIC CHEMISTRY. [{ 308
pose with evolution of nitrogen. The formation of phenol may be ,_ represented thus: ^j . ••
CeHj OH CeHs OH CeHjOH
I I -^ Phenol
- HCl + N— N N=N :
•VnDiaso- pq TT hydroxide
Diasonium chloride
and that of chlorobenzene thus:
N=N +
CHs CI CeHs CI CJIbCI
Chlorobenaena
Ha + N— N N=N.
QY H chloride
The reactions between diazonium salts and alcohol are explained as follows:
CeHs OC2H5 /CeH^ OC^H^X CeH.-OCjH, lF^™ti«^ef^a
CI H CI— H CI— H
CeHs H CeHj — H lFo"tt*ti<»o^**»y<*rocarbon.)
N=N 4- -♦ NEEN
CI C2H5O ClOCjHs [Decompoeition into Hamnd aldehyde. G1H4O.)
As these transformations of diazonium salts cannot be repre- sented by the aid of the other possible structural formula, CoH5«N^N«X, it is evident that it must be rejected (306).
Most of the sz/ndiazo-compounds are very unstable. They change readily into an/idiazo-compounds, in which it is assumed that the phenyl-group and acid-residue are not contiguous, and therefore can no longer unite :
CqHs X CJFIj
I
N=N
N=N I
X
•l/nDiaso-com pound ; an/iDiaio-compound ;
CflHft and X can unite CsHs and X cannot unite
In certain oasos, such as that of the diazocyanides, Hantzsch has been able to isolate these intermediate [)roduct8, and thus a£ford a proof of these views. For example, when cyanides are added to diazotizcd p-chloroanilinef Cl«CoH4*NH2, p-chlorobemonUrile, Cl»C6H4«CX, is not immediately formed: it is possible to isolate a yellow intermediate product, Cl*CcH4«N2*CN, which yields p-
i 3091 REACTIONS OF THE DIAZONIUM COMPOUNDS. 419
chlorobenzonitrile after addition of copper-dvist, the action being accompanied by an energetic evolution of nitrogen. This yellow intermediate p-chlarobemenesyndiazocyanide is, however, very un- stable, and speedily changes to an isomeride (the an/t-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. Diazoamino-compounds are obtained by the action of primary and secondary amines upon diazonium salts:
C6H5.N2' pTHlNHCgHg - CeHfi.Ng.NHCeHs+HCl.
DiasoaminobenseDe
They are also produced when nitrous acid reacts with free aniline, instc^ad of with an aniline salt. It may be supposed that in this reaction benzenediazonium hydroxide, or benzenediazohydroxide is first formed, and is at once attacked by a molecule of the aniline still present:
I. CeHs-NHa+HNOa = CeHg-Na-OH+HaO.
n. CfiHs-Nz- pH+HJNHCeHs = C6H5.N:N.NHC6H5+H20.
Benienediasohydroxide t
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:
C6H6-N:N.NHC6H5-fHN02+2HCl = 2C6H5.N2-C1+2H20.
The most characteristic property of the diazoamino-compounds is the readiness with which they can be transformed into isomerides, the aminoazcxompounds:
CeHfi.NrN— Nh/^^H ->C6H6.NrN<(^^NH2.
Diazoaminobensene Aminoasobenxene
This is effected by adding aniline hydrochloride to a solution of diazoaminobenzene in aniline, and warming the mixture on the water-bath.
The araino-group in aminoazobenzene is in the para-position to the azo-group. When the para-position is already occupied, the amino-group takes up the orZ/io-position. Aminoazobenzene and many of its derivatives are dyes (340) .
420 ORGANIC CHEMISTRY. [§310
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 still 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, inter aliay 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:
C6H5>N2'pnr,C6H4'N(CH3)2°C6H5-N:N>C6H4'N(CH3)2+HCL
Dimethylaniiine DimethylaminoasobenaeDe
3. They react similarly with phenols, forming hydroxyazthcam^ pounds. This combination takes place in presence of alkalis:
C6H5'N2-|C1+H|C6H40H = C6H6.N:N.C6H40H+HCL
Phenol Hydroxyacobensene
Important dyes are also derived from hydroxyazobemene (341).
Vm. HYDRAZINES.
310. The typical derivative of hydrazine is phenylhydrcLzine, C6H5-XH-NH2, 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:
C6H5-X2-C1+4H = CeHs-NH— NH2-HC1.
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 hydmchloric acid:
I. C6H6-N2-Cl+Na2S03 = CoH5-N:N.S03Na+NaC!L
Sodium diasobenxenesulphonate
II. C6H5.N:N.S03Xa+2H = CeHs-NH-NH-SOaNa.
Sodium phenylhydrasinesulphonata
III. CsHs-NH-NH-SOaXa+HaO = Cells -NH-N Ha +NaHS04.
Phenylhydrazine
§ 311] PHENYLHYDRAZINE. 421
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, C6H6'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 boiling-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, its sulphate being oxidized to the diazonium salt by mercuric oxide. Oxidation usually goes further, however, the nitrogen being elimi- nated from the molecule. Thus, an alkaline copper solution con- verts it into water, nitrogen, and benzene. Phenylhydrazine has a wholly basic character: it yields well-defined cr}'stalline salts.
Phenylhydrazine is proved thus to have the constitutional for- mula C6H6-NH-NH2. A secondary amine is converted by nitrous acid into the corresponding nitrosoamine:
CeHfi . N < ^ jj^ -> CeHs • N < ^^^.
Monomethylaniline Nitrosomethylaniline
On careful reduction, this substance yields methylphenyUiydraziney
NH CeH5-N<Qrj^, 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 methylphenylhydrazine is formed :
CttH5.NH.NH2 -> C6H.vN <^'j^^ -> CfiHs-N < J?2^^
IX. AROMATIC MONOBASIC ACIDS: B£^ZOic ACID AND ITS
HOMOLOGUES.
311. Benzoic acid, CeHs-COOH, can lx> prepared by many methods, of which the most important will be described.
422 ORGANIC CHEMISTRY. [§311
1. By the oxidation of any aromatic hydrocarbon with a side- chain:
CeHs • CnH2n+i —* CeHg • COOH.
Bein^ 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, CeHs-CCla, is first formed, and is converted into benzoic acid by heating with water:
OH CeHg-CCl+HOH-HjO = CeHs-COOH+SHCl.
OH
Benzoic acid thus prepared often contains traces of chlarobemaic acid, C6H4CI. COOH.
2. By the oxidation of aromatic alcohols or aldehydes, such as
XT
benzyl alcohol, C6H5-CH20H, 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 on3 carbon atom directly linked to the benzene-nucleus.
3. By the introduction of the nitrile-group into the benzene- nucleus, and hydrolysis of the benzoniirile, 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 potassium cyanide (307, 5).
(h) By distilling potassium benzenesulphonate with potassium cyanide:
CeHs-SOgK-fKCN = C6H5.CN+K2SO3.
4. By the action of carbon dioxide and sxlium oa bromoben- zene, whereby sodium benzoate is formed:
C6H5Br-fC02-f2Na = 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.
(n) In presence of aluminium chloride, benzene and carbonyl
5 312] BENZOIC ACID. ' 423
chloride react together, with formation of benzoyl chloride^ the chloride of benzoic acid, and hydrochloric acid:
CeHfilH+Cll-COCl = CeHg-CCXIl+HCl.
Bensoyl chloride
Benzoyl chloride is converted into benzoic acid by treatment with hot water.
(6) 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 :
CeHfilH + Cll'CONHg = CeHs-CONHg + HCl.
Beniamide
(c) Bromobenzene is converted by sodium and ethyl chloro- formate into ethyl benzoate:
CeHs
Br-hCl
Na Nal
.COOC2H5 _ CeHs-COOCoHs + NaCl + 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. 77). 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 i>er cent, of acid (point B); the other consists principally of the acid, containing 95*88 per cent, (point D), Above this temperature an effect like that described in 74 is produced: the mutual solubility of these layers is repre-'
424
ORGANIC CHEMISTRY.
[{313
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
Fig. 77. — Solubility-curve op Benzoic Acid in Water.
layers becomes more and more alike as the temperature rises, since the water dissolves more benzoic acid, and the acid more water. At 110° they are identical in composition: that is, the liquid has agiun become homogeneous.
If more benzoic acid is added to the acid layer only, at 90**, it is necessary to raise the temperature to keep all the acid fused: the line DF is thas obtained, ending at F at the melting-point of pur^ Ixjnzoic acid, 121-4°. DF therefore represents the melting-point- curve of the acid, on addition of increasing amounts of water.
Derivatives of Benzoic Acid.
313. Benzoyl chloride, CeHs-COCl, can be obtained by the action of phosphorus pentachloride or oxychloride 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,
ijr
( ^Hs-Cq, with chlorine. Unlike acetyl chloride, which is rapidly
decomposed, it is very slowly acted upon by water at ordinary temperatures.
HonzoyI chloride is employed in the introduction of the benzoyl- group. CgHs-CO — , into compounds. This is effected by a method
§ 313] DERIVATIVES OF BENZOIC ACID. 425
discovered by Baumann and Schotten, which consists in agitat- ing the substance in alkaUne 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-CCXJeHs, is formed by the inter- action of a benzoate and benzoyl chloride:
CeHfi-CO.OfNa+ClJ.OCCeHs = NaCl+CyisCO.O.CCXIeHs.
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), C6H5-CONH2, can be prepared by the 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- gen 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 0-ether, benzoic iminoether,
CftH.-Cv t 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 A^-alkide,
/NHCjHs CeHs-Cv , is formed. This is proved by the decomposition of
the latter substance into ethylamine and benzoic acid, so that the silver compound must have different constitutions at ordinary tem- peratures and at 100° (262).
426 ORGANIC CHEMISTRY, [5 314
Benzonitrile) CsHs-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 homologues of benzoic add, such as the tcluic acids, CH3-C6H4-COOH, the xylic acids, (CH3)2C6H3-COOH, and so on, are cr>'^stalline solids, very slightly soluble in water* They are prepared by methods analogous to those employed for benzoic acid.
X. AROMATIC ALDEHYDES AND KETONES.
Aldehydes.
H 314. Benzaldehyde, CoHs-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, CeHs -0112011, and bv distillation of a mixture of a benzoate and a formate. It is manufactured by heating benzol chloride, CeHs-CHCh, with water and calcium carbonate, a method the aliphatic analogue of which is of no practical importance:
CeHs'CH CI2 -Htj oh"~^^^ ~ ^6^5 -Oq -I-2HC1.
The following methods are employed in the preparation of the homologues of benzaldehyde.
1. When ethyl chloro-oxalate is brought into contact with an aromatic hydrocarbon in presence of aluminium chloride, the ethyl ester of an o-kctonic acid is produced:
CoH.+nco— COOC^IU = CJls-^^O-rOOC^Hs + HCl.
Kthyl chloro-oxalate
The free acid is obtained by saponification, and on dry distillation loses CO2, with formation of the aldehyde:
Cells-CO-CO^H ^(Vls-^o-CO..
2. An aromatic hydrocarbon is treated with a mixture of carbon monoxide and hydrochloric acid in presence of aluminium chloride
§ 315] ALDEHYDES. ^'n
and a trace of cuprous chloride. It may be assumed that formyl chloride, HCOCl, is obtained as an intermediate product :
CH,.CJI.-hC10CH = CH,-C.H4-CQ+Ha.
315. Benzaldehyde occurs in the natural product, amygdalin, C20H27O11N (256) ; on this account it is called oH of hitter 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 the atmosphere (especially when exposed to sun- light), reduces an ammoniacal silver solution wuth 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 yield a compound like acetaldehyde-ammonia, but produces hydrobenzamidcy (C6H5CH)3N2, formed by the union of three molecules of benzaldehyde and two molecules of ammonia:
SCeHs-CQ +2H3N = (C6H6CH)3N2 + 3H20.
At —20°, however, ammoma combines with benzaldehyde to henzaldehy de-ammonia y 2CeH5'CHO,NH„ probably
NH[CH(CeH,).OHL, which separates in platen molting at 45°. After a time it decomposes into hydrobenzamide, benzaldehyde, and water. It is an intermediate i)roduct 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, 108). Thus, benzalde- hyde yields potassium benzoat^ and benzyl alcohol:
2C6H6-CQ-hKOH = CeHs-COOK+CoHs-CHaOH.
The aromatic aldehydes condense readily with dimethylaniline or phenols, forming derivatives of triphenyl methane (373) :
428 ORGANIC CHEMISTRY, [§315
p Tj pH| HIC6H4OH p„ r-w ^^^^^^OH ^
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, benzylideneanUine, C6H5-CH:X.C6H5, cr}\stallizes.
The action of chlorine on benzaldehyde is described in 313.
Benzaldehydephenylhydrazoney CeHs-CH^N-NH-CeHs, is very readily precipitated, with evolution of considerable heat, by addition of benzaldehyde drop by drop to a sulphurous-acid solution of phenylhydrazino. 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 oxygon 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, the same amount of ox\'gen is absorbed in oxidizing the indigo derivative as in converting the benzaldehyde into benzoic acid. VoN" Baeyer has shown that benzoyl-hydrogen peroxide C«H*CO'0'OH, is fonned as an intermediate product, and oxidizes the indigosul- phonic acid, being itself reduced to benzoic acid:
CeH,.CHO + 0. - C.H,.CO.O.OH;
C.H».CO.O.OH + lndigo = CoH»-COOH+ Oxidized indigo. The oxidation of benzaldehyde in the air must be considered, there- fore, to take place thus :
C,H,.CHO + 02 - CoH.-CO.Q.OH; C«H5-C()-0-0H+C,H,.CH0 = 2C«n,.C00H.
Vox Baeyer has, in fact, proved that benzoyl-hydrogen peroxide dissolves when added to benzaldehyde, but that the liquid gradually sohdifies to pure benzoic acid.
5316] KETONES, 429
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 acetophenonef CeHs-CO'CHa. 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.'*
Benzophenone, CeHs-CO-CeHs, is a true aromatic ketone, and can be obtained by the dry 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 >'ields henzhydroly CeHs-CHOH-CeHg; benzpinacone,
(C^KshC C(C6H8)2 . . ,, , , , , ,
• • IS simultaneously formed (150).
Although there is still uncertainty as to Friedel and Crapts's synthesis of the homologues of benzene (287, 2),- Boeseken has explained the mechanism of this sjiithesis of aromatic ketones. He has proved that the acid chloride first unites with the aluminium chloride*
CeH^COCl + AlCU = C,H,C0C1-AICL.
On addition of one molecule of benzene, one molecule of hydrochloric acid is evolved, with formation of a crystalline compound:
C«H.-C0Cl-AlCl3 + C,He = CeH,.CO-CoH5-AlCL + HCl.
When this compound is treated with water, a quantitative yield of the ketone is obtained:
CoH,.CO-C,H,-AlCl3 + nH.O = C«H,-CO-C„H, + AlCl,-nH,0.
The reaction therefore takes place in three stages.
Boeseken's researches on the Friedel and Crafts reaction have proved the scheme indicated to he inapplicable to other examples of this synthetic method. In the formation of ketones,
430
ORGANIC CHEMISTRY.
[§317
equimolecular proportions of the acid chloride and almninium chloride are necessary; but in other modifications of the method only a trace of aluminium chloride is required to start the reaction, the chloride being merely a catalyst. This type of reaction is exemplified by the formation of diphenylmethane, C«H*-CH2'C«Hi, from benzyl chloride and benzene (37a). Usually, aluminium chloride acts only as an "activator" when it enters into combi- nation with the organic halogen compound.
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 b 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. 78
Fig. 78. — Enantiotropic Substance.
Fig. 79. — Monotropic 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. Sincc^ rise of tcmix?rature ultimately occasions the fusion of all solid forms, above a certain temperature, definite for each substance, the liqui<l phase must be the most stable; in other words, it must have the lowest vn pour-pressure. O/i is the melting- point of the metastable niodifieation, which is higher than the transition-point: 0/.. is that of the stable modification.
§318] KETONES AND OXIMES. 431
AB can, however, be so situated that/i and/, are below 0 (Fig. 79). Here the melting-point is lower than the transition-point 0, so that the latter (?annot 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 enantiotropy, on rise of temperature the compound first attains the transition-pomt, then undergoes transformation, and finally melts.
Ozimes.
318. Some of the oximes of the aromatic aldehydes and ketones exhibit a peculiar kind of isomerism. Thus, there are two isomerides of benzaldoxime : benzsintialdoxime (a), melting at 35°; and benzsynaldoxime (^ ^^ ^^^)» which melts at 128**, and on treatment with acetic anhydride readily loses water, forming benzonitrile:
CeHsCjH
! = CeHs-C^N+HaO. iOH
With acetic anhydride, the an/mldoxime yields an acetyl-derivative. It has been proved that no isomerides of the ketoximes
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- i^tituted, two isomeric oximes can be obtained. M onochlorobenzophe- none, C6H5«C0'C6H4C1, monohromobenzophenone, C6H5«CO'C6H4Br, phenyltolylketone, CH3 • C6H4 • CO • Cells, and plienyhinisfjlketone, CH30-C6H4-CO-C6H5, are examples of ketones which yield two isomeric oximes. Many other compounds of this type could be cited.
After several inefTectual attempts to explain such isomerism by the ordinary structural formulae, the followinc; stereochemical explanation of the observed facts has been adopted. It is assumed that the three affinities of tlie N-atoin are directed towards the angles of a tetrahedron, the nitrogen atom itself being situated at the fourth angle:
432
ORGANIC CHEMISTRY.
[{ 318
When the three nitrogen bonds are linked to carbon, as in the nitriies, the following spacial representation is obtained:
CH
GH
N
Stereobomerbm 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:
^Y
and
These can be more readily represented by
X— C— Y X— C— Y
I and |l .
N— Z Z— N
It is apparent that different configurations for such compounds 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.
It can also he determined which configuration represents each ^ isomeride. The two isonicric benzaldoximes liave the formulse
5 319] ;^ ; ' OXIMES, 433
OtHg — C — H CcHj — C — H
I and II
N— OH HO— N
Bens«]/nal(loxime Bensanftaldoxime
1. 11.
In formula I., H and OH are nearer together than in formula II. This proximity explains the facility with which one molecule of water is eliminated from one aldoxime (syn), and not from the other (anti). On this account configuration I. is assigned to the synaldox- ime, and configuration II. to the an^taldoximc.
The configuration of the ketoximes can be determined by the Beckmann transformation (103), as is made clear in the following example. Two isomeridesof phenylanisylketoxime are known,
CH3O • CcH^— C— CcHs CH3O . C«H4— C— C«H5
I and I ,
N— OH HO— N
I. II.
the first melting at 137° and the second at 116°. By the Beckmann transformation, the oxime of higher melting-point yields the anilide of anisic acid; that of lower melting-point, the aniside of benzoic acid. The former must therefore have configuration 1., and the second configuration II.. because in I. the groups OH and CeHj are adjacent, and exchange places:
CH3O • CeH^— C— OH CHjO • Ce,H,— C=0
I - I .
N-C«H5 NH— CeHs
The anilide of anisic acid, CH80*CflH4«COOH, is thus produced. In II., anisyl (llJHaO-CcH^ — ) and OH are adjacent, and exchange places, yielding the aniside of benzoic acid :
HO— C— Cells 0=rC-CJIs
CHsO-CflH^-N CHaO-CcH^— NH
XL AROMATIC PHOSPHORUS AND ARSENIC DERIVATIVES.
319. Compounds of phosphorus and arsenic with aromatic hydro- carbons, having constituents similar to those of the nitro-com- pounds, azo-compounds, and amino-compounds, arc known.
Phosphinobcnzene, CeHi-POj, cannot he obtained analogously to nitrobenzene, by the interaction of metaphosphoric acid and benzene.
434 ORGANIC CHEMISTRY. I§ 319
It is prcpanni by the uction of phenylphosphinic acid (79) upon its chloride :
Ce,H5.PO(OH)3+CeH5.POCl, - 2CeH5-PO,+2Ha.
Phenylphoaphinic Q^oride
acid
It is a white, crystalline, odourless powder.
Phenylpfiosphine, Cells* FH,, is obtained by distilling phosphenyl cJiloridCj CoHg' PCI2, 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.
Phoaphobemene, CcHj-PrP-CeHj, is got by treating phenyl- phosphine with phosphenyl chloride:
CcHs'PlCla + HglP-CeHs - CeH5.P:P.CeH6+2Ha
It is a pale-yellow powder, insoluble in water, alcohol, and ether. It b energetically oxidized by weak nitric acid, forming phosphenyUms
acid, OP^H . \0H
Phosphenyl chloride, CeHj- PClj, 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.
Arsinobaizcne, CcHj-AsOj, is obtained by the elimination of water from phenylarsinic acid, C«H6-AsO(OH)j, under the influence of heat.
ArsenobenzenCy CeHt-AslAs-CeHs, is formed by the reduction of phenylarsine oxide, CeHs-AsO, with phosphorous acid. It forms yello'.v needles, and is converted by oxidation into phenylarsinic acid, C«H5-AsO(OH),.
Other aromatic arsenic derivatives are mentioned in 339.
The following series of cora|X)unds are known:
CeH^.XO, CsH^-X.-CoH. CeH,.NHt
Nitrobenzene Axobenzene Phenylamine
CJIs-PO^ CeHi-P.-CeH, C«H..PH,
Phosphinobenzene Phosphobcnzcne Phenylphosphine
CMli-AsOo C«H5.As,.CeIl6 —
'^Arsiuobonzoue Arsenobonrene
Although these roniiwuiuls have analogous formula?, both the methods employed in the preparation of the individual members
§ 3201 AROMATIC METALLIC COMPOUNDS, 435
of each series, and the properties of the individuals themselves, exhibit wide divergences.
Xn. AROMATIC METALLIC COMPOUNDS.
320. Mercury, tin, lead, and magnesium are the only metals which yield aromatic compounds: they are ipuch less important than the metallic compounds of the aliphatic series. Mercury phenide, Hg(C6Ht)s, is obtained by the action of sodium-amalgam upon bromobenzene. It is crystalline, and resembles the corre- sponding alkyl-derivatives in its stability towards atmospheric oxygen. WTien 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 phcnylmercury acetate, CJIft'Hg-OOC-CHi, the acetic-acid salt of the base phenylmercury hydroxide f CJI»-Hg»OH. The homologues of benzene, nitio* benzene, and other substances jdeld analogous compounds.
Aromatic magnesium compounds are referred to in 289.
.^
*^.il'i
BENZENE HOMOLOGUES WITH SXTBSTITUTED 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 type 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.
I. 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. Compoimds of the type X-C6H4-CH3 are called halogen-toluenes , 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-chlorotoluene and p-chlorotoluene; when, however, chlorine or bromine is brought into contact with boiling toluene (110°), benzyl chloride, C6H5«CH2C1, or benzyl bromide^ C6H5«CH2Br, is almost exclusively formed.
2. Sunlight. — A striking example of the influence of light is fumish(»d 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
436
§321] HALOGEN AT ION OF TOLUENE. 437
disappearance of the bromine, with formation of hydrogen bromide and bromotoluenes. On exposing the mixture to dayUght, it becomes decolorized in a few minutes, the bromine entering the side-chain only.
Many instances of the influence of Ught 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 Ught.
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 per cent, 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 gramme-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 Unked as those in the monohalogen-l^enzenes. 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
438 ORGANIC CHEMISTRY. [§322
has a powerful and unbearably irritating odour, productive of tears.
The prolonged action of chlorine on boiling toluene yields bemal chloride j CeHs -011012, and benzotricMoride, CeHs^CCla.
n. PHENYLNITROMETHANE AND THE PSEUDO-ACIDS.
322. Phenylmtromethanej CeHs -0112X02, is an aromatic com- pound with a iiitro-group in the side-chain, as is evident from its formation by the action of benzyl chloride or iodide on silver nitrite:
CH.-CH^rCl-fAgiNO, = CeH6-CH2N02+AgCl.
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. Phenylnitromethane 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 crystalline substance of the 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 ver>' probable that the sodium compound and the unstable modification corresponding with it have the constitutions
CeH»-Cn:XO.OXa, and CJI^-CHiXO-OH.
The presence of a hydroxyl-group is proved by the formation of dibenzhydroxarnic acid on treatment with benzoyl chloride:
CJL-CHiX^ +0100. CJI. -* OelL-OHiNf -*
X)Xa X)-OC-CJB,
Sodiophenyliio- uitromethunc
- OJL-OO— X— 0-00-OJI,.
H
Dibenxhydroxamic acid
Another proof of the presence of a hydroxyl-group is that isonitro- C()in])()un(ls, unlike onlinar>' nitro-conipounds, react vigorously with phenyl isory'diiiiie at low teniperaturos.
§ 323] PSEUDO-ACIDS. 439
From these facts it may be inferred that when phenyhiitro- methane, CJL-CHaNOa'is converted into a salt, it first changes to an isomeric modification. Inversely, when it is liberated from its sodium compound, the wo-modification, or oci-modification, is first produced, and slowly changes to the ordinary form.
The dilute aqueous solution of m-nitrophenylnitromethane 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 iso-compound into its normal isomeride.
The discharge of the colour is attended by another phenomenon : the electric conductivity of the Uquid is considerably greater imme- (Uately after the addition of the hydrochloric acid than it is several minutes later, when the colour has nearly vanished. The explana- tion of this is that the iso-form 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.
Compounds which change to an act-modification on formation of metallic derivatives are called pseudo-acicfe. In addition to phenyl- nitromethane and its ring-substituted derivatives, other psendo-SLcids are known, most of which were prepared by Hantzsch.
323. Besides the properties indicated above, the pseudo-acids 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 oci-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 neutralization. This " slow neutralization " is a characteristic of the pseudo-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, .NO,
CHs-Cl +HC1-CH8-C,( +Naa,
^NO-ONa "^NO-OH
act-Dinitruet hane
is so rapidly converted into the normal compound, CHs«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 pscudo-Sicid. An
440 ORGANIC CHEMISTRY, [§ 324
acid which is so weak that its solution is a bad conductor of elec- tricity yields alkali-metal salts which undergo strong hydrolytic dissociation, and therefore have a strongly alkaline reaction ("Inorganic Chemistry," 66). Such a substance as sodiodinitroe* thane forms a non-alkaline solution, and must therefore be derived from an acid other than diuitroethane, since this substance has a neutral reaction and is a non-conductor in aqueous solution.
The difference in structure between the salt of a pseitdo-acid and the free acid can also be detected by their refraction. Compar- ison of the molecular refraction of an aqueous or alcoholic solutiou 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-corapound which yields a pseuda-SLcid, 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 pseudo-acid into its oa-form to be an intermediate process preceding the formation of the salt.
m. ACIDS WITH CARBOXYL IN THE SIDE-CHAIN.
324. One of the compounds with a saturated side-chain is phenylacetic acid, CeHs-CH-j-COOH. It is prepared by the interaction of potassium cyanide and l)enzyl chloride, followed by hydrolysis of the resulting nitrile, benzyl cyanide ^ C6H5-CH2-CN, Phenylacetic acid melts at 76°, and is converted by oxidation
CH
into benzoic acid ; whereas the isomeric toluic acids, C6H4 <^pr\f\ijr
arc transformed by oxidation into the dibasic phthalic acids.
Mandelic acid has both hydroxyl and carl)oxyl in the side- chain. Its constitution is CeHs-CHOH-COOH, as its synthesis from benzaldehyde and hydrocyanic acid indicates. In this reaction mandelonitrile , CgHs-CHOH-CN, is an intermediate product. Addition of quinine to the mixture of benzaldehyde and hydrocyanic acid makes the synthesis asymmetric, so that an optically active mandclonitrile 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 hevo-rotatorv. The* synthotirul acid can be resolved by the action of cultures obtained from mildew (Penicillium glaucum), the dextro-rotatory acid being left intact. The
§§ 325, 326) BENZYL ALCOHOL AND BENZYLAMINE, 441
decomposition is also effected by the formation of the cinchonine 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 less soluble in water.
IV. AROMATIC ALCOHOLS.
325. Benzyl alcohol, C6H5-CH20H, is the typical aromatic alcohol 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, henzaldehyde (314). and also to benzoic 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.
V. COMPOUNDS WITH THE AMINO-GROUP IN THE SIDE-CHAIN.
326. Benzylajnine, C6H5«CH2'NH2, is a typo of the amines with XH2 in the side-chain. It can be obtained by the various methods employed in the preparation of aliphatic amines, such as the action of benzyl chloride upon ammonia, by which dihenzyl- amine and trihenzylamine are also formed ; the addition of hydrogen to benzonitrile, CgHs-CN; the reduction of phenylnitromethans, C6H6-CH2'N02, and so on. The method for its formation and its properties prove that l)enzylamine Ix^longs to the primary amines of the aliphatic series: thus, it docs not yield diazonium
442 ORGANIC CHEMISTRY. [5 326
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.
337. Styrole, CeH»*CH :CHt, is a coal-tar product, and derives its name from its occurrence in storax. It can be obtained from cinnamic acid, C«H»- CH :CH* COOH, by heating it, whereupon carbon dioxide is eliminated. It is a liquid of agreeable odour, and boils at 146^. Heating converts it into a vitreous mass called meUtstyrole, a poly- meride of unknown molecular weight, the same transformation taking place slowly at ordinary temperature. Like other substances with a double linking, styrole has the power of forming addition- products. On treatment with nitric acid, it yields niirostyrole, CeHi-CHrCH-NOi, 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
CeHj.CO + HjCH.NO, « CeHft-CH:CH.NO, + H,0.
Phenylacetylene, CeHj-CSCH, can be obtained by treating acetophenone with phosphorus pentachloride, and acting on the resulting compound, CeHj-CClj-CHs, with caustic potash; or from phenylpropiolic acid, CaHg-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 acid, it takes up one molecule of water, forming acetophenone.
Alcohols and Aldehydes.
Cinnamyl alcohol, CeHs-CHiCH-CHjOH, is the only repre- sentative of the unsaturated alcohols which need be mentioned. It is a crystalline substance with an odour of hyacinths, and is present
443
444 ORGANIC CHEMISTRY. [J 328
as an ester in storax. Careful oxidation converts it into cinnamic acid (328), and more vigorous oxidation into benzoic acid.
XT
Cinnamaldehydej CeHs-CH :CH-Cq, is the chief constituent
of oil t)f 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 resinificd by strong acids, and with ammonia yieldiB hydrodnnamide, Nj(C6H«CjH3)3, analogous to hydrobenzamide (3x5).
Acids.
328. Cinnamic add, CeHs-CHsCH-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:
C6H6.Cq+H2CH.CO.O.CO.CH3~-C6H5-CH:CH.CO.O.CX).CH8;
Beozaldehyde Acetic anhydride
+ H2O = CeHs • CH : CH • COOH + HO • CO • CH3.
Qnnamic acid Acetic 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), C«H5«CHCl2, 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)2C|H, + 0|9;^«^5 = CHs-CH :CH .COOH +CO2 +HA
a
Malonic acid
Cinnamic acid is a cr}'stalline 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 Baeyer's reagent (113).
Its constitution indicates that two stereoisomcrides are possible:
CeH,— r— H Cells— C—H
li and ||
II- C— COOH COOH— C— H
3281 CINNAMIC ACID, 445
Four modifications, however, are known: ordinary cinnamic acid; sHocinnamic addj melting at 68°; and two v8ocinnarmc acids j 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 crystallizes out. i4i/ocinnamic acid and the isocinnamic acids can be prepared by partial reduction of phenylpropiolic acid, CeHj-C^^C-COOH (327); and must, therefore, have the m-configuration (I.), as is evident from a model. It follows that ordinary cinnamic acid has the (rans-configuration (II) :
H-C-CeH» CJI».C-H
I. I ; n. II
H-C-COOH H-C-COOH
Cia Trant
It can be converted into the m-form by exposing its solution benzene to the ultraviolet rays of a "uviol" lamp for ten days.
POLYSUBSTITUTED BENZENE DERIVATIVES.
329. 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 poly halogen compounds will be dis- cussed first, then the substituted nitrobenzenes, sulphonic acids, phenols, and so on.
The general rule holds that substitucnts 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 polyhcdogen 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 para-position, but the orf/io-compound and a small pro- portion of the me^a-compound arc simultaneously formed. vci-Dichlorobenzene and vci'dibrotnobenzene can be prepared by reduction of m-dimtrobenzene (331), and subsequent diazotiza- tion of the product. The /)ara-dihalogcn compounds are solid, the isomeric or//io-compounds and ?7ie/a-compounds are liquid. When three halogen atoms enter the nucleus, the main product is the l:2:4-trihalogenbenzene,
X
V
9
X
446
§330] POLYSUBSTITUTED DERIVATIVES. 447
since the same product is obtained from each of the three dihalogenbenzenes. Prolonged chlorination of benzene sub- stitutes its six hydrogen atoms, with formation of Julin's chioro- carbon, CoCle, 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.
IL HALOGEN-NITRO-COMPOUNDS.
330. Nitration of a monohalogenbenzene yields only the ortho- 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^hloronitrobenzeney and about 30 per cent, of O'chloronitrobenzene, C1-C6H4- NO2. m-Chloronitroben- zene is readily prepared by chlorination at elevated temperature of a mixture of nitrobenzene with 20 per cent, of its weight of antimony pentachloride. m-Halogen-nitrobenzenes can also be prepared from m-nitroaniline by the diazotization-method.
Unlike the halogen in the monohalogenbenzejies, 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 mcthoxide, 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/Ao-position and the para-position to halogen causes a marked increase in the adaptability for double decomposition. The Cl-atom in picryl chloride,
CI
N02/^N0j
2 NO,
V
'2
is replaceable by a great variety of substituents. This substanco
44S 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, C6H2>TrT H^ ' ' .
m. POLYNITRO-DERIVATIVES.
331. ui'Dinitrobenzene is obtained by the nitration of benzene with a mixture of concentrated sulphuric acid and faming nitric acid. It forms colourless needles melting at 90°. On reduction, it yields m-pJienylenediaminej and is therefore employed in the prepa- ration of coal-tar dyes: it is also used in the manufacture of explo- sives, since it can be exploded by mercur>' fulminate. In addition to the m-compound, small quantities of o-dinitrohenzene and traces of p-dinitrobenzene are formed. Stronger nitration, effected by a mixture of nitric acid and fuming sulphuric acid heate<l to 140®, converts m-dinitrobenzene into symmetrical trinitrobenzene (123*5), which melts at 121°.
The hydrogen atoms and nitro-groups in the polynitrobenzenes are much more readily replaced than those in mononitrobenzene. Thus, m-dinitrobenzene is converted by oxidation into 2:6- dinitrophenol, and US^o-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 (Miinitrobenzene and p-dinitrobenzene can be replaced by OC2H5 and OCH3:
C6H4<5jg2^NaOCH3 « C6H4<g^^^+NaN02.
It is remarkable that this substitution does not take place with 7«-<linilr()henzeno, although in 1 :32r)-triuitrobenzene, with each of its substituents in the rneta-poshi va t ) the other two, one of
§ 3321 POLYSUBSTITUTED DERIVATIVES. 449
the iiitro-groups can be readily replaced by OCH3 (*' Laboratory Manual," XXXIII, 3).
When boiled with sodium hydroxide, o-dinitrobenzene yields o-nitrophenol, and when heated with alcoholic ammonia, o-nitro- aniline:
.NOal-fNaOH yOH
C6H4< ^ = C6H4C +NaN02.
NO2 2 \NOi
CaH4 <g^4±^NH2 ^ CeH.<NH2^HN02.
NO22 " " NO2
It has not been possible to introduce more than three nitro- groups into benzene 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.
Triniirobutylxyleney containing a tertiary butyl-group, has a power- ful odour resembling that of musk. It is a perfume, and is called "artificial musk."
IV. SUBSTITUTED BENZENESULPHONIC ACIDS.
332. Digestion of monochlorobenzene or monobromobenzene with concentrated, or better fuming, sulphuric acid yields exclu- sively p-chlarobenzenesulphonic acid or p-broniobenzenesulphonic arid. The properties of these substances approximate closely to those of the unsubstituted bcnzenesulphonic acid.
On fusion with potassium hydroxide, each of the three bromoben-
OH 1 zenesulphonic acids is converted into resorcinol, C6H4<QTTo^oneof
the few instances of substitution at a position other than that occu- pied by the group replaced. Additional examples of the same phenomenon \^ill be mentioned subsequently (333).
Both nitration of bcnzenesulphonic acid and sulphonation of nitrobenzene yield chiefly ni-nitrobenzenesul phonic acidj with simultaneous production of a small percentage of the isomeric orthchcompound and pars.-compound.
When benzene and its homologues are heated at a high tem- perature with fuming sulphuric acid, disulphonic acids and fri-
450 ORGANIC CHEMISTRY. I§ 333
sulphonic 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 benzenetrisulphonic acid. With respect to the production of disulphonic acids^ benzene yields chiefly benzene-m-disulphonic acid, a substance partially converted into benzene-p-disulphonic acid by prolonged heating at a high temperature with sulphuric acid. Inversely, under the same conditions the para-compound is partially trans- formed into henzene-Ui'disvlphonic acid. Benzene-o-disulphonic acid is not produced by direct sulphonation of benzene.
V. SUBSTITUTED PHENOLS AJH) POLYHYDRIC PHENOLS.
Halogenphenols.
333. The direct action of chlorine or bromine on phenol yields o-chlorophenol and p-chlorophenol, or o-broniophenol 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 2:4:6-tribromophenol by add- ing bromine-water at ordinar\^ temperature to an aqueous solution of phenol (293). The oW/io-compounds have a pungent, very penetrating odour. At ordinary temperature, the or^Ao-isomerides and mda-isomerides of the chlorophenols and bromophenols arc Ii(|uid; the para-isomerides are solid (288). Fusion with potassium hydroxide replaces their halogen by hydroxyl, although the corresponding liydroxy-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 displa3'ed by the hydrogen atoms of the honzeno-nucleus after introduction of a hydroxyl-group is illustrated by the behaviour of the phenols
§334] NITROPHENOLS. 451
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-nitrophenol. The two isomerides can be separated by distillation with steam, with which only the or^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/feo-compound in forming highly coloured phenoxides. Further particulars of the nitrophenols arc given in 330 and 331.
334. The most important nitrophenol derivative is picric acid, or 1:2:4: 6-trinitrophenol,
NO.
(NO,A ^OH
NO,
•
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 aquecus 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 petroleum-ether, in which there is no ionization, is colourless; the anion, however, also undergoes tautomerization' (373). It is slightly soluble in cold water, and is not volatile with steam. It melts at 122^; a.ul has an excessively bitter taste, which suggested its name (ttikpos, bitter) .
A consideration of the following reactions shows that picric
452 ORGANIC CHEMISTRY. [§334
acid is comparable with the carboxylic acids. Phosphorus penta- chloride replaces the hydroxyl-group by chlorine, with formation of picryl chloride (330). Silver picrate and methyl iodide yield methyl picrat^: 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.
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 compound of the formula CioH8«C6H2(N02)3-OH. These derivatives crystallize well, and have definite melting-points. They are sometimes employed with advantage in the separation of hydrocarbons, or in their identi- fication. 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 isopurpuric 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'Phenolsul phonic acid and p-phenolsidphonic acid' are ob- tained by dissolving phenol in concentrated sulphuric acid. m-Phenolsulphonic acid is produced by fusing m-benzenedi- sulphonic acid with caustic potash. -The o-acid is characterized by being easily converted into the p-compound. Phenol sulpho- natcs more reatlily than benzene, its solution in sulphuric acid being transformed into the o-.sulphonie acid and p-sulphonic acid even at ordinar}' temperatures.
S§ 335, 3361 NITROSOPHENOL. 453
Nitrosophenol.
335. In certain respects nitrosophenol reacts as though it had
NO the constitution C6H4 <qjj, although its formation from quinone
. . . . ^^^H
and hydroxylamine points to the constitution C6H4«^ . It is
^0 prepared by the action of nitrous acid upon phenol, or of caustic potash upon nitrosodimethylaniline (299) :
CoH.<^fjtH^NO^CeH.<NO^H.O;
0N<^^^~^ = HN(CH3) 2 + 0N<(~\0R,
Like other oximes, nitrosophenol, or quinone mono-oxime, amites 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 Q-compound, C6H4<qtt o> catechol ('' pyrocatechol '' or
" pyrocatechin "), 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.
OCH 1 The monomethyl ether, C6H4<qtt ^9' ^^ called guaiacol; it is
454 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 veratrole, and is characterized by its agreeable odour.
OH 1
Resorcinol {** resorcin '')> or m-di hydroxy benzene, C6H4<^tt «,
can be obtained by fusing wi-phenylenedisulphonic acid,
SO Hi. C6H4<^Q^TT o, with potassium hydroxide, the method for its man- ufacture. It yields a deep-violet coloration with ferric chloride: bromine-water converts it into tribromoresorcinol. It is a colour- less, cr>'stalline 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 347.
Styphnic acidy CaHLtq \ (O'I'Q) ^ ^ ^YP^ of a nitrated dihy-
droxybcnzene, 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-nitrophenol 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 styphnic acid:
OH OH OH
no,/Nno, no,/\no,
NO, NO,
2: 3: 4: 6-Tetranitrophenol Styphnic acid
Quinol ('* hydroquinone "), or p-dihydroxy benzene, melts at 17(F! its chief characteristic is the loss on oxidation of two hydrogen atoms with formation of quinone, CGH4O2 (338), which is readily reconverted into quinol by reduction. The reducing effect of quinol is employed in photography for the development of nofrativcs. With ammonia it <!:ive.s a r(Hl-l)rown coloration, due to th(* formation of complex derivatives. Like its isomerides, it is readily sohible in water.
The dihydroxvhenzenes can Ik* separated from one another by the action of lead acetate. With this reagent, catechol gives
J3371 TRIHYDRIC PHENOLS. 455
a white precipitate, resoroinol does not yield a precipitate, and quinol gives a precipitate only in presence of ammonia.
Trihydric Phenols. 337- PyrogaUol ("pyrogallic acid'O,
/OHl CoHs^OH 2, \0H3
•
is obtained by heating gallic acid (346), CO2 being split off:
C6H2(OH)3-COOH- C6H3(OH)3 + C02.
Gallic acid Pyrogallol
Pyrogallol 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 browTi 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.
/OH 1 Phloroglncinol (symmetrical trihvdroxybenzene), CeHa^OH 3,
\0H5 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 phloroglncinol from diethyl sodio- malonate was discovered by vox 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,(COOC2H4)2-hC,HsOH = CH, • COOCHs-hCOaCCsH*)*.
Ethy! acetate Ethyl carbonate
The ethyl acetate CDndonses with diethyl malonate to form the diethyl ester of unsymmetrical netorudicarboxylic acid:
{C00C.H6)aCH,-hC,H»00C • CH,
= (C00C,H»)2CH-C0-CH,+C,H*0H.
Diethyl urctonedicarbozylate
456 ORGANIC CHEMISTRY. [$ 337
This product then condenses with another molecule of diethyl malonate, with production of diethyl phloroglucinoldicarboxylate:
(C00C,H,)2CHi-C0-Ca CO OC2H5 CH, CO
H
(C00C,H»)2C— CO— CH,
I
OCiHftI CO-CHfCO
Diethyl phloroglucinol- dicarboxylate
On fusing this substance with potassium hydroxide, the ethyl-cax- boxyl-groups ( — COOCaH^) are replaced b}' hydrogen, with forma- tion of phloroglucinol.
Phlqroglucinol should therefore have constitution I.
CO H,C CHa HO-^ ^
H OH
OC CO
\/
CH, I. II.
OH
H
In other words, it is ci/c/ohexane in which three of the methyl- ene-groups, CH2, have been replaced by carbonyl, CO; it must, therefore, be called triketocydohexane. It has been proved that phloroglucinol docs behave as though it had this constitution: thus, with three molecules of hydroxylaniine 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 trihydroxybenzcne, 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 hexamcthylen(».
This view explains the interaction of phloroglucinol, and other polyhydric phenols, and a mixture of caustic potash and an alkyl iodid(» to form derivatives with alkyl-groups attachcMl to carbon and not to oxygen; for the hydrogen in the metliylene-groups of the tautomeric form must l)e replaceable^ by metals (200;.
Tlie problem of assigning the enolie or ketonic formula to free phloroglucinol is settled by an examination of the absorption-
§3381 HIGHER PHENOLS AND QUI NONES. 457
spectrum of this substance in alcoholic solution. The ultraviolet region of this spectrum contains a band approximating closely in position to a similar band in the spectrum of the trimethyl ether of phloroglucinol. Since this ether is undoubtedly an enoUc compound, phloroglucinol itself must have the enolic formula; because the distribution of the bands in the absorption-spectra of enolic com- pounds has been proved by other researches to be wholly different from that of the b ands in the spectra of their ketonic isomerides.
Higher Phenols.
The chief of the higher phenols is hexahydroxybemenej Ce(0H)6. Its potassium derivative, potassium carbonylj Ce(OK)e, is formed in the preparation of potassium, and acquires an explosive char- acter on exposure to the air (" Inorganic Chemistry," 227). It can be obtained by heating potassium in a current of carbon monox- ide, a direct synthesis of a derivative of benzene. Distillation with zinc-dust 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.
Dihydroxybenaene Quinone
The simplest quinone is benzoquinone, C6H4O2: it is also called quinone. It is obtained by the oxidation of many jxlerivatives of
benzene, such as p-arainophenol ^%^A<r^Y{ a^ sulphanilic acid,
C6H4<gQ^|j ^, and p-phenolsulphonic acid, ^6H4<gQXTi, and
also by the oxidation of anilme with chromic acid — the ordinary method of preparation. It is also formed in the oxidation of quinol (336), though the latter is usually prepared by the reduction of quinone. Oxidation of quinol by ferric chloride yields quin- hydrone, a compound in equimolecular proportions of quinone and quinol, crystallizing in beautiful, intensely coloured, long needles.
458 ORGANIC CHEMISTRY. [§ 338
o-Dihydroxyberizene 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 para-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 od<miu^
They volatilize with steam with partial decomposition, an5 have
oxidizing^roperties. The constitution of benzoquinone is best
expressed by
CO
/\ HC CH
HC CH
\/ CO
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 yiekiiog
with hydroxylamine first a quinone mono-oxime (381), and then a
quinone-dioxime:
C=NOH C=NOH
/\ /\
HC CH HC CH
II II and II II .
HC CH HC CH
CO 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 bonzeno dorivative, but the diketone of a p-di hvi Irobenzenc :
CH2
/\ HC CH
HC CH
\/ CH,
§ 339]
SUBSTITUTION-PRODUCTS OF ANILINE.
459
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:
CO
HC
HC
CH
CH CO
4- 3O2 =
HC
HC
OOH
+ 2CO2.
OOH
VI. SUBSTITUTION-PRODUCTS OF ANILINE.
339. Aniline is attacked very energetically by chlorine and bromine. The direct introduction of these halogens must* be effected by their slow addition to solution of acetoanilide in glacial acetic acid, the main products being the para-compounds. The or//w)-halogenanilines and the meto-halogenanilines are pre- pared by reduction of the corresponding halogen-nitrobenzenes. The production of 2'Ai^tribromoanlline is described in 296, The basic character of aniline is weakened by the introduction of halogens.
Nitroanilines.
NitroanilineSf or compounds containing nitro-groups and an amino-group, can be obtained by the partial reduction of dinltro- compounds by means of ammonium sulphide. Another method for their production consists in the nitration of anihnes, 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-compound is employed, p-nitroanilinc is the chief product : with sulphuric acid, m-nitro- aniline and p-nitroaniline arc formed in almost equal ratio, and a very small proportion of o-niiroanilinc. The formation of nitro- anilines from ehloronitrolxinzenes and bronionitrobenzenes is men- tioned in 330.
460 ORGANIC CHEMISTRY. H 339
The amino-groups in o-nitroaniline and p-nitroaniline, but not that in m-nitro.:nilme, arc excliangcd for hydroxyl by heating with a- solution of potassium hydroxide, the corresponding potassium m'trophenoxide being formed. The amino-group in picramide or 2:4:''ij'trinitroaniline, C6H2(N02)3-NH2, is very readily replaced by hyd. oxyl.
In these substances there- is a weakening of the basic character, o-nitroanir.ne, for example, yielding salts which are decomposed by water.
o-Xitroaniline; m-nitroanihne, and p-nitroaniline, C6H4<t^TT^,
are yellow, crystalline compounds, almost insoluble in cold water, but readily soluble in alcohol. Their melting-points are respect- ively 71°, 111°, and 147°.
p-Aminobenzenesulphonic Acid or Sulphanilic Acid.
SuLphanilic acid is obtained by heating aniline with fum- ing sulphuric acid; or by heating p-chlorobenzenesulphonic acid at 200° uith ammonia, in presence 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
.8(3
probably CgH4 <yTj > ; that is, it is an inner salt. On fusion
with potassium hydroxide, it does not y\o\A 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 inner, salt of henzeuedinzoniumsxdphonic acidic precipitated, being nearly insoluble in water:
This ronipound is of ^rrcat Importimce in the preparation of azo- dyes, such as hdinnthine (341).
i 3391 AMINOPHENOLS. 461
^Aminophenols.
Aminophends 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 with acids. In the free state the aminophenols are colourless solids, crystallizing in leaflets, and readily turned brown by atmospheric 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 anhydra-hases:
/CfOl.CH
H
3
0=>-<^-
Aoetyl-Klerivstive EthenyUminophenol,
Anhydro-baae
On treatment with acids, aminophenol and acetic acid are regen- erated.
p-Aminopheyiol 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 present. The trade-name of this solution is ''rodinal.'' It finds application as a photographic developer.
LuMikRB has discovered certain general conditions which aro- matic compounds must fulfil to be available as photographic devel- opers. They must either contain some hydroxyl-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 hydroxy l-group, not less than two such unsubstituted groups must be present in the molecule.
A derivative of p-aminophenol used in medicine is **phenacetin *'
(yc H
or acetylphenetidiney ^n^i'^^^u.n u o» ^^® acetamino-derivative of
phenetole, CeH6-OC2H5.
When aniline hydroarsenate, CtKb • NH2,HjAs04, is heated, a mole- cule of water is eliminated, with formation of p-aminophenyUirsinic acid, NH,*C6H4-AsO(OH)i. The presence of a free ammo-group
402 ORGANIC CHEMISTRY. [§ a3&
is proved by the possibility of diazotizing the compound; iodine converts it into p-iodoaniline, with elimination of the arsenic-acid residue. The formation of p-aminophenylarsinic acid is analogous to that of sulphanilic acid by heating aniline hydrogen sulphate:
CcH, • NH,,H2S04 - H,0 = NH, • C.H4 • SO,H.
ine hvdro] sulphate
Aniline hvdrogen Sulphanilic acid
' >hii
Sodium p-aminoplienylarsinate or " atoxyl," and sodium p-oce^yZ- aminophenylarsinate or " arsacetin,"
CH, . CO . NH • CeH4 • AsO < 3^^,
arc valuable remedies for the treatment of trypanosomiasis or sleeping sickness.
When phenol is heated with arsenic acid, it yields the analogous P'hydroxyphenylarsinic acid, HO*C6H4*AsO(OH)2, converted by careful nitration into S-nitroA-hydroxyphenylarsinic acid,
H0/~^
O2N
Reduction transforms this product into the corresponding dia minodihydroxyarsenobemene,
H0/^As=As/~^ H2N NH2
The dihydroMoride of this substance is the " salvarsan " discovered by Ehrlich and IIata, and has been employed with jj;oo(l results in the treatment of diseases of protozoal origin. It is a er>'stalline powder, readily soluble in hot water; but the solution (U composers rapidly.
Pohjami no-compounds are obtained by the reduction of poly-
nilro-dcrivativcs. ni-Pfienylenediamine, CgH4<yit'^o, is formed
from b(Miz(Mi(' by nitration and subsocjucnt reduction.
l^-Phiniylvnedianiine can be prepared by the reduction of amino-
§ 3391 POLYAMINO-COMPOUNDS. 463
azobenzene (309) with tin and hydrochloric acid, aniline being also formed :
C6H5-N:!X.C6H4-NH2 = C6H5-NH2H-H2N-C6H4-NH2. 2H|2H
Triaminobenzenes are prepared similarly (341).
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- tones, yielding quinoxalines:
H2 0
H2 O
C— R y\ N=C— R
I C— R'
I +2H2O. N=C— R'
m-Phenylenediamine in aqueous solution gives an intense brown coloration \vith nitrous acid, even when the acid solution is very dilute (341). p-Phenylenediamine is converted by oxidation into bcnzoquinone.
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^ HN^CeH^iNH, a compound derived from p-phenylencdiamine, has the same rclatioiLship 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
C»H6-N:C«H4:X-CJI4-NH-C.H4-XH-C»H4-N:C»H4:N.C.H4»
N:C.H4:NH,
indicating union of the eight aniline-residues by nitrogen and not by carbon. One of the arguments in favour of this formula is the
464 ORGANIC CHEMISTRY. [§340
almost quantitative conversion of aniline-black by further oxidation into benzoquinone, also a proof that each of the eight aniline-residues is linked at the para-position.
Azo^diss— '
340. The azo-derivatives of the polyamino-compounds are known as azo-dyes. They are of great technical importance, being extensively employed in dyeing wool, silk, and cotton. They are azobcnzenes in which hydrogen atoms have been replaced by amino-groups. They arc 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 ncccssar}' 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 is necessary, therefore, to draw a distinction between coloured substances, or chromogens^ 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. Witt has propounded the thcor>' that the colouring-power of a compound depends upon two factors. The first of these is the presence of certain groups, which he calls chromophorc-groups, among them being the azo- group, — X=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 chromophorc-group, along with an auxochrornnc-group, such as NHj, OH, SO3H, or in general any group which imparts to them an acidic or basic character, arc dyes: an example is aminoazobenzene. Another example is nitrohonzeno, which has a pale-yellow colour, and contains the chromophorc nitro-group, but is a chromogon, not a dye: on the other hand, /)-nitroanilin(» and p-nitrophenol are dyes.
Baly lia.s shown that many colourless compounds, especially those witli double carbon linkings, arc characterized by absorption- bands in the ultraviolet spectrum. The introduction of auxo-
§ 341] AZO'DYES, 465
chromeTc 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 re;noved by washing the fabric after dyeing. The dye must, therefore, have undergone a change. It is assumed that it unites with the constituents of the animal or vegetable fibres to form a compound, a kind of salt, since dyes always have a basic or acidic character. A proof of this is given for rosaniline (374).
The fabric does not always 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, Uke 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 unite 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," SnCl4.2XH4Cl. 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 hydroljrtic dissociation, and the base or acid, for example aluminium hydroxide or stannic acid, is deposited in a fine state of division in the fabric. The dye unites with this base or acid, forming an insoluble, coloured compound 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 :
C6H5-N2[Cnnil<^^N(CH3)2=C6H5-N:N.C6H4-N(CH3)2+HCl;
Diasonium chloride Dimethylaniline Dimotbylaminoatobensene
C0H5. N2[C1Th|/~\0H = CeHs- N : N- C«H4- OH + HCl.
x^— / Hydroxy aaobcnsene
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
466 ORGANIC CHEMISTRY. [§341
intermediate product, which can be converted into the aminoazo- derivative by wanning with the amine hydrochloride. In this formation of aminoazo-compounds and hydroxyazo-compoimds, the para-H-atom always reacts with the diazonium chloride : when this atom is replaced by a substituent, the formation of dye either does not take place, or is very incomplete.
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 conrnion salt, which precipitates it in flocculent masses. It is freed from water by means of filter-presses, and packed either &s 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 aminoazobenzenc : it is seldom used now, its place having been taken by other yellow dyes.
Chrijsmline or diaminoazobenzene, C6H5-N:N-C6H3<tTTT^, is
obtained from benzencdiazonium chloride and m-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.
k'brown or vesuvine is formed by addition of nitrous acid to an aqueous solution of 7?i-phenylenedi amine. It is a mixture of various dyes, among them triaminoazobenzeney manu*
J 3411 AZO-DYES, 467
factured by diazotizing one of the NHa-groups in w-phenylene- diamine, and treating the product thus obtained with a second molecule of this base :
<^^N2[CiTHl<^^
H2N H2N HoN H2N
TrlaminoasobCQsene
Bismarck-brown consists mainly of more complex derivatives, formed by diazotization of both the amino-groups of w-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 w-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.
Helianthine, or dimethylaminoazobenzenesulphonip acid, is pre- pared by the interaction of p-sulphobenzenediazonium chloride and dimethylaniline hydrochloride in aqueous solution :
H03S.C6H4-N2Cl-hHC6H4-N(CH3)2 =
=HCl-hH03S.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 viethyl-orange. Resorcin- yellow or dihydroxyazobenzenesulphonic acid,
HO3S • C6H4 • N 2 X • C6H3 <()ij >
is obtained from rcsorcinol (336) and p-sulphobcnzencdiazonium chloride.
The azo-dyes are converted into amino-compounds by energetic reduction with tin and hydrochloric acid. Thus, aminoazobenzene yields aniline and jo-phenylenediamine :
CoHs • N=N . C6H4 • NH2 -^ CeHs • NH2 4- C6H4 <5J JJ J J.
468 ORGANIC CHEMISTRY. [§342
This decomposition on reduction affords a means of determining the constitution of these dyes, and indicates the methods by which they are obtained. For example, 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
NH2-C6H4— N:;N— CeHa <^^l.
This decomposition also indicates that the dye can be obtained by diazotizing a molecule of diaminobenzene, and treating the product with a second molecule of diaminobenzene, in accordance with the equation on the previous page.
Vn. SUBSTITUTED BENZOIC ACmS; POLYBASIC ACIDS AND THEIR
DERIVATIVES.
Halogenbenzoic 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 m-chlarobenzoic acid, it being associated with polychloro-acids very difficult to separate. wi-Chlorobenzoic acid can also be obtained from the corresponding amino-derivative by the diazotization-method, a reaction well adapted to the preparation of the halogenbenzoic acids. The interaction of phosphorus pentachloride with the hydroxybenzoic acids proceeds less smoothly. p-Chlorobenzolc acid and p-frromo- henzoic 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 10^ A; of the halogenbenzoic acids is greater than that of benzoic acid itself. For benzoic acid \Q^k is 0-6; for o-chloroben- zoic acid 13-2; f or m-chlorobenzoic acid 1 • 55 ; for p-chlorobenzoic acid 0- 93. Those values prove that the chlorine atom in the ortho- position exercisers the greatest influence and that in the para- position tlic least, while for the m-compound 10^ A; is intermediate in value.
§3431 NITROBENZOic AND SULPHOBENZOIC ACIDS. 469
Nitrobenzoic Acids.
ui-Nitrobenzdic add is the principal product obtained by nitrating benzoic acid; about 20 per cent, o-nitrobenz&ic acid and a very small proportion of p-nitrobenzoic acid are simultaneously formed. The or^/w-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 acid itself is 0-6, for o-nitrobenzoic acid 61-6, for the m-acid 3 -45, and for the p-acid 3 'OB. The melting-points of these acids are respectively 148°, 141°, and 241.°
Sulphobenzoic Acids.
343. o-Benzoic sidphinidCf
C6H4 <^Q^> NH^
,S02,
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, l:>eing eliminated unchanged from the body. Direct sulphonation of benzoic acid yields m-sulphobenzoic 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-toluene- sulphonyl chloride and o-ioluenesvlphonyl chloride^ the former being the chief product. The o-chloride is converted into its sidphon- amide J 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 :
nu PM _^ P TT ^^^2^1 1_^ p Tj ^S02«NH2_^ l^6rl5-Orl3 — > \^6"4 \ripT 9 ^ "* CH
Toluene o-Toluene^ulnhonyl chloride o>Sulphonamide
_x P W ^S02- NH2_^ p TT ^S02v, VR — > O6I-I4 <pQQ|^ —> 06X14 <(^Q> -i^*".
o-Sulphonamide of Saccharin J
beniolc acid —
470 ORGANIC CHEMISTRY. [§344
Saccharin is a white, crystalline powder, soluble with diflSculty in cold water, and readily soluble in alcohol and ether. It takes up one molecule of water, yielding the sulphamide of o-sulpho- benzoic acid, which docs not possess a sweet taste.
Remsen found that the "saccharin " of conunerce is a mixture of o- benzoic sulphinide; p^idphaminohenzoic acidy COOH4«C6H4«SOiNHj; and potassium hydrogen o-sidphohenzoatej COOH«C»H4«SOiOK, con- taining less than fifty per cent, of the sulphinide. The melting-point of the pure sulphinide is 220°.
Monohydroxy-acids.
'344. The most important of the monohydroxy-acids is
OH 1 o-hydroxy benzoic acid, or salicylic acid, ^^^*^ POOH 2* ^^
derives its name from salicin, a glucoside in the bark and leaves of the willow {salix). On hydrolysis, this substance yields saligenin and dextrose:
C13H18O7+H2O = C7H8O2+C6H12O6. '
Saltcia Saligenin Dextrose
Saligenin is the alcohol corresponding to salicylic acid, into which it is converted by oxidation:
p XT ^ OH _^n jj ^ OH Utt4 < CH2OH ^^"^^ ^ COOH'
Saligenin SalicyLc acid
Salicylic acid is present as methyl ester in oil of wintergreen (GauUfieria procwrtbena) ^ 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 .COOH
<^ — ► C6H4<^
^011 ^OH
Salicylic acid is manufactured by a process discovered by KoLBK and improved by Schmidt, in which sodium phenoxide is heated with carbon dioxide in an autoclave at 130°.
§ 3441 MONOHYDROXY-ACIDS, 471
At the ordinary temperature at a pressure of about H atmos- / pheres, sodium phenoxide and carbon dioxide react to form sodium phenylcarbonate:
I CeHfi • O • Na + CO, - CeHs • O • COONa.
This compound is to be regarded as an intermediate product in the synthesis of salicyclic acid! Its conversion into this substance is represented by the scheme
.COONa X)H
— » CJiHiv H \COONa
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, CeH4C^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-
<0.C0.CH3 , are employed in COOH
When the acid is heated to 220°, it loses carbon dioxide and water, with formation of phenyl salicylate:
<^H4<coofHl+C6H4\^|^jj = ^^2+H20+C6H4<cooCeH6-
This compound is employed as an antiseptic under the name **salol.'' By heating to 300°, its sodium derivative is converted into sodium phenylscUicylate:
^6^* < COOCeHfi ^® * ^ COONa-
472
ORGANIC CHEMISTRY,
[§345
345. A large number of vegetable dyes related to salicylic acid
b known. They are classified in two divisions, the xanthone-group
and the flavone-grovpf and have been investigated mainly by vON
KosTANECKi. Distillation of salicylic acid with acetic anhydride
OC H yields first the phenyl ether of salicylic acid, C6H4<pqq|£, further
converted by elimination of water into xanihone,
O
•>'
CO
Euxanihone or Indian yellow is a 1 :2'-dihydroxyxanthone.
Flavoney
O
C
CH
CO
is obtained by condensation of the ester of the ethyl ether of salicylic acid with acetophenone:
n XT ^OCaH* _P IT ^OCsH*
• * C0|qC2H»^HCH,-C0-CeH» * * CO-CH,-CO-C.H»
+C,H»OH
On heating this condensation-product with hydrogen iodide, one of the carbonyl-groups is reduced to CHOH. Water and alcohol are then eliminated, \Mth formation of flavone:
pi TT ^0(. 2II5
^•^^^C^O-CH.-CIIOH-CaH,
The flavone-group includes chrytfin or 1 'S^ihydroxyflawne, the yellow dye of |)oplar buds; lut<;olin or ly^'^'^-i'-tetrahydroxy^ flaroju'j tlie d\T of weld and dyers' broom; moririy or 1 :3:2'l4'-(«£ra- hydroxy flavone, the dye of Moras tinctoria ; and other products.
m-H ifdroxt/benzolc acid iind p-hydroxijhejizolc acid yield no colora- tion with ferric chloride. Their basic barium salts are insoluble.
Dihydrozy-acids.
Among the dihydroxy-acids is protocatcchuic acid,
/COOU 1
^^^*<QO.CH :C.C,H»*
\
OH
§346] DIHYDROXY'ACIDS AND TRIHYDROXY-ACIDS. 473
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 anmioniacal 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.
346. The best-known trihydroxy-acid is gallic add,
/COOH 1 p „ /oh 3
\0H 5
It is a constituent of gall-nuts, tea, and "divi-divi," a material used in tanning. It is usually 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-t>lack 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 neutrahzed 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 the pen a dark-blue colour, which changes by the process described to a deep black.
474 ORGANIC CHEMISTRY, [§ 346
The tannins, or tannic acids, are very closely related to gal- lic acid, and are widely distributed in the vegetable kingdom. The tannins are compounds which are soluble in water, have a bitter, astringent taste, yield a dark-blue or green precipitate with ferric salts, convert substances containing gelatin — such as animal hides — into leather, and precipitate proteins from their solutions.
A distinction is drawn between the diflferent kinds of tanning- substances, which have properties analogous to those of tannin, but diflfer from it in composition. They are named after the plants in which they are found: kino-tannin ^ catechu-tannin, moringa- tannin, coffee-tannin, oak-tannin, quinine-tannin, and others are known.
The most typical tanning-material is tannin or tannic acid, con- tained in oak-bark. It is converted by hydrolysis with dilute sulphuric acid into gallic acid and dextrose. This decomposi- tion has induced Emil Fischer to regard tannin as probably having the constitution of a pentadigcdloylglucose,
C6H706[C6H2(OH)3-CO.O.CeH2(OH)2CO]5 or C76H52O46,
a view in good accordance with all previous observations of its optical activity, molecular weight, and slight acidity. Emil Fischer has succeeded in synthesizing from dextrose and gallic acid an artificial product, and although it is not identical with tannin, it resembles it closely in optical activity, the power of precipitating gelatin and alkaloids, the formation of a colora- tion with iron salts, slightly acidic character, solubilities, and taste.
The best source of tannin is furnished by gall-rfuts — path- ological excrescences on the leaves and branches of the oak, caused by an insect. Turkish gall-nuts are especially rich in tannin, yielding as much as 65 per cent.
Tannin imparts its characteristic bitter taste to many beverages — to tea which has been too long infused, for 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
5 346 AMINOBENZOiC ACIDS. 475
ether. It forms salts with two equivalents of the metals, and precipitates many alkaloids, such as strychnine and quinine, from their aqueous solutions (407).
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 dries to a hard, horn-like substance, or in the moist condition becomes rotten. When satu- rated with tannin it remains pHant, 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 internally, it shows that the conversion into leather is incomplete.
During the process of tanning, oxj'gen is taken up, indicating that the reaction involved is one of oxidation.
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 HooGEWERFF and VAN Dorp (259), by treating phthalimide with bromine and potassium hydroxide. The potassium salt of phthal- atninic acid is first formed, and then changes into anthranilic acid :
Phthalimido Potassium phthalaminate Anthranilic acid
476 ORGANIC CHEMISTRY, [§347
Anthranilic acid melts at 145°, 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.
Phthalic Acid.
347. Phthalic acid is the or^/io-dicarboxylic acid of benzene, and
POOH 1 . .
has the formula C6H4 <r«()r)H 9- It is obtained by the oxidation
of aromatic hydrocarbons with two side-chains in the ortho- 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 or^/io-derivatives completely into carbon dioxide and water. Phthalic acid is employed in tho preparation of artificial indigo (405), and is manufactured by oxi- dizing naphthalene (377), CioHg, by heating with very concen- trated sulphuric acid.
Phthalic acid is crystalline, and dissolves readily in hot water, alcohol, and other. It has no definite melting-point, since on heating it loses water, yielding phthalic anhydride, which sublimes in beautiful, long needles:
/NcoqiH _ „^ _ A^5
COIOH - H^O = I j >0-
Phthalic anhydride
If they followed the ordinary course of the reaction form- ing acid chlorides, phosphorus pentachloride and phthalic acid
would react to produce a chloride of the constitution C6H4<pj:vp|
That they do not and that phthalyl chloride has the structure
/CCl., C6H4C >0,
4\
CO
§ 348] PHTHALIC ACID. 477
can be proved in various ways. When aluminium chloride reacts with phthalyl chloride in presence of benzene, there results a com- pound with the formula
yC C6H5
CbHZ >0 .
called phthdhpherume, the constitution of which follows from its formation by the elimination of water from triphenylcarbinolcar" boxylic add:
/ ^'^^-HjO-CbHZ >0 .
0
OH
Triphenylcarbinol- Phthalopbenone
carboxylic add
Another proof of the constitution indicated above for phthalyl chloride is the fact that reducing agents, such as sodium-amalgam and water, or zinc and hydrochloric acid, cause the replacement of its halogen atoms by hydrogen, with formation of phthalide. This substance has no aldehydic properties, but has the constitution .CHo
acids it yields o-hydroxymethyWeazoic acid:
C6H4^ > (), since on treatment with sodium hydroxide or dilute
^CH^ yCH20H
C6H4< >0-fH =C6H4<
;0 OH X300H
By elimination of water, this acid is reconverted into phthalide. These transformations prove phthalide to be a lactone, and not a
PHO dialclehyde, C0H4 <puQ; as it should be if the formula of phthalyl
( lilorido were C6H4 <riQr'i-
348. The oxygen of the carbonyl-group in phthalic anhydride can also participate in other reactions. Thus, when this sub- stance is heated with phenols and sulphuric acid, phthaleins are formed :
478 OBGAXIC CHEMISTRY. (f 34g
yCBH«OH
C,H4< 1 ' 2.^«»jOH _ HjO+CHZ >0
Cd<^
*\:o
FbthaJie aobydrvie Pheoolphthalein
FhenolphthaUin, the simplest member of the phtbalein series, is a yellow powder. On account of its phenolic character it dis- solves in alkaline solutioas, with formation of a fine red colour, and is a sensitive indicator for alkalimetry.
Resarcinolphthalein or fluorescein is characterized by the display
of an intease yellowLsh-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 21(y, in presence of
zinc chloride as a dehydrating agent. On treatment with bromine,
fluorescein yields tetrabrofnojluorescein:
AHBraCOH)
>0. C6H4<^^| X'eHBraCOH)
r CO^
Its potassium derivative, C2oH605Br4K2, is the beautiful dye eosin. The constitution of the phthaleins is inferred from their being convertible into (lorivatives of triphenylmethane (373).
In the pn»paration of phenolphthalein a by-product, fluoron, insoluble in alkalis is formed. According to the researches of R. Meyer, this substance has the formula
.COv
or
I.
in which the two phenol-residues are united at the orMo-positions to the phthalic-anhydrido-rosiduo, and not at the /xira-positions, as in phenol phtlialein. Huoran contains the pyrone-nucleus,
/\
C C
\o/
c
§ 349] PHTHALIMIDE. 479
R. Meter has pointed out that many derivatives containing thie nucleus fluoresce. He proved that fluorescein is dihydroxyfluoran.
with the formula
/COv
HOk J\^Jv JoH O
.CO
349. Phihalimide, C^Yi^^^ > NH, is of importance on account
x:!0
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 phthcdimide 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 :
.CO /CO
C6H4C >N|K+Br.[CnH2n+i -^CgHK >N-CoH2n+l
\co Ni^o
Potaanum phthalimide
— *C6H4<QQQjj^4-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 cthylenebromohydrin, CH2Br.CH20H, hydroxyethylamine, NH2-CH2-CH20H; etc.
Another example is Emil Fischer's synthesis of ornithine (243). Potassium phthalimide is brought into contact with trimethylene bromide:
CO
C6H4<co>N|K-}-Br].CH2-CH2-CH2Br
QjH4<^>N CH2-CH2-CH2Br.
480 ORGANIC CHEMISTRY. [§ 350
The compound obtained is treated with diethyl monosodiomalonate, and yields C6H4<^q>N.CH2-CH2-CH2-CH(COOC2H6)o, the ter- tiary hydrogen atom of which can be substituted by bromine. Saponihcation and elimination of CO2 give
C6H4<^o>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<QQ>N.CH2.CH2-CH2-CH(NH2)-COOH = +20HH
= C6H4<pnnS+H2N-CH2-CH2-CH2-CH(NH2)-(X)OH.
^^'-'^ Ornithine
These examples make it evident that this method can be ap- plied to the preparation of the most variously substituted primary amines.
HooGEWERFF and VAN Dorp found that ammonia reacts with
ON
phthalyl chloride, yielding o-cyanobenz&ic add, ^^^<cc^l\'
It must be assumed that an isoimufe of phthalic acid is formed as an intermediate product:
/CCI2 /C=NH /CN
C6H4<; > O -♦ C.H4< > O - CeH^C
N::o ^co x:ooh.
Phthalyl t<oImide o-CyanobensoIc
chloride acid
Although they have not been able to isolate the tso-imide itself, they have prepared a number of derivatives in which the imino-hydrogen is replaced by hydrocarbon-residues.
2soPhthalic and Terephthalic Acids, C«H4(C00H), (1 :3) and (i:4).
350. isoFhthalic acid can be obtained by the oxidation of com- pounds with two sido-chains in the yneta-posiiion, and also by the oxidation of resin (colophonium) with nitric acid. It dissolves with difficulty in water, and does not yield an anhydride. Symmetrical jncthylisophthalic acid is mentioned in 231.
5 3511 SUBSTITUTED ALDEHYDES. 481
Terephthcdic acid can be prepared by several methods; for example, by the oxidation of turpentine. It is almost insoluble in water, alcohol, and ether. It docs not melt at the ordinary preasure, but at high temperatures sublimes without decomposition. Like rso- phthalic acid, it does not form an anhydride.
Higher Polybasic Acids.
Tricarboxylic, tetracarboxylic, pentacarboxylic, and hexacar- boxylic acids are known. The most remarkable is the hexacar- boxylic mellitic acid, a constituent of the mineral lioney-stone, found in brown-coal seams. Honey-stone is the aluminium salt of mellitic acid, and has the formula Ci20i2Al3-hl8H30: it forms yellow quad- ratic octahedra. Mellitic acid is produced by the oxidation of wood- charcoal with an alkaline solution of potassium j^errfianganate. 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,
P„^C0>^2 C0^^5 which takes up water, and yields pyromellitic acid, C6H2(CX)OH)4.
Vra. SUBSTITUTED ALDEHYDES.
351. m-Nitrobenzaldehyde is the main product formed in the nitration of bcnzaldehyde, o-nitrohenziddehyde being a by-product in the reaction. The best mode of preparing the or^/io-compound is to oxidize o-nitrotoluene with manganese dioxide and sulphuric acid. In sunlight it is rapidly transformed into o-niirosobenzoic acid:
.NO2 .NO
C6H4^ — > C6H4^
XJHO XIOOH
Hydroxyaldehydes.
Hydroxyaldehydes can be obtained artificially by a synthetical method generally applicable to the preparation of aromatic hydroxyaldehydes. It consists in treating the phenols in ethereal
482 ORGANIC CHEMISTRY. [§ 361
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 -f HCl = C6H4 < q jj . ^^ ^C\*
On treatment with warm water, the imide-salt is converted into the hydroxyaldehyde and ammonium chloride:
C6H4<cH:NH.HCl'^^20 - C6H4<(.jjq+NH4C1.
P'HT/droxybenzaldehyde is here obtained from phenol.
/OH 1 Salicylaldehyde, CgHj^ y-H , occurs in volatile oil of spirwa.
It can be prepared artificially by Reimer's synthesis, another reaction generally applicable to the production of aromatic hydroxyaldehydcs, and depending on the action of chloroform and potassium hydroxide on phenols:
.OH .OH 1
C6H4<^ — > C6H4^ pH rt
^[H + Cl|CHCl2 ^ O ^'
Salicylaldehyde
The 0-hydroxy aldehydes colour the skin deep yellow. To this class of substances belongs vanillin.
/ ^O CeHair-OCHa 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 \aoeugenolj
/OH C6H3— OCH3
\CH:CH.CH3
S 362] HYDROXY ALDEHYDES. 483
This substance is obtained by boiling eugenxlf
/OH CeH3^-OCH3 ,
X!Hj^.CH:CH2
with alcoholic potash, which alters the position of the double link- ing in the side-chain. Eugenol is the chief constituent of oil of cloves.
Vanillin has been synthesized by Reimer's method, the action of chloroform and sodium hydroxide on guaiacol (336) :
CHCI2
Zi
Intermediate products - Vanillin
Piperonal is mentioned in 353.
IX. POLYSUBSTITUTED BENZENE DERIVATIVES WITH SUBSTIT-
UENTS IN THE SIDE-CHAIN.
OH 352. P'Hydroxyphenylpropionic acid, CqU^Kqj^ q^ .COOH
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
CoHuOaN, and its structure HO.C6H4-CH2-C^OOH; it isthe
NNH2
a-amino-acid of j>-hydroxyphenylpropionic acid. Being an amino-
acid, it yields salts with acids as well as with bases.
OH o-Hydroxycinnamic acidy C6H4<pTT.pTT^PQQTj, exists in two
forms, coumaric acid and coumarinic acidy which are easily converted 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
4cS4 ORGANIC CHEMISTRY. (§ 353
molecule of water, yielding coumaririj the aromatic principle of woodruff {Asperula odorata). Coumaric acid, on the other hand, does not yield a corresponding anhydride: removal of water pro- duces coumarin, which is converted into salts of coumarinic acid by treatment with alkalis. This behaviour recalls that of fumaric acid and maleic acid (169) , and it may be assumed that the stereoisomer- ism of these acids is similar. Both can then be represented as follows:
H.C.C6H4-OH H.C.C6H4-OH H-C-CeH*
II II -H2O = II >0.
HOOC-C.H H-CCOOH H-C-OO
Coumaric acid; Coumarinic acid ; Coumarin
gives no correBpondixig only known in the form
anhydride of salts
Coumarin can be obtained from saUcylaldehyde by Sib Wiluam Pebkin's synthesis*(328) : acetyl coumaric acid,
PH ^01C2H30
^^* 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^methylenedihydroxy^ cinnamenylacrylic acid, C12H10O4, is a decomposition-product of piperinc (390). Oxidation converts piperic acid into piperotud or heliolropiriy
/0/NcH:CH.CH:CH.COOH
Piperic acid Piperonal
The constitution of this substance is established by two reactions. First, on heating with hydrochloric acid it is converted into proto* caiechualdehyde and carbon:
CHO.C6H3<Q>CH2 = CHO.C6H3<q5J+C-
§3531
PIPERONAL AND ADRENALINE,
485
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 reembles that of heliotropes. In presence of caustic soda, piperonal condenses with acetaldehyde to piper onylacr aldehyde:
CH2<q>C6H3«Cq -hCHs'CQ =
= CH2 < i-i > CfiHs • CH 2 CH • C^ H- H2O.
By Perkin's synthesis (328), piperonylacraldehyde is con- verted by the action of sodium acetate and acetic anhydride into piperic acid:
CH2<Q>C6H3-CH:CH-CQ-fCH3.COOH = = CH2<o>C6H3.CH:CH.CH:CH.COOH-fH20.
Adrenaline or suprareninej C9H13ON, is prepared from the suprarenal capsules of the horse and other animals. It is char- acterized by its powerful haemostatic properties. On oxidation, it yields protocatechuic acid, and on distillation with sodium hydroxide, methylamine. With benzoyl chloride it forms a tri- benzovl derivative.
It is prepared by a synthetic method. Chloroacetyl chloride reacts with catechol (I.) to form chlaroaceiylcatechol (II.). On treatment with methylamine, this substance yields an amino- ketone (III.), reducible to adrenaline (IV.):
HO HO
I.
H0/\C0.CH,C1 H0/\
HO
II.
HO
III.
COtCHz.NH.GHs
HO/ ^CHOH.CHz'NH.CHs
IV.
Hoi;;
Adrenaline
486 ORGANIC CHEMISTRY. I§ 353
Many organic bases of phenolic character have valuable phar- macological properties. Other t>i)e8 of this class are hordenine,
4 1
HO • C«H4 • CHs • CHs • N (CH«)i, present in germinating barley ; and P'hydroxyphenykthylamine, HO • CiHi • NH • CtH», the active principle of ergot.
ORIENTATION OF AROMATIC COMPOUNDS.
354. OrientcUion 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 exammation, 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. Absolute determination 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 K6rner*s principle, by which it is possible to ascer- tain whether substances C6H4X2, containing two substituents, are
487
488 ORGANIC CHEMISTRY. [J 355
or^/io-compounds, 77i€to-compouncls, or para-compounds, effected by determining the number of trisubstitution-products correspond- ing with them.
When a third group, Y, is introduced into an or^/io-compound, C6H4X2, whether Y is the same as or different from X, only two isomerides can be formed,
X
/\^
and I I •
N Y
The introduction of a third group 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,
X
lY
t \
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 Kor.NEii's method.
I. Absolute Determination of Position for or^^-Compounds.
355. l'<Jr the or//io-s(Tios, thv slrurture of a dibromobcnzene melting at o-ii^ is determined by means of Korner's principle: this body yields two isomeric nitnxli^romobenzenes. The con- Ktitution of a xylene boiling at 142^ and melting at —28® has also been establisheJ by this method : it gives rise to two isomeric
§355]
ORIENTATION.
489
nitroxylenes when treated with nitric acid. This xylene is con- verted into phthalic acid by oxidation, proving that the latter is an ar//io-compound.
The oxidation of naphthalene (377). CioHg, to phthalic acid also proves that the carboxyl-groups of this acid are in the or^Ao-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 C4H4 has, therefore, been converted into two carboxyl-groups :
N02-C6H3<C4H4 ^ N02.C6H3<g2oH-
Nitronaphthalene Nitrophthalic acid
If, however, the nitro-group is reduced, and the aminonaphthalene thus obtained oxidized, phthahc 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
The oxidation of nitronaphthalene and aminonaphthalene H expressed by the scheme
AjA
NO.
and
^COOH
. JcOOH NO5,
HOOC-^
HOOC^y
490 ORGANIC CHEMISTRY. I j 356
Phthalic acid must, therefore, be an or^Ao-compound, because if it be assumed to have the m^to-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 both nitronaphthalene and aminonaphthalene.
2. Absolute Detennination of Position for meto-Compounds.
356. The proof that mesitylene is symmetrical trimethylbenzene (1:3:5) is stated thus by Ladenburg. If this compound has the constitution
H CHa/XCH,
CH3
the three hydrogen atoms directly linked to the benzene-ring must be of equal value. U 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)3HHH, the dinitro-oompound may be arbitrarily assumed to be
. XL C«(CH3)3N02N02H.
One of the nitro-groups of the dinitro-compound is reduced, and the resulting ainiiio-coinpound is converted into an acetyi-derivativet suppose that this acetyl-derivativc is
III. 00(0113)3X02X11 (CoHaO)^. This substance can be again nitrated, when there must result
i 3561 ORIENTATION. 491
C,(CH,),NO,NH(c5h30)NO,,
It is possible to eliminate the acetylamino-group, NHCC^H^), from this compound by saponification, subsequent diasotizalion, etc. A dinitromesitylene with the formula
Cc(CHa)8N02HNOa
is obtained, identical with the former dinitro-product, the nitro- groups of which are at a and 6. It follows that
Nitromesidine, aih, 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 diazo-reaction, there is formed
IV. Cc(CHa)aN02HH.
This substance is reduced, and converted into an acetyl-compound, aoetylmesidine,
Ce(CHs)8NH(C^H80)HH,
which can be again nitrated, yielding
Ce(CH3)8NH((^H30)N02H.
It is immaterial whether the nitro-group of this compound is at h or c, since the equality of these positions relative to a has been already proved.
On eliminating the acetylami no-group from the last substance, a mononitromesitylene is produced, identical with the compound IV. Hence, a'=h'='C, which completes the proof of the equality of the three hydrogen atoms.
From the known constitution of mesitylene it is possible to deduce the structure of many other compounds. For example, partial oxidation converts it into mesitylenic acid;
^COOH
C6H3;--CH3 , \CH3
which is in turn converted into xylene by distillation with lime: this
492 ORGANIC CHEMISTRY. [§ 357
xylene must be the meto-compound. Oxidation converts m-xylene into isophthalic acid, indicating that the carboxyJ-groups in the latter occupy the me'to-position. These determinations of position have been fully substantiated by the application of Kornek's principle. Thus, Noltixg has prepared three isomeric nitroxyl- enes, in which the relative positions of the methyl-groups are the same as in the xylene obtained from mesitylenic acid.
Among other 7W€to-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 dirminobenzoic acids by elimina- tion of CO2, so that it also must be a weto-compound.
3. Absolute Determination of Position for para-Compounds.
357. Kohneh's principle has been of gniut service in determin- ing the constitution of some members of the para-series. 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 of a hydroxy- benzoic acid melting at 210° as a para-compound. The starting- 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 salicylic 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-com- pouncls which would yield the same aminobenzoic acid on reduction could not be obtained from
S 3581 ORIENTATION. 493
Br/|^
The bromine atom must, therefore, occupy the mcta-position or or^o-position to the carboxyl-group. A hydroxybenzoic acid melt- ing at 200°, corresponding with this acid must be, therefore, meta or ortho. Since the isomeric salicylic acid can also be only a meia' compound or an or<fco-compound, there remains no possibility, except the paro-structure, for the third hydroxybenzoic acid melt- ing at 210°.
Determination of Position for the Trisubstituted and Higher- substituted Derivatives.
358. This orientation can usually be effected by ascertaining the relation in which they stand to the di-derivatives of known constitution. For example, since a certain chloronitroaniline,. C6H3C1(N02)(NH2), is obtained by nitrating mK^hloroaniline,
NH2
and yields p-chloronitrobenzene,
NO2
CI
by exchange of the amino-group for hydrogen, it must have the constitutional formula
NH2
N02/\
KJcv
A more complicated example of orientation is afforded by the determination of the positions of the groups in jticric acid. Careful nitration converts phenol into two mononitrophenols,
N..
494 ORGANIC CHEMISTRY. [S 35S
OH NO,
0
and
NOa
M.P. 45° M.P. 114°
One of these mononitrophenols must be the ort^o-compound and the other the para-compound, 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 m/*to-nitroaniline, and subsequent exchange of NHa for OH by diazotizing.
When further nitrated, both nitrophenols yield the same dinitro- phenol, which can therefore only have the formula
OH NO.
0
NO,
The mononitrophenol melting at 114° is converted by oxidation into lx?nzoquinone (338), and must, therefore, be the para-com- pound. For the Ixxiy melting at 45° there remains only the ortho- structure. On nitration this o-nitrophenol yields, in addition to the 1 :2:4-<linitrophenol (OH at 1), another di nitrophenol ¥dth its gr«>up6 at 1:2:6,
OH NO,/^|NO,;
u
for on conversion of this into its methyl ether, and heating the latter with aicohohc ammonia, the group OCH, is replaced by NH,; and this substance, which has the formula
NHj NO/'^NOj,
is onvortod by suh-^titution of hydrogen for the NHj-group into the or«.iii»ary ^Nf^Miinitrolviizono. Thus, we have two dinitn>- pheiiols of known stru tun'.
8359] EQUIVALENCE OF BENZENE HYDBOGEN ATOMS. 495
NO. and NO
Further nitration converts both into picric acid, which must, there- fore, have the constitution
OH NO,/^NO,
NO,
From the constitution of picric acid may be inferred the position 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 282 that benzene does not yield isomeric mono-substitution-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, 6, c, d, c, 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), is treated with methyl iodide, and sodium it yields toluene. On nitration, three isomeric nitrotoluenes are obtained — the proportion of the m^to-compoUnd being very small. In these compounds the CH, group is at a, so that the nitro-groups may be arbitrarily assumed to be at 6, c, and d respectively. On reduction, the three corre- 8pK)nding toluidines result:
CJI..CH,(rt) -CH,-C»H4-NO,(6:c:(f) -.COOH.CeH4-NH,(6:c:(f).
After protection of the amino-group in each of these compounds by iicetylation, the three aminobcnzoic acids are obtained by oxidation. These acids yield, by elimination of COj, the same aniline, identical with the original substance. It follows that
496 ORGANIC CHEMISTRY, [§ 360
^•"*^N0, b "*
COINH, -. CJI.Br -. Cai.-CH,^-^C.H4<^To* ^ -*
a a ' *
' \
r* Tj ^ COjH a
^ TT ^ CO2H a
The starting-point of the proof of the equivalence of e and / to a, 6, c, and c/ is o-toluidine, in which the CHj-group may be assumed to be at a, and the NHj-group at b. Nitration of its acetyl-deriva- tivc, followed by elimination of the acetyl-group, produces simul- taneously four nitro-o-toluidincs. Since a and b are occupied, the nitro-groups must be at c, </, e, and / respectively. Replacement of the amino-group by hydrogen yields four nitrotoluencs, aic, a : d a : e, and a :/. The first two arc m-nitrotoluene and p-nitro toluene; they are also obtained by direct nitration of toluene, as described in the previous paragraph. The nitrotoluene a : c is identical with a : c, and a : f with a : 6, which indicates the equivalence of c to e and of b to/, thus completing the proof:
/CH, a
CJI^^NH, b
^NO, c
CH b / /CHj a >^ QTj
/CH, a CiH^NHi b
yCHj a Qjj ^
CeHs^XHj b >CeH4<xrrfc* t %.
\\0,/ ^02f-6
Inffuence of the Substituents on Each Other.
360. On introduction of a second substituont into a monosub- stitutc'd i)onzenc derivative, C0H5X, tlio tliroo tlieorotieally possible di-<lerivativc\s iin^ formed in very uncMjual proportion. There
S3601 INFLUENCE OP SUBSTITUENTS ON EACH OTHER. 497
are two main types of substitution: either the pora-derivative and the or(/w>-derivative predominate; or the meia-derivative constitutes the chief product. The table summarizes the moat Important types of substitution, the numbers In bracltets indicat- ing the by-products, and being arranged in order of diminishing proportion.
|
Element or Gcoup'iilreBdy ptBMOt (in Powlion 1). |
Po.it>«D <-' |
Ured by B |
|||
|
Cl |
Br |
' |
SCU |
xo. |
|
|
4{2)(3) 4(2)0) 4 4(2) 3 4(2) 4(2) 3 |
4(2) (3) 4(2) (3) 4(2) 3 3 |
4 4 4(2) 4 4(2) 3 |
4 4 4 4(2) 3(2)(4) 4(2) |
4(2) |
|
|
NOT "'.::. '.::'.'.'.'.'.'.'.'.':'- |
|||||
|
NH. |
|||||
|
cS::::::::::::::::::::: |
|||||
|
3(2)(4) |
|||||
|
CN |
|||||
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 application, and in known as the rule of the constancy of substUu- 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 0° of fluorobenzene yields 12*4 per cent, of the ortAo-nitro- product, and 87*6 per cent, of the paro-nitro-
498 ORGANIC CHEMISTRY.^ [§ 361
product. Nitration at the same temperature of chlorobcnzene proc^uces 30-1 per cent, of o-chloronitrobcnzene, 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-nitrobenzolc acid, 85-0 per cent, of 77i-nitrobenzoic 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° with excess of sulphuric acid gives 53-5 per cent, of p-tolucnesul phonic acid, 3-8 per cent, of m-toluenesulphouic 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 halogcnation-processes the nature of the catalyst influences the proportion of the isomerides formed. The chlorination of chlorolxmzcnc with 0-5 per cent, of aluminium chloride as catalyst yields 60-7 per cent, of p-dichlorobenzene, 29-6 per cent, of o-dichlorobenzenc, 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 fonned by the introduction of C into CeHA and C«H«B respectively, and the proportion of each, is it possible to predict the isomerides CellsABC formed by the introduction of Cinto C6II4AB, and the proportion of each?
In a qualitative sense prediction is possible, but the problem is much more complex than a suporficial consideration indicates. For a benzene derivative C'gH4AB with formula I.,
{ 36H INFLUENCE OF SUBSTITUENTS ON EACH OTHER. 499
Apo
6 2
I.
Apo
6 3 II.
Bm
in which both A and B direct substitution to the oriAo-position and paro-position, 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 under 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 weto-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-cresol,
OH [^CH,,
6 3
V
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 thjD 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 orth(H position than at the meto-position.
A study of the different examples of substitution in compounds CJI4AB, 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
500 ORGANIC CHEMISTRY. [§ 362
groups causing substitution at the para-position and the artho- 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
C00H>S03H>N0,.
Inversely, knowing these orders of velocity, it is possible to predict the isomerides obtainable in a given reaction; thus, in chloro- phenol the substituent would be introduced mainly at the ortho- position and the para-position to hydroxyl; but in chlorobenzoic acid chiefly in the ori/to-position and para-position to chlorine.
362. This opposition between or^/io-derivatives and para- derivatives on the one hand, and msto-dcrivatives on the other, is not only observed in their preparation, but also in many of their properties. -\s a class, the wieto-compounds are more stable towards reagents than the ori/io-derivatives and para-derivatives. An example is given in 331.
Orf/w-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 A(eyeu and his students found, however, that esterification of acids containing two groups in the oriAo-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 alky! halide) the ester so formed can only be saponified with difficulty. When the two substituents occupy any of the other positions, these peculiarities do not manifest themselves, or at least
§ 362] INFLUENCE OF SUBSTITUENTS ON EACH OTHER. 501
not to the same extent. Ketones substituted in the two artho^ positions,
CH3
;o.R,
CH3
where R is an alkyl-radical, cannot be converted into oximes, wherein they differ from all other ketones. 0-0-Dimethylaniline,
CH3
CH3
is not converted by treatment with an alkyl iodide into a quateiv nary salt. Pentamethylbenzonitrile, C6(CH3)6CN, cannot be hy- drolyzed to the corresponding acid. The methyl-hydrogen in o-O' dinitrotoluene,
/NO22
CoHar-CHa 1,
\NO26
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-nitro^licylonitrile,
OH /\CN
^'no,*
to the corresponding acid,
OH
OCOOH NO, '
has not been effected.
502 ' ORGANIC CHEMISTRY. U 362
Groups occupying positions further separated sometimes exert a similar effect. One of the N()2-groups of symmetrical trinitro- benzene is replaced by OCH3 through the action of sodium methoxide: for trinitrotoluene,
NO2
NO2
this substitution is not found possible, the methyl-group preventing exchange of the nitro-group even in the para-position.
In^ances are, however, known of or^Ao-substituents increas- ing the reactivity of a group situated between them.
HYDROCYCLIC OR HYDROAROMATIC 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 derivatives. These hydrocyclic or hydroaromaiic com- pounds are readily converted into aromatic bodies. Caucasian petroleum contains naphthenes, with the formula 0^2ix^ which have two hydrogen atoms less than the corresponding saturated hydrocarbons, CnH2n+2> but nevertheless display all the properties cliaracteristic of saturated compounds. The explanation is that they lack multiple bonds, but have a closed carbon chain; thus,
eye jo Hezane
The terpeneSj C10H16, are v^etable-products, and are the prin- cipal consiituents of the "essential oils." These oils also contain compounds of the formulae CioHieO, CioHigO, and C10H20O, among them the camphors. Like the naphthenes, the terpenes and cam- phors are readily converted into aromatic compounds, and therefore belong to the hydrocyclic series. The progress recently made in this division of organic chemistry has rendered a systematic classi- fication of these compounds possible.
Two principal methods arc 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 ryiopentanone (277). By the same treatment calcium pimelate is converted into (^yoXohexanone:
^"2<cHr-CH2*COO^^* ^ CH2<cH22 cH2'>C0 + CaC03.
Calcium pimelate cycloHexanone
503
I
504 ORGANIC CHEMISTRY. [§ 363
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 :
CH2-CHo.C0 CH2-CH2-COOH
I I - I
CH2-CH2-CH2 CH2-CH2-COOH
cyc/oHexanoDo Adipic acid
Diethyl succinate constitutes an important basis for the sjm- thesis of other c</c/ohexane derivatives. In presence of sodium, two molecules of it condense to diethyl succinylsuccinate, which melts at 127° :
/C00C2H5 /C00C2H6
CH2/ CH2/
+
CH2 ^CHz
^n^yjyjyj- C2H5(
C2HsOOC/ CzHsOOc/
Diethyl succinate
H2C CH. 00002115
I +2O2H6OH.
OH-
OaHsOOO-HO OH2
Diethyl succinybuccinate
The free acid, obtained by saponification, is decomposed at 200°, with elimination of two molecules of carbon dioxide, jnelding
<CH«> CHov >co. CH2 CHa-^
The structural formula of this substance is indicated by this 8>ti- thesis, and also by Its reduction to rz/rZohexanone.
The second method of obtaining hydrocyclic compounds has been much simplified by the researches of Sabatier and Sex- DERKXs. Thev found that manv aromatic hydrocarbons, such as benzene and its hoinologu(\s, are readily hydrogenated to hexa- methylene^ and its (lerivativ(\s by passing their vapours mixed with
§ 364) HYDROCYCLIC COMPOUNDS, 505
hydrogen over heated, finely-divided nickel, which is obtained by reduction of the oxide, and exerts a catalytic influence :
CeHe-f 3H2=CoHi2.
Bensene cyc/o Hexane
, Benzoic acid can be hydrogenated to hexahydrobenzoic acid by the action of sodium on its solution in amyl alcohol at the boiling- point. The phthaUc acids and polybasic aromatic acids are hydro- genated by treating them in aqueous solution with sodium- amalgam.
In describing the hydrocyclic compounds, it is convenient to treat the cymene derivatives, or terpenes, separately, for they exhibit many characteristic properties. The other hydrocycUe compounds will first be briefly reviewed.
364. eycloHexane is the simplest member of this group. It is best obtained by the method of Sabatier and Senderexs (363). Like its homologues, it is a colouriess 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 c?/cZohexane 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 cyclohexsme insoluble, the sep- aration of the latter can be readily eff'ected. The melting-point (82) affords the best criterion of the purity of c//cZohexane. 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 ct/c/ohexane, with formation of benzene; while at 100°-110° this catalyst transforms a mixture of benzene and hydrogen into q/cZohexane. He has also observed the remark- able fact that at 300° palladium-black is incapable of abstracting hydrogen from cither q/cfcpentane or ct/c Johcptane. This phenomenon affords a very valuable method of ascertaining whether a cyclic hydrocarbon is a derivative of ct/cZohcxane or not, previously a very difficult matter. The application of this reaction is exemplified by a hydrocarbon of the formula Cellii, which might be either cycfohexane, (CH2)«, or meihy\cydlopeni&ne, (CH2)4>CH-CH,.
S06 ORGANIC CHEMISTRY. [§ ^64
Chlorine reacts very energetically with ci/dohexane 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 compound by hydroxy! is not readily effected : treatment with alcoholic potash converts it into tetrahydrobenzene, 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, cyclohexanol is formed. It is a colourless somewhat thick liquid : it boils at 160-5°, and at a low temperature solidifies to a camphor-like mass, which melts at 20°.
P'Diketocyclohexatie (363) melts at 78°. Careful reduction with sodium-amalgam in an atmosphere of carbon dioxide converts it into the dihydric alcohol quinitol:
<CH2»CH2v yCH2*CH2N.
>C0+4H = H0.CH< >CH.OH.
CHa-CHz^ X;H2-CH2/
p-Diketocvctohoxane Quinitol
Two modifications of quinitol arc known, distinguished by the prefixes m* and trans. They are best prepared from quinol by the reduction-method of Sabatier and Sexdbrens (363). They can be separated by means of their acetyl-derivatives. The stereochemical character of their isomerism is indicated by a consideration of Fig. 33 (168), in which a c?/cZopentyl-ring is repre- sented. If the pentagon is supposed to lie in the plane of the paper, one of the ireo linkings of each carbon atom will lie above, and the other l)elow, this plane. If a c?/cZohexyl-ring is simi- larly constructed, there is obtained the perspective figure
u
in which the affinities 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 c/s-modification
i 3641 HYDROCYCLIC COMPOUNDS. 507
are situated on the same, and of the trans-modification on the opposite, side of the hexagon:
|
H |
|
|
H H |
H H |
|
• |
H |
H |
|||
|
OH H |
\ |
F H |
H H |
\ |
H 0] |
|
Ir h (niM^uinitoKM P. 130°) |
H H
ei»-Quinitol (MP. 101«)
Inositol, C6H12O6, is a hexahydric alcohol derived from cyclo- hexane. Its molecular formula is the same as that of the hexoses: on account of its sweet taste and its occurrence in many leguminous plant?, it was formerly classed with the sugars. Its relation to cyclohexsLne 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.
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 benzaldchyde to form a well-crystallized condensation-product:
<CH2«CH5K -f-OCH'CeHs CHa-CIIz/ +OCH.C6H5
CH2< ^CO
\UH2»CIl2 cyc/oHexanone
y^CH2 • C^^=CH • CeHs =2H20+CH2<. >C0 .,j
X;H2 • C=CH • CeHs
DibensalcycIohezaDone
This reaction furnishes a good test for cydohexanone.
The properties of the hydrocyclic acids are analogous to those of the aliphatic acids. Thus, hexahydrohenz&ic acid has a rancid odour, like that of capric acid. It melts at 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.
508 ORGANIC CHEMISTRY. [§365
365. The terpenea are hydrogenated derivatives of eymene and its substitution-products. Many of them are 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 vaciLO 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 Raeyer has^ devised a rational nomenclature for the numerous derivatives of hydrogenated eymene. He numbers the carbon atoms of this hydrocarbon as in the scheme
I
c
C/KG
C\*/C 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 mcnihane. It is not a natural product, but can be obtained by the interaction of eymene and hydrogen with nickel as a cata- lyst. It boils at 1GS°.
The saturated alcohols and ketones derivable from menthane are very important. Among them is menthol or S-menthanol, C10H20O, the principal constituent of oil of peppermint, from which it crystallizes on cooling. It forms colourless prisms of character- istic peppermint-like odour. It melts at 43°.
Menthol has the constitution
§ 3661 TERPENES, 509
ca
^4
CH
/\ 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 menthone, a constituent of oil of peppermint. Since there are ?everal 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 dibromomenihone, from which quinoline eliminates 2HBr, forming thymol (294),
CH:.
V JOH- 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 hydroxyl- group must be in the meto-position.
366. T'er/nn,CioHi8(OH)2, a dihydric alcohol, is also a derivative of menthane. Its hydrate ^ C10H20O2 -HH2O, is obtained by keeping oil of turpentine in contact with dilute nitric acid and a small pro- 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 distil- ling at 258^.
Terpin can be synthesized from geraniol,
2
510 ORGANIC CHEMISTRY. [{ 366
'\c=CH .CHj .CHa .C=CH .CHjOH. ^^3 CHs
Gerauiol
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
H2C CH2OH + 2H2O - HaC CH2OH - HjO-*
CH CH
II I
C C-OH
/\ /\
CH3 CH3 CH3 CH3
Geraniol Terpin hydrate
CHs
C-OH / \ „
H2C CH2
-^ T I .
H2C CH2
\ /
CH C-OH
CH3 CH3
Terpin
This mode of 3301 thesis indicates that terpin is l:8-dihydroxy- menthane, and there is other evidence in favour of this view. Hydriodic acid reduces it to menthane, proving the presence of a
cyment'-nudcus.
Tlu.' ct>ihstitutioncil formula indiciited for terpin is confirmed by the synthesis of this eoinpound effe'.'ted by W. H. PerkIiV Jun. Ethyl sodiocyanoacetate and ethyl -^-iodopropionatc react thus:
$366] TERPENES. 511
2CN • CHNa • COOCzHe + 21 • CH2 • CH2 • COOC2H5 = 2NaI +
CN. yCHa-CHa-COOCzHs + >C< +CN-CH2.COOC2Hfi.
C2H60(XX X;H2.CH2-C00C2H5
I.
Hydrolysis of compound I. simultaneously eliminates carbon dioxide with formation of the acid
XH2.CH2.COOH HOOC.CH<
X;H2.CH2-C00H
from which water and carbon dioxide are eliminated by heating with acetic anhydride, with formation of the ketonic acid
<CH2 • CH2V >C0. CH2'CH2/
The carbethoxyl-group and the carbonyl-group of the ester of this acid react readily with methyl magnesium iodide (91 and 102), forming a compound of the formula
CHsv XHz-CHz. /OM
CH3AC.CH< >C<
I.MgCX XIHa-CHo^ XJIL
converted by dilute mineral acids into the product
CHgv^ /CH9"CH2v yOH
>C.CH<( ' >C< ,
identical with terpin.
Elimination of water from terpin yields, among other products (367), a substance of the formula CioHigO, which is neither an alco- hol nor a ketone, and is identical with cineol, a constituent of many essential oils. Oil of eucalyptus and oil of wormseed (Oleum cince) contain a large proportion of this compound. Its mode of formation and properties indicate that cineol has the const!* tutional formula
512
ORGANIC CHEMISTRY.
[§367
CH
3
H2C CH2
HoC
CH,
CH
Or
o
/ \
CH3 CH3
Cineol
367. Some of the unsaturated derivatives of menthane are also very important. The mentheneSy CioHig, hydrocarbons with one double Unking in their molecule, need not be considered, but the alcohol terpineol and the ketone yulegone, derived from them, merit description.
Terpineol, 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 has been eliminated from 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
CH3 CH3
C
/\ H2C CH
C.OH H2C CH2
H2C CH2
\/
CH
H9C CH'
CH
C-OH C-OH
/\ /\
CH3 CH3 CH:, CHs
Terpineol Terpin
Carbon atom 4 in the formula given is asymmetric, whereas removal
§ 367] TERPEN ES. 513
of water from C-atoms 4:8, 8:9 (=8:10), or 1:7 could not produce
an asymmetric carbon atom.
Pxdegone, CioHjeO, 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:
CH3 CH3
CH CH
^ /\ /\
H2C CH2 H2C CH2 \ /
H2C CO H2C CHOH A
C GH. '
II i
C CH
/\ /\
CH3 CH3 CH3 CHi
Pulegone 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 linkings are the hydrocarbons terpinolene j(\4imonen€ , and l-linwnene, and their racemic form, dipentene. Each has the formula CiqHio.
Terpinolene boils at 185®. It is formed when terpineol is boiled with oxalic-acid solution, one molecule of water being eliminated. Theoretically, two reactions are possible:
|
CH3 |
CH3 |
CH3 |
|
|
• c |
• c |
• c |
|
|
H2C CH H2C CH2 Yh |
-HgO- |
HjC CU > 1 or H]G CHa \/ C |
H2C CH 1 1 . H2C CH2 Yh |
|
COH |
8 |
• C |
|
|
CH3 CHs Terpineol I. |
* |
CU3 Oris TsipinoleDa 11. |
CH2 CH3 d- and /- Limooen* 111. |
514 ORGANIC CHEMISTRY. I§368
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 as3rni- metric, as in terpineol itself, formula 1.
Formula III. is that of the optically active limonene, which occurs in many essential 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 |
CH3 |
CHs |
|
C-OH |
C.Br |
^ 4 |
|
„ /\ |
/\ |
/\ H |
|
U2C CH.2 |
H2C CH2 |
HjsC CH |
|
m H2C CI12 |
H2C CH2 |
1 1 H2C CH2 |
|
^ |
^ |
^ |
|
C.OH |
C-Br |
ft-<^ |
|
CH3 CH3 Terpin |
CH3 CH3 Dibromomenthane |
H /\ CH2 CHg limonene |
Dipcntene, a constituent of oil of turpentine, is also obtained by mixing (i-limonene and Z-limonene in equal proportions by weight. Like the limoncncs, it yields a well-crystallized tetrabro- mide, indicating the presence of two double Unkings in its molecule. The preparation of isoprene from limonene is men- tioned in 127.
368. Carvone, C10H14O, is an important ketone belonging to this group. It is the principal constituent of oil of carraway, and has its chanicteristic odour. It boils at 228°. Related to carvone is carvncrol, which is obtained from it by heating with potassium- hydroxide sohition:
3681 TERPENES. 515
CH2 CHg
Otrvooe
The hydroxyl-group in carvacrol is linked to C-atom 2, since, on heating with phosphoric oxide, propylene is evolved, and o-cresol (2^) formed. The carbonyl-group in carvonc 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 CH3
C C.Cl
H2C CH H2C C:NOH
T \ +NOCI- I I ; -HC1 =
|C CH2 H2C CH2
JH CH
• •
c c
CH2 CHg CH2 GHg
limooen* Lim-)n*>na nltroao-
chlort'de
CHa C
^
HC C:NOH
H2C CH2
c
/\
CH2 CH3
Carvoxime
516
ORGANIC CHEMISTRY.
[§369
This reaction proves that carvone contains one double linking J^*®. but leaves it doubtful whether the other double linking is JO Qp ji : 7 In ^jjg 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.
Polycyclic Terpene Derivatives.
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 four hydrogen atoms less than the saturated cyclic menthane, C10H20, 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 di£Ferent ways, as the formulae indicate:
CH3 CH3
CH
/\
CH
H2C
CHjCCHa Canuie
HaC/^ p>CH
CH
H.,C
CH, \
ca
CH
Pinane
cn3«c«CH3
§3691
TERPENES.
517
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 pentamethy lette- ring. Several members of these three groups will be considered.
Carane itself is unknown, but there is a synthetic derivative, carone, which is not a natural product. It has the structural formula
CH3
CH
H2C CO
H2C CH
\/ \ OH CH_^C<^g3
Carone
for opening of the trimethylene-ring at 3:8 yields derivatives of p-cymene, and at 4:8 derivatives of m-cymene.
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 boils 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 c5mpound of the formula CioHi6-HCl, called "artificial camphor," which resembles camphor both in appearance and odour. Pinene also readily forms an addi- tion-product with nitrosyl chloride. Pinene has the formula
CH,
518 ORGANIC CHEMISTRY. [§ 370
The presence of a tetramethylene-ring is assumed in order to ex- plain the constitution of oxidation-products of pinene, such as pinonic add and pinic add, 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 209.1°.
The camphor-odour is characteristic of many compounds theo- retically derived by substitution of all the hydrogen atoms attached to a single carbon atom; that is, of tertiary compounds. Very few of the relations between odour and chemical constitution have been discovered, but many compounds containing a double bond are characterized by their pleasant aroma, while that of substances with a triple bond is frecjuently disagreeable.
Camphor is a saturated ketone — saturated because it does not yield addition-products, and a ketone l)ecause it forms an oxime. Reduction converts it into a second arj^ alcohol, borneol or " Borneo camphor ":
C9H,6.CO+2H = CyHio-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 — . An explained in 199, the hydrogen of such a inothyleno-<!jroup can lx» replaced by the oxime-group by the action of aniyl nitrite and hydrochloric acid. Camphor reacts similarly, th(\so n^agonts converting it into isonitrosocamphor, which molts at 153°:
S 3701 CAMPHORS. 519
/CH2 /C=NOH
CgHiZ 1 -»C8H,4< I
x;o Nx)
Oamphor ixoNitroeocamphor
Elimination of the oxime-group from isonitrosocamphor yields
camphar-quinone,
.CO
C8Hi4k I .
XJO
On treatment with hydrogen peroxide, this compound is oxidized, forming the anhydride of camphoric acid,
r% TT ^COOH
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 laevo- rotatory isocamphoric acid, with the same constitution as camphoric acid. These facts indicate that the molecule of camphoric acid must contain two dissimilar asymmetric C-atoms (i88).
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, isobutyric acid, carbon dioxide, and carbon:
(CH3)2C.COOH (CH3)2C.COOH
CHa-C-COOH = CH3-CH.C00H +
CH2-C00H +C-hH2-hC03
and
Ounphoronio acid
(CH3)2CH.COOH +
CH CH
+CO2.
+oSf)CH-COOH +
520
ORGANIC CHEMISTRY.
IS 370
From these facts it is possible to deduce a formula for camphoric acid, which also accounts for its other properties:
COOH COOH CH2 CH COOH
CH3 — C — CH3
CHi
CH3 — C — CHg
-COOH CH,
<X)OH
CH3
Gamphoronic acid
CH,
<7H-
CH
■— C— C
CH3
Camphorio
■CH2
H3
CH,
(^ampTlOT'
This structural formula for camphor was originally proposed by Bredt. His v\v\\ has lx?en confirnied by the synthesis of camphor, effected by W. H. Pekkin, jrx., and Thorpe, and by Komppa, but the details of the processes involved art* l^eyond the scope of this work. The formula of camphor contains tw^o dissimilar, asymmetric C-atoms, n'i)n»sented in italic.
The position of the carbonyl-group in camphor follows from its conversion int o cai*vacrol by the action of iodine : in this compound the hydroxvl-group is in the or(/io-position to the methyl-group (368).
Borneol contaias a CHOH-group instead of the COgroup 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.
CHa— C— CH;
I
I
C
CH,
CH3
Camphane
According to the formula, tlie conversion of CO into CH2 should destroy the asymmetry of both the asymmetric C-atoms of camphor, and camphane is, in fact, optically inactive.
§ 370] CAMPHORS. 521
The formula of canlphor contains an isopropyl-group and there- fore accounts for the conversion of camphor into cymene by heat- ing with phosphorus pentasulphide. The complete syntheses of camphoric acid previously mentioned have 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 confirming structural formulae based on purely chemical methods, and also in indicating the correct formulae in cases to which chemical processes are inapplicable. Among the principles underlying the refraction method, two have been very useful in these investigations: (a) a double carbon linking increases the riiolecular refraction; (6) the formation of a ring has no influence on the molecular refraction, except that the production of a trimethylene-ring causes an exaltation of the constant, although less than that due to a double bond.
Examples. — 1. The molecular refraction determined for camphor is identical with that calculated, proving the absence of double carbon bonds from the camphor molecule.
2. A camphor derivative, thujone or tanacetone^ CioHieO, has the molecular refraction fll/j =44-78; wliile that calculated for a saturated ketone CioHieO is 44* 11 ; and for a ketone CioHicO 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.
POLYTERPENES.
The pohjterpenes include a number of compounds of the for- mula (C5H8)n, ^ being greater than 2.
The most important member of the class is caoutchouc or india-rubber y the latex or coagulated milky juice of various tropical plants, chief among them Hevea brasiliensis. Caoutchouc is purified by dissolving it in chloroform or another solvent, and precipitating it with alcohol in a white, amorphous form. It is vulcanized by the action of sulphur or sulphur nionochloride, S-iClj, a process considerably augumenting its elasticity and durability. Un vulcanized caoutchouc l^ecomes sticky at 30®, and loses its elasticity at 0°. Over-vulcanization yields ebonite or vidcanile.
The constitution of caoutchouc has in great measure been elucidated by Harries. He passed ozone through its solution
522 ORGANIC CHEMISTRY, (§ 370
in chloroform, and obtained a vitreous mass of the formula CioHieOe, which proved to be a diozonide, thus demonstrating the presence of two double bonds in the molecule of caoutchouc. This diozonide is converted quantitatively by water into IcBVulal- dehyde and laevulaldehyde peroxide. On the basis of these facts, the structure of the hydrocarbon corresponding with this ozonide must be assumed to involve a ring of eight atoms with two double bonds :
CH3 CH3
C (V'C CH3 CHO
HC CH2 HC CH2 OC CHo
H2O H2C CH2 > H2C CH2 ""^ CH2 4" CH2
[2C CI II .11 f . .V,
H2C CH H2C CH CH2 C< I
\j' \/i I no
C C-O3 CHO CH3
CH3 CH3
1 t5-Dimethylri/cZo- Dioionide L»vu1aldehyde Peroxide
octadiene
Caoutchouc is a polymeride of li5-dimethylcyc\ooctadien€.
Tht great technical importance of this substance has led to many attempts to prepare it synthetically, finally effected by the polymerization of isoprene, C5H8 (127). No method for manufacturing this hydrocarbon on a commercial basis has hitherto been devised.
BENZENE-NUCLEI LINEXD TOGETHER DIRECTLY, 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 best prepared by heating iodobenzene with finely-divided copper at 220°. Another method for the preparation of the derivatives of diphenyl, the conversion of hydrazobenzeneinto 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 affords 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?
ft 1*
fvV^
^
^
Diphenyl
\
A monosubstitution-product can exist in three isomeric forms, the BUbstituent being in the or/Zio-position, TTi^/a-position, or para-posi- tion to the bond between the benzene-nuclei. In a disubstitution-
523
524 ORGANIC CHEMISTRY. §372]
product, both substituents may be linked to the same benzene- nucleus, or to different benzene-nuclei, and so on.
Benzidine is of technical importance, because many of the azo- dyes are derived from it.
Diphenylmethane, C6H5-CH2'C6H6.
372. Diphenylmethane can be obtained from benzyl chloride r C6H5'CH2C1, or from methylene chloride, CH2CI2, by means of benzene and aluminium chloride. Its homologues are obtained b^' the action of benzene and concentrated sulphuric acid upon alde- hydes. Thus, acetaldehyde yields unsymmetrical diphenylethane:
CH3.CH 0 + »i§gj = CH3.CH<g2j+H,0.
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 resembUng that of orange-peel. Oxidation with chromic acid converts into lx»nzophcnono (316).
A derivative of diphcnvlmcthane, in which the benzene-nuclei are direct Iv linked, is/worf/t^', | /(^H,. It is formed bv leadiiiic
c.h/
the vai>our of diphenylmethane through a red-hot tube. From alcohol it (Tystallizes in leaflets: the rrystals are fluorescent, a cir- cumstance which gave this compound its name. It melts at 113**, and boils at 295°. It yields red ne»edles with picric acid.
The constitution of fluorene is thus established. It is converted by the action of oxidiziiig agents into diphcnyleneketone, the formula
CflH4v of which, I ^CO, is established bv its formation when the cal-
CeH..CO|0
cium salt of (hphemc and, | I /^a, is distilled. Diphenic
C«H,.CO()^
acid, for its part, is obtained from 7??-hy(lrazol)enzoic acid by the
S 3731 FLUORENE AND TRIPHENYLMETHANE. 525
benzidine-transformation (301), and subsequent elimination of the amino-groups:
^O^NH— Nh/o^ -» HN
I I
COOH HOOC HOOC COOH
It follows that the earbonyl-group in diphenyleneketone is linked at the or^/to-position in both the benzene-nuclei : it has, therefore, the structure
^ \ \^^^» *°^ fluorene itself
y
CO CH,
This view receires confirmation from the fact that phthalic acid is the only product obtained by its oxidation.
The hydrogen of the CH^-group in fluorene can be replaced by potassium. Oxidation of fluorene with lead oxide at 310^-330® yields di-diphenylene'€thylen€f
CeH4v /CeHi
CeH/ \CeH4
which melts at 188°. It is characterized by its deep-red colour, most hydrocarbons being colourless, at least in thin layers (288).
Triphenylmethane and its Derivatives.
373. Triphenylmethane J CH(C6H5)3, is formed from benzal chlor- ide, C6H6-CHC12, 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 rosanilineSy is derived from this hydrocarbon. Triphenylmethane itself is not employed as a basis for theu: preparation, but simpler substances which are converted into its derivatives. The formation of the dye takes place in three stages: malachite-green furnishes an example.
526 ORGANIC CHEMISTRY, [§37:5
' When bcnzaldehyde and dimethylaniline are heated with zinc chloride, tetrameihyldiamiru^phenylmethane is formed:
H CeHs'C:
H
0 + H
H
\_/N(CH3)2 "t/C6H4N(CH3)2
y s^^ = H20+C6H6'C^
< >N(CH3)2 X:6H4N(CH3)2
The carbon atom of the aldehyde group, therefore, fumishies 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
,, ,. ,. , C5H5C[CeH4N(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 malachile-green. The elimination of water may be represented in several ways; it is usually supposed to take place thus:
.C6H4N(CH3)2-HC1 C6H6-C< •H2O-
I X)6H4>N(CH3)2-fH]Cl
iOH|
X6H4N(CH3)2-Ha
Cl
Quinonoid form
This "quinonoid reaction " is analogous to the formation of quinone from quinol, in which the colourless quinol is converted into the deep-yellow quim)ne.
The conversion into a quinonoid form also explains many other instances of the formation of coloured substances; for example, the
§3731 QUINONOID STRUCTURE. 527
conversion of the colourless phenolphthalein (348) into its red metal- lic derivative.
Bernthsen has proved that this indicator in the colourless
state is a lactone, '
C(C6H40H),
C.H4<^0 ;
CO
but that its red salts are derivatives of a carbozylic add oontaining a quinonoid-group,
^CeH4:0
>Me*
^»"4
COOl
When the phenolphthalein is regenerated from this salt by the action of an acid, it changes, like the pseudo-SLcids (322), into the colour- less lactone-form, the transformation in this case being instantaneous.
The distinguishing characteristic of the group >C«H4< 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
/NOa normal structure CftH4\ , and for the coloured products of the
OR
NO -OR quinonoid structure C«H4X^ , the nitrophenols being regarded
^O
as pseudo-Sicids with a quinonoid oci-form.
Von Baeyer has pointed out that the development of colour is not always due to transformation into a quinonoid form. The intensely coloured acid salts of trianisylcarhinoly (CH80*CeH4)3C*OH, and of similar compounds undoubtedly are not quinonoids. Their colour is probably caused by intramolecular rearrangement of an ob- scure type. Von Baeyer has named this phenomenon halochramy.
* Me rppresents one equivalent of a metal.
528 ORGANIC CHEMISTRY, [% 374
374. The three stages necessary to the formation of the dye, may, therefore, be defined as follows.
1. Formation of a leuco-base (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, HC1)2 ^C6H4NH2-C1
Reduction reconverts the dyes into their leuco-bases, two hydrogen atoms being taken up during the reaction.
CryHud'Violct (hexamethyltriaminotriphenylmethane) 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 ps<?Mdo-acids (322). For this reason the colour-base may be looked upon as a pseudo-6a^c. Thus, on addition of the equiva* lent quantity of NaOH to crystal-violet, the true base,
(CH3),N.CoH, p_^=\_ (CH3),
is at first present in the solution : after standing for several hours at
25°, however, this true base changes into the colour-base {ps€udi>-
base),
(CH3)2X'CfiH4 p ChH^'N (0113)2. (CH3)2N-CcH,>^'^OH
Hantzsch has l)oon able to i(l(Mitify as pseudo-h&scs substances* other than those mentioned.
5 374] TRIPHENYLMETHANE DYES. 529
^ Pararosaniline 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 to!uidine thus furnishes the "methane carbon atom " of triphenylmethane:
yC6H4.NH2 yC6H4NH2
CHa-^CeHs-NHa-fSO = HO— C^6H4NH2 +2H2O. C6H6.NH2 \C6H4NH2
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 paraleucaniline, 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 formatioa 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 triaminotriphenylcarbinol, which, like rnR|fto>iifA-grA<>^^ loses water under the influence of acids, forming the dye:
yC6H4NH2 /C6H4NH2
cA:eH4NH2 -H2O = C^6H4NH2 I X;6H4NH2.HC1 X:6H4:NH2.a.
Another important dye related to triphenylmethane i^osaniline/ 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.CH3 + C6H4(CH3)NH2 + C6H5.NH2 +
p-Toluidine o-Toluidine
+ 30 = 2H20 + HO.C^8H4NH2 -> Ci<36H4NH2
\C6H4NH2 XeHiiNHz-Cl.
Colour-boae Magenta
The chloride obtained from the rosaniline colour-base, by combination with one equivalent of hydrochloric acid and elimina-
530 ORGANIC CHEMISTRY, 15 374
tion of one molecule of water, is called iruigenta. 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 salts — 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.
Many derivatives of pararosaniline and rosaniline 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-violet is obtained by the oxidation of dimethylaniline with potassium chlorate and cupric chloride, the methane carbon atom being obtained from one of the methyl-groups.
Anilinc-bluo, or tnphemjlrosaniliTie 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 triphenylme thane are also knowTi, but are much loss valuable than those just described, on account of the difficulty of fixing them. Rosdic acidy
5 375] , TRIPUENYLMETHYL. 531
C^~C6H40H Xyi4=0
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.
It is stated in 340 that the fixing of dyes upon vegetable or animal fibres must be regarded as a chemical combination of the compounds contained in the fibre with the dye, analogous to the formation of salts. The following is a proof. The colour-base of rosaniline is colourless: when, however, wool or silk is immersed in its colourless solution, it becomes gradually coloured, as though an acid had been added. This phenomenon can only be explained by supposing that a compound in the fibre unites with the colourless base, forming with it a salt of tlie same colour as a solution of the dye in water.
The phthaleins, dyes related to triphenylmethanc, have been mentioned (348).
375. GoMBERG has investigated the action of zinc upon a benzene solution of triphenylcMoromethane: zinc chloride separates and the solution contains a compound which can be precipitated by addition of acetone or ethyl formate. This compound ho regards as triphenylmethyl, (C6H5)3C — , with one free linking. Its power of forming addition-products is remarkable. It is at once oxidized by atmospheric oxygen to a peroxide ^
(C6H5)3C-0~0-C(Cr.H5)3. It decolorizes iodine-solution instantaneously, forming triphenyl- methyl iodide. It yields addition-products with ether and many other compounds.
A close investigation of triphenylmcthyl has revealed the existence of two foi-ms, one Ixjing colourless and the other yellow . The solid, colourless hydrocarbon is converted by solution into the yellow isomcride, the only highly reactive form. In solu- tion, the two modifications attain an equilibrium dependent on the temperature and the naturt* of the solvent. Since the mo- lecular weight indicated by the cryoscopic method corresponds with nearly twice the empirical formula, the equilibrium
532 ORGANIC CHEMISTRY. [<} 376
2(CoH5)3C ^ (C6H5)3C -0(06115) 3 Triphenylmethyl Hexaphenylethane
requires the presence of only a small percentage of the yellow modification.
The colourless form consists of hexaphenylethane ^ and the yellow isomeride of triphenylmethyl. In tridiphenylmethyl , (OeHs- 06114)30, the unimolecular form predominates strongly, the solution having an intense violet colour. These compounds recall the parallel instance of nitrogen peroxide, known ia a 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 arc very remarkable: first, triphenylmethyl contains a tervalent carbon atom; second, the cjtrbon 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 pentaphenylethane, a sub- stance readily decomposed at high temperature, but proved by its synthesis to have the structure (06H5)30 -011(06115)2.
Dibenzyl and its Derivatives.
376. Dibenzyl, 06H5-0H2-0H2-06H6, can be obtained by the action of sodium upon benzyl chloride:
C^H5'rH2|(M-hNao+Cl|0H2-06H5 - 06H5-0H2-0H2-C6H5+2Naa.
This meth(Kl of formation shows it to be symmetrical diphenyU ethane. It melts at 52°.
Symmetrical diphcnylcthylcne, CeHs-CHiCH-CeHs. M.P. 125^ is called siilhcne. It can be obtained by various methods : for example, by heating an aqueous solution of phenylsodionitromethane, which is thereby decomposed into stilbene and sodium nitrite:
2Cens-CH:N0.0Xa - CflH5-CH:CH.CoH5 + 2NaNO,.
Stilbene forms an addition-product with bromine, from which tolan, C^II.'C ^C'ColIs, is produced by elimination of 2HBr. Tolan can be reconverted into stilbene by careful reduction.
P'DiaminostdbcnCf Nn2'Con4*CH:Cn«CoH4«NH2, can be ob- tained by treatment of />-nitrolx»nzyl chloride, ClH2C-CeH4-NOa,
S 3761 BENZILIC ACID. 533
with alcoholic potash, and subsequent reduction of the p-dinitro' aiilbene thus formed. It is used as a basis for the preparation of certain dyes.
Derivatives of dibenzyl are got by the condensation of benzal- dehyde in presence of potassium cyanide. For example, benzoin IS thus formed:
CeHfi-cS T'^C.CeHg - CeHs-CO.CHOH.CeHg.
^ "*" ^ Benaoln
It has the character of a keto-alcohol, since it takes up two hydrogen atoms, with formation of a dihydric alcohol, hydro- benzoin, CeHg.CHOH.CHOH.CeHg. On oxidation it yields a diketone, henzU, 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.
Bemildioxime exists in three isomeric forms, the number indi- cated by the stereoisomerism of nitrogen derivatives (318):
CoHs-C C.C0H5 CoHb-C— C-C6H5 CeHs-C C-CbHs
il II II II II I
NOH NOH HON NOH NOH HON
ampfttBenzildioxime an/tBenzildioxime •vj//*Benzildioxime
•
One of these oximes readily yields an anhydride, and is therefore assumed to have the two hydroxyl-groups in close proximity, the «2/n-formula. One of the other dioximes is the most stable of the three compounds, and can be obtained by various means. The third dioxime can be easily transformed into this stable modifica- tion. It is probable that the stable dioxime has the symmetrical or anii-formula, so that the amp^i-formula must be that of the unstable modification.
When heated with alcoholic potash, benzil takes up one mole- cule of water, midergoing an intramolecular transformation, with production of benzilic acid, a reaction analogous to the formation of pinacolin from pinacone (150) :
CflHfi.CO.CO.CeHfi+HgO - §gJ>C<coOH
CONDENSED BENZENE-NUCLEI.
377. Condensed-ring compounds contain two or more closed chains, with C-atoms 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, carbolic oil, and of the third fraction, creosote-oil. The anthracene-oil contains anthracene and phenanthrene, and other hydrocarbons. These three compounds and some of their deriva- tives will be described.
I. NAFHTHALEUE, CioHa*
Naphthalene is present in con idorable proportion in roal- tar, from which it is readily obtained pure. On cooling, the criuh^ 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 sulphonic acids on warming the crude product with small quantities of con- centrated sulphuric acid, and distilling with steam or subhming. 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 hot 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 dves.
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 coaj-tar.
534
i 3771 NAPHTHALENE. 535
. • The constitution of naphthalene is proved in 355 to be '
H\/\/H H H
This view is conBrmed by two syntheses.
1. o-Xylylene bromide is converted by treatment with tetraethyl disodioethanetetracarboxylate into tetraethyl hydronaphthalenetetra" carboxylate:
XHjBr NaCCCOOCaHs), XHj-ClCOOCjHft),
^CHjBr NaCCCOOCjHs), ^CHj-ClCOOCHs),
o-Xylylene bromide
On saponification, this compound loses two molecules of carbon dioxide, forming hydronaphihalenedxcarboxylxc add:
^CHj— CH-COOH C8H4V I
^CHj-CH-COOH
The silver salt of this acid readily gives up two molecules of carbon dioxide and two atoms of hydrogen, yielding naphthalene.
2. On heating, phenylvinylacetic acid is converted into a-naph^ thai, a hydroxy-derivative of naphthalene:
H CH
hA/\ch i^^^
H\/H XH, " \/\J X
H 00-^ OH /
HO
Phenylvinylacetic acid a-Naphthol
Naphthalene behaves in all respects as an aromatic hydrocarbon. With nitric acid it yields a nitro-derivative; with sulphuric acid a sulphonic acid: its hydroxy l-deri vat ives 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.
536
ORGANIC CHEMISTRY.
[S378
Fonnula I. (Fig. 80) is analogous to the centric formula for ben- zene : it is difficult to represent its configuration in space.
I. Fig. 80.
II. Fig. 81.
/W\
III.
Fig. 82.
Fig. 80. — Centric Naphthalene-pormula. Fig. 81. — Thiele's Naphthalene-formula. Fig. 82. — Simple Naphthalene-formula.
Thiele has suggested fonnula II. (Fig. 81), with inactive double Unkings (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. 82), which leaves the problem unsolved fully accounts for the isomerism of the derivatives of naphthalene.
As with l^enzene, partial hydrogenation of naphthalene changes its characteristic aromatic character; for naphthalene dihydride, CioHjo, 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
H
6
2
^5 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 series of monosubstitution-products are in fact known: those in which
§3781 . NAPHTHALENE. 537
the 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 10, 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 still greater for three dissimilar ones. The disubstitution-products with the substituents in the same ring are called ortho, 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 p^\ The positions 1:8 and 4:5 are also called the pm-positions : in certain respects they resemble the or^/io-positions. For example, pen-naphthalenedi'' carhoxylic 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 difficult, 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
538 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 the same ring, and the orientation of these groups in this acid should indicate their relative position in the naphthalene derivative. Lastly, if oxidation yields a mononitro 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 — methyl-derivatives, ethyl-derivatives, etc. — are unimportant. They can be prepared by FriTiG's method, or that of Friedel and Crafts (287, 1 and 2).
a-Methylnaphthalene is a liquid, and boils at 240°-242® : ^^-methyl- naphthalene is a solid, and melts at 32^. Both are present in coal- tar. On oxidation, they yield a-naphthoic acid and ^-naphthoic acid respectively, which resemble benzoic acid in their properties. They are converted into naphthalene by distillation with lime.
a-Chloronaphthalene and a-bromonaphthalene 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 charac- terizes the corresponding /9-compounds, which are not obtained by the direct action of halogens upon naphthalene, but can be pre- pared from other ;?-com pounds, such as amino-derivatives, sulpho- derivatives, etc., by the methods described under benzene (292, 293, and 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 -nitronaphthalene.M. P. Ql^, which is proved to belong to the or-scrios by its conversion into the same* naphthol as is obtained from phenyl vinylacetic acid (377).
The position of the substituents in a great number of mono- sul)stitution-pro(lurts can Ix* determined from a knowledge of that of the nitro-group in this nitronaphthalene, for the nitro-group
i 3791 NAPHTHALENE SUBSTITUTION-PRODUCTS. 539
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-nitrO'a-naphthyl- amine.
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 S-isomeride. Both are crystalline and very hygroscopic.
On fusion with caustic potash, the naphthalenesulphonic acids are converted into naphtholsy 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-naphthol 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 P-dinaphiholf HO-CioHe-CioHe-OH. The violet precipitate obtained with a-naphthol is possibly an iron derivative of a-dinaphthol.
a-Naphthylamine and ^-naphthylamine, Ciori7-N"H2, 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 faecal-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
540 ORGANIC CHEMISTRY. [§330
product with a sulphonic acid of naphthylamine. The dye is the sodium salt of the acid thus formed :
H2N .C8H,--CoH4 • NH2 -> CI • N^ . CoH4--CeH, . N^a + 2C.0H, < ^JlJ^ -»
Bensidine Beniidinediasonium chloride Naphthylaminesul-
phonic acid
|^»^>C,oH5.N:N.C6H,.CoH,.N:N.CloH5<|^•J^^
NaO H.
Congo-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 poly substituted naphthalene derivatives is 2'A'dinitro-a-naphthol, obtained by the action of nitric aciJ upon the monosulphonic or disulphonic acid of a-naphthol. Its sodium salt is Martins' s yeliow: •it dyes wool and silk directly a golden- yellow. Nitration of a-naphtholtrisulphonic acid yields dinitro- naphtholsul phonic acid, the potassium salt of which is naphihol" 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 :^naphthylamin€8ulphonic acid,
SO3H
/
I I
\
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 qui nones of naphthalene are known:
0 0 0
• • ••
0 0
a B amphi Bensoquinone
§381] NAPHTHAQUINONES, 541
a-Naphihaquinone, 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 for the prepara- tion of the corresponding benzene derivatives. It crystallizes from alcohol in deep-yeUow needles, melting at 125°. On oxi- dation, it yields phthalic acid, proving both oxygen atoms to be attached to the same ring. With hydroxy lamine at yields an oxime. I^owing the structure of a-naphthaquinone, it is possible to deterriiine that of other di-derivatives. If, on oxida- tion, they yield this quinone by elimination of the substituents, they must be l:4-derivatives.
P'Naphthaquinoney C10H6O2, is formed by oxidation of 1:2- aminonaphthol.
Simphi'Naphthaquinonej or 2 : ^-naphthoquinone, 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 hydriodic acid, turn ferrous ferrocyanide blue, and oxidize sulphurous acid. a-Naphtha- quinone exhibits none of these characteristics, but resembles benzoquinone in odour and volatility. /9-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 dihydronaphihalency CioH,o, to dodccahydronaphthaicnc, C10H20, are known, each member having two hydrogen atoms more than its immediate predecessor. The first-named is obtained by the action of
542 ORGANIC CHEMISTRY. I§381
sodium and alcohol upon naphthalene. Oxidation converts it into o^henylenediacetic acid:
H H H H,
Hf \/\H Hj^\/\H /^\CH,.COOH
b\\Jk -*H^/'l J'h-* 'v^jcH,.COOH- H H H H,
Naphthalene Dihydnde o-PbeDylenediacetic 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, ^-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 compouiid converted into the o-carboxylic acid of dihydrocinnamic acid,
p TT ^CH2*CH2»COOH
which must evidently result from a tetrahydride with the above structure if the oxidation takes place at the C-atom linked to the NHj-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 rin^j: would pnHluce a compound with double bonds, capable of yieldinji; an addition-product with bromine.
The reduction-product may, therefore, be regarded as benzene
5381] NAPHTUYLAMINES. 543
with a saturated side-chain, •— CH2-CH2-CH(NH2)-CH2— , linked to two ortho-C'Sitoms,
a-Naphthylamine can also be reduced by amyl alcohol and sodium, but the tetrahydride formed is different in character from that obtained from /?-naphthyIamine, 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
CH2 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 /alue 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 /3-naphthylamine. The molecular refraction
544 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 /3-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, CuH
io>
382. Anthracene is present only in small proportions in coal- tar, var}'ing between 0-25 and 0-45 per cent.; nevertheless, it is the basis of the manufacture of the important dyestuflf, 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 carhazole^ • >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 disulphide, 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 dianthracene, which in the dark becomes depolyroerized to anthracene, one of the rare instances of a reversible photochemical reaction:
Light Dark
Several modes of preparing anthracene are known which give an insight into its constitution. One of th^e is its synthesis by
§383]
ANTHRACENE.
545
Anschutz's method from benzene, aluminium chloride, and tetra- bromoethane :
BiCHBr XH.
C6H6+ I +C6H6 = C6H4< I >C6H4 + 4HBr.
BrCHBr XJH^
This Synthesis proves that anthracene contains two benzene- nuclei united by the group C2H2, linked to two or//io-C-atoms of each, as proved for anthraquinone in 383. Its constitutional formula is
7
6
Anthracene
2 3
It follows that it must yield a very large number of isomeric 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. Anthraquinanef C14H8O2, 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
y
546 ORGANIC CHEMISTRY. [J 383
since it is formed by the interaction of phthalic anhydride and benzene in presence of a dehydrating agent such as aliuninium chloride:
C6H4<gg>[OTHr|CeH4 = C6H4<^>C6H4-hH20.
Phthalic anhydride
The reaction takes place in two stages: o-benzoylbenzoic acid, C6H4 <qqq4^*, is first formed, and then loses one molecule of water, forming anthraquinone;
CO
C6H4^ NUflHs — H2O = C6H4<p,y-.>C5H4.
XXX)H ^"
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 anthraquinone, 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 that employed in prov- ing the constitution of naphthalene (355), the marking of one of the nuclei by the introduction of a substituent affording a means of identifying the nucleus eliminated by oxidation.
On treatment with benzene and aluminium chloride, bromo- phthalic anhydride reacts analogously to phthalic anhydride, yield- ing bromoanthraquinone by elimination of water from the bronuh- bemoylbemolc acid first formed:
COv I. xCO
y^Uv I. y^u\ II.
Br-CeH/ yO - Br.CeH,<: X^eH,
\C0/ \COOH
Bromophthalio anhydride Bromobensoylbcncolc
acid
I yCOv^ii.
Bromoanthraquinone
Since bromoanthraquinone is a derivative of phthalic acid, its two carbonyl-groups must be united to two o-C-atoms of nucleus I.
§ 3841 ANTHRAQUINONE. o47
Its Br-atom can be replaced by a hydroxyl-group by heating with potassium carbonate at 160^, and the hydroxyanthraquinone 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 II. HO-COv^ II.
CO/ HO-CO/
Hydroxyanthraquinone Phthalic acid
384. Anthraquinone crystalUzes 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 anthragumone is in some measure incorrect, for this substance lacks some of the properties characteristic of quinones, such as being easily reduced, great volatility, pungent odour, etc., and has much more the character of a di ketone. With fused potassium hydroxide it yields benzoic acid, and with hydroxyl- amine an oximc. On wanning with zinc-dust and sodium- hydroxide solution, it forms the disodium-derivative of anthra-
quinol,
COH
COH
Anthraquinol 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, oxanthronef
CO
C6H4\^P>C6H4.
H OH
548 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 t>'pe of desmotropy characterized by the great stability of both forms.
On reduction with tin and hydrochloric acid, anthraquinone is converted into anthrone,
CO
CH2
a substance converted by boiling with alkalis into the tautomeric anthranolf
COH
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. Anthrone is to be regarded as a pseudo-acid, anthranol being its aci-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, ruhenjthric acid, C26H28O14. When boiled with dilute sulphuric acid or hydrochloric acid, this glucoside jields dextrose and alizarin:
C26H,80i4 + 2H20=2C6H,206-hCi4H602(OH)2. Ruberythric acid Dextrose Aliiarta
The (lyo is now prepared almost wholly by a synthetical method. It is one of the organic dyestufifs known in antiquity.
§ 385] ALIZARIN. 549
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 /3-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<QQ>C6H3.S03Na-h3NaOH4-0 =
Sodium anthraquinone- monosulphonate
C6H4 < ^Q >C6H2(ONa)2 +2H2O -fNaaSOa.
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, uzid slightly soluble in alcohol. On account 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
550 ORGANIC CHEMISTRY. \% 385
lakes. AVhen 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:
C6H4<QQ>0+C6H4<Qjj 2 == C6H4<QQ>C6H2<Qjj 2+HaO-
Phthalic anhydride Catechol Alisarin
It follows that the choice lies between the two structural formuUs
O OH O ^ ^ *
o
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, aa example being purpurin or ^:GiS-trihydroxyanthraquinone,
CeIL<(CO)2>C«H(OH)3,
ii constituent of madder-root. The power of the hydroxyanthraqui- n()n(\s to form dyes with mordants is conditioned by the presence of two hydroxyl-groups in the orMo-posit ion to one another. Other
iSd] PHENANTHRENE. 551
anthraquicone derivatives with hydroxyl^roupa and amino-groupa, or with amino-groups only, are also valuable dyea.
The very fast, brilliant colours of the indaalliren-^froup are derivatives of 2-aminoan^ra^tnon«,
CO
CXX).
CO
being obtained by its oxidation. /ndanlArnv-Uue is supposed to have the structural formula
m. PBXNANTHREHE, C.iHio.
386, Phenatithrene is isomeric with anthracene, and is present with it in " anthracene -oil." They arc separated by the method already described (382). It crystallizes in colourless, lustrous plates, which dissolve in alcohol more readily than anthracene, yielding a blue fluorescent solution. It melts at 96°, and boils at 340°.
On oxidation with chromic acid, it yields first pkenanlhra^ quinone, and then diphenic acid (372),
HOOC
i COOH
This reaction proves that phenanthrene possesses two benzene- nuclei directly linked to one another, and is therefore a diphenyi- derivative, and also a di-orfAo-compound. Diphenyl with two hydrogen atoms substituted,— CaH^ -06114 — , or — C12H8 — .differs
552
ORGANIC CHEMISTRY.
[$386
from phenanthrene by C2H2. This must link together two o-poei* tions, so that phenanthrene has the constitution
CH=CH / \
/T~ 10
or
8 7 6
X
1
V
PhenaDtbreDe
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 — CeHs CH — C5H4
II -H2=|| I .
CH — CeHs CH — C0H4
Stilbene
PhenanthreDe
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 bromine, and that on oxidation it behaves as an ordinary side-chain.
C6H4— CO Phenanthraqumone^ \ 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 Perkix reaction (328) :
CeH
/
NO-
^O + HaC/
\COOH
o-Nitro- benzaldchvde
Phenylacetic acid
H2O+C6H4C /CeHs
/NO2
\CH:C<('
XJOOH
PbeDyl-o-nitrocinDamic acid
§ 3861 PHENANTHRENE. 553
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
^/^V /\/\c.cooH /VVh
VJN?
Diaio-deriTative of o-phenyt* Phenanthrene- Phenanthrene
a-aininocinnamic acid carbozylic 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
\<TT. /\ OCH3]
OCH3 f\
\/
Methyl ether of o-nitrovanillin PTT
0CH31 I
Dimethylmorphol
"^AA^^yif^^ ■ Z
Y'^r
B. HETEROCYCLIC COMPOUNDS.
NUCLEI CONTAINING NITROGEN, OXYGEN, AND
SULPHUR.
I. PYRIDIWE, C,H.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 ** Dippers 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 ver}' stable, l^eing unattackcd 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 ferrocyanide dissolves with difficulty, and is employed in the purification of the base. With platinum chloride, the hydro-
554
§388) PYRIDINE, 555
chloride yields a double salt, (C»HsN)iHjPtCl6, freely soluble in water. When the solution is boiled, two molecules of hydrochloric ' acid are eliminated, with production of a yellow compound, .(CiHiN)jPtCl4, 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, CJHiN •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 piperidine from pentamethylenediamine is mentioned in 159. Piperidine can be oxidized to pyridine by heating with sulphuric acid :
H yCH2 — CHgy /C'CH
CH2< >NH->H(X: >N.
\CH2— CH2/ \C-CH
Piperidine TT
. *-^
Pyridine
The formation of j^-chloropj/ridine from pyrrole is described in 395
The converse of these syntheses is the decomposition of piperi- dine, discovered by von Braun. On treatment of bemoylpiperidine, CsHjoN'COCoHs, with phosphorus pentabromide, PBrs, the oxygen is replaced by two bromine atoms. Distillation converts this dibromo-derivative into penlameihylene dibromide and benzonitrile:
XHj-CHjv .CH,-CH2-Br
< >N.CBrj.C6H5 - CHj< +NC.C6H5.
CH-
CHj-CHj^ ^CHj-CHj.Br
i2V yii •v/xji2-v>BAX6 — v^x*2\
A practical method is thus afforded of preparing pentamethylene dibromide, a substance of importance in various syntheses.
Since pyridine is reduced to piporidinc by sodium and alco- hol, Jind piperidine can be oxidized to pyridine, it may be assumed that pyridine has the same closed chain as piperidine; that is, one of fivr ( -atoms and one N-atom. Moreover, it can be proved that
556 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 nitroeo- derivative, for example, pyridbe 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 uriih one hydrogen atom, A substance of the formula
|
N |
N |
||
|
6 2 |
«'A |
||
|
or |
|||
|
6 3 |
^Ky |
||
|
r |
a
should yield three monosubstitution-products, 2(a)=6(a0f 3(^) = 5(/?')f and 4(7'). Moreover, for similar substituents, six disubstitution-products 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 i-emains 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 linkings. 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 ,5- nitropyridinej 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.
§ 3891 HOMOWGUES OF PYRIDINE, 557
The principle of the orientation of pyridine is the same as that 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.
Homologues of Pyridine.
389. The homologues of pyridine are the meihylpyddines or picolines, dimfithylpyr^idines or {jtHdineSf and f,rimj>.t.hylpyrh(ljjip.!i or coUidines, Many of them can beoBtatned 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 homologues 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.
Hantzsch has discovered an important synthesis of pyridine derivatives— the condensation of one molecule of aldehyde-ammonia with two molecules of ethyl acetoacetate :
CH3
OCH CjHfiO-OC.CH, CH,.C0-0C,H6
CHa-CO CO-CH,
HNHa
CH, CHjOOC-C C-COOC,H»
11 II + 3H,0.
CH,C C-CH,
\N/ H
Diethyl dihydrocolltdinedicarboxylate
On oxidation with nitrous acid, this substance loses two H-atoms, one from the CH-group and one from the Nil-group, with forma- tion of ethyl coUidinedicarboxylate. On saponification with caustic
658 ORGANIC CHEMISTRY. . H 390
potash, and subsequent heating of the potassium salt with quick- lime, the carboxyl-groups are eliminated, and coUidine,
CHjls^'CHa
N distils.
In this S3mthesis acetaldehyde may be replaced by other alde- hydes, and ethyl acetoacctate by the esters of other ^ff-ketonic acids, so that it affords a method of preparing numerous pyridine deriva- tives.
Some of the homologucs 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 (299).
390. a-Propenylpyridine is of theoretical importance. Laden- burg obtained it by the condensation of a-picoline with acetalde- hyde :
NC5H4-CH3-hOCH.CH3 = NC6H4-CH:CH.CH3+H20.
or-PicoliDe Acetaldehyde or-Propenylpyridine
By its aid he effected the first synthesis of a natural alkaloid, that of coniino, CgHiyX (409). rt-Propcnylpyridine was reduced with sodium and boiling alcohol, yielding a -propyl piperidiney
H2
H •CH2 •CH2 •CH3'
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 crystal- lization of its tartrate, the dextro-rotatory isomeride being named isoroni'ine because heating at 300° transforms it into an isomeride identical with natural coniine. Ladenburg attributes the difference between coniine and woconiine to asymmetry of the nitrogen atom.
S 391) PYRIDINECARBOXYLIC ACIDS. 559
The constitutional formula of a-propylpiperidine indicates that the carbon atom in luiion with the propyl-group is asymmetric. T'-Propylpiperidine does not contain an asymmetric carbon atom, and should therefore be optically inactive. The side-chain cannot be at the /^-position, for coniine )4elds ammonia and normal octane when strongly heated with hydriodic acid. Thus treated, a /9-propylpiperidine or /'-propylpiperidine must yield an octane with a branched carbon-chain, which proves that coniine is an a-com- pound.
Piperidine is present in pepper in combination as piperine^ CitHwOsN. 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 NH». group:
yO/NcH:CH.CH:CH.CO.N
H2CI JCHi
Pipeline CHj
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.
Pjrridinecarbozylic Acids. 391. Three pyridinemonocarboxylic dcids are known^
N N N
QjCOOH Qt^(3()H, and Q|.
COOH
Pieolinio aeid (a) Nicotinic acid (0) uoNicoiinic acid (j)
The orientation of the carboxyl-groups in these acids can be carried out as follows. It is stated in 390 that the side-chain in coniine occupies the a-position. On oxidation, this substance yields pico-
560
ORGANIC CHEMISTRY.
[J 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) has the formula
It is naphthalene with one of the a-CH-groups replaced by N. On oxidation, quinoline yields a pyridinedicarboxylic acid, quinolinui add, which must therefore have the structure
N /\C00H
fi
\y
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 ^'-structure for isonicotinic acid.
The p>Tidinemonocarboxylic acids are formed by the oxidation of the homologues of pyridine containing a side-chain. Nicotinic acid derives its name from its formation by the oxidation of nico- tine. The monocarboxylic acids are crystalline, 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, 1x5 concluded that they are applicable to acids with a carboxyl- group in the a-posilion.
§392]
FURAN.
561
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
II II HC— CH
A
or
or
a
?
/\
a
This formula is supported by the resemblance in properties between some of its derivatives, such as Jurfuraldehyde (furfural or furfvrole),
XT
C4H30-Cq, and the corresponding benzene derivatives. More- over, the 0-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 hydroxy lamine or phenylhydrazine, indicating that it has no carbonyl-group.
Furan derivatives can be obtained from the l:4-diketones, R«CO«CH2«CH2«CO«R, by treatment with dehydrating agents, such as acetyl chloride. This reaction may be regarded as the result of the conversion of the diketone into an imstable, tauto- meric form, R-C:CH«CH:C-R, which loses water:
OH OH
HC=C<' I X)IH
OH
\r
-H2O
* The Chemical Society op London adopts the name furan for the O
simple ring
i.,Q,
the corresponding radical being furyl. The double syl-
lable furfur ... is reserved for derivatives with a side-chain, containing the O
ring|["K.
562
ORGANIC CHEMISTRY.
[S393
This method yields 2:5-furan derivatives, the Oatoms 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 furfurdLde^
Ar/c^e C4H30*Cq, and pyroimicic acid, C4H30»COOH: both have
long been known.
Furfuraldchyde is prepared from pentoses by the method men- tioned in 207. It has the character of an aromatic aldehyde: like bcnzaldehyde (314), it is converted by alcoholic potash into the corresponding acid, p3n*omucic acid, and the corresponding alcohol, furfuryl alcohol, C4H3O.CH2OH:
C)
Furfuraldehyde
COOH
O
Pyromucic acid
n
. JCH2OH.
o
Furfuryl aloobol
With ammonia it >nelds furfur amide, (051140)3X2, analogous in composition to hydrobenzamide (315). Just as benzaldehyde con- denses in presence of potassium cyanide to benzoin (376), furfur- aldehvde under the same conditions yields the similarly constituted
H
fwfuroln, CiHsO'C'CO'C^HsO. The resemblance in properties
OH between the two compounds is, therefore, very striking.
Furfxiraldehyde is proved to have the 2-8tructure by various means: for example, by its formation from pentoses (207), a reac- tion which may be represented by the scheme:
IHO H I I
CH-C^
I I \
HO|H
OH
H
o
\pH ^O
CH=CH
Pentose
H O
Furfuraldehyde
§ 393] FURFUR AIDE HYDE. 563
Furfuraldehyde 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 hydroxymethylfurfur aldehyde,
a
HC — CH
II II H HO-CHa-C C-C^,
o
effected by heating with dilute acids. The structure of this sub- stance is proved by its oxidation to the dibasic dehydramucic acid,
HC — CH
HOOC-C C-COOH. O
Heating with hydrochloric acid or dilute sulphuric acid converts hydroxymethylfurfuraldehyde almost quantitatively into formic acid and Isevulic acid:
C,H.0,+2H,0 = H • COOH+CiHaOa.
lydroxymetbyl- LsbvuHo
furfuraldebycie acid
The formation of hydroxymethylfurfuraldehyde 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 (209) from the natural product, since in the inversion of the sucrose by heating with dilute acid a small proportion of hydroxymethylfurfuraldehyde is formed.
As its name indicates, pyromucic acid is formed by the dry dis- tillation of mucic acid (211). 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.
564 ORGAMC CHEMISTRY. [{ 394
Pyromucic acid wholly lacks the character of an aromatic com- pound: its properties in no way resemble those of benzoic acid, but are like those of the unsaturated aliphatic acids. Thus, it easily undergoes oxidation: it almost instantaneously decolorizes von Baeyer'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 >o
HC=:C
i
^OOH
with two double bonds, must be assigned to it.
III. PYRROLE, C^HftN.
394. Pyrrole 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-products of proteins. Pyrrole is a constituent of *' Dippel's oil" (387). The fraction of this oil which distils between 120® and 130® is employed in the preparation of pyrrole. After removal of the pyridine bases by treatment with dilute sulphuric acid,andof the nitriles by boiling with sodium carbonate, the frac- tion is dried, and treated with potassium. Potassio-pyrrole, C4II4NK, is 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 acquiref 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, ^'pyrrolo-red.'' This reaction furnishes a delicate test for p3Trole and its derivatives.
Pyrrole can be synthesizod by several methods: for example, bv the inloraction of succindialdohvdc and ammonia:
$395]
PYRROLE.
565
CH2— c^ + NH3 CH2-CH < §2
i
.0
NH,
Ha— eg + N H3 CH2— CH < Qg=
CH=CHv
>NH+NH3+2H20.
h=ch/
i
Pyrrole
Inversely, succinald-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 l:4-diketones:
HC=C<^
HC=C/
R
OH , H OH + H
R
1 : 4-Diketone (tautomeric form)
/R HC=C NH = I ^NH+2H20.
HC=C<:
\r
oa'-Pyrrole
The nomenclature of the pyrrole derivatives is indicated in the scheme
NH NH
5 3
or
a
,/\.
fi'
a.
This structure is inferred from the foregoing syntheses 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 aliphatic 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 1-methylpyrrole into 2'methyl pyrrole under the influence of heat resembles the conversion of methylaniline into p-toluidine (299) :
C4H4N. CH:, -► C^U•^(CH:,) • XH.
l-Methylpyrrole 2-Mcthylpyrrole
Just as sodium phenoxide is converted by carbon dioxide into
I
566 ORGANIC CHEMISTRY. [§396
salic3'lic acid (344), so potassiopyrrole and carbon dioxide yield 2-pyrrolecarboxylic acid. Like phenol, pyrrole unites with l)en- 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 Oatoms of the p3aTole- nucleus, forming ^-chloro pyridine:
NH N
+ CHCla-i
Pyrrole )9-Chloropyridioe
On reduction with zinc-dust and cold hydrochloric acid, p3Trole takes up two hydrogen atoms, forming 2:S'dihydropyrrole* C4II7X, which boils at 91°. Like the partial reduction-products of aromatic compounds, dihydropyrrole behaves as an unsaturated compound, another indication of the aromatic character of pyrrole.
IV. XmOPHEN, C4II4S.
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 methylthiophen, and thioxen or dimethylthiophen, 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 indopheniri'reaction, 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 \ye regenerated by the action of superheated steam.
A l)otter 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 oxyacetaie, C,H^S(HgO()C^-Cn3).ngOH, which is reconverted into thiophen by distillation with moderately concentrated hydrochloric acid. It is formed i)y i)assing acetylene over pyrites at 300°.
* Tho CuKMiCAL SoCiKTY OP LoNDON cmploys iho nsLme dihydropyrrole for tho compound (^HjX, and tetrahydropyrrole for C^HgX. In the nomen- clature of the (Jkkman Chemical Society the corresponding terms are pyrrUin and pyrrolidin.
§ 396] THIOPHEN, 567
Thiophen can be synthesized by various methods, the most important being the interaction of succinic acid and phosphorus pentasulphide. On heating a mixture of these substances, a vigor- ous reaction ensues, carbon disulphide is evolved, and a liquid, con- sisting chiefly of thiophen, distils.
It is 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 dibromothiopheriy C4H2Br2S, along with a small proportion of the monobromo-derivative.
The notation of thiophen derivatives is indicated by the schemes
• S S
^
^
and
The homologues of thiophen can be obtained by Fittig's syn- thesis (287) 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, ace tony lace tone yields dimeihylihiophen:
/CH3 r>,TT
/OH ^ „X_f,X^ • \CH3 ^^8
Acetonylaoetone 2 : 5-Dimethylthiophen
(tautomeric form)
2:5-Dialkylthiophens are obtained from l:4-diketones: the 3:4-alkyl-compound8 can be prepared by another method. As stated, thiophen results from the interaction of succinic acid and phosphorus pentasulphide:
H H2C— COOH HC=d
H2C— COOH HC=C
H
Succinic acid Thiophen
568 ORGANIC CHEMISTRY. 15 397
Similarly, a monoalkylsuccinic and symmetrical dialkylsuccinic acid respectively yield a 3-alkylthiopheii and a 3 :4-alkylthiophen:
CH3CH-COOH CH3.C-CH
I - I >S.
CH3.CH-COOH CHs-C— CH
Symmetrical dimethyl- 3 : 4-Dimethyl-
succinio add thiophen
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 monocarboxylic acids, 2-4hiophencarboxylic acid and 34hiophencarboxylic acid^
S S
/NCOOH and /\
COOH
!
is cr>'stallized 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-isomcridcs. On oxidizing a mixture of 2-thiotolen and 3- thiotolen, an apparently homogeneous acid is obtained: from its method of formation, however, it can only be a mixture of the corresponding acids.
A thiophensul phonic acid is also known : it is more easily formed than bcnzcnesulphonic acid, which is the basis of Victor Meyer's mctliod of separating thiophen and benzene.
When a mixture of acetic anhydride and concentrated nitric acid is added to thiophen, nwnonitrothiophen 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. PYRAZOLE, C,H4X2.
398. Pj/razole derivatives an* produced by the interaction of the esters of unsaturated acids and ethyl dia'.o.icetate. An exampla is the union with explosive energ>' of diethyl acetylenedicar-
$398]
PYRAZOLE.
569:
boxylate and ethyl diazoacetate to form Irieihyl pyrazoletri- carboxylate :
C2H5OOC.C CH.COOC2H5 CzHfiOOC-C C-COOCzIIe
CzHoOOC-C+p^N
N
Diethyl acetylene- dicarboxylate
= CzHfiOOC-C N
\/ Nil
Triethyl pyrasoletricarboxylate
Pyrazole is formed in several reactions, one of them being the combination of hydrazine with propiolaldchydeaceta! (142) :
(^H:^C.CH(OC2H5)24-Il2N.NH2 =
Pn>.)iolaltlehy(leacetal
= CH=CCH=N-NH2+2C2H50H;
Intermediate product (not isolated)
C— CH
CH /'^ NH2
Intermediate product
CH— CH
\nh
Pyraiole
or
NH
5 2
N.
This synthesis proves that pyrazole has the formula indicated, so that it may be regarded as pyrrole in which one of the CH-groupa 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.
The identity of the 3-derivatives and the 5-derivative8 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
r 5 2
N
N
5 21
NH
M>
4 3
4 3
570 ORGANIC CHEMISTRY. [§399
39g. The derivatives of pyrazole are not important, but there are valuable products related to its dihydride, pyrazdine, C3H6N2. Substances of this type are prepared by condensing ethyl diazo- acetate with esters containing a double linking:
C2H5OOC.CH CH.COOC2H5 C2H5OOC.CH— C.COOC2H5
C2H5OOC.CH+ b^N = C2H5OOC.CH N
N \/
NH
Diethyl f umaraie Triethyl pyraiolinetricarbozylato
Pyrazoline (I.) is formed by the interaction of hydrazine hydrate and acraldehyde. Bromine converts it into pyrazole. Pyrazolone (II.) is a ketonic derivative of pyrazoline :
NH NH
H2C N OC N
I II \ \\
H2C — CH H2C — CH
I. II.
Substitution-products of pyrazolone are obtained by the interac- tion of ethyl acetoacetate and phenylhydrazine :
CH3— C^ H2JN CH3.C=N
I + ,1 ^ I >N.aH5.
H2C— CO . IOC2H5 H^NCeHfi H2C— CCT
Methylphenylpyrazolone is thus formed. Methylphenylhydrazine, CeHs-NH-NH-CHa, condenses similarly with ethyl acetoacetate, yielding a dimethylphenylpyrazolone of the formula
CH3.C— NCCHs) II >N.C6H5. HC— CO
This substance Is called '* antipyrine/' and was discovered by Knoru; it is extensively employed in medicine as a febrifuge. It
i 3991 PYRAZOLINE DERIVATIVES. 571
crystallizes in white leaflets melting at 113°. It cannot be dis- tilled without undergoing decomposition. It is readily soluble in water and alcohol : the aqueous solution gives a red coloration with ferric chloride, and a bluish-green coloration with nitrous acid.
'J Salipyrine [[ is a compound of antipyrine and salicylic acid.
(CONDENSATION-PRODUCTS OF BENZENE AND
HETEROCYCUC NUCLEI.
I. QUINOLINE, C9H7N.
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 0°. 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 diffi- 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 dkz H H
AUvlaniline
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/'x .
In Konig's synthesis the oxidizing agent is the lead oxide; in this
reaction it is the nitrobenzene, which is rcduccil to aniline. Arsenic
acid can be substituted for nitrobenzene.
Vox Baeyer and Drewsen have discovered another method of
synthesis which .proves the constitution of quinoline: it involves
572
§ 4011 QUINOLINE, 573
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:
V H -H2O -
<HAminocianAmaldehyde Quinoltne
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'v^^H' H
On distillation with quicklime, quinolinic acid yields p)Tidine. From these facts it must be concluded that quinoline contains a benzene-nucleus and a p3Tidine-nucleus, with two ortho-C-SLtoma 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 prs:ible. Twenty-one disubstitution-products are pf)ssible for similar substituents, while the number of tri-derivatives possible is much greater, and so on.
401. There are three methods for the orientation of quinoline derivatives.
First, the relative method (354, 1).
Second, oxiJiui )n. This process usually removes the benzene- nUclous, leaving tlu pyridinc-nucleus intact, and thus furnishes a means of d(^tonnining which substituents are present in each.
574
ORGANIC CHEMISTRY.
K401
Third, Skraup's synthesis — an important aid to orientation. It can be carried out not only with aniline, but with many of its substitution-products, such as homologues of aniline, nitroanilines, aminophenols, and other derivatives. The quinoline compounds thus obtained have their substituents in the benzene-nucleus. But this synthesis also indicates the positions of the side-chains when an (>r^Aa-substituted or a para-substituted aniline is used: thus.
X
a
Ortho
NHj
X N
can only yield
and yI J ^^y
Para
while ( J can yield
Meta
or
All four possible quinoline derivatives with substituents in the benzene-nucleus can, therefore, be prepared by Skraup's sjm- 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.
S§ 402,403] iBoQUINOUNE AND INDOLE. 575
Carho8tyTilf or 2-hydroxyquinoline, can be synthesized by the elimination of water from o-aminocinnamic acid :
iHAmtnooinnamlo add Carboetyril
It has a phenolic character: thus, it dissolves in alkalis, and is reprecipitated by carbon dioxide.
II. woQUINOLINE, C.HtN.
402. isoQmnoZine is present in coal-tar, from which Hoogewerff and VAN Dorp isolated it in the form of its sparingly soluble sulphate. It is a colourless substance with an odour Uke that of quinoline. It melts at 2r, and boils at 237 "*. It has the formula
(<^^N
««oQuinoUne
\ This constitution is indicated by its oxidation to cinchameronic acid and phthalic acid, in accordance with the scheme
CO
n^hooc/Nn. ^^ /y^N^AcooH
HOOC»\/J-' *°*' \/\/ KJCOOH'
Cinehomeronic acid Phthalic aoid
The synthesis of isoquinoline furnishes additional confirmation of the structure indicated.
m. INDOLB, C.H7N.
403. The relation between indigo and indole is made evident by the following series of transformations, chiefly the discoveries of VON Baeter.
On treatment with nitric acid, indigo, CieHio02N2, yields an
576 ORGANIC CHEMISTRY. [§403
oxidation-product, isaiin^ C8H5O2X, which can also be synthe- sized by treating o-nitrobenzoyl chloride with silver cyanide. When hydrolyzcd, the resulting nitrilc yields o-nitrobenzoyl- formic acid:
r.H ^^^2 1 n XT ^N02 . p Tj ^N02
o-Xitrob€li«oyl | o-Nitrobenioyl o-Nitrobenxoyl-
chloridc 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
o-Aminobenzoylformic acid Isatin
When reduced with zinc-dust and hydrochloric acid, isatin takes up two hydrogen atoms, forming dioxindole, C8H7O2N. This com- pound also results on the elimination of water from the unstable o-aminomandelic acid, which determines its constitution:
\^T-TIPr >JM Xl.
^"*<rHOH-COlOH"^20 = C6H4s^^>CO.
o-AminomandeLo acia
OH
I^oxjndole
When reduced with tin and hydrochloric acid, dioxindole yields oxindoUy CsHyOX, which is also obtained by reduction of o-nitro- phenylacetic acid and subsequent elimination of water:
NHIH /^^
{^-Atniiiophcnylucetic aci<l C^xindole
Distillation with zinc-dust converts oxindole into indole, CgHyN, which must, therefore, have the structure C6II4V 'CH;or
403] INDOLE. 677
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.
Z-Methylindole^ or scatole,
NH
^ C8H4\ ,^CH, C.CH3
is present in faeces, and occasions 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 indolecUaninef C11H12O2NJ, 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. Z^Indolealdehyde (I.) is formed as an intermediate product, and condenses with hippuric acid to indolyl- bemoylaminoacrylic acid (II.). On treatment with sodium and alcohol, the double bond of this compound adds two hydrogen atoms and the benzoyl-group is simultaneously eUminated, with formation of racemic tryptophan (III.) :
CHO . r ^ iCH:C-COOH
NH-COCeH*
CHi-CH-COOH NH,
NH
Tryptophan
III.
578 ORGANIC CHEMISTRY. [§ 404
Indigo. 404. The constitution of indigo is inferred from its formation from isaiin chloride, obtained by the interaction of isatin and phosphorus pentachloridc. On reduction with zine-dust and acetic acid, it is transformed into indigo:
H = G6H4 < pQ > C=C < pQ > C6H4 + 2HCI.
Since on treatment with sulphuric acid, and subsequent reduc-
■ . ^- , ^L 7J ,7 C6H4«C^C—C^C -06114 .
lion, o-d mil rod I pneny la lacetylene, . . ,iscon-
NO2 NO2
verted 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, lx»ing unaffected by light, acids, alkalis, or washing. It can be prepared from certain plants, among them Indigofera sumatrana and /. arrecta. 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 since its introduction, synthetic indigo (405) has to a ver>' great extent 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. Indigo is not pn»sent in the plant as such, but in combination as the glueoside itidican, which occurs chiefly in the leaves, and can be extractx^d with hot water. It is crystalline, and has the formula Ci4lIi7()6N,3H20. In addition to the glueoside, 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 prepaRnl, hot water must be employed in the extrac- tion. With cold water, both indican and the unchanged enzyme dissolve, and the glucosid(j decomposes into dextrose and indoxi/l, (VH7OX, or ^-,t
!(OII)'
S 405] INDIGO. 579
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. Indigotin 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. This method is employed by the Badische Anilin- uxd Soda- Fabrik of Ludwigshafcn-on-Rhine. Anthranilic acid, or o-amino-
benzoic acid (346), ^6H4<^qqtt, combines with monochloro-
acetic acid to form phenyhjUjcine-o-carhoxylic acid:
NHiHTcilHaC-COgH ^ _ .NHfli;
C6H4 <coOH "" ^^^^ ^C!0 lOH
iCO^H
Phenylglycine-o-carboxylic acid
Fusion with sodium hydroxide transforms this compound into
indoxyl, CeHK ^CH, which in alkaline solution is con-
^C(OH)^
verted by atmospheric oxidation into indigo.
580 ORGANIC CHEMISTRY, IJ405
The production of indigo by this method has been rendered possible by the disovery of a satisfactory process for the manu- facture of anthranilic acid. It is obtained by oxidizing naphtha- lene to phthalic acid (347), which can be converted into anthranilic acid, with intermediate formation of phthalimide (346).
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 alkalis. 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-whito, 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 Ix* dyed. Reduction is best effected with a salt of hyposul- phurous acid, PI2S2O4 ('' 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 hyposulpliite, a concentrated alkaline solution of indigo-white Ix^ing obtained in a short time. On adding 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 almost none of the indigo is lost.
Indigo is the longest-known and most important member of the series of vat-dycstuffs. They include pigments insoluble in water, but characterized ])y 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 preparation 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 d^'cstuffs.
S405]
INDIGO.
581
Vat-dyestufifs derived from indigo, and others related to anthra- quinone, are known. Those of the first class are called indigoidSy 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 dihromoindigOf
CO
C=C
NH
03
Br'
NH
is the celebrated "Purple of the ancients" employed in antiquity for dyeing Tyrian 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 dyestufif can be so much altered by substitution as to render possible the pro- duction of almost every colour.
ALKALOIDS.
406. Plants of certain families contain substances, 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. ^lost of the alkaloids are related to pyridine, quinoline, or isoquinoline, while a smaller number belong to the aliphatic series. Some of the latter class are described along with the compounds of similar chemical character: among them are betaine (242), mus- carine (22g), choline (160), caffeine, and theobromine (272). Only alkaloids which are derivatives of pyridine 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 than 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 conilne and nicotine, are liquids: most of them are crjrstalline. Many are optically active and laevo-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.
Many alkaloids can be identified by characteristic colour-reac- tions. Some substances prt»cipitate many of the alkaloids from their aqiu'ous or acid solution: such general alkaloid-reagents are tannin (346). phosphomolybdic acid, mercuric potassium iodide,
582
§ 408] ALKALOIDS. 583
KI.Hgl2 ("Inorganic Chemistry," 273), and others. Some alka- loids are excessively poisonous.
Strong tea is sometimes employed as an antidote, the tannin present precipitating the alkaloid, and rendering it innocuous.
Most of the alkaloids are tertiary amines, and consequently yield addition-products with methyl iodide: none of them possesses the character of a primary amine. Many contain acid-residues or methoxy 1-groups : the former are removed by saponification, efiFected by heating with bases or acids, the latter by heating with hydriodic acid, which yields methyl iodide. Hydroxyl-groups can be iden- tified in the ordinary way with acid chlorides or acetic anhydride (8q and 90). On dry distillation, or on heating with zinc-dust, substituted pyridines are sometimes formed.
On account of the complex constitution of the alkaloids, the structures of many of them remain imdetermined, so that a rational classification is not yet possible.
408. 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 imder 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 making the mixture 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.
INDIVIDUAL ALILALOIDS.
Conilne, CgHiyN.
409. The synthesis nicnnltne is describod in 390. It is present in spotted hemlock (Conium 7naciUatum)y and is a colourless liquid of stupefying odour. It boils at 167*^, is but slightly soluble in water, and is very poisonous.
584 ORGANIC CHEMISTRY. [§§410,411
Nicotine, C10H14N2.
410. Nicotine is present in combination with malic acid and citric acid in the leaves of the tobacco-plant {Nicotiana tabacum). 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 di tertiary base: on oxidation with potassium permanganate, it is converted into nicotinic acid (391)1 proving it to be a ^-derivative of p3Tidine.
The constitutional formula of nicotine is
CH2 — CH2
-CH CH2;
\/ 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 la»vo-rotatory isomeride is iden- tical with natural nicotine. The dextro-rotatory form is much less poisonous than the lapvo-rotatory, and also differs from it in other respects in its physiological action.
Atropine, C17H23O3N.
411. Atropine is present in the berry of the deadly nightshade (Atrojxi belladonna) and in the thorn-apple, the fruit of Datura stramonium. It is crystalline, melts at 115-5**, and is very poison- ous. It exercises a "mydriatic '' action — that is, when dropped in dilute solution on the eye, it expands the pupil: 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:
(^7H2303N + IIi>0 = CsH.sON + CoHjoOa.
Atn>pine Tropine Tropic acid
S 411] ALKALOIDS, 585
It can be regenerated from these two substances by the action of hydrochloric acid. Atropine 'is, therefore, the tropine ester of tropic acid, which is a-phenyl-/?-hydroxypropionic acid,
CoH5«CH<QQQjT . The constitutions of atropine and tropine
are:
I. II. H2C — CH CH2 H2C — CH CH2
N.CH3 CHO.CO-CH.CHaOH
N.CH3 CHOH.
I I CeHs and H2C — CH CH2 H2C — CH CH2
Atropine Tropine
This formula for tropine was proposed by Willstatter and is based on the decomposition-products of this substance. They are
1. MeihylsuccirdmidCj (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:
CgHisON-HaO = CgHigX.
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 (III.), 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— COv /\
CH2 CH2 CH2V
III. I \co.
CH2 — CH2 — CH2
* Cf, footnote, 395.
586 ORGANIC CHEMISTRY. (§§ 412, 413
Cocame, C17H21O4N.
' 412. On account of its use as a local anaesthetic, cocaine is the best known of the alkaloids present in coca-leaves {Eryihroxylon 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.COCeHs.
CH2»CH CH2 CH2»CH CH2
I. II.
By bcnzoylating and mcthylating ecgonine, cocaine is regenerated. Ecgonine is a tropinecarboxylic acid.
Morphine, C17H19O3N.
413. Morphine is the longest-known alkaloid : it was obtained from opium in 1S06 by Sekturxer. Opium is the dried juice of the seed-capsules of Papaver somniferum, a variety of poppy. It is a very complex mixture, containing caoutchouc, fats, resins, gums, sugars, proteins, mineral salts, meconinic acid,
(CH30)2C6H2 (CH2OH) (COOH),
some more organic acids, and other substances, together with numerous alkaloids. Twenty of the last-named have been identi- fied : of these morphine is present in largest proportion, and con- stitutes about 10 per cent, of opium.
Morphine is cr>'stalline, and melts with decomposition at 230°. It is slightly soluble in water, is without odour, and is employed as an anodvne and narcotic.
The reactions of morphine indicate that one of its three oxygon 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 phenanthreno, Ci 41110, so that the empirical formula may Ik* expanded to
C',7n,.j<)3X = C:,H,oX[CH][01[On][HOH].
§ 413] ALKALOIDS. 587
Treatment with methyl iodide in alkaline solution methylates the phenolic hydroxyl; the simultaneous addition of methyl iodide at the nitrogen (I.) proves morpliine 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-methylmorphiffiethine (II.). On heating with acetic anhydride, methylmorphimcthine yields a product free from nitrogen (III.), and one containing nitrogen (IV.) The first is methylmorphol or ^'hydroxy-S'tnethoxy-phenanthrene, convert- ible by further methylation into a synthetic product, dimethyl- morphol (386), a reaction indicating its structure. The second is hydroxy ethyldlmethylamiixe, CH2OH • CH2 • N(CH3) 2 :
CH30»CoH2 — CH2 CH30»CtiH2 — CH
04 I ^04
HO.CeH— CH. /I HO-CeH— I >N^CH3 I
CH2— CHo^ \CH3 CH2 — CH2-N(CH3)2
I. II.
^"t?^> CeH2-CH
H
HO
C6H4-
1— CH III.
HO.CH2^H2-N(CH3)2 IV.
By combining these facts with others it has been poesible to assign provisionally to morphine the structural formula
H
ho/\h
AA.H2
O I jH
.KD-™'
HOH ^jj. H2 H2
It represents morphine as a combination of a partially hydro- genated dihydroxyphenanthrene containing an ether-linked oxygen
588
ORGANIC CHEMISTRY.
[§414
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 undergoing hydrolytic dissociation. It con- tains three methoxyl-groups, and has formula I. Nomarcotine has the formula Ci9Hi404N(OH)3. On hydrolysis, narcotine yields cotarnine (II.), a derivative of isoquinoline, and the anhy- dride of meconinic acid, or meconin (III.) :
CH2<(
OC-C
OCH3 C OH-
■CH
OCC
CH2 CH CH2
CH3 O-OC-C CH3O.C
A.CH
I.
Narcotine
C 6CH3
OCH3
C CHOH
0 CH2
c
OH:
<
OC-C
CHsO-C
c
CH
OC.c/\/^ (.jj 0C-C/\CH
CHa
CH CHa
OGHa II. III.
Cotarnine Meeonin
Bromine converts narcotine into dibromopyridinQ.
1415]
ALKALOIDS.
5S&
415. The barks of certain trees of the Cinchona and Remya famiiies contain a great number of alkaloids: of the>e twenty-four have been isokted, but it is probable that nK^re are present. The most important of them, on account of its anti-febrile effect, is quinine. Cinchonine. C19H..2OX2, is the next best-known: its physiological action is similar to that of quinine, but is less pro- nounced.
In addition to alkaloids, these barks contain \-arious acids, such as quinic acid, quinovic acid, and quinotannic acid: neutral sub- stances, such as quinovin. quina-red. etc.. are also present.
Quinine is ver>- slightly soluble in water, and is Uevo-n>tatorL-. In the anhydrous state it melts at ITi^, and at 57^ when it cv>n- tains three molecules of water of cr\'stallization. It is a strong base, and both X-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 ser^-es as a test for the base.
The constitution of quinine has been elucidateil, chiefly through ibe researches of Skr.vup and of Koxics, the latter assigning to it the formula
n.
CH
HoC^ ^.pj VH-C'HtCHa
CH C CH.OH
CH30.c/''?^CH
I.
HC
w
CH
which expresses the following properties of quinine. On fusion with potassium hydroxide quinine yields quinoline, p-fncthyl-
590 ORGANIC CHEMISTRY. I§416
quinoline or lepidine, and p-methoxyqmnoline from the part of the molecule numbered I. in the structural formula; and ^- ethylpyrldine from part II. On oxidation, a/?^-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.
Strychnine, C21H22O2N2.
416. Three extremely poiisonous alkaloids, strychnine, brucine, and curarinCj are present in the seeds of Strychnos nux vomica^ as 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, pR^edeil by tetanic spasms — that is, contraction of the muscles; ounirine is, therefore, employed as an antidote.
Strychnine is crystalline, and melts at 263° ; it is almost insoluble in water. It is a moiiohydric, tertiary base, only one of its X- atoms exhibiting basic properties. On fusion with potassium hydroxiile, it yields (juinoline and indole; and when distilled with slaked lime, it is converted into ,.?-picoline (380). Heating with zinc-ihist prtxhices carbazole (382) and other substances.
W. If. Pkhkix. jux., and Robixsox consider the chemical
properties of strychnine to be n^presented most completely by
the formula
nio CH
CH CH
I I
CH CH CH>.
X c en CH>
I I CO X en CH>
CIL> CH-OH
Rruoine rii::ors ::\v.n strychiiine i:i haviir^ nK-thoxyl-grx^uckS as ^u^^:ituol;:^ in i:'0<i:ioii< 1 and 4.
lolthei
n old-style Bgun
tbb index ii imbLguLty n.
(1| The numl
(2) loallinBl,. they nrB ijved m ol
(3) When ■ f
by B hypbtn arc treated a^ word:
A.
AbbreviBtcd thermometers, 32. Abel, Sir Frederfck, 38. Absolute alcohol, 56. Acetal, 254, 255.
Chloro-, 298. Acetaldehyde, 67, 132, 133, 137-140, 143-145, 166, 175, 177, 179, 182, iSg, 105. 227, 228, 231, 254. 255, 26S, 3U0, 316, 416. 485, 524, 55S. -ammonia, 137, 557. Syiithi---iis of. 189. Awtiils, 137-138, 185, 280. Acetamidc, 128.
hydri>chloride, 128. Acetaminohydrazobeitzene, p-, 409. Acetates, 112.
Acetic acid, 2, 15,54,59,93, 105, 106, 108, iio-ii>, 117-123, 125, 132, M-,. 172, 188, 189, 192, 203, ^■-'", 'i'i^, 225, 2.52, 300. 302. :jiil, 107, 420, 421, 429, 444, .1S4, /,iili. S78. Glacial. Hi, 30. 1 [1,402,541. Chloro-, 202. 20:5, aao, an, 226,
316, 31S. 3I'J, .^79. Synlhi^ia of, ISO. anhydridp, lao, 136, 138, 191, 192, 260. 277, 295, 431, 444, 472, 485, 56S, 583, 587. fermentation, 286. Acctoacctie acid, 301. osier. Sefl ethyl aecloacelaU. sj-nthesis, 301-304. Acetoanilide, 402, AOH. 4.'>9. A cctobromo dextrose, 277. Acetoferric uectute, 112, Acetone, 16. 54, 59. «0, 8.5, 99, 132, 13.1. IJ.'i. 146, 153, 1.54, 100-162, 105, 166. I77, 17B, 181, 182, 186, iSg, 2:1:1, 297,300,302,310,311, 387. 513, 531. Synthesis of, 189.
Acetonitrile, 103.
Ace (Anuria, 146.
Ace tony lacetone, 354, 304, 567.
Acetophenone, 439, 443, 472.
Acetoxime, 135, 310.
hydrochloride, 135. Acetyl-ftcetone, 353, 354, 307,
chloride, 119, lao, 121, 136, 249, 253, 300, 306, 349, 424, 429, 561. ' acid, 484,
-mesidine, 491,
-pheneiidine, 461.
-salicylic acid, 471. Acetylene, 158-161, 176, 183. 184, 189,341,387,443,566.
hromide, 166.
-ilicarboxyhc acid, 216. Acid-nlhiiinms. Sec meta-protam.
anhydrides, 120, 208, 209.
nzidcs, 139, 358, 359.
chlorides, 119. lao, 12S, 133.
dcconi|>osition, 301, 302, 303.
hydra lidca, 129.
-ureides. See wrtdea. Acids, Ci,H,nO,, 105-118. 130, 169. 191, 192.
CnHjo-iO,, 169-173.
CnH,-,0,. 173, 174.
C,II/)i, 171. Ac idyl lily collie acid esters, 323. A ci-modlfi cations, 439. Aconitic aeid, 218.
Acraldehyde, 167, 175, 176, 189, 190, 202, 263. 557, 570, 672.
-acetal, 176.
-ammonia, 175, 557.
•anihne, 572. AcrolclTi. See acraldehyde. Arrose, 263.
Acrvlic acid, 107, 169, 170, 175, 317. Adilit ion-react ions, 229. Adipic acid, 199, 501, 543.
anhydride, 377.
591
592
INDEX.
Adjacent compounds, 385. Adrenaline, 485. AgarictJL8 muscarius, 298. Aur-condenser, 21. Alanine, 316, 319, 334, 336.
d-, 322.
^. 322.
nitrile, 316. Albumin, 328, 333, 338. Albuminates. See meta-proleins. Albuminoids. See sclero-proieins. Albumins, 326, 328, 329, 330, 331,
332. Albumose, 329. Alcohol. See ethyl alcohol, Alcoholates. See alhoxides. Alcoholic fermentation, 54, 268, 269,
285-288, 320. Alcohols, Aromatic, 441.
CnHzn+i^OH, 49-66, 77, 78, 80, 83, 86, 119-121, 128, 129, 147. Higher, 66. Aldehyde. See acetaldehyde,
-resin, 139, 140.
sulphite compounds, 134. Aldehydes, 130-145, 148, 159, 183,
185-187, 198, 224, 259, 310, 374,
4126-428. Aldehydo-acids, 299.
-alcohols. See sugars, Aldohexoses, 257, 259, 273. Aldol, 139, 140, 176, 267. Aldopentoses, 273, 274. Aldoses, 257, 258. Akioximes, 135, 136. Alicyclic compounds, 157, 373, 375-
379. Aliphatic compounds, 34, 35-371.
Alizarin, 544, 548-550.
diacetatc, 549. Alkali-albumins. See meta-proteins. Alkaloid-reagents, 582. Alkaloids, 288, 474, 582-590. Alkoxides, 49, 66, 67, 74, 78, 106, 147. Alkyl-anilines, 406.
-groups, 37.
halides, 69-72, 74, 78, 83, 84, 96, 97, 147, 153, 165, 179.
-hydrazines, 88.
magnesium halides, 100, xox, 105, 122, 135, 314.
nitrites, 91.
-nitroiic acids, 93.
-sulphiiiic^ acids, 80.
-sulphonic acids, 80.
Bulphonyl chlorides, 80.
-sulphuric acids, 72, 73, 79, 149.
-ureas, 355. Alkylcnes. See olefines.
Allanto!ne, 363, 364. il^cinnamic acid, 445. Allotropy of carbon, 19. Alloxan, 362-364, 366. Alloxantine, 363.
AUyl alcohol, 165, 166, 167, 168, 175, 184, 188, 189, 190, 195. -aniline, 572. bromide, 166, 183, 184. chloride, 165, 166. iodide, 166, 168, 169, 171, 189, 190. isothioc^anate, 348. magnesmm bromide, 171. sulphide, 168. Allylene, 157, 158. Aluminium acetate, xx2, 465. acetylacetone, 254. melhtate, 481. Amber, 205. Amic acids, 202. Amidines, 129. Amidoximes, 129. Amine hydrohalides, 84. Amines, 82-9X, 95, X36, 395, 401-412,
479. Amino-acetal, 298. -acetaldehyde, 298. -acetic acid. See glycine, -acids, 316-323, 334. Di-, 334.
Dibasic mono-, 334, 336. Hydroxy-, 334. Monobasic mono-, 334. -alcohols, 197. -aldehydes, 298. -anthraquinone, 2-, 551. -azo-dyes, 466.
-benzene, 419, 420, 462-464, 466, 467. -barbituric acid, 364. -benzenesulphonic acid, p-. See
sulphanilic acid, -benzoic acid, o-. See arUhraniUc acid, acids, 475, 476, 495. -benzoylformic acid, o-, 576, -butyric acid, 7-, 317.
Lactam of 7-, 317. -caproic acid, ae-. See lysine, -chlorides, 128, 129. -cinnamaldehyde, o-. 573. -cinnamic acid, o-, 575. -glutaric acid, a-, 320, 331, 334, 336. -guaniciinc, 361. -6-guanino-n- valeric acid, or-. See
arginine. -i«o-butylacctic acid. See leucine, -ketones^ 298. -mandehc acid, o-, 576.
INDEX.
593
Amlno-/3-methylvaleric acid, or-. See idoleucine. -naphthalene, 489, 490. -naphthol, 1 : 2-, 541. -nonolc acid, 9-, 174. -phenol, 0-, 461.
P-, 411, 453, 457, 460, 461. -phenols, 461. -phenyl-acetic acid, 0-, 576. -arsinic acid, p-, 461, 462. -p-acetaminophenylamine, p-, 409. -propionic acid, a-. See alanine,
/3-, 317. Hsuccinamic acid. See aaparagine. -succinic acid. See aspartic acid. -thiophen, 568.
hydrochloride, 568. -valeric acid, a-, 334. Ammonium carbamate, 358. cyanide, 342. formate, 341, 342. wo-cyanate, 354, 355. oxalate, 202, 340. picrate, 452. succinate, 209. thiocyanate, 360, 361. Amygdalin, 342, 427. Amyl acetate, tso-, 121. alcohol. Normal, 51, 52, 78, 147,
309, 505, 542. alcohols, 51, 54, 63, 63, 64, 390. bromide. Normal primary, 71 chloride, Normal primary, 71. iodide. Normal primary, 71.
Optically active, 63, 64. Movalerate, wo-, 121. nitrite, 252, 518. -sulphuric acids, 151. Amylene, Normal, 148. Amylenes, 147, 148, 151, 153. Amylocellulose, 291. Amyloid, 395, 296. Amrsthetics, 180. Analysis, Example of, 10, 11. , Angehc acid, 169. Anhydro-bases, 461.
-formaldehydeaniline, 403. Anilides, 402.
Aniline, 259, 266, 296, 396, 403, 404, 405, 412, 414, 419-422, 428, 434, 457, 459, 460, 463, 495, 529, 530, 543, 572, 579. -black, 463, 464. -blue, 530.
-dyes. See coal-lar colours. hydroarsenate, 461. hydrochloride, 404-406, 419, 420, 530.
Aniline hydrogen sulphate, 462.
nitrate, 413.
-yellow, 466, Ammal fats, 34, 113-115. Anisanilide, 433. Anisole, 400, 401. Anschutz, 545. Anthracene, 534, 544, 546, 548, 549.
-oil, 389, 534, 544, 551. Anthranilic acid, 475, 476, 492, 579,
580. Anthranol, 548. Anthraquinol, 547, 548.
Disodium derivative of, 547. Anthraquinone, 545-548, 549, 550, 581.
oxime, 547.
-sulphonic acids, 549. An throne, 548.
Antifebrine. See aceloanUide. Antimony pentamethide, 97. Antipvrine, 570. Antiseptics, 182, 400, 471. Apiose, 277. Apricot-stones, 265. Arabinosazone, 265. Arabinose, 262, 264, 265, 275-277, 287, 288, 298.
-methylphenylhvdrazone, 273. Arabitol, 193, 262^ 265. Arabonic acid, 265. Arginine, 334, 336, 361. Argol, 238. Armstrong, 397. Aromatic compounds, 34, 373, 380-
553- " Arsacetin," 462.
Arsenobenzene, 434.
ArSines, 95, 96.
Arsinobenzene, 434.
Artificial camphor, 517.
Aspara^ine, 245, 287, 320.
Aspartic acid, 320, 331, 336.
Asperula odoraUif 484.
Asphalt, 39.
*' Aspirin.'* See acelyhalicylic acid.
Asymmetric carbon atoms, 64, 65,
321, 322.
nitrogen atoms, 98, 99.
silicon atoms, 97.
sulphonium compounds, 93i 99.
sulphur atoms, 98.
synthesis, 288, 289.
tm atoms, 100. Atomic refraction, 157. Atoms, Law of the even number of,
46. " Atoxyl," 462. Atropa belladonna J 584.
594
INDEX.
Atropine, 584, 585. AutogcDouR welding, 161. Auxochromeic groups, 464, 465. Azelaic acid, 173, 199. Azo-bcnzene, 408, 409, 411, 412, 434, 464.
-dyes, 460, 464-468. Azoxy-benzene, 408, 411, 412.
-phcnetole, p-, 408. Azulminic acid, 341.
B.
Bacillus acidi lavolacticij 247. Badische Anilin- und Soda-Fabrik,
579. Baeyer, von, 148, 156, 209, 216,
263, 314, 381, 428, 455, 508, 527,
564, 572, 575. Balsam of Peru, 423.
Tolu, 380, 423. Baly, 464. Bamberger, 412. Barbituric acid, 364. Barium acetate, 172.
carbide, 342.
cyanide, 342.
ethoxide, 67.
ethylsulphate. 73.
stearate, 172.
thiocyanate, 346.
trithiocarbonate, 352. Baumann-Schotten reaction, 425. Baxjmhaier, von, 57. Beck.mann, 136.
-transformation, 136, 174, 346, 433. Beer, 56, 110. Beeswax, 122. Behenolie acid, 222. Beilstein's test, 5. Benzal chloride, 426, 438, 444, 525. Benzaldehvde, 277, 342, 411, 422, 424, 426-428, 440, 441, 443, 444, 507, 526, 533, 562.
-ammonia, 427.
-phenylhydrazone, 428. Benzaldoximes, 431. Benzaiaide, 423, 425, 426. Bonzanisid<», 433. Benza^/'uldoximo (a), 431, 433. Benzene, IT), 30, 34, 101, 1(30, 333,351, 373; 37S, 380-391, 303, 395, 477. 430, 43(1, 4}r) 4.")2, 457, 462, 47(>, 495, 496. .")()!, .">().">. 507, 524, 525, ')3.'), .")!."), .")4(), 552, .'").')7, 500- 5GS.
<'(»ii>tituti()ii of, 3sO 3^4.
-(lia/.(>li>ili().\i(i(*, 419.
-<li:i/(»niuiii <lilnridt', 416-421, 405, 400, M\, bijb.
Bcnzene-diazonium hydroxide, 410, 414,415,419. nitrate, 413, 414. sulnhate, 416. -sulphonic acid, 460. xanthate, 417. -disulphonic acid, rw-, 450, 452. o-, 450. P-, 450. Molecular weight of, 11. -sulphonamide, 398. -sulphonic acid, 386, 397, 417, 505,
518, 568. -sulphonyl chloride, 397, 398. -^yndiazo-chloride, 418. -hydroxide, 415, 418. Benzhvdrol, 429.
Benzidine, 409, 523, 524, 539, 540. -diazonium chloride, 540. sulphate, 409. -transformation, 409, 525. Benzil, 533.
dioximeS; 533. Benzilic acid, 533. Benzine, 38.
Benzoic acid, 29, 318, 333, 380, 431- 424, 425, 426, 428, 429, 437,
440, 441, 444, 468. 469, 498, 505, 507, 523, 530, 538, 564.
anhydride, 425.
iminoether, 425.
sulphinide, o-. See *' saccharin.** Benzoin, 533, 562. Benzo-nitriie, ^22, 426, 431, 441, 555.
-o-sulphami(le, 469, 470.
-phenone, 429, 430, 524. -oximes, 431.
-purpurins, 539, 540.
-quinone, 454, 457-459, 460, 464, 494,507, 526,540,511. dioxime, 458. mono-oxime, 453, 458.
-trichloride. 422, 438. Benzoyl-benzoic acid, o-, 546.
chloride, 423-425, 429, 438, 485.
-formic acid, 289.
-hydrogen peroxide, 428.
-piperidine, 555.
-serine, 335. Benzi)inac()ne, 429. Honz.s7//<:ildoxime (/3 or iso), 431, 433. Benzyl alcohol, 422. 42(), 427, 441.
-amine, 43S, 441. 442, 543.
bromide, 43r), 4'i7.
chloride, 430, 436, 437, 438, 4i0,
441, 524. 532. evanide. 4 M). h'dides, 43t')-43S. iodide, 437, 438.
INDEX.
595
Benzylidene-aniline, 428.
-phenylhydroxylamine, 411 Bernthsen, 527! Berthelot, 2, 28, 122. Berzelius, 1. Betaine, 318, 319, 582. Betaines, 319. Beyerinck, 286. Bimoleoular reactions, 85, 125, 126,
256. Bioses. Sec dioses. BiOT, 63.
Blsmarck-brown, 466, 467. Bismuthines, 97. Bismuth mercantides, 70. Bismuthonium oases, 97. Bitter almonds, 342, 396, 427. Biuret, 327, 356, 357.
-reaction, 327, 329, 330, 333, 338,
356.
Blasting; j^elatine, 193. BOESEKEN, 429.
Boiling-point apparatus, Eykman's, 17, 18. Determination of, 31. BONDT, 184.
Borneo camphor. See homeol. Borneol, 518, 520. Bornyl fumarate, 289.
pyroracemate, i-, 289. Brain-substance, 197. Bran, 265.
Branched chains, 45. Brand V, 56.
Brassidic acid, 173, 221, 223. Brassy lie acid, 199. Braun, vox, 555. Bredig, 323. Bredt, 520.
Brimtit effect, 193, 296, 349. Bromination-method of Victor
Meyer, 1S3. Bromlauge, 104, 357. Bromo-acetald(»hyde, 262.
-acetic acid, 220.
-acetyUdene, 166.
-anlhra(iuinone, 546.
-benzene, 11, 381, 386, 389, 394, 395, 404, 405, 416, 417, 422, 435, 449, 45)"), 538. -sulphonic acids, 449.
-benzoic acid, w-, 468. P-, 468, 492, 493.
-benzophenone, 431.
-benzovlbenzoic acid, 546.
-butylene, Mono-^ 154.
-camphorsidphonic acid, 99.
-erucic acid, 222.
-ethylamine, 479.
Bromo-fumaric acid, 214, 215.
-wobutyric acid, 171.
-maleic acid, 214. anhydride, 215.
-malonic acid, 232.
-naphthalene, a-, 538.
-phenol, 0-, 450, 498. «-, 450, 498.
-phthaHc anhydride, 546.
-propionic acid, a-, 229, 322.
-propylene, /3-, 166.
-succinic acid, 210.
-thiophen, 567.
-toluenes, 437. Bromoform, 181. Brucine, 590. Bruhl, 157. Bruyn, Lobry de,.67. BucHNER, Eduard, 285, 286. BuNSEN, 97, 357. Butane, 36, 37, 41, 42, 46.
cydo-, 375, 376. Butanol, cyclo-j 376. Butanone, cyclo-y 376.
BUTLEROW, 154.
Butt<ir, 113.
of antimony, 380. Butyl-acetylene, 158. alcohol, W0-, 51, 52, 60. Normal, 51, 52, 60. Secondary, 51, 52, 60, 125. -amine, w-, 87.
cyclo'f 376. bromide, cyclo, 376.
Normal primary, 71. bromopropionate, iso-^ 230. -carbinol, i67>-, 51, 62, 320. Secondary, 51, 62, 320. Tertiary, 51. -carboxylic acid, cydo-^ 376. chloride, Normal primary, 71. derivatives, cyclo-, 375, 376. -dicarboxylic acid, cyclo-, 375. -group, 37. iodide, iso-, 153.
Normal primary, 71.
secondary, 193. Tertiary, 149, 153. -sulphuric acid, Tertiary, 149. Butylene, cyclo-^ 376. ?.so-, 149, 153, 154. Normal, 148. pscudo-, 220. Butyraldehyde, Normal, 131. Butyric acid, iso-, 113, 220, 224, 515. Normal, 107, 108, 113, 118, 139, 170, 171, 260, 269, 333. fermentation, 269.
596
INDEX.
Butyrolactone, 226, 231. ButjTyl chloride, Normal, 131. -group, 109.
C.
Cacodyl, 97.
chloride, 97.
oxide, 97.
-test for acetates, 97, 112. Cadaverine. See pentamethylenedia"
mine. Cafifeine, 365, 366, 367-369, 582. Calcium acetate, 54, no, 132, 146, 189.
acetylene. See calcium carbide,
adipate, 376, 377, 503.
benzoate, 380.
carbamate, 358.
carbide, 161, 162, 348,
citrate, 248.
cyanamide, 348.
diphcnate, 524.
etnylsulphate, 72.
glycollate, 226.
-ifiobutyrate, 114.
-n-butyrate, 114.
oxalate, 206.
pimelate, 503.
salicylate, Basic, 471.
suberate, 378.
succinate, 206.
tartrate, 238. Calculation of formuke, 9-18.
percentage-composition, 9-1 1 . Calico-printing, 112, 249. Camphane. 516, 517, 520.
-group, 518. Camphor, 518-521.
-odour, 518.
-quinone, 519.
Synthesis of, 520.
-sulphonic acid, rf-, 99. Camnhoric acids, 519, 521.
anhydride, 519. Camphoronic acid, 519-520. Camphorj?, 37S, 392, 503, 518-521. Cane-sugar. Sec sucrose. Caoutchouc, 162, 184, 352, 521, 522,
586. Capric arid, 108. 145, 172, 303, 507. Caproio arid, 108, 113. Caprylic arid, lOS. Caprvlonitrile, 104. (\iranicl. 279. Caraiic, .OK), 517. (^arhaniic acid, 35^. CaH)ainyl chloride, 423. Carbamide. iSce urea.
Carbazole, 544. 590.
Carbides, Metallic. See meUdlie acet*
ylenes. Carbinol. See methyl alcohol, Carbinols, 52. Carbocyclic compounds, 373, 375-
553. Carbohydrates. See sugars. Carbolic acid. See pherud,
oil, 389, 398, 534. Carbon chains, 45, 46.
disulphide, 28, 181, 309, 352, 353,
544, 567. oxy-chloride. Sec carbonyl chloride, • -sulphide, 347, 348, 353. suboxide, 205. tetra-bromide, 36, 179. -chloride, 36, 179, 181. -fluoride, 393. Carbonic acid, 351.
esters, 352. Carbonyl cnloride, 180, 312, 351, 354, 407, 422, 423, 429. -haemoglobin, 332. Carbostyril, 575. Carbylamines. See isonitriles, Carbylamine-test, 104, 403. Carius, 8. Carone, 517. Carvacrol, 514, 520. Carvone, 514, 515. Carvoxime, 515. Casein, 328, 335, 336. Caseinogon, 328. Castor-seed, 114.
Catalytic action of aluminium halides, 430, 437. antimony pentachloridc, 184. calcium chloride, 144. copper, 133. ferric halides, 183, 393, 437,
446, 468, 498. hydrogen ions, 323. mineral acids, 125, 138, 144,
145. nickel, 35, 134, 151, 505. ])alladium, 505.
rhodium and other platinum- group metab, 110. sulphuric acid, 144, 145. Catechol, 453, 454, 458, 473, 485, 550, Catechu-tannin, 474. Cayley, 47. (Vllose, 295. Celluloid, 296. Cellulose, 294-297. ( Vtyl alcohol, 06.
CllATTAWAY, 350.
Chelidoiiic acid, 311, 312.
INDEX.
597
Chelidonium majus^ 311. Chemical reduction-products, 410. Chemistry of silicon, 97. Cherry-gum, 265. Chevreul, 115. Chitin, 298. Chitonic acid, 298. Chitose, 298.
Chloral, 58, 179, 221, 254-256. alcoholatc, 255.
hydrate, 254, 255, 256, 299, 305. Chloro-acetic acids, 221. -acetone, 153, 158, 164. -acetyl chloride, 485.
-catechol, 485. -aniline, wi-, 493.
P-, 418, 463. -benzene, 386, 394, 416, 418, 447, 449, 498, 538. -sulphonic acid, p-, 449, 460. -«2//idiazocyanide, p-, 419. -benzoic acid, w-, 468. 0-, 468. P-, 422, 468. -benzonitrile, p-, 418, 419. -benzophenone, 431. -but>'ric acid, a-, 220. /3-, 220. 7-, 220. -butyronitrile, 7-, 321. -caffeine, 368. -carbon, 447. -carbonic esters, 352. -cyc/ohexane, 506. -other, 195. -ethers, 195. -formic esters. See cKiorocarhonic
esters. -methylene, 180. -naphthalene, or-, 538. -nitro-aniline, 493. -benzene, w-, 447, 498. 0-, 447.
P-, 447, 493, 498. -phenol, 0-, 450, 498.
P-, 450, 498. -propionic acid, a-, 319. -propylene, a-, 164, 165.
/3-, 164, 165. -pyridine, 3-, 555, 566. -succinic acid, 233. rf-, 321. /-, 321. -toluene, o-, 436, 499. P-. 436. Chloroform, 16, 28, 58, 104, 179-181, 221, 255, 256, 342, 482, 483, 525, 566. 577. Chlorophyll, 564.
Chlorophyll-grains, 289. Chloropicrin, 360. Choline, 196, 197, 582. Chondrin, 328, 330, 331. Chondroitinsulphuric acid, 331. Chondrosin, 331. Chromogens, 464. Chromophore-groups, 464, 581. Chromo proteins, 329, 332. Chrysolaine, 466. Chrysin, 472. Cinchomeronic acid, 575. Cinchonine, 589, 690.
malate. 233.
mandelates, 441.
d-tartrate, 246.
/-tartrate, 246. Cineol, 511, 512. Cinnamaldehyde, 444. Cinnamic acid, 444, 445. AlU)', 445.
acids, iso'^ 445. Cinnamyl alcohol, 443, 444. Citral. See geranicU. Citric acid, 248, 249, 282, 584. Cilromyces glaber, 248.
pfeferianuSf 248. Claisex, 252, 253, 301. Classification of organic compounds,
34. Clupeine, 336. Coagulated proteins, 329. Coagulation, 326, 327. Coal, 158.
-gas, 35, 147, 158, 161, 388, 391 ' 534.
^mine-explosions, 36.
-tar. See tar. colours, 388, 404. Cocaine, 586. Cocoa, 366. Codeine, 587.
methyl-iodide derivative, 587. Coefficient of distribution, 29. Coffee, 366.
-tannin, 474. Cognac, 56. Coke, 388. Collagens, 330, 331. Collidine, 557, 558. Collidines, 557, 558. Collie, 313. Collodion, 296. Colloids, 326, 338. Colophonium, 480. Colour-bhdes, 528, 629. Combustion-furnace, 6.
of peat. 141. wood, 141.
598
INDEX.
Combustions, 5-7. Compound ethers. See eaters. Condensation, 140. Condensed rings, 373, 534. Confectionery, 268. Conglomerate, 247. Congo-dyes, 539, 540.
-red, 539, 540. Coniine, 558, 559, 582, 583.
iso-, 558. Conium maculatumy 583. Conjugated proteins, 329, 331, 332.
linking, 383.
system, 163. Constancy of substitution-type, Rule
of, 497. Constitutional formula, 44, 51. Constitution of alcohols,
Cnllzn+i- OH, 49-51. Contact-difference of potential, 371,
410,411. Copper acetylacetone, 254.
acetylene, 159, i6i.
disodium tartrate, 239.
mercaptides, 79.
-oxide test, 4.
-zinc couple, 150. Coral, 331. Corneiin, 331. Cotarnine, 588. Cotton. 294.
-wool, 295, 296. Coumaric acid, 483, 484. Coumarin, 484. Couniarinic acid, 483, 484. Crafts, 389, 390, 429. ''Cream of tartar," 238. Creosote-oil, 389, 398, 534. Cresol, m-f 509.
0-, 470, 499, 515.
p-, 333, 400. Crcsols, 398, 400. Crismer, 91. Critical temperature of solution, 90,
91. Croconic acid, 377. Crotonaldehyde, 140, 176.
-unimonia, 557. Crotonic acid, 169, 170, 171, 173, 174, 17r),j210, 212, 220,225. iso-j 171.
Solid. See crotonic acid. Crvoscopic nu'thods, 14-17, 338.
solvents. 14, 15, 10, 391. Crvst:illni<ls, 320. ('ry>tal-vi(»let, 528. Ciinifiic, '.\\)\. Cuprif cvariido, 310.
phciiylprupiolutc, 443.
Cupric xanthate, 353. Cuprous cyanide, 340.
xanthate, 353. Curarine, 590. Current-density, 207. CuRTius, 263, 323. Cyamelide, 344, 345, 350, 354. Cyanamide, 334, 348, 356, 360, 361. Cyanic acid, 344, 345, 346, 347.
W0-, 345» 354, 355. esters, 345.
wo-» 345» 346, 353, 355, 358. Cyanides, 340, 341, 342-344. Cyano-acetic acid, 202, 203. -benzoic acid, o-, 480. -hydrin-synthesis, 134, 135, 224, 227, 248, 264, 265, 270, 275, 276, 288, 303. -propane, a-, 184. -quinolines, 574. Cyanogen, 200, 340, 341. chloride, 345. derivatives, 340-350. Cyanuric acid, 344, 345, 349, 350, 354, 357. Insoluble. See cyamelide, ISO', 349, 350. bromide, 349. chloride, 345, 350. esters, 349, 350. ISO-, 345, 349, 350. Cyclic compounds, 34, 157, 254, 373-590. hydrocarbons, CnHin, 375-379, 503-505. Cymene, 380, 391, 392, 508, 509, 516, 521. m-, 517.
p-. See cymene. Cysteine, 335. Cystine, 335, 336.
D.
Datura stramonium, 584.
Davy, J., 351.
Decamethylenedicarboxylic acid, 199.
Decane, 41.
Definition of organic chemistry, 1.
Dchydromucic acid, 563.
Deiman, 184.
Dcnaturation of albumins, 326.
ethyl alcohol, 54, 58. Deoxy-raflVi no, 3()9. -coni[)Oun(ls, 3(»9. DeprcssinietiT, Kykman's, 16, 17. Depression of the freezing-point, 14^ 17. Molecular, 15, 16.
INDEX.
599
Desmotropy. See iauiomerism. 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, 57, 91. Determination of boiling-point, 31. melting-point, 31. molecular weight, 11-18. specific gravity, 32. vapour-density, 12, 13. Developers, 201, 455, 461. Dextrin, 291, 293, 294. Dextrins, 291.
Dextrose, 54, 227, 248, 266-269, 270, 272, 275, 277-279, 281, 284, 286-291, 295, 342, 470, 474, 548, 578. a, 267, 268. 281. /3-, 267, 268, 281. e-, 207, 268. Diabetes meUituSj 146, 266. Diacetoneamine, 145. Diacetyl, 252^ 300, 301. Diacetylcnedicarboxylic acid, 217. Dialdehydes, 250, 251. Dialkyl-phosphines, 1)5. -phosphinic acids, 90. Diallyl, 251. Diamines, 196, 209. Diamino-azobcnzene. See chrysmdine, -dihydroxyarsenobenzene, 462.
dihydrochloride. See salvarsan, -stilbone, p-, 532. -trihydroxydodecanic acid, 335. Diamylonc, lol. Diantliracene, 544. Diastase, 55, 277, 201. Diazo-acetic ester. See ethyl diazo- acetate. -aniinobenzene, 419, 420. -compounds, 323, 324, 413-420. ariti'^ 413, 418. syn-, 413, 417, 418. -hydrates, atiti-. See diazohy- drojrideSf anti-. Diazonium compounds, 398, 403,
413-420, 421. Dibasic acids, 198-217, 232-245,
470-481. Dibenzalci/f^hoxanono, 507. Dibenzhydroxamic acid, 438. Dibonzyl, 532, 533. -amine, 441.
Dibromo-acetic acid, 299.
-benzene, m-, 381, 446, 492. 0-, 381, 488. P-, 381.
-brassidic acid, 222, 223.
-butyric acid, 174.
-erucic acid, 221, 222.
-indigo. Symmetrical, 581.
-menthane, 514.
-menthone, 509.
-nitroethane, 93.
-propane, era'-. See trimethylene bromide,
-propane, of/3-, 184.
-pyridine, 588.
-succinic acid, 213, 214, 233. W0-, 213, 214, 215.
-thiophen, 567. Dicarbonyl-bond, 279. Dichloro-acetyl, 255.
-acetic acid, 220, 221.
-acetone, 248.
-benzene, m-, 446, 498. 0-, 498. P-, 463, 498.
-ethylene, 184.
-hydrin, Symmetrical. See glycerol dichlorohy drill. Didiphenylene-ethylene, 525. Dietnoxy-8-chloropurine, 2 : 6-, 368. Diethyl. See also ethyl.
-acetonedicarboxj'late, 455.
-acetylenedicarboxylate, 568, 569.
-carbinol, 51.
carbonate, 351, 354. 358.
c//cZobutyldicarboxylate, 375.
diacetylsuccinate, 304.
dibromomalonate, 305.
dihydrocoUidinedicarboxylate, 557.
disodiomalonat^, 203, 218, 375.
disulphide, 79.
ether. S(^i ether.
malato, 233.
maloiiato, 203-205, 455, 456.
mono.sodiomalonato, 203, 204, 200, 217, 218, 300, 321, 455, 480.
oxalate, 202, 312.
phlorogluoinoldicarboxj'latc, 456.
succinate, 207, 504.
succinylsu ccinate, 504.
sulphate, 72, 73.
-sulphonedimethylmethane. See sul phonal.
xanthocholidonate, 312. Dihydric alcohols. See glycols.
phenols, 453-455. Dihydro-cinnaraic acid o-carboxylic acid, 542.
600
INDEX,
Dihydro-naphthalene. See naphtha- lene dihydride. -pyrrole, 2:3-, 566. Dihydroxy-acetone. See glycerose. -acids, 233-245, 472, 473. -anthraquinone. See alizarin. -azobenzcnesulphonic acid. See
resorcin-yeUow. -benzene, m-. See resorcinol, 0-. See catechol, p-. See quincl. -flavone, 1 : 3-. See chrysin, -fluoran. See fluorescein. -naphthalene, 2:6-, 541. -phenanthrene, 587. -xanthone, 1:2'-. See euxanthone. Di-iodop urine, 367. Diwopropyl, 45. Diketo-cyc/ohexane, p-, 504, 506.
-piperazine. See glycine anhydride. Diketones, 250-254. Dimethoxyphenanthrene. See di-
methylmorphol. Dimethyl-acetylene, 160. -allene, 162. -alloxan, 366.
-amine, 84, 87, 142, 406, 407. -aminoazobenzene, 420, 465.
-sulphonic acid. See helianthine. -aniline, 405-407, 420, 427, 465, 626, 530. hydrochloride, 467. 0-0-^ 501. -arsinic acid, 96. -benzenes. See xylenes. -cj/cZooctadiene, 1 :5-, 521. -diethyhnercaptole, 146. -ethylcarhinol, 51, 162. -ethylene. Symmetrical, 148.
Unsymmetrical, 148. -hexane, 2:5-, 48. -ketone, 132. -morphol, 553, 587. oxalate, 202. -phenylpyrazolone. See antipy-
rine. -phosphinic acid, 96. -pyridines. See liUidines. -p\Tone, 312-314.
hydrochloride, 313. sulphate, 73, 87, 92. -thiophcn. See thioxen. Dinaphthol, a-, 539.
/3-, 5:^9. Dinit riles, 198.
Dinitrf honzonc, m-, 446, 448, 494. (>-, 4 IS, 449. P-, 44S. -cellulose, 296, 297.
Dinitro-compounds, 195, 196, 448, 449.
-diphenyldiacetylene, a-, 578.
-ethane, 439, 440. ad', 439.
-a-naphthol, 540.
-sulphonic acid, 540.
-phenol, 2 : 6-, 448.
-stilbene, p-, 633.
-toluene, 1:2:4-, 501. o-O', 501. Dioses, 257, 264, 276-289. Dioxindole, 576, 577. Diozonides, 251. Dipentene, 513, 514.
tetrabromide, 514. Dipeptides, 337, 338. Diphenic acid, 524, 525, 551. Diphenyl, 389, 409, 435, 523, 524,
551 652.
-amme, 402, 404, 405, 409, 530.
-ethane. Symmetrical. See di- henz7jl. Unsymmetrical, 524.
-ethylene. Symmetrical. See stU' bene.
-methane, 430, 524. Diphenyleneketone, 524, 525. Dippel's oil, 554, 564. Dipropyl, 44, 45. Direct dyes, 465. Dispersion, 34. Distearin, 192. Distillation, 21-28.
-apparatus, 21-24, 26, 27.
-flask, 21.
of wood, 53. Divi-divi, 473. Dodeca-hydronaphthalene, 541.
-methylenedicarboxylic acid, 199. Dodecane, 37, 41. Dodecyl-group, 37. Dorp van, 346, 475, 480, 575. Double bonds, 154-157. Drewsen, 572. Dry-cleaning process, 38. Dulcitol, 193, 194, 273. Dumas, 2, 7. Dutch liquid, 184. Duty on alcohol, 58. Dyers' broom, 472. Dynamite, 193.
E.
Earth-wax, 39. Khonito. See vulcanite. P^buUioscopio methods, 14, 16-18. solvents, 16.
Ecgonine, 586. Eder's solution, 202. Egg-albumin, 328.
-yolk, 197. Ebrlich, 320, 462. Eicosane, 41. ElMdic acid, 173, 174.
transformation, 173. Elftstin, jaS, 33(1, 331, 336. Electric conductivity, Molecular, 34.
Uectro-f,
Elements in carbon compounds, 3. Elevation of the boiling-point, 14,
16-18. Emulsin, 290, 34a, 440. Enantiomorphism, 346, 247. Enanliotropy, 430, 431. Engler, 39. Enolic form, 308-310. Ensilage, 227. Enzymes, 64, 192, 247, 269, 277, 385-
387. EoBin, 202, 478. Epichlorohydrin, 195. Equilibrium, 122-125. Ergot, 486. Errors in carbon -estimations, 9.
hydrogen-estimations, 9. Eruoic acid, 169, 173, 221, 222. Erythritol, 193. Erythrose, 276. Erythroxyhn coca. 586. Esterification, 121-125. Ester-method, Fischer's, 334, 335. Eaters, 68-73, "1. 130-137, 128. Estimation of carbon, 5-7, 9-11,
halogrnR, 8, 9.
hydrogen, 5-7,9-11. ions, 323.
nitrogen, 7, 8, 10, 11.
oxygen, 9-11.
I>bosph()riis, 8.
sulphur, 8. Ethane. 36, 37, 41-43, 95, 100, 151,
160, 183, 207. •tricarboxylic aci<), 206. Ethenylaminophenol, 461. Ether, 16, 28-30, 73, 74-76, 101, 150,
180, 195,309,314. Chloro-, 195.
-synthesis, Williamson'h 74. Ethcrw, 69, 74-76, 77, 78-80, 147, 400,
Ethylacetal«,107, I30, 131, 122-1 2S, 128, 253, 297, 301. 456.
acetoacetatc, 30i-3<»9. 557, 658, 570.
-acetylene, 158.
d-alanine, 322.
alcohol, 16, 30, 49-51, 51, 54-58, 67, fi9, 72, 74-76, 78, 91,110. 120-126, 12a, 137, 143, 150, 179-182. 187, 188, 195, 204, 250, 254, 255, 2(>6, 368, 269, 277, 299, 301, 304, 307, 309, 320, .349, 416, 425, 509. Test for. ^ri- ioila/orm-lest.
-amine, 87, 102, 103, 197, 407, 425.
-benzene, 389, 391. ,
benzoate, 433, 425.
bromide, 69-71, 73, 389.
n-butylacetoacetate, 303.
butyrate, 121,207.
cwbonate, 455.
-carbylamine, 102, 103.
chloride. 71, 180, 183.
chloro-carbonate, 217, 306, 351, 358, 423. -formate. See elkj/l cUorocar-
bonate. -oxalate, 426.
collidincdicaHMxylate, 557.
coppcr-acetoacetate, 312.
cyanide, 102, 103.
7-cyanopropylmalonate, 321,
cyan urate, 345.
diazoacetale, 333. 334. 378, 568, 569.
di-iodoacetate, 323.
ether. See ether.
formate, 531.
fumarate, 218, 324, 570.
-group, 37.
hydrogen sulphate. Sec ethyUul-
phurie aeiii iodide. 49, 64, 71, 72, 74, 80, 85,
91,96, 107,401. -^iodopropionatc, 510. uocyanate, 345. magnesium bromide, 101. maleate, 215. -mercaptan, 146. mesoxalate, 305. mcthanetricarboxylate, 217. methyl-n-butylacetoacctate, 303. monochloroacctatc, 206, 218, 304,
323.
;, 72.
602
INDEX.
Ethyl n-octylacetoacetate, 303. orthoformate, 180. phosphate, Normal, 72. potassium malonate, 207.
succinate, 207. psetu/ophcnylacetate, 378. -pyridine, a-, 585.
/S-, 590. -salicylic acid, 472. sodio-acetoacetatc, 301-304, 305- 309. -cyanoacetate, 510. sulphate, 72, 73. sulphide, 79. -sulphonic acid, 80. -sulphuric acid, 72, 73, 75, 150, 151, 397. Ethylene, 88, 148, 149, 150, 151, 152, 153, 183, 184, 186. -bromohydrin, 479. bromide, 150, 152, 158, 164, 167,
184, 206. 375, 479. chloride, 152, 183, 184, 187, 188. cyanide, 206. -diamine, 196.
oxide, 187, 188, 197, 209, 561. Ethylidene chloride, 133, 152, 158. Eugenol, 483.
M0-, 482. Euxanthone, 472. Exaltation of refraction, 521, 543,
544. Extraction with solvents, 28-30. Eykman, 15-17.
F. Fffices, 577. Faraday, 391. Fats, 2, 39, 114, 115, 116, 172, 184,
iQi, 192, 325, 586. Fatty acids, 105-107, 108, 109-118. compounds. See aliphatic com- pounds. Fehlinu's solution, 239, 240, 258,
331, 421. Fermentation, 54, 55, 285-288. butyric acid. See butyric acid, Normal. Ferric acetate, 264. Aceto-, 112. liasic, 112. succinate, 20(). thiocvanate, 347. Fihriii/,TJ8. FihriIU)^('n, 328, Fil^roiii. 331, 3i^6, 338. Filtcriim-fla.^k, 30. Filtration, 30.
Fire-damp, 35, 36.
Fischer, Emil, 234, 272, 277, 280,
286, 288, 298, 322, 334-338, 365,
367, 368, 474, 479. FiTTiG, 226, 389, 394. Fittig's synthesis, 389, 394, 538, 567. Flash-point, 38.
apparatus of Abel, 38. Flavone, 472.
dyes, 472. Flax, 295. Fluoran, 478. Fluorene, 524, 525. Fluorescein, 478, 479. Fluoro-benzene, 497.
-nitrobenaene, o-, 497. P-, 497, 498. Force, Vital, 1. Fonnaldehyde, 54, 88, 132, 141-143.
263, 283, 403. Formaldoxime, 143. " Formalin." See formaldehyde. Formamide, 128. Formates, 109. Formic acid, 102, 108-110, 112, 118,
141, 142, 145, 176, 180. 190, 191,
200, 255, 269, 344, 349, 391, 563. Formonitrile. See hydrocyanic add. Formose, 263.
Formulae, Calculation of, 9-11. Formyl chloride, 427.
-group, 109. Fortified wines, 56. Fractional crystallization, 30.
distillation, 22-26. curves, 25. Fractionatinp-apparatus, 21.
-columns, 23, 24, 55. Franciiimont, 355, 405. Friedel, 189, 389, 390, 429.
and Craft's synthefsis, 389, 390, 429, 538. Fructosiizone, d-. See d-glucosazone. Fructose, c/-. See Icevulose. Fruit -esse noes, 121.
-sugar. See Icendose. "Fulminating mercur>','* 349. Fulminic acid, 349. Fumaric acid, 210-215, 218, 233, 243,
244, 484. Puran, 374. 561, 562, 566. Furfural. See furfurahhhyde. Furfuraldeliyde, 266, 562, 563. Furfuraniido. r)()2. Fu rf u ra n . Sec fu ra n . Furfuroin, o{V2.
Furfurolc. S(»e fur fur aldehyde. Furfuryl alcohol, 502. Furs, 455.
INDix,
603
FiJRTH, VOX, 328.
Fusel-oil, 55, 58, 60, 62, 151, 320.
G.
Galactonic acid, cf-, 273.
Galactose, d-, 194, 265, 273f 278, 287,
290. Gallic acid, 455, 473, 474. Gall-nuts, 473, 474.
-stones, 335 Gas, Coal-, 35, 147, 158, 161, 388,
391, 534. Gas-manufacture, 388. Gastric juice, 333. Gattermann, 416, 482. Gaultheria procumbenSf 470. Gelatin, 143, 328, 330, 331, 336, 474. Gclatose, 329. Geranial, 176, 177. Geranic acid, 176. Geraniol, 176, 509, 510. Gerhardt, 2. Germanium alkides, 97. German process for vinegar, 110. Gernez, 63. Gin, 56.
Glacial acetic acid, 30, xix, Gladstone, 150. Gliadin, 328. Gliadins, 328. Globin, 332.
Globulins, 328, 329, 330. Globulose, 329.
Gluconic acid, d-, 267, 272, 278, 279. Gluco-proteins, 328, 329, 332. Glucosamic acid, d-, 298. Glucosamine, 298.
hydrochloride, 298. Glucosazone, d-, 267, 270, 271, 273. Glucose, d-. See dextrose.
t-, 266.
/- 266 287. Glucosides, 277, 279-281, 342, 470, 548, 578.
Artificial, 279-281. Glucosone, d-, 271. Glue, 318. Glutamic acid. See aminoghUaric
acidy a-. Glutamine, 320. Glutaric acid, 199, 208, 265, 377.
anhydride, 208. Glutelins. 328.
G4yceraldehyde, 262, 263, 272. Glyceric acid, 188, 300. Glycerol, 54, 114, 115, 175, 188-193, 194, 195, 262, 268, 572.
Glycerol-dichlorohydrin, 195, 248. Glycerophosphoric acid, 197. Glycerosazone, 262. Glycerosc, 262. Glyceryl diacetate, 192.
monoformate. See monoformin.
trinitrate. See nitroglycerine. Glycine, 224, 316, 317, 318, 319, 331, 334. 336-338.
anhydride, 337.
Copper salt of, 318.
ethvl ester, 323, 337.
hydrochloride ethyl ester, 318. GlycocoU. See glycine. Glycogen, 294. Glycol, 166, 186, 187, 188.
-chlorohydrin, 149, 187.
diacetate, 192.
diethyl ether, 187.
monoethvl ether, 187. Glycollaldehyde, 262, 334. Glycollic acid. 224, 225, 226, 232,
250, 270, 299. GlycoUide, 226, 232. Glycolose. See glycollaldehyde. Glycols, 185-188, 198, 209. Glycyl-alanine, 338.
-glycine, 336, 337. Glyoxal, 233, 250, 251, 299. Glyoxylic acid, 299, 305, 324, 363.
GOLDSCHMIDT, 420. GOMBERG, 531.
Gout, 365.
Granulose, 291.
Grapes, 266.
Grape-sugar. See dextrose.
Graphic method, Eykman's, 15.
Green oil. See anihracene-oil,
Griess 413
Grignard, ioO, 101, 105, 122, 135,
314. Guaiacol, 453, 454, 483. Guanidine, 360, 361.
thiocyanate, 360, 361. Guanine, 332, 365. Guanylic acid, 329. Gum-arabic, 265.
-benzoin, 380, 423.
Cherry-, 265. Guncotton, 193, 296, 297, 349«
H.
Haber, 412. Hsmatin. 332.
hydrochloride, 332. Hajmin, 332.
Haimoglobin, 329, 332, 336, 339. Haemoglobins. See chtomo'proteins.
604
INDEX.
Halochromy, 527. Halogen-benzenes, 393, 394, 437.
-benzoic acids, 437, 468.
-carriers, 393, 437, 446.
derivatives of methane, 179-182. homologues, 182-185.
-hVdrins, 195.
-phenols, 450.
-substituted acids, 219-223.
-sulphonic acids, 449.
-toluenes, 436. 437. Hambly, 354. Hantzsch, 413, 415, 418, 439, 528,
557. Hard water, 116. Harries, 251, 521. Hata, 462.
Heating substances, 20, 21. Heavy oil. See creosote oU, Helianthine, 460, 467. Heliotropin. See piperonal, Hempel, Fractionating column of,
23. Heneicosane, 41. Hentriacontane, 37, 41. Heptachloropropane, 181. Heptane, 4i> 64.
cyclo-j 505. Heptonic acids, 264. Heptoses, 257, 264. Heptyl alcohol, Normal, 52. Heptylic arid, 108, 303. Heroin, 588. Herrinp-brine, 87. Heterocyclic compounds, 373, 554-
590.^ Hevea hrasiliensis^ 521 . Hexa-bfomobenzene, 393. -chloro-benzene, 393.
-ethane, 181, 183, 184. -contane, 36, 41. -decane, 41.
-hydric alcohols, 258, 260, 261, 271. -hydro-benzoic acid, 505, 507.
-cymonc. See vienthane.
-phenol. See hexanol, cyclo-. -hydroxvbenzcne, 377, 457. -methylbenzene, 160. -methylene. See hexane, cyclo-.
-tetramine, 142. -mclliyltriaminotriphenylmethane.
See crystal-violet , -phcnvlothanc, 532. Hexane,\36. 41, 44, 45, 47, 80, 309. cydo', 37S, 381, 450, 503-506. derivatives, cyclo-, 378, 381, 503-
507. Hexanol, cyclo-, 506, 507.
Hexanone, cydo-^ 503, 504, 507.
Hexodioses, 257.
Hexonic acids, 258, 270-272.
Hexoses, 257, 259-261, 264, 265, 266-
276, 277, 286, 290, 304, 507, 563. Hexotrioses, 257, 289. Hexyl alcohol, Normal, 62.
iodide. Normal secondary, 260.
-methylamine, cyclo-, 379. Hexylene, 148.
Higher alcohols, CiiH»n+i»OH, 66. Hippuric acid, 318, 423. Histidine, 335, 336. Histones, 328. HoFF, van 't, 16, 64-66. HOFMANN, 83, 87.
Homologous series, 40. Honey, 269.
Artificial, 663.
-stone, 481. HooGEWERFF, 346, 475, 480, 575. Hops, 56. Hordenine, 486. Hormathic compounds. See aliphatic
compounds. Howard, 349. Humic substances, 273. Hydrazines, 420, 421. Hydrazinoacetic acid, 324. Hydrazo-benzene, 408, 409, 411, 412, 523.
-benzoic acid, w-, 524. Hydrazones, 136, 137, 258, 259. Hydro-aromatic compounds, 378, 387, 503, 522.
-benzamide, 427, 444, 562.
-benzoin, 533.
-carbons, CnHm, 76, 147-157, 164,
375-379, 503-507. CnH,n+2, 35-48, 148, 379.
CnHjn-2, 157-163, 165. -cinnamide, 444. -cyanic acid, 224, 228, 259, 277,
286, 298, 319, 333, 341, 343, 344,
347, 427, 482. -cyclic compounds. See hydro^
aromatic compounds, -ferrocyanic acid, 314. -naphthalenedicarboxylicacid, 535. -phthalic acids, 507. -auinone. See quinoL Ilydrolysis, 104. Hydrolytic dissociation, 115. Hydroxamic acids, 94. Hydroxy-acetic acid. See glycoUic
aril I. -acids, Dibasic, 232-248.
Monobasic, 223-232. -aldehydes, 481-483. -anthraquinones, 547-550.
INDEX.
C03
Hydroxy-azo-benzene, a-, 408. P-, 408, 420, 465. -dyes, 466. -benzaldchyde, p-, 482. -benzoic acid, rw-, 472. 0-. See salicylic acid, P-, 472, 492. -butyric acid, a-, 139. /3-, 169, 225. 7-, 226, 231. -cinnamic acid, a-, 483. -cymene, p-. See ihymoL -ethyl-am ine, 479.
-dime thy lamine, 587. -isobutyric acid, a-. 224. methyl-benzole aciS, o-, 477.
-furfuraldehyde, 563. -3-methoxyphenanthrene, 4-. See
methylmorphol. -phenyl-arsinic acid, p-, 462. -ethylamine, p-, 486. -propionic acid, p-, 483. -proline, 335. -propionic acid, a-. See lactic acid,
/3-, 225. 226. -propylene, /3-, 166. -quinoline, 2-. See carbostyrU. -quinolines, 574, 575. -stearic acid, 173. -succinic acid. See malic acid. -tetrahydiopyrrolecarboxylic acid.
See hydroxyproline. -toluenes. See cresols. Hyoscyamine, dl. See atropine. Hypnone, 429. Hypoxan thine, 332, 365.
I.
Imino-chlorides, 129.
-ethers, 129. Immiscible liquids, Separation of,
28-30. Increment for the double bond, 157. Indanthren-blue, 551.
dyes, 551. "Indian yellow." See euxanthone. India-rubber. Sec caoutchouc. Indican, 578. Indigo, 403, 428, 451, 475, 476, 575,
578-581. -brown, 679.
-sulphonic acids, 428, 579.
-vat-dyeing, 580.
-white, 580. Indigofcra arrecta^ 578.
sumatrnna, 578. Indiglucin, 579.
Indigoids, 581. Indigotin, 579. Indirubin, 579. Indole, 575-577, 590.
-alanine. See tryptophan.
-aldehyde, 3-, 577. IndolylbenzoylaminoacryKc acid, 577. Indophenin-reaction, 566. Indoxyl, 578, 579. Industrial spirit, 58. Infusorial earth. See kieaelgukr. Ink, 473. Inoculation, 245. Inositol, 507.
hexa-acetate, 507. Introduction, 1-34. Inulin. 269.
Inversion, 266, 279, 283, 284, 295. Invertase, 286. Invert-sugar, 227, 366, 269, 279, 284,
563. lodal, 181. lodo-acetic acid, 220.
-aniline, p-, 462.
-benzene, 393, 394, 523. dichloride, 394.
-butane, a-, 184.
-phenol, 450.
-propionic acid, ^-, 170, 317. Iodoform, 58, 181, 182.
-test. .58, 182. lodosooenzene, 394. lodoxybenzene, 394. lonization-constant, 117. lonone, 177, 178. Iron, Catalytic action of, 183, 393,
446. Irone, 178. Isatin, 576, 578.
chloride, 578. /so-amyl acetate, 121. wovalerate, 121.
-butyl alcohol, 51, 52, 60. bromopropionate, 230. -carbinol, 51, 62, 320. iodide, 153.
-butylene, 149, 153, 154.
-butyric acid, 113, 224, 519.
-camphoric acids, 519.
-cinnamic acids, 445.
-crotonic acid, 171.
-cvanic acid, 345, 354, 355. esters^ 345, 353, 355, 358.
-cyanuric acid, 350. esters, 345, 349, 350.
-dibromosuccinic acid, 213, 214, 215.
-eugenol, 482, 483.
-leucine, 319, 320.
606
INDEX.
i«a-maltose, 291. -nicotinic acid, 559, 560. -nitriles, 102-104, 180, 181. -nitroso-camphor, 518, 519.
-ketones, 252. -phenylacetic acid, 378. -phthalic acid, 480, 481, 492. -propyl alcohol, 51, 59, 60, 125, 146, 186, 189. -amine, 83, 84. -benzene. See cumene, -carbinol. See 'wohutyl alcohol, iodide, 44, 45, 113, 153, 189, 190, 191. -purone, 369. -quinoline, 575, 582, 588.
sulphate, 575. -saccharic acid, 298. -thiocyanic esters, 347, 348, 353. -urea, 356.
-valeraldehydeammonia, 319. -valeric acid, iso-^ 211. Isomeric compounds, Physical prop- erties of, 48. Isomerides, 42.
Number of possible, 46, 47. Isomerism, 3, 42.
ot the alcohoLsCnHsn+i-OH, 51,52. amines, 83. paraffins, 42-48. Optical, spacial, or stereochemical. See stcreoiaomerism. Isoprene, 162, 514, 522.
J.
Japan camphor. See camphor. JuLiN, 447.
K.
Kalkstickstoff. See lime-nitrogen, Kekul£, 380, 384. Keratin, 328, 330, 336. Keto-alcohols. See sugars. -aldehydes, 252. -he.xainethylene. See hcxanone,
cyclo-. -hexosos, 257, 563. -pentamethylene. See ptntanone,
cyclo-. -stearic acid, 174. Ketone (hn'omposition, 301, 302, 304. Ketones, 60, 130-137, 146, 155, I08, I.V.), 1S3, 186, 194, 224, 310, 429-
431
isonitro.^o-. 252.
Mixed, 133.
Ketones, Unsaturated, 177, 178. Ketonic acids, 300-305.
form, 308-310. Ketoses, 257, 258. Ketoximes, 135. Kieselguhr, 193. Kino-tannin, 474. Kipping, 100. Kjeldahl, 8. Klason, 350. Knop, 357. Knorr, 308, 570. KoLBE, 2, 52, 207, 470. KoMPPA, 520. KoNiGs, 572, 589. Korner's principle, 487, 488, 492. KossEL, 328, 336.
KOSTANECKI, VON, 472.
Krafft, 172. Kreussler, 7. KusTER, 239.
L.
Laboratory-methods, 19-34. Lact-albumin, 328. Lactams, 317.
Lactic acid, 223-225, 226-228, 229, 269. d-, 228, 246. /-, 228, 246, 289. Hacemic, 228, 246.
fermentation, 227, 286. Lactide, 225. Lactobionic acid, 279. Lactones, 221, 226, 230-232, 264, 265,
271, 280, 527. Lactonitrile, 228, 316. Lactose, 227, 278, 279, 280. Ladenburg, 490, 558. La^vulaldehvde, 522.
peroxide, 522. Lajvulic acid, 177, 273. 304, 305, 563. Lipvulose, 194, 206, 267, 269-271, 279,
281, 287, 290, 303. Lakes, 550. Lassaicnk's test, 4. Latex, 521. Laurknt, 2.
Pohirimetcr of, 32, 33. Lauwerenburch, 1S4. Law of Hertuelot, 28. dilution, 117.
the oven number of atoms, 46. Lead acetate, 112, 283. I^a.sic, 112.
merraptidrs, 79.
olc^ate, 172.
pulmitate, 172.
INDEX.
607
Lead stearate, 172.
Lecithin, 197.
Lecithins, 197.
Lecitho-proteins. See conjugated
proteins. Lemonade, 249. Lemon-grass, Oil of, 176. Lepidine, 590.
Leucine, 319, 320, 331, 333, 334, 336, 338.
ISO', 319, 320. Leuckart, 417. Leuco-bases, 528.
-malachite-green, 526. Leuconic acid, 377, 378.
pento.xime, 378. LiEBiG. 2, 5, 8, 20, 285, 344, 357.
Condenser of, 20, 21. Liebermaxn's reaction, 405.
LlEDREICH, 256.
Light oil, 389, 554.
petroleum. See petroleum-ether, Lignin, 265, 294, 296. Ligroin, 38. Lime-nitrogen, 348.
-\v a tor- test, 4. Limonene nitrosochloride, 515. Limonenos, 513, 515. Linen, 294, 293. LiNNEMAN, Fractionating-column of,
23. Liqueurs, 268. Liquid crystals, 408. Liquids, Separation of solids and, 30. Lister, 400. Lithium urate, 365.
LORENTZ, 34. LORENZ, 34.
Ix)W wines, 55. Lubricating oil, 38. LuMifeuE, 461. Lupine seeds, 320. Luteolin, 472. Lutidines, 557. Lvddite, 452. Lysine, 320, 321, 334.
M.
Madder-root, 548. Madeira, 56. Magenta, 141, 529, 530. Magnesium halidcs, Alkvl, loi, 105,
122, 135, 314. Malachile-green, 525, 526, 529. Malelc acid, 210-215, 233, 242-244, 459, 484.
anhydride, 210, 212, 215.
Malic acid, 210, 232, 233, 320, 584. rf-, 321. Z-, 321. Malonic acid, 199, 202-205, 208, 217, 305. 364, 444.
anhydride, 205.
-ester synthesis, 204, 205. Malonvlurea. See barbituric acid. Malt, 55, 56. Maltase, 281, 286. Maltobionic acid, 278. Maltosazone, 278.
Maltose, 54,. 55, 277, 278, 280, 286, 291,295.
180-, 291. * Mandelic acid, 440, 441. rf-, 440, 441. /-, 246, 440. r-, 246, 2«9, 440, 441. Mandelonitrile, 440. Manneotetrose, 290. Mannitol, 193, 194, 262, 271, 272,
296. Manno-heptonic acid, 288.
-UQnose, 288.
-saccharic acid, d-, 272, 275. Mannonic acid, a-, 272.
i-, 272. Mannosazone, d-. See d-glucosazone. Mannose, d-, 194, 262, 271, 272, 275, 287, 288, 295.
t-, 272.
hydrazone, rf-, 271. Marckwald, 246. Margaric acid, 108. Margarine, 113. Margarylmethylketone, 172. Marsh-gas. See methane. Martius's yellow, 540. McKenzie, 289. Meconin, 588. Meconinic acid, 586, 588. Melediose, 290. Melissyl palmitate, 122. MeUitic acid, 481. Mendel6eff, 57, 97. Mendius's reaction, 104. MENsrurxKiN, 85, 402. Menthane, 508, 510, 516. Menthanol, 3-. Sec rneJithol. Menthenes, 512.
Menthol, 246, 289, 508, 509, 513. Menthone, 509. Mercai)tans, 77, 78, 79, 80, 120, 347,
359. Mercaptides, 78, 79. Mercurialis perennia^ 87. Mercuric cyanide, 254, 340, 343.
formate, 109.
608
INDEX.
Mercuric fulminate, 296, 349, 352,
448. Mercurous formate, 109. Mercury acetate, 435. alkides, 101. mercaptides, 78. pheniae, 435. thiocyanate, 347. Mesitylene, 300, 387, 391; 490, 491. Mcsitylcnic acid, 491, 492. Mesoxalic acid, 305, 303. Mesoxaly lurea. See alloxan, Metacetaldehyde, 143-145. A/cto-compounds, 381. Metallic acetylenes, 39, 159.
alkidea, 100, 101. Meta-proteins, 326, 329, 332.
-styrole, 443. Methacrylic acid, 171. Methane, 34, 35-37, 40, 41, 42, 43, 100, 112, 133, 142, 160, 179, 380, 436. homolo^ues, Halogen derivatives
of, 182-185. -tricarboxylic acid, 217. Methoxy-lutidine, 314.
-quinoline, p-, 590. Methyl acetate, 126.
-acetic acid. See -propionic acid. -acetoanilide, 405. alcohol, 52-54, <>7, 78, 85, 88, 91, 109, HI, 125, 141, 142, 202, 294, 309, 356, 377, 405, 406. -alloxan, 366.
-allylphenylbenzylammonium hy- droxide, 99. -amine, 84, 87, 142, 310, 342, 347,
356, 485. -aniline, 404, 405, 421, 565.
hydrochloride', 558. anthranilate, 476. -arsinic acid, 96. -benzene. Sec toluene, bromide, 71. -n-butylacetic acid,y03. -carbylamine, 103. chlond<', 36, 71, 150, 389, 406. cyanide, 103. rf/f/o-butane, 376. -pentane, 505.
-ethyl-arctic acid. Sec valeric acid, A dive. -acotylfno, 100. -aniiiic, S3, S7. -f{irl)iii(>l. See bulyl alcohol^ Sec-
itluT, 74.
-ketone. 133, 1.S4, 145, 252.
-maluuic acid, 204, 229.
Methyl-fflucoside, 280.
a-, 281.
/3-, 281. -glyo.xal, 268, 269.
osazone, 268. -KTOup, 37. -heptane, 2-, 48.
3-, 48.
4-, 48. -heptenone, 177. -indole, 3-. See acalole. iodide, 43, 44, 71, 204, 310. 376,
405, 421, 452, 454, 495, 555, 556,
583, 587. -isophthalic acid. Symmetrical.
See utniic acid. -wopropyl-benzene, p-. See cy- mene.
-carbinol, 51, 162.
-ketone, 163. -ketones, 134, 159, 302. magnesium iodide, 511. -malonic acid, 204. mercaptan, 78. -morphimethine, 587. -morphol, 587. -naphthalene, ac, 538.
/3-, 538. nitrite, 92.
-nonylketone, 145, 303. -o-nitrovanillin, 553. -orange, 467.
-phenyl-hydrazine, 271, 273, 421, 570.
hydrazones, 273.
-pyrazolone, 570. -phosphine, 96. -phosphinic acid, 96. picrate, 452. -propvl-carbinol, 51.
-ketone, 132. -pyridines. See picclines. -p\Trole, 1- (or A'-;, 565.
2- (or a-), 565. -quinoline, p-. See lepidine. -succinimide, 585. sulphate. See dimethyl sulphate, -thiophen. See ihiotolen, -ureas, 356, 366. -violet, 530. Metliylated ether, 75.
spirit, 58, 75. Methylene, 149, 150. chloride, 181, 524. -diphenyldiaininc, 403. iodide, 182, 4S5. Mkykk. K. H., 308. U., 47S. 470. Victor, 12, 183, 500, 566, 568.
INDEX.
609
Michael, 125. Michler's ketone, 407. Middle oil. See carbolic oil. Milk, 278, 328.
-sugar. Sec lactose. Millon's reagent, 327. Mineral acids, Catalytic action of,
125, 138, 144. Mixed crystals, 247, 568.
ketones, 133. Mobile equilibrium, Principle of, 114,
125.
MoiSfiAN, 109.
Mola^^es, 318.
Molecular association, 41, 53, 391. depression of the freezing-point,
15, 16.
electric conductivity, 34.
elevation of the boiling-point, 16.
refraction, 34.
weight of carbon, 19. Mono-alkyl-phosphines, 95. -phosphinic acids, 96.
-basic hydroxy-acids, 223-232.
-bromo-. S(»e bromo-.
-carbonyl-bond, 278, 279.
-chloro-. See chloro-.
-ethyl. See ethyl.
-formin, 190, 191.
-halogen compounds, 393, 394.
-hydroxy-acicis, 470-472.
-iodo-. See tVx/o-.
-methyl. See tnethyl.
-nitro-. See nitro-.
-stearin, 192.
-sulphonic acids, 397, 398. Monoses, 257-276, 278, 281, 286, 290,
334. Monotropy, 430, 431. Mordants, 112, 465, 550, 580. Morin, 472. Moringa-tannin, 474. Morphine, 553, 586-588. Moras tinctoria, 472. Motor-Fpirit, 38. Mucic acid, 273, 563. Mucins, 329, 332. Murex Irawlaris^ 581. Murexide, 363.
-test, 363. Muscarine, 298, 582. Musk, Artificial, 449. Mustard-oils, 348, 359.
-seeds, 348. Mutarotation, 267. Myosin, 328.
Sohible, 328. Myosinogen, 328. Myricyl alcohol, 66.
N.
Naphtha, 38, 58.
Naphthalene, 15, 373, 388, 476, 489, 490, 534-544, «'>45, 546, 580. Constitution of, 535, 536. -dicarboxylic acid, Peri-, 537. dihydride, 536, 541. -sulphonic acid, or-, 539. /?-, 539. Naphthaquinone, a-, 540, 541. /3-, 540, 541.
amphi' (or 2:6), 540, 541. -oxime, a-, 541. Naphthenes, 503. Naphthionic acid, 540. Naphthoic acid, a-, 538.
/?-, 538. Naphthol, a-, 535, 538, 539. /3-, 539.
-disulphonic acid, a-, 540. -monosulphonic acid, a-, 540. -trisulphonic acid, a-, 540. -yellow, 540. Naphthvlamine, a-, 539, 540, 543. /3-, 539, 542. 543. -sulphonic acid, 1 : 4-. See naph*
thiovic aci/l. tetrahvdride, a-, 543. /3-, 542. 543. Narcotine, 588. Nef, 103, 166, 349. Nern.st, 371. Neurine, 167. Nicotiana labacum^ 584. Nicotine, 560. 564, 582, 584. Nicotinic acid, 559, 560, 584.
ISO-, 559. Nitrilcs, 102-104, 127, 129, 136, 155.
W0-, 102-104, 180, 181. Nitro-amine, 359. -amines, 355, 405. -aniline, m-, 447, 451, 459, 460, 494. 0-, 449, 459, 460. P-, 459, 460, 464. -anilines, 459, 460. -benzaldehvde, w-, 481.
0-, 481, 552, 553. -benzene, 15, 27, 386, 395, 396, 399, 403, 407, 408, 410-412, 416, 434, 447, 448, 451, 461, 464, 505, 529, 568, 572. -diazonium chloride, p-, 416. -sulphonic acid, 7/1-, 449. 0-, 449. P-, 449. -benzoic acid, m-, 469. 498. a-, 469, 498. P-, 469, 498.
610
INDEX.
Nitro-benzoyl chloride, o-, 576.
-formic acid, 576. -benzyl chloride, p-, 532. -butane, Tertiary, 92. -cellulose, 296, 297. -celluloses, 296, 297. -cinnamaldebyde, o-, 573. -compounds, 91-94, 395, 397.
Primary, 93.
Secondary, 93.
Tertiary, 93. -dimethylaniline, p-, 406. -ethane, 91-93. -glycerine, 192, 193. -guanidine, 361. -4-hydroxyphenylarsinic acid, 3-,
462. -mannitol, 296. -mesidine, 491. -mesitvlene, 491. -methane, 92, 443. -naphthalene, a-, 489, 538, 539.
/3-, 539. -«-naphthylamine, 2-, 539. -paraffins, 91-94. -phenol, 7^^-, 451, 454.
0-, 449, 451, 494.
P-, 451, 464, 494. -phenols, 399, 450-452, 527. -phenyl-acetic acid, o-, 576.
-nitromethane, m-, 439. -phthalic acid, 489. -propane, Secondary, 92. -prusside-tcst, 5. -pyridine, (i-, 556. -salicylonitrile, o-, 501. -stryrolc, 443. -thiophen, 508. -toluene, in-, 396, 495, 496.
0-, 396, 397i 404, 469, 481, 495, 496.
P-f 396, 397, 404, 495, 496. -urethime, 339. -vanillin, o-, 553. NitroRon, Quinquivalency of, 99,
415. Nitroso-aniincs, 86, 88, 405. -benzene, 410, 411, 412. -benzoic acid, o-, 4X1. -oanijjhor, /.so-, 518, 510 -dinu'thylanilinp, 406, 412, 453.
hydnx'liloridc 400. -k('l()n(\s, 7.S0-, 252. i
-]>lu'ii()l, p-. See hcnzoquiiLonc 1
imnio-iixitni . i
-I)ij)«-riilin«'. ").")(>. Nitrous-acifl test for amines, SO. ;
nit ro-c«nnpoiiiKls, 93. j
Nomenclature of the alcohols
CnHin+i-OH, 51, 52. Nonane, 41.
-dicarboxylic acid, 199. Nonoses. 264, 286. Nonyl alcohol. Normal, 52. Nonylic acid, 108. Normal chains, 45. Nornarcotine, 588. Notation, 46.
of Chemical Society of London, 183, 184. the monoses, 267. Nucleic acids, 332. Nucleo-proteins, 329, 332. Nucleus, Benzene-, 385. Number of carbon compounds, 2, 45. possible isomerides, 46, 47.
O.
Oak-tannin, 474. OctaHiecapeptides, 338.
-peptides, 337. Octane, n-, 37, 41, 48.
cyclo-y 379. Octoses. 264.
Octyl alcohol. Normal, 52. -amine, Normal, 87, 104. bromide, 85. iodide. Normal, 303. Odour, 518.
Oil, Fusel-, 55, 58, 60, 62, 151, 320. Lubricating, 38. of bitter almonds, 380, 427. carraway, 380, 392, 514. castor-seed. 114. cinnamon, 444. citron, 176. cloves, 483. cumin, 380. eucalyptus, 392, 511. garlic, 108. lemon-grass, 176. orange-rind, 176. peppermint, 508, 509. polei, 513. rue, 303. spinea. 4S2.
the Dutch chemists, 184. thyme, 'M)2.
turpentine,. 32, 481, 500, 514, 517. \vint<'rt:r('(*n, 470. wormseed, 511. Olive. 31.
Paraflin-. Sec naphtha. Train-, 30. Oils, 115. 172, 184, 191.
INDEX.
611
Olefines, i47-i57i 186, 379. Oleic acid, 114, 169, 172, 173, 174, 191, 197.
series of acids, 169-173. Oleum cincBf 511. Olive oil, 31. Opium, 586. Optical activity, 32, 62, 98-100.
isomerism. See stereoisomerism. Organic analysis, 5-11.
chemistry, Definition of, 1.
compounds, Classification of, 34. Orientation, 385. 487-502, 537, 538,
545, 557, 573, 574. Ornithine, 321, 334, 361, 479, 480. Ortho-acetic acid. 111.
-carbonic esters, 360.
-compounds, 384.
-esters, 106, 180, 185, 194, 360.
-formic acid, 180. Osazones, 258, 259. Osmotic pressure, 11, 14, 15. Osones, 271.
OSTROMISSLENSKY, VON, 245.
Ost's solution, 240, 258.
OSTWALD, 117.
Over-proof spirit, 57. Oxalacetir acid, 268. Oxalic acid, 171, 190, 191, 199-202,
208, 250, 282, 299, 311, 313, 340. Oxalis, 200. Oxaluric acid, 362. Oxalyl chloride, 202.
-urea. 8ee parabanic acid, Oxamic acid, 202. Oxamide, 202. Oxanthrone, 547, 548. Oximes, 135, 136, 431-433.
Tautomerism of, 310. Oxindole, 576. Oxonium salts, 313-315. Oxy-rollulose, 296.
-2: t»-dichloropurine, 8-, 367.
-hii'inojrlobin, 332.
-methylenes, 142. Oxypcn-carricrs, 8.
Detection of, 5.
Estimation of, 9. Ozokerite, 39. Ozonides, 251, 522.
P.
Palmitic acid, 108, 114, 172, 197. Pancreas, 192. Pancreatic juice, 338. Papaver somniferum, 586. Paper, 294, 295, 296.
Parabanic acid, 362, 363.- Paracetaldehyde, 138, 139, 143, 144,
145. Para-compounds, 384.
-cyanogen, 340.
-formaldehyde, 142.
-leucaniline, 529.
-mandelic acid, 441.
-myosinogen, 328.
-rosaniline, 529. Paraffin, Liquid, 31, 39.
-oil. See naphtha.
-wax, 39, 108, 114. Paraffins, 37, 38, 157, 390. See also saturated hydrocarbons.
Isomerism of the, 42-48.
Structure of the, 42-47. Parchment-paper, 296. Parsley, 277. Partial valencies, 384. Pasteur, 241, 245, 246, 285. Peat, Combustion of, 141. Pelargonic acid, 145, 173, 174. Penicillium glaucum, 247, 440. Penta-chloro-ethane, 181, 183.
-digalloylglucose, 474.
-hydric alcohols, 258.
-methyl-aminobenzene, 406. -benzonitrile, 501. -pararosaniline. See melhyU violet,
-methylene. See pentane, cyclo-. -diamine, 196, 320, 555.
hydrochloride, 196. dibromide, 555.
-phenylethane, 532.
-triacontane, 36, 41. Pentane, 36, 41, 46, 63, 70, 151, 157, 182, 554.
cyclo-, 157, 376, 377, 505.
derivatives, cyclo-, 376-378. Pentanone, cyclo-, 376, 377, 503. Pentonic acids, 258, 264. Pentosans, 264. Pentoses, 257, 264-266, 277, 290, 562,
503. Pentosuria, 265. Pentyl iodide, 153. Pepper, 559.
Peptones, 329, 332, 333, 337, 338. Percen tage-composi tion , 9-11. Perchloroethane. See hexachloro^
ethane. Percolation, 583. Percussion-caps, 349. Perfumes, Artificial, 178. Peri-compounds, 537. Perkin, W. H., Jdn., 510, 520, 590.
Sir William, 444, 484, 485, 552.
612
INDEX,
Petroleum, 38, 39, 91. American, 38, 39. Caucasian, 377, 503. -ether, 28, 38, 101. Formation of, 39, 40. Java, 39.
-jelly. See iHiseline -lamp-fires, 38. Pharaoh's serpents, 347. Phenacetin, 461. Phenanth-aquinone, 551, 552. Phenanthrene, 534, 544, 551-553, 58(). -carboxylic acitl, /3-, 553. Phenetole, 401, 410, 418, 461. Phenol, 14, 15, 388, 389, 398-400, 401, 416, 418, 420, 450-453, 465, 471, 482, 506, 507, 539, 566. -phthalein, 478, 527. -sulphonic acid, m-, 452. 0-, 452, 453. p-, 452, 457. acids 4^2 PhenoLs, 398-400, 401, 427, 481, 482,
534. Phenoxides, 399, 401. Phenyl-acetic acid, 440, 552. ISO-, 378. pseiido-y 378. -acetylene, 443. -alanine, 334. -amine. See aniline. -aminopropionaldehyde, /3-, 572. -anisyl-ketone, 431.
-ketoxime, 433. -arsine oxide, 434. -arsinic acid, 434. -chloroamine, 403. ether, 400, 401.
-glucosazone. See glucosazoney d-. -Rlycine-o-carboxylic acid, 579. -hydrazine, 136, 137, 258, 259, 273, 278, 293, 420, 421, 428, 561, 570. hydrochloride, 421. -hydrazones. See hydrazones, -hydroxylamine, 410, 411, 412. -/3-hydrox>^)ropionic acid, a-. See
tropic arid. -iodide chloride. See iodobenzenc
dichloridc. wocyanate, 438. inapnesium bromide, 394. mercury aretato, 435.
hy(lr()xi<lo, 435. -nitromethano, 438, 441. -o-aininocinnamic acid, a-, 553. -<Hazo('innamio acid, a-, 553. -nitrocinnamic acid, a-, 552.
Phenyl-phosphine, 434.
-phosphinic acid, 434.
-phosphinyl chloride, 434. '
-propiolic acid, 443, 445.
salicylate, 471.
-salicylic acid, 472.
-sodionitromethane, 5.^2.
-tolylketone, 431.
-vinylacetic acid, 535, 538.
xanthat^, 417. Phenylene-aiacetic acid, o-, 542.
-diamine, tm-, 446, 448, 46a, 463, 466, 467, 492, 494. 0-, 463. ;>-, 462, 463, 492.
-disulnhonic acid, m-, 454. Phloroglucinol, 296, 455-457.
triacetate, 456. Phosgene. See carhonyl chloride, Phosphenyl chloride, 434. Phosphenylous acid, 434. Phosphines, 95, 96. Phosphinobenzene, 433, 434. Phospho-benzene, 434.
-proteins, 325, 328, 330. Phosphonium bases, Quatemarv, 95,
97. Photo-chemical reactions, 544.
-graphic film, 297.
-synthesis, 263. Phthalelns, 478, 531. Phthalic acid, 476-478, 489, 490, 537, 541, 546, 547, 575, 580. iso-, 480, 481,492. Tere-, 380, 480, 481.
acids, 440, 476-481, 487, 605.
anhydride, 476, 477-479, 646, 550. Phthalide, 477. Phthalimide, 475, 479, 580. Phthalisoimide, 480. Phthalophenone, 477. Phthalyl chloride, 476, 477, 480. Physical properties of isomeric com-
pounds, 48. Picoline, a-, 558.
/3-, 557, 590. Picolines, 557. Picolinic acid, 559, 560. Picramide, 448, 452, 460. Picric acid, 327, 448, 451, 452, 493-
495, 524, 544. Picryl chloride, 447, 452. Pimelic acid, 199, 507. Pinacolin, 187, 533. Pinaconc, 186, 187, 533. Pinacones, 186. Pinane, 516. Pinene, 517, 518. Pinic acid, 518.
INDEX.
613
**Pink salt/' 465. Pinonic acid, 518. Piperic acid, 484, 485, 559. Piperidinc, 90, 196, 555, 556, 559. Pipeline, 484, 559. Piperonal, 483, 484, 485. Piperonvlacraldehyde, 485. Pitch, 389. Platinotypes, 202. Polarimeter, Laurent's, 32, 33. Polarimctry, 32, 33, 283, 284. Polv-amino-compounds, 462-468.
-basic acids, 198-218, 476-481. hydrox>'-acid3, 248, 249.
-halogen derivatives, 179-185, 446, 447.
-hydric alcohols, 185-194. phenols, 453-457.
-methylene compounds. See all- ey die compounds.
-nitro-derivatives, 448, 449.
-oxy methylene, a-, 142. i3-, 142. 7-, 142. «-, 142.
-peptides, 337-339.
-sulphonic acids, 449, 450.
-terpenes, 521, 522. Polymerization, 139, 142, 143.
of aldehydes, 138-145. Polvoses, 257, 262, 264, 266, 289-297,
334. Pope, 98-100. Port, 56.
Potash-bulbs, 6, 7. Potassiopyrrole, 564, 566. Potassium acetate, 207, 267, 306, 441.
alkides, 100.
anilide, 404.
antimony I d-tartrate, 238.
benzenesulphonate, 398, 422.
bonzoato, 427.
carbazole, 544.
carbonyl, 457.
coppor-pr()i)i()late, 217.
cuprous c'vanido, 417.
cvanato, 340, 31.'), 354, 357, 365.
cyanide, 102, 104, 134, 169, 171, 'ISO, 19(5, 202, 206, 217, 249, 340, 343, 422, 440, 533, 562, 574.
diacetylenotlicarboxylate, 217.
ethoxide, 67, 353.
ethysulphate, 73i 78, 79, 102.
ferric oxalat<^, 201, 202.
ferricyanide, 217.
fcrrocyanide, 102, 104, 341, 343, 344.
ferrous oxalate, 201.
Potassium formate, 2U0, 343.
glycollate, 220.
hydrogen acetylenedicarboxylate. 216. iresotartrate, 243. saccharate, 267. o-sulphobenzoate, 470. d-tartrate, 238.
monochloroacetat«, 202.
oxalate, 200.
phthalaminate, 475.
phthalimide, 479.
propiolate, 216.
rf-tartrate, 238.
tetra-acetylenedicarboxylate, 217.
thiocyanate, 346, 347.
trithiocarbonat<j, 352.
xanthate, 353, 417. Potato-starch, 291, 293, 294. Presssaft, 285.
Primary alcohols, 52, 60, 61, 107, 126, 130, 133, 147.
amines, 83, 84, 86, 87, 91,^104, 136, 181, 355, 401-404.
arsines, 96.
carbon atoms, 46.
compounds, 52.
nitro-compounds, 93.
phosphines, 96.
reduction-products, 410. ~- Principle of mobile equilibrium, 114, 125. the counter-current, 282. Prino, 36. Producer-gas, 53. Proline, 335, 336. Proof-spirit, 57, 58. Propanal, cyclo-f 376. Propane, 36, 37, 41, 42, 44, 45, 183.
cyclo-, 375, 379.
-tricarbox3'lic acid, apa'-. See tricarbailylic acid. Propargyl alcohol, 166, 168.
compounds, 166. Propenylpyridine, a-. 558. Pn)i)crties of alcohols, CnHi»+i«OH,
52, 53. Propiolaldehyde, 176.
-acetal, 176, 569. Propiolic acid, 168.
series of acids, 173, 174. Propionaldehyde, 59, 132, 134, 153,
165. Propionic acid, 59, 60, 102, 103, 108,
112, 117, 118, 132, 145, 160, 170,
220, 225, 229, 300. Propionitrilc, 103. Propionyl-group, 109. Propyl-acetylene, 160.
614
INDEX.
Propyl alcohol, iso-, 51, 59, 60, 125, 146, 186, 189. Normal, 51, 52, 59, 60, 74, 125, 165, 168. -amine, ?5o-, 83, 84.
Normal, 83. 84, 87. -benzene, iso-. See cuinene. bromide. Normal, 71, 85. -carbinol, iso-. Sec isobutyl alco- hol. Normal. See butyl alcohol, Nor- mal. -carboxylic acid, cyclo-, 171, 375. chloride, Normal, 71. derivatives, cyclo-y 375. -dicarboxylic acid, cyclo-, 375. -group, 37. iodide, wo-, 44, 45, 113, 153, 189,
. 191.
Normal, 44, 45, 71, 113, 153.
-piperidine, a-, 558, 559. /3-, 559. 7-, 559.
'PseudnmiToXQ, 93. Propylene, 148. 152, 153, 184, 189, 191,375,509,515.
chloride, 153, 165, 189.
-glycol, 223, 227. Propvlidene chloride, 153, 164. Prosthetic group, 328, 329. I^otamines, 32S. Proteans, 329.
Protein-derivatives, 329, 330.332.333. Proteins, 2, 54, 55. 143. 282, 283,
286, 288, 316, 318-320, 325-339,
361, 400, 474, 483, 557, 564, 577,
586. Proteoses, 329. 333. Protocateehu aldehyde, 482. 484. Protocateeluiic acid, 472, 473, 485. Protopla-sm. 2S2. 285, 287. Prussian-blue test, 4. Prussic acid. See hydrocyanic aci'L PsciioHu, 552. Pscwh-iiMa, 438-440, 527, 548.
-bases. S(m» colour-bams.
-'u)ni)ni\ 177.
-nit roles, 93.
-ra<'(Mnic mixed cr3'stals, 247, 248.
-uric acid, 3(>5. PtoniaiiH's, 196, 333. Pulc^onr'. 512, 513. Purine, oi'trt, 367. Pur'»rn'. '''A\\>.
i.-n-, '.\{\\). "T!;ilil«' of tlie ancients." 5^1. Pur;>':rin. .").')0. Putr«><iin'. ^5(M» titratnethylcnc-
diathim..
Pvknometer, 32. Pyrazole, 324. 374, 568-570. Pyrazolinc, 570. Pyrazolone, 570.
Pyridine, 259, 272, 307, 373, 388, 389, 554-560, 573, 582, 584, 585, 588.
-carboxylic acids, 559, 560.
ferrocyanide, 554.
-sulphonic acid, 554.
-tricarboxvlic acid, or/37-, 590. Pyro-catechin or pyrocatechol. See catechol.
-gallic acid. See pyrogaUol,
-gallol, 455, 473.
-mellitic acid, 481. anhydride, 481.
-mucic acid, 562-564.
-racemic acid, 224, 238, 268, 300, 301.
-tartaric acid, 238. P>'rone derivative's, 311-315, 478.
-dicarboxvlic acid. See chelidonic acid. Pyrrole, 37^, 555, 564-566, 577.
-carboxylic acid, 2-, 566.
-red, 564. *'Pynolidin." Hce tetrahydropyrrole, * ' Py rrolin . ' ' Sec dihydropyrrole. Pyruvic acid. See pyroracemic acid.
Q.
Quadrivalent oxygen, 313. Quadroxalates, 201. (Qualitative analysis, 3-5. Quantitative analysis, 5-11. (Quaternary ammonium bases, 83, 84, 407.
arson ium bases, 96.
carbon atoms, 46.
phosphonium bases, 95.
stibonium bouses, 97. Quick process for vinegar, 110. (^uina-red, 589. (^uinhydrone, 457. (^uinic acid. ri89. (Quinine, 440, 475, 589, 590.
-tannin, 474. Quinitol, 506.
cis-y 506, 507.
iratis-f 506, 507. Quinol, 454, 455, 457, 463, 526. Quinolinc, 272, 374, 389, 509, 554, .V).->, 560, 572 575, -'^^2, 589, 590.
diclironiatc, 572.
^"^"-. 575. •\>'>2, 5S8.
sulpliatc, 2NO-, .575.
-suli)lionic acids, 574.
INDEX.
615
Quinolinic acid, 560, 573. Quinone. See bemoquinone.
di-imide, 463. Quinones, 457-459> 545, 548.
0-, 458. Quinonoid forms. 526, 527. Quinotannic acia, 589. Quinovic acid, 589. Quinovin, 589. Quinoxalines, 463.
R.
Racemic acid. See tartaric acid, r-.
substances, 228, 241. Resolution of, 245-248. Racemoids, 247. Raffinose, 289, 290. Raphides, 200. Reactions. Bimolccular, 85, 125, 126.
Reversible, 122, 138.
Tlnimolecular, 126. Reagent, Schiff's, 141. Reduction-products, Chemical or sec- ondary, 410. Electrolytic or primarj', 410. Reflux-condenser, 20. Refraction, 33, 34, 148, 156, 157, 308, 440, 521, 543, 544.
Atomic, 157.
Index of, 33.
Molecular, 34, 157, 440, 521, 543, 544. Refractive power. See refraction. Reimer's synthesis, 482, 483. Remsex, 470. Rennet, 328. Resinification, 139, 140. Resorcin. See rcsorcinol.
-yellow, 467. Resorcinol, 449, 454, 455, 458, 467, 478, 563.
-phthalcin. See fluorescein . Reversible reactions, 122, 138. Rhodium, Catalytic action of, 110. Rice-starch, 292. RiCHTER, 374. Riciniis comviuniSy 114. Rigor mortis y 328. Ring conii)ounds. See cyclic com^
pounds. RoBiNsox, 590. Rodinal, 461.
KoozEiJooM, Bakhuis, 248. Rosa ni lino, 465, 529, 530. RosaniliiH's, 525-531. Rosenheim, 32S. Roaplic acid, 530, 531.
Rotation of plane of polarization, 32,
33, 62. Rotatory power. Specific, 32, 33. Ruberythric acid, 548. Rum, 56.
Ruta grai^olensy 303. Rye-starch, 292.
S.
Sabatier, 35, 151, 504-506. Saccharates, 261, 281, 282. Saccharic acid, d-, 267, 276.
ISO-, 298. Saccharides. See sugars. Saccharification, 55. '
"Saccharin," 469, 470. Saccharose. See sucrose. Saint Giles, P£an de, 122. Salicin, 470. Sahcylaldehyde, 482. Salicvhc acid, 470-472, 492, 493, 566,
571. Saliji^enin,-470. "Salipvrine," 571. Sahnme, 328, 336. ♦•Salol," 471. "Salt of sorrel," 201. "Salting-out," 115, 326, 330, 466. "Salvarsan,'U62. Sandmeyer, 416. Saponification, 125-127.
of fata, 113, 114, 115, 126. Sarcolactic acid, 228. Saturated hydrocarbons, CnHm+i,
35-48, 100, 148, 157, 179, 185,
379. See also -paraffins. Sauerkraut, 227. Sawdust, 200. Scatole, 333, 335, 577. Schiff's rcapcnt, 141, 255, 281. Schizomycetvs, 285. SchizosQccharomyccs octosporus, 286.
SCHORLEMMEH, 70.
Sclero-protoins, 328, 330, 331. Schmidt, 470.
SCH LTZEXfiERGER, 333-335.
Schweitzer's reagent, 295, 297. Scutching, 295. Sehacic acid, 199.
Secondary alcohols, 52, 61, 125, 130-133, 135, 147.
amines, 83, 84, 86, 87, 104.
arsin('s, 1)6.
carbon atoms, 46.
coinj)<)un(ls, 52.
nitro-coinpounds, 93.
phosphines, \){).
reduction-i)roducts, 410.
616
INDEX.
Selenium compounds, 81. Semi-carbazide, 357.
-carbazones, 357. Semidine-transformation, 409. Senderens, 35, 76, 150, 504-506. Senier, 189, 344, 350. Senter, 322. Separating-funnel, 28. Separation of amines, 86.
immiscible liquids, 28-30. solids and liquids, 30. from one another, 30. Scricin, 331. Sericoin, 338. Serine, 334. Sertl'rner, 586. Serum-albumin. 326, 328.
-globulin, 328. Sherry, 56. Side-chain, 48, 385. Silicancs, 98. Silicoheptane, 98. Silicon alkides. See silicanes.
atoms, Asymmetric, 100. •
Chemistry of, 98.
tetraethide, 98. Silk, Artificial, 297.
-gum. See scricin. SiLVA, 189. Silver acetate, 107, 185, 186.
acetylene, 159.
cyanamidp, 348.
cyanate, 345.
cyanide, 341, 576.
cyanurate, 350.
formate, 109.
fulminate, 349.
hevulatc, 273.
-mirnjr-test, 141.
picrate, 452.
thiocvanato, 347. Simpson, 180. .Skravp, 572, 574, 589. Slcf^ping sickness. See Irypanosomia-
sin. Smokeless jx^wder, 297. Soap, (Ireen, 115.
Hard, 115.
Pota-ssium-, 115.
Sodium-, 115.
Soft, 115. Soaps, 115, 116. S(Mh\-lime-tc.'<t, 4. Sorianiidc, 2')'.^, 530. Sodio-acciylatM'toiH', ,306.
-//-amylarctyloru', 2')3.
-ilinitrocthane, 4.39, 440.
-nitro-c'tlianr, 92.
-j)r()paiu', Sccondarj', 92.
Sodio-phenyl-nitromethane, 438.
-i«onitromethane, 438. Sodium acetate, 105, 112, 260, 444, 485. acetylene, 173. alkides, 100, 105. ammonium racemate, 245, 248. fZ-tartrate, 245. /-tartrate, 245. anthraquinonesulphonate, 549. benzoate, 422, 425. cyanide, 343.
diazobenzenesulphonate, 420. ethoxide, 66, 67, 92, 180, 185, 204, 205, 252, 253, 302, 321, 367, 448, 455. formate, 200. hydrogen urate, 365. met hide, 105. methoxide, 66, 67, 74, 92, 106, 310,
394, 447, 448. -nitroprusside-test, 5. oxalate, 200.
-p-acetylaminophenylarsinate. See arsdcetin.
-aminophenylarsinate. Socaiozyl. phenoxide, 399, 401, 470, 471, 565. phenyl-carbonate, 471. -hydrazinesulphonate, 420. -salicylate, 471. stearate. 107. i sulphanilate, 460. 1 urate, 365.
, Solubility-curve for two liquids, 89. -curvos for triethylamine and water, 89. , Soluble myogen-fibrin. See myosin^ I *>oluhh. Solvents, Cryoscopic, 14, 15, 16. Ebullioscoj)ic, 16. Extraction with, 28. Soporifics, 146, 254, 256, 429. Sorl.itr)!, f/-, 202. I Sorbose-bacteria, 262. Sjiacial isomerism. See stcremsomer*
ism . Specific gravity', Determination of, 32. rotatory power, 32, 33. Spent lee.s, 5o,
wa.sh, 55. Spermaceti, 66. Spirits, 55.
of wino, 56. Sponnin, .331.
Starch, 51. 263, 266, 269, 277, 291- 294. •Jl).'). Maniifaciuro of, 294. , Steam-distillation, 26-28.
INDEX,
617
Stearic acid, 15, io8, 114, 172, 191, 192. Structure of, 172. "Stearine,"114.
candles, 114. Stearolic acid, 173, 174. Stearyl alcohol, 107. Stereochemical isomerism. See stereo^
isomerism. Stereochemistry of the monoses, 273-
276. Stereoisomerism, 64, 65, 66, 210-215, 221-223, 228-230, 233-238, 273- 276, 321-323, 339, 431-433, 444, 445.
of nitrojren, 431-433.
VAN 't HoFr*s theory of, 64-66. Stibines, 97.
Tertiary, 97. Stibonium bases. Quaternary, 97. Stilbene, 532, 552. Storax, 443. Strain-theory, von Baeyer*s, 156,
209. Straw, 266, 295. Strecker, 316. Strength of acids, 118. Strong hydrolysis, 301. Structural or constitutional formula,
44,51. Structure of the paraffins, 42-48.
Strychnine, 246, 475, 590.
i-mannonate, 272. Strychnos nux vomica, 590. Sturinej 328. Styphmc acid, 454. Styrole, 443.
Suberanecarboxylic acid, 378, 379. Suberic acid, 199. Suberone, 378, 379, 585. Substitution. 36, 229. Succindialdehyde, 251, 564, 565.
Oxime of, 565. Succinic acid, 29, 30, 54, 199, 205, 206, 208-210, 215, 231, 233, 238, 567.
anhydride, 208. Succinimide, 209.
Succinonitrile. See ethylene cyanide.
Sucrose, 32, 113, 200, 227, 248, 265,
266, 279-284. 285, 286, 290, 563.
Manufacture ot, 282, 283.
Quantitative estimation of, 283, 284.
Velocity of inversion of, 284. Sugar-beet, 265, 279, 282, 283, 318.
-cane, 279.
Cane-. See sucrose,
o^ lead. See lead acetate.
Sugars, 257-297, 320, 325, 328,332,
586. Sulphaminobenzoic acid, p-, 470. Sulphanilic acid, 457, 460, 462. Sulphinic acids, Alkyl-, 80. Sulphite-method, 295. Sulpho-benzenediazonium chloride, j>., 467.
-benzoic acid, m-, 469. 0-, 470. acids, 469, 470.
-cyanic acid. See thiocyanic acid, Sulphonal, 146. Sulphonamides, 398. Sulphones, 80, 374. Sulphonic acids, 80, 449, 450, 452,
460, 469, 470. Sulphonium compounds, Asymme- tric, 98. Sulphonyl chlorides, Alkyl-, 80.
Aromatic, 397. Sulphonium hahdcs, 79.
hydroxides, 79.
iodides, 79. Sulphoxides, 80. Sulphur; Estimation of, 8. Supertension, 371. Symmetrical compounds, 385. Syntonins. See meta-proteins.
Tafel, 368, 370. Tanacetone. See thujone. Tannic acids. See tannins. Tannin, 291, 327, 331, 474, 475, 583. Tanning, 475. Tannins, 474, 475. Tan RET 267.
Tar, 388, 389, 391, 398, 534, 544, 554, 566, 572, 575. Wood-, 54. '• Tartar-emetic," 238. Tartaric acid, d-, 233, 234, 236, 237, 238, 240, 241, 242,245, 247, 268, 289, 300. i-, 233, 234, 236, 237, 240, 245,
247, 289. Meso-, 233, 234, 237, 240, 241-
243, 276. r-, 233, 234, 238, 240, 241, 242, 243, 247, 300. acids, 233-245, 287. Tartronic acid, 188, 232. Tautomcrism, 305-310, 339, 548 Tea, 366, 473, 474, 583. Tellurium compounds, 81. Tercphthalic acid, 38C, 480. 481.
618
INDEX .
Terminal carbon atoms, 46. Terpenes, 378, 392, 503, 508-518,
521,522. Terpin, 509-511, 512, 514.
hydrate, 509, 510, 512. Terpineol, 512, 513, 514, 518. Terpinolcne, 513, 514. Tertiary alcohols, 52, 01, 122, 125,
135, 147. amines, 83, 84, 86, 87, 104. arsincs, 96, 97. bismiithines, 97. carbon atoms, 46. compounds, 52. nitro-compounds, 93. phospliines, 96. Tervalency of carbon, 532. Test, Beilstein's, 5.
Carbylamine-, 103, 104, 403. Copper-oxide-, 4. Iodoform, 58, 182. Lassaic.ne's, 4. Lime-water-, 4. Prussian -blue-, 4. Silver-mirror-, 141. Soda-lime-, 4. Sodium-nilroprusside-, 5. Test for absolute alcohol, 50, 57, 91.
acetates, Cacodyl-, 97, 112. Ferric-chloride, 112.
amines, Nitrous-acid-, 86.
anthraquiuone, 517.
bl()o<l, 332.
collulose, 295.
cyr/ohexanone, 507.
dextrose, 207.
double bonds, Optical, 157. VON Haeyer's, 148.
glycerol, KSO.
hexoses, 273.
identity of substances, 31.
ketoses, 271.
lignin, 294, 296.
nitric acid, 404.
nitro-com{)ounds. Nitrous-acid-, 93.
nitrous acid, 463, 467.
pentoses, 200.
phenols, 399. 400.
phthalic acid, 478. anhydride, 478.
primary amires, IIofmann's, 87, 103, 104.
pyrrole, 5(il.
rc.-orcinol, 478.
Btarcl), 291.
xyl<)-;f', 2i\i\. Tests tor aMcliydes, 1 U.
ariiit)('^, SO, vS7, loi, 102.
Tests for aniline, 403, 404.
ethyl alcohol, 58, 182, 425. hydroxyl-Rfoup, 49, 50, 119, 120. monoses, 258, 259. primary, secondary, and tertiary
alcohols, 61. proteins, 327.
tautomeric forms, 308-310. Tetra-acetylenedicarboxylic acid, 217. -alkylammonium iodides, Velocity
of formation of, 85. -bromo-ethane, 545. -fluorescein, 478. -methane. See carbon telrabro' miAe. -chloro-ethane, 183, 184. -ethylene, 181, 183. -methane. See carbon tetrachlo" ride, -decane, 41.
-ethvl-ammonium hydroxide, 88. disodioethanetetracarboxylate,
535. hydronaphthalenetetracarbox-
ylate, 535. -methane, 98. orthocarbonate, 360. -hydro-benzene, 506. -pyrrole, 566, 585. -carboxylic acid. See proline, -hydroxy flavone, 1 : 3 : 2': 4'-. See morin. 1 :3:3':4'-. ^oQliUeolin. -methvl-ammonium hvdroxide, 88. -butane, 2: 2': 3: 3'-, 48. -diamino-bcnzophenone, 407. -triphenyl-carbinol, 526. -methane, 526. -succinic acid, 219. -uric acid, 368. -methylene. Sec biUanef cyclo-, bromide, 376. -diamine, 196, 321. -nitrophenol, 2:3:4: 6-, 454. -peptides, 337. Tetrolic acid, 174. Tetroses, 264. 290. Theine. See caffeine. Theobromine, 365-367, 582. Theory of stereoisomerism, van 't
Hokf's. 04-()0. Thermometers, Abbreviate<l, 32. TniKLK, 31. 1()3, 3S3, 384, 536. Thienylnielhylketone, 2-. See aceio^
thicnonc. Thio-acids, 127.
-cyanic acid. 31(). 347. esters, 347, 348. ^«^'-» 347 > 348, 353.
INDEX,
619
Tbio-ethers, 77-79, 80.
-indifto, 581.
-methylene, 348.
-phenol, 386.
-tolen, 566, 568.
-urea, 359, 360. Thiophen, 374, 566-568.
-carboxylic acid, 2-, 568. 3-. 568.
Dimethyl-. See ihioxen,
mercury oxyacetate, 566.
Methyl-. Scolhiololen,
-sulphonic acid, 568. Thioxen, 566, 567. Thorpe, 520. Thujone, 521. Thymol, 400, 509. Tickle, 313. Tiplic acid, 169. Tin atoms. Asymmetric, ICO.
ethid<', 101. Toadstool, 298. Tolan, 532.
Toluene, 380, 388, 389, 390, 391, 396, 397, 400, 422, 436-438, 469, 495, 5i)(>.
-sulphamidc, o-, 409.
-sulphonic acid, m-, 498. 0-, 498. 7>-, 498.
-sulphonyl chloride, o-, 469. p-y i09. Toluic acids, 426, 440. Toluidine. vi-, 495.
0-, 404. 495, 529.
p-, 15, 404, 495, 529, 558, 565.
hydrochloride, p-, 400. Tram-oil, 39. Triacetoneamine, 145. Trialkyl-nhosphines, 95.
-phosphine oxid^^, 96. Trianiino-jizohenzcne, 466, 467.
-benzenes, 463.
-triphcnyl-carbinol, 529. Trianiylenc, 151. Trianisvlcarbinol, 527. Triba.sic acids, 217, 218, 248, 249,
481. Tribe. 8ee Gladstone. Tribenzovladrenaline, 485. Tribenzylaniine, 441. Tribromo-aniline, 2:4:6-, 402, 459.
-hvdrin, 168, 183. 189, 217.
-phenol, 2 : 4 : 6-, 399, 450.
-resorcinol, 454. Tricalcium saccharate, 282. Tricarballvlic acid, 217, 218. Trichloro-acetal, 254, 255.
-acet aldehyde. See chloral.
Trichloro-acetic acid, 125, 220, 22X, 255.
-ethylene, 183, 184.
-hydrin, 189.
-phenol, 450.
-purine, 2:6: 8-, 367. Tricosane, 41. Tridiphenylmethvl, 532. Trietliyl-amine, 85, 88, 89, 90.
-arsine, 96.
-bismu thine, 97.
citrate, 247.
-methane, 98.
-phosphine, 96. oxide, 95, 96.
l)yrazoletricarboxylate, 569.
pyrazolinetricarboxylate, 570. Trihalopenbenzenes, 1:2: 4-, 446. Trihydric alcohols, 188-193.
phenols, 455-457. Trihydroxy-acids, 473-475.
-anthraquinone, 5:6:8-. See pur pur in.
-glutaric acid, 265, 270. 274, 275. Tri-iotlo-hvdrin. 190.
-phenol, 507. Triketohexamethylene. See phloro*
glucinol. Trimethyl-acetic acid, 219.
-acetvl chloride, 1H7.
-amine. 8,3, 87, 88, 142, 167, 197, 319, 376.
-carbinol, 51, 61, 125, 135.
-ethyl(»ne, 162.
-glycine, 318.
-oxonhim iodide, 314.
-phloroglucinol, 457.
-phosnhine oxide, 96.
-pyridines. See coHidines,
-succinic acid, 519. Trimethvlene. See propane, cyclo-.
bromide, 184, 185, 196, 375, 479.
cvanide, 196.
-iliamine, 196.
-glycol, 185. diacetate, 185. Trinitro-aniline, 2:4:6-. See pic ramulc.
-benzene, Symmetrical, 448, 495, 502.
-butyl.xylene, 449.
-cellulose. 296.
-oxycellulose, 296.
-phenol, 2:4:6-. See picric acid, Trios(?s, 257, 2t»2, 264, 286. Tripeptides, 337. Triphenyl-amine, 402, 40S
620
INDEX.
Triphenyl-carbinolcarboxylic acid, 477.
-chloromethane, 531.
-methane, 407, 427, 478, 525. dyes. See rosnnilines.
-methyl, 531,532. iodide, 531. pero.xidr, 531 .
-rosaniline hydrochloride. See ani- line-blue.. Tri.stearin, 191, 192, 338. Trithio-carboni'o acid, 352.
-methylene, 34S. Troostwyk, Paets van, 184. Tropic acid, 584, 585. Tropidinc, 585. Tropine, 584, 585.
-carboxylic! acid. See ecgonine. Trypanosomiasis, 462. Tryptophan, 305, 577. Tube-furnace, 8, 9. Turkey-red, 550. Tyrian purple, 581 . Tyrosine, 331, 333, 334, 336, 338,
483.
U.
Undecane, 41. Undecylenic acid, 169. Under-proof spirit, 57. Unimolecular reactions, 126. Unsaturated acids. Monobasic, 169- 174.
alcohols, 166-168.
aldehydes, 175-178.
compounds, 148.
dibasic acids, 210-217.
halogen compounds, 164-166.
hydrocarbons, 76, 147-163, 379, 443.
ketones, 177. 178. Unsymmetrical compounds, 385. Uranium oxalate, 201. Urea, 1, 349, 352, 353-357, 363, 366.
iso-f 356.
nitrate, 354, 355.
oxalate, 355. Ureides, 362. Urcldo-acids, 362. Urethane, 15, 358, 359. Urethanes, 358, 359. Uric acid, 305, 362-368, 369.
group, 362-371. Urino, M(», 353, 354, 357, 365. Urochloralic acid, 256. ''rrotropinc," 142. Uviol lamp, 445. Uvitic acid, 300, 480.
V.
Vacuum-distillation, 21, 22. Valency of carbon, 19, 64, 99, 103. 151-155, 166, 532. ^ ' ' ' Valeraldehyde, 132.
-ammonia, 150-, 319. Valeric acid, 62, 108, 118, 333. Active, 204, 229. isr>-, 277. Valcrolacetonc, 221. Valervl-group, 109. Vanilla, 380, 482. Vanillin, 482. 483.
Vapour-density apparatus, Victor Meyer's, 12. Determination of, 12, 13. Victor Meyer's method for. 12, 13. Vaseline, 38, 39. Vat-dyeing, 580.
-dyestuffs, 580, 681. Vegetable-fats, 34, 113.
-ivory nut, 271. Velocity of formation of tetra-alkyl-
ammonium iodides, 85. Veratrole, 454.
Vesuvine. See Bismarck-brown, Vici<i augustifolia, 277. Vicianin, 277. Vicianose, 277. Vicinal compounds, 385.
ViLLIGER, 314.
Vinegar, German or Quick process for, 110.
-manufacture, 110. Vine-lice, 352. Vinyl-acetic acid, 171.
alcohol, 166, 167.
bromide, 164, 165, 166.
chloride, 165, 166.
-ethylene, 157.
-group, 167. Violets, 178. Violuric acid, 364. Viscose, 297. Viscosity, 111. Vital force, 1. Vitellin, 328. Volatile fatty acids, 113.
VOLHARD, 347. VORLANDER, 408.
Vulcanite, 521. Vulcanization, 184, 352, 521.
W. Wadmore, 350. Walden, 230, 321-323. inversion, 321-323.
Walker, JiOCEB, 364. Wiot,66.
Earth-, 39.
Paraffm-, ag, 198, 114. Weak hydrolvais, 301, Weigel, 20. Weld, 472. Webnbr. 99, 32S. Whey, 278. Whiskv, 56. White load, 112.
WlU'ARTB, 8.
WnxiAMsoN, EtheT'SyatbesiH of, 74.
WiLLSTATTER, 5S5.
Wine, 56, 110.
Spirits of, 56. Wines, Fortified, 56. WiNKLKn, 97.
WiSLlCENUB, 252.
Wnr, 464.
W6HLBR, 1, 2, 344, 354, 35S.
WOLLAHTON, 335.
Wood, 265 296, 296.
-charcoal, 481.
Combustion of. 111.
Distillation of, S3, 64.
-spirit, 54, 58, 146.
•flugar. SeexylMe.
-Ur, 54. Woodruff, 484. Wottra, Zi, 346.
FrsctionatinR column of, 23.
Xantho-chdidonic acid, 311, 312.
-protdn-reaction, 337, 330, 333. Xanthone, 472.
dvee, 472. Xylene; m-, 391. 393. 491, 492.
0-, 393, 488, 489.
P-, 39», 492- Xylenesul phonic acids, 392. Xylenes, 389, 390, 487, 666. Xylic acida, 428. Xylidines, 404. Xvlitnl, 153, 262, 265. Xvbnic acid, 265. Xylose, i6a, 164 165, 274. Xylylene bromide, »-, 536.
Yeast, 55, 185, 320.
-cells, 54, 38s, 386. yotiNQ, SoNBT. 23, 41, 42, 53. Formula of, 41, 42, 53.
Fractionating-oolunin of, 23.
Zelhtskt, 605.
Zinc allddeB, 100, 101, 105,
ethide, 100.
lactate, 227.
methide, 100, 133, 187.
propide, 100. Zymase, 286.
M