June 20, 1959
REACTIONS WITH DISULFIDEA N D
Exposed samples of X-pentylhexanamide were extracted with water and the extract evaporated t o dryness. T h e lowmelting residue was recrystallized from isooctane t o obtain white crystals melting a t 88-90’ (hexanamide melts a t 9798’). The identity of these crystals as hexanamide was established by the exact correspondence of the X-ray diffraction pattern obtained from them with t h a t given by authentic hexanamide. Addition of l o yo sodium hydroxide solution t o photooxidized N-pentylhexansmide caused evolution of suflicient amounts of either ammonia or an amine t o be detected by litmus paper. Quantitative estimation by the ninhydrin procedure and by the method of Vat1 Slyke and C ~ l l e n estab’~ lished t h a t less t h a n 2 mg. of ammonia was formed upon exposure of 10 g . of N-pentylliexanamide for 285 hours. Qualitative tests for hydroxylamine and hydrazineI6 were (15) P. B. Hawk, B. L. Oser and W. H. Summerson, “Practical Physiological Chemistry,” twelfth edition, Blakiston Co., Philadelphia, Pa., 1917, I). 50. (16) P. Feipl, “Spot Tests,’’ translated by R . E. Oesper, third edition, Elsevier Publishing Co.. New York, N. Y., 1947, p. 180.
[CONTRIBUTIOS FROM
THE
hfERCAPTANS
3005
negative. Infrared spectra of irradiated N-pentylhexanamide and of the residual amide after acids had been removed showed no indication of nitriles. Gas samples were analyzed by t h e Orsat procedure using a Burrell build-up laboratory model analyzer. Carbon dioxide, oxygen a n d unsaturated hydrocarboiis were determined by usual absorbing reagents. Hydrogen and carbon monoxide were determined by combustion over hot copper oxide in the normal way. Oxygen was added and paraffin hydrocarbon: were burned t o carbon dioxide over platinized silica at 500 . Inert residual gas was reported a s nitrogen. Identity of the inert gas was verified by Inass spectrometric analysis.
Acknowledgments.-We are indebted to Dr. J. H. Peterson of this Laboratory for radioactivity measurements. Many helpful discussions with Professors C. S. Marvel and Carl Niemann are gratefully acknowledged. WII~MINGTOS 98, DEL.
DEPARTMENT O F CHEMISTRY
OF
BRANDEIS UNIVERSITY]
Some Light Ihduced Reactions with Disulfide and Mercaptan BY CHI HUAWANGAND SAULG. C O H E N ~ RECEIVEDDECEMBER l G , 1958 Thiyl radicals from a-thioglycerol and from sun lamp irradiation of bis-(2,2’-carboxyphenyl)disulfide (11) failed to abstract hydrogen from acetic acid or a n electron from acetate anion, and irradiated I1 failed to undergo intramolecular hydrogen or electron transfer. On irradiation, I1 was reduced t o thiosalicylic acid I by ethanol and 2-propanol, and compound I was oxidized t o I1 by acetone. Pinacol appeared t o be the major product of oxidation of 2-propanol by di-n-butyl disulfide and nf reduction of acetone by thiosalicylic acid Disulfide I1 was not reduced under our conditions by t-butyl alcohol, diisopropyl ether, isoprop) 1 acetate, benzene, toluene, chloroform and lactic acid, but appeared t o be reduced by ethyl lactate, leading t o ethyl pyruvate. The course of these reactions IS discussed.
I n the course of our study of the exchange of diphenylniethyl radical, produced from azo-bisdiphenylmethane, with diphenylmethane, we have observed? catalysis of this process by thiophenol by the reversible process 1. Conditions were (C6Ha)2CH.
+ CGH;SH
a
+
(CGHI)?CHB C ~ H S S . (1) b
found under which approximately half of the diphenylmethyl radicals which became free reacted with mercaptan (reaction la) before dimerizing or reacting with thiyl radical, while approximately one-fourth of the thiyl radicals so formed abstracted a-hydrogen from solvent diphenylmethane (reaction l b ) before dimerizing or reacting with diphenylmethyl. It seemed desirable to review and investigate hydrogen transfer reactions of mercaptans and thiyl radicals. Mercaptans are oxidized by a variety of reagents, including organic free radicals, the first product normally isolated being the disulfide. The transient thiyl radicals may, before entering into radical combination processes, act as hydrogen abstracting agents. Thiyl radicals, formed by reaction of 2-cyano-2-propyl radicals with mercaptans, oxidize 9,10-dihydroanthracene to a an aliphatic azo derivative of 9,9’-di~~nthranyl,~ compound to an azine,4 and a disubstituted hy(1) T o whom inquiries should be addressed. (2) C. H. Wang and S. G . Cnhen, THISJ O U R N A L , 79, 1924 (1957). ( 3 ) P. Bruin, A. F. Bickel a n d E. C. Rooyman, Rec. Irav. chim., 71, 1115 (1952). (1) A. F. Bickel a n d I?. C . Knoyman, N o t e r r , 170, 211 (1952).
drazine to an aliphatic azo c ~ m p o u n d . ~They may also abstract hydrogen from the carbonyl carbon of aldehydes, catalyzing their decarbonylation,6leading in this case to chain reactions. The disulfides are also very reactive, undergoing rupture of the S-S linkage under acidZaOb and basicia,c catalysis and by radical dissociation.8a,h The dissociation into thiyl radicals may be thermal, a t elevated teniperature,gJ and this may be facilitated by radical-type initiator^,^^ or it may be induced by light. Diisoamyl disulfide, presumably acting by formation of thiyl radicals, aromatize.; tetralin and ionene, gb and diphenyl disulfide aromatizes’O tetralin and other hydroaromatics a t 260’ and is reduced by cyclohexene a t 140’. The photolysis of disulfides initiates the polymerization of styrene,” catalyzes the addition of mercaptans to olefins12 and converts diphenylmethane to tetraphenylethane.2 Disulfides in ( 6 ) M . Okawara, 3. Chent. SOC.Japan, 68, 142 (1955); C. A , , SO, 4012 (1956). (6) (a) E, F. P. Harris and W. A. Waters, Natzwe, 170, 212 (1952); (h) K. E. J. Barrett and W. A. Waters, Disc. Faraday SOC.,14, 221 (1963). (7) (a) A. P. Ryle and F. Sanger, Biochem. J . , 6 0 , 536 (1965); (b) R . E. Benesch and R. Benesch, THISJ O U R N A L , 80, 106G (1958); (c) A. Fava, A. Iliceto and E. Camera, i b i d . , 79, 833 (1957). ( 8 ) (a) G. Leandri and A. Tundo, A n n . chi7n. ( R o m e ) ,4 4 , f13 (l9:4!; (b) 11. 2. Lecher, Science, 140, 220 (1954). (9) (a) A. Schonberg, E. R u p p and W. Gumlich, Ber., 6 6 , 1932 (1933); (b) J. J. Ritter and E. D. Sharpe, THISJ O U R N A L , 69, 2351 (1937). (10) M. Nakasaki, J . Chem. SOC. JaDan, 74, 403, 518 (1953). (11) T. Otsu, J . Polymer Sci., 21, 569 (196G). (12) h l . S. Kharasch, W. Nudenberg and T. H . hfeyer, J. Org. Chrm., 18, 1233 (1933).
light convert benzohydrol to benzopinacol and benzyl alcohol to some extent to benzaldehyde, wliilc mercaptans convert benzophenoiie to ben7opinacol. l 9 These nroniatic systems may be particularly reactive, p1iotochemic:il reductioti of benzophenone to benzopinacol being very readily effected by alcohol14and even by ether,I4 and ccrtain hydrocarbons'j"; such reductions are sensitive to structural change'j" in both components. It seemed to us to be of interest to examine the oxidation-reduction reactions of disulfide-mercaptan with some organic compounds in which reactivity was not highly enhanced by allylic or bcnzyltype resonance. I n most of the experiments solutions or suspensions of a disulfide were irradiated with a sun lamp in Pyrex for several days. Iii one group of experiments the action of thiyl radical on carboxylic acids and carboxylate anion was examined. In some preliminary experiments nzo-bis-isobutyronitrilewas tlecoinpnsed in acetic acid containing potassium acetate and a-thioglycerol, and in others the acetic acid-sodium ncetate-mercaptan solution was warmed with hexaphenylethane. Thiyl radicals presumably were formed in both cases, but there did not appear to be any appreciable reaction between them and the acetic acid or the acetate anion. In the experiment with the azo compound the loss in weight was less than the theoretical weight of the nitrogen to be evolved, indicating that abstraction by the thiyl radical of the carboxyl hydrogen or the carboxylate electron, which would lead to evolution of carbon dioxide, probably had not occurred. The reaction in thc presence o f hexaphenylethane was examined for succinic acid, but none was found, indicating t h a t abstraction of a-hydrogen had not occurred. Irradiation of bis-(2,2'-carboxyphenyl) disulfide (11) then was examined as a source of thiyl
radicals in a variety of solvents. This compound was used primarily because both the mercaptan and disulfide could be isolated fairly readily as solids without excessive inconvenience. 12 suspension of this in acetic acid was irradiated for 92 hours, t h e disulfide being recovered in 73% yield as the only isolable product. Similarly, irradiation of (i) a suspension of the disulfide in water for ten days, (ii) of a solution of the disulfide in dioxan-water for one day, and (iii) of a solution of the potassiuin salt of the disulfide in water for six hours led to recovery of the original disulfide in greater than no(;; yield. In this example the carboxyl group or carboxylate anion and the sulfur radical appear to be well located for interaction. The re:ictions would be revcrsible, and, on energetic ( I . { ) 11. NxkaqaLi, J O i ~ J i l . Cinmicinn ;in11 P,, er, Aw , 3 4 , 13L1 (1901); 44, 1 X 1 k (l!ll I). (I.-,) ( 3 ) IC. I k r j i m a n n and S. I c u j i w , . A n n , 483, fi5 (1930); (I,) 1'. Ilcrgmann :ind Y . Hirshberg, Tws J O Y R N A I . . 65, 1 $ 2 0 (1'3.13). ( l ( i ) X
