ACID-CATALYZED CLEAVAGE OF SULFOXIDES
Oct. 5, 1961 [CONTRIBUTION FROM
THE
4019
RICHARD BENBRIDGE WETHERILL LABORATORY OF CHEMISTRY, PURDUE UNIVERSITY, LAFAYETTE, IND. ]
An Acid-catalyzed Cleavage of Sulfoxides1 BY WILLIAMJ. KENNEY,JAMES A. WALSHAND DEREKA. DAVENPORT RECEIVED MARCH27, 1961 The synthesis and characterization of a series of R-substituted mercapto-, sulfinyl-, sulfonyl-, his-(mercapto)-acetic acids (where R = C6H5-, p-CH3C6H4-, m-CH(&H4-, p-( CH3)3CC6H4-, p-C1C6H4-, p-\SOzCsH4-) and some related cpmpounds are reported. The acid-catalyzed oxidation-reduction cleavage of a-sulfinyl acids, a-sulfinyl ketones and 8-disulfoxides
has been investigated and a mechanism is proposed
of a-sulfinyl ketones. Among the more indirect evidence may be mentioned the work of Fitger,Y Schoberl,lo Barnett,ll Hiinig and Boes,I2 Bordwell and Pitt,I3 and Sosnovsky.14 From these investigations, and those to be reported in the Experimental, the following generalizations may be made : (a) a-Sulfinyl acids, a-sulfinyl esters, a-sulfinyl ketones and p-disulfoxides disproportionate under a wide variety of acidic conditions to give products in which the sulfur atom has been reduced and the a-carbon atom oxidized. The oxidation-reduction products are formed in high yield. (b) Acid catalysis is a necessary factor, since the sulfoxides may be recrystallized from aprotic solvents and ethyl phenylsulfinylacetate may even be distilled without decomposition. (c) For the disproportionation to occur a t all, the carbon atom alpha to the sulfoxide must bear a hydrogen (d) When the a-carbon also bears a strongly electron-withdrawing group, the reaction is greatly 2C6HjSOCHzCOOH + f a ~ i l i t a t e d . ~ - lHowever, ~ dibenzyl sulfoxide,2 diI (CC&S)2CHCOOH OHCCOOH Hz0 isoamyl sulfoxide* and methyl 2-methylallyl sulfoxidelj are reported to disproportionate readily. I1 I11 Aryl P-acylvinylsulfoxides appear to be stable. ( C B H ~ S ) Z C H C O C ~ HC~HE,COCHO ~ -k HzO (e) In the arylsulfinylacetic acid series, the v VI presence of a p-CHS- group promotes the disproportionation whereas a +NO2- group retards ~CBHSSOCHZCOC~H~ it.17 IV J+2HOAc (f) By means of acetic anhydride,3 dry hydrogen halide^,^ thionyl chloride13or acetic acid, it is pos2CeHjSCH(OAc)COCeHj 2Hz0 sible to convert some sulfoxides into esters of VI1 a-hydroxythioethers. Recently, Sosnovsky has C6HjSOCH2SOC6Hj +(C&S)2 [HCOOH] reported14 that peresters convert thioethers to VI11 IX esters of a-hydroxythioethers, a reaction which Such reactions are by no means unknown. almost certainly goes through the sulfoxide. Since the first report by Smythe2 of the ready It is not yet known whether these compounds are cleavage of dibenzyl sulfoxide by dry hydrogen formed intramolecularly or, more reasonably, chloride, there have been reports of similar in- whether they are formed by initial cleavage to stabilities of sulfoxides in the presence of acids, inercaptan and the appropriate carbonyl compound, varying from dilute mineral acids, through dry followed by hemithioacetal formation and subhydrogen halides, to mercuric chloride. Thus sequent esterification. P ~ m r n e r e r , ~H i l d i t ~ h , ~ Larsson and J o n s ~ o n , ~ (8) B. Holmberg, J . p v a k l . Cheiiz., 141, 93 (1934); B. Holmberg. Hellstrom and LauritzsonB and Tananger? report Avkiv. Keini M i i z e v a l . Geol., 1 2 6 , 28 (1938); 1 4 6 , 9 (1940); 1 6 8 , instances of the disproportionation of various 20 (1942). (9) P. Fitger, Ber., 64, 2952 (1921). a-sulfinyl acids and esters under acidic conditions. A. Schoberl, A n n . , 607, 111 (1933); A . Scboberl and H. Eck, Holmberg* reports similar reactions for a number i b i(10) d . , 622, 97 (1936).
Introduction Preparatory to a study of their chelating tendencies, we have recently prepared a variety of bifunctional sulfoxides and sulfones. During the course of these preparations, usually carried out in acetic acid solution, we observed that oxidation of the appropriate thioethers led to anomalous products if the reaction mixtures were not kept cold. These anomalous products resulted because of the quite general instability of a-sulfinyl acids, a-sulfinyl ketones and 0-disulfoxides in acid solution. In each case, an a-carbon atom was oxidized and sulfur reduced. Thus, phenylsulfinylacetic acid (I) gives bis-(phenylmercaptojacetic acid (11) and glyoxylic acid (111); wphenylsulfinylacetophenone (IV) gives bis- (w-pheny1mercapto)-acetophenone (V) and phenylglyoxal (VI) or w-phenylmercapto-(acetoxy)-acetophenone (VII) ; bis- (phenylsulfinyl)-methane (VIII) gives diphenyl disulfide and, presumably, formic acid.
t
+ +
+
+ +
(1) Taken in p a r t from t h e thesis submitted by William J. Kenney in partial fulfillment of t h e requirements of t h e M.S. Degree. (2) J. A. Smythe, J . Chem. SOC.,95, 349 (1909). (3) R. Pummerer, Ber., 42, 2282 (1909); R. Pummerer, i b i d . , 43, 1401 (1910). (4) T. P. Hilditch, i b i d . , 44, 3583 (1911). (5) E. Larsson and K. Jonsson, i b i d . , 67B, 1263 (1934). ( 6 ) N. Hellstram and T. Lauritzson, ibid., 69B,2003 (1936). (7) A. Tananger, Arkiv. Kemi Mineral. Geol., 2 4 6 , 10 (1947).
(11) J. Barnett, J . Chem. SOL.,5 (1944). (12) S. Hiinig and 0. Boes, A n n . , 679, 23 (1953). (13) F. G. Bordwell and B. M. P i t t , J . A m . Chein. Soc., 77, 572 (1955). (14) G. Sosnovsky, J . Oug. Chem., 26, 281 (1961). (15) H. P. Koch, J . Chein. Soc., 2892 (1950). (16) N. K. Kochetkov and V. N. Vinogradova, J . Gen. Chewz. L'.S.S.R., 27, 2785 (1957). (17) J. A. Walsh and D. A. Davenport, t o be published.
WILLIAMJ. KENNEY,JAMES A. WALSHAND DEREKA. DAVENPORT
4020
Vol. 83
TABLE I
R
Yield,
%
--M.p., Exgtl.
Recrystti.
solvent
RSH Jr ClCHtCOrH X XI XI1
XI11 XIV
xv
XVI
100 CaHip-CHaCsIh9G ~ x - C H C O H P 90 P-l-BuCsHe 84 p-ClCsHr 87 80 P-OrNCsHc 75 CtHr
HZ0
95% E:tOH '35% EtOH Petr. etli. Petr. etii. Ha0 Distilled
-
63.6 88.5-00 67-68 58.5-50.0 104-105 149-151 Liquid
Carbon, Hydrogen, Calcd. Found Calcd. Found
'C.--
Lit.
NaOH
.
RSCKSCOZH4-NaCl f Ht0
63 5"
...... ...... ......
XVII XVIII XIX XX XXI
CSHV
82
P - C H I C ~ H ~ 53 ~c-CHICOHI- 50 p-l-B~CsHc79 9-CICsHr 54 P-OaNCsH474
RtOAc-CaIIi (1:3) HOAc HOAc Et20
MeKO Aq. MerCO
lOblO0
CsHr P-CH6CcHc 0-f-BuCsHc
XXVI
P-ClCaHc P-OsNCsH4-
xxv
62 98 '32 45 44
Ha0 Ha0 CsHo HnO i\q. MeiCO
5.1.65 54.55 69.98 43.93 41.93
00-91 125-1263 127.5-128 140-141' 177.0-177.5
RSCHtCOzH XSII XXIII XXIV
...... ...... ...... ......
+ 2H201
acetic acid
.. .. . I
*.
.. ..
%Neut. e w i v bound Cnlcd. Found
........ ........ ........ ........
168
168.2 182.2 182.2 224.3 202.7
180 183 224 204
184.2 198.2 . . . . . . . . 198.2 . . . . . . . . 240.3 10.05k 218.7 16.21' 6.111 G.05I 220.2
185 197 100 238 220 232
........ ............. . . . . . . . . 120.2 110
0 RS-CHSCO~H f HIO
......
112.5-113' 112-113
..
5.43 5.70 7.43
......
RSCH~COZH HaOn -+ cold I
..
5.53 5.53 7.10
...... ......
105' 156.7' 118d~m
acetic acid
+
......
50.31 59.20 50.31 59.57 04.26 64.06
r-Other Calcd.
64.98 54.57 60.00 44.14 42.06
*.
..
6.00 5.00 6.71 3.23 3.08
5.05 5.20 63.00 3.10 3.36
........ ........
0
+ KS-CHICO~H -l- 2HzO 0
111.5-112.5 110-110.5'' 114-115 , ,, 128-128.8 120.6-121.5 122' 171-172 1670
. .. ......
......
..
..
50.42 49.90 56.24 50.48
4.60 6.20
4.87 6.48
......
. I .
.*.
.. ..
.. ..
........
200.2 214.4 256.3 234.7 245.2
200 211 255 237 251
........
276.3 304.4 388.6 345.3
270 303 388 341
........ ........ ........ ........
0 acid 2RSCHzCOnH --f (KS)zC€ICOzH 4- OHCCOzH f H2O A
I1 XXVII XXVIII XXIX
XXX XXXI XXXII XXXIII XXXIV
xxxv
CsH53-CHaCsHifif-BuCsHcP-CICsH4-
00 82 87 70
CsHs0-CHaCsHr m-CHaCsHc 0-f-BuCaHr O-CICsHr CnHr
81
81
.. 95 .. >8B
A s . HOAc
101-103
Aq. HOAC 123-126 Aq. HOC 121.5-122 HOAc 180.5-181
HOAc HOAc HOAc Aq. EtOH Aq. EtOH Ao. HOAc
110-120 134-135 89-90 159.5-160 190.5-191 102-103
104-10Bh
......
..
..
......
63.13 62.83 68.00 68.27 48.69 48.58
5.38 7.26 2.92
5.25 7.41 3.14
118-110' 135i
...... ......
.. ..
..
......
5 5 . 5 6 55.81 61.71 61.64 42.73 42.98
4.97 7.07 2.76
4.85 7.04 2.78
...... ......
...... ......
104d
......
..
..
..
........
........
20.5zk 20.&
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.4Ik 10.35'
.............
H. D. Crockford and T. B. Douglas, J . Am. C h e m SOC.,56, 1472 (1934). H. Gilman and F. J. Webb, ibid., 71, 4062 (1949). 0. Behaghel, J . prakt. Chem., 114, 287 (1926). d H. Bohme, Ber., 69B, 1610 (1936). e K. Friesand G. Schiirmann, ibid., 47, 1200 (1914). J. Troeger and C. Budde, J. prakt. Chem., [ 2 ] 66, 146 (1902). 0 A. V. Sunthankar, B. D, R. Otto and J. Troger, Ber., 2 5 , 3426 (1892). Tilak and K, Venkataraman, Proc. Indian Acad. Sci., 38A, 23 (1953). ' R. L. Shriner, H. C. Struck and W. J. Jorison, J. A m . Chem. SOC., 5 2 , 2060 (1930). i E. Fromm, A. Foster and B. V. Scherschwitzki, .4nn.,394, 348 (1912). b Chlorine, %. 2 Nitrogen, %. B.p. (11 mm.). in 1.05 moles of aqueous sodium hydroxide was added 0.55 mole of chloroacetic acid. After refluxing for 2 hours and subsequent acidification, the acids were filtered and recrystallized from the solvents specified in Table I. Ethylmercaptoacetic acid (XVI) was isolated by continuous extraction of its aqueous solution with ether followed by distilExperimental lation under reduced pressure. Most of the experimental dataZoaBbare summarized in Preparation of Sulfkylacetic Acids.-Equirnolecular Table I. The general methods were as follows. amounts of 30y0 by weight hydrogen peroxide and merPreparation of Mercaptoacetic Acids.-To 0.5 mole of capto-acid were mixed in redistilled acetic acid, the tempurified thiol (all commercial products except p-NOz- perature being kept a t 0" for several hours. On concentraCaHlSH which was n a d e by the method of Price and Stacyz1) tion, the sulfinylacetic acids crystallized. They were recrystallized with the minimum amount of heating. (18) N . Kornblum, J. W. Powers, G. J. Anderson, W. J. Jones, 0. Preparation of Sulfonylacetic Acids.-One mole of Levand and W. M. Weaver, J . Am. Chem. SOC.,79, 0562 (1957); N. mercaptoacetic acid in redistilled acetic acid was oxidized Korohlum, W.J. Jones and G . J. Anderson, i b i d . , 81, 4113 (1959); with slightly more than two moles of 30% by weight hydroI. M. Hunsberger and J. M. Tien, Chemislry C Industry, 88 (1950). gen peroxide, the temperature being kept a t 0" for several (19) N.Kornblum, W.J. Jones and G. J. Anderson, 1.Am. Chem. hours and then allowed to warm to room temperature. Sac., 81, 4113 (1959); H . R. Nace and J. J. Monagle, J . Org. Chcm., In the case of the p-C1- and p-NOz- compounds, the re24, 1792 (1959);M.M.Baizer. ibid., 26, 670 (1960). action mixture was then heated a t 70' for 1 hour. Removal (20) (a) All melting points are uncorrected. All equivalent weights of the solvent by distillation gave the crude acid. The were determined in water (or acetone-water) to a phenolphthalein endrather poor yields for some of these preparations were caused point. All yields are of pure materials. (b) Microaoalyseu are by by the difficulties encountered in purifying the crude maUr. C. S. Yeh aud Mrs. I. Groten of this depurtirxnt aud by Galbrsith terial, formed in close to quantitative amounts.
Mechanisms for these reactions and their possible relationship to the recently much-investigated reactions of dimethyl sulfoxide with alkyl halides1* and tosylateslBwill be suggested in the Discussion.
hlicroanalytical Laboratories, Knoxville, Tena. are by Mrs. W. Dilling.
The infrared spectra
(21) C. C. Price and G. W. Stacy, J . Am. Chcm. Soc., 68,498(1846).
Oct. 5, 1961
ACID-CATALYZED CLEAVAGE OF SULFOXIDES
402 1
The Cleavage of Sulfinylacetic Acids.-The sulfinylacetic Anal. Calcd. for Cl,HnO&: C, 68.83; H, 4.95. Found: acids were dissolved in redistilled acetic acid and refluxed C, 68.73; H , 5.00. overnight. With the p-Cl- and @--Nor compounds, warmOxidation of this sulfoxide with an excess of 30% by ing with 6 N sulfunc acid was found to be more effective weight hydrogen peroxide in cold acetic acid, followed by than refluxing with acetic acid. On removal of the solvent, removal of the solvent and recrystallization from 95% the products were washed with water and recrystallized. ethanol, gave a 53% yield of w-phenylsulfonylacetophenone, The glyoxylic acid in the wash water was identified as the m.p. 92-93'. Mixed melting point with an independently 2,4dinitrophenylhydrazone and also as the semicarbazone. synthesized sample" showed no depression; infrared abBy using an aliquot and weighing the derivative, the yields sorption (CHCb): 1690,1328,1274, 1157 cm.-'. of glyoxylic acid were shown to be considerably higher Preparation of w-Phenylmercapto-(acetoxy)-acetophenone than those reported in Table I, which are based on the (VU).-Refluxing of o-phenylsulfinylacetophenone (IV) in amount of pursed bis-(mercapto)-acetic acid obtained. glacial acetic acid for 11 hours, removing the solvent In the case of the @ - N o r compound, no bis-(p-nitrounder reduced pressure, extraction from aqueous suspension pheny1mercapto)acetic acid was obtained but instead with ether, evaporation of the ether and subsequent rethe corresponding disulfide (m.p. 181') was isolated in crystallization from isopropyl alcohol and drying in V ~ C U O moderate yield. The cleavage product of m-tolylsul- gave a 4570 yield of fluffy, white needles, m.p. 65.0-66.0'; finylacetic acid (XVIII), presumably the expected bis-(m- infrared absorption (CCL): 1770, 1715, 1370, 1225, 1050 toly1mercapto)-acetic acid, was obtained only as an intrac- cm.-l. table oil. On oxidation with excess hydrogen peroxide in Anal. Calcd. for CleHl,O,S: C, 67.10; H, 4.93; S, acetic acid solution, this oil yielded the expected bis-(m- 11.20. Found: C, 67.00; H, 4.84; S,11.18. tolylsulfonyl)-methane (XXXII). A 22% yield of bis-( w-pheny1mercapto)-acetophenone Preparation of Bis-(sulfonyl)-methanes.-The bis-(mer(V) also was isolated from this reaction of the sulfoxide. capto)-acetic acids obtained from the oxidation-reduction Preparation of w-Phenylsulfonyl-(acetoxy)-acetophenone. cleavage of the phenylsulfinylacetic acids were refluxed in redistilled acetic acid with an excess of 3070 by weight of --o-Phenylmercapto-(acetoxy)-acetophenone (VII) was dishydrogen peroxide. After several hours, the solvent was solved in glacial acetic acid and oxidized with excess 30% removed and the crude product washed with water. Re- by weight hydrogen peroxide at room temperature. Recrystallization from the solvent specified gave the yields moval of the solvent under reduced pressure and then recited in Table I. The yield reported for bis-(ethylsulfony1)- crystallization from isopropyl alcohol gave a 48% yield of w-phenylsulfonyl-(acetoxy)-acetophenone, as white needles, methane (XXXV) is the over-all one from ethylmercaptoinfrared absorption (CHCla): 1775, acetic acid (XVI) since the intermediate compounds were m.p. 93.0-94.5'; 1700,1332,1187,1072 cm.-'. not isolated. Anal. Calcd. for CleHlrObS: C, 60.36; H, 4.43; S, Preparation of w-Phenylmercaptoacetophenone.-w-Phen10.06. Found: C, 60.31; H, 4.52; S, 10.10. ylmercaptoacetophenone was prepared by the method of Delisle,** equimolecular amounts of sodium ethoxide, Acid-catalyzed Cleavage of Bis-(phenylsulhy1)-methane thiophenol and w-bromoacetophenone being mixed in ice- (VIII).-Bis-(phenylsulfinyl)-methane (VIII) was prepared cold absolute ethanol. After 2 hours the reaction mixture by the method of Shriner and Struck.26 On refluxing in was allowed to stand a t room temperature for 12 hours. acetic acid for 48 hours (or heating with 6 N sulfuric acid The solvent then was removed in vacuo and the residue for 24 hours) an 80% (or 77%) yield of diphenyl disulfide, washed free of sodium bromide with cold water. Recrystal- recrystallized from acetic acid, m.p. 58.0-58.5O, was oblization from ethanol gave a 61% yield of beautifully tained. The identity of this compound was verified by its formed, white needles, m.p. 53-54' (lit.rz 52-53'); in- infrared absorption spectrum and mixed melting point. frared absorption (CCL): 1670, 1264 cm.-l; 2,4-dinitroThe other product, presumably formic acid, was not isophenylhydrazone recrystallized from (1:1) ethanol-ethyl lated. acetate, as brilliant, brick-red needles, m.p. 150.0-150.5°. Formation of Fe(II1) and Cr(II1) Chelates.-Chelates A d . Calcd. for c&l&O~s: C, 58.82; H, 3.95; N, (or organic-solvent soluble salts) of phenylmercaptoacetic acid (X), phenylsulfinylacetic acid ( I ) and phenylsulfonyl13.72. Found: C, 58.88; H , 3.62; N, 13.49. If the above reaction mixture is refluxed, then bis-(w- acetic acid ( X X I I ) with both Fe(II1) and Cr(II1) were pheny1mercapto)-acetophenone (V) is formed. Recrystal- formed by the gradual addition of one mole of base t o an aqueous solution of the components in the mole ratio of lization from glacial acetic acid gives m.p. 98.5-100" (lit.*s 99-100'); infrared absorption (CHCl'): 1688, 1270 3:l. The products were all singularly unattractive compounds which were difficult to obtain in an analytically cm .-1. form. Typical was the compound, C2,HflO1&Fe, Anal. Calcd. for CloHleOSl: C, 71.40; H, 4.79; S, pure which was formed by gradual addition of sodium hydroxide 19.06. Found: C,71.30; H,4.81; S, 19.25. to a n aqueous solution of phenylsulfonylacetic acid and Preparation of Bis-(w-phenylsulfonyl)-acetophenone.ferric chloride. The compound was ruby-red, soluble in Oxidation of bis-( wpheny1mercapto)-acetophenone (V) organic solvents and had no well-defined melting point. in glacial acetic acid with excess 30% by weight hydrogen Anal. Calcd. for C24H21012QFe: C, 44.13; H, 3.24. peroxide gave a 61% yield of bis-( w-phenylsulfonyl)acetophenone. Recrystallization from acetic acid gave Found: C, 44.29; H, 3.50. In the case of the chromium compounds, it was necessary m.p. 182-183'; infrared absorption (Nujol): 1688, 1333, to heat the solution in order to cause reaction to occur. 1275,1178,1155,849,755cm.-1. anhydrous ferric chloride was added to a solution Anal. Calcd. €or C20H1606Sl: C, 59.98; H, 4.03; S, of When sodium ethoxide and bis-(phenylsulfiny1)-methane 16.02; neut. equiv., 400.4. Found: C, 59.71; H , 4.23; (VIII) [or bis-(phenylsulfonyl)-methane] in absolute S, 16.13; neut. equiv., 401. ethanol, the precipitation of sodium chloride indicated that Preparation of w-Phenylsulfinylacetophenone (IV).reaction had occurred but no pure compound could be w-Phenylmercaptoacetophenone (0.04 mole) was dissolved isolated. in 50 ml. of acetic acid, cooled to 0' and oxidized with an We do not intend to study these chelate compounds exact equivalent of 3oyo by weight hydrogen peroxide, further. added dropwise. After standing a t room temperature for Discussion 12 hours, the solvent was removed under reduced pressure to yield a yellow oil. Effecting crystallization of this oil The products in these disproportionations can proved difficult. All traces of acetic acid had to be removed and the ethereal extract very thoroughly dried with anhy- be rationalized if we assume the intermediate formation of mercaptan and the corresponding adrous sodium sulfate before the sulfoxide precipitated. Trituration of the sulfoxide with water, filtration and carbonyl compound. Then, we can have acidvacuum drying over phosphorus pentoxide gave a 60% catalyzed hemithioacetal (or hemithioketal) forrnayield of a white powder, m.p. 76-77'; infrared absorption tion, followed by two competing reactions: with (CHCb): 1685,1276,1047 cm.-I. (22) A. Delisle, Ber., 22, 309 (1S99). (23) F. Weygand and H. J. Bestmann, 2. Naturforsch., lob, 296 (1966).
(24) R. H. Knospe, Ph.D. Thesis, Purdue University, January, 1955, p. 49. (25) R. L. Shriner and H. C. Struck, J . A m . Chcm. Sod., 62, 2060
(isao).
WILLIAMJ. KENNEY, JAMES A. WALSHAND DEREKA. DAVENPORT
4022
Vol. 83
mercaptan to give the thioacetal (or thioketal) or to the mercapto and sulfonyl compounds. In with solvent acetic acid to give the a-acetate of the sulfoxides, there is a sulfur atom susceptible the hemithioacetal (or hemithioketal). It is to protonation and an oxygen atom which might known that such reactions occur readily under our effect a nucleophilic displacement; in the sulexperimental conditions and their mechanisms fones, there is only a less basicz6 oxygen atom are well understood. to displace on the carbon; in the mercapto comOur problem, therefore, reduces to the sugges- pounds there is a sulfur to protonate but no oxygen tion of a suitable mechanism for formation of atom to displace on the carbon. The stability mercaptan and the corresponding a-carbonyl of protonated sulfenic esters, of which C is a rather compound from a-sulfinyl acids, a-sulfinyl esters, specialized example, is hard to gauge. Sulfenic a-sulfinyl ketones and 8-disulfoxides. esters are known and some of their reactions with The general nature of the reaction, the acid acids have been ~ u m m a r i z e d . ~They ~ are all, catalysis, the effect of p-substitution on the rate however, of the non-activated type (Y = H or of disproportionation in the arylsulfinylacetic R") and their reactions may not necessarily acid series,17 and the absence of iodine formation parallel those of the present investigation. We when the reaction is catalyzed by hydriodic acid, intend to attempt the preparation of some actiall point to a heterolytic mechanism. Simple vated sulfenic esters and to study their reactions cleavage of the carbon-sulfur bond (with or with acids. In the above scheme, it is conceivable that steps without acid-catalysis) seems unlikely in view of the contrasting stability of the corresponding 2 and 3 blend into a synchronous process. Our mercapto and sulfonyl derivatives. The follow- belief that such is not the case is supported, in ing mechanism would seem to account in a reason- part, by an obvious parallel between this disproable manner for the experimental facts. portionation reaction and that mentioned above between dimethyl sulfoxide and various alkyl halides and tosylates. :O: I
r
+
R-S-CR'Y I
I'
:o:
H'Z
H
CH,-S:
I CHj D
B
A
I
1@
+
XCR'Y
1
H
~
-
i
L
J
R-S
It-s
H
C H3- S,-I
-
Hr
O=('lt Y
CH, H G
He, H O A ~
I
1
1.s
c
R-S
I
G
c:
B
r
H
1
E
r H
-+
-+
I------+
I i
1 CR Y
1
~
AcO
+ ILO
('R Y
HA
(4)
\H-,RsI:~~
C'R Y I H20
R-S
+
In A, where Y is any electron-withdrawing group, the oxygen atom is probably more basic than the sulfur atom, but the protonation of oxygen is barren of possibilities, while protonation of sulfur could lead to c v i a an SNi displacement reaction. This suggests a reason for the marked dzerence in stability of the sulfinyl as opposed
A
CH,
HX
Compounds of type F and G are both knownIz8 but it has not yet been established which is the primary product in the oxidation of activated alkyl halides E, to give dimethyl sulfide and the corresponding carbonyl compound. It is certainly suggestive that the halides which undergo oxidation most readily-benzylic bromides, phenacyl bromides and a-bromo acids and estersare precisely those which are known to give cleavage in the analogous sulfinyl compounds. (26) C. C. Addison and J. C. Sheldon, J . Chem. Soc , 2705 (1856); R.J. Gillespie and R.C.Passerini, ibid., 3850 (1956); R. G.Laughlin, J . Org. Chcm., 26, 864 (1960). (27) N. Kharasch, S. J. Potempa and H. L. Wehrmeister, Chem. Revs., 39. 328 (1946). (28) R. Kuhn, Angew. Chem., 17, 570 (1957); R. Kuhn and H. Trischmann, Ann., 611, 117 (1958); S. G. Smith and S. Winstein, Tetrahedron, 3, 317 (1958).
