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SIN CHEONG WONG. Can. J. Chem. 56,935 (1978). The rates of hydrolysis of thioacetic, thiobenzoic, and three substituted thiobenzoic acids increase with concentration of solvent sulfuric or perchloric acid to a maximum in 30-40% acid and then decrease. Yates-McClelland r, Bunnett-Olsen 6, and Hammett p parameters, and entropies of activation indicate an AA,2 mechanism over this range of acid concentrations. In acid concentrations above 50-60% the rates increase sharply and the same mechanistic criteria now indicate an AA,l mechanism. The difference between the rate-acidity profile of thiobenzoic acid and that of ethyl thiolbenzoate can be explained by the different response of the activity coefficients of their transition states to increase in sulfuric acid concentration. JOHN T. EDWARD, GRAEME WELCH et SIN CHEONG WONG. Can. J. Chem. 56,935 (1978). The hydrolysis of thiocarboxylic acids is catalyzed 1 by acid (I). 1Hipkin and Satchel1 (2) investigated the rates of hydrolysis of thioacetic and thiobenzoic acids in varying concentrations of hydrochloric acid, up to 4.80 M. The pseudo-first-order rate constants kb followed [H,O+] rather than the Hammett acidity function h,. This was taken to indicate an A-2 rather than A-1 mechanism for the acid-catalyzed hydrolysis. However, we have recently shown that although thiol esters are hydrolyzed by an AAc2 mechanism in 30-60% sulfuric acid, this mechanism is superceded by a very fast AAcl reaction in higher acid concentrations (3, 4). Consequently, it became of interest to investigate the acid-catalyzed hydrolysis of the thio acids over a wider range of acid concentrations. In this paper we report kinetic studies of the hydrolysis of thioacetic acid, thiobenzoic acid, and three substituted thiobenzoic acids in concentrations of sulfuric acid up to 80% and of perchloric acid up to 67%. Experimental MaterialsThioacetic and thiobenzoic acids were conlmercial products. p-Methoxy-, p-methyl-, and p-chlorothiobenzoic acids were obtained by a standard procedure (5) from the substituted benzoyl chlorides and potassium hydrosulfide. The thioacids were freshly distilled before each kinetic run; titration against standard alkali then indicated them to be approximately 99.9% pure. (On standing several days the titre dropped, presumably because of oxidation to the disulfide.)Mineral acid solutions were prepared by dilution of reagent grade perchloric acid (70%) or sulfuric acid (96%) with distilled water and their concentrations determined by titration against standard alkali to phenolphthalein end point.

. 55, 812 (1977).The ionization of 16 thiocarbonyl indicators of overlapping range has been used to establish an acidity function EI, for 10-90% ssulfuric acid. Agreement with an earlier HT scale of Tissier and Tissier using different thiocarbonyl indicators is good. Protonation constants PKTHC derived by the classic Hammett-Deyrup approach are in good agreement with those derived by the Bunnett-Olsen relations, but in less satisfactory agreement with those derived by the Marziano-Cimino-Passerini relations.

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SIN CHEONG WONG. Can. J. Chem. 57,1456 (1979.The tropane-3-spiro-5'-hydantoin (a isomer) obtained from tropinone by the BuchererBergs reaction has been shown by 13C nmr and X-ray diffraction studies to have the 4'-carbonyl group in the equatorial position; the isomer, obtained via the Strecker reaction, has this group axial. The results of these two reactions on cis-bicyclo[3.3.0]octan-3-one and on cis-3,4-dimethylcyclopentanone show, on the basis of the 'H nmr, 13C nmr, and X-ray diffraction studies of the products, a stereochemical course related to the preferred conformation of the cyclopentane rings.