MECHANISMS OF REACTIONS OF THIOLSULFINATES (SULFENIC ANHYDRIDES) .3. SULFIDE-CATALYZED DISPROPORTIONATION OF ARYL THIOLSULFINATES

In acetic acid-1 % water containing some sulfuric acid the disproportionation of phenyl benzenethiolsulfinate (1) to phenyl disulfide and phenyl benzenethiolsulfonate is markedly catalyzed by added alkyl or aryl sulfides. Although the formal kinetics of this sulfide-catalyzed disproportionation are exactly the same as those of the previously studied sulfide-catalyzed 1-sulfinic acid2 and 1-mercaptan3 reactions, i.e., the reaction is first-order in both 1 and sulfide and subject to specific-H+ catalysis, the dependence of its rate on sulfide structure (Table IV) is entirely different from that observed for the other two sulfide-catalyzed reactions. Experiments using esr offer no indication that free radicals are intermediates in the reaction. For this reason the only mechanism for the sulfide-catalyzed disproportionation which appears to be compatible with both the kinetics and the dependence of rate on sulfide structure is the one shown in Chart III. This involves as its key step the sulfenylation of 1 by the ion R2S + SPh (2); and, while it might seem that this would normally lead to a greater than first power dependence of rate on thiolsulfinate concentration, it is shown that this is not the case, provided the sulfenylation step is faster than the hydrolysis of 2 to PhSOH and sulfide. Since arguments can be given why this should be the case, the mechanism in Chart III appears to be an acceptable one. © 1969, American Chemical Society. All rights reserved.