Sulphines. Part VIII. Kinetics and mechanism of the reaction between aryl sulphines and perbenzoic acid

Abstract

Aryl sulphines are converted by perbenzoic acid into benzophenones, sulphur, and sulphur dioxide. The reaction shows kinetic features, namely the rate law as well as substituent and solvent effects, similar to those reported for the oxidation of thiones, sulphides, alkenes, acetylenes, and diazoalkanes with the same peroxyacid. The reaction is an example of oxidation of a cumulative, double-bond system and a multi-step reaction mechanism is advanced. The rate-limiting step is electrophilic attack of the peracid on the carbon–sulphur double bond of the CSO group to form a cyclic sulphinic ester; this intermediate, by rapid cleavage, gives the ketone and sulphur monoxide, the latter disproportionating into sulphur and sulphur dioxide. The reaction rates of the E- and Z-isomers of mesityl phenyl sulphine compared with that for diphenyl sulphine, give further evidence for the proposed mechanism.