Oxidation of organic sulphides by chlorine and iodosylbenzene diacetate: kinetics and mechanism

Abstract

Chlorine oxidises diphenyl sulphide and a range of cyclic analogues, and also the corresponding sulphoxides, in a reaction which is first order with respect to both chlorine and substrate; the order with respect to chloride ion is –1. These results are consistent with a mechanism similar to that usually accepted for oxidation by bromine or iodine. Oxidation of the same substrates by iodosylbenzene diacetate is acid catalysed, but zero order with respect to oxidant. A mechanism is proposed, involving rate-determining rehybridisation of a tetrahedral protonated sulphide, or sulphoxide, to a trigonal pyramidal form from which the oxidant abstracts a hydride ion simultaneously with nucleophilic attack by water. The same mechanism can account for the formation of sulphonium salts as by-products from the more reactive sulphides. Structural influences on reactivity can be rationalised in terms of electronic and steric effects.