Oxidation of substituted phenyl methyl sulphides by N-chloroacetamide in acidic medium: A kinetic and mechanistic study

Abstract

The kinetics of oxidation of several substituted phenyl methyl sulphides by Nschloroacetamide (NCA) yielding sulphoxides have been studied in acidic aqueous acetonitrile medium. The reaction displays first-order dependence each in [sulphide], [NCA]and [H⁺]<em>. </em>The reaction rate is not influenced by the addition of acetamide, mercuric acetate &amp;I1dacrylamide. Presence of electron releasing substituents in the phenyl ring enhances the rate while that of opposite ones retards it. A good Hammett correlation between the rate data and a constants is obtained with a &rho;-value of - 3.29 at 313K (r = 0.999). The results point to a polar mechanism involvingthe rate-limiting formation of a chlorosulphonium cation by the electrophilic attack of a protonated NCA on the sulphide sulphur. The chlorosulphonium cation presumably hydrolyses to sulphoxide in a fast step.