Correlation analysis of reactivity in the oxidation of some organic sulfides by tetrabutylammonium tribromide : A kinetic and mechanistic study

The oxidation of thirty-four sulfides by tetrabutylammonium tribromide (TBATB) resulted in the formation of corresponding sulfoxides. The reaction is first order with respect to both TBATB and the sulfide. The solvent composition effect indicated that the rate of reaction increases with an increase in the polarity of the medium. The reaction failed to induce the polymerization of acrylonitrile. There is no effect of added benzyltrimethylammonium chloride or potassium bromide ions. Chlorobromate ion has been postulated as the reactive oxidizing species. The rates of oxidation of meta- and para-substituted phenyl methyl sulfides were correlated with Charton's LDR equation. The rates of oxidation of the ortho-compounds showed excellent correlation with the LDRS equation. The oxidation of meta-compounds exhibited a greater dependence on the field effect. The reaction is subject to steric inhibition when an ortho-substituent is present. The oxidation of alkyl phenyl sulfides is subject to both polar and steric effects of the alkyl groups. The polar reaction constants are negative indicating an electron-deficient sulfur centre in the rate-determining step. A mechnaism involving formation of a halogenosulfonium cation in the slow step has been proposed.