Kinetics and correlation analysis of reactivity in the oxidation of organic sulfides by butyltriphenylphosphonium dichromate

Abstract

The oxidation of a number of monosubstituted aryl methyl, alkyl phenyl, dialkyl, and diphenyl sulfides by butyltriphenylphosphonium dichromate (BTPPD), to the corresponding sulfoxides, is first order with respect to BTPPD and is second order with respect to sulfide. The reaction is catalysed by hydrogen ions and the dependence is of second order. The oxidation of meta- and para-substituted aryl methyl sulfides correlated best in terms of Hammett equation, the reactions exhibited negative polar reaction constant. The ortho-substituted compounds correlated best in terms of Charton’s triparametric equation with negative polar constant and a small degree of steric hindrance. The oxidation of alkyl phenyl sulfides exhibited a good correlation in terms of Pavelich-Taft equation confirming that the electron-donating power of the alkyl group increases the rate, however, the reactivity is not markedly controlled by the bulkiness of the alkyl group. The rates of oxidation of sulfides were determined in nineteen organic solvents. An analysis of the solvent effect by multi-parametric equations indicated the relatively greater importance of the cation-solvating power of the solvents. A mechanism involving a single-step electrophilic oxygen transfer from BTPPD to the sulfide leading to polar transition state has been proposed.