Mechanism of Sulfide Oxidations by Peroxymonocarbonate

Abstract

A detailed mechanism for the oxidation of aryl sulfides by peroxymonocarbonate ion in cosolvent/water media is described. Kinetic studies were performed to characterize the transition state, including a Hammett correlation and variation of solvent composition. The results are consistent with a charge-separated transition state relative to the reactants, with an increase of positive charge on the sulfur following nucleophilic attack of the sulfide at the electrophilic oxygen of peroxymonocarbonate. In addition, an average solvent isotope effect of 1.5 ± 0.2 for most aryl sulfide oxidations is consistent with proton transfer in the transition state of the rate-determining step. Activation parameters for oxidation of ethyl phenyl sulfide in tert-butyl alcohol/water are reported. From the pH dependence of oxidation rates and ¹³C NMR equilibrium experiments, the estimated pK_a of peroxymonocarbonate was found to be ∼10.6.