Oxidations by iron(VI). Kinetic study of uncatalysed and osmium(VIII) catalysed oxidation of dimethyl sulphoxide in alkaline medium

Summary Uncatalysed and Os^VIII-catalysed oxidation of dimethyl sulphoxide (DMSO) by potassium ferrate [Fe^VI] has been studied in alkaline medium in the 9.8–11.9 pH range, in the presence of IO₄^– as a stabilizing agent. The order in [Fe^VI] and [DMSO] was found to be unity for the uncatalysed reaction and zero and fractional respectively for the catalysed reaction. The [Os^VIII] order was unity in the catalysed reaction. The rate of oxidation decreased with increase in pH and the order in [H⁺] was fractional for the uncatalysed oxidation. However in the catalysed oxidation, the rate at first decreased and then increased with increase in pH. The effect of changing [IO₄^–] and [buffer] on the oxidation rate was negligible in both cases. Suitable mechanisms consistent with the observed kinetics have been proposed.