Kinetics of the oxidation of dimethyl sulfoxide with aqueous hydrogen peroxide catalyzed by sodium tungstate

Abstract

The oxidation of dimethyl sulfoxide (DMSO) by hydrogen peroxide in the presence of a catalytic amount of sodium tungstate (Na 2 WO 4 ) has been studied kinetically by means of iodometry of hydrogen peroxide. The reaction is first-order with respect to the substrate and the catalyst, but independent of the concentration of hydrogen peroxide which is present in excess of the catalyst. The polarographic study implies that in solutions two main kinds of peroxytungstic acids (H 2 WO 5 and H 2 WO 8 ) are formed which contain active oxygen in ratios (active oxygen):(Na 2 WO 4 ) of 1:1 and 4:1, respectively. The effect of acidity on the oxidation rate and a probable mechanism involving a rate-determining attack of peroxytungstic acids are discussed.