Kinetics of the Selenium Dioxide-Catalyzed Hydrogen Peroxide Oxidation of Dimethylaniline in Aqueous Methanol

Abstract

Abstract The selenium dioxide-catalyzed oxidation of dimethylaniline with hydrogen peroxide was investigated kinetically at 40∼60° in 50∼95 volume % aqueous methanol. The rate of the consumption of hydrogen peroxide at constant acidity of the reaction mixture was expressed as v=k[H2O2] [SeO2] [Dimethylaniline]+k′[H2O2] [SeO2] The first term of this equation seems to correspond to the rate of a reaction between dimethylaniline and a complex (I) produced rapidly from selenium dioxide and hydrogen peroxide, while the second term corresponds mainly to a slow reaction between selenium dioxide and hydrogen peroxide to yield the complex (II) followed by a rapid reaction with dimethylaniline. The energy of activation was 11.7 kcal. When perchloric acid was added to the reaction mixture, the pseudo-first-order rate constant with respect to hydrogen peroxide first increased and then decreased via a maximum, which was explicable by the assumptions of the dissociation of the intermediate and the protonation of dimethylaniline. Electron-releasing groups tended to increase the rate. An increase of the water content in the solvent methanol decreased the rate. There was no evidence for the radical mechanism under these experimental conditions.