Kinetics of Oxidation of Dimethyl Sulfide by Hydrogen Peroxide in Acidic and Alkaline Medium

Abstract

The kinetics of oxidation of dimethyl sulfide (Me2S) by hydrogen peroxide has been investigated spectrophotometrically in acidic and neutral medium. The rate law and other data indicate the reaction is first order with respect to both H2O2 and Me2S and is subject to catalysis by strong acids. The catalytic effect was found to be pronounced at a pH value of 1 or less. Differences in activation energies for acidic solutions (pH <7) and neutral solution (pH 7) indicate two different reaction mechanisms were operative. The rate law in strongly acidic medium was found to be -d[Me2S]/dt = (k'H + kHKH[H+])[H2O2][Me2S], where k'H is the observed rate constant in uncatalyzed neutral solution, the product kHKH is the catalytic constant for the acid-catalyzed reaction, kH is the equilibrium constant for the reaction of H+ with H2O2, and kH is the rate constant for the reaction of HOOH2+ with Me2S. For solutions of the same normality, the catalytic effect of HCl was found to be double that of H2SO4 at 20 °C. © 1986, American Chemical Society. All rights reserved.