Reactions of aryl sulfides and phosphorus(V) esters of thiols with acidic hydrogen peroxide

Oxidations of sulfides and phosphorus(V) esters of thiols by H2O2 are catal yzed by H2SO4 and HClO4. Sulfides are 4-ZC(6)H(4)SMe, 1a-1e, respectively, Z = MeO, Me, H, Cl, NO2; PhSCH2CH2Cl, 2, Ph2S, 3, and the esters are Ph(R)P O . SEt, 4a, 4b, R = Ph, EtO. Electron donation by Z moderately accelerates reaction, but the sulfides are much more reactive than the eaters. Reactio ns are first order in H2O2 and substrate, and second-order rate constants, k(2), in H2SO4 are related to excess acidity, X. Plots of log k(2) against X have slopes in the range 0.61-0.85. Rate constants are similar for given concentrations of H2SO4 and HClO4, except that with greater than 50 wt.% H2 SO4 peroxymonosulfuric acid is formed and the observed rate constants then increase. Methanesulfonic acid is a less effective catalyst than the minera l acids. Oxidations of the sulfides are also catalyzed by strongly acidic i on-exchange resins.