MOLYBDENUM(VI) CATALYSIS IN PERBORATE OXIDATION - OXIDATION OF SOME PARA AND ORTHO-SUBSTITUTED S-PHENYLMERCAPTOACETIC ACIDS

Molybdenum(VI) catalyzed perborate oxidation of S-phenylmercaptoacetic acid in aqueous acetic acid is zero order in perborate, first order i n S-phenylmercaptoacetic acid and second order in molybdenum(VI). The oxidation is independent of [H+] and solvent composition. The kinetic results point to dimeric tetraperoxy-1,a-molybdate anion as the reacti ve oxidizing species. Electron-releasing substituents accelerate the o xidation rate and electron-withdrawing substituents decelerate the rat e. Linearity of Exner's plot indicates operation of a common mechanism throughout the series. Hammett plot with negative rho value implies d evelopment of electron-deficient sulfur in the transition state. Study of ortho effect reveals insignificant steric effect. Resonance and in ductive effects are equally dominant.