MOLYBDENUM(6)-CATALYZED OXIDATION OF HYDRAZINE BY METHYLENE BLUE

The Mo(VI)-catalyzed oxidation of N2H5+ by methylene blue (MB) has been studied at pH 1.60. The reaction was found to be kinetically pseudo first order, with the rate dependent on Mo(VI) and N2H5+ concentrations and independent of MB concentration. The rate constant and activation parameters are essentially identical with those for the oxidation of N2H5+ by Mo(VI). To obtain information on the catalyzed reaction, the oxidation of MoV2 by MB has also been studied and has been found to proceed at a much faster rate than the catalyzed oxidation of hydrazine and with first-order kinetics, again independent of MB concentration. The results for the catalyzed oxidation of N2H5+ have been interpreted in terms of a slow oxidation of N2H5+ by Mo(VI) giving Mo(IV), followed by a fast oxidation of Mo(IV) by MB to regenerate Mo(VI). Small quantities of Mo(V) and MB radical, which are probably formed by competing reactions of Mo(IV) with Mo(VI) and the subsequent reaction of Mo(V) and MB, were detected by esr. A mechanism for the reaction involving Mo(IV), Mo(V), and MB radical as reactive intermediates is proposed.