Kinetics and mechanism of oxidation of benzoic acid hydrazide by bromate catalyzed by Anderson type hexamolybdochromate(III) in aqueous acidic medium

The reaction between benzoic acid hydrazide and potassium bromate catalyzed by Anderson type hexamolybdochromate(III) was carried out under pseudo-first-order condition keeping large excess of hydrazide concentration over that of the oxidant. The reaction is accelerated by the hydrogen ion concentration due to the involvement of the prior protonation equilibria of both catalyst and the hydrazide. The protonated forms of the catalyst and the substrate are the active species in the reaction. The initiation of the reaction occurs through oxidation of the catalyst H[CrMo6O24H6](2-) to [O = (CrMo6O24H6)-Mo-V](3-) which then reacts with the hydrazide to give product without any intervention of free radical. The oxidized form of the catalyst [O = (CrMo6O24H6)-Mo-V](3-)was isolated and characterized by its FTIR spectra. The rate of the reaction also increases with increase in ionic strength and the decrease in the relative permittivity of the medium. Along with the effect of ionic strength and relative permittivity the activation parameters determined also support the mechanism. The detailed mechanism and the rate equation are proposed for the reaction.