Kinetics and mechanism of oxidation of benzohydrazide by bromate catalyzed by vanadium(IV) in aqueous acidic medium

The reaction between benzohydrazide and potassium bromate catalyzed by vanadium(IV) was studied under pseudo-first-order condition keeping large excess of hydrazide concentration over that of the oxidant. The initiation of the reaction occurs through oxidation of the catalyst vanadium(IV), VO2+, to vanadium(V), VO2+, which then reacts with hydrazide to give N,N'-diacylhydrazine and benzoic acid as the products. The order in [H+] is found to be two, and its effect is due to protonation and hydrolysis of oxidized form of the catalyst to form HVO3. The oxidized form of the catalyst, VO2+, forms a complexwith the protonated hydrazide as evidenced by the occurrence of absorption maxima at 390 nm. The rate of the reaction remains unaffected by the increase in the ionic strength. The activation parameters were determined, and data support the mechanism. The detailed mechanism and the rate equation are proposed for the reaction. (c) 2008 Wiley Periodicals, Inc.