<正> The kinetics of oxidation of thiocarbohydrazide in the free and zinc（Ⅱ）-bound states byacid bromate have been studied in aqueous and water-acetic acid（1:1,V/V）media under varyingconditions,both in the absence and presence of added bromide ion.The rates of oxidations show firstorder kinetics in[bromate]in all the cases,but exhibit different kinetic behaviour in[substrate]and[H+].Oxidation of TCH in aqueous medium shows zero order in[TCH]and nearly second order in[H+],while oxidation in aqueous acetic acid shows two ranges in[H+].The rate shows first and fractionalorder kinetics in[TCH]in the first and second acid ranges.Kinetics observed in the presence of Br-are similar to those observed for oxidation of TCH in second acid range.In addition,the reactionshows fractional order in[Br-].Oxidation of TCH in Zn（Ⅱ）-bound state exhibits first order kinetics in[substrate]and second order in[H+].Increase in ionic strength of the medium decreases the rate in allthe cases.Increase in acetic acid composition of the solvent increases the rate.Mechanisms consistentwith the observed results have been considered and the rate laws deduced.The rate limiting steps havebeen identified and the coefficients of these steps have been calculated at different temperatures.Therelated activation parameters have also been computed.The validity of the deduced rate laws has alsobeen tested by recalculating the rate constants from them as[TCH]and[H+]are varied.
