Kinetic and mechanism of oxidation of thiocarbohydrazide and its metal complex by acid bromate in aqueous and partial aqueous media

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 inbromate]in all the cases,but exhibit different kinetic behaviour insubstrate]andH~+].Oxidation of TCH in aqueous medium shows zero order inTCH]and nearly second order inH~+],while oxidation in aqueous acetic acid shows two ranges inH~+].The rate shows first and fractionalorder kinetics inTCH]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 inBr~-].Oxidation of TCH in Zn(Ⅱ)-bound state exhibits first order kinetics insubstrate]and second order inH~+].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 asTCH]andH~+]are varied.

Kinetic and mechanism of oxidation of thiocarbohydrazide and its metal complex by acid bromate in aqueous and partial aqueous media

The kinetics of oxidation of thiocarbohydrazide in the free and zinc(II)-bound states by acid bromate have been studied in aqueous and water-acetic acid (1:1, V/V) media under varying conditions, both in the absence and presence of added bromide ion. The rates of oxidations show first order 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 fractional order 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 reaction shows 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 all the cases. Increase in acetic acid composition of the solvent increases the rate. Mechanisms consistent with the observed results have been considered and the rate laws deduced. The rate limiting steps have been identified and the coefficients of these steps have been calculated at different temperatures. The related activation parameters have also been computed. The validity of the deduced rate laws has also been tested by recalculating the rate constants from them as TCH] and H⁺] are varied.