Kinetics and mechanisms of oxidation of carbohydrazide by N-chloro and N-bromo benzenesulphonamides and hypochlorite ion in aqueous perchloric acid and buffered media

Abstract

Kinetics of oxidation of carbohydrazide (CH) by N-chloro- and N-bromo-benzenesulphonamides and hypochlorite ion have been studied aqueous perchloric acid and buffered media under varying conditions. In aq. perchloric acid the rates first decrease, then remain nearly constant and finally increase with increase in [H⁺] giving inverted bell shaped rate-[H⁺] profiles in all the cases. The reaction is first order in [oxidants] in all the ranges of [H⁺], with all the three oxidants. But the rate dependence in [substrate] is [H⁺] dependent. It shows varying orders ranging from fractional to first order. Addition of benzenesulphonamide, or the variation in either ionic strength or dielectric constant of the medium has no significant effect on the rates of oxidations, in all the cases. In buffered media also the reaction is first order in [oxidant], fractional order to first order in [CH],but is independent of <em>p</em>H<em>. </em>Two-pathway mechanisms have been considered to explain the observed results. The rate-limiting steps have been identified and the coefficients of these steps are calculated at different temperatures and hence the corresponding activation parameters. The rate constants predicted from the rate laws are in reasonable agreement with the experimental values.