Kinetics & Mechanism of Oxidation of Thiosemicarbazide by N-Chloro- & N-Bromo-Succinimides in Aqueous & Partially Aqueous Media

Abstract

Kinetics of oxidation of thiosemicarbazide (TSC) by N-chlorosuccinimide (NCS) and N-bromosuccinimide (NBS) have been investigated in aqueous perchloric acid and aqueous acetic acid (1 : 1, v/v) media in the presence and absence of mercuric acetate. Oxidation of TSC by NCS in both the media shows first order dependence in [NCS], inverse fractional order dependence in [H⁺] and fractional order dependence in [TSC]. While NBS oxidation in aqueous medium is first order in [NBS], inverse first order in [H⁺] and zero order in [TSC], that in aqueous acetic acid medium follows complex kinetics with first order in [NBS], fractional order in [TSC] and inverse fractional order in [H⁺]. Generally increase in ionic strength of the medium slightly decreases the rate, while variation in dielectric constant of the medium or the addition of reaction products has negligible effects on the rates. Mechanisms consistent with the observed rate laws have been suggested and constants of the rate limiting steps have been computed.