Kinetics and mechanism of uncatalysed & Ir(III)-catalysed oxidation of oxalate ion by N-bromosuccinirriide in basic medium

Abstract

The title reaction in the presence of sodium hydroxide is first order in [NBS] both in the presence and absence of Ir(III) catalyst. However, the order in [C₂O₄]^2- is unity in the absence and fractional in the presence of Ir(III) catalyst. Increase in [OH^-] accelerates the reaction while the added succinimide retards the reaction rate. Increase in the ionic strength of the reaction medium increases the reaction rate in the case of uncatalysed reaction. The rate increases with decrease in dielectric constant of the reaction medium. All these observations show that the rate-determining step involves two negative ions. A mechanism involving the hypobromite ion as the reactive species of the oxidant has been proposed. Individual rate constants (<em>k</em>)<em>, </em>the formation constant (<em>K</em>_f) of the complex between oxalate ion and the catalyst at different temperatures and the corresponding thermodynamic parameters have been computed.