Kinetics and mechanism of iridium(III) catalyzed oxidation of ethylene glycol by cerium(IV) in sulfuric acid media

Abstract

The kinetics and mechanism of trace iridium(III) catalyzed oxidation of ethylene glycol by cerium(IV) in sulfuric acid media has been investigated by titrimetric technique of redox in the temperature range of 298-313K. The reaction is first order with respect to Ce(IV) and Ir(III), and a positive fractional order with respect to EG. It is found that the pseudo-first order ([EG]>>[Ce(IV)]>>[Ir(III)]) rate constant, kobs, decreases with the increase of [HSO₄⁻] and increases with the increase of [H⁺]. Under nitrogen atmosphere, the reaction system can initiate polymerization of acrylonitrile, indicating the generation of free radicals. On the basis of the experimental results, a reasonable mechanism has been proposed. Rate equations derived from this mechanism can explain all the experimental results. From the dependence of kobs on the concentration of HSO₄⁻, the kinetically active species has been found to be Ce(SO₄)₂. The rate constants of the rate determining step and the activation parameters have been evaluated.