KINETICS AND MECHANISM OF IRIDIUM(III) CATALYZED OXIDATION OF ETHANOLBY CERIUM(IV) IN AQUEOUS SULFURIC-ACID MEDIA

Kinetics and mechanism of iridium(III) (ca. 10(-6) mol dm(-3)) catalys ed oxidation of ethanol by cerium(IV) in aqueous sulphuric acid medium have been investigated at different temperatures (25 - 40 degrees C) under the conditions [C2H5OH](T) >> [Ce(IV)](T) >> [Ir](T). The rate l aw conforms to: -d ln[Ce(IV)]/dt= k(0) - A(1)[C2H5OH](T) [Ir](T)/(B-1 + C-1 [Ir](T)) D [C2H5OH](T) +E where A(1), B-1, C-1, D and E are cons tants at a particular temperature at a fixed [H+], and [Ir](T) gives t he total concentration of iridium added as catalyst. An intermediate i nvolving the oxidant, catalyst and substrate has been proposed as bein g formed in pre-eqilibrium steps before the electron transfer step thr ough the Ir(III)/Ir(IV) catalytic cycle. The electron transfer (inner- sphere mechanism) leads to the partially oxidised product(i.e. ethoxid e radical) which is rapidly oxidised by cerium(IV) at a fast step. Fro m the hydrogensulphate dependence, Ce(SO4)(2+) has been found as the k inetically active species.