Kinetics and mechanism of iridium(III) catalysed oxidation of butan-2-ol by cerium(IV) in aqueous sulphuric acid media

Abstract

The kinetics and mechanism of Ir(III) catalysed oxidation of butan-Z-ol by Ce(IV) in aqueous sulphuric acid media have been followed at different temperatures (20-35&deg;C) under the conditions, [butan-2-0l]_T&gt;&gt;[Ce(IV)]_T. &gt;&gt; [Ir]_T(<em>ca</em>. 10^-6 mol dm^-3). In 1.0 mol dm^-3 sulphuric acid media, the observed rate law conforms to: -<em>d</em>ln[Ce(IV)]ldt=<em>K</em>_obs=a[butan-2-ol]_T [Ir]_T/(b+c[butan-2-ol]_T) where, [butan-z-ol], and [Ir]Tgive the total concentrations of the substrate and catalyst respectively; a, band care constants at a particular temperature and fixed [H₂SO₄]. From the [H_SO₄&middot;] dependence, Ce(SO₄)₂ has been found kinetically active. The proposed mechanism involves a pre-equilibrium interaction between the catalyst and substrate leading to an outer-sphere complex followed by the electron transfer at the rate determining step involving Ce(IV)&nbsp; and outer-sphere complex formed in pre-equilibrium step. It operates through the Ir(III)/Ir(IV) catalytic cycle. The process is acid catalysed. Activation parameters have been determined to investigate the effect of temperature.