Kinetics of the oxidation of isopropanol by aquocobalt(III) ions in aqueous perchlorate media

Abstract

The kinetics of the oxidation of isopropanol by Co^III_aq have been studied using conventional and stopped-flow spectrophotometry in aqueous perchlorate media at high values for the ratio (initial [isopropanol])/(initial[Co^III_aq]) where Δ[Co^III_aq]/Δ[acetone]= 2.0. The rate is first order in [Co^III_aq] and first order in [isopropanol], and there is no evidence for intermediate complexes at very high [isopropanol]. The variation of the observed second order rate constant with acidity fits a mechanism where both Co^III_aq and Co^IIIOH^–_aq react with the unprotonated alcohol, and energies E and entropies ΔS^* of activation are compared with E and ΔS^* for the oxidation of isopropanol by other cations and for the oxidation of other substrates by Co^III_aq in aqueous perchlorate media. The published data for the rates of oxidation of other alcohols by Co^III_aq conform to a mechanism similar to that for isopropanol, and the rate constants for various substrates with a range of oxidants are compared.