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

Abstract

The kinetics of the oxidation of isopropanol by CoIIIaq have been studied using conventional and stopped-flow spectrophotometry in aqueous perchlorate media at high values for the ratio (initial [isopropanol])/(initial[CoIIIaq]) where Δ[CoIIIaq]/Δ[acetone]= 2.0. The rate is first order in [CoIIIaq] 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 CoIIIaq and CoIIIOH–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 CoIIIaq in aqueous perchlorate media. The published data for the rates of oxidation of other alcohols by CoIIIaq conform to a mechanism similar to that for isopropanol, and the rate constants for various substrates with a range of oxidants are compared.