Kinetics of oxidation of catechol (o-dihydroxybenzene) by thallium(III) in aqueous perchlorate media

Abstract

The reaction of Tl^III aquo-ions with catechol (H₂cat) in excess, giving o-quinone (qno), has been studied at [HClO₄]= 0·30–2·00, I= 2·00M, and 12·0, 18·0, 25·0, and 35·0 °C, by means of a stopped-flow technique. No spectrophotometric evidence of intermediate-complex formation has been found. The rate of oxidation is first order in both [Tl^III] and [H₂cat]. The rate increases with decreasing [H⁺] and this is explained by assuming that the reactive species is [TlOH]²⁺(aq) or a deprotonated intermediate complex. The overall activation parameters have also been evaluated. Possible reaction mechanisms are discussed with reference to other Tl^III oxidations and two alternative reaction paths are suggested.