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

Abstract
The reaction of TlIII 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 [TlIII] 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 TlIII oxidations and two alternative reaction paths are suggested.
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