Kinetics and mechanism of the oxidation of phosphorous acid by thallium(III) in perchloric acid solutions

Abstract

Phosphorous acid and thallic perchlorate react at 60–70°C in solution as in (i). The rate law (ii) holds, where, Tl^III+ H₃PO₃+ H₂O → Tl^I+ H₃PO₄+ 2H⁺(i), –d[Tl^III]/dt=kK[Tl^III][H₃PO₃]/([H⁺]+K[H₃PO₃])(ii)k and K were found to be 4·95 ± 0·1 × 10^–3 min^–1 and 29 at 60°C and µ= 3·15M. E_a and ΔS^‡ for the slow step were found to be 26·5 ± 1 kcal mol^–1 and 0·2 cal mol^–1 K^–1 respectively. ΔH and ΔS associated with K were found to be 10·2 ± 2 kcal mol^–1 and 7·3 cal mol^–1 K^–1 respectively. Four alternative mechanisms with different reactive species of thallium(III) and phosphorus(III) are consistent with the rate law.