Stoicheiometry and kinetics of the reaction between thallium(III) and antimony(III) ions in perchloric acid solution

Abstract

The rate of the reaction between Tl^III and Sb^III ions in perchloric acid solution (stoicheiometry 1 : 1) is measurable by conventional methods at 60 °C. After ca. 70–80% reaction, a precipitate is obtained consisting mainly of Sb^V ions, with small amounts of Tl^I, and adsorbed Tl^III and Sb^III ions. The rate of reaction is independent of the ionic strength, and reaction appears to occur via two transition states, [TlOH,HSbO₂]²⁺ and [Tl,HSbO₂]³⁺, the first path accounting for ca. 85% reaction. The tentative rate law is as in (i), where K₁ and K₂ are hydrolytic constants for the ions Tl³⁺ and SbO⁺ respectively. –d[Sb^III]//_dt=[Tl^III][Sb^III]//_([H⁺]+K1)(k₃K₁K₂//_[H⁺]+k₃′K₂)(i) The quantities k₃K₂ and k₃′K₂ were found to be 2·66 and 0·30 s^–1 respectively at 60 °C, and the overall energy and entropy of activation were 16·0 ± 0·4 kcal mol^–1 and –13·1 ± 1·8 cal K^–1 mol^–1 respectively. In the presence of chloride ions, the reaction is complex because of the formation of various chloro-complexes with the ions Tl^III, Sb^III, and Sb^V.