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

The rate of the reaction between TlIII and SbIII 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 SbV ions, with small amounts of TlI, and adsorbed TlIII and SbIII 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[SbIII]//dt=[TlIII][SbIII]//([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 TlIII, SbIII, and SbV.