Metal-ion oxidations in solution. Part XX. The mechanism of the reaction of thallium (III) with 2-mercaptosuccinic acid in perchlorate media

Abstract

The oxidation of 2-mercaptosuccinic (thiomalic) acid (HRSH) by thallium(III) proceeds via an inner sphere mechanism. Spectrophotometric and kinetic evidence are provided for the formation of a sulphur-bonded thallium(III) intermediate. The data are consistent with the reaction scheme[Formula: see text]in which the complex decomposes via a one-electron intramolecular transfer k2 = 3.8 × 10−4 s−1 at 25 °C, with K2 = 1650 M−1. The enthalpy of activation ΔH2≠ for the redox reaction (11.8 ± 1.2 kcal/mol) is considerably smaller than for other systems of this type and reflects the greater ease of reaction. Comparison is made of possible one- and two-electron transfer pathways.