σ-Bonded organotransition-metal ions. Part VIII. The kinetics and mechanism of displacement of chromium(III) from some penta-aquo-organochromium(III) ions by thallium(III). A route to monoalkylthallium(III) halides

Abstract

Penta-aquopyridiomethylchromium(III) ions react rapidly with thallium(III) chloride in aqueous acidic solution to give the corresponding monopyridiomethylthallium(III) chloride ion. The reaction is first-order in the organo-chromium ion and first-order in thallium(III) chloride and the observed rate coefficients can be accommodated by assuming that separate reaction occurs through the species TlCl₂⁺, TlCl₃, and TlCl₄^–. The reaction is believed to involve the direct bimolecular displacement of five-co-ordinate [Cr(H₂O)₅]³⁺ by attack of the thallium halide species on the methylene group. The rate of reaction of the thallium halide species is determined by the position of substitution on the pyridine ring and the stereochemistry of the thallium halide species rather than by coulombic forces between the charged reagents.