Aqueous chemistry of thallium(II). Part II. Kinetics of reaction of thallium(II) with manganese(II), iron(II), and cobalt(III) ions

Abstract

Thallium(II) ions generated by flash photolysis of thallium(III) solutions oxidise manganese(II) and iron(II) and reduce cobalt(III). Rate constants for the reactions are: (Tl²⁺+ Mn²⁺→ Tl⁺+ Mn³⁺)(1·9 ± 0·2)× 10⁴(0·5M-acid, I= 0·75M, and 22 ± 3 °C); (Tl²⁺+ Fe²⁺→ Tl⁺+ Fe³⁺)(2·6 ± 0·1)× 10⁶(0·25M-acid. I= 0·30M, and 25 °C); ΔH^‡= 4·8 ± 2 KJ mol^–1; and (Tl²⁺+ Co³⁺→ Tl³⁺+ Co²⁺)(9·5 ± 0·5)× 10⁶ l mol^–1 s^–1(0·5M-acid. I= 0·55M, and 22 ± 3 °C). The reactions are apparently outer sphere in type, and comparison of the standard free energies of reaction and the activation free energies for these and other one-electron-transfer reactions involving thallium(II) with the same parameters for two-electron transfers of thallium(III) shows that the latter have activation free energies which are some 25 KJ mol^–1 larger than those for one-electron-transfer reactions with the same standard free-energy change, reflecting the increased organisation needed in the transition state for the transfer of two electrons.