Metal-ion oxidation in solution. Part VIII. Characterisation of the intermediate formed in the cobalt(III)-ion oxidation of chloride

Abstract

The rate of formation of the intermediate formed in the Co^III–Cl^– reaction has been examined in the range 2·5–13 °C by use of a stopped-flow device. The secondary oxidation is sufficiently slow that only complex formation need be considered.

Rate constants for the reaction (i) and (ii) have been evaluated together with the formation constant k₁ corresponding to equilibrium (i). At 8 °C, k₁= 2·5 ± 1 l. mole^–1 sec.^–1 and k₂= 200 ± 80 l. mole^–1 sec.^–1, the Co³⁺+ Cl^– [graphic omitted] CoCl²⁺(i), CoOH²⁺+ Cl^– [graphic omitted] CoOHCl⁺(ii) activation energies for the reactions being 26 ± 8 and 12 ± 6 kcal.lmole respectively. Comparison with date for other systems suggests that the complex is formed via an S_N1 mechanism. By use of the temperature variation of K₁, the thermodynamic parameters for reaction (i) have been derived as ΔH₁= 3·8 ± 5 kcal.lmole and ΔS₁= 20 ± 10 cal. mole^–1deg.^–1.