Kinetics of the reversible uptake of carbon dioxide and sulphur dioxide by thecis-(hydroxo) (imidazole)bis(ethylenediamine) cobalt(III) ion in aqueous medium. A comparative study

Abstract

The addition of SO₂ tocis-(hydroxo) (imidazole)bis(ethylenediamine) cobalt(III) ion-generated-oxygen-bonded sulphito complex, the kinetics of which have been studied by the stopped-flow technique. The rate and activation parameters for the formation ofcis-[(en)₂(imH)CoOSO₂]⁺, the elimination of SO₂ from this O-bonded sulphito species which is H⁺-catalysed and of second order, and formation of the corresponding carbonato complexcis-[(en)₂(imH)CoOCO₂]⁺, by the reaction of CO₂ withcis-[(en)²(imH)CoOH] have been determined. The bicarbonato complex,cis][(en)₂(imH)CoCO₂H]²⁺, undergoes spontaneous CO2 elimination. The relatively low ΔH^‡ and large negative values of ΔS^‡ for CO₂ uptake bycis-[(en)₂(imH)CoOH]²⁺ are in contrast to the values for other analogous complexes of cobalt(III) reported in the literature. Some specific effects of cobalt(III)-bound imidazole on CO^2-addition processes have been inferred.