KINETICS OF THE REVERSIBLE UPTAKE OF CARBON-DIOXIDE AND SULFUR-DIOXIDE BY THE CIS-(HYDROXO)(IMIDAZOLE)BIS(ETHYLENEDIAMINE)COBALT(III) ION IN AQUEOUS-MEDIUM - A COMPARATIVE-STUDY

The addition of SO2 to cis-(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 of cis-[(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 complex cis-[(en)2(imh)CoOCO2]+, by the reaction of CO2 with cis-[(en)2(imH)CoOH] have been determined. The bicarbonato complex, cis-[(en)2(imH)CoCO2H]2+, undergoes spontaneous CO2 elimination. The relatively low DELTAH(double dagger) and large negative values of DELTAS(double dagger) for CO2 uptake by cis-[(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 CO2-addition processes have been inferred.