Heterogeneous catalysis in solution. Part XII. Racemisation of (+)589-tris(ethylenediamine)cobalt(III) by a carbon black, and kinetics of reacting systems involving racemisation

Abstract

The McKay equation for radioactive exchange has been applied to optical-isomerisation reactions. A modified equation has been derived to take into account a first-order chemical side reaction. All these processes show first-order kinetics and concentration-dependence studies are required to establish the mechanism. An equation has also been derived to describe the redistribution of optical activity between bulk and adsorbed states. Experiments carried out on the racemisation of (+)₅₈₉-tris(ethylenediamine)cobalt(III) tri-iodide in aqueous solution at 40 °C catalysed by a carbon black have shown the surface reaction to be rate determining. The rate is second order in adsorbed [Co(en)₃³⁺] and first order in adsorbed [I^–]. The racemisation does not proceed through a cobalt(II) intermediate under the experimental conditions employed.