Acid-catalysed oxygen-18 exchange, racemisation, and aquation studies with the trisoxalatocobaltate(III) anion in aqueous solution

Abstract

Kinetic data on the acid-catalysed exchange of oxygen between the trisoxalatocobaltate(III) anion and solvent water, obtained by use of oxygen-18, are reported. At 25°C, in the presence of 1M-HCl, the carbonyl oxygen exchanges ca. 50 times faster than the bridging oxygen. Owing to the concurrent decomposition the bridging oxygen exchange could be followed for only 0·1 t_½ for exchange. Kinetic data for inversion and decomposition have been obtained under the same experimental conditions as used for studying the oxygen exchange. The data exclude the possibility that the mechanism of inversion involves ‘one-ended dissociation’. A twist mechanism is favoured.