Kinetics of the solvolysis of chloropentacyanocobaltate(III) ions in water +t-butanol mixtures

Abstract

Rates of the solvolysis of [Co(CN)5Cl]3− ions have been determined in mixtures of water with the hydrophobic alcohol, t-butanol over a range of temperatures. No linear correlation of log k with the reciprocal of the dielectric constant is found, suggesting that changes in solvent structure are an important factor influencing these rates. This result is confirmed by the good correlation found for the extrema in the enthalpy and entropy of activation with the extrema in the physical properties of the mixtures influenced by changes in solvent structure. The application of a free energy cycle to the loss of the chloride ion from the Co3+ in the transition state shows that [Co(CN)5]2− in the transition state is stabilised in the mixtures relative to [Co(CN)5Cl]3− in the initial state.