Kinetics of the solvolysis of the trans-dichlorotetrapyridinecobalt(III) ion in water + t-butyl alcohol mixtures

Abstract

The investigation of the effect of solvent structure on the solvolysis of the trans-[Copy₄Cl₂]⁺ ion has been extended to water + co-solvent mixtures where the co-solvent, t-butyl alcohol, has a greater effect on the solvent structure than the co-solvents used earlier. A non-linear plot is found for log (rate constant) against reciprocal of dielectric constant, but the enthalpy, ΔH^*, and the entropy, ΔS^*, of activation exhibit extrema in the same composition region where the physical properties indicate that sharp changes in the structure of the solvent are occurring. The application of a free-energy cycle to the nearly complete separation of Co and Cl in the transition state shows that the influence of solvent structure on the complex ion is greater in the transition state than in the initial state: values for the free energy of transfer of the complex ion in the transition state from water into the mixture are calculated.