Kinetics of the solvolysis of the trans-chloroazidobis(diaminoethane)cobalt (III) ion in water + t-Butyl Alcohol Mixtures

The kinetics of the solvolysis of the ion trans-[Coen₂N₃Cl]⁺ have been investigated at several temperatures in mixtures of water with t-butyl alcohol with concentrations of the latter ranging up to 50 vol% or a mol fraction of 0.16. Values for the enthalpy and entropy of activation show sharp changes with changing solvent composition which can be correlated with extrema in the physical properties of the mixture concerned with sharp changes in solvent structure. Plots of log(rate constant) against the reciprocal of the dielectric constant and against the Grunwald-Winstein Y factor are both curved. The application of a free energy cycle shows that the effect of changes in solvent structure on the solvolysis dominates on the cobalt(III) cation in the transition state over that on the cation in the initial state.