Influence of the solvent on the rates of SN1-type solvolysis reactions of metal complexes in water + co-solvent mixtures

Abstract

The relationships developed for the variation of rate with dielectric constants have been extended to include effects derived from changes in solvent structure in order to interpret the linear plots for log (rate constant) against reciprocal of dielectric constant which show slope invariant with the identity of the co-solvent for some metal complexes in water + co-solvent mixtures. In order to apply free energy cycles to such reactions, the free energies of transfer of halide ions from water into water + co-solvent have been determined for water + ethanol and water + dioxan mixtures. The application of these cycles to SN₁-type solvolysis shows that, not only do changes in solvation of the transition state have a dominant effect on the rate for a wide range of metal complexes with a range of co-solvents, but that the same conclusion can be drawn for some organic halides.