Substitution at saturated carbon. Part IX. Free energies of transfer from methanol to aqueous methanol of tetra-alkyltins and the transition states in the bimolecular substitution of tetra-alklytins by mercuric chloride

Abstract

Standard free energies of transfer (on the molar scale) from methanol to various methanol–water mixtures have been determined for tetramethyl-, tetraethyl-, tetra-n-propyl-, and tetra-n-butyl-tin. When combined with similar previous data for mercuric chloride, and with the known free energies of activation for reaction (1), these free energies R₄Sn + HgCl₂→ RHgCl + R₃SnCl (1) of transfer yield values of ΔG_t°(Tr), the standard free energy of transfer from methanol to aqueous methanol of the corresponding transition states in reaction (1). It is shown that the reductions in the free energy of activation of reaction (1) observed when solvent methanol is replaced by aqueous methanol are due to very large increases in the standard free energy of the initial states on transfer from methanol to aqueous methanol.

Standard entropies of transfer (on the molar scale) have also been calculated for the reactants and transition state in reaction (1; R = Et). The influence of various methanol–water mixtures on the value of ΔS‡ is shown to be due to a combination of initial-state and transition-state effects.