Substitution at saturated carbon. Part XV. The effect of t-butyl alcohol–methanol mixtures on the free energy of reactants and transition states in the substitution of tetraethyltin by mercury(II) salts

Abstract

Standard free energies of transfer from methanol to t-butyl alcohol–methanol mixtures have been determined for tetraethyltin, mercury(II) chloride, mercury(II) iodide, mercury(II) acetate, and for the transition states in reaction (i; X = Cl, I, and OAc). It is shown that the increases in ΔG^‡ on change of solvent from methanol to t-butyl Et₄Sn + HgX₂→ EtHgX + Et₃SnX (i) alcohol–methanol mixtures observed for reaction (i; X = Cl, I, and OAc) are due largely to increases in the free energy of the transition states. An analysis of reaction (i; X = Cl) in terms of the Kirkwood function (ε– 1)/(2ε+ 1) suggests that the [Et₄Sn–HgCl₂]^‡ transition state possesses the very high dipole moment of ca. 14 D.