Substitution at saturated carbon. Part XVIII. The effect of alcoholic solvents on rate constants for SN and SE reactions

Abstract

Rate constants are reported for reactions between the following nine pairs of reactants, using a number of pure alcohols as solvents: Et₃N and Etl,Prⁿ₃N and Mel, Me₄Sn and HgCl₂, Me₄Sn and Hgl₂, Et₄Sn and HgCl₂, Et₄Sn and Hgl₂, Et₄Sn and Hg(OAc)₂, Me₄Sn and I₂, and Et₄Sn and I₂. Comparisons have been carried out between the effect of alcoholic solvents on ΔG^‡ values for 21 S_N and S_E reactions, and it is shown that no simple solvent parameter can adequately correlate such solvent effects on the various reactions. However, in general, the retarding effect of the less polar alcohols on the organometallic substitutions lies between the very large solvent effect on the S_N1 reaction of t-butyl halides and the much smaller solvent effect on the S_N2 Menschutkin reactions. The reaction between Et₃N and Etl and that between Prⁿ₃N and Mel are anomalous in that molar rate constants in t-butyl alcohol are as high as rate constants in the much more polar solvent methanol.