Solvation of ions. Part VIII. SN2 reactions of phenoxide and carboxylate anions with methyl iodide in methanol and in dimethylformamide

Abstract

Rate data for the S_N2 reactions of methyl iodide with the sodium of lithium salts or some phenols, carboxylic acids, and 4-nitrothiophenol in methanol and in dimethylformamide are reported. The reaction of methyl iodide with methanol containing sodium picrate is shown to be methanolysis, rather than an S_N2 reaction of picrate ion as reported in Part II. Hydrogen-bonding solvation of phenoxide and carboxylate ion by methanol decreases as the negative charge on oxygen becomes more dispersed. Both acetate and phenoxide ion are powerful hydrogen-bond acceptors. Nucleophilic tendencies change significantly on transfer from methanol to dimethylformamide.

The decrease in enthalpy of activation of the S_N2 reaction and the decrease in v_max. of the electronic absorption spectrum of phenoxides, on transfer from methanol to dimethylformamide, are compared.