Solvation of ions. Part VIII. S N2 reactions of phenoxide and carboxylate anions with methyl iodide in methanol and in dimethylformamide

Abstract

Rate data for the SN2 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 SN2 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 SN2 reaction and the decrease in vmax. of the electronic absorption spectrum of phenoxides, on transfer from methanol to dimethylformamide, are compared.