The influence of the solvent on organic reactivity. Part 4. Spectroscopic parameters of Lewis basicity and acidity of hydroxylic solvents. A comprehensive correlation analysis of the log k values for the reactions of diazodiphenylmethane with benzoic acid in aprotic and hydroxylic solvents at 37 °C

Abstract

Solvent Lewis basicity parameters B, and solvent Lewis acidity parameters E, are presented for 23 alcohols, including 2-methoxyethanol. The Lewis basicity parameters were derived from the effect of the hydroxylic compound on ν_OH for phenol in dilute solution in carbon tetrachloride, and the Lewis acidity parameters were derived from the Dimroth–Reichardt E_T values. Rate coefficients at 37.0 °C for the reactions of diazodiphenylmethane with benzoic acid in the same solvents are also presented. All these results, combined with the corresponding results for 44 aprotic solvents obtained previously, permit a successful comprehensive correlation analysis of the solvent effect for the above reaction in both aprotic and hydroxylic solvents, along the lines used previously with the aprotic solvents alone (Koppel–Palm analysis). The most satisfactory procedure, however, involves the separate consideration of the Lewis acidity parameters of the two classes of solvent, so that terms in E_OH and E_AP may acquire characteristic coefficients in the multiple regression. The direct use of E_T, rather than the separate use of E and dielectric [(ε– 1)/(2ε+ 1)] parameters, is also examined.