Solvent effects on the stability of simple secondary amides†

Abstract

Enthalpies of solution for N-methylpropionamide and 2-pyrrolidone in water, propan-1-ol, acetone and toluene were measured by calorimetry. Heats of vaporization were determined for the amides by ebulliometry, and enthalpies of solvation from gas phase were obtained. Enthalpies of solvation were the same for the two nearly-isomeric amides in polar, protic solvents, but in acetone and toluene dimerization of 2-pyrrolidone caused differences in enthalpies of solvation. For N-methylpropionamide, solvation enthalpy from the gas phase is highly correlated with the ability of the solvent to donate hydrogen bonds, but not well correlated with the ability of the solvent to accept hydrogen bonds, the polarity/polarizability of the solvent, or solvent relative permittivity.