Solvation of amides of carboxylic acids in aqueous solutions of ethylene glycol

Enthalpies of solution of amides of formic, acetic, and propionic acids wit h different degrees of N-substitution in aqueous solutions of ethylene glyc ol were measured at 298.15 K. The concentration of ethylene glycol did not exceed 4 mot kg(-1). The reasons for increasing endothermic values of the e nthalpies characterizing the amide transfer from water to a mixed aqueous-o rganic solvent on going from primary to tertiary amides and from formamides to the corresponding acetamides are discussed. The enthalpic coefficients of pair interactions between amides and ethylene glycol in water were calcu lated. The endothermicity of the interaction of the alkyl groups of the ami de molecules with ethylene glycol results in positive values of the coeffic ients. The coefficient values increase with the enhancement of the hydropho bic properties of hydrophilic non-electrolytes (urea, formamide, ethylene g lycol) due to an increase in the contribution of the hydrophobic component and a decrease in the contribution from the interaction of the polar groups of amides to the total interaction.