Thermochemical study of solvation of aliphatic carboxamides in aqueous formamide solutions

The entahlpies of solution of formamide, acetamide, and propionamide in aqu eous formamide solutions (formamide concentration less than or equal to8 mo l kg(-1)) at 298.15 K were measured. The entahlpies of transfer of amides f rom water to the mixed aqueous-organic solvent were calculated and compared with published data on the enthalpies of transfer of amides into aqueous u rea solutions. The opposite trend in variation of the enthalpies of transfe r of amides in these systems with increasing concentration of the nonaqueou s component is due to different proton-donor power of formamide and urea re lative to water. The enthalpy coefficients of pair interaction of amides wi th formamide in ternary aqueous solutions were calculated. Their positive v alues are due to endothermic interaction with formamide of the alkyl groups of amide molecules. The relative hydrophobicity of amides with different d egrees of substitution of the amide group was estimated.