Solute-solute interactions in non-aqueous solvents. Enthalpic interaction coefficients of substituted acetamides dissolved in N,N-dimethylformamide

Enthalpies of dilution of acetamide, N-methylacetamide, N-ethylacetamide, N-propylacetamide, N-butylacetamide, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dipropylacetamide and N,N-dibutylacetamide dissolved in N,N-dimethylformamide as solvent have been measured calorimetrically at 25°C. The results are interpreted in terms of the McMillan-Mayer theory. The enthalpic interaction parameters are obtained for pairs, triplets and some quadruplets of solute molecules. All enthalpic pair interaction coefficients but one in this non-aqueous solvent are negative, whereas the triplet coefficients are positive. The concept of ‘solvophobic interaction’ can be used to explain these results in connection with the assumption of the formation of solute-solvent associates. The enthalpic pair interaction coefficients can be described by the additivity approach of Savage and Wood.