ENTHALPY CHARACTERISTICS OF DILUTE-SOLUTIONS OF AMIDES IN ACETONITRILE

The enthalpy of mixing of formamide, N-methylformamide, N,N-dimethylfo rmamide, and hexamethylphosphoric triamide with MeCN was measured in t he 283-328 K range. The enthalpic coefficients of the binary and terna ry interactions between the amide molecules are calculated within the framework of the McMillan-Mayer theory. The contributions to the entha lpy of dissolution due to cavity formation in the solvent (DELTA(cav)H 0) and due to solute-solvent interaction (DELTA(int)H0) were determine d. The enthalpies of specific and nonspecific solvation of amides in M eCN were calculated. The main contribution to the enthalpy of solvatio n of formamide and N-methylformamide is from specific interactions, wh ile for N,N-dimethylformamide and hexamethylphosphoric triamide it is from nonspecific interactions. The values obtained are compared with t hose for solutions of the amides mentioned in water and methanol.