Enthalpy characteristics and state of N,N-disubstituted amides of formic and acetic acids in water-formamide mixtures

The enthalpies of solution of N,N-disubstituted amides of formic and acetic acids at 298.15 K throughout the entire range of compositions of the water -formamide mixed solvent were measured. The enthalpies of solvation and tra nsfer of the amides from water into the mixed solvent were calculated. The effects of the structure and properties of the solutes and also of the comp osition of the mixed solvent on their thermochemical characteristics were c onsidered. The monotonous weakening of solvation of the alkylamides through out the entire range of mixture compositions results from reduced exothermi city of their nonspecific and specific solvation. Analysis of the deviation s of the enthalpies of transfer from additivity in composition showed that the hydrocarbon radicals of the amides are slightly more solvated by formam ide, while the polar functional groups, by water.