Enthalpies of transfer of formamide, N-methylformamide and N,N-dimethylformamide from water to aqueous acetonitrile mixtures at 298 K

Abstract

The enthalpies of transfer of formamide, N-methylformamide and N,N-dimethylformamide from water to aqueous acetonitrile mixtures have been measured. Analyses of these results shows that there is a marked discontinuity in the solvating properties of this system at an acetonitrile mole fraction of 0.3. This transition is characterized by changes in both the degree of preferential solvation of, and the extent of disruption of the solvent structure by, the solutes. Comparison of these results with those for other solvent systems indicates that in the water-rich domain the acetonitrile may cause greater rigidification of the water structure than do the simple alcohols, while the acetonitrile-rich media are less structured than the alcohols and more closely resemble purely non-aqueous mixtures.