Solvation of Aniline in Mixtures of Water with N,N-Dimethylformamide and Acetonitrile

Thermal effects of aniline solution in water-N,N-dimethylformamide (DMF) and water-acetonitrile mixtures were measured at 25°C. In almost the whole range of compositions of the mixed solvents, the thermal effects are more positive in aqueous acetonitrile than in aqueous DMF. Particular attention was given to binary solvents with a very low content of the organic cosolvent. In the mixture with the mole fraction of DMF of 10^{- 3}, the enthalpy of aniline solution is higher than in water by 5%, and in the mixture with the mole fraction of acetonitrile of 4 × 10^{- 4}, even by 15%. Features of specific solvation of aniline and an aliphatic amine (n-BuNH₂) in the water-DMF mixture were discussed taking into account the acid-base properties of the mixtures. The coefficients of pair interactions aniline-organic solvent in water and aniline-water in the organic solvent were calculated using the McMillan-Mayer theory. These coefficients correlate with the enthalpies of hydration of aprotic solvent molecules.