Effects of Solvation of 2-Methylpyridine and 2,6-Dimethylpyridine in Dilute Solutions in Water and Methanol οn the Limiting Partial Molar Compressibility and Volume

The limiting partial molar volumes and isentropic compressibilities of 2-methylpyridine and 2,6-dimethylpyridine in aqueous and methanolic solutions were calculated from the densities and speeds of sound at 293.15 and 298.15 K. All the limiting functions are smaller than the respective functions for the pure amines, due to the hydrogen bonds O-H... N between the amine molecules and those of water or methanol. The standard functions of transfer of the amines from methanol to water are negative which results from different nature of interactions in the aqueous and methanolic solutions. Most probably, the hydrophobic effect contributes to the limiting partial volumes and compressibilities of the amines diluted in water. That makes them smaller than the respective functions for the amines in methanol.