Enthalpies of transfer of pyridines from the gas phase to solution in weakly and moderately polar aprotic solvents

Abstract

The enthalpy of solution of pyridine and of its methyl-, chloro-, and cyano-derivatives has been measured calorimetrically in some aliphatic and aromatic hydrocarbons and in carbon tetrachloride. The enthalpy of transfer from the gas phase to a given solvent has been calculated and is discussed in terms of specific and non-specific solute–solvent interactions. It is shown that dispersion forces play the dominant role in the solvation process; the contribution of dipole–dipole, dipole–induced dipole, and specific interactions seem not to exceed 20% of the overall effect. The specific interactions involve primarily the π-electron system of the pyridines. No correlation of the enthalpies of solvation with the N-donor ability of the pyridines has been found. The effect of substituent groups on the enthalpies of solvation is approximately additive.