Thermodynamics of solvation of pyridine in methanol-acetonitrile binary solvents

Heats of solution of pyridine (PY) over a range of compositions of methanol-acetonitrile (MeOH-AN) mixed solvents are measured at 298.15 K by calorimetry. Standard enthalpies of transferring PY from MeOH into its mixtures with AN are calculated from the obtained data. It is established that upon moving from methanol to acetonitrile, the solvation of PY becomes less exothermic, and marked changes in the energetics of amine solvation are observed at mole fraction ζAN = 0.8–1.0. It is shown that pyridine resolvates in the given range of mixed solvent compositions, predominantly through resolvation of the nitrogen atom in the amine group as a result of a considerable increase in the basicity of the mixed solvent. It is established that in the 0.0–0.8 range of AN mole fractions, PY molecules are predominantly solvated by MeOH molecules.