Hydrogen-bonded complexes between pyridine and phenol in carbon tetrachloride solutions

Abstract

The applicability of the technique of thermometric titrimetry, using an accurate titration calorimeter, to the investigation of the reaction between pyridine and phenol, has been examined. Clear evidence for the existence of more than one complex has been obtained for experiments where pyridine was not in great excess. In very dilute solutions of phenol (0.01 mol dm^–3) the available evidence fits best with the hypothesis that only the 1:1 complex is present, and that the formation constant is 40 dm³ mol^–1 at 25°C. The molar enthalpy of formation of PyPh is estimated to be –27.0 kJ mol^–1. In more concentrated phenol solutions some PyPh₂ appears to be present. The enthalpy of formation of this species is at least –34.6 kJ mol^–1 using a standard state identical with that used for the molar enthalpy of formation of PyPh. More extensive calorimetric data than are currently available should, if sufficiently precise, be able to test the scheme put forward in this paper, and provide thermodynamic parameters for the higher complex species.