Reactive distillation of pyridine mixtures with an organic acid. I. Determination of the reactive distillation equilibrium

Abstract The reactive distillation equilibrium has been experimentally determined by chromatographic analysis of the vapor phase for various mixtures of two pyridines plus an organic acid in stoichiometric deficiency in an organic solvent. Protonation of pyridines by a weak acid seems to involve ion pair formation, while protonation by a strong acid seems to result in free ion formation, and may involve a small quantity of triple molecule ions (two pyridine molecules for one acid molecule). Steric effects are not significant in such ion formation and the chemical equilibrium constant can be predicted from the pyridine pKa difference using a linear relationship. Despite the possible formation of triple molecule ions, the reactive distillation equilibrium at constant acid quantity can be reasonably well described as an ideal liquid‐vapor equilibrium combined with an ideal chemical equilibrium. However, the increase of the chemical equilibrium constant with the acid quantity should be taken into account in a more refined model.