Thermodynamic study of phase transitions of imidazoles and 1-methylimidazoles

The vapor pressures of imidazole, N-methylimidazole and of their dichloro and dicyano substituted compounds were measured at different temperatures, in the crystalline phase for two of them, and in crystalline and liquid phases for the other four. From these measurements, enthalpies and standard entropies of sublimation and vaporization were derived. The results allowed the determination of the triple points (p, T) coordinates of the four compounds studied in both condensed phases as well as the calculation of their enthalpy of fusion. Enthalpies and temperatures of fusion were also determined using d.s.c. The experimental results enabled the estimation of the enthalpy of the intermolecular N–H⋯N bonds in the imidazoles studied.

► Sublimation vapor pressures of imidazole, N-methylimidazole and four derivatives were measured. ► Liquid vapor pressures were also measured for four of the compounds studied. ► Vapor pressure results enabled determination of sublimation, vaporization, and fusion enthalpy. ► From enthalpies of sublimation, enthalpies of intermolecular N–H⋯N bonds were estimated.