Imidazolium-based ionic liquids. 1-methyl imidazolium nitrate: thermochemical measurements and ab initio calculations.

In this work data of the molar enthalpies of formation of the ionic liquid 1-methylimidazolium nitrate [H-MIM][NO3] was measured by means of combustion calorimetry. The molar enthalpy of fusion of [H-MIM][NO3] was measured using DSC. Experiments to vaporize the ionic liquid into vacuum or nitrogen stream in order to obtain vaporization enthalpy have been performed. Ab initio calculations of the enthalpy of formation in the gaseous phase have been performed for the ionic species using the G3MP2 theory. The combination of traditional combustion calorimertry with modern high-level ab initio calculations allow the determination of the molar enthalpy of vaporization of the ionic liquid under study. The ab initio calculations indicate that [H-MIM][NO3] is most probably separated into the neutral species methyl-imidazole and HNO3 in the gaseous phase at conditions of the vaporization experiments.