Experimental determination of enthalpy of 1-butyl-3-methylimidazolium iodide synthesis and prediction of enthalpies of formation for imidazolium ionic liquids

The enthalpy of the 1-butyl-3-methylimidazolium iodide synthesis, its heat capacity and parameters of fusion were determined from calorimetric measurements. The standard molar enthalpy of formation for this compound in the crystal and liquid states at T = 298 K was determined from these results to be −(138 ± 6) kJ · mol−1 and −(119 ± 6) kJ · mol−1, respectively. With the use of the literature data and the results obtained in this work, a simple equation for calculation of ΔfHm∘ for 1-butyl-3-methylimidazolium compounds in the crystalline and liquid states is proposed. It was demonstrated that the additive scheme by Domalski and Hearing (1993) can be used for calculation of ΔfHm∘ in the homologous series of ionic liquid forming compounds in the liquid state. However, for the crystalline state, all the analyzed additive schemes did not provide satisfactory description of the experimental data.