Abstract
Heat capacity for 1-butyl-3-methylimidazolium trifluoromethanesulfonate [C 4mim]OTf in the temperature range of (5–370) K has been measured in an adiabatic calorimeter. The temperature T fus = (290.98 ± 0.01) K and the enthalpy of fusion Δ fus H m ° = ( 19.43 ± 0.02 ) kJ mol − 1 were determined. A solid-phase transition was observed near T = 120 K. Thermodynamic functions for the compound in the condensed state were calculated. Trends in the solid–liquid phase change entropies, ∑ Δ tr S m, for 1-alkyl-3-methylimidazolium salts [C n mim]An were analyzed. The increment to ∑ Δ tr S was shown to increase with n. It was found that ∑ Δ tr S m = 66.4 ± 1.3 J K −1 mol −1 for all the studied [C 4mim]An ionic liquids except [C 4mim]NTf 2. This difference can be partly explained by formation of two distinguishable conformers of the NTf 2 anion in the liquid state.
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