Thermodynamics of 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium chlorides

A comprehensive thermodynamic study of two ionic liquids EmimCl and BmimCl were carried out by experimental and calculation methods. Isobaric heat capacity of crystal and liquid EmimCl was determined by low temperature vacuum adiabatic calorimetry in the temperature range from 8 to 376 K. Experimental heat capacity curve of crystal EmimCl and literature data of BmimCl were fitted by linear combination of Einstein's functions and were integrated; as a result, the following thermodynamic functions for EmimCl and BmimCl were calculated: standard entropy S0m(T), heat content H0m(T)-H0m(0) and Gibbs energy G0m(T)-H0m(0). Melting parameters of these substances were measured by DSC and adiabatic calorimetry. Standard enthalpies of dissolution of crystal EmimCl and BmimCl in water at 298.15 K were measured by isothermal solution calorimetry. Based on these data, standard enthalpies, entropies and Gibbs energies of formation were calculated for crystal and liquid phases of EmimCl and BmimCl at 298.15 K. Standard enthalpies of EmimCl and BmimCl formation in the gaseous state at 298.15 K were defined via quantum chemistry methods. The analysis and comparison of the obtained thermodynamic characteristics with the literature data was carried out.