Measurement of evaporation entropy, evaporation enthalpy, and Gibbs free energy for the [C4Dmim]Gly and [C4Dmim]Ala

Abstract

Two new amino acid ionic liquids, 1 - butyl − 2, 3 - dimethylimidazole glycine ([C4Dmim]Gly) and 1 - butyl − 2, 3 - dimethylimidazole alanine ([C4Dmim]Ala), were prepared and their structures were determined by NMR and elemental analysis. The thermogravimetric experiment of two ionic liquids were carried out by using a thermogravimetric analyzer. The thermogravimetric experiment included non - isothermal thermogravimetric experiment and isothermal thermogravimetric experiment. The non - isothermal thermogravimetric experiment could determine the initial decomposition temperature of the sample and the temperature range of isothermal thermogravimetric experiment which provided favorable conditions for the following isothermal thermogravimetric experiment. The isothermal thermogravimetric experiment can record the change of the mass of the experimental sample with time in the experimental temperature range, which provides reliable data for the following work. Langmuir equation and Clausius - Clapeyron equation were used to fit the data, and the evaporation enthalpies of the two ionic liquids at average temperatures were obtained. It was found that the change of anions will affect the evaporation enthalpy of ionic liquids with the same cations, and the evaporation enthalpy [C4Dmim]Ala > [C4Dmim]Gly. It is inferred that the difference may be related to the spatial structure difference of anions. In addition, the evaporation entropy and Gibbs free energy of two ionic liquids are discussed, and the vapor pressure, evaporation entropy and Gibbs free energy at any temperature can be obtained by transforming them.