Low-temperature Heat Capacity Research Of Ether-based Functionalized Ionic Liquids

Due to its remarkable physical and chemical performance,ionic liquids no longer just stayed in the laboratory preparation.Nowadays,ionic liquids have been extended to the industrial testing,or even advanced to the industrialization stage.Their application fields have gradually expanded and achieved rapid development.Most ionic liquids have higher viscosity than common solvents,which has not only directly affected their transportation,but also has reduced their application efficiency to a certain extent.It has seriously hindered the industrialization promotion of ionic liquids.Therefore,the preparation of low viscosity ionic liquids is still the research trend in the future.Ether-based functionalized ionic liquids can show lower viscosity.Moreover,the melting point of ether-based functionalized ionic liquids is also low.In this paper,six ether-based functionalized ionic liquids have been measured for their low-temperature molar heat capacities.And their corresponding thermodynamic functions have been worked out.Six ether-based functionalized ionic liquids have been prepared by the two-step synthesis method:[C_n2O1IM][SCN]?n=1,2,4?,[C₂2O1IM][NO₃],[C₂2O1IM][TfO],[C₂2O1IM][NTf₂].The structures of the products have been characterized by 1H NMR and 13C NMR,respectively.The results of ¹H NMR have proved that the hydrogen composition of the products is consistent with the target,and there is no hydrogen impurity.The results of ¹³C NMR have proved that the carbon composition of the products is consistent with the target,and there is no carbon impurity.Before observing the heat capacities of the subjects,the calorimeter used must need to be calibrated by the empty equivalent and the international reference material?-Al₂O₃ to ensure the stability,reliability and accuracy of the experimental data.The results have showed that the precision and accuracy of this calorimeter are±0.211%and±0.172%,respectively.They are both within the experimental measurement standard.Then,the molar heat capacities of six ether-based functionalized ionic liquids in the temperature region of 78 K?400 K have been determined separately.After that,the obtained experimental heat capacity values in each temperature range have been fitted by the least square piecewise polynomial fitting method.Furthermore,the measured values and the fitted values have been substituted into the specific formula to gain the relative deviation,which are both within±0.5%.Ultimately,the thermodynamic functions H_T-H_298.15,S_T-S_298.1598.15 and G_T-G_298.1598.15 of these six ether-based functionalized ionic liquids have been computed,when the temperature range from298.15 K to 400 K.The effects of anions and imidazole cations substituted by alkyl groups on the thermochemical properties of ionic liquids have been also discussed separately.