Study On The Thermodynamic Properties Of [C_nOC₂mim][a-Ac] And [C_nOC₂mim][Pro]（n=1,2） Ionic Liquids

In this paper,four ether based functionalized ionic liquids,1-（2-methoxyethyl）-3-methylimidazoliumacetate[C₁OC₂mim][Ac],1-（2-methoxyethyl）-3-methylimidazoliumpropionate[C₁OC₂mim][Pro],1-（2-ethoxyethyl）-3-methylimidazoliumacetate[C₂OC₂mim][Ac]and1-（2-ethoxyethyl）-3-methylimidazolium propionate[C₂OC₂mim][Pro],were synthesized by two-step synthesis method.The four ionic liquids were characterized by ~1H NMR,¹³C NMR and Elemental analysis.The non-isothermal thermogravimetric experiments and isothermal thermogravimetric experiments were carried out on the above four ionic liquids by thermogravimetric analyzer.The decomposition temperature of four ionic liquids was determined by non-isothermal thermogravimetric experiments.The variation law of the instantaneous mass with time of the four ionic liquids was studied by isothermal thermogravimetric experiments.The results showed that the mass loss of the four ionic liquids were caused by evaporation rather than decomposition.Langmuir equation was used to study the relationship between vapor pressure and temperature of the four ionic liquids.The results showed that the vapor pressure of four ionic liquids increases with the increase of temperature.The evaporation enthalpy（35）_l^gH_m^o（T_a）of four ionic liquids was calculated by using the combination of Langmuir equation and Clausius-Clapeyron equation.The results showed that when the cations of ionic liquids are the same,but the anions are different,the smaller the relative molecular weight of anions,the greater the evaporation enthalpy（35）_l^gH_m^o（T_a）.When the anions of ionic liquids are the same,but the cations are different,the longer the cationic alkyl chain,the greater the evaporation enthalpy（35）_l^gH_m^o（T_a）.According to Clausius-Clapeyron equation,the hypothetical boiling point T_b of the four ionic liquids was predicted.The evaporation enthalpy（35）_l^gH_m^o（T_i）,evaporation entropy（35）_l^gS_m^o（T_i）and Gibbs free energy（35）_l^gG_m^o（T_i）of four ionic liquids at any temperature T_i（from room temperature T=298.15 K to their hypothetical boiling point T_b）were calculated.The results showed that the evaporation enthalpy（35）_l^gH_m^o（T_i）,evaporation entropy（35）_l^gS_m^o（T_i）and Gibbs free energy（35）_l^gG_m^o（T_i）of the four ionic liquids decrease with the increase of temperature.The glass transition temperature of the four ionic liquids was measured by differential scanning calorimetry analyzer.The molar heat capacity of the four ionic liquids was calculated.The results showed that the change trend of the molar heat capacity of the four ionic liquids with temperature is basically the same as that of the heat flow temperature curve.