Experimental Determination Of Thermodynamic Properties Of Ether-functionalized Ioinc Liquids And Their Prediction By Empirical Methods

Five ether-functionalized ionic liquids?ILs?1-ethyl-3-?2-methoxyethyl?-imidazo-lium acetate,[C₂2O1IM][OAc],1-ethyl-3-?2-methoxyethyl?-imidazolium thiocyanate,[C₂2O1IM][SCN],1-ethyl-3-?2-methoxyethyl?-imidazolium trifluoromethanesulfonate,[C₂2O1IM][TfO],1-ethyl-3-?2-methoxyethyl?-imidazolium dicyanamide,[C₂2O1IM][DCA],1-ethyl-3-?2-methoxyethyl?-imidazoliumbis?trifluoromethylsulfonyl?imide,[C₂2O1IM][NTf₂]were prepared and characterized by ¹H NMR spectroscopy,¹³C NMR spectroscopy,ESI-MASS spectra and Elemental Analyses?EA?.Their mass fraction of water and halogen?Br^-?were also determined.The purities of these five IL are more than0.99.The density,surface tension,refractive index of[C₂2O1IM][X]?X=OAc,SCN,DCA,TfO,NTf₂?were measured in the temperature range of 298.15 K to 338.15 K with an interval of 5 K.Since[C₂2O1IM][X]?X=OAc,SCN,DCA,TfO?can strongly form hydrogen bonds with water,which is considered as impurity,the standard addition method?SAM?was applied in these measurements.Based on the experimental values,the volume property,surface property,speed of sound,thermal expansion coefficient,molar polarization and molar susceptibility of[C₂2O1IM][X]?X=OAc,SCN,DCA,TfO,NTf₂?have been discussed.Using the concept of the molar surface Gibbs free energy,the traditional E?tv?s equation was improved into a modified one which can be well applied to the ILs.The molar surface entropy,s,and molar surface enthalpy,h,for[C₂2O1IM][X]?X=OAc,SCN,DCA,TfO,NTf₂?have been gotten.As a new theoretical model,the ionic molar surface Gibbs free energy,g_i,was put forward.The ionic molar surface Gibbs free energy,g₊,for cations[C_nmim]⁺?n=2-6?and[C₂2O1IM]⁺,and ionic molar surface Gibbs free energy,g_-,for[OAc]^-,[SCN]^-,[DCA]^-,[TfO]^-,[NTf₂]^-,[EtSO₄]^-,[Ala]^-,[Pro]^-,[Val]^-,[Lact]^-,[Gly]^-,[BF₄]^-were obtained in terms of the extrathermodynamic assumptions.By using the values of these g_i,the predicted values of molar surface Gibbs free energy,g_est,and surface tension,?_est,for45 ionic liquids[C_nmim][OAc]?n=2-5?,[C_nmim][SCN]?n=2,4,5?,[C₂mim][DCA],[C_nmim][TfO]?n=4,6?,[C_nmim][NTf₂]?n=2-6?,[C_nmim][EtSO₄]?n=2,4?,[C_nmim][Ala]?n=3-5?,[C_nmim][Pro]?n=2-6?,[C_nmim][Val]?n=2-6?,[C_nmim][Lact]?n=2-6?,[C_nmim][Gly]?n=2-6?,[C_nmim][BF₄]?n=2-6?and other 5ether-functionalized ionic liquids[C₂2O1IM][X]?X=OAC,SCN,DCA,TfO,NTf₂?were estimated.In comparison,the predicted values correlate quite well with their matching experimental ones.In terms of the new scale of polarity for ILs,the polarity of[C₂2O1IM][X]?X=OAc,SCN,DCA,TfO,NTf₂?and 11 molecular liquids were estimated.The results show that the polarity order of these molecular liquids predicted by the dielectric constant is consistency with its estimated by the new scale of polarity for ILs.