Study On The Molar Surface Gibbs Free Energy Of Amino Acid Ionic Liquids 1-alkyl-3-methylimidazolium Threonine Salts [C_nmim][Thr](n=3,5,6)

Ionic liquids are ionic compounds which are composed entirely of anions and cations at room temperature or near room temperature.It is easy to obtain a variety of of ionic liquids by changing the anion or cation,because of the interaction between the cation and anion in the mechanism.Ionic liquids are different from conventional laboratory reagents,which are difficult to be volatilize.Moreover,it has been found that the ionic liquid can be easily extracted as a reaction solvent and recycled,so it is called green solvent.However,many physical and chemical properties of ionic liquids are not perfect(there are some disadvantages of ionic liquids),which lead to the inconvenience of using ionic liquids in practice.Therefore,it is necessary to study the physical and chemical properties of ionic liquids.These three ionic liquids have been synthesized in this experiment,including 1-propyl-3-methylimidazole threonine salt,1-amyl-3-methylimidazole threonine salt,1-hexyl-3-methylimidazole threonine salt.Nuclear magnetic resonance spectroscopy(1H NMR)and nuclear magnetic resonance spectroscopy(13C NMR)were used for qualitative analysis.Threonine ionic liquid density,?,surface tension,?,and the refractive index,nD,was measured at 5 K intervals of the temperature range(288.15-328.15 K)and an atmospheric pressure.Based on the experimental data,the values of the molar surface Gibbs free energy,g,have been calculated.Using the molar surface Gibbs free energy,the traditional E?tv?s equation was improved to be a new E?tv?s equation.The slope of new E?tv?s equation is the molar surface entropy,and intercept is molar surface enthalpy.In terms of the thermodynamic relationship,the molar surface entropy,s,enthalpy,h,and the molar entropy of vaporization of surface,(35)Svs were calculated and the ratio of molar surface internal energy to molar internal energy of vaporization,Er was estimated.With the refractive index and the molar surface Gibbs free energy,an equation to predict surface tension of the ILs was derived and the predicted surface tension was found to be highly similar to the experimental surface tension values.