Physical And Chemical Properties Of 1-Butyl-2,3-Dimethylimidazole Amino Acid Ionic Liquids

Amino acid ionic liquid（AAILs）,as a kind of renewable biocompatible ionic liquid,has strong polarity,strong hydrogen bonding ability,stable chiral center and excellent biodegradability,and has great application potential in almost all biological,medical,pharmaceutical and biotechnology processes.Studying the physicochemical properties of AAILs in terms of volume properties and surface properties will help to understand the great potential applications of AAILs in different fields such as chemical,pharmaceutical and petrochemical industries.Three kinds of amino acids ILs were synthesized in this paper,which are 1-butyl-2,3-dimethylimidazo-glycine（[C₄Dmim][Gly]）,1-butyl-2,3-dimethylimidazo-alanine（[C₄Dmim][Ala]）,1-butyl-2,3-dimethylimidazo-threonine（[C₄Dmim][Thr]）.Three kinds of amino acid ionic liquids were characterized by nuclear magnetic resonance hydrogen spectrum and nuclear magnetic resonance carbon spectrum to determine the synthesis target ionic liquids.Then the physical and chemical properties of the three kinds of amino acid ionic liquids,such as volume properties,surface properties and viscosity properties,were measured and studied:Firstly,the density,surface tension,refraction and viscosity of the ionic liquid of three amino acids were measured.The standard addition method was used to eliminate the influence of residual water on the measured results.The molecular and molar volumes of the ionic liquids of three amino acids were calculated.The standard entropy（S^θ）,thermal expansion coefficient（α）and lattice energy(U_POT)of three amino acid ionic liquids at 298.15 K were calculated by Glasser theory.When the cation（[C₄Dmim]⁺）was the same,the standard entropy of different anions increased with the increase of molecular volume.At the same time,the surface properties of three target ionic liquids are studied and analyzed.It includes the calculation of surface entropy（S_a）and surface energy（E_a）of three amino acid ionic liquids.Experience at the same time,the use of Lorentz-Lorenz equation of three target ionic liquid molar polarizability（R_m）and polarization Moore（α_p）were calculated and analyzed,three target ionic liquid of polarizability and polarizability and no obvious change trend along with the change of temperature,polarizability and polarization has nothing to do with the change in temperature.A new E（?）tv（?）s empirical equation can be derived by substituting the definition of the Gibbs free energy of the molar surface into the traditional E（?）tv（?）s empirical equation.The Gibbs free energy of the molar surface of three target ionic liquids is predicted by the new E（?）tv（?）s empirical equation.The predicted Gibbs free energy value g_s（pre）is close to the experimental value g_s.Then the surface tension is predicted.By fitting the experimental value of surface tension with the corresponding predicted value,it is found that the predicted value and the experimental value maintain a high consistency.Finally,the correlation between the viscosity and temperature of amino acid ionic liquids[C₄Dmim][Gly],[C₄Dmim][Ala]and[C₄Dmim][Thr]was studied by using Vogel-Fulcher-Tammann empirical equation.The activation parameters（ΔG^≠、ΔS^≠andΔH^≠）of three amino acid ionic liquids were calculated based on Eyring viscosity equation and thermodynamic formula.