Prediction Of Physicochemical Properties Of Ionic Liquids By Empirical Methods And Its Experimental Determination

Five Acetic acid ionic liquids （AcAILs）[C_nmim][OAc]（n=2,3,4,5,6）（1-alkyl-3-methylimidazolium acetate） were prepared by the neutralization methodand characterized by¹H NMR spectroscopy and differential scanning calorimetry（DSC）. Since the AcAILs can strongly form hydrogen bonds with water, the smallamounts of water are difficult to remove from the AcAILs by common methods. Inorder to eliminate the effect of the trace water, the standard addition method （SAM）was applied to these measurements. The values of their density, surface tension andrefractive index were measured at the temperature ranging of （298.15to338.15±0.05） K with an interval of5K, and the density, surface tension and refractive indexof pure ionic liquids[C_nmim][OAc]（n=2,3,4,5,6） at298.15K were fitted using thestandard addition method （SAM）.The values of density, surface tension and refractive index were measured for aclassic series of air and water stable ionic liquids （ILs） based on tetrafluoroborate,[C_nmim][BF₄]（n=2,3,4,5,6）（1-alkyl-3-methylimidazolium tetrafluoroborate） in thetemperature range of （298.15to338.15±0.02）K with an interval of5K.In terms of Glasser’s theory, the standard molar entropy and lattice energy of theILs at298.15K were calculated. Using Kabo’s method, the molar enthalpy ofvaporization of the ILs at298.15K,△_l^gH_m⁰（298K）, were estimated. Using the valuesof refractive index of the ILs, the molar polarization and polarizability werecalculated. According to the interstice model, the thermal expansion coefficient of ILs,, were calculated and in comparison with experimental values, their magnitudeorders are in good agreement.As a new concept, ionic parachor was put forward.[OAc]^-was seen as areference ion and its individual value of ionic parachor was determined in terms oftwo extrathermodynamic assumptions and the ionic parachors for all correspondingimidazolium cations,[C_nmim]+, were calculated. Then, the values of ionic parachorsof a number of anions:[NTf₂]^-,[Ala]^-,[AlCl4]^-,[GaCl₄]^-, were obtained by using the value of ionic parachor of reference ion, the parachor and surface tension of theinvestigated ionic liquids [C_nmim]（[NTf₂],[Ala],[AlCl4],[GaCl₄]） in literature wereestimated. In comparison, the estimated values correlate quite well with theirmatching experimental values.To test this new concept of ionic parachor and verify the values of the ionicparachors for imidazolium cations,[C_nmim]+are reliable, which were determined interms of two extrathermodynamic assumptions.[BF₄]-was chosen as a reference ion, the ionic parachors for all correspondingimidazolium cations,[C_nmim]+, were calculated and in good agreement with thoseobtained estimation by [OAc]^-which was seen as a reference ion, which explains thesecond extrathermodynamic assumption more suitable for the ionic parachorcalculation. According to the ionic parachors for all corresponding imidazoliumcations,[C_nmim]+, the17anion ionic parachors were also obtained. In terms of ionicparachor, surface tension and refractive index of the investigated ionic liquids[C_nmim]（[NTf₂],[Lact],[OAc],[Val]）were estimated and the estimated valuescorrelate quite well with their matching experimental values. According to theestimated values of the parachors for [C_nmim][BF₄]（n=2,3,4,5,6）, the refractive indexand the thermal expansion coefficient of [C_nmim][BF₄]（n=2,3,4,5,6） were estimatedand the estimated values correlate quite well with their matching experimental values.