Study On The Physico-chemical Properties Of Acetic Acid Ionic Liquids

Ionic liquids (ILs), as greener alternatives to volatile organic solvents, have more attracted attention from both academic and industrial community as new function materials. They have now become one of interdisciplinary cutting-edge research areas. Acetic acid ionic liquids have a broad prospect in the separation and extraction of chiral amino acids, the enzymes split of Amino acids, promoting acyclovir drug penetrate through subcutaneous tissue, catalyzing Heck reaction and so on. In addition, it has low cost, and can be easily degradated, so it is considered more environmentally friendly function ionic liquids. The physico-chemical properties of ionic liquids are required for their applications. Under the guidance of the concept, this paper did the following jobs:1-butyl-3-methy-limidazolium acetic acid ([C₄mim][Ac]) was synthetized and characterized by 1H-NMR and DSC.Densities of [C₄mim][Ac] were measured using density balance, and the density of pure ionic liquid [C₄mim][Ac] at 298.15 K was fitted using the standard addition method (SAM). Then the molecular volume, the standard molar entropy and the lattice energy were calculated. Surface tensions of [C₄mim][Ac] were measured with the maximum bubble pressure method, and the surface tension of pure ionic liquid [C₄mim][Ac] at 298.15 K was fitted using the standard addition method (SAM). Then the surface excess entropy, the surface excess energy and the molar enthalpy of vaporization were calculated.On the basis of above data, the densities, the standard molar entrop entropy and the lattice energy of [Cnmim][Ac] (n = 2, 3, 5, 6) were estimated using the molecular volume. The surface tension, the molar enthalpy of vaporization and the thermal expansion coefficient of [Cnmim][Ac] (n = 2, 3, 5, 6) were estimated using the parachor. The critical temperature of [C₄mim][Ac] was calculated from surface tension, then the molar enthalpy of vaporization and the saturated vapor pressure of [C₄mim][Ac] at different temperatures were fitted and estimated. The saturated vapor pressure is also very small at 420℃, this is consistent with our experience.The refractive index of [C₄mim][Ac] was determined at different temperatures using Abbe refractometer. The molar polarizability and the molecular polarizability were calculated. On the basis of this and surface tension, the refractive indexes of [Cnmim][Ac] (n = 2, 3, 5, 6) were estimated.The ratio of cavitation radius and the average of ionic radius is smaller than 0.6, this is consistent with our experimental values. The cavitation model theory explains that why the viscosity of [Cnmim][Ac] (n = 3,4,5,6) is large.The viscosities and conductivities of [Cnmim][Ac] (n = 3,4,5,6) were determi- ned at different temperatures. We discussed that whether the Arrhenius equation and the Fulcher equation apply to the acetic acid ionic liquids.John M. Slattery proposed a method to estimate physicochemical properties, which was discussed in this paper. The resuits showed that the method could be estimated the viscosities and conductivities of acetic acid ionic liquids.