Study on Enthalpy and Molar Heat Capacity of Solution for the Ionic Liquid [C₂mim][OAc] (1-Ethyl-3-methylimidazolium acetate)

An acetic acid ionic liquid (AcAIL) [C₂mim]­[OAc] (1-ethyl-3-methylimidazolium acetate) was prepared by the neutralization method. Using the solution-reaction isoperibol calorimeter, molar enthalpies of solution, Δ_sol<i>H</i>_m, for the ionic liquid [C₂mim]­[OAc] with different molalities were measured in the temperature range from (288.15 to 308.15 ± 0.01) K with an interval of 5 K. In terms of Archer’s method, the standard molar enthalpies of solution, Δ_sol<i>H</i>_m^θ, for [C₂mim]­[OAc] were obtained in the temperature range of (288.15 to 308.15 ± 0.01) K. Plotting Δ_sol<i>H</i>_m^θ against (<i>T</i> – 298.15) K, a good straight line was obtained, with the slope of the line being the standard molar heat capacity of solution, Δ<i>C</i>_p,m^θ = 411 J·K^–1·mol^–1, for [C₂mim]­[OAc], and the specific heat capacity of solution, Δ<i>C</i>_p^θ = 2.4 J·g^–1·K^–1, was also obtained

Prediction of Thermophysical Properties of Acetate-Based Ionic Liquids Using Semiempirical Methods

Five acetate-based ionic liquids (AcAILs) [C_<i>n</i>mim]­[OAc]­(<i>n</i> = 2, 3, 4, 5, 6) (1-alkyl-3-methylimidazolium acetate) were prepared by the neutralization method and characterized by ¹H NMR spectroscopy and differential scanning calorimetry (DSC). Their density, surface tension, and refractive index were measured at 298.15 to 338.15 K. Since the AcAILs can form strong hydrogen bonds with water, small amounts of water are difficult to remove by common methods. In order to eliminate the effect of the impurity water, the standard addition method (SAM) was applied to these measurements. On the basis of the experimental data, the molecular volume (sum of positive and negative ion volumes), <i>V</i>_m, of [C_<i>n</i>mim]­[OAc]­(<i>n</i> = 2, 3, 4, 5, 6), the entropy of surface formation, <i>S</i>_a, the Gibbs energy of surface formation <i>E</i>_a, the parachor, <i>P</i>, and the molar refraction, <i>R</i>_m, the polarization coefficient, α_p, were calculated. The results show that <i>E</i>_a, <i>P</i>, and <i>R</i>_m are approximately temperature-independent and the contribution to these properties per methylene (−CH₂−) on alkyl chain of [C_<i>n</i>mim]­[OAc]­(<i>n</i> = 2, 3, 4, 5, 6) was discussed. According to both Kabo’s and Rebelo’s methods, the molar enthalpy of evaporation of the [C_<i>n</i>mim]­[OAc]­(<i>n</i> = 2, 3, 4, 5, 6) was estimated using surface tension and molar volume. In the same time, the surface tension of the AcAILs may be estimated using the parachor and the refractive index. The estimated values of the surface tension and the corresponding experimental one are extremely similar

Ionic Parachor and Its Application in Acetic Acid Ionic Liquid Homologue 1-Alkyl-3-methylimidazolium Acetate {[C_<i>n</i>mim][OAc](<i>n</i> = 2,3,4,5,6)}

Five acetic acid ionic liquids (AcAILs) [C_<i>n</i>mim][OAc](<i>n</i> = 2,3,4,5,6) (1-alkyl-3-methylimidazolium acetate) were prepared by the neutralization method and characterized by ¹HNMR spectroscopy and differential scanning calorimetry (DSC). The values of their density and surface tension were measured at 298.15 ± 0.05 K. Since the AcAILs can strongly form hydrogen bonds with water, the small amounts of water are difficult to remove from the AcAILs by common methods. In order to eliminate the effect of the trace water, the standard addition method (SAM) was applied to these measurements. As a new concept, ionic parachor was put forward. [OAc]⁻ was seen as a reference ion, and its individual value of ionic parachor was determined in terms of two extrathermodynamic assumptions. Then, the values of ionic parachors of a number of anions, [NTf₂]⁻, [Ala]⁻, [AlCl₄]⁻, and [GaCl₄]⁻, were obtained by using the value of the ionic parachor of the reference ion; the parachor and surface tension of the investigated ionic liquids in literature were estimated. In comparison, the estimated values correlate quite well with their matching experimental values