Study on thermodynamic property for ionic liquid [C₄mim][Lact](1-butyl-3-methylimidazolium lactic acid)

Abstract

Lactic acid ionic liquid [C₄mim][Lact] (1-butyl-3-methylimidazolium lactic acid) was synthesized by the neutralization method. Using the solution–reaction isoperibol calorimeter, the molar enthalpies of solution, Δ_sol H _m, with different molalities were determined 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 enthalpy of solution for [C₄mim][Lact], $\Delta _{\text{sol}} H_{\text{m}}^{\theta }$, was obtained, and then, the values of apparent relative molar enthalpy, ^Φ L, and the Pitzer’s parameters $\beta_{\text{MX}}^{(0)\text{L}}$ and $\beta_{\text{MX}}^{(1)\text{L}}$ were determined for [C₄mim][Lact]. The plot of $\Delta _{\text{sol}} H_{\text{m}}^{\theta }$ versus (T—298.15) K is a good straight line, and its slope is the standard molar heat capacity of solution, $\Delta C_{\text{p,m}}^{\theta } = 240\,{\text{J}}\,{\text{K}}^{ - 1}$. According to Glasser’s theory of lattice energy, the hydration enthalpy of cation and anion, (ΔH ₊ + ΔH ₋) = −471 kJ mol⁻¹, in infinite dilution and the hydration enthalpy of anion, ΔH ₋([Lact]⁻) = −257 kJ mol⁻¹, were obtained at 298.15 K. The heat capacity of aqueous [C₄mim][Lact], C _p(sol), and the apparent molar heat capacity, ^Φ C _p, of various specific molalities were also obtained.