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

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, ΔsolHm, 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], ΔsolHmθ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \Delta _{\text{sol}} H_{\text{m}}^{\theta } $$\end{document}, was obtained, and then, the values of apparent relative molar enthalpy, ΦL, and the Pitzer’s parameters βMX(0)L\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \beta_{\text{MX}}^{(0)\text{L}} $$\end{document} and βMX(1)L\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \beta_{\text{MX}}^{(1)\text{L}} $$\end{document} were determined for [C4mim][Lact]. The plot of ΔsolHmθ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \Delta _{\text{sol}} H_{\text{m}}^{\theta } $$\end{document} versus (T—298.15) K is a good straight line, and its slope is the standard molar heat capacity of solution, ΔCp,mθ=240JK-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \Delta C_{\text{p,m}}^{\theta } = 240\,{\text{J}}\,{\text{K}}^{ - 1} $$\end{document}. 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], Cp(sol), and the apparent molar heat capacity, ΦCp, of various specific molalities were also obtained.