The Enthalpy of Solution of the Alanine-Based Ionic Liquid [C4mim][Ala

Abstract

The molar enthalpies of solution of an alanine-based ionic liquid (IL) [C4mim][Ala], 1-butyl-3-methylimidazolium alanine, containing various amount of water and various molalities ΔsolHm(wc), were measured with a solution-reaction isoperibol calorimeter at (298.15±0.01) K, where wc denotes water content. According to Archer’s method, the standard molar enthalpies of solution of [C4mim][Ala] containing known amounts of water, \(\Delta_{\mathrm{sol}}H_{\mathrm{m}}^{\mathrm{o}}(\mathrm{wc})\) , were obtained. In order to eliminate the effect of the small amount of residual water in the source [C4mim][Ala], a linear fitting of \(\Delta_{\mathrm{sol}}H_{\mathrm{m}}^{\mathrm{o}}(\mathrm{wc})\) against water content was carried out, yielding a good straight line where the intercept is the standard molar enthalpy of solution of anhydrous [C4mim][Ala], \(\Delta_{\mathrm{sol}}H_{\mathrm{m}}^{\mathrm{o}}(\mathrm{pure}\ \mathrm{IL})=-(61.42\pm 0.08)\) kJ⋅mol−1. The hydration enthalpy of the alanine anion [Ala]− was estimated using Glasser’s lattice energy theory.