Study on the enthalpy of solution and enthalpy of dilution for the ionic liquid [C3mim][Val] (1-propyl-3-methylimidazolium valine)

A new amino acid ionic liquid (AAIL) [C3mim][Val] (1-propyl-3-methylimidazolium valine) was prepared by the neutralization method. Using the solution-reaction isoperibol calorimeter, molar solution enthalpies of the ionic liquid [C3mim][Val] with known amounts of water and with different concentrations in molality were measured at T = 298.15 K. In terms of standard addition method (SAM) and Archer’s method, the standard molar enthalpy of solution for [C3mim][Val] without water, ΔsHm∘ = (−55.7 ± 0.4) kJ · mol−1, was obtained. The hydration enthalpy of the cation [C3mim]+, ΔH+ ([C3mim]+) = −226 kJ · mol−1, was estimated in terms of Glasser’s theory. Using the RD496-III heat conduction microcalorimeter, the molar enthalpies of dilution, ΔDHm(mi → mf), of aqueous [C3mim][Val] with various values of molality were measured. The values of ΔDHm(mi → mf) were fitted to Pitzer’s ion-interaction model and the values of apparent relative molar enthalpy, φL, calculated using Pitzer’s ion-interaction model.

Graphical abstractThe thermodynamic cycle for estimation of the hydration enthalpy of ionic liquid [C3mim][Val].Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A new amino acid ionic liquid [C3mim][Val] was prepared. ► The molar enthalpies of solution of the ionic liquid. ► The hydration enthalpy of the cation [C3mim]+ was estimated. ► The molar enthalpies of dilution, of aqueous [C3mim][Val] were measured.