Solubilities of Cinnamic Acid Esters in Ionic Liquids

The solubilities of three cinnamic acid esters, namely, methyl ferulate, methyl p-coumarate, and methyl sinapate, in eight imidazolium-based ionic liquids composed of the PF6− and BF4− anions have been measured at (30, 39, and 48) °C. Higher solubilities of the three esters were observed in the ionic liquids composed of the BF4− anion than those composed of the PF6− anion. Also, higher solubilities are observed in alkyl-substituted (on the imidazolium cation moiety) ILs than in polar-substituted ILs, whereas, as the alkyl chain length on the cation moiety increases, the solubility increases as well. Moreover, using the van’t Hoff equations, the apparent Gibbs energy, enthalpy, and entropy of solution were calculated. Positive values of the three thermodynamic functions were found in all cases. Finally, successful correlations of the experimental data were achieved with the UNIQUAC and the NRTL activity coefficient models.