Measurement and thermodynamic modelling of the solubilities of caffeic acid, p-coumaric acid and ferulic acid in three choline chloride-based deep eutectic solvents

This work presents experimental solubility measurements for three cinnamic acid derivatives (CADs) namely caffeic acid (CA), p-coumaric acid (p-CA) and ferulic acid (FA) in three Deep Eutectic Solvents (DESs), choline chloride-1,2 butanediol (ChCl:1,2 butanediol (1:4)), choline chloride-1,4 butanediol (ChCl:1,4 butanediol (1:4)) and choline chloride-acetic acid (ChCl:Acetic Acid (1:2)). All measurements were performed in the temperature range of 293.15 to 323.15 K and at atmospheric pressure. Density and viscosity measurements of pure DESs ChCl:1,2 butanediol (1:4) and ChCl:1,4 butanediol (1:4) are also reported. ChCl:1,4 butanediol (1:4) and ChCl:1,2 butanediol (1:4) reveals the highest solvation capacity for CADs among the examined solvents, while pCA was found to be less soluble than CA and FA in all solvents. Thermodynamic functions of dissolution were also determined using the Van't Hoff equation and the results imply that the process is endothermic for all systems studied. Finally, UNIQUAC and NRTL activity coefficient models were satisfactorily implemented to correlate the experimental solubilities.