Solubility of paracetamol in binary mixtures of biodegradable betaine/ethylene glycol deep eutectic solvent and water: measurement and correlation

The goal of this work is determining paracetamol (PCM) equilibrium solubilities in aqueous pseudo-binary mixtures of betaine/ethylene glycol deep eutectic solvent (Bet/EG DES) through the shake-flask technique from 293.15 to 313.15 K and atmospheric pressure (approximate to 85 kPa). The equilibrium solid phase crystal of PCM is characterized with X-ray powder diffraction analysis to identify no polymorphic transformation, solvate formation or crystal transition during the whole solvent crystallization process. The results indicate that addition of DES to water significantly enhances PCM solubility; so that, by adding 0.9 mass fraction of Bet/EG DES to water increases PCM solubility by more than 42.9 times. Moreover, the solubility data are successfully represented with the commonly used cosolvency models including Jouyban Acree, Jouyban-Acree-van't Hoff and so on together with the activity coefficient models of NRTL and Wilson. The accuracy of each model is determined through calculation of average relative deviations (ARD%) and the results present that the Jouyban-Acree (ARD% = 6.3) and Wilson activity model (ARD% = 0.8) have better capabilities in PCM solubility correlation than the others. Finally, thermodynamic behavior of PCM in Bet/EG DES + water is studied by determination of apparent thermodynamic functions of dissolution obtained from the van't Hoff and Gibbs equations.