Solubility and thermodynamic behavior of vanillin in propane-1,2-diol + water cosolvent mixtures at different temperatures

The solubilities of bioactive compound vanillin were measured in various propane-1,2-diol + water cosolvent mixtures at T = (298-318) K and p = 0.1 MPa. The experimental solubility of crystalline vanillin was determined and correlated with calculated solubility. The results showed good correlation of experimental solubilities of crystalline vanillin with calculated ones. The mole fraction solubility of crystalline vanillin was recorded highest in pure propane-1,2-diol (7.06 × 10−2 at 298 K) and lowest in pure water (1.25 × 10−3 at 298 K) over the entire temperature range investigated. Thermodynamic behavior of vanillin in various propane-1,2-diol + water cosolvent mixtures was evaluated by Van't Hoff and Krug analysis. The results showed an endothermic, spontaneous and an entropy-driven dissolution of crystalline vanillin in all propane-1,2-diol + water cosolvent mixtures. Based on solubility data of this work, vanillin has been considered as soluble in water and freely soluble in propane-1,2-diol.