Equilibrium solubility of kojic acid in four binary solvents: Determination, model evaluation, Hansen solubility parameter, thermodynamic properties and quantum chemical calculations

Abstract

Using the laser monitoring method, the solubility of kojic acid (KA) in the four binary solvents {[(N, N-dimethylformamide) DMF, (N, N-dimethylacetamide) DMAC, (dimethyl sulfoxide) DMSO and (N-methylpyrrolidone) NMP] + ethyl acetate} was measured at various temperatures. The results revealed that the experimental solubility values of KA have positive correlations with mass fraction of co-solvents and temperature in investigated four binary solvents. The solubility order of KA with mass fraction of co-solvents being w1 = 0.2000, 0.4000 and 0.6000 is: DMSO + ethyl acetate > NMP + ethyl acetate > DMAC+ ethyl acetate > DMF + ethyl acetate, respectively. However, in DMAC (w1 = 0.8005) + ethyl acetate, the solubility values of KA overtook that in NMP (w1 = 0.8004) + ethyl acetate at the higher temperature. The miscibility behaviors of KA with tested four binary solvents was revealed by the Hansen Solubility Parameters (HSPs). According to the calculated interaction energy, KA can be more easily dissolved in the solvent which has larger interaction energy with KA. Additionally, the measurement solubility data was mathematically correlated by the NRTL, Three-Suffix Margules, UNIQUAC models and Apelblat equation. The thermodynamic parameters (ΔdisGo, ΔdisHo, ΔdisSo, ζH, ζTS) of KA dissolution processes in investigated four binary solvents were evaluated utilizing the van't Hoff equation. The positive ΔdisHo and ΔdisSo, indicate that the dissolution processes of KA are endothermic and entropy-driven in all chosen binary solvents. And the main contributor of ΔdisGo is positive enthalpy.