Solubility of caffeine in N-methyl-2-pyrrolidone + ethanol mixture at different temperatures

The solubility profile of caffeine in the binary non-aqueous mixtures of N-methyl-2-pyrrolidone (NMP) and ethanol at different temperatures is determined and the obtained data are fitted to some linear and non-linear cosolvency models including the van't Hoff, the double log-log, the mixture response surface, Yalkowsky, Jouyban-Acree, Jouyban-Acree-van't Hoff, and the modified Wilson models. The measured density data of caffeine saturated solutions as another physico-chemical property are also correlated with the Jouyban-Acree model and the results are discussed. In order to investigate the accuracy of the applied models, the mean relative deviations (MRD%) of the back-calculated solubility data is calculated. Furthermore, the apparent thermodynamic properties of caffeine dissolution process are also calculated by using van't Hoff and Gibbs equations.