Key words: molecular association, solubility, supercritical fluid, methylxanthine
Experimental data on solubility of methylxanthines (theophylline and theobromine) in the system «supercritical (SC) CO2-methanol» at various concentrations of methanol is analyzed in the framework of the ASL (Associated Solution + Lattice) model based on the molecular association theory and the simple lattice concept. 1H NMR spectroscopy is applied to investigate hetero-association of methylxanthines with methanol at 313 K. The contribution of molecular association to the solubility of methylxanthines in a mixed SC CO2-methanol solvent is discussed. It is shown that the presence of NH groups in methylxanthine molecule (i.e. theobromine and theophylline vs. caffeine) leads to the increasing contribution of solubility component related to the molecular association.