Influence of molecular association on the solubility of methylxanthines in supercritical solvent CO2–methanol

Abstract

Analysis of the experimental data on the solubility of methylxanthines (theophylline and theobromine) in supercritical (SC) solvent CO₂–methanol at various concentrations of methanol within the framework of the ASL model (Associated Solution + Lattice) based on molecular association theory and the simple lattice model is presented. Hetero-association of methylxanthines with the molecules of methanol is studied by means of ¹H NMR spectroscopy at 313 K. The contribution of molecular association to the solubility of methylxanthines in the mixed SC solvent CO₂–methanol is analyzed. It is shown that the presence of NH group in the molecule of methylxanthine, when passing from caffeine to theophylline or theobromine, leads to an increase of the contribution of the component related to molecular association to solubility.