The solubility of benzocaine, lidocaine, and procaine in liquid and supercritical carbon dioxide

The solubility of three local anesthetics (benzocaine, lidocaine, and procaine) was measured in liquid and supercritical carbon dioxide at (298, 308, and 318) K and at pressures between (70 and 280) bar. The solubilites were experimentally measured by observing the cloud point using a variable-volume stirred vessel with visual access. Interestingly, although the three anesthetics were structurally very similar, the solubilites of lidocaine and benzocaine were strong functions of only density while that of procaine was a function of both density and temperature. The Peng-Robinson equation of state did not adequately predict the solubilites, while a simple enhancement factor correlation did predict them. The hydrochlorides of lidocaine and procaine did not have any measurable solubility in carbon dioxide over the conditions tested.