Solvent effect on the distribution equilibrium of 8-quinolinol derivatives between supercritical carbon dioxide and water

The distribution constants (KD,CO2)(KD,CO2) of 8-quinolinol derivatives (HA) between supercritical carbon dioxide (SC-CO2) and water were determined at 45 °C. The values of KD,CO2KD,CO2 increased with an increase in the SC-CO2 pressure, that is, the SC-CO2 density (ρCO2)(ρCO2). The values of KD,CO2KD,CO2 were evaluated by a comparison of the distribution constant (KD,org) of HA between heptane and water. Based on a linear relationship between log KD,org and log KD,CO2log KD,CO2, it was suggested that the interaction of heptane molecules with HA is similar to that of CO2 molecules. The solvent effect on the distribution behaviors of HA between SC-CO2 and water was evaluated based on a regular solution theory. The solubility parameters of HA in the SC-CO2–water extraction system are smaller than those in the organic solvent–water extraction system, suggesting that the interaction between HA and CO2 molecules, such as the dispersion force, dipole–dipole and dipole-induced dipole interactions, is weaker than that between HA and the organic solvent molecules.

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