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

The distribution constants ( K D,C O 2 ) of 8-quinolinol derivatives (HA) between supercritical carbon dioxide (SC-CO2) and water were determined at 45 °C. The values of K D,C O 2 increased with an increase in the SC-CO2 pressure, that is, the SC-CO2 density ( ρ C O 2 ) . The values of K D,C O 2 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   K D,C O 2 , 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.