Highly CO2-soluble 5-Amido-8-hydroxyquinoline Chelating Agents for Extraction of Metals in Sc-CO2

摘要

Novel C02-soluble 8-hydroxyquinoline (8-HQ) chelating agents were synthesized and evaluated for solubility and metal ion extraction ability in supercritical C02 (Sc-C02). Among them, secondary anude-containing 8-HQ derivatives cannot be dispersed well into SC-CO2, but tertiary aniide-containing derivatives can dissolve completely in SC-CO2 even at low C02 pressures, perhaps owing to the predominant intermolecular interaction between the chelating agent and the CO2 molecule. Based on 8-HQ chelating agent solubility data, we investigated the extraction of metal ions (Co~(2+), Cu~(2+), Sr~(2+), Cd~(2+), and Zn~(2+)) using two highly C02-soluble 8-HQ derivatives (4d, 4e) in SC-CO2. The extraction efficiency of tertiary amide-containing 8-HQ ligands, both fluorinated and non-fluorinated forms, was dramatically increased in the presence of diethyl amine (organic base). We suggest that diethyl amine could play an important synergistic role in the stronger metal binding ability of 8-HQ through an in situ deprotonation reaction in SC-CO2 medium.