Preorganized complexing agents as a tool for selective solvent extraction processes

Solvent extraction as a well-established process in hydrometallurgy, waste treatment, and material preparation requires selective and effective complexing agents with high lipophilicity. The extractant types used in industry reach from simple acids, ethers, and esters to more complex chelating agents. Nowadays the progress of supramolecular chemistry offers interesting possibilities to control the selectivity of metal extraction and to achieve a tailored ligand. In this paper, solvent extraction studies are presented for transition-metal ions with position isomers of alkylated 8-hydroxyquinolines from the chelating type as well as for amino and imino cage compounds and their acyclic counterparts from the supramolecular type. In all cases the extraction selectivity and efficiency strongly depend both on the extractant architecture and on the aqueous-phase composition. It is clearly shown that manipulation of the chemistry in the investigated systems leads to significant changes of the graduated extractabilities.