LIQUID-LIQUID-EXTRACTION OF AG(I), HG(II), AU(III) AND PD(II) BY SOME OLIGOTHIA MACROCYCLIC LIGANDS INCORPORATING AROMATIC AND HETEROAROMATIC SUBUNITS

A series of hydrophobic tri- to hexa-dentate sulfur containing macrocyclic ligands incorporating aromatic and heteroaromatic subunits have been studied with respect to their extraction properties toward Ag(I), Hg(II), Au(III), and Pd(II) in aqueous//organic systems. The stoichiometry of extracted species and their extraction constants have been determined. The different ligands are compared with structure related open-chain compounds. The influence of substitution, solvent, and anion on the extraction equilibrium is also discussed providing a basis for future design of selective extractants and for the development of improved separation methods. The extractability of the various metal ions strongly depends on the nature and the number of donor atoms of the corresponding ligands and on the properties of the metal ion itself. In some cases, simple open-chain ligands show extraction properties comparable to the present macrocycles. A trithia crown with incorporated benzo subunit highly prefers Ag(I) to Hg(II). Furthermore a distinct selectivity for Au(II) and Hg(II) over Pd(II) with pyridine substituted macrocycles was found.