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

A series of hydrophobic tri- to hexa-dentate sulfur containing macrocy clic ligands incorporating aromatic and heteroaromatic subunits have b een studied with respect to their extraction properties toward Ag(I), Hg(II), Au(III), and Pd(II) in aqueous//organic systems. The stoichiom etry of extracted species and their extraction constants have been det ermined. The different ligands are compared with structure related ope n-chain compounds. The influence of substitution, solvent, and anion o n the extraction equilibrium is also discussed providing a basis for f uture design of selective extractants and for the development of impro ved separation methods. The extractability of the various metal ions s trongly depends on the nature and the number of donor atoms of the cor responding ligands and on the properties of the metal ion itself. In s ome cases, simple open-chain ligands show extraction properties compar able to the present macrocycles. A trithia crown with incorporated ben zo subunit highly prefers Ag(I) to Hg(II). Furthermore a distinct sele ctivity for Au(II) and Hg(II) over Pd(II) with pyridine substituted ma crocycles was found.