DIALKYL PYRIDINEDICARBOXYLATES EXTRACTION ABILITY TOWARD COPPER(II) FROM CHLORIDE SOLUTIONS AND ITS MODIFICATION WITH ALCOHOLS

Dipentyl pyridinedicarboxylates (denoted hereafter as L) with differen t positions of the ester groups were synthesized and used for copper(I I) extraction from chloride solutions containing up to 10 mol . L(-1) Cl-. The effect of decanol addition on copper extraction was studied. A molecular modeling technique was used to estimate the structures of extractants, copper complexes, and associates with alcohol. It was fou nd that the ability of pyridinecarboxylates to extract copper depends on the aqueous phase composition and the position of the ester groups in the pyridine ring. All the investigated compounds except dipentyl p yridine-2,6-dicarboxylate extract copper(II) by formation of CuCl(2)L( 2) complexes. Dipentyl pyridine-2,6-dicarboxylate forms another type o f complex, probably CuCl(2)L. However, this compound is not suitable f or copper extraction as its copper complex precipitates. Dipentyl pyri dine-3,5-dicarboxylate was found to be the most suitable extractant am ong the various compounds listed. Finally it is shown that the possibi lities to modify the extraction ability of pyridinecarboxylates with a hydrophobic alcohol such as decanol are relatively weak. Some enhance ment was, however, observed when 20% of decanol was added to the organ ic phase containing dipentyl pyridine-3,5-dicarboxylate.