Multidentate nitrogen/oxygen donor ionophores; their use as selective extracting and mobile-carrier agents for copper(II) ions

Two new N2O2-type Schiff base extractants, N,N′-bis(2-hydroxyacetophenone)-1,2-propanediimine (L1) and N,N′-bis(5-bromo-2-hydroxybenzaldehyde)-1,2-propanediimine (L2), have been synthesized by the reaction of corresponding ketone and aldehyde (2-hydroxyacetophenone and 5-bromo-2-hydroxybenzaldehyde, respectively) and 1,2-diaminopropane in ethanol. Distribution study of the prepared ligands between sodium chloride aqueous phase and dichlomethane shows their suitability for using in solvent extraction process. Liquid–liquid extraction experiments were performed for illustrating extractive performance of L1 and L2 ligands towards copper(II) ions. Both ligands transfer copper ions into the dichloromethane organic phase by a cation exchange mechanism. Analysis of the extraction data reveals that Cu2+ ions are extracted as the complexes with a 1:1 metal to ligand ratio by both extractants. The ability of the studied Schiff base ligands for separation of copper ions from its mixture with other normally associated metal ions was demonstrated by performing competitive extraction experiments of copper ions from solutions containing Pb2+, Zn2+, Ni2+, Cd2+ and Co2+ ions. The efficiency of L1 as a mobile-carrier of copper ions from ammoniacal media through bulk liquid membranes has been also studied. The parameters influencing the transport process i.e. pH of the feed phase, type and concentration of stripping agent in the receiving phase, carrier concentration in the membrane, diluent and time dependency of the process, were investigated and discussed. It is shown that the presence of sodium dodecylsulfate (SDS), an anionic surfactant, enhances both efficiency and selectivity of the transport. The applicability of the method was checked for the separation of copper ions from synthetic samples.