Design, synthesis and evaluation of diazadibenzocrown ethers as Pb2+ extractants and carriers in plasticized cellulose triacetate membranes

The ligands 4,7-diaza-2,3,8,9-dibenzo-15-crown-5 (L1), 4,10-diaza-2,3,11,12-dibenzo-18-crown-6 (L2), 4,10-diaza-2,3,11,12-di(4′-tert-butylbenzo)-18-crown-6 (L3) and N,N-di(methylenecarboxyethoxy) 4,10-diaza-2,3,11,12-dibenzo-18-crown-6 (L4) have been prepared. Partition coefficients and acid dissociation constants for these four diazadibenzocrown ether compounds were determined in water-chloroform. Their effectiveness was assessed in solvent extraction of Pb2+ from aqueous solutions into toluene. Ligands L3 and L4 provide high selectivity for Pb2+ over Cd2+ and Zn2+ in transport across plasticized cellulose triacetate membranes.