Molecular design of acyclic polyether dicarboxylic acids possessing pseudo-18-crown-6 frameworks for selective lead(II) extraction

Citation
T. Hayashita et al., Molecular design of acyclic polyether dicarboxylic acids possessing pseudo-18-crown-6 frameworks for selective lead(II) extraction, ANALYT CHEM, 71(4), 1999, pp. 791-795
Citations number
20
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry & Analysis","Spectroscopy /Instrumentation/Analytical Sciences
Journal title
ANALYTICAL CHEMISTRY
ISSN journal
0003-2700 → ACNP
Volume
71
Issue
4
Year of publication
1999
Pages
791 - 795
Database
ISI
SICI code
0003-2700(19990215)71:4<791:MDOAPD>2.0.ZU;2-D
Abstract
1,2-Bis[2-(2'-carboxyalkyloxy)phenoxy]ethanes (3-6), 1,2-bis[2-(2'-carboxyh eptyloxy)phenoxy]benzene (7), 1,2-bis[2-(2'-carboxyheptyloxy)ethoxy]benzene (8), and 1,2-bis[2-(2'-carboxyheptyloxy)ethoxy] ethane (9), which possess pseudo-18-crown-6 frameworks, are synthesized for use in selective Pb(II) e xtraction. For comparison, monocarboxylic acid analogues of 2-phenoxyoctano ic acid (1) and 2-(2'-methoxyphenyloxy)octanoic acid (2) are also prepared. Extraction of Pb(II) and Cu(II) from buffered aqueous solutions of varying pH into chloroform by these ligands is examined in relation to their molec ular structure, Polyether dicarboxylic acids 3-9 exhibit higher Pb(II)/Cu(I I) selectivities than the monocarboxylic acids 1 and 2. The alkyl chain len gth variation from hexyl to octyl to dodecyl to hexadecyl does not affect t he Pb(II)/Cu(TI) selectivity. Due to steric stress of the binding site, tri benzo ligand 7 shows a low Pb(II)/Cu(II) selectivity. For 3, 8, and 9, no s ignificant difference in Pb(II)/Cu(II) selectivity is noted, even though th e flexibility of the binding site increases in the order of 9 > 8 > 3, 7, S lope analysis reveals that ligands 3-6 mainly form 1:2 (metal/ligand) compl exes in both Pb(II) and Cu(II) extraction, whereas ligand 9, which possesse s a flexible binding site, tends to form 1:1 complexes. The extraction sele ctivity for heavy metal ions increases in the order Pb(II) > Cu(II) > Zn(II ), Cd(II) > Ni(IT). On the basis of the induced-fit mechanism of the pseudo -18-crown-6 binding site with Pb(II), the polyether dicarboxylic acids 3-9 are shown to have an excellent extraction selectivity for Pb(II).