Synthesis and Characterization of New Unsymmetrical Diglycolamides for Trivalent Lanthanide Metal Extraction
Tokheim, Benjamin George
MetadataShow full item record
Twelve new unsymmetrical diglycolamide (UDGA) ligands have been synthesized as solvent extraction reagents for trivalent lanthanide ions from highly acidic nitrate media. The asymmetry in the extractant design arises from attaching nonpolar alkyl chains (hexyl, octyl, 2-ethylhexyl, 3,7-dimethyloctyl) to one amide group and smaller, more compact, cyclic alkyl groups (pyrrolidinyl, piperidinyl, morpholino) to the other amide moiety. This structural variant of a well-known cation receptor reduces the interfacial footprint of the extractant and is designed to increase the rate of phase transfer of the target cations. The partitioning of 152,154Eu(III) between aqueous phases of varying nitric acid concentrations (0.01-3 M) and a 0.05 M UDGA in 5% v/v 1-octanol/n-dodecane organic phase was measured radiometrically and compared to the symmetrical diglycolamide, N,N,N′,N′-tetraoctyldiglycolamide (TODGA). All twelve UDGA ligands quantitatively extracted trivalent Eu(III) cations from 1 M nitric acid. Separate solvent extraction slope analysis experiments were used to determine the stoichiometry and conditional extraction equilibrium constant (K'ex) of the extracted Eu-UDGA complex in 5% v/v 1-octanol/n-dodecane. The metal-ligand complex stoichiometry in the extracted species was found to be approximately 1:3 for the UDGA ligands and TODGA while the conditional extraction equilibrium constants (K'ex) decreased with increasing ligand size and alkyl chain branching. Luminescence spectroscopy investigations established the relative stability and stoichiometry of the complexes in acetonitrile. The overall trends in the conditional extraction equilibrium constant (K'ex) and the 1:3 conditional stability constant (β103) followed a similar pattern, indicating a correlation between complex stability and ligand structural features.