Two new unsymmetrical diglycolamide (UDGA) ligands have been synthesized as extractants for trivalent lanthanide ions from highly acidic nitrate media. The asymmetry in the extractant design arises from attaching nonpolar dodecyl chains to one amide group and smaller, more compact, cyclic alkyl groups (pyrrolidinyl or piperidinyl) to the other amide moiety. The dodecyl chain should improve organic phase (e.g., dodecane) solubility while the cyclic alkyl groups should increase interactions with the aqueous phase (e.g., 1 M HNO3). These structural variants of the tridentate cation receptor, tetraoctyldiglycolamide (TODGA), reduce the interfacial footprint of the extractant and are designed to increase the rate of phase transfer of the target lanthanide cations. Biphasic solvent extraction experiments were performed under low acidity (e.g., 0.01 M HNO3) and high acidity (e.g., 1 M HNO3) using both UDGA ligands and the results were quantified using ICP-MS for all the lanthanides. Spectrophotometric titrations were also performed with Nd(III) to determine metal-ligand complexation constants. Both UDGA ligands formed a 1:3 Nd(III)-ligand terminal complex, which is consistent with the preferred nine-coordinate tricapped trigonal prismatic molecular geometry of the lighter lanthanides. Stability constants were also calculated for the 1:1, 1:2, and 1:3 Nd(III)-UDGA complexes.

New unsymmetrical diglycolamide extractants for lanthanide ion complexation

2019 Spring National Meeting

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