Diamide extractants for f-element separations are well known as versatile reagents for nuclear fuel reprocessing applications. In this exploration of size-property relationships of this class of extractants for lanthanide/actinide separations, novel unsymmetrical diglycolamide ligands have been synthesized and investigated using radiotracer solvent extraction methods. The purpose of this study is to determine whether the more slender geometry provided by the asymmetric –R groups can favorably impact the phase transfer/compatibility properties of this class of reagents. The following ligands have been synthesized in good overall yield (≥70%): N,N-dihexyl-Nʹ-pyrrolidinyl diglycolamide (DHpyrDGA), N,N-dihexyl-Nʹ-piperidinyl diglycolamide (DHpipDGA), N,N-di-2-ethylhexyl-Nʹ-pyrrolidinyl diglycolamide (DEHpyrDGA), N,N-di-2-ethylhexyl-Nʹ-piperidinyl diglycolamide (DEHpipDGA), N,N-dioctyl-Nʹ-pyrrolidinyl diglycolamide (DOpyrDGA), and N,N-dioctyl-Nʹ-piperidinyl diglycolamide (DOpipDGA). Radiotracer 152,154Eu(III) has been used to measure the ability of each ligand to extract the trivalent lanthanides from a nitric acid aqueous phase into an aliphatic organic phase. The dihexyl derivatives achieve near quantitative metal extraction but exhibit a tendency toward third phase formation at higher acid concentrations. The solubility properties of the remaining ligands are greatly improved by the addition of a phase modifier, 1-octanol, to the aliphatic diluent, n-dodecane. The dioctyl derivatives display strong metal extraction at high acid concentrations but the back-extraction of the metal at dilute acid concentrations is an issue. The di-2-ethylhexyl derivatives, however, exhibit improved solubility, satisfactory metal extraction at higher acid concentrations, and the weak extraction needed at more dilute acid concentrations. It is likely that the addition of a longer carbon chain with similar branching could further improve solubility while maintaining favorable metal extraction. Support provided by the U.S. Department of Energy, Office of Nuclear Energy, Nuclear Energy University Programs project number 10-881

Synthesis, characterization, and extraction performance of new diglycolamide ligands

250th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.