Design, synthesis and extraction studies of a new class of conformationally constrained (N,N,N′,N′-tetraalkyl)7-oxabicyclo[2.2.1]heptane-2,3-dicarboxamides

Abstract

A new class of conformationally constrained 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxamides (OBDA) of three secondary amines was synthesized, and their extraction behavior for trivalent and tetravalent actinides in HNO₃ medium was studied. Amongst the diamides, N,N-bis-2-ethylhexyl substituted diamide showed the best results for actinide extraction. This diamide also exhibited a very low level of extraction for Sr(II) and Ru(III) which is desirable, thus providing higher selectivity for actinides. The stripping of extracted metal ions was achieved using 0.1 M oxalic acid for Pu(IV) or pH ∼ 2 solution for Am(III). Third phase formation was not observed for the OBDA ligand even for a higher concentration of Eu up to 5 g L⁻¹ with retention of good D_Eu. The tridentate nature of the OBDA ligand was ascertained by studying the IR and NMR spectra of the Eu(III) complex with the ligand. The OBDA showed the formation of a mixture of mono- and di-solvated species of Eu(III) as indicated by the slope analysis method and ESI-MS. Density functional theoretical (DFT) study was carried out to determine the energy optimized structure of the free ligand and its Am³⁺ complex.