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

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 DEu. 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 Am(3+) complex.