Synthesis and Am/Eu extraction of novel TODGA derivatives

Various ligands with structural modifications of the N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) skeleton were synthesised in good yields. These modifications include (1) the increase in chain length from one carbon to two carbons between the central ether oxygen atom and the amide moieties, (2) the addition of substituents on the carbon between the central oxygen atom and the amide moieties on one and both sides of the central oxygen, (3) the replacement of the central oxygen by a (substituted) nitrogen atom and (4) synthesis of a rigidified glycolamide. The effect of the structural modifications on their extraction behaviours toward Am(III) and Eu(III) at various nitric acid concentrations was studied. In most of the cases, the extraction does not exceed that of TODGA in the entire acidity range of 0.001–4 mol/l HNO3. The extraction behaviour of monomethyl–TODGA derivative 10a resembles that of TODGA at high nitric acid concentrations. However, at lower acidities, its D values are much lower, which is beneficial for possible back-extraction steps. The aza-tripodal ligands 18a,b show reverse extraction properties compared to TODGA as far as the pH influence is concerned: at pH 2, the D Am values are 49.9 and 3.1, the D Eu values are 5.9 and 0.2, and the S Am/Eu values are 8 and 11, respectively.