Comparison of extraction behaviour and basicity of some substituted malonamides

The extraction behaviour for Am(III), Eu(III) and nitric acid is compared for eight different malonamides together with experimentally determined basicities and calculated gas-phase basicities. Water extraction data for two of the malonamides are also presented and shows that the water is co-extracted or solubilised by malonamide-HNO3 species. The relationship between metal extraction from aqueous nitric acid solution, basicity and the structure of the malonamide was investigated and it was found that the highest metal extraction was achieved with ligands of lowest basicity. The introduction of phenyl substituents on the nitrogens in the malonamide or the replacement of a carbon of the central carbon chain by an ether oxygen decreases the basicity and thus increases the metal extraction, The relative order of calculated gas-phase basicities, using ab initio methods, is in good agreement with the experimentally determined basicity scale.