Extraction of europium(III) ion with tetrahexylmalonamides

The extraction of europium(III) nitrate from sodium nitrate with a series o f tetrahexylmalonamides has been investigated. The tetrahexylmalonamides co nsidered were N,N,N'N'-tetrahexylmalonamide (THMA), N,N,N'N'-tetrahexyl-2-m ethylmalonamide (MeTHMA), and N,N,N'N'-tetrahexyl-2,2-dimethylmalonamide (D iMeTHMA). This series allowed for a systematic determination of the effects of alkyl substitution of the methylene carbon. Equilibrium modeling of the extraction data indicates that the malonamide/Eu ratio in the extracted co mplexes is 3 for all three malonamides investigated. This stoichiometry is different than that determined for isolated complexes. This can be rational ized by the formation of complexes with monodentate-bound diamide ligands i n the extracts. The extraction constant for Eu decreases by seven-fold in g oing from THMA to MeTHMA and a precipitous drop in the extraction constant occurs upon substitution of a second methyl group on the methylene carbon ( i.e., for DiMeTHMA).