Non-heterocyclic N-donor ligands of nitrilotriacetamide for Am3+/Eu3+ separation

Abstract For figuring out the relationships between chemical structure and extraction properties of the soft non-heterocyclic N-donor ligand nitrilotriacetamide (NTAamide), eight representative ligands with different substituent groups based on NTAamide were synthesized on purpose. Their extraction behaviors toward Am 3+ and Eu 3+ were investigated. In the examined HNO 3 concentration ranging from 0.01 to 0.50 mol/L, the distribution ratios ( D ) of Am 3+ and Eu 3+ increased with increasing the extractant concentration or decreasing the aqueous phase acidity. The highest separation factor ( SF Am/Eu ) of 12 with D Am  = 5.8 and D Eu  = 0.49 could be obtained in the case of the extraction by 0.10 mol/L N,N,N',N',N“,N” -hexadecylnitrilotriacetamide (NTAamide( n -Dec)) in MIBK as diluent from 0.10 mol/L HNO 3 solution. The extractability of eight ligands decreased in the order of NTAamide( n -Dodec) > NTAamide( n -Dec) > NTAamide( n -Oct) > NTAamide( n -Bu) > NTAamide( i -Bu) > NTAamide(Et- p -MePh) > NTAamide(Et-Ph) > NTAamide(2-EtHex). The aliphatic substituent groups with longer straight chain are advantageous to the extraction, while the aromatic ones with larger steric hindrance and electron-withdrawing property are disadvantageous. The log β values between NTAamides and Eu 3+ were obtained by fluorescence titration for the first time. Moreover, HRMS indicated the formation of 1:1 complexes of NTAamides with Eu 3+ , which was in good accordance with the extraction results obtained from slope analysis.