Linear 2-Ethylhexyl Imidophosphoric Esters as Effective Rare-Earth Element Extractants.

Imidophosphoric organic esters containing phosphoryl groups are potential polydentate ligands and promising extractants of rare-earth elements. For their preparation, a monophosphazene salt [PCl₃=N−PCl₃]⁺[PCl₆]⁻ and short phosphazene oligomers of the general formula [Cl–(PCl₂=N)_n–PCl₃]⁺[PCl₆]⁻, where n = 4–7, were synthesized via living cationic polymerization of Cl₃P=NSiMe₃ and used as starting compounds. All phosphazenes were reacted with 2-ethylhexanol to obtain the corresponding esters of imidophosphoric acids (EIPAs). The formation of imidophosphoric acids occurs due to the phosphazene-phosphazane rearrangement of –P(OR)₂=N– or –P(OH)(OR)=N– units, where R = 2-ethylhexyl. The prepared EIPAs were characterized by ¹H, ³¹P NMR, and MALDI-TOF analyses and their extractive capacity towards lanthanide ions in aqueous solutions of nitric acid was examined. The EIPAs are mixtures of mono-, di-, and trifunctional compounds of the type H_xA, where x = 1–3, which can form chelate complexes of lanthanide ions [Ln(A)_z], where z = 3–6, depending on the chain length. The longer chain EIPAs are more suitable for collective rare-earth elements extraction. A comparison of the extraction properties of the EIPAs with the industrially used polyalkylphosphonitrilic acid (PAPNA) was drawn. [ABSTRACT FROM AUTHOR]