| Summary: | Imidophosphoric organic esters containing phosphoryl groups are potential polydentate ligands and promising extractants of rare-earth elements. For their preparation, a monophosphazene salt [PCl<sub>3</sub>=N−PCl<sub>3</sub>]<sup>+</sup>[PCl<sub>6</sub>]<sup>−</sup> and short phosphazene oligomers of the general formula [Cl−(PCl<sub>2</sub>=N)<sub>n</sub>−PCl<sub>3</sub>]<sup>+</sup>[PCl<sub>6</sub>]<sup>−</sup>, where n = 4−7, were synthesized via living cationic polymerization of Cl<sub>3</sub>P=NSiMe<sub>3</sub> 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)<sub>2</sub>=N− or −P(OH)(OR)=N− units, where R = 2-ethylhexyl. The prepared EIPAs were characterized by <sup>1</sup>H, <sup>31</sup>P 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<sub>x</sub>A, where x = 1−3, which can form chelate complexes of lanthanide ions [Ln(A)<sub>z</sub>], 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.
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