Journal Article

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

Esin, Andrey S., Bykovskaya, Anna A., Kireev, Vyacheslav V., Gorlov, Mikhail V., Sinegribova, Oksana A., Bredov, Nikolay S., Ryabochenko, Maria D.

2020

Overview

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 HxA, 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.

• Publisher: MDPI AG
• Subject: 2-ethylhexyl esters / extractants / imidophosphoric acids / living cationic polymerization / Metals / phosphazenes / Phosphorus / Polymerization / rare-earth elements / Scientific imaging / Vacuum distillation