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

Abstract

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.

Novel Approach for the Synthesis of Chlorophosphazene Cycles with a Defined Size via Controlled Cyclization of Linear Oligodichlorophosphazenes [Cl(PCl2=N)n–PCl3]+[PCl6]−

“…Linear high molecular weight phosphazenes are of great interest due to their unique properties such as high flexibility of the polymer chain, low glass transition temperature, high thermal stability and high values of quadratic electro-optic effect [ 1 , 2 ]. Thereby, these polymers find applications as elastomers [ 3 ], solid polyelectrolytes [ 4 ], photosensitive materials [ 5 ], gas separation membranes [ 6 ], liquid crystals [ 7 , 8 ], non-linear optic materials [ 9 ], sensors and actuators [ 10 ], extractants [ 11 ] etc.…”

Novel Approaches to Chemically Cross-Linked Phosphazene Structures: Hydrosilylation vs Piers–Rubinsztajn Reaction

“…The main disadvantage of this polymer is its high tendency to crystalline phase formation, which in turn leads to a decrease of ion conductivity [5]. On the other hand, phosphazene polymers are good candidates for polyelectrolyte materials since they obtain high flexibility of polymeric chain, high chemical and thermal stability, biocompatibility, fire-proofing and easy backbone derivatization [6][7][8][9][10][11]. Moreover, phosphazene chain can also contribute to metal cations coordination due to the presence of electron rich nitrogen atoms in the P=N structure [8,9,12].…”

“…On the other hand, phosphazene polymers are good candidates for polyelectrolyte materials since they obtain high flexibility of polymeric chain, high chemical and thermal stability, biocompatibility, fire-proofing and easy backbone derivatization [6][7][8][9][10][11]. Moreover, phosphazene chain can also contribute to metal cations coordination due to the presence of electron rich nitrogen atoms in the P=N structure [8,9,12]. The most known efficient phosphazene alternative for PEO is poly(methoxyethoxyethoxy)phosphazene (PMEEP) -fully amorphous polymer [5,13,14].…”

Chelating Extractants for Metals

“…Imidophosphoric acid esters, which are polydentate ligands that form strong complexes with these elements and can be used for recovery of REEs from ores can be used for recovery of REEs. In [39], 2-ethylhexyl derivatives of imidophosphoric acid (26 and 27) were described and showed high efficiency for collective extraction of trivalent REEs Y, Pr, La, Ce, Nd, Sm, Gd, Dy, Yb and Ho from nitric acid water solutions. A mixture of C 9 -C 13 hydrocarbons was used as a diluent.…”