Separation of trivalent rare earths from nitrate medium using solvent extraction with a novel extractant 2-ethylhexyl ((2-ethylhexylamino)methyl) phosphonic acid

α-Aminophosphonates, -Phosphinates, and -Phosphine Oxides as Extraction and Precipitation Agents for Rare Earth Metals, Thorium, and Uranium: A Review

“…To the best of our knowledge, only one acidic α-aminophosphinate-based extractant ( 21 ) has been published so far in 2022 [ 50 ]. The development of this new extractant was driven by the findings from the previous studies carried out for the α-amino-functionalized organophosphorus extractants, which showed that most of the time, the α-amino-functionalized counterparts outperform traditional commercial extractants.…”

“…α-Aminophosphonates 8 – 14 together with α-aminophosphinate 21 and α-aminophosphine oxides 22 – 32 were synthesized using the same procedure, by refluxing the reagents either in benzene, toluene, or acetonitrile and using p -toluenesulfonic acid as the acid catalyst [ 11 , 36 , 37 , 39 , 40 , 41 , 42 , 43 , 44 , 50 , 51 ]. The progress of the reaction was monitored by measuring the amount of water formed into the Dean–Stark trap.…”

“…For 2-ethylhexyl ((2-ethylhexylamino) methyl) phosphonic acid (EEAMPA) 21 and bis(2-ethylhexyl) ((2-ethylhexylamino)methyl) phosphine oxide (DEHAPO) 32 , the phosphorous moieties were synthesized first by forming a Grignard reagent from 2-ethylhexyl bromide by mixing it with magnesium powder in THF and refluxing for 2 h, yielding (2-ethylhexyl)magnesium bromide. For compound 21 , the synthesized (2-ethylhexyl)magnesium bromide was reacted with triethylphosphite, yielding diethyl 2-ethylhexylphosphonite, which was then converted into ethyl 2-ethylhexylphosphinate by treating it with 6 M HCl [ 50 ]. In the case of 32, (2-ethylhexyl)magnesium bromide was reacted with diethylphosphite, yielding bis(2-ethylhexyl)phosphine oxide.…”

“…Because the α-aminophosphine oxides lack both the P–OH and P–O–C functionalities, only P=O and NH absorptions are relevant for the complex formation studies, but in the case of acidic α-aminophosphinates, derivatives of the α-aminophosphinic acid, P–OH absorption bands can also be investigated. The coordination affinities of α-aminophosphinic acid 21 and α-aminophosphine oxide 32 were investigated towards Lu( iii ) and Ce( iv ), respectively, by IR [ 50 , 51 ].…”

“…Similarly to the acidic α-aminophosphonates above, 21 exhibited an absorption band for P–OH stretching at 2318 cm −1 that disappeared after the Lu( iii ) complex was formed, indicating deprotonation of the P-OH group due to the metal coordination [ 50 ]. Shifting of the P=O group was also observed during the coordination for both 21 and 32 , as the free ligands showed a stretching absorption band at 1146 cm −1 and 1054 cm −1 , which then shifted to 1162 cm −1 and 1040 cm −1 in the metal complexes, respectively [ 50 , 51 ]. The NH absorption bands were observed to shift from 1614 cm −1 to 1644 cm −1 for 21 , and from 3311 cm −1 and 1675 cm −1 to 3396 cm −1 and 1666 cm −1 for 32 , indicating coordination of the NH functionality to either the metals or sulfate ions.…”