Are fancy acidic or neutral ligands really needed for synergism in ionic liquids? A comparative study of lanthanoid extraction in CHCl₃ and an ionic liquid

Abstract

The study of trivalent lanthanoid (La, Nd, Eu, Ho and Lu) extraction by two individual ligands: one acidic as pyrazolone derivative, 3-methyl-1-phenyl-4-(4-phenylbenzoyl)-pyrazol-5-one (HL), and one neutral as 5,11,17,23-tetratert-butyl-25,26,27,28-tetrakis-(dimethylphosphinoylmethoxy)calix[4]arene (SIV) was performed in CHCl3 and in one ionic liquid, IL (1-methyl-1,3butylimidazolium-bis(trifluoromethanesulfonyl)imide ([C1C4im][Tf2N]) in order to establish and examine the impact of the diluent onto the individual and synergistic extraction processes. Chloride aqueous medium and constant ionic strength μ = 0.1 M were set in both cases. The parameters of the extraction processes were determined. Comparison between the two diluents was made on the basis of: i) Composition of the extracted species: LnL3·HL in CHCl3 vs LnL3 in IL with HL as a single extractant (L − represents the HL anion), and LnL3·SIV in the presence of the phosphorus-containing calix[4]arene in both diluents; and ii) Values of the equilibrium constants and the synergistic enhancements; the separation factors between metals were evaluated as well.The IL medium appears far superior to the molecular solvent in terms of individual and overall synergistic extraction efficiencies. However, the huge differences in extraction efficiencies observed in CHCl3 for chemically different ligands are erased in the IL medium, thus modifying the lever arms on which chemists should rely in order to obtain even better extracting systems in ionic liquid media.

Uncertainty Principle in the Elucidation of the Extraction Mechanism of Ions from Aqueous towards Ionic Liquid Phases. PtCl62− and [C1C8IM][NTf2] as a Textbook Case

“…Cases that are not expected to fall under this uncertainty principle are those where a metal cation is bound to charged extracting agent forming a neutral species, or bound to a functional group of a task‐specific ionic liquid under the form of a neutral complex with the counter ions of the metal for instance. Similarly, the case where a metal is extracted as a neutral complex formed with a counter ion in the aqueous phase would not be expected to follow either this principle.…”

Solvent extraction of intra-lanthanides using a mixture of TBP and TODGA in ionic liquid

“…11 Recently, investigators have examined the synergic effect of mixed systems involving various extractants and ionic liquids. [12][13][14][15][16][17][18][19][20][21] Ionic liquids (ILs) are a new class of solvents with a melting point usually below 100°C and composed of dissociated ions. 22 Many ILs are stable to air and water, nonvolatile and non-flammable.…”

“…The extraction of europium(III) with the βdiketone benzoylacetone (HBA) alone and in combination with octyl(phenyl)-N,Ndiisobutylcarbamoylmethyl phosphine oxide (CMPO) or 5,11,17,23-tert-butyl-25,26,27,28tetrakis(dimethylphosphinoylmethoxy) calix [4]arene onto imidazolium-and pyrrolidinium-based ionic liquids was studied by Atanassova et al 14 The same group also examined pyrazolone derivative and calix[n]arene organic ligands dissolved in imidazolium-based ionic liquid for the extraction of lanthanides(III) (lanthanum, neodymium, europium, holmium and lutetium) from aqueous chloride media. 18 The extraction of trivalent lanthanides with a blend of CMPO and β-diketone type anionic ligands from 4-acylpyrazolone family or β-diketone 2-thenoyltrifluoroacetone (HTTA) dissolved in imidazolium-based ionic liquids has been also reported. 16,30 Some studies on the extraction of metal ions with mixtures of two electrically neutral extractants in ILs have been published.…”

Extraction Ability of 4-Benzoyl-3-phenyl-5-isoxazolone towards 4f-Ions into Ionic and Molecular Media

“…Unlike conventional molecular systems, where metals generally form neutral hydrophobic complexes, in IL systems the situation is remarkably different in view of intensive ion exchange that sometimes creates atypical complexes via multiple mechanism processes. [5][6][7][8][9] A variety of ligands developed to operate in molecular media have nowadays proven to be effective in ILs too, such as crown ethers, 7,10,11 N,N,N′,N′-tetraoctyldiglycolamide (TODGA), 12 octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), 5,13,14 β-diketones, 6,7,9,[15][16][17][18] calix[n]arenes [19][20][21][22] and other compounds. This has a supplemental advantage, so that researchers may draw on the massive library of known compounds, many of which are highly specific for a given group of metallic species, in order to design new ones.…”