Browsing by Author "Kurteva V."

Now showing 1 - 9 of 9
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    Aliquat 336 in Solvent Extraction Chemistry of Metallic ReO4− Anions
    (2024-05-01) Atanassova M.; Petkova Z.; Kurteva V.
    A study of the liquid–liquid extraction of ReO4− anions from hydrochloric acid solutions using the ionic liquid Aliquat 336 (QCl: trialkyl(C8–C10)methylammonium chloride) via the well-known method of slope analysis along with the determination of the process parameters is presented. This study employs CCl4, CHCl3 and C6H12 as diluents. This study was carried out at room temperature (22 ± 2) °C and an aqueous/organic volumetric ratio of unity. The ligand effect on the complexation properties of ReO4− is quantitatively assessed in different organic media. The organic extract in chloroform media is examined through 1H, 13C and 15N NMR analysis as well as the HRMS technique and UV-Vis spectroscopy in order to view the anion exchange and ligand coordination in the organic phase solution. Final conclusions are given highlighting the role of the molecular diluent in complexation processes and selectivity involving ionic liquid ligands and various metal s-, p-, d- and f-cations. ReO4− ions have shown one of the best solvent extraction behaviors compared to other ions. For instance, the Aliquat 336 derivative bearing Cl− functions shows strongly enhanced extraction as well as pronounced separation abilities towards ReO4−.
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    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
    (2015-07-27) Atanassova M.; Kurteva V.; Lubenov L.; Varbanov S.; Billard I.
    The study of trivalent lanthanoid (La, Nd, Eu, Ho and Lu) extraction by two individual ligands, one acidic such as a pyrazolone derivative, 3-methyl-1-phenyl-4-(4-phenylbenzoyl)-pyrazol-5-one (HL), and one neutral such as 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis-(dimethylphosphinoylmethoxy)calix[4]arene (SIV), was performed in CHCl3 and in one ionic liquid, IL 1-methyl-1,3-butylimidazolium-bis(trifluoromethanesulfonyl)imide ([C1C4im][Tf2N]), in order to establish and examine the impact of the diluent on 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 CHCl3vs. 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.
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    Chemical and mechanistic modelling of green solvent extraction of metallic species with 4-acylpyrazolones
    (2024-12-01) Atanassova M.; Kukeva R.; Kurteva V.
    Solvent extraction chemistry of metals needs the use of suitable organic ligands like 4-acylpyrazolones to coordinate the studied cation, to make it soluble in an organic phase and then allow its phase transfer from the aqueous phase. The competitive solvent extraction test of almost 25 metal ions by one powerful ligand, i.e. 3-methyl-1-phenyl-4-(4-trifluoromethylbenzoyl)-pyrazol-5-one diluted in one ionic liquid ([C1Cnim+][Tf2N−]) has been conducted to get a snapshot of its efficacy. Effect of diluents on the liquid–liquid extraction of 4f-ions with a series of chelating ligands of 4-acylpyrazolones family (∼5) is presented comparing ionic liquids and typical organic diluents: 14 in number. In addition, the solvent extraction of 12 refractory metals with a series of chelating extractants is investigated in five diluents: four 4-acylpyrazolones with different radicals. The solvent extraction stoichiometry of MoO42− and Zr4+ is studied in detail using molecular and ionic diluent for comparative purposes through slope analysis method. Ethylene glycol is used to develop a non-aqueous process for Gd3+ switchable extraction, i.e. boost of two immiscible organic phases. Furthermore, EPR, NMR, IR and DTA-TG-MS spectroscopies have been used to study the extracted d- and f-species in the obtained organic extracts in ionic liquid solutions.
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    Comparing extraction, synergism and separation of lanthanoids using acidic and neutral compounds in chloroform and one ionic liquid: Is the latter always ``better``?
    (2014-01-01) Atanassova M.; Kurteva V.; Lubenov L.; Billard I.
    The complexation properties of a pyrazolone derivative, 3-methyl-1-phenyl-4-(4-trifluoromethylbenzoyl)-pyrazol-5-one (HL), in chloroform were examined and it was found that it possesses improved complexation ability in comparison with 4-benzoyl, 4-(4-methylbenzoyl) and 4-(4-fluorobenzoyl) derivatives. Mixed ligand chelate extractions of trivalent lanthanoids (La, Nd, Eu, Ho and Lu) with HL and 5,11,17,23-tetra-tert-butyl-25,26,27- tris(dimethylphosphinoylpropoxy)-28-hydroxy-calix[4]arene (S1) or 5,11,17,23-tetra-tert-butyl-25,27-bis(dimethylphosphinoylpropoxy)-26, 28-dihydroxy-calix[4]arene (S2) as synergistic agents were also carried out in chloride medium at constant ionic strength μ = 0.1 and CHCl3 as organic phase. The interactions between the extractants in deuterochloroform were studied by 1H, 13C, and 31P NMR. The composition of the extracted species was established as LnL3· HL (L- represents HL anion) with HL as a single extractant, and as LnL3·S in the presence of the phosphorus-containing calix[4]arene. On the basis of the experimental data, the values of the equilibrium constants were calculated. The influence of the number of PO groups of tert-butyl-calix[4]arene on the extraction process was discussed. The synergistic enhancement and separation factors between metals were evaluated. Finally, the extraction of La(iii) and Eu(iii) ions was performed by using an ionic liquid, 1-butyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide, as a solvent and varying the type of ligands. By comparison to CHCl3, the ionic liquid offers increased distribution ratios, at the expense of a levelling off of the separation factors. Reasons for such a phenomenon are discussed. © the Partner Organisations 2014.
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    Coordination chemistry of europium(III) ion towards acylpyrazolone ligands
    (2015-01-01) Atanassova M.; Kurteva V.; Billard I.
    Two Eu(III) complexes were synthesized using 4-acylpyrazolone ligands: 3-methyl-4-(4-methylbenzoyl)-1-phenylpyrazol-5-one (HPMMBP) and 3-methyl-1-phenyl-4-(4-phenylbenzoyl)-pyrazol-5-one (HPPMBP). The composition of the obtained solid complexes was determined as Eu(PMMBP) 3 .C 2 H 5 OH and Eu(PPMBP) 3 .3H 2 O based on elemental analysis and was further studied by IR, NMR and TG-TSC data. The lanthanoid complexation in solid state and in solution during liquid-liquid extraction (molecular diluent and ionic liquid) is discussed. 2015
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    Data on the synthesis and characterization of two novel polydentate ligands possessing unsymmetrical NH–urea fragment
    (2018-10-01) Todorova S.; Atanassova M.; Kurteva V.
    The data represent the synthesis and structural characterization of two novel polydentate ligands possessing unsymmetrical NH-urea fragment: an open-chain substituted aromatic compound with unsymmetrical urea and secondary amine units (S1) and fused aryloxazinone with unsymmetrical urea fragment (S2). The data include the analyzed NMR spectra, turbo-spray mass spectra, melting points and Rf-values. 1D and 2D NMR spectra are given in the article. The efficiency of the ligands as synergists in the isolation and separation of lantanoid ions is reported in rerence. [1].
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    Mutual Solubilities between Ethylene Glycol and Organic Diluents: Gas Chromatography and NMR
    (2023-07-01) Atanassova M.; Kurteva V.
    In this work, the mutual solubilities of sets of organic diluents (CHCl3, C6H6, C2H4Cl2, CCl4, C6H12, and n-hexane) with the organic compound ethylene glycol are investigated via gas chromatography (GC). The experimental data measured for these binary organic systems are used to adjust the future nonaqueous systems for the solvent extraction of various metals with ligands. The obtained results showed that the solubility of ethylene glycol decreased in the order CHCl3 > C6H6 > C2H4Cl2 > CCl4(0%) ≈ C6H12 ≈ n-hexane. On the other hand, the solubility of the tested traditional organic diluents in ethylene glycol decreased in the following order: C6H6 > CHCl3 > C2H4Cl2 > n-hexane > C6H12 > CCl4. 1H NMR was also used as an analytic method in order to compare the obtained results for the samples showing significant solubility only, including an additional study with 1,2- or 1,3-propanediol. The enhanced solubility of the C6H6 compound in ethylene glycol was identified here as critical due to the GC technique, which will be without future consequences in chemical technology. Therefore, it was found that the best molecular diluent for the recovery of metals among the tested ones is C6H12, with a green protocol as the new paradigm, replacing the aqueous phase with another nonaqueous phase, i.e., a second organic diluent.
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    New Sustainable Solvent Extraction Pathways for Rare Earth Metals via Oximes Molecules
    (2023-11-01) Atanassova M.; Kukeva R.; Kurteva V.
    A study on the synergistic extraction of Eu(III) ions with a series of chelating ligands and determination of the process parameters is presented by employing ionic liquids and typical organic diluents. The investigations of the liquid–liquid extraction, commonly applied in the separation science of 4f and 5f-ions acidic chelating compounds, 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (HP), 4-benzoyl-3-phenyl-5-isoxazolone (HPBI), and 2-thenoyltrifluoroacetone (HTTA) alone and in combination with two synergistic agents, meso-hexamethylpropyleneamine oxime (S2: HM-PAO) and its bis-imine precursor (S1: pre-HM-PAO), are presented. The interaction between the two extractants (acidic/neutral) in deuterochloroform was studied using 1H, 13C, and 1H-1H NOESY experiments. Several conclusions are given highlighting the role of the ionic diluent in complexation processes and selectivity with an employment of the two synergistic agents for various metal s-, p-, d-, and f-cations in the Periodic table, with almost 25 metal ions. The objective was to optimize a system for 4f-ions solvent extraction based on the new oxime molecules with β-diketone/isoxazolone/pyrazolone partnership. As detailed above, slight enhancements of extraction efficiencies were obtained either by using basic synergistic agents such as HM-PAO and/or using pre-HM-PAO. A competitive solvent extraction test of nearly 18 f-ions by various ligands (HTTA, S1, S2, and HPBI) and the two mixtures HTTA−S1 and HTTA−S2 diluted in ILs or organic diluents was also conducted in order to evaluate the switchable diluent impact. Additionally, electron paramagnetic resonance (EPR) spectroscopy was used to study the established chemical species with Cu2+ cations in the obtained organic extracts involving the two synergistic molecules.
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    NMR Study on the Possible Interactions between Imidazolium Based Ionic Liquids and Extractants Widely Applied in Solvent Extraction and Separation of f-Ions
    (2015-12-01) Kurteva V.; Atanassova M.; Billard I.
    A detailed NMR study on the possible interactions between a series of imidazolium based ionic liquids (1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide, RmimTf2N, n = 4, 6, 8, 10), and compounds commonly applied in the solvent extraction and separation of 4f and 5f-ions as acidic chelating agents and neutral extractants is presented. The analytical techniques applied are 1H, 13C, 19F and 31P NMR spectra and NOESY experiments. Investigation of the types and strengths of the solvent-solute interactions is necessary for a better understanding of the chemical solubility, reactivity and selectivity, as ILs have a strong influence on the solvent extraction mechanism of metal ions. The goal of the scientific research is to gain insight on the role of ILs as a perspective efficient ``green`` medium in the solvent extraction processes. The experimental results show that no IL-ligand interactions occurred in chloroform solution independently on the length of the imidazolium alkyl chain or on the structure and acidity of the ligand.