Competitive Solvent Extraction Research Articles

Chemical and mechanistic modelling of green solvent extraction of metallic species with 4-acylpyrazolones

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.

New Sustainable Solvent Extraction Pathways for Rare Earth Metals via Oximes Molecules.

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.

Synthesis of ditopic ligands for the selective extraction of copper(II) nitrate and crystal structures of their Cu(II) complexes

We have synthesized two ditopic ligands for selective extraction of copper(II) nitrate. We also synthesized one cation-only binding analog for comparison. All three ligands were characterized by conventional techniques. Competitive two-phase metal ion solvent extraction experiments were performed at 25 °C over a period of 24 h. These ligands showed significant selectivity for Cu(II) ions, having the ditopic ligands extract 81 and 73% of the Cu(II) ions in a solution of different metal ions {Ni(II), Co(II), Cu(II), Zn(II), Cd(II), Pb(II)} at pH 5.09. Competitive transport experiments (water/chloroform/water) were undertaken employing each ligand separately as the ionophore in the membrane (chloroform) phase. No metal ion transport was observed, but a large concentration of Cu(II) was present in the membrane phase. Competitive anion extraction and transport were carried out with the ditopic ligands, yielding selective extraction and transport of nitrate. Furthermore, a pH isotherm of the best ditopic ligand (H2L2) with Cu(II) was determined from pH 1.0 to 6.0, producing a pH½ value of approximately 2.6. Finally, crystal structures of the ditopic ligands complexed with Cu(II) were determined and refined. The coordination geometry around the metal centers are distorted square planar and the Cu(II)-donor bond lengths fall within the normal range.

Extraction properties of tetraheptylresorcin[4]arenes in relation to Cr(III) ions

Resorcin(4)arene-based ligand bearing four heptyl chains at the lower rim of the molecule was prepared and modified by four tetradietoxyphosphoryl groups in the upper rim. The compounds obtained were characterized by NMR spectroscopy and their extractability toward chromium(III) ions was studied. The influence of process parameters such as the pH of aqueous phase, agitation time and also extractant's structure and concentration on efficiency of Cr(III) ions solvent extraction is presented. The highest yield of Cr(III) solvent extraction was obtained for two-hour agitation time of 5.010 −4 M metal solution of pH 5.0 and 5.010 −3 M chloroform solution of the tetradietoxyphosphorylated derivative of heptyl- resorcin(4)arene. Under optimal conditions, competitive solvent extraction of Cr(III), Zn(II), and Cd(II) ions was performed and separation factor values were established as 77.0 and 24.9 for Cr(III)/Cd(II) and Cr(III)/Zn(II) ions pairs, respectively. The stoichiometry of formed metal-ligand complexes 1:1 was found by classical slope analysis method.

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-5 ligands in the cone conformation: effect of acidic side arm length for solvent extraction of divalent metal ions

Several new di-ionizable p-tert-butylcalix[4]arene-1,2-crown-5 compounds were prepared in the cone conformation. For comparison with reported ligands, the systematic structural variation was a change of the pendent acidic groups from two adjacent –OCH2CO2H or –OCH2C(O)NHSO2Z (with Z=–Me, –Ph, –C6H4–4-NO2, –CF3) units to two adjacent –O(CH2)4CO2H or –O(CH2)4C(O)NHSO2Z groups. Competitive solvent extractions of alkaline earth metal (AEMC) cations from aqueous solutions into chloroform by these ligands were performed. Also single species solvent extractions were conducted for the divalent heavy metal cations of Pb2+ and Hg2+. Comparison of the extraction data for the new ligands with those reported reveal that the ligands with shorter proton-ionizable side arms are more effective divalent metal ion extractants.

Di-ionizable calix[4]arene-1,3-crown-4 ligands with an enlarged crown ring: synthesis and metal ion extraction

Di-ionizable calix[4]arene-1,3-crown-4 ligands with an enlarged crown ring were synthesized for comparison as metal ion extractants with analogues having identical pendent acidic groups, but a “normal” crown ring. The ligand conformation and regioselectivity are verified by NMR spectroscopy. Competitive solvent extraction of hard alkali metal cations and alkaline earth metal cations from aqueous solutions into chloroform by these new ligands were performed. Single species solvent extractions were conducted with intermediate Pb2+ and soft Hg2+. Comparison of the results with those from di-ionizable calix[4]arene-1,3-crown-4 ligands having “normal” crown rings provides insight into the effects of enlarging the crown ring as a function of the metal ion species being extracted and the identity of the pendent ionizable groups. Enlargement of the crown ring produced the largest increase in extraction efficiency with soft Hg2+.

Alkali metal cation complexation by 1,3-alternate, mono-ionisable calix[4]arene-benzocrown-6 compounds

Alkali metal cation extraction behaviour for two series of 1,3-alternate, mono-ionisable calix[4]arene-benzocrown-6 compounds is examined. In Series 1, the proton-ionisable group (PIG) is a substituent on the benzo group of the polyether ring that directs it away from the crown ether cavity. In Series 2, the PIG is attached to one para position in the calixarene framework, thereby positioning it over the crown ether ring. Competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform shows high Cs+ efficiency and selectivity. Single-species extraction pH profiles of Cs+ for Series 1 and 2 ligands with the same PIG are very similar. Thus, association of Cs+ with the calixcrown ring is more important than the position of the PIG relative to the crown ether cavity. Solid-state structures of two unionised ligands from Series 2 are presented. Also described is a crystal containing two different ionised ligand–Cs+ complexes.

LEAD(II) REMOVAL FROM AQUEOUS SOLUTIONS BY SOLVENT EXTRACTION WITH TETRACARBOXYLRESORCIN(4)ARENE

A novel tetracarboxylresorcin(4)arene was synthesized and its selective complexing ability towards Pb(II) ions was examined. The influence of several parameters such as pH of aqueous phase, agitation time, extractant and modifier concentrations on solvent extraction of Pb(II) ions from the aque- ous nitrate phase into chloroform organic phase was studied. The stoichiometry of the formed metal- ligand complexes was established by slope analysis. Pb(II) ions were quantitatively extracted in the form of 2:1 Pb(II)-resorcin(4)arene complex from aqueous solutions of pH 5.5 to the solution of ligand in chloroform. Competitive solvent extraction experiments in the presence of Zn(II) and Cd(II) ions were also carried out and high selectivity of the extractant towards Pb(II) over Zn(II) and Cd(II) was found. The selectivity order was: Pb(II) >> Cd(II) > Zn(II).

Extraction of s-block metals by nano-baskets of calix[4]crown-3

Three kinds of nano-baskets including 1,2-alternate and cone conformers of di-ionizable p-tert-butylcalix[4]arene-1,2-crown-3 and the cone conformer of p-tert-butylcalix[4]arene-1,2-thiacrown-3 were synthesized and the competitive solvent extractions of alkali and alkaline earth metal cations were studied. The novelty of this study is including three binding units of the calixarene’s bowl, the crown ether’s ring, and electron-donor ionizable moieties in a unique scaffold, in which their sizes were selected based upon their complexation ability to show equal binding tendency towards the cations. The objective of this work is to assess the extraction efficiency, selectivity, and pH1/2 of such complexes. The results of solvent extraction experiments indicated that these compounds were effective extractants of alkali and alkaline earth metal cations. Their selectivities were greatly influenced by the acidity of the solution and the conformations of the calixcrown. One conformer was highly selective to Na+ and the other to Ba2+ in acidic and basic solutions, respectively.

Di-ionizable calix[4]arene-1,3-crown-4 ligands in 1,3-alternate, cone, and partial-cone conformations: synthesis and metal ion extractions

Di-ionizable calix[4]arene-1,3-crown-4 compounds locked in 1,3-alternate, cone, and partial-cone conformations are synthesized for evaluation in metal ion separations. The ionizable functions include carboxylic acid and N-(X)sulfonyl carboxamide groups in which the acidity is tuned by variation of the electron-withdrawing ability of X. Similar synthetic routes were employed for preparation of the cone and 1,3-alternate ligand series. A different preparative route utilizing protection and deprotection was required to obtain the partial-cone analogues. Ligand conformations were confirmed by their proton and/or carbon NMR spectra. X-ray diffraction verified an unusual 1,2-alternate conformation in the solid-state for one synthetic intermediate. Effects of ligand conformation and ionizable group variations on competitive solvent extractions of alkali and alkaline earth metal cations from aqueous solutions into chloroform were assessed. Single species solvent extractions of Hg2+ and Pb2+ were also performed.

Effect of Crown Ring Size and Upper Moiety on the Extraction of s-Block Metals by Ionizable Calixcrown Nano-baskets

Eight ionizable nano-baskets of cone 25,26-di(carboxymethoxy)calix[4]arene-crown-3,4,5,6 were synthesized and were verified by H and C NMR spectroscopy, IR spectroscopy and elemental analysis. The competitive solvent extractions of alkali and alkaline earth metal cations were studied using such nano-baskets. The novelty of this study is including three binding units of calixarene's bowl, crown ether's ring and electron-donor ionizable moieties in a unique scaffold to assess the binding tendency towards the cations. The objective of this work is to study the extraction efficiency, selectivity and pH1/2 of such complexes. The result of solvent extraction experiments indicated that these compounds were effective extractants of alkali and alkaline earth metal cations. Their selectivities were greatly influenced by the acidity of solution and the conformations of the calixcrown. One conformer was selective to Na in pH ≥ 4, while the other was highly selective to Ba in pH 6 and upper.

Structure Optimization of Di-ionizable Calixarene Nano-baskets for Competitive Solvent Extraction of Alkali and Alkaline Earth Metals

The competitive solvent extractions of alkali and alkaline earth metals by di-ionizable calix[4]arene nanobaskets were studied using nine conformers of calix[4]arene nano-baskets. The objective of this work is to assess the variation of macrocycle conformation, orientation and position of pendant moieties upon the extraction parameters (efficiency, selectivity and pH1/2) of the complexes. The results revealed that alternation of ring conformation in calixarene scaffold affects the solvent extraction parameters towards alkali and alkaline earth metals, while changing the orientation of pendant moieties from orthoto paraas well as cisto transanalogues depicted no changes in those extraction parameters.

Binding and extraction of alkali and alkaline earth metals by nano-baskets of calix[4]arene-1,2-crown-3

The proton di-ionizable p-tert-butylcalix[4]arene-1,2-crown-3 in cone and 1,2-alternate conformations and the p-tert-butylcalix[4]arene-1,2-thiacrown-3 in cone conformation were synthesized and the competitive solvent extractions of alkali and alkaline earth metal cations were studied using such nano-baskets. The novelty of this study is investigation of three binding units of calixarene’s bowl, crown ether’s ring and electron-donor ionizable moieties in a unique scaffold. The calixarene’s bowl, crown ether’s ring and electron-donor ionizable moieties were selected base upon their complexation ability to show equal binding tendency towards the cations. The objective of this study is to assess the extraction efficiency, selectivity and pH1/2 of such complexes. The result of solvent extraction experiments indicated that these compounds were effective extractants towards alkali and alkaline earth metals. Their selectivity was influenced by the acidity of solution and the conformation of calixcrowns. p-tert-butylcalix[4]arene-1,2-crown-3 diacid in cone conformation was highly selective to Na+ and p-tert-butylcalix[4]arene-1,2-thiacrown-3 diacid in cone conformation was highly selective to Ba2+ in acidic and basic solutions, respectively.

Competitive solvent extraction of alkaline earth metals by ionizable nano-baskets of calixarene

The competitive solvent extraction of alkaline earth metals using different nano-baskets was investigated. The novelty of this work is to study the correlations between the isomer structure of calixarenes and their extraction properties. The objective was to quantify the effects of aryl groups in the ionisable pendant moieties, calixarene conformation, steric orientations (cis- and trans-) and relative positions (ortho- and para-) of pendant moieties upon the extraction efficiency, pH1/2 and the selectivity of calix[4]arene complexes. Alkaline earth metals were extracted from aqueous solutions into chloroform by di-ionisable calix[4]arenes and were measured using ion chromatography. The results revealed that alternation of aryl group in the pendant moieties, changing their orientation from cis- to trans-analogues as well as from ortho- to para- analogues, showed no changes in the selectivity, the extraction efficiency and the pH1/2 of calix[4]arene complexes. Changing the scaffold of calixarene's ring to the cone, 1,2-alternate and partial-cone conformers altered their complexation ability towards alkaline earth metals and their extraction efficiency.

Synthesis and metal ion extraction of calix[4]arene mono- and diacids with 2-methoxyethoxy pendant groups

A mono-ionizable calix[4]arene-based ligand with three 2-methoxyethoxy pendant groups is synthesized. A di-ionizable analogue with two 2-methoxyethoxy pendant groups is also prepared. Competitive solvent extractions of alkali metal cations and of alkaline earth metal cations by these ligands are performed, as are single species extractions of Hg2+ and of Pb2+. The number of proton-ionizable groups in the ligand is found to influence the metal ion binding behavior.

Solvent extraction of divalent metal ions by lipophilic di-ionizable acyclic polyethers: effect of end group variation

Three series of lipophilic acyclic di-ionizable polyethers are synthesized to probe the effect of structural variation within the acidic end groups on the solvent extraction selectivity and efficiency for divalent metal cations. Common polyether spacers of –O(CH2CH2O)3– connect the two aromatic carboxylic acid or N-(X)sulfonyl carboxamide end groups. For the latter, variation of the X group from methyl to phenyl to 4-nitrophenyl to trifluoromethyl serves to ‘tune’ the acidity of the ionizable group. Results for competitive solvent extractions of alkaline earth metal cations and single species extractions of Hg2+ and of Pb2+ from aqueous solutions into chloroform are reported.

Effect of Na+ on solvent extraction of alkaline earth metal cations by proton-ionizable calix[4]arenes

Metal ion recognition by proton-ionizable calixarenes is often affected by interference from the Na present in many aqueous solutions. To assess the Na-effect on calixarene selectivity towards alkaline earth metal cations (AEMC), competitive solvent extraction of Mg, Ca, Sr, and Ba from aqueous solutions into chloroform by di-ionizable calix[4]arene N(trifluoromethylsulfonyl)carboxamides and corresponding carboxylic acids, conformationally mobile and restricted to cone, partial cone and 1,3-alternate conformations, was investigated in the absence and in the presence of aqueous-phase Na. The extraction selectivities were found to be altered due to contrasting Na-induced changes in the AEMC uptake. Observed increases in loadings of smaller AEMC are rationalized by their co-extraction with Na.

Sterically congested, geminal aryl-substituted, proton-ionizable sym-dibenzo-16-crown-5 lariat ethers: synthesis and alkali metal cation extraction

Three series of proton-ionizable sym-dibenzo-16-crown-5 ethers with sterically demanding 1- naphthyl, 2-naphthyl, and 9-phenanthryl geminal groups are synthesized and characterized. Variation of the proton-ionizable group includes oxyacetic acid and N-(X)sulfonyl oxyacetamide units with X = Me, Ph, C6H4-4-NO2, and CF3. For the latter series, variation of X provides 'tunable' acidity of the ligand. The metal ion-complexing properties of the proton-ionizable sym- (aryl)dibenzo-16-crown-5 compounds are probed by competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform.

Aminopyridyl derivative of thiacalix[4]arene-carboxylic acid as ionizable highly selective Ag+ ionophore

A novel mono-ionizable receptor 2 possessing three aminopyridyl and one carboxylic group in 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. For competitive solvent extraction of alkali metal (Na+, K+ and Cs+) and some transition metal (Cu2+, Zn2+, TI+, Ag+) cations from aqueous solutions into chloroform, it was found that the introduction of proton-ionizable group (carboxylic acid moiety) into the aminopyridyl-thiacalix[4]arene derivative could further improve its Ag+ extractability with high selectivity.

Calix[4]arene-thiacrown-5 di(carboxylic acid) regioisomers as metal ion extractants

A regioisomer of a previously reported p-tert-butylcalix[4]arene-1,3-thiacrown-5 di(carboxylic acid) is prepared in which the thiacrown ring attachment sites are moved from distal phenolic oxygens of a cone p-tert-butylcalix[4]arene scaffold to proximal phenolic oxygens. The influence of this structural variation in the di-ionizable calixcrown ligand on competitive solvent extractions of alkali metal cations and of alkaline earth metal cations and single species solvent extractions of Hg2+ and Pb2+ from aqueous solutions into chloroform is evaluated.