Influence of the Steric Hindrance,Ligand Hydrophobicity,and DN of solvents on Structure and Extraction of Cu(II) Complexes of 1‐Alkyl‐2‐Ethylimidazoles

Abstract

Formation of Cu(II) complexes of 1‐alkyl‐2‐ethylimidazoles (where alkyl=propyl, butyl, pentyl, hexyl, and octyl) has been studied by using the liquid‐liquid partition method, at 25°C and a fixed ionic strength of the aqueous phase (I=0.5; (HL)NO₃, KNO₃). The complexes were extracted with 2‐pentanone, 2‐butanol, isoamyl alcohol, 2‐ethyl‐1‐hexanol, dichloromethane, trichloromethane, and toluene. The length of the 1‐alkyl group and the nature of solvent have been shown to influence the extraction process. Extraction curves (log D_M vs. pH) are displaced towards lower pH's with increasing chain length of the 1‐alkyl substituent and donor number of the solvents. Stability constants of the complexes in aqueous solution were determined as well as their partition ratios between the aqueous and organic phase. The stability of the Cu(II) complexes increased with increasing 1‐alkyl chain length. The stability constants are comparable with β_n ones for the Cu(II) complexes of 1‐alkyl‐2‐methylimidazoles, but smaller than those of the Cu(II)–1‐alkylimidazole counterparts. The P_c‐partition ratios of the 1‐alkyl‐2‐ethylimidazole complexes with Cu(II) are high, and increased with increasing 1‐alkyl chain length and the donor number of the solvents. Both the strong steric effect of the ethyl substituent at position 2 and the bulkiness of the 1‐alkyl‐2‐ethylimidazole molecules as well as the strong electron‐donating properties of the solvent molecules have an effect on the change of the coordination number of Cu(II) from 6 to 4. The 4‐coordinate Cu(II) complexes (distorted tetrahedron) are more readily extractable by organic solvent than are the 6‐coordinate ones and for this reason their partition constants, P_c, are high. This finding offers the possibility of extraction of the Cu(II) ions from a mixture cations.     

The Influence of the Alkyl Chain Length on Extraction Equilibrium of Cu(II) Complexes with 1‐Alkylimidazoles in Aqueous Solution/Organic Solvent Systems

Abstract

The partition of Cu(II) complexes with 1‐alkylimidazoles (with alkyl ranging from 1‐n‐butyl through 1‐n‐hexadecyl) between the aqueous ((0.5HL, K)NO₃) and organic phase has been studied at 25°C. The organic solvents used were toluene, p‐xylene, tetrahydronaphthalene, dichloromethane, 2‐ethyl‐1‐hexanol, and others. Extraction curves have been shown to be displaced towards lower pH values with increasing alkyl chain length of the alkyl substituent. Stability constants of the Cu(II) complexes with the 1‐alkylimidazoles have been determined in the aqueous phase as well as the number of compounds extractable into the organic solvent, and their partition ratios. Stability constants of the complexes did not depend on the alkyl chain length. One or two complexes were transferred to the organic phase. Partition ratios of these complexes, P ₁ and P ₂, increased rapidly with increasing alkyl chain length. They were higher in magnitude than those of their Co(II), Ni(II), and Zn(II) counterparts.     

Effect of Alkyl Chain Length on the Extraction of Copper(II) Complexes with 1‐Alkyl‐2‐Methylimidazoles

Abstract

By using the liquid‐liquid partition method, the formation of Cu(II) complexes with 1‐alkyl‐2‐methylimidazoles (where alkyl=isobutyl, pentyl, isopentyl, hexyl, octyl, decyl, and dodecyl) has been studied at 25°C and at fixed ionic strength of the aqueous phase (I=0.5; (HL)NO₃, KNO₃). The complexes were extracted with 2‐ethyl‐1‐hexanol, dichloromethane, trichloromethane and, in one system only, toluene. Stability constants of the complexes in aqueous solution as well as partition constants of the extractable species were determined. It has been shown that the stability constants are invariable and do not depend on the 1‐alkyl chain length. The constants were smaller than those of the previously studied Cu(II) – 1‐alkylimidazole complexes owing to the steric effect of the methyl group at position 2. The partition constants of the complexes incereased with increasing alkyl chain length. Branched 1‐alkyl substituents (isobutyl, isopentyl) suppressed both stability constants and the partition constants of the complexes.     

The Influence of Alkyl Chain Length in 1,2-Dialkylimidazoles on the Extraction Capacity and Structure of Their Copper(II) Complexes

Abstract

Formation of Cu(II) complexes of 1,2-dialkylmidazoles (where 1-alkyl = ethyl, propyl, butyl, pentyl, and hexyl, and 2-alkyl = propyl, butyl, and pentyl) has been studied using the liquid-liquid partition method, at 25°C and at a fixed ionic strength of the aqueous phase (I = 0.5; (HL)NO₃, KNO₃). The complexes were extracted with 2-ethyl-1-hexanol, and chloroform. The length of the 1-alkyl, and 2-alkyl groups, and the solvent nature have been shown to influence the extraction process. Extraction curves (log D_M vs. pH) are displaced towards lower pH with increasing chain length of the 1-alkyl and 2-alkyl substituents. Stability constants of the complexes in aqueous solution as well as their partition constants between the aqueous and organic phase were determined. The stability of the Cu(II) complexes increased with increasing 1-alkyl chain length. The stability constants were comparable with β _n values for the Cu(II) complexes of 1-alkyl-2-ethylimidazoles, but smaller than those of the Cu(II) – 1-alkylimidazole counterparts. The length of the 2-alkyl substituent has been found to affect both the pH_1/2 values and the partition constants of the complexes. The partition constants P₁ are small for all of the 1,2-dialkylimidazole complexes with Cu(II), whereas P₂ and P₃ are high and they increase with elongation of the 1-alkyl chain owing to a decrease in the co-ordination number of Cu(II), probably from 6 to 4 at the second and third complexation step. This change is likely to produce square coplanar species, readily extractable with organic solvent. This finding offers the possibility of extraction of the Cu(II) ions from a mixture cations.     

The Influence of Alkyl Chain Length and Steric Effect on Extraction of Zinc(II) Complexes with 1‐Alkyl‐2‐Methylimidazoles

Abstract

The extraction of Zn(II) complexes with six 1‐alkyl‐2‐methylimidazoles (alkyl is from C₅H₁₁ up to C₁₂H₂₅) from nitric solution was studied as a function of pH of the aqueous phase. As the organic solvents toluene, p‐xylene and 1,2,3,4‐tetrahydronaphthalene were used. The stability constants of the complexes in the aqueous phase as well as partition constants of the extractable species were determined. It was demonstrated that both the stability constants (β_c) and the partition constants (P_c) of the complexes increased with increasing alkyl chain length. Pseudo‐tetrahedral complexes were found to dominate at the second and third complexation steps, thus increasing the stability constants and facilitating extraction of the Zn(II) complexes with 1‐alkyl‐2‐methylimidazoles.     

The Influence of Alkyl Chain Length and Steric Effect on the Stability Constants and Extractability of Co(II) Complexes with 1-Alkyl-2-Methylimidazoles

Using the liquid-liquid partition method, the formation of Co(II) complexes with 1-alkyl-2-methylimidazoles (where alkyl = C₄H₉ trough C₁₂H₂₅) at 25°C and at a fixed ionic strength of the aqueous phase (I = 0.5, (HL)NO₃, KNO₃) were studied. Dichloromethane, trichloromethane, and 2-ethylhexanol were used as diluents. The tetrahedral and octahedral complexes were formed. Stability constants (β_n) of the complexes as well partition ratios (P_n) of the extracted species were determined. It was shown that both β_n and P_n increased with an increasing 1-alkyl chain length. Tetrahedral complexes are more readily extractable by organic solvent. Their P_n values are the highest.     

The Influence of the Alkyl Chain Length and Steric Effect on Stability Constants and Extractability of Co(II) Complexes with 1‐Alkyl‐4(5)‐methylimidazoles

Abstract

Extraction of Co(II) complexes has been studied with nine derivatives of 1‐alkyl‐4(5)‐methylimidazoles (with R=C₂H₃ to C₁₀H₂₁) from aqueous solution [I=0.5(KNO₃) at 25°C] with toluene, trichloromethane, and 2‐ethyl‐1‐hexanol. Stability constants of the complexes formed in the aqueous phase (β _c ) as well as partition constants (P _c ) of the extracted species were determined. It was demonstrated that both the stability constants and partition constants of the complexes increase with an increasing of the 1‐alkyl chain length. The tetrahedral together with octahedral complexes were formed beginning from the second step of complexation. Furthermore, the influence of the bulkiness of the 1‐alkyl group on separation process of Co(II) from Zn(II) for extractions with toluene and 2‐ethyl‐1‐hexanol were determined.     

Search for Optimum Conditions of Extraction of Transition Metal Complexes with Alkylimidazoles. II. Extraction of the Co(II), Ni(II), and Zn(II) Complexes of I-Ethylimidazole and I-Butylimidazole

Abstract

Extraction studies of the Co(II), Ni(II), and Zn(II) complexes of 1-ethyl-and 1-butylimidazole reveal correlations between magnitudes of the extraction process and α _n functions characterizing reactions of stepwise complex formation in aqueous solution. Further, the effect of alkyl substituents in the imidazole ring on extractability of successive complexes has been established. For each of the systems studied, the number of complexes passing to the organic phase has been determined, and appropriate distributicn constant values, P_n , have been calculated.     

Solvent extraction of copper ions by 3-substituted derivatives of β-diketones

ABSTRACT

Two derivatives of acetylacetone (acac, 1), namely 3-butyl-acac (2) and 3-allyl-acac (3), were synthesized. A liquid–liquid partition and spectrophotometric methods were used to examine the process of complexes formation of all ligands with Cu(II) ions. It has been shown that 2 and 3 were forming two very stable complexes of ML and ML₂ type. The absorption spectra proved that the extraction of copper was simplified because flat-square complexes were formed. The high values of partition ratios of two types of complexes confirm this fact. The rate of extraction of Cu(II) complexes decreases in the order 3 > 2 > 1.     

Search for Optimum Conditions of Extraction of Transition Metal Complexes with Alkylimidazoles. I. Extraction of the Co(II), Ni(II), and Zn(II) Complexes of 1-Methylimidazole and of the Co(II) and Zn(II) Complexes of 2-Methylimidazole

Abstract

It has been shown that for the Co(II), Zn(II), and Ni(II) complexes of 1-methylimidazole and for the Co(II) and Zn(II) complexes of 2-methylimidazole, the partition coefficient D between the aqueous and organic phases is proportional to the degree of formation α _n of a definite complex. Tetrahedral species have been found to be extracted with the Co(II) and Zn(II) complexes of 2-methylimidazole and with the Zn(II) complexes of 1-methylimidazole.     

Comparative Equilibrium Studies on the Sorption of Metal Ions with Macroporous Resins Containing a Liquid Ion-Exchanger

Abstract

The distribution of five metal ions (M ^m+) including Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) between dilute sulfate solutions and macroporous resins containing di(2-ethylhexyl) phosphoric acid (D2EHPA, HR) was investigated. Experiments were carried out as a function of aqueous pH, D2EHPA concentration in the resin phase, and temperature. The equilibrium data were numerically analyzed. It was shown that the sorption reaction could be described by assuming the formation of metal complexes with a general composition MR _m (HR) _n in the resin phase. For several systems a change of complex stoichiometry with temperature was observed and discussed. The apparent thermodynamic data for the formation of these complexes were also calculated.     

DISTRIBUTION OF N- AND ISO- BUTYRALDEHYDES BETWEEN TRI-N-BUTYL PHOSPHATE/ N-DODECANE AND NITRIC ACID

ABSTRACT

The distribution of n- and iso-butyraldehydes between tri-n-butyl phosphate(TBP) n-dodecane(nDD) and HNO₃ were measured. The distribution ratio of n-butyraldehyde in the TBP/nDD and HNO₃ system was nearly the same as that of iso-butyraldehyde. The distribution ratios of n- and iso-butyraldehydes increased with TBP concentration in the organic phase. The equilibrium constant of the extraction reaction was about 2. In a uranium, neptunium and plutonium separation process, most of the n- and iso-butyra1dehydes fed into theNp separation stepor into thePu/U partition will be left with the TBP solvent. The two compounds will be partly back-extracted to the aqueous phase in the U purification and in the solvent washing steps of the PUREX process.     

Studies on Extraction of Transition Metal Complexes of 3,4-Dimethylpyridine and 3,5-Dimethylpyridine with Oxygen-Containing Solvents

Abstract

On the basis of a correlation between the degrees of formation αn of successive 3,4-dimethylpyridine and 3,5-dimethylpyridine complexes of Co(II), Ni(II), Zn(II), and Cd(II) in aqueous solution; extraction percent E; and partition coefficients D; the distribution constants Pn of successive complexes passing to the organic phase during extraction have been determined. The measurements were carried out at a fixed ionic strength I = 0.5 at 25°C, using solutions of the dimethylpyridines in oxygen-containing solvents.     

Extraction of Uranium(VI) and Plutonium(IV) with Tetra-Alkylcarbamides

ABSTRACT

The use of tetra-alkylcarbamides as novel extractants for the separation of uranium(VI) and plutonium(IV) by solvent extraction from spent nuclear fuels is investigated in this study. Batch extraction experiments show that tetra-alkylcarbamides strongly extract U(VI) with high distribution ratios. Plutonium(IV) can be co-extracted with U(VI) at high nitric acid concentration, while high U(VI)/Pu(IV) selectivities can be reached at lower acidity. Loading capacity experiments with high uranium concentrations show that alkyl chains longer than butyl are necessary to avoid third phase formation. Nevertheless, the viscosity of uranium-loaded solvents gets too high with alkyl chains longer than pentyl. Overall, this study shows that with TPU extractant (with four pentyl chains), an efficient co-extraction of uranium and plutonium can be reached (D_U,Pu > 1) for a concentration of nitric acid higher than 4 mol?L^?1, while the partition between uranium(VI) and plutonium(IV) could be operated even at 2 mol?L^?1 nitric acid without redox chemistry.     

Solution Studies of Tris(2-aminoethyl)amine with Metal Ions of Biological Interest: The Electroanalytical Determination of the Phosphate Triester Hydrolysis

Complex formation of tris(2-aminoethyl)amine, Tren, with both Zn(II) and Cu(II) ions in aqueous solution was investigated spectroscopically by using ¹H NMR and UV-visible titrations as well as electrochemically by using cyclic voltammetry. Analysis of the titration data indicated that the aqua complexes [(Tren)Zn(OH₂)](ClO₄)₂ 1 and [(Tren)Cu(OH₂)](ClO₄)₂ 2 deprotonate at pH = 10.6 and 9.7, forming the dinuclear bridged hydroxo species {[(Tren)Zn]₂(μ-OH)}³⁺ 3 and {[(Tren)Cu]₂(μ-OH)}³⁺ 4, respectively. The catalytic hydrolysis of the activated phosphate ester tris(p-nitrophenyl)phosphate (TNPP) by using these model complexes was examined and the released phenolate anions were determined by using spectroscopic and electroanalytical techniques.     

Strong and Selective Ni(II) Extractants Based on Synergistic Mixtures of Sulfonic Acids and Bidentate N-Heterocycles

ABSTRACT

Bidentate 5,5?-alkyl-3,3?-bi-1H-pyrazole and 2-(5-alkyl-1H-pyrazol-3-yl)pyridine ligands, L⁵ and L⁶, have been shown to be stronger synergists for the solvent extraction of Ni(II) from sulfate solutions by dinonylnaphthalene sulfonic acid (DNNSAH) than the structurally related tridentate ligand 2,6-bis-[5-n-nonylpyrazol-3-yl]pyridine, L¹, previously reported by Zhou and Pesic. The bidentate ligands are highly selective, providing the option of sequential recovery of Ni(II) and Co(II) and rejection of other metals commonly found in the liquors resulting from the acidic sulfate leaching of laterite ores. They were the strongest synergists identified in a screening carried out on 18 types of bidentate and tridentate N-heterocyclic ligands, including the recently reported 2-(2?-pyridyl)imidazoles, L^9?11. X-ray crystal structures of Ni(II) complexes of model ligands for L⁵ and L⁶, having t-butyl rather than long-chain alkyl groups and with 2-naphthalene sulfonate rather than DNNSA^? as counteranions, show that the [Ni(L)₃]²⁺ complexes form strong H-bonds from the pyrazolyl NH groups to the oxygen atoms of the sulfonate groups, an arrangement that will stabilize [Ni(L)₃·(DNNSA)₂] assemblies and shield their polar functionalities from diluent molecules of the water-immiscible phase. UV–visible spectra and mass spectrometry provide evidence for the strong synergists displacing all water molecules from the inner coordination sphere of the Ni(II) ions.     

SOLVENT EXTRACTION OF METALS WITH 4-DINITROBENZOYL-2, 4-DIHYDRO-5-METHYL-2-PHENYL-3H-PYRAZOL-3-ONE (DMPP)

ABSTRACT

The mechanism of the extraction of copper (II), nickel (II), cobalt (II) and thorium (IV) from aqueous buffer media with 4-dinitrobenzoyl1-2, 4-dihydro-5-methyl-2-phenyl-311-pyrazol-3-one (DMPP) in benzene has been investigated. The values of log K^*where K^*refers to the extraction equilibrium Mn⁺+-nHL ? MD_n+ nH⁺are Cu(II)& lpar; + 0.3), Co(II) (?6.65), Ni(II) (?5.04) and Th(IV) ( + 6.1). Solid complexes synthesized have the composition CuL₂· 2H₂O, NiL₂· 2H₂O and ThL₄respectively (L = anion of the ligand). DMPP seems to be superior to the corresponding 4-benzoyland 4-nitrobenzoyl derivatives of 2,4-dihydro-5-methyl-2-phenyl1-3 H-pyrazol1-3-one (MPP) and also better than thenoyltrifluoroacetone, the popularly employed fluorinated β-dike tone in the system investigated.     

The Extraction of TcO− 4 and Pd(II) by Dihexyl-N,N-diethylcarbamoylmethylphosphonate from Nitric Acid

Abstract

The extraction behavior of TcO^? ₄ and Pd(II) from aqueous HNO₃ was studied using dihexyl-N,N-diethylcarbamoylmethylphosphonate. Distribution ratios were studied as a function of contact time; concentration of solute, acid, and extractant; and extraction temperature. Extraction measurements of TcO^? ₄ were also made using H₂SO₄ in the aqueous phase. It was found that the extractant dependency for TcO^? ₄ is third power. Distribution measurements for TcO^? ₄ as a function of temperature in the range of 0–50°C led to a calculation of the thermodynamic quantity ΔH. A third-power extractant dependency for Pd(II) is suggested but is not strongly corroborated. Interpretation of Pd(II) data was hindered by slow kinetics (approximately 1 h to reach equilibrium and variations in distribution ratios with aqueous Pd(II) concentration.     

Synergistic Solvent Extraction and Transport of Zn(II) and Cu(II) across Polymer Inclusion Membranes with a Mixture of TOPO and Aliquat 336

Separation of zinc(II) and copper(II) ions from aqueous solutions by synergistic extraction and transport through polymer inclusion membranes (PIMs) has been investigated. A mixture of trioctylphosphine oxide (TOPO) and trioctymethylammonium chloride (Aliquat 336) was used as a selective extractant as well as an ion carrier in polymer membranes. The effects of hydrochloric acid concentration in the aqueous phase and extractants concentration in the organic phase on the separation process of zinc(II) and copper(II) ions have been studied. Zn(II) ions were successfully separated from Cu(II) ions in solvent extraction process using 0.025 M TOPO and 0.06 M Aliquat 336 in kerosene. Polymer inclusion membranes (PIMs) containing a mixture of TOPO and Aliquat 336 as the ion carrier have been prepared and the facilitated transport of Zn(II) and Cu(II) ions has been studied. The influence of membrane composition on the transport kinetic of Zn(II) and Cu(II) has been evaluated. Zn(II) ions were preferably transported from the aqueous solutions containing Cu(II) and above 87% of Zn(II) ions were effectively recovered from the 0.5 M HCl solution as the source phase through PIM into 0.5 M H₂SO₄ as the stripping phase.     

NEW XANTHIC ACID DERIVATIVES AS POTENTIAL REAGENTS IN THE SOLVENT EXTRACTION OF PRECIOUS METAL IONS: EXTRACTION OF PALLADIUM(II) WITH 13-BIS(0-BUTYLXANTHATO)PROPANE

ABSTRACT

Two series of new xanthic acid derivatives namely, the bis (O-butylxanthato) alkanes ( abbreviated as BBXAs or simply as bis-xanthates in this paper) have been synthesized in connection with the solvent extraction of precious metal ions. From an aqueous medium containing 0.1 M NaC10₄ (1 M=l mol dm^-3), these compounds exhibited high selectivity for extraction of Pd(II) and Ag(I) in dichloroethane, over most of the base metals as well as Pt(IV) and Au(III) ions. Towards Pd(II) and Ag(I) ions, the bis compounds act as SS chelating agents where the stabilities of the extractable complexes are determined by the length of the alkylene chain existing between the donor atoms. Pd(II) extraction has been studied in detail taking 13-bis(O-n-butylxanthato)propane (BnBXP) as the representative member of the series of bis-xanthates synthesized in this work. The extraction of palladium(II) was found to be quite slow in pure chloride medium. But, a mixed acid medium containing H₂SO₄ or HNO₃ in the presence of smaller amount of chloride ion provided optimum reversible extraction of palladium in dichloroethane, where Pd(II) forms 1:1 extractabic complexes with BnBXP. Pd(II) extraction is described in terms of the aqueous phase compositions, extraction and back-extraction data, extraction equilibrium, selectivity considerations and probable mechanisms of extraction.