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.     

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 Steric Effect,Alkyl Chain Length,and Donor Number of Solvents on the Extraction of Copper(II) Complexes with 1-Alkyl-4-Methylimidazoles

Abstract

The formation of Cu(II) complexes with 1-alkyl-4-methylimidazoles (where alkyl = butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl) 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). 2-Ethylhexanol, dichloromethane, chloroform, p-xylene, and toluene were used as a solvent. Stability constants, β_n, of the complexes in aqueous solution were determined as well as their partition ratios between the organic and aqueous phase. Under the influence of the steric effect, the methyl group in position 4 as well as the length of the alkyl group in position 1 of the ligands and electron-donating properties of solvents, both the polyhedral structure and the co-ordination numbers of the Cu(II) complexes are changed, thus resulting in an increase in the solvent/water partition ratios, P_n, of the complexes and lowering of the pH_1/2 of the extraction.     

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.     

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.     

Effect of the Alkyl Chain Length in N,N‐Dialkylpyridine‐3‐carboxamides upon their Extraction of Copper(II) from Aqueous Chloride Solutions

Abstract

Three nicotinamide derivatives with two butyl, hexyl, or octyl alkyl chains at amide nitrogen were synthesized. These model individual compounds were used for copper(II) extraction from acidic chloride solutions at constant ionic strength I = 1.0. It was found that during the extraction N,N‐dialkylpyridine‐3‐carboxamides form two complexes with copper(II) and chloride ions; these can transfer into the organic phase. In these complexes the molar ratio of copper:chlorine:extractant = 1:2:2 or 1:2:3. The obtained stability constants of N,N‐dihexyl‐ and N,N‐dioctylpyridine‐3‐carboxamides complexes with copper(II) chloride in water are comparable, but N,N‐dibutylpyridine‐3‐carboxamide complexes stability constants are significantly lower. The partition constants of these complexes in toluene–water system depend on amide hydrophobicity, increasing with increasing carbon chain length in N,N‐dialkylpyridine‐3‐carboxamides.     

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.     

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.     

Modulation of Aggregation Behaviour of Anionic Surfactant in the Presence of Aqueous Quaternary Ammonium Salts

The self-aggregation of sodium dodecylsulphate (SDS), an anionic surfactant, in aqueous solutions of tetraalkylammonium bromide salts (R₄NBr, where R = propyl, butyl and pentyl) was determined at various temperatures in the range 288.15–318.15 K. The critical micelle concentration (CMC) determined from conductivity data was used to study the thermodynamics of the surfactant. The presence of bromide salts was found to affect the micellization of SDS in accordance with the hydrophobicity of the tetraalkylammonium cations, thus the CMC values follow the order no additive > Pr₄NBr > Bu₄NBr > Pen₄NBr. The results from conventional conductivity methods were combined with those of spectroscopic techniques like fluorescence and UV–Vis studies.     

Synthesis and Characterization of a Novel Series of Amphiphilic Mercapto-1,2,4-Triazole Schiff Base Ligands: Investigation of their Behavior in Hydro-Organic Solutions

A novel series of four Schiff base amphiphiles derived from 3-mercapto-1,2,4-triazole and different alkyl chains were successfully prepared by a new synthetic three-step method. The chemical structures of the different ligands were characterized by elemental analysis, FT-IR spectroscopy, ¹H-NMR and ¹³C-NMR spectra. The effect of the chain length on the solution behavior of the amphiphilic ligands were studied, in both homogeneous and heterogeneous systems, using pH-metric and spectrophotometric methods. Based on the electronic spectroscopy data, some parameters governing their surfactant properties, such as the critical micelle concentration (CMC), the micellization free energy (ΔG _mic) and the hydrophilic-lipophilic balance (HLB) were evaluated in chloroform and discussed. The behavior of the four Schiff bases in the heterogeneous chloroform-water mixture was then explored through the establishment of their acidity (pK_A) and distribution (Log K _d) constants in 1 M chloride medium and the acidity constants in aqueous medium (pK_a) were deduced. Results showed that an increase of the alkyl chain decreases the distribution of the ligands and increases their acidity. The extractive performance of the Schiff base amphiphiles were investigated towards Ni(II) from a chloride medium at 30 °C. The analysis of extraction data revealed that the synthesized Schiff bases exhibit a better and faster extractability than many ligands reported in the literature.     

Removal of Cu(II), Fe(III), and Cr(III) from Aqueous Solution by Aniline Grafted Silica Gel

Abstract

The aniline moiety was covalently grafted onto silica gel surface. The modified silica gel with aniline groups (SiAn) was used for removal of Cu(II), Fe(III), and Cr(III) ions from aqueous solution and industrial effluents using a batch adsorption procedure. The maximum adsorption of the transition metal ions took place at pH 4.5. The adsorption kinetics for all the adsorbates fitted better the pseudo second‐order kinetic model, obtaining the following adsorption rate constants (k₂): 1.233 · 10^?2, 1.902 · 10^?2, and 8.320 · 10^?3 g · mg^?1 min^?1 for Cr(III), Cu(II), and Fe(III), respectively. The adsorption of these transition metal ions were fitted to Langmuir, Freundlich, Sips, and Redlich‐Peterson isotherm models; however, the best isotherm model fitting which presented a lower difference of the q (amount adsorbed per gram of adsorbent) calculated by the model from the experimentally measured, was achieved by using the Sips model for all adsorbates chosen. The SiAn adsorbent was also employed for the removal of the transition metal ions Cr(III) (95%), Cu(II) (95%), and Fe(III) (94%) from industrial effluents, using the batch adsorption procedure.     

Solvent extraction of some metal ions with di‐2‐methylnonylphosphoric acid into heptane

Di‐2‐methylnonylphosphoric acid (HA) as an extractant was investigated for the extraction of divalent metal ions into heptane at an aqueous ionic strength of 0.10 mol dm^?3 (NaClO₄) and at 25 °C. The extraction ability of metal complexes decreased in the order Cd(II) ≈ Mn(II) > Cu(II) > Co(II) > Ni(II). The metal complexes extracted were found to be all monomeric species for these metal ions using a slope analysis method. The curve fitting method was also applied to analyze the types of metal complexes extracted: MnA₂3HA and MnA₂4HA for manganese(II), CdA₂3HA and CdA₂4HA for cadmium(II), CuA₂2HA and CuA₂3HA for copper(II), CoA₂3HA and CoA₂4HA for cobalt(II) and NiA₂4HA and NiA₂5HA for nickel(II). Further, the extraction constants for the extracted metal complexes were evaluated. © 2002 Society of Chemical Industry     

EXTRACTION OF Mn(II) WITH HEPTANOIC ACID IN THE PRESENCE OF 1,10-PHENANTHROLINE AND SOME PYRIDINE BASES

The distribution of 1,10-phenanthroline between 1.0 M NH₄C1 aqueous solution and benzene solutions of heptanoic acid was characterized by means of the partition constant k_{D. phen} = 3.725 ± 0.180 and the logarithmic extraction constants log k_ex(11) = 2.965 ± 0.015 and log k_ex(12) = 3.910 ± 0.060 corresponding to the complexes [phen HR]_o and [phen (HR)₂]_o, respectively.

Manganese (II) extraction with heptanoic acid in the presence of 1.10-phenanthroline occurs when the pH of the aqueous phase is greater than 4. The mononuclear complex is formed according to the equation: The effect of pyridine bases on manganese (II) extraction is relatively low. In the presence of pyridine. 3-methylpyridine and chinoline the manganese (II) extraction decreases. The manganese (II) complexes formed in the presence of 3-methylpyridine are similar to those in the system in which the pyridine bases are absent.     

1,5-Bis(2,5-Difluorophenyl)-3-Mercaptoformazan. A New Tetrafluorinated Dithizone Analogue

Abstract

1,5-Bis(2,5-difluorophenyl)-3-mercaptoformazan (2,2′, 5.5′-tetrafluorodithizone, F₄ H₄ Dz) has been synthesized; its electronic spectra was found to be significantly different from that of dithizone. Its pH_½ in chloroform (8.4) and in carbon tetra-chloride (7.4) are lower than the corresponding values (10.6 and 8.8, respectively) for dithizone. The partition coefficient of the reagent is remarkably decreased in chloroform (270) and in carbon tetrachloride (160) due to the presence of fluorine atoms, compared to the corresponding values (10⁴.89 and 10⁴.18, respectively) for dithizone. The extraction constants of its complexes with Cd(II), Cu(II), Pb(II), Co(II), Hg(II), and Zn(II) were found to be higher than the corresponding values of dithizone complexes, thus enabling their extraction from more acidic solutions. The new reagent seems also to be slightly more sensitive for Bi(III), Cd(II), Co(II), Cu(II), and Hg(II).     

Potentiometric Studies on Ternary Complex Formation between Cu(II), Ni(II), Zn(II), Cd(II), nitrilotriacetic acid and amino acid

The formation of ternary complexes of the type MAB (where M = Cu(II), Ni(II), Zn(II) or Cd(II); A = nitrilotriacetic acid and B = glycine, α-alanine or dl-aspartic acid) has been shown by potentiometric studies. The nature of titration curves indicates that the secondary ligand B is added stepwise to the initially formed metal nitrilotriacetates. The formation constants (log K_MAB) and the free energies of formation (ΔF°) of the mixed complexes have been calculated at 25 ± 1 °C and m̈ = 0.10 (KNO₃) at different pH values. The formation constants of the resulting 1:1:1 ternary complexes follow the order Cu(II) > Ni(II) > Zn(II) > Cd(II).     

SOLVENT EXTRACTION EQUILIBRIA OF LEAD(II) WITH ACIDIC ORGANOPHOSPHATE AND PHOSPHONATE

Distribution equilibria of lead(II) in the extraction with di(2-ethylhexyl)phosphoric acid and 2-ethylhexyl 2-ethylhexylphosphonic acid in toluene from aqueous ammonium nitrate solutions were measured at 303 K to elucidate the concentration dependencies of the reactant species on the distribution ratio. It was found that lead(II) is extracted as the mononuclear complex, PbR₂2HR, with the former extrac-tant while it is extracted not only as the complex, PbR₂2HR, but also as the complex, Pb(NO₃)R;HR, accompanied by simultaneous transfer of nitrate anion with the latter ex-tractant. The extraction equilibrium constants of these complexes were evaluated as well as the stability constants of lead(II) -nitrato complexes, Pb(NO₃)⁺, Pb(NO₃)₂and Pb(NO₃)^? ₃.     

Selective Transport of Cu(II) across a Polymer Inclusion Membrane with 1-Alkylimidazole from Nitrate Solutions

The selective transport of copper(II), zinc(II), cobalt(II), and nickel(II) ions from nitrate solutions across polymer inclusion membranes (PIMs), which consist of cellulose triacetate as polymeric support, o-nitrophenyl pentyl ether as plasticizer, and 1-alkylimidazole (alkyl from hexyl- to decyl) as ion carrier was reported. PIM was characterized by using atomic force microscopy (AFM) technique. The results show that Cu(II) can be separated very effectively from other transition metal cations as Zn(II), Co(II), and Ni(II) (at a concentration of 10^?3 mol/dm³ each). Alkyl substituents at position 1 of the imidazole ring have been found to affect the hydrophobic properties and initial flux of the transported metal ions. The efficiency of separation of metal ions by 1-alkylimidazole followed the sequence: Cu(II) > Zn(II) > Co(II) > Ni(II). The highest selectivity coefficient for Cu(II) was found with 1-hexylimidazole and its 1 mol/dm³ solution in PIM. Separation of the ions was more effective for the nitrates(V) than for chlorides.     

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.     

Supported Liquid (SLM) and Polymer Inclusion (PIM) Membranes Pertraction of Copper(II) from Aqueous Nitrate Solutions by 1-Hexyl-2-Methylimidazole

The facilitated transport of Cu(II) ions from different aqueous nitrate source phases (c _Me = 0.001 M, pH = 6.0) across supported (SLMs) and polymer inclusion membranes (PIMs) doped with 1-hexyl-2-methylimidazole as ion carrier was reported. The membrane is characterized by means of atomic force microscopy (AFM). The results show that Cu²⁺ can be separated very effectively from other transition metal cations as Zn²⁺, Co²⁺, and Ni²⁺ from different equimolar mixtures of these ions. The highest initial fluxes of Cu(II) were found for PIM, while lower values were observed for SLM. However, after taking into account the morphology of the membranes (porosity, tortuosity), the values of the initial flux of Cu(II) transport across PIM is less than that across SLM. The recovery factor of Cu²⁺ ions during transport across PIM from different mixtures of cations is above 91% after 24 hrs and above 76% during transport across SLM. Also, the stability of PIM and SLM doped with 1-hexyl-2-methylimidazole was confirmed in replicate experiments.