Distribution of Cu(II) between Buffered Aqueous Phases and Organic Phases Containing N,N’- ethylenebis(4-propionyl-2,4-dihydro-5-methyl-2- phenyl-3H-pyrazol-3-oneimine (H2PrEtP) in Chloroform

Complexation of Copper (II) ions from aqueous media into chloroform solution of N,N’ethylenebis(4-propionyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-oneimine) (H2PrEtP) Schiff base in chloroform was studied. Effect of various parameters for the extraction such as pH of aqueous media, concentration of the ligands and concentration of Cu(II) were all investigated Original Research Article Nwadire et al.; IRJPAC, 13(3): xxx-xxx, 2016; Article no.IRJPAC.30386 2 alongside the synergistic effect of 4-propionyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one (HPrP) under a well-defined extraction condition. Complexation of Copper (II) ions was found to be highly dependent on pH of aqueous media and occurred more readily in acidic media. Single ligand complexation gave a pH1⁄2 (pH at which 50% extraction occurred) of 4.57 with the partition coefficient statistically determined to be LogDCuH2PrEtP 1.56±0.01 and extraction constant (Log Kex) CuH2PrEtP -3.25±0.10. Complexation with mixed ligand system gave a pH1⁄2 of 3.0, partition coefficients LogDCuH2PrEtP/HPrP of 1.70±0.05 and extraction constant Log KexCuH2PrEtP/HPrP of -3.12±0.10 showing that the complexetion of Cu(II) was slightly higher in the mixed ligands system. Optimum concentration of 3.5×10 -2 M H2PrEtP which gave 97.61% E was observed on varying the ligand concentration in the absence of the synergist while in the presence of the synergist, optimum concentration of 4.0×10 -2 M which corresponds to 98.53% E was observed for the main ligand. Variation in synergist concentration gave optimum result of 97.85% E at 2.25×10 -2 M HPrP. Analysis of slope was used to predict stoichiometry of the extraction reactions and to propose extracted metal complexes structure in both single and mixed ligands system as Cu(HPrEtP)o and Cu(HPrEtP.HPrP)o respectively.


INTRODUCTION
Schiff bases have been widely used as ligands because of the high stability of their coordination compounds and their solubility in common solvents [1]. Schiff bases are typically formed by the condensation of primary amines and a ketone or an aldehyde [2]. The resultant functional group Ŕ─C═N─Ȑ is called an imine [3], and it is regarded as one of the most important chelators for easy formation of new metal chelates [4] via the N─ atom lone pair especially when in combination with one or more donor atom to form a polydentate ligand [3,5]. The mechanism of imine formation begins as a nucleophilic addition to carbonyl group; in this case, the nucleophile is the amine which reacts with the aldehyde or ketone to give an imine [6]. Schiff bases with N and O donor atoms arranged in Ar ─ OH and ─CH═N─ group tends to show high selectivity towards Cu(II) and Fe(III) ions [7]. Metal complexes of Schiff base are studied extensively due to synthetic flexibility of these compounds and their selectivity as well as their sensitivity towards the central metal atom [8,9,10,11]. The π─System in Schiff bases often impose a geometrical constriction and affect the electronic structure as well [1]. The thermodynamic, theoretical and catalytic aspects of this class of compounds have been extensively investigated [12]. Complexes containing Schiff base ligands and their derivatives play important roles in oxidation chemistry for instance; (Salen) Chromium (V) oxo complexes are active oxidants for the stoichiometric and catalytic epoxidation of olefins [12]. Schiff bases have been used in catalysis, antibacterial activity, anti-oxidative activity, medicine as antibiotics, anti-inflammatory agents [13] and on the industrial scale for anti-corrosion properties, dyes and pigments [14]. They are also very important sensory molecules for fabricating cation and anion selective electrodes and have been used for the enrichment and separation of trace amount of metals ions [13,14]. The selective transport of metal ions across a membrane is known to play an essential role in many biological processes [15]. Dinuclear copper complexes containing two metal centers in close proximity are the subject of recent extensive investigation as a result of its structural involvement in a variety of important biochemical processes such as oxygen transport and oxygen activation by oxidase and monooxygenase enzymes [16]. Copper-Schiff bases complexes have been reported for the catalytic oxidation of alcohols and phenols [17]. Solvent extraction of Copper (II) and Lithium (I) using Cyanex272 in synergism with TBP has been reported [11]. In continuation of our work on the synthesis, characterization of 1-phenyl-3-methyl-4acylpyrazolone-5 derivatives and their application in the extraction of bivalent transition metal ion such as Ni(II) [8] and Co(II) [18]. We report the use of the Schiff base N,N'-ethylenbis(4propionyl-2,4-dihydro-5-methyl-2-phenyl-3Hpyrazol-3-oneimine) as a potential extractant for Copper(II) ions.

MATERIALS AND METHODS
All reagents were of analytical grade. H 2 PrEtP (Schiff base) was synthesized by the method reported elsewhere [9,12]. The ligands purity after recrystallizations from aqueous ethanol were determined by elemental analysis for C, H and N; analysis of IR and NMR spectral data at Institute for Inorganic Chemistry Technology, University of Dresden Germany [9,12].
All other reagents used were purchased from Aldrich and BDH.

Extraction Procedure
A buffered solution (2 ml) containing 7.87×10 -4 M of Cu(II) ions at the required pH was prepared in a 10 ml extraction bottle. Equal volume (2 ml) of 0.05 M solution of H 2 PrEtP in chloroform was added. For the mixed ligand complexation, the organic phase was 0.05 M H 2 PrEtP and 0.05 M HPrP solution in chloroform mixed in the ratio of 9:1 by volume. The mixture was mechanically agitated for 30 minutes at room temperature to enable the attainment of equilibrium. The phases (aqueous and organic) were allowed to settle and separated with the aid of a micropipette. Concentration of Cu(II) ions in the aqueous phase was determined with a Buck Scientific Atomic Absorption Spectrophotometer (AAS) at 324.7 nm. The concentration of Cu(II) ion complexed into the organic phase was determined by the difference between the concentration of Cu(II) ion in the aqueous phase before and after the extraction. The distribution ratio (D) can be expressed as C org /C aq where C org and C aq are the concentrations of Copper (II) in the organic and the aqueous phase, respectively.

Effect of Buffer Solution on Complexation of Copper (II) ions
Distribution of Cu(II) from aqueous solution into chloroform phase having the Schiff base H 2 PrEtP can be represented by the Eqn. (1) Cu Eqn. (1) Substituting D into eqn. 2 after rearrangement gives Equation (4) showed that the extraction of copper (II) ions into chloroform solution of H 2 PrEtP increased with increase in pH of aqueous solution and reached a peak at pH 6.10, where a percentage extraction of 97.38% was achieved. Thereafter, further increase in pH resulted in a decrease in percentage extraction of the metal. The partition coefficient, logD was determined statistically from the plot to be 1.56±0.01. The pH½ was 4.57.

Effect of Addition of HPrP (synergist) on the Complexation of Cu(II) ions
On addition of HPrP, quantitative extraction of 98.23% was obtained at pH 6.10. The pH ½ was significantly lowered from pH 4.57 (acidic) to a more acidic pH of 3.0.
The partition coefficient was found to be 1.70± 0.05 and was determined statistically from the plot as shown on Fig. 2. Plot of LogD against pH in the mixed ligands system also gave a slope of approximately 1, indicating that 1 mole of hydrogen ion were displaced during the extraction process. Thus, the possible reaction equation for the extraction may be written as:

Effect of Ligand (H 2 PrEtP) and Synergist (HPrP) Concentrations on the Complexation of Cu(II) ions at Different pH
All extraction processes studied showed that the extraction of Cu(II) into chloroform solution of H 2 PrEtP and HPrP increased as the ligands

Proposed Structures for Copper (II) complexes with H 2 PrEtP and H 2 PrEtP/HPrP
Based on the results and statistical analyses of data, we proposed the structures in Figs. 8 and 9 for copper (II) complexes with H 2 PrEtP and H 2 PrEtP/HPrP respectively where X is anionic species from the buffer incorporated to stabilize the charge on the copper ion.

CONCLUSION
On studying the complexation of Copper (II) in buffered aqueous medium with chloroform solution of H 2 PrEtP, a pH ½ of 4.57 was observed. The synergistic effect of HPrP shifted the pH ½ from pH 4.57 to a more strongly acidic pH of 3.0. The partition coefficients were H 2 PrEtP D 1 1.56± 0.01 and H 2 PrEtP/HPrP D 2 1.70±0.05 for single and mixed ligands extractions respectively, indicating that there is a slight difference in the distribution of the metal ions into chloroform solution of H 2 PrEtP and into mixture of H 2 PrEtP/HPrP. The extraction constants KexCu 1 is -3.25±0.10 and KexCu 2 was found to be -3.12 ± 0.10. The values indicated that Cu(II) distributes better into the mixed ligands system from the buffered media. From all the observations, we concluded that the extraction of Cu(II) ion is more effective in a strong to moderately acidic medium.