Solvent Extraction Method for the separation of
Zinc(II) By use 2 [4bromo2,6diethyl phenylazo]
-4,5-diphenylimidazole(BDPI)
Sahar Akeel Hussein1 R.K.Al-Kubaisy2 Taghreed H. Al-Noor31,2&3Department of Chemistry, College of Education for Pure Science, Ibn Al-Haitham Baghdad University, Iraq.
Abstract: Extraction experiments for Zn(II) ions from aqueous phase by new laboratory prepared Azo derivation as complex agent 2- [4-bromo-2,6-diethyl phenylazo] -4,5-diphenylimidazole(BDPI)shows the optimum conditions for this extraction method was (pH= 8) (10 minutes) shaking time and 50µg concentration of Zn(II)ions in aqueous phase. Organic solvents effect study shows there is not any linear relation between distribution ratio (D) for extraction of Zn+2 ions and dielectric constant (ε)for organic solvents used but there is in effect for organic solvent structure on the extraction of Zn+2 ions and distribution ratio (D) values. Stoichiometric studies demonstrated the more probable structure ion pair complex extracted for Zn+2 was 1:1.
Keywords: Zn(ΙΙ), Solvent extraction, 2- [4-bromo-2,6-diethyl phenylazo]-4, 5-diphenylimidazole(BDPI) I. INTRODUCTION
Previously used the azo compounds and its derivatives for the extraction methods and used to spectrophotometric determination of transition elements, Determination of Zn(II) 2-[2-pyridil azo]-4-benzen naphthol and 2-[(4-Hydroxy phenyl azo]-4,5-diphenyl imidazol were synthesized and used for the extraction of Zn(II) and Cd(II) from aqueous solutions. Study effective factors on the extraction method such as pH, metal concentration, shaking time organic solvents. Stoichiometry shows the complex extracted was [M+2(PABN-(Cl-)] and [M+2(HPADPI)]2Cl- when (M2+=Zn2+,Cd2+)[121] [1].The extraction of Zn(II) and Cd(II) with mixtures of neutral organophosphorus extractants (aliphatic trialkyl phosphine oxide, Cyanex 923, or branched cyclic trialkyl phosphine oxide, Cyanex 925) and amine extractants (N,N-di(1-methylheptyl) acetamide, N503, or trialkyl amine, N235)Synergistic effects were observed for Zn(II) with Cyanex 923+N503 and for Cd(II) with Cyanex 923+N235 and Cyanex 925+N235. However, the other mixing systems do not have synergistic effects on Zn(II) and Cd(II). The stiochiometry of extracted species studied with slope analysis and constant moles in the three synergistic systems[2].] Extraction of micro amount Coper (II) and Nickel(II)by organic reagent2-[(3-Acyl methyl phenyl)azo]-4,5-di phenyl imidazole(3-AMePADPI) and spectophotometric determination of Copper (II) and Nickel(II) used for in different samples, studies conditions for complex formation was pH= 8 and 11 , shaking time 15 minutes for Cu+2 and Ni+2 respectively[3].
II. EXPERIMENTAL
A. Apparatus:
All spectrophotometric measurements and absorbance were registered by using a biochrom double beam UV-Vis Spectrophotometer model (biochrom libra S60) (A Harvard Bio science company ,Cambridge UK), IR-Spectra for the complexes were recorded by using FTIR S 8400 (England).The determination of melting point 5063 Stuart Melting Point Apparatus (England),as well analytical unit 1108 C.H.N Element analyzer.
B. Reagents - Materials and Solutions:
All chemical materials received from commercial sources with high purity and used as received [4] The stock solution of Zn(II)ions (1 mg/ml) prepared by dissolved 1 gm of Zn metal in (15 ml) of dilute hydrochloric acid (1 : 1) and then diluted this solution to 1 liter by distilled water in volumetric flask. A working standard solutions prepared by dilution with distilled water, needful prepared buffer solution (pH = 5) for determination of Zn(II)by dissolved (50 gm) of unhydrous sodium acetate and (30 gm) of glacial acetic acid in 250 ml volumetric flask, as well as necessarily prepared sodium thiosulphate solution (10%) also for Zn(II)determination. Dithizone standard solution (1× 10-2 M) prepared by dissolved (0.05232 gm) in (10 ml) CCl4, and working solution (1×10-4 M) prepared by dilution with CCl4 solvent. For extraction experiments prepared stock solution of organic reagent 1×10-2M (BDPI)in Chloroform prepared by dissolving 0.459 from (BDPI)in 100ml of CHCl3.
III. SYNTHESIS OF ORGANIC REAGENT
The organic reagents was synthesized according to the procedure published elsewhere[5]by dissolving (2.28 g 0.01 mole) of 4-bromo-2, 6-diethyl aniline..In a solution of 4 mL concentration HCl and 25 mL
distilled water. After cooling this solution 0 °C, added1.4 g of sodium nitrite dissolved in 10 mL distilled water with maintaining the temperature at 0 °C. The mixture was set aside for 15 min in order to complete diazotization reaction. afterward, the diazonium solution was added drop by drop to solution contain (2.2 g , 0.01 mole) of 4,5-diphenyl imidazole and 1.2 g sodium hydroxide dissolved in 150 mL ethanol with keeping temperature at 0 °C. After complete addition , the left contains for two hours , then added 150 mL of cooled distilled water was added, the pH of the solution maintained at 6 by HCl , a brown moleacules was precipitated and left for 24 h. The solid product was filtered off, and washed with cold water, crystallized twice from hot absolute ethanol and dried over CaCl2 to give yield of 76%, Mp (153-154 ˚C) and chemical formula of (C25H23N4Br)with Mw. ( 459.38 g mol-1) .The azo reagent synthesized in this work were identified by UV–Vis., FTIR, and. The UV-Vis. spectrum and IR spectrum figure 1 and figure 2.
Figure 1: UV-Vis. spectrum of organic reagent 2- [4-bromo-2,6-diethyl phenylazo] -4,5-diphenylimidazole(BDPI)
Figure 2: IR-spectrum of organic reagent (BDPI) Table 1: Demonstrate the structure of azo ligand prepared a. UV-Visible spectral peaks (nm) b. IR spectral bands (cm-1)
peaks(nm) Assignments 239 π-π* Benzene ring. 280 π-π* Aromatic ring. 438 n-π*(-N=N-) . Bands (cm-1) Assignments 3414.12 N-H stretching 3339.03 aromatiocCH stretching 1616.4,1392.65 C=Nstretching and bending
1494 for –N=N- 1556.16 C=C
3045.7 CH aliphatic
Figure 3: Calibration curve for Zn(II)ion in aqueous solutions Dithiazon spectrophotometric method. IV. COMPREHENSIVE METHOD FOR EXTRACTION
For extraction experiments have to take (5 ml) of aqueous phase contain exact quantity of Zn(II)ions at optimum pH, and then adding (5 ml) of organic phase contain exact concentration of ligand in organic solvent, afterward shaken the two phases at optimum time, after complete the shaken time separate the two layers and determine the Zn(II)ions remainder in aqueous phase by spectrophotometric method [4], for (5 ml) aqueous phase add (2 ml) of buffer solution and (2 ml) of thiosulphate solution and shaken with five portions of (1×10-4 M) dithizone solution, every portion equal to (1 ml), until the last portion do not change their green color. Afterward collect the portions in (5 ml) volumetric flask and then shaken with 5 ml of dilute ammonia solution to separated unreacted dithizone, after that determine the absorption of solution at λmax = 538 nm by use CCl4 as blank, from absorbance and calibration curve Figure (3) can be determine the quantity of Zn(II)reminder in aqueous phase. But for determination the quantity of Zn(II)ions in organic phase as a complex with the ligand (4-CMePADI), by stripping method which is include shaken the organic phase three times with nearly concentrated hydrochloric acid HCl for dissociation the Zn – complex and
transfer the Zn(II)ions to the aqueous phase and then determine the quantity of Zn(II)ions by spectrophotonetric method, previous method, afterward divide the quantity of Zn(II)ions in organic phase on the quantity of Zn(II)ions in aqueous phase to determined distribution ratio (D).
V. RESULTS AND DISCUSSION
A. Absorption UV–Vis spectrum:
Absorption UV–Vis spectrum in Figure 4 shows maximum absorption for ion pair complex extracted at λmax= 548nm
Figure 4:absorption UV–Vis spectrum for ion pair complex
B. Effect of acidic function:
Extracted 50µg Zn(II) in 5mL aqueous phase with 5ml of (1×10-4M) organic reagent solution (BDPI) dissolved in chloroform at different pH of aqueous phase (6-12) and shaking the two phases for (10 minutes) after that separate the two phases and determination of distribution ratio (D)as in the general method, as well as determine absorbance of organic phase against organic reagent as blank. The result as in figures (5, 6)
Figure (5): Effect of pH on complex formation as extraction
Figure(6):D=f(pH)
The results shows optimum pH for extraction was pH=8 at the pH obtained higher Absorbance and D- value that is measure reached higher extraction .Efficiency at this pH and at pH less than pH=8 lour suitable to reach favorable thermodynamic equilibrium for extraction and by decrease pH value increase hydration shell of Zn(II)as well as increase protonated of complex agent and decrease complexation ,but at pH value more than optimum value also lead to decrease extraction efficiency.
C. Effect of Metal ion concentration:
Extraction of different concentrations of Zn(II)ions(1-70) µg in(5ml) aqueous solution at(pH=8) by(5ml) of (1x10-4 M of (BDPI)) dissolved in chloroform , shaking the two layers for suitable time, and separate the two layers and determine the remainder quantity of Zn(II)ion in aqueous phase by followed spectrophotometric method [5], and calculation distribution ratio (D) as well as determine absorbance of organic phase at λmax=548nm against organic reagent as blank. The result was as in figures (7,8)
Figure (8): Effect of Zn(II) concentration on thermodynamic equilibrium for complex
formation and extraction Figure (7): Effect of Zn(II)concentration on
activity of extraction and D value
According to thermodynamic equilibrium for complexation reaction. Zn2+aq+(BDPI)org +2Cl-aq ↔ [Zn(BDPI) ] +2;2Cl- org
The results show 50µg Zn2+/5mL was the optimum concentration giving higher efficiency of extraction because effect to increase rate of forward direction of thermodynamic equilibrium that is mean increase formation and extraction of ion pair complex concentration of Zn(II)less than optimum value not enough to
reach favorable thermodynamic equilibrium that is mean decrease in ion association complex formation and extraction so that Absorbance and D-value from other hand any concentration of Zn(II)more than optimum value effect to decline extraction efficiency and decrease absorbance and D-value became effect to increase rate of back ward direction of thermodynamic equilibrium according to the chatelier principle and mass action law.
D. Effect of shaking time:
For the kinetic side of the extraction methods are carried out by studying the effect of shaking time on the extraction activity and distribution ratio values. After extracted 50µg Zn(II)ions in 5ml aqueous phase at (pH=8) by 5ml of (1×10-4 M) organic reagent (BDPI) dissolved in chloroform by different shaking time, the results of this study in figure (9,10) demonstrate the optimum shaking time of two layers was (10min.) to reach the equilibria of extraction and at this time obtain the maximum distribution ratio value (D), and Absorbance at 548nm shaking time but less than optimum no allow to reached the equilibria of extraction, so that shaking time more than optimum favorite the dissociation equilibria and minimize the distribution ratio(D)and absorbance.
Figure (9):D=f(shaking times) Figure (10): shaking time effect on complex formation and extraction
E. Effect of organic solvent:
According to solvent extraction method which is depends on the organic solvent used in extraction method. Extracted 50μg Zn(II)ions from 5mL aqueous phase by 5mL (1×10-4 M) organic reagent (BDPI) dissolved in different organic solvent differ in dielectric constant after shaking the two phase for 10mintes ,so separate organic phase from aqueous phase determine D-value according to the procedure detailled in the general method the results was as in the table (2) .the results show there not any linear relation between Distribution ratio and Dielectric constant of organic solution ,that is mine there is not effect for polarity of organic solvent on extraction activity but there in effect for organic solvent structure this result reflect participation organic solution in complex formation .Thermodynamic parameter for extraction in different organic solution include transition free energy ΔGt and association constant kA as well as extraction constant kex and free energy of extraction ΔGex by application relation s below
The results in Table (2) showed free energy of transition ΔGt for Zn(II)ions from aqueous phase to organic phase increase with dielectric constant of organic solvents decrease but kex and ΔGex showed the high value by using Chloroform organic solvent which demonstrate sharing organic solution and increase the stability of ion pair complex extracted and increase the approach between the cation and anion association complex extraction which is contract ion pair or loose ion pair.
Table 2: Organic solvent effect on the extraction of Zn(II)ions andΔGT, KA, KEX,ΔGEX
Organic Solvents ε Abs. at
λmax=548 D %E -ΔGt KAx104 Kexx108 -ΔGex
Nitro benzene 35.74 0.287 10.11 91 0.0418 7.26 68.15638 60.4354 Amyl alcohol 15.8 0.173 7.77 89.2 0.13714 5.73 40.2686 59.1605 1,2-Dichloro ethane 10.65 0.292 11.19 91.8 0.21977 7.97 83.55384 60.9289 Dichloro methane 9.08 0.188 8.25 88.6 0.26361 6.054 45.47691 59.4552 Chlorobenzene 5.708 0.16 7.33 88 0.43927 5.448 35.85185 58.879 Bromo benzene 5.4 0.201 8.8 89.8 0.46625 6.409 51.67269 59.7646 Chloroform 4.806 0.418 24 96 0.52805 1.634 384 64.6239 Benzene 2.804 0.212 9.2 90.2 0.92916 6.6714 56.47675 59.98 Toluene 2.438 0.314 11.8 92.2 1.07372 8.382 93.14968 61.1923 Carbone tetrachloride 2.38 0.404 19 95 1.1007 1.307 240.6667 63.492
F. Stoichiometry:
By using spectrophotometric methods to know the more probable structure of complex extraction which are slope analysis, mole ratio, continuous variation method, slope ratio. The results are as in Figure (9–12)
Figure 9: Slope analysis method
The methods show the more probable structure of complex extracted was 1:1 Zn (II): (BDPI)
G. Spectrophotometric Determination
Solvent extraction as sensitive and selective method used for spectrophotometric determination of Zn2+ in different samples such as soil, vegetable, fruit etc. The samples digestion it have been using dry digestion method[11]. Prepared calibration curve at λmax=548nm to the determination Zn2+ in different samples. Afterward prepared sample solution according to solvent extraction method and after separation the two layers measured the absorbance of organic phase at λmax=548nm against organic reagent solution as blank.
0.00819 % RSD 0.000159mol /L Detection limit 2669.24 L mol-1cm-1 ε 0.024493mg cm-2 Sandel’s sensitivits
Figure 10: Calibration curve for spectrophotometric determination of Zn(II) in different samples Table 3: Accumulated quantity of Zn(II) in different samples[6-8].
ACKNOWLEDGMENT
Thanks to Prof. Dr. Shawket Kadhim Jawad, Chemistry Department The College of Education For Girls /University of Kufa to help in work and have shared your knowledge with me and Thank you for advice amd support.
REFERENCES
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The samples ppmZn(II)
Cow meat(Beef) 28.1 Fish farms 32.2 Dates 1.23 Orange(Egypt) 2.9 radish 40 Onion 32 Najaf sea 121
Old holy city 109
Soil of Al-Salam Valley 113 Drinking water (Al-Ataba) 3.2
Tap water 1.2
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