FORMATION OF SCHIFF’S BASE (ACACEN) USING ETHYLENEDIAMINE AND EFFECT OF pH ON ZINC (II) ION ON COATED SILICA GEL BY COLUMN METHOD
Acetylacetone ethylenediamine (ACACEN) is a Schiff base resulting from the condensation of pentan-2,4-dione and 1,2-diaminoethane. Solid-phase extraction of Zn (II) by column method in the pH range 1-12 have been studied in trichloromethane using acetylacetone ethylenediamine (ACACEN). Zn (II) extraction using 2% ACACEN in CHCl3 is sufficient or abundant in the pH of 5.0. The aqueous ACACEN shows a maximum absorption at 320nm.The Zn (II) complex has maximum absorption at 572nm.The acid dissociation constants of H2B (ACACEN) are obtained of by titrating with 0.179M NaOH and are found to be pKaiD = 11.55 and PKa2D = 11.55 corresponding to the formation of HB- and B2 respectively. pKaID and pKa2D share the common value since H2B (ACACEN) has two ionizable hydrogen atoms located in the same chemical environment. Electronic spectrum of ACACEN suggests that ACACEN absorbs maximally in the ultraviolet regions of the spectrum and not in the visible region since it is not displayed in the spectrum. The physical modification of the silica gel using ACACEN has also been studied. The optimal pH value is found at the pH5.
TABLE OF CONTENT
Title page i
Certification page ii
Dedication page iii
Table of contents vi
1.0 Introduction 1
1.1 Background of the study 1
1.2 Objectives of the study 3
1.3 Statements of the problem 4
1.4 Hypotheses of the study 5
1.5 Significance of the study 5
1.6 Limitation of the study 6
2.0 Literature review 7
2.1 Metal ion under study zinc (II) ion 10
2.1.1 Uses/properties of zinc 10
2.2 Solid phase extraction 11
2.3 Mechanism of solid phase extraction process 13
2.4 Solid phase extraction process 19
2.5 Sorbent in SPE 22
2.6 Coupling Solid Phase Extraction with various
3.0 Materials and Method 40
3.1 Materials 40
3.1.1 Instruments/Equipment 40
3.1.2 Chemical reagents 41
3.2 Methods 46
3.2.1 Synthesis of the Schiff’s base acetylacetone
3.2.2 Activation of silica gel 47
3.2.3 Preparation of stock solution of the ligand,
acetlyacetone ethylenediamine 47
3.2.4 Preparation of the buffer solutions (pH1- pH 12) 48
3.2.5 Preparation of immobilized Schiff’s base
(ACACEN) silica gel 48
3.2.6 Preparation of the extraction column 49
3.2.7 Effect of pH on the modified silica gel 49
3.2.8 Determination of the acid dissociation constant
of the ACACEN 50
3.2.9 Determination of wavelength of maximum
absorbance (⋋max) of aqueous ACACEN 51
4.0 Result and Discussion 52
4.1 Results 52
4.1.1 Activation of silica gel 52
4.1.2 Properties of ACACEN 52
4.1.3 Electronic spectrum of ACACEN 53
4.1.4 Acid dissociation constants of ACACEN 54
4.1.5 Effect of sample volumes on modified silica gel 55
4.2 Discussion 56
4.2.1 Activation of silica gel 56
4.2.2 Properties of ACACEN 56
4.2.3 Electronic spectrum of ACACEN in aqueous
4.2.4 Acid dissociation constants of ACACEN 57
5.0 Conclusion and Recommendation 59
5.2 Recommendation 60
1.1 BACKGROUND OF THE STUDY
Schiff’s bases are important class of organic compounds (Arulmurugan et al., 2010). They were first reported by Hugo Schiff in 1864. Schiff’s bases are condensation products of primary amines with carbonyl compounds. The common structural feature of these compounds is the azomethine group with the general formula RHC=N-R1, where R and R1 are alkyl, aryl, cycloalkyl or heterocyclic groups (Arulmurugan et al., 2010). Structurally, a Schiff’s base (also known as imine or azomethine) is a nitrogen analogue of an aldehyde or ketone in which the carbohyl group (>C=O) is replaced by an imine or azomethine group. Schiff’s bases have also been shown to exhibit a broad range of biological activities, including antifungal, antibacterial, antimalarial, anti-inflamatory, antiviral and antipyretic properties (Przybylski et al., 2009). Imine or azomethine groups are present in various natural, naturally derived and non-naturally compounds. The imine group present in such compounds has been shown to be critical to their biological activities (Guo et al., 2007). Schiff’s bases are important compounds owing to their wide range of industrial applications (Li et al., 2003). Schiff’s bases are used in the photostabilization of poly (vinyl chloride) polymers against photodegradation by ultraviolet radiation (Yousif et al., 2011) are also used to improve poly(methyl methacrylate) from degradation (Yousif et al,. 2012) and to prevent polystyrene from photodegration by their addition to polymer films (Yousif et al., 2012).
Acetylacetone is an organic compound that famously exists in two tautomeric forms that rapidly interconvert. The pair of tautomers rapidly interconvert and are treated as a single compound in most applications. Although the compound is formally named as the diketone form, pentane-2,4-dione, the end form forms a substantial component of the material and is actually the favoured form in many solvents. It is a colourless liquid that is precursor to acetylacetonate (acac), a common bidentate ligand. It is also a building block for the synthesis of heterocyclic compound.
The keto and enol forms of acetylacetone coexist in solution; these forms are tautomers. The end form has the hydrogen shared equally between the two oxygen atoms in the gas phase, the equilibrium constant, Keto-enol is 11.7, favoring the end form. The two tautomeric forms can easily be distinguished by NMR spectroscopy, IR spectroscopy and other methods.
1.2 OBJECTIVES OF THE STUDY
The main purpose of this study is the development of new sorbent for preconcentration and separation of metal ions from aqueous solutions. The research work will be focused on the following objectives.
a. To develop new sorbent for pre-concentrating metal ions from aqueous solution.
b. To institute and synthesize Schiff base which can be used in the solid support surface to get a new sorbent with high sorption/adsorption efficiency.
c. To enhance the condition for extraction.
d. To improve trace elemental determination of selected elements commonly found in our environment.
e. To determine lmax of acacen ligand.
f. To activate and modify the silica gel.
1.3 STATEMENT OF PROBLEM
Heavy metal mobility and bioavailability depend strongly on their chemical and mineralogical forms in which they occur. Several specification studies have been conducted to determine and study different forms of heavy metals rather their total metal content. Solid phase extraction (SPE) is an increasingly useful sample preparation technique. With SPE many of the problems associated with liquid/liquid extraction can be prevented, such as incomplete phase separations, less than quantitative recoveries, use of expensive, breakable specialty glassware and disposal of large quantities of organic solvents. SPE is more efficient than liquid/liquid extraction, yield quantitative extractions that are easy to perform, rapid, and can be automated. Solvent use and laboratory time are reduced.
SPE is used most often to prepare liquid sample and extract semi-volatile or non-volatile analysis, but also can be used with solids that are pre-extracted into solvents. SPE products are excellent for sample extraction, concentration and clean-up. They are available in a wide variety of chemistries, absorbents and sizes. 1.4 HYPOTHESES OF THE STUDY
Ho (Null Hypotheses): The solid phase extraction of trace metals with Schiff base (ACACEN) by column method.
Ha (alternative hypothesis): Solid phase extraction of trace metalswithout Schiff’s base (ACACEN).
1.5 SIGNIFICANCE OF THE STUDY
The significance of this research work is to enlighten the scholars, educationists and the public on the importance of solid phase extraction as a means of extracting metal ions from complexes and to give background information on experimental procedure of the study. This research work will also serve as a stepping stone for subsequent researches.
1.6 LIMITATION OF THE STUDY
This research study is limited to the Schiff’s base known as acetylacetone ethylenediamine. It is also limited to or important to the determination of only zinc (II) ion. It involves extraction using column method.