ABSTRACT

3,5-Bis[(2-hydroxy-benzylidene)-amino]-benzoic acid (H2B) and its
cobalt(II) and nickel(II) complexes were synthesized and characterized via:
electronic, IR, 1H NMR and 13C NMR. Job’s continuous variation method was
used to determine the mole ratio for both metal complexes. Solvent extraction
studies were carried out on H2B in 5% DMF with its cobalt(II) and nickel(II)
complexes using CHCl3 as organic solvent; with variable condition effects of
equilibrium time, buffer pH, mineral acids, salting-out agents and complexing
agents. IR spectral study indicates coordination through (N2O2) azomethine and
protonated hydroxyl groups. Job’s continuous variation method showed a metal to
ligand ratio, 1:1, for both metal complexes of H2B. Cobalt(II) complex of H2B
showed quantitative extraction in pH range 5 – 7, while nickel(II) complex of H2B
showed quantitative extraction in pH range 6 – 8. Nickel was successfully
separated from cobalt by four-cycle extraction at 10-3 M HNO3 aqueous mixture of
Ni(II) and Co(II) {10 μgcm-1 each} in 5% H2B/DMF using 0.05 M cyanide as
masking agent and CHCl3 as organic solvent.

TABLE OF CONTENTS

Title page. . . . . . . . . . . i
Declaration . . . . . . . . . . ii
Certification . . . . . . . . . iii
Dedication . . . . . . . . . . iv
Acknowledgment . . . . . . . . . v
Abstract . . . . . . . . . . vi
Table of Contents . . . . . . . . . vii
List of Tables . . . . . . . . . xi
List of Figures . . . . . . . . . xii
CHAPTER ONE:
1.0 General Introduction …………………………………………………. 1
1.1 Background of Study…………………………………..…………… 2
1.2 Scope of Study…………………………………………..…………… 3
1.3 Significance of Study………………………………..……………… 4
1.8 Aims and Objectives…………………………………………… 4
CHAPTER TWO: Literature Review
2.0 Brief Chemistry of Metals under Study………,…………….. 6
2.1 Cobalt ……………………………………………………… 6
2.1.1 Aqueous Chemistry of Cobalt …………………………………… 8
2.1.2 Oxidation States.…………………………… …………….. 8
2.2 Nickel………… ……………………………………………. 13
2.2.1 Aqueous Chemistry of Nickel ………………………………. 15
viii
2.2.2 Oxidation States………………………………………………… 16
2.2.3 Uses of Nickel and its Compound……………………..………… 17
2.2.4 Nickel and Human Health……………………………………. 18
2.3 Theoretical Fundamentals of Liquid-Liquid Extraction ……..….. 19
2.3.1 Distribution Law …………………………………………………. 20
2.3.2 Limitation of Nernst Distribution Law ………………………….. 22
2.3.3 Thermodynamic Partition Law Constant……………………… 24
2.3.4 Distribution Ratio ……………………………………………… 27
2.4 Efficiency of Extraction ………………………………………… 28
2.4.1 Percentage Extraction ………………………………………….. 29
2.4.2 Separation Factor ……………………………………………… . 31
2.5 Quantitative Treatment of Solvent Extraction Equilibrium …….. 33
2.6 Extraction Methods in Solvent Extraction ……………………… 37
2.6.1 Batch Extraction ………………………………………………… 37
2.6.2 Continuous Extraction …………………………………………… 42
2.6.3 Discontinuous Countercurrent Extraction ……………………….. 43
2.7 Classification of Inorganic Extraction System …………………. 45
2.7.1 Metal Chelate……………………………………………………. 46
2.7.2 Ion-association Complexes …………………………………….. . 53
2.7.3 Additive Complexes ……………………………………………. 54
2.8 Factors that Influence Stability and Extractability of Metal
Chelate Complexes……………………………………………. 57
2.9 Brief Work on Solvent Extraction of Metals under Study… 62
ix
2.10 Previous Work on 3,5-Bis[(2-Hydroxy-Benzylidene)-Amino]-Benzoic
Acid……………………………………………………………. 66
2.10.1 Salens………………………………………………………… 68
2.10.1.1 Salen Ligand Synthesis…………………..………………….. 69
CHAPTER THREE:
3.0 Experimental…………………………………………………… 73
3.1 Equipments……………………………………………………….. 73
3.2 Preparation of Metal Stock Solutions…………………………… 73
3.3 Synthesis of 3,5-Bis[(2-Hydroxy-Benzylidene)-Amino]-Benzoic
Acid ………………………………………………………………. 77
3.4 Synthesis of Co(II) and Ni(II) Complexes of 3,5-Bis[(2-Hydroxy-
Benzylidene)-Amino]-Benzoic Acid……………………….… 77
3.5 Determination of the Composition of the Extracted Species….. 78
3.6 Extraction Procedures ……………………………………………. 78
3.6.1 Extraction from Buffer Solution ………………………………… 79
3.6.2 Extraction from Acid Media……………………………………… 80
3.6.3 Extraction in Salting-out Agents………………………………….. 80
3.6.4 Extraction in Complexing Agents ………………………………… 81
3.7 Measurement of Distribution Ratio……………………………….. 82
3.8 Spectrophotometric Analysis of the Metal Ions…………………… 82
3.9 Calibration Curve………………………………………………….. 83
3.10 Separation Procedures……………………………………………. 84
CHAPTER FOUR:
4.0 Results and Discussion…………………………………………… 85
4.1 Electronic Spectra………………………………………………… 85
x
4.2 IR Spectra…………………………………………………………. 86
4.3 1H NMR Spectra …………………………………………………. 96
4.4 13C NMR Spectra ………………………………………………… 97
4.5 Metal–Ligand Mole Ratio…………………………………………. 104
4.6 Molecular Formula of the ligand and the Complexes …………. .. 104
4.7 Solubility Data …………………………………………………… 109
4.8 Dissociation and Protonation Constants of the Ligand ………… … 111
4.9 Equilibration Time……………………………………………….. 115
4.10 Effect of pH Buffer on Extraction of Co(II) and Ni(II) …………… 115
4.11 Effect of Acidity …………………………………………………… 120
4.12 Effect of Salting-out Agent on Extraction …………………………. 122
4.13 Effect of Complexing Agents on Extraction ……………………. 125
4.14 Degree of Metal Separation ………………………………………. 128
4.15 Summary and Conclusion ………………………………………….. 128
4.16 Recommendation………………………..………………………….. 130
4.17 Contribution to Knowledge……….………………………………….. 131
References…………….……………………………………………. 132

CHAPTER ONE

INTRODUCTION
1.0 General Introduction
Extraction is the transfer of a solute from one phase to another. Common
reasons to carry out an extraction in chemistry are to isolate or concentrate the
desired analyte or to separate it from species that would interfere in the analysis.
The most common case is the extraction of an aqueous solution with an organic
solvent that are immiscible with and less dense than water; they form a separate
phase that floats on top of the aqueous phase1.
Solvent or liquid-liquid extraction is based on the principle that a solute can
distribute itself in a certain ratio between two immiscible solvents, one of which is
usually water and the other an organic solvent such as benzene, carbon
tetrachloride or chloroform. In certain cases the solute can be more or less
completely transferred into the organic phase. The technique can be used for
purposes of preparation, purification, enrichment, separation and analysis, on all
scales of working, from microanalysis to production processes. In chemistry,
solvent extraction has come to the forefront in recent years as a popular separation
2
technique because of its elegance, simplicity, speed and applicability to both tracer
and macro amounts of metal ions2.
The ability of a solute (inorganic or organic) to distribute itself between an
aqueous solution and an immiscible organic solvent has long been applied to
separation and purification of solutes either by extraction into the organic phase,
leaving undesirable substances in the aqueous phase; or by extraction of the
undesirable substances into the organic phase, leaving the desirable solute in the
aqueous phase.3
1.1 Background of Study
Although solvent extraction as a method of separation has long been known
to the chemists, only in recent years it has achieved recognition among analysts as
a powerful separation technique. Liquid-liquid extraction, mostly used in analysis,
is a technique in which a solution is brought into contact with a second solvent,
essentially immiscible with the first, in order to bring the transfer of one or more
solutes into the second solvent4. The separations that can be achieved by this
method are simple, convenient and rapid to perform; they are clean as much as the
small interfacial area certainly precludes any phenomena analogous to the
undesirable co-precipitation encountered in precipitation separations.
3
Solvent extraction has one of its most important applications in the
separation of metal cations. In this technique, the metal ion, through appropriate
chemistry, distributes from an aqueous phase into a water-immiscible organic
phase. Solvent extraction of metal ions is useful for removing them from an
interfering matrix, or for selectivity (with the right chemistry) separating one or a
group of metals from others4.
Solvent extraction is one of the most extensively studied and most widely
used techniques for the separation and pre-concentration of elements. The
technique has become more useful in recent years due to the development of
selective chelating agents for trace metal determination5
1.2 Scope of Work
The Scope of this research is limited to synthesis of the Ligand
Bis(salicylidene)3,5-diaminobenzoic acid, its Co(II) and Ni(II) complexes,
spectrophotometric characterization via UV, IR, H and NMR(1H and 13C),
extraction of cobalt and nickel metal ions in water using chloroform as organic
solvent and separation of Ni(II) from aqueous mixture of Ni(II) and Co(II).
4
1.3 Significance of Study
The introduction of versatile organic reagent, ‘dithizone’, dimethylglyoxime
about five years later and 8-hydroxylquinoline in the 1940s opened a new in liquidliquid
extraction studies which suffered a lull from 1900 till then.6
The search for new extractants for metals continues to draw attention with
the quest for reagents that will be discriminatory enough for particular metal ions
and avoid interferences at the conditions of extraction.
Ukoha et al7 reported the utilization of the compound Bis(4-hydroxypent-2-
ylidene) diaminethane as a good reagent to extract copper(II) and also separated
the element from a mixture of silver(I).
In this research, we are able to synthesize a schiff base Bis(salicylidene)3,5-
diaminobenzoic acid as a ligand to investigate the extraction characteristics of
cobalt(II) and Nickel(II) in various media. The complexes of cobalt(II) and
nickel(II) were characterized spectrophotometrically via UV-visible, IR, and
NMR(1H and 13C)
1.4 Aims and Objectives
This research is aimed at synthesizing a Schiff base ligand: 3,5-Bis-[(2-
hydroxy-benzylidene)-amino]-benzoic acid; its Co(II) and Ni(II) complexes;
characterization of the ligand and its Co(II) and Ni(II) complexes via, Uv-visible,
5
IR, 13C and 1H NMR; using the ligand to extract Co(II) and Ni(II) from aqueous
solutions of varying conditions. Thus, the optimum extraction condition for the
extraction of Co(II) and Ni(II) from aqueous solution with 3,5-[(2-hydroxybenzylidene)-
amino]-benzoic acid will be achieved and a favourable condition for
the separation of Ni(II) from Co(II) with the ligand will also be ascertained. Hence,
the true nature of the Co(II) and Ni(II) complexes of the ligand will be known.
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