ABSTRACT
The divalent metal chelates of Mg,Co,Cu and Zn with 4-acetyl (hpmap), 4-
benzoyl(hpmbp),4-butyryl(hpmbup),4-capyroyl(hpmcp),4-propiony
(hpmprp) and 4-palmitoyl(hpmpp) derivatives of 1-phenyl -3-methyl
pyrazol-5-one have been synthesized and characterized by UV ,IR, and
conductivity measurements. It is shown that the ligands behaved like
bidentate enols, all forming neutral chelates with the metal ions , bonding
through oxygen of the enolic hydroxyl group and /or the oxygen atom of
the carbonyl group of the ligands keto-enol tautomer. The i.r spectra of the
ligands and their chelates have been measured between 4000cm-1 and
400cm-1and assignments proposed for observed frequencies. The effect of 4-
acyl substituents on the carbonyl stretching frequencies of the complexes
was also investigated and the results showed that there was an increase in the
carbonyl stretching frequency bands as the length of the alkyl substituent
increased for magnesium (II),cobalt(II) and copper (II) chelates and the
reverse trend was observed for zinc (II) chelates.The infrared carbonyl and
metal oxygen stretching frequencies of the transition metal chelates were
also compared with the Irving and Williams stability order for transition
metal complexes(Cu > Ni >Co >Mn >Zn) and it was observed that the
magnitude of the M-O stretching frequencies followed closely the Irving
Williams stability order while the C=O stretching frequencies did not. This
+has been attributed to electronic and steric effects.
TABLE OF CONTENTS
Title page …………………………………………………………………………….. ii
Certification …………………………………………………………………….. iii
Acknowledgement ……………………………………………………………….. iv
Dedication …………………………………………………………………. v
Abstract ……………………………………………………………………… vi
List of figures ……………………………………………………………… xi
List of tables ……………………………………………………………………. xiii
Abbreviations ………………………………………………………………… xiv
CHAPTER ONE
1.0 Introduction ……………………………………………………… 1
CHAPTER TWO
2.0 Literature review ……………………………………………………………… 4
2.10 Concept of Chelation ………………………………………………………….. 4
2.11 Metal chelate complexes …………………………………………………………. 5
2.12 Ion –pair complexes …………………………………………………………….. 5
2.13 Additive complexes ……………………………………………………………….. 5
8
2.20 Chelation with β-diketones ……………………………………………………… 6
2.30 Chelation with 4-acylpyrazolones ………………………………………………… 8
2.40 Stability of metal chelates ……………………………………………………. 10
2.41 Nature of the chelating agent …………………………………………………..10
2.42 The size of the chelate ring ……………………………………………… 11
2.43 The nature of the central metal …………………………………………….. 11
2.44 The nature of the metal-ligand bond ……………………………………….. 11
2.50 Previous work done with β-diketones …………………………………… 12
2.51 Physical properties and structure elucidation ……………………………… 13
2.52 Isolation and spectroscopic studies …………………………………………. 15
2.60 Previous work on metal chelates of β-diketones ………………………………..17
2.61 The chemistry of magnesium ……………………………………………………17
2.62 Review of previous work done on magnesium chelates of β-diketones ………..19
2.70 Chemistry of cobalt ………………………………………………………19
2.71 Review of previous work done on cobalt chelates of β-diketones …………….23
2.80 The chemistry of copper ………………………………………………………..24
2.81 Previous work done on copper chelates of β-diketones …………………………26
2.90 The chemistry of zinc …………………………………………………………… 28
2.91 Previous work done on zinc chelates of β-diketones ………………………………29
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2.92 Spectroscopic techniques used in the study of ligands and metal complexes …… 30
2.93 Ultraviolet spectroscopy ……………………………………………………… 30
2.94 Infrared spectroscopy ………………………………………………………… 31
CHAPTER THREE
3.0 Experimental …………………………………………………………. 33
3.1 Laboratory apparatus and equipments ……………………………………….. 33
3.2 Laboratory reagents ……………………………………………………………. 33
3.3 Synthesis of 1-phenyl-3-methyl-4-acylpyrazol-5-ones …………………………35
3.31 Synthesis of 1-phenyl-3-methyl-4-acetylpyrazol-5-ones (HPMAP) …………… 35
3.32 Synthesis of 1-phenyl-3-methyl-4-benzoylpyrazol-5-ones (HPMBP) …………… 35
3.33 Synthesis of 1-phenyl-3-methyl-4-propionylpyrazol-5-ones (HPMPRP) ……… 36
3.34 Synthesis of 1-phenyl-3-methyl-4-butyrylpyrazol-5-ones (HPMBUP) ………… 36
3.35 Synthesis of 1-phenyl-3-methyl-4-hexanoylpyrazol-5-ones (HPMCP) …………. 36
3.36 Synthesis of 1-phenyl-3-methyl-4-palmitoylpyrazol-5-ones (HPMPP) ………… 36
3.40 Synthesis of 1-phenyl-3-methyl-4-acyllpyrazolonates …………………… 36
3.41 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato magnesium II complex 36
3.42 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato copper II complex ……37
3.43 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato cobalt II complex …… 38
3.44 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato zinc II complex …… 39
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3.45 Preparation of 3M hydrochloric acid solution ……………………………………39
3.50 Physical and spectroscopic analysis …………………………………………… 42
3.51 Melting point determination …………………………………………….. 42
3.52 Conductivity measurement ……………………………………………. 42
3.53 Electronic spectra measurement ……………………………………………… 42
3.54 Infrared spectra measurement …………………………………………… 42
CHAPTER FOUR
4.0 Results and Discussion …………………………………………………. 43
4.10 Structure of ligands and complexes ……………………………………… 43
4.20 Physical data ………………………………………………………………….. 45
4.30 Conductivity Measurement ………………………………………………… 48
4.40 Solubility survey of ligands and complexes ………………………………… 49
4.50 Electronic spectra of ligands and complexes ………………………………….. 51
4.60 Infrared spectra of ligands and complexes …………………………………… 53
4.70 The effect of 4-acyl substituents on the infrared carbonyl stretching frequency of
metal(II) chelates of some 1-phenyl-3-methyl 4-acylpyrazolone ………………………64
4.80 Conclusion ……………………………………………………………… 69
References ……………………………………………………………….. 71
Appendices ……………………………………………………………………………… 86
CHAPTER ONE
1.0 INTRODUCTION
There has been a lot of interest in the chemistry and stereochemistry of metal
complexes in recent years because of its growing applications in both biological and chemical
processes. The chemistry of these groups of compounds was first proposed in 18931 by a
Swiss chemist, Alfred Werner who used his coordination theory of primary and secondary
valences to account for the phenomenon by which apparently all stable saturated molecules
combine to form molecular complexes.2,3 Werner showed that the properties of many
complexes formed by various transition metals could be explained by the postulate that the
metal atoms have a ligancy of six or four, with the attached groups arranged about the central
atom at the corners of a circumscribed regular octahedron or tetrahedron.4 Almost every
kind of metal atom can serve as a central atom in a complex , although some metals like the
transition metals do so more readily than others.5 When a metal atom coordinates with two or
more donor groups of a single ligand called the chelating agent , a chelate is formed. One of
the significant features of these chelating agents is that whereas complex formation may
involve more than one intermediate step, Chelation is a one step process. 6,7
Since Urbain,s work on the structure and reactivity of β-diketones in 1896,8 these
groups of chelating agents have been of utmost importance to chemist and research workers
alike. These β-diketones are ligands bearing two carbonyl groups separated by a methylene
group. The intervening methylene group bears an active hydrogen atom.9. The acidity of the
hydrogen atom is caused by the electron withdrawing powers of the two carbonyl groups that
flank them. Owning to electronic and field effects , the hydrogen atoms are capable of
migrating to any of the carbonyl groups giving rise to tautomers.10
1-phenyl -3-methyl -4-acyl pyrazolone , a typical β-diketone whose synthesis was first
described by Jensen, 11,12 has gained considerable popularity in recent years.13-15 The
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structural features of these keto-enol tautomerides attracted the attention of research workers
like Okafor 16-19 and Uzokwu 20-22 who synthesized and characterized a good number of their
metal Chelates. Research into these group of β-diketones has been stimulated by their
potential application in the extraction of metal ions from acid solutions. 23-24 Some other
workers have used the 4-chloroacetyl and 4-triflouroacetyl derivatives of this ligand for the
spectrophotometric determination and extraction of trace elements from aqueous solution.
Mirza and others synthesized the benzoyl derivative of 1-phenyl-3-methyl-4-acyl- Pyrazolone
and used it in the extraction and separation of thorium from titanium, uranium and the rare
earths,27 while Hassany and Quereshi reported the extraction of group IB, IIB and III- IVA
elements using the 4-trichloroacetyl derivative of the pyrazolone moeity. Okafor 16,19,28 has
equally used the triflouro derivative in the isolation of a good number of metal chelates.
Apart from the application of these groups of compounds in qualitative and
quantitative analysis , 4-acyl pyrazolones have found application in medicine, as strong active
ingredients in analgesic 29-30 and in chromatography for the construction of mixed ligand
resins for trapping toxic metals.30 The antipyrene and some other derivatives have been found
to exhibit some biological and pharmacological properties.25,29,31 They have equally found
use in antihistamines, antipyretines, antirhematics and antiinflamatory drugs.32-33 Some
derivatives of this compound containing azo groups have also been used as antifungal and
antiparasitic agents. Recently, several pyridoxine and pyrollo- pyrazole derivatives of the
pyrazole moiety have been synthesized and reported to be useful as inhibitors of
phosphodiestrate(iv) and tumour narcosis factor.35-38 They have also been applied in the
treatment of asthma, arthritis and septic shock.35 The acyl hydrazine compounds of
pyrazolone have been found to serve as inhibitors for many enzymes and an excellent
component of many chemotherapeutic drugs for the treatment of cancer.39 Some other
derivatives have been used as corrosion inhibitors for steel in hydrochloric acid solution.40
To date, a lot of research work has appeared in literature on the structure, reactivity and
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spectral properties of 4-acyl pyrazolones and their derivatives11-40. This project investigates
the effect of the 4-acyl substituents on the carbonyl and metal-oxygen stretching frequencies
of some 4-acyl pyrazolones and their Mg(II) ,Co(II), Cu(II) and Zn(II) chelates.
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