The effect of 4-acyl substituents on the infrared stretching frequencies of some 1-phenyl -3- methyl -4- acylpyrazol -5-ones and their magnesium (ii) ,cobalt(ii), copper (ii) and zinc (ii) chelates

Project Abstract

<p> </p><p>The divalent metal chelates of Mg,Co,Cu and Zn with 4-acetyl (hpmap), 4-<br>benzoyl(hpmbp),4-butyryl(hpmbup),4-capyroyl(hpmcp),4-propiony<br>(hpmprp) and 4-palmitoyl(hpmpp) derivatives of 1-phenyl -3-methyl<br>pyrazol-5-one have been synthesized and characterized by UV ,IR, and<br>conductivity measurements. It is shown that the ligands behaved like<br>bidentate enols, all forming neutral chelates with the metal ions , bonding<br>through oxygen of the enolic hydroxyl group and /or the oxygen atom of<br>the carbonyl group of the ligands keto-enol tautomer. The i.r spectra of the<br>ligands and their chelates have been measured between 4000cm-1 and<br>400cm-1and assignments proposed for observed frequencies. The effect of 4-<br>acyl substituents on the carbonyl stretching frequencies of the complexes<br>was also investigated and the results showed that there was an increase in the<br>carbonyl stretching frequency bands as the length of the alkyl substituent<br>increased for magnesium (II),cobalt(II) and copper (II) chelates and the<br>reverse trend was observed for zinc (II) chelates.The infrared carbonyl and<br>metal oxygen stretching frequencies of the transition metal chelates were<br>also compared with the Irving and Williams stability order for transition<br>metal complexes(Cu &gt; Ni &gt;Co &gt;Mn &gt;Zn) and it was observed that the<br>magnitude of the M-O stretching frequencies followed closely the Irving<br>Williams stability order while the C=O stretching frequencies did not. This<br>+has been attributed to electronic and steric effects.</p><p>&nbsp;</p> <br><p></p>

Project Overview

<p> 1.0 INTRODUCTION<br>There has been a lot of interest in the chemistry and stereochemistry of metal<br>complexes in recent years because of its growing applications in both biological and chemical<br>processes. The chemistry of these groups of compounds was first proposed in 18931 by a<br>Swiss chemist, Alfred Werner who used his coordination theory of primary and secondary<br>valences to account for the phenomenon by which apparently all stable saturated molecules<br>combine to form molecular complexes.2,3 Werner showed that the properties of many<br>complexes formed by various transition metals could be explained by the postulate that the<br>metal atoms have a ligancy of six or four, with the attached groups arranged about the central<br>atom at the corners of a circumscribed regular octahedron or tetrahedron.4 Almost every<br>kind of metal atom can serve as a central atom in a complex , although some metals like the<br>transition metals do so more readily than others.5 When a metal atom coordinates with two or<br>more donor groups of a single ligand called the chelating agent , a chelate is formed. One of<br>the significant features of these chelating agents is that whereas complex formation may<br>involve more than one intermediate step, Chelation is a one step process. 6,7<br>Since Urbain,s work on the structure and reactivity of β-diketones in 1896,8 these<br>groups of chelating agents have been of utmost importance to chemist and research workers<br>alike. These β-diketones are ligands bearing two carbonyl groups separated by a methylene<br>group. The intervening methylene group bears an active hydrogen atom.9. The acidity of the<br>hydrogen atom is caused by the electron withdrawing powers of the two carbonyl groups that<br>flank them. Owning to electronic and field effects , the hydrogen atoms are capable of<br>migrating to any of the carbonyl groups giving rise to tautomers.10<br>1-phenyl -3-methyl -4-acyl pyrazolone , a typical β-diketone whose synthesis was first<br>described by Jensen, 11,12 has gained considerable popularity in recent years.13-15 The<br>16<br>structural features of these keto-enol tautomerides attracted the attention of research workers<br>like Okafor 16-19 and Uzokwu 20-22 who synthesized and characterized a good number of their<br>metal Chelates. Research into these group of β-diketones has been stimulated by their<br>potential application in the extraction of metal ions from acid solutions. 23-24 Some other<br>workers have used the 4-chloroacetyl and 4-triflouroacetyl derivatives of this ligand for the<br>spectrophotometric determination and extraction of trace elements from aqueous solution.<br>Mirza and others synthesized the benzoyl derivative of 1-phenyl-3-methyl-4-acyl- Pyrazolone<br>and used it in the extraction and separation of thorium from titanium, uranium and the rare<br>earths,27 while Hassany and Quereshi reported the extraction of group IB, IIB and III- IVA<br>elements using the 4-trichloroacetyl derivative of the pyrazolone moeity. Okafor 16,19,28 has<br>equally used the triflouro derivative in the isolation of a good number of metal chelates.<br>Apart from the application of these groups of compounds in qualitative and<br>quantitative analysis , 4-acyl pyrazolones have found application in medicine, as strong active<br>ingredients in analgesic 29-30 and in chromatography for the construction of mixed ligand<br>resins for trapping toxic metals.30 The antipyrene and some other derivatives have been found<br>to exhibit some biological and pharmacological properties.25,29,31 They have equally found<br>use in antihistamines, antipyretines, antirhematics and antiinflamatory drugs.32-33 Some<br>derivatives of this compound containing azo groups have also been used as antifungal and<br>antiparasitic agents. Recently, several pyridoxine and pyrollo- pyrazole derivatives of the<br>pyrazole moiety have been synthesized and reported to be useful as inhibitors of<br>phosphodiestrate(iv) and tumour narcosis factor.35-38 They have also been applied in the<br>treatment of asthma, arthritis and septic shock.35 The acyl hydrazine compounds of<br>pyrazolone have been found to serve as inhibitors for many enzymes and an excellent<br>component of many chemotherapeutic drugs for the treatment of cancer.39 Some other<br>derivatives have been used as corrosion inhibitors for steel in hydrochloric acid solution.40<br>To date, a lot of research work has appeared in literature on the structure, reactivity and<br>17<br>spectral properties of 4-acyl pyrazolones and their derivatives11-40. This project investigates<br>the effect of the 4-acyl substituents on the carbonyl and metal-oxygen stretching frequencies<br>of some 4-acyl pyrazolones and their Mg(II) ,Co(II), Cu(II) and Zn(II) chelates.<br>18 <br></p>