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

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.

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

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

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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