SYNTHESIS OF SOME HETEROCYCLIC COMPOUNDS AND THE STUDY OF SOME OF THE METAL CHELATES

Abstract

Heterocyclic compounds form a part of important natural products and play vital role in biological processes. Some of them have been successfully used in therapy. They are also extremely important in analytical chemistry. Many of their derivatives have found significant uses in identifying and estimating certain elements even in traces. Present report comprises of two aspects of heterocycles. 1. Synthesis of some new heterocyclic compounds, and 2. Physico-chemical studies of their metallic complexes. The synthesis of 2-acyl benzofurans is described in Chapter I. The acyl group at position 3 has been oximated with hydroxylamine and the oxime can be used as suitable ligand for complexation with various metal ions. Similarly 2-acetyl benzofuran ketoxime forms complexes with various metals. 2-Benzoyl benzofuran and its deriva tives mainly 2-benzo furyl phenyl ketoxine have been synthesized by the interaction of 2-benzoyl benzofuran, hydroxylamine hydrochloride and sodium acetate in ethanol. The complexing properties of this oxime with Fe(lII), Co(II) and Cu(ll) are studied in detail in methanolic medium. -ii- The composition of Cu(ll), Co(II) and Fe(lll) complexes with 2-benzofuryl phenyl ketoxime in methanolic medium has been determined conductometrically and pHmetrically as 1:1 for Cu(II) and 1:2 for Fe(lII), Cu(II) and Co(II) complexes. The values of stability constant (leg K) are 19.5 for [~Fe (C15H1002N)2(OH) (H20)] , 13.35 for [cu(C15H1002N)2] and 9.92 for [Co(C"15(C^H^C^N^ . These complexes have been isolated in solid form and their composition also established by analysis. In Chapter II 5-bromo dehydracetic acid (3-acetyl- 4-hydroxy-5-bromo-6-methyl-2-pyrone) has been synthesized by the method of Harris and coworkers. As dehydracetic acid is a self-condensation product of two molecules of acetoacetic ester. The bifunctional nature of the compound is a matter of interest since it can be used in the synthesis of a large number of heterocyclic compounds having an a-pyrone ring'substituted at appropriate positions. In case of 5-bromo dehydracetic acid ring cleavage occurs in presence of a base, therefore, piperidine in chloroform has been employed in the formation of cinnamoyl derivatives (analogous to chalcones). These chalconetype derivatives on condensation with phenyl hydrazine lead to the formation of hydrazones which under suitable condition rearrange to the pyrazolines substited with a pyrone ring at position 3. Their structure has been confirmed on the basis of NMR spectra. -111- +4- 5-Bromodehydracetic acid form chelates with Fe and Cu++ and their composition and stability has been confirmed by applying different physico-chemical methods namely spectrophotometric methods, pH-metric and amperometric titrations. The values of pE as determined by pH-metric half titration method was found to be 5.0,different from the value for DAA (5.30) in aqueous solutions, which may be due to bromine attached at 5-position. Vosburgh and Cooper's method showed the existence of one complex in each case. The results of Job's method and molar ratio method indicated the formation of 1:2 (metal:BrDAA) complex. The stochiometric ratio 1:2 was further confirmed by amperometric titrations. Bjerrum's method was also applied to find out the composition of the reaction products. The stability constants as determined by Bjerrum's method were found to be 1.78xl05 and 19.4xl05 for Fe(lll) and Cu(ll) complexes of BrDAA respectively. The values of magnetic moments (|ieff) were 5.70 and 1.80 BM and of molar conductance in acetone were 80 mhos and 0.01 mhos for Fe(IIl) and Cu(Il) complexes respectively. These values indicated highly paramagnetic character of the complexes and their binary electrolytic and non-electro lytic nature respectively. The complexes of Fe(IIl) and Cu(Il) with BrDAA were isolated in the solid form. On the basis of i.r. spectra, BrDAA was found to contain -Iv an intramolecular hydrogen bonding. The structure of metal chelates were also established on the basis of i.r. spectra. The Chapter III deals with the synthesis of 2- amino-4-phenyl-5-arylazo thiazoles and 2-amino-4(4- bromo phenyl)-5-arylazo thiazoles were synthesized by the interaction of 2-amino-4-phenyl and 2-amino-4- (4-bromo phenyl) thiazoles with aryl diazonium chlorides from different anilines. 2-Substituted amino derivatives have also been synthesized by using substituted thioureas in place of thiourea in the modification of synthesis of thiazole by Dodson and King. Coordination studies have been carried out with 5-phenylazo derivatives of 2-amino-4- phenyl thiazole. The complexes of Ag(l) and Hg(ll) with these thiazoles have been studied in detail using diff erent electroanalytical techniques. The thiazole deriva tives form soluble, red coloured stable complexes. The pK values of 5-azophenyl derivatives,viz. 5-azophenyl, 5-azo(o-methoxy phenyl), 5-azo(p-methoxy phenyl) and 2,5-dichloro phenyl) of 2-amino-4-phenyl thiazole as determined pH-metrically were found to be 9.8, 9.5, 9.4 and 8.5 respectively. The composition and formation constants of their complexes with silver have also been determined in 70/. aqueous ethanol using Job's method, molar ratio method and Bent and French method and confirmed by amperometric and conductometric titrations. -VThese complexes have also been isolated in the solid state, purified by crystallization from ether and dried in a desiccator. The effect of different groups on the stability of silver complex was found in the order Cl>p-OCH* = 0-OCH3>H. The interaction of 5-(2,5-dichloro phenylazo) and 5-(phenyl azo) thiazole with mercury (II) have been studied in alcoholic medium. The pH-metric titrations with these compounds were also carried to confirm their compositions. Thiazoles were also titrated conductometrically with mercuric chloride which also indicated the formation of 1:2 (M:L) complex. The stochiometric ratio was further confirmed by carrying out amperometric titrations. Chapter IV consists in the synthesis of 5-arylazo derivatives of 2-hydroxy-4,6-dimethyl pyrimidine hydro chloride and 6-methyl uracil. 2-Hydroxy-4,6-dimethyl pyrimidine has also been used as a ligand, and forms complex with mercury(II) in aqueous medium. The combining ratio of the complex as determined by pH-metric method was found to be 1:2 (M:L).