CHAPTER ONE
INTRODUCTION
1.1 SCHIFF BASES
Schiff bases are condensation products of primary amines with carbonyl compounds and they were first reported by Schiff (Cimerman et. al., 2000). The common structural feature of these compounds is the azomethine group with a general formula RHC=N-R1, where R and R1 are alkyl, aryl, cyclo alkyl or heterocyclic groups which may be variously substituted. The common structural feature of these compounds is the azomethine group with a general formula RHC=N-R1, where R and R1 are alkyl, aryl, cyclo alkyl or heterocyclic groups which may be variously substituted. These compounds are also known as anils, imines or azomethines. Several studies (Singh et. al., 1975, Perry et. al., 1988, Elmali et. al., 2000, Patel et. al., 1999, Valcarcel et. al., 1994, Spichiger et. al., 1998,Lawrence et. al., 1976)showed that the presence of a lone pair of electrons in an sp2 hybridized orbital of nitrogen atom of the azomethine group is of considerable chemical and biological importance.
A Schiff base is a nitrogen analog of an aldehyde or ketone in which the C=O group is replaced by C=N-R group. It is usually formed by condensation of an aldehyde or ketone with a primary amine.The formation of a schiff base from an aldehydes or ketone is a reversible reaction and generally takes place under acid or base catalysis, or upon heating.
Schiff bases are generally bidentate (1), tridentate (2), tetradentate (3) or polydentate (4) ligands capable of forming very stable complexes with transition metals. They can only act as coordinating ligands if they bear a functional group, usually the hydroxyl, sufficiently near the site of condensation in such a way that a five or six membered ring can be formed when reacting with a metal ion.
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