CHAPTER One

1.0 INTRODUCTION 1.1 Azo Dyes Azo compounds are a class of chemical compounds that are continuously receiving attention in scientific research (Kirkan and Gup, 2008; Seferoglu, 2009 Otutu et al., 2011). They are usually strongly coloured compounds which can be intensely yellow, red, orange, blue or even green, depending on the exact structure of the molecule. As a result of their colour, azo compounds are of tremendous importance as dyes and also as pigments for a long time (Ebenso et al., 2008). For a dye to be suitable for use, the colored material must have the following desirable properties: intense colour, solubility in water and substantivity for the substrate (Nkeonye, 1987). In fact, about half of the dyes in industrial use today are azo dyes, which are mostly prepared from diazonium salts (Robert et al., 2011; Zollinger, 2003). The structural features in organic compounds, that usually produce colour are >C=C<, –N=O, –N=N–, >C=O and –NO2. Most importantly, the groups that invariably confer colour are the azo (–N=N–) and nitroso (–N=O) while the other groups actually do so under certain circumstances (Abrahart, 1977). Furthermore, azo dyes have been studied widely because of their excellent thermal and optical properties in applications such as optical recording medium (Samieh et al., 2008), toner (Kirkan and Gup, 2008), ink-jet printing and oil-soluble light fast dyes (Gregory, 1990). Recently, azo compounds as organic dyes have also attracted attention due to their interesting electronic features in photoconductors (Yildiz and Boztepe, 2002). However, the traditional application field of the synthetic azo dyes still remains the textile industry, and the finishing of fibrous materials. In recent years, several heterocyclic and non heterocyclic compounds are extensively used in azo dye chemistry for textile and non-textile applications (Katritzky and Rees, 1984). These dyes are now marketed to produce a full range of azo dyestuffs without the use of colorants based on hetero-aromatic diazo components. Most of the heterocyclic dyes are 2 derived from the diazo components consisting of five-membered rings containing one or more nitrogen heteroatoms, with the rings being fused into another aromatic ring (Griffiths et al., 1984; Towns, 1999; Samieh et al., 2008; Otutu et al., 2011).

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