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The color of the azo dyes is determined by the azo bonds and their associated chromophores and auxochromes. In general, the chemical structure of an azo dye is represented by a backbone, the auxochrome groups, the chromophoric groups and the solubilizing groups according to Figure 1. These are essential to give the color of the dye, with their shades of different intensities. The azo group may be bonded to benzene rings, naphthalenes, aromatic heterocycles or to enolizable aliphatic groups. There are other methods of synthesis of azo dyes among these are : reduction of nitroaromatic derivatives in alkaline medium, reduction of nitroso compounds by AlLiH 4, oxidation of primary amines by permanganate potassium or lead tetraacetate, condensation of hydrazines and quinones, condensation of primary amines with nitroso derivatives, etc. Most azo dyes are synthesized by diazotization of an aromatic primary amine, followed by coupling with one or more electron-rich nucleophiles such as amino and hydroxy. In addition, the distribution of dyes in water increased with the increase in the molecular weight of the azo dyes, probably caused by the increase in the molecular weight of the azo dyes in the form of increased azo bonds, resulting in a decrease in the rate degradation of azo dyes. Īzo dyes are the most important synthetic colorants which have been widely used in textile, printing, paper manufacturing, etc.Īs well as their harmful effects of azo dyes on humans and aquatic life, have aroused urgent calls for the treatment of effluents containing azo dyes to eliminate them or convert them into useful and safe products. These compounds are characterized by the functional group (-N=N-) uniting two symmetrical and/or asymmetrical identical or non-azo alkyl or aryl radicals. Approximately 70 % of all the dyes used in industry are azo dyes. Īzo dyes are the most used dyes and account for more than 60 % of total dyes.
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Different routes and modifications are made to obtain the desired color properties, yield and particle size of the dye for improved dispersibility. These dyes are synthesized from a simple method of diazotization and coupling. They play a crucial role in the governance of the dye and printing market. Azo dyes represent the largest production volume of dye chemistry today, and their relative importance may even increase in the future.