Azo Dyes


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azo dyes

[′a·zō ‚dīz]
(organic chemistry)
Widely used commercial dyestuffs derived from amino compounds, with the ‒N‒ chromophore group; can be made as acid, basic, direct, or mordant dyes.

Azo Dyes

 

organic dyes whose molecules contain one or several azo groups—N=N—which connect aromatic radicals. Depending on the number of such groups, the dyes are called mono-, dis-, tris-, or polyazo dyes. Usually, azo dyes contain substituted or unsubstituted NH2 and OH groups in

the aromatic nucleus and also NO2, CI, SOH3H, COOH, and others. The presence of acid groups ensures the water solubility of the dyes.

Synthesis of azo dyes is achieved by combining aromatic diazo compounds ArN2Cl with phenols, aromatic amines, and their derivatives. For example, see above.

Usually, a dye is precipitated from a sodium chloride solution, dried, and then pulverized.

The simplest monoazo dyes are usually yellow, orange, or red in color. An increase in the number of azo groups, a substitution of phenyl radicals with naphthyl radicals, and an increase in the number of oxy- and amino- groups will intensify the color. Depending on their structure and the character of their interaction with textiles, azo dyes are divided into several groups: basic, acid, direct, mordant, ice-color, active, and others. Basic dyes contain NH2 groups; acid dyes, usually one or several sulfo groups. The latter are used in dyeing silk and wool. Large amounts of direct azo dyes are produced for use in coloring cotton fabrics; usually these are polyazo dyes based on benzidine and α-naphthylamine and its sulfo acids. With Fe3+, Cr3+, and other ions, mordant azo dyes form insoluble complexes on the fiber which are well retained. The formation of dye-fiber chemical bonds is characteristic of the active azo dyes. These azo dyes, in production since 1952, not only afford beautiful tints but also are outstanding in their resistance to water and other processing agents. Ice colors are obtained directly on fabrics. Some azo dyes in a fine-dispersion state are used in polygraphy and the paint and varnish industry. Azo dyes are used mainly for coloring textiles but also for coloring leather, paper, rubber, and certain plastics.

REFERENCES

Chekalin, M. A. Khimiia i tekhnologiia organicheskikh krasitelei. Moscow, 1956.
Chekalin, M. A., B. V. Passet, and B. A. Ioffe. Tekhnologiia organicheskikh krasitelei i promezhutochnykh produktov. Leningrad, 1972.
References in periodicals archive ?
Azo dye biodegradation by Microbial cultures immobilized in alginate beads.
Reduction of azo bonds in anaerobic condition is the first step in the breakdown of azo dyes, forming aromatic amines (Pandey et al.
Chang et al, (27) reported decolorization of azo dyes using the azo reductase genes of a wild strain of Pseudomonas luteola.
The first step in the synthesis of azo dyes is the conversion of amine compounds into diazonium salts.
2004), have been used to carry out putative enzymatic biodegradation and consequent decolorization of different azo dyes.
2012), this situation is worrying, as this author states that almost all foods consumed by Brazilians currently consist of azo dyes, with emphasis on Tartrazine, Ponceau 4R and Red 40 dyes.
Australian retailers issued recalls because they found out a small number of azo dyes are harmful when there is prolonged and direct contact to the skin.
Modernising the rules on food additives and labelling of azo dyes [Web page].
Azo dyes are synthetic dyestuffs which contain the azoic group in their chemical structure and are commonly used in textiles.
Azo dyes represent the largest class of commercially produced dyes, in which the chromophores are the azo group (Sutherland, 2004; Wallace, 2001).
Aviyente, Modeling the Substituent Effect on the Oxidative Degradation of Azo Dyes, J.