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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Our further investigations will be focused on the mechanism by which the HP-[beta]-CD played and the degradation of aromatic amines caused by azo dye reduction.
Kinetic characteristics of bacterial azo dye decolorization by Pseudomonas luteola.
coli has been reported in association with Pseudomonas aerugi nosa in the degradation of azo dyes (Isik and Sponza, 2003).
Degradation of azo dyes by environmental microorganisms and helminths, Environmental Toxicology and Chemistry 54: 435-41.
The first step in the synthesis of azo dyes is the conversion of amine compounds into diazonium salts.
They are: Erythrosin included in the class of xanthene dyes; Blue indigotine included in the indigotin class of dyes, Patent Blue V, Fast Green and Brilliant Blue in class of triphenylmethane dyes, Bordeaux Red, Ponceau 4R, Red 40, Azorubine, Tartrazine Yellow and Sunset Yellow, included in the class of azo dyes (POLONIO; PERES, 2009).
Khataee, "Photocatalytic degradation of azo dye acid red 14 in water on ZnO as an alternative catalyst to Ti[O.sub.2]," Journal of Photochemistry and Photobiology A: Chemistry, vol.
Decolorization and degradation of azo dye methyl red by an isolated Sphingomonas paucimobilis: biotoxicity and metabolites characterization.
An insight into the synergistic relationship between the fungi group and the bacteria group for azo dye wastewater treatment was given without artificial modification of any operational, environmental, and physiological conditions.
In general, during azo dye degradation initial reductive cleavage of the azo bonds takes place, with the help of azoreductase enzymes which results into the production of colorless solutions containing potentially hazardous-aromatic amines (Van der Zee and Villaverde, 2005) which are further degraded aerobically or anaerobically (Joshi et al., 2008).