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 ?
Decolonization of naphthalene-containing sulfonated azo dyes by Kerstersia sp.
(2012) noted a decrease in the removal efficiency from 98 to 67% by increasing the concentration of Acid Red 14 azo dye from 50 to 800 mg [L.sup.-1].
The rate law and rate of the reaction was established for the reactive azo dyes is represented as:
Wan, "The effect of substituent groups on the reductive degradation of azo dyes by zerovalent iron," Journal of Hazardous Materials, vol.
Similarly three types of structurally different four azo dyes Reactive Black 5, Reactive Blue BRS, Direct Blue and Disperse Yellow were used for enrichment of the medium to isolate bacteria.
The stability of textile azo dyes in soil and their impact in microbial phospholipid fatty acid profiles.
Degradation of azo dyes using low iron concentration of Fenton and Fenton-like system, Chemosphere 58(10): 1409.
Azo dyes are synthetic colours which help in creating dark shades of colours in food, and Labigne has revealed the Valrhona Signature range is free of this ingredient.
"These products are considered hazardous because they contain dangerous chemicals like phthalates and/or azo dyes," it said.
TEHRAN (FNA)- Azo dyes are widely used in color and textile industries due to their high mechanical and thermal stability and they are applied in pharmaceutics as drug carriers.