Products
Azo dyes are available as pure substances in specialized trade. The first representatives were synthesized in the 19th century. Today, they are among the most important dyes worldwide.
Structure and properties
Azo dyes contain the following general structural element and chromophore, which is called an azo group or azo bridge. R1 and R2 are substituted aromatics and may be identical or different: R1-N=N-R2 The substances are prepared synthetically. The term is derived from, French for nitrogen (N).
Substances
Approved azo dyes include (selection):
- Allura red (E 129) – red
- Amaranth (E 123) – red
- Azorubin (E 122) – red
- Brilliant black BN (E 151) – black
- Brown HT (E 155) – reddish brown
- Cochineal red A (Ponceau 4R, E 124) – red
- Yellow orange S (E 110) – orange
- Litholrubin BK (E 180) – magenta
- Tartrazine (E 102) – yellow
Fields of application
As colorants for food, sweets, beverages, cosmetics and pharmaceuticals. This article does not apply to technical applications (eg textiles).
Undesirable effects
Azo dyes are controversial. They can cause pseudoallergic reactions (intolerance reactions) in sensitive individuals. Azo dyes have also been linked to the attention-deficit/hyperactivity disorder ADHD. In the EU, foods containing some azo dyes have been required to carry the warning “May impair activity and attention in children” since 2010. In many countries, such labeling is not yet required. The connection is not certain. Finally, some azo compounds are known to have carcinogenic properties. However, authorities classify the approved azo dyes as safe.