Azo compounds are ones containing the R-N≡N-R’ structure.
As a consequence of п-delocalization, aryl azo compounds have vivid colours, especially reds, oranges, and yellows. Therefore, they are used as dyes, and are commonly known as azo dyes.
Most azo-dye syntheses require careful cooling of the reaction mixtures but this is a simple preparation and one that can be carried out in a test tube on the bench in minutes.
Azo-Dyes – Risk assessment