Historical Background, Literature Review on the Synthesis and Applicability of Azo-Dye Compounds: An Extensive Review

In this article, the detailed information was presented about azo-dyes, including a general description of this class of compounds, which included a historical overview, observations on the chemical structure of these compounds, particularly focusing on the azo group (-N=N-) responsible for their coloring properties. In addition, we provided a schematic of the first synthesized azo-compound. Furthermore, we mentioned the general properties of them and viewed a detailed explanation for the categorization of them either aliphatic or aromatic, subdivisions for each category or which category is the most widespread, and then illustrated the types for this class of organic compounds. The effective operator in these compounds called diazonium-salt was also explained in detail (reactions and formation methods of which). The generation approaches of these compounds were demonstrated either. The widely used diazotization and coupling approach for the generation of azo-dyes is demonstrated, along with a literature review of studies employing this method. Lastly, some important applications of azo-dyes were briefly discussed.