chrysoidine

Chrysoidine is a yellow crystalline base with the chemical formula C₆H₅N=NC₆H₃(NH₂)₂. It is synthesized by diazotizing aniline and reacting it with meta-phenylenediamine. A common form, chrysoidine hydrochloride, is reddish-brown and used as a biological stain and for dyeing leather and paper.1

Chrysoidine was the first azo dye developed for wool, in use since 1875. Azo dyes, characterized by a -N=N- unit, are a significant class of synthetic dyes produced through the reaction of aryldiazonium ions with phenols or aryl amines. This process, discovered in the mid-19th century, became crucial for the synthetic dye industry, offering a wide range of colors and good fastness properties.2