Many synthetic dyes, often called diazo dyes, are based on diazonium chemistry that has been used for over 100 years in synthetic chemistry, and this experiment is an example of the synthesis of one such dye, 1-phenylazo-2-naphthol or more simply Sudan I.
The reaction involves two steps, the first being the preparation of a solution of the diazonium salt, benzenediazonium chloride, 2, from aniline, In the second step, the solution of 2 is added to 2-naphthol, to produce the diazo dye,