Coupling reaction (azo dye)
Benzene diazonium chloride reacts with phenol or an aromatic amine at the para position to give a coloured azo compound.
Benzene diazonium chlorideC₆H₅N₂⁺Cl⁻Diazonium salt - Step 1
phenol, NaOH (OH⁻), 273 to 278 K
p-HydroxyazobenzeneC₆H₅N=NC₆H₄OHCompound
How it works
- The diazonium ion is a weak electrophile.
- It attacks the activated para position of phenol or aniline.
- The azo compound (-N=N⁻) forms, an orange or yellow dye.
What it makes
p-Hydroxyazobenzene from phenol and p-aminoazobenzene from aniline.
Where it fails
The coupling partner must carry a strongly activating group (OH or NH2).
Class 12, Chapter 9 Amines
Coupling reaction (azo dye): quick answers
Where does coupling occur?
At the para position of the phenol or aniline.
What is the product with phenol?
p-Hydroxyazobenzene.
What are azo compounds used for?
As dyes.