Azo Coupling
Azo Coupling: An aryl diazonium salt reacts with an activated aromatic ring to form an azo compound. Step-by-step mechanism, reagents and practice.
What happens
An aryl diazonium salt reacts with an activated aromatic ring to form an azo compound. This is an electrophilic aromatic substitution that makes a new C–N bond and a new –N=N– group. Azo compounds often have strong colors because the –N=N– group connects conjugated aromatic systems, which is why azo chemistry is especially important in dyes and pigments.
Reaction summary
Aryl diazonium salt + activated aromatic ring → azo compound (new –N=N– group, new C–N bond)
Reagents and conditions
- Starting material: Benzenediazonium (aryl diazonium salt)
- Reagents: Phenol (activated aromatic ring)
- Products: 4-Hydroxyazobenzene (azo compound)
Memory trick
AZO = N=N bridge.