Which position of phenol is involved in coupling reaction with benzene diazonium chloride?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → para
In the coupling reaction with benzene diazonium chloride, phenol reacts at the para position (or ortho if para is blocked) to form p-hydroxyazobenzene (an orange dye), due to the hydroxyl group activating the ring and directing electrophilic attack to the electron-rich para and ortho positions, with para being preferred for steric reasons.
Key Details:
- Position: The coupling typically occurs at the para position of the phenol ring, relative to the hydroxyl (-OH) group.
- Mechanism: This is an electrophilic aromatic substitution (EAS) reaction where the diazonium ion (\(C_{6}H_{5}N_{2}^{+}\)) acts as the electrophile, attacking the activated phenol ring.
- Conditions: The reaction is usually performed in a weakly alkaline (basic) medium (like NaOH) at low temperatures (0-5°C).
- Product: The resulting product is p-hydroxyazobenzene, a red-orange dye.