Question

What is the intermediate product obtained in the preparation of phenol from aniline?

• A. Sodium phenoxide
• B. Benzene diazonium chloride
• C. Anilinium cation
• D. Benzene

Answer 1

The Correct Option is B

Correct Answer: Option 2 - Benzene diazonium chloride
The preparation of phenol from aniline involves a two-step chemical process, and the key intermediate formed during this reaction is benzene diazonium chloride.

Step 1: Diazotization of Aniline
• In the first step, aniline (C₆H₅NH₂) is reacted with nitrous acid (HNO₂) in the presence of hydrochloric acid (HCl) at low temperatures (0–5°C).
• Nitrous acid is usually generated in situ by reacting sodium nitrite (NaNO₂) with dilute HCl.

The reaction is:
C₆H₅NH₂ + HNO₂ + HCl → C₆H₅N₂Cl + 2H₂O

• The compound formed here is benzene diazonium chloride, which is a stable intermediate only at low temperatures.

Step 2: Hydrolysis to form Phenol
• In the second step, this intermediate benzene diazonium chloride is heated with water (hydrolysis), often in the presence of dilute acids.
• This decomposes the diazonium salt and releases nitrogen gas (N₂), forming phenol (C₆H₅OH) as the final product.

The reaction is:
C₆H₅N₂Cl + H₂O → C₆H₅OH + N₂ + HCl

Conclusion:
The intermediate product formed during the conversion of aniline to phenol is benzene diazonium chloride. This compound plays a critical role in many substitution reactions in aromatic chemistry and is an essential intermediate in organic synthesis.