Question

Identify 'C' in the following reaction sequence: C₆H₅NO₂ Sn/HCl A [273K]NaNO₂/HCl B [283K]H₂O C

• A. C₆H₅CHO
• B. C₆H₅OH
• C. C₆H₅NH₂
• D. C₆H₅CH₂OH

Hint:

Benzene diazonium chloride is a versatile intermediate. You can also convert it to: - Chlorobenzene using CuCl/HCl (Sandmeyer reaction). - Benzene using H₃PO₂ or Ethanol. - Iodobenzene using KI.

Answer 1

The Correct Option is B

Concept: This sequence represents the conversion of nitrobenzene into phenol through the formation of a diazonium salt. Key reaction steps: • Reduction of Nitro compounds: Conversion of -NO₂ to -NH₂. • Diazotization: Formation of benzene diazonium chloride from aniline. • Hydrolysis of Diazonium salts: Replacement of the diazonium group with a hydroxyl group.
Nitrobenzene (C₆H₅NO₂) is reduced by Tin and concentrated Hydrochloric acid (Sn/HCl). This is a standard method to prepare primary aromatic amines. C₆H₅NO₂ + 6[H] Sn/HCl C₆H₅NH₂ + 2H₂O Thus, 'A' is Aniline.
Aniline reacts with nitrous acid (prepared in situ from NaNO₂ and HCl) at a low temperature (0-5C or 273K). This process is called diazotization. C₆H₅NH₂ NaNO₂ + HCl, 273K C₆H₅N₂^+Cl^- Thus, 'B' is Benzene diazonium chloride.
When the aqueous solution of benzene diazonium chloride is warmed to about 283K (room temperature or slightly above), it undergoes hydrolysis to form phenol and evolves nitrogen gas. C₆H₅N₂Cl + H₂O 283K C₆H₅OH + N₂ + HCl Thus, 'C' is Phenol (C₆H₅OH).