How to convert Aniline to nitrobenzene?

To convert aniline (C₆H₅NH₂) into nitrobenzene (C₆H₅NO₂), you cannot directly nitrate aniline because the –NH₂ group is strongly activating and reacts violently with concentrated nitric acid, giving unwanted oxidation products (like tar).

So, the conversion is done in two main steps:

Step 1: Protect the –NH₂ group (Acetylation)

• Aniline is first treated with acetic anhydride (CH₃CO)₂O or acetyl chloride (CH₃COCl).
• This converts –NH₂ into acetamide (–NHCOCH₃), forming acetanilide.
• This protection reduces the reactivity of the amino group and prevents side reactions.

Reaction: C₆H₅NH₂ + (CH₃CO)₂O → C₆H₅NHCOCH₃ (Acetanilide)

Step 2: Nitration of Acetanilide

• Acetanilide is then nitrated using conc. HNO₃ + conc. H₂SO₄ (nitrating mixture).
• A nitro group (–NO₂) enters the aromatic ring, mainly at the para position (major product).

Reaction: C₆H₅NHCOCH₃ → (Conc. HNO₃/H₂SO₄) → p-Nitroacetanilide

Step 3: Hydrolysis

• The nitroacetanilide is then hydrolyzed using acid or base.
• This removes the acetyl (–COCH₃) group and regenerates the –NH₂ group, giving p-nitroaniline.

Reaction:

p-Nitroacetanilide + H₂O/H⁺ → p-Nitroaniline

Instead of hydrolyzing, you would need to oxidize the –NH₂ group of aniline strongly, which replaces the amino group with nitro.

That is achieved by using Oxidation with peracids (e.g., Caro’s acid H₂SO₅) or Sandmeyer Reaction steps:

• Diazotization of Aniline: C₆H₅NH₂ + NaNO₂ + HCl (0–5 °C) → C₆H₅N₂⁺Cl⁻ (benzene diazonium chloride)
• Replacement with –NO₂ (via Sandmeyer type reaction): Treat with CuNO₂/HNO₂, replacing –N₂⁺ with –NO₂, forming Nitrobenzene.

Final Answer: Aniline → (NaNO₂/HCl, 0–5 °C) → Benzene diazonium chloride → (CuNO₂/HNO₂) → Nitrobenzene