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Organic conversion

Aniline to chlorobenzene

2 steps: diazotisation, then Sandmeyer reaction

Class 12, Chapter 9 Amines

  1. NH2
    AnilineC₆H₅NH₂Amine
  2. Step 1

    NaNO₂ + HCl

    273 to 278 K

    Diazotisation
    i

    Diazotisation: keep at 273 to 278 K or the salt decomposes. The acid generates HNO₂ in situ.

    N+NCl−
    Benzene diazonium chlorideC₆H₅N₂⁺Cl⁻Diazonium salt
  3. Step 2

    Cu₂Cl₂, HCl

    Sandmeyer reaction
    i

    Sandmeyer reaction: cuprous chloride with HCl replaces N₂⁺ by Cl.

    Also written: Cu powder, HCl

    Cl
    ChlorobenzeneC₆H₅ClHaloarene

Exam answer

  1. Step 1: Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K.
  2. Step 2: Benzene diazonium chloride to chlorobenzene: Cu₂Cl₂, HCl.
Alternative routes (2)
  • Aniline → Benzene diazonium chloride → Benzene → Chlorobenzene
    1. Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K.
    2. Benzene diazonium chloride to benzene: H₃PO₂ + H₂O.
    3. Benzene to chlorobenzene: Cl₂, anhydrous FeCl₃.
  • Aniline → Benzene diazonium chloride → Phenol → Benzene → Chlorobenzene
    1. Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K.
    2. Benzene diazonium chloride to phenol: H₂O, warm.
    3. Phenol to benzene: Zn dust, heat.
    4. Benzene to chlorobenzene: Cl₂, anhydrous FeCl₃.
Why these reagents

Reagent and reason, step by step

  • Step 1: Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K Diazotisation: keep at 273 to 278 K or the salt decomposes. The acid generates HNO₂ in situ.
  • Step 2: Benzene diazonium chloride to chlorobenzene: Cu₂Cl₂, HCl Sandmeyer reaction: cuprous chloride with HCl replaces N₂⁺ by Cl.
Questions

Aniline to chlorobenzene: quick answers

How many steps does it take to convert aniline to chlorobenzene?

2 steps: Aniline, then benzene diazonium chloride, then chlorobenzene.

Which named reaction is used to convert aniline to chlorobenzene?

Diazotisation and Sandmeyer reaction. A primary aromatic amine reacts with nitrous acid (NaNO2 and HCl) at 273 to 278 K to give a diazonium salt.

What is the reagent for step 1 of aniline to chlorobenzene?

Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K. Diazotisation: keep at 273 to 278 K or the salt decomposes. The acid generates HNO₂ in situ.

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