Numford
Organic conversion

Aniline to benzoic acid

3 steps: diazotisation, then Sandmeyer reaction, then hydrolysis

Class 12, Chapter 9 Amines; Class 12, Chapter 8 Aldehydes, Ketones and Carboxylic Acids

  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

    CuCN, KCN

    Sandmeyer reaction
    i

    Sandmeyer reaction: cuprous cyanide replaces N₂⁺ by CN, adding a carbon.

    N
    BenzonitrileC₆H₅CNNitrile
  4. Step 3

    H₃O⁺, heat

    i

    Complete hydrolysis goes through the amide to the acid.

    OHO
    Benzoic acidC₆H₅COOHCarboxylic acid

Exam answer

  1. Step 1: Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K.
  2. Step 2: Benzene diazonium chloride to benzonitrile: CuCN, KCN.
  3. Step 3: Benzonitrile to benzoic acid: H₃O⁺, heat.
Alternative routes (4)
  • Aniline → Benzene diazonium chloride → Chlorobenzene → Toluene → Benzoic acid
    1. Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K.
    2. Benzene diazonium chloride to chlorobenzene: Cu₂Cl₂, HCl.
    3. Chlorobenzene to toluene: CH₃Cl, Na, dry ether.
    4. Toluene to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
  • Aniline → Benzene diazonium chloride → Bromobenzene → Phenylmagnesium bromide → Benzoic acid
    1. Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K.
    2. Benzene diazonium chloride to bromobenzene: Cu₂Br₂, HBr.
    3. Bromobenzene to phenylmagnesium bromide: Mg, dry ether.
    4. Phenylmagnesium bromide to benzoic acid: (i) CO₂ (dry ice), dry ether (ii) H₃O⁺.
  • Aniline → Benzene diazonium chloride → Bromobenzene → Toluene → Benzoic acid
    1. Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K.
    2. Benzene diazonium chloride to bromobenzene: Cu₂Br₂, HBr.
    3. Bromobenzene to toluene: CH₃Br, Na, dry ether.
    4. Toluene to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
  • Aniline → Benzene diazonium chloride → Benzonitrile → Benzaldehyde → Benzoic acid
    1. Aniline to benzene diazonium chloride: NaNO₂ + HCl, 273 to 278 K.
    2. Benzene diazonium chloride to benzonitrile: CuCN, KCN.
    3. Benzonitrile to benzaldehyde: (i) SnCl₂ + HCl (ii) H₃O⁺.
    4. Benzaldehyde to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
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 benzonitrile: CuCN, KCN Sandmeyer reaction: cuprous cyanide replaces N₂⁺ by CN, adding a carbon.
  • Step 3: Benzonitrile to benzoic acid: H₃O⁺, heat Complete hydrolysis goes through the amide to the acid.
Questions

Aniline to benzoic acid: quick answers

How many steps does it take to convert aniline to benzoic acid?

3 steps: Aniline, then benzene diazonium chloride, then benzonitrile, then benzoic acid.

Which named reaction is used to convert aniline to benzoic acid?

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 benzoic acid?

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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