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Organic conversion

Benzene to 2,4,6-tribromoaniline

3 steps: substitution, then reduction, then substitution

Class 11, Chapter 9 Hydrocarbons; Class 12, Chapter 9 Amines

  1. BenzeneC₆H₆Arene
  2. Step 1

    conc. HNO₃ + conc. H₂SO₄

    323 to 333 K

    i

    Nitration: the nitronium ion is the electrophile; keep below 333 K to avoid dinitration.

    O−N+O
    NitrobenzeneC₆H₅NO₂Nitro compound
  3. Step 2

    Sn + conc. HCl

    i

    Metal in acid reduces the nitro group; the amine comes out as its salt, so add NaOH at the end.

    Also written: Fe + HCl; H₂, Pd (in ethanol)

    NH2
    AnilineC₆H₅NH₂Amine
  4. Step 3

    Br₂ water

    i

    The NH₂ group is so activating that three bromines enter at once; a white precipitate forms.

    NH2BrBrBr
    2,4,6-TribromoanilineC₆H₂Br₃NH₂Amine

Exam answer

  1. Step 1: Benzene to nitrobenzene: conc. HNO₃ + conc. H₂SO₄, 323 to 333 K.
  2. Step 2: Nitrobenzene to aniline: Sn + conc. HCl.
  3. Step 3: Aniline to 2,4,6-tribromoaniline: Br₂ water.
Why these reagents

Reagent and reason, step by step

  • Step 1: Benzene to nitrobenzene: conc. HNO₃ + conc. H₂SO₄, 323 to 333 K Nitration: the nitronium ion is the electrophile; keep below 333 K to avoid dinitration.
  • Step 2: Nitrobenzene to aniline: Sn + conc. HCl Metal in acid reduces the nitro group; the amine comes out as its salt, so add NaOH at the end.
  • Step 3: Aniline to 2,4,6-tribromoaniline: Br₂ water The NH₂ group is so activating that three bromines enter at once; a white precipitate forms.
Questions

Benzene to 2,4,6-tribromoaniline: quick answers

How many steps does it take to convert benzene to 2,4,6-tribromoaniline?

3 steps: Benzene, then nitrobenzene, then aniline, then 2,4,6-tribromoaniline.

Which named reaction is used to convert benzene to 2,4,6-tribromoaniline?

None of the steps has a name. They are substitution and reduction and substitution, so write the reagent and the condition for each step.

What is the reagent for step 1 of benzene to 2,4,6-tribromoaniline?

Benzene to nitrobenzene: conc. HNO₃ + conc. H₂SO₄, 323 to 333 K. Nitration: the nitronium ion is the electrophile; keep below 333 K to avoid dinitration.

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