Numford
Organic conversion

Benzene to m-bromophenol

4 steps: substitution, then 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

    Br₂, anhydrous FeBr₃, heat

    i

    The nitro group is meta directing, so bromination must come after nitration to reach the meta isomer.

    O−N+OBr
    m-Bromonitrobenzenem-BrC₆H₄NO₂Nitro compound
  4. Step 3

    Sn + conc. HCl

    i

    Metal in acid reduces the nitro group; the bromine is not touched.

    NH2Br
    m-Bromoanilinem-BrC₆H₄NH₂Amine
  5. Step 4

    (i) NaNO₂ + HCl, 273 to 278 K (ii) H₂O, warm

    i

    Diazotisation then warming with water, written as one step; the diazonium salt is not isolated.

    OHBr
    m-Bromophenolm-BrC₆H₄OHPhenol

Exam answer

  1. Step 1: Benzene to nitrobenzene: conc. HNO₃ + conc. H₂SO₄, 323 to 333 K.
  2. Step 2: Nitrobenzene to m-bromonitrobenzene: Br₂, anhydrous FeBr₃, heat.
  3. Step 3: m-bromonitrobenzene to m-bromoaniline: Sn + conc. HCl.
  4. Step 4: m-bromoaniline to m-bromophenol: (i) NaNO₂ + HCl, 273 to 278 K (ii) H₂O, warm.
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 m-bromonitrobenzene: Br₂, anhydrous FeBr₃, heat The nitro group is meta directing, so bromination must come after nitration to reach the meta isomer.
  • Step 3: m-Bromonitrobenzene to m-bromoaniline: Sn + conc. HCl Metal in acid reduces the nitro group; the bromine is not touched.
  • Step 4: m-Bromoaniline to m-bromophenol: (i) NaNO₂ + HCl, 273 to 278 K (ii) H₂O, warm Diazotisation then warming with water, written as one step; the diazonium salt is not isolated.
Good to know

Points to note

  • Step 3Metal in acid reduces the nitro group; the bromine is not touched.
  • Step 4Diazotisation then warming with water, written as one step; the diazonium salt is not isolated.
Questions

Benzene to m-bromophenol: quick answers

How many steps does it take to convert benzene to m-bromophenol?

4 steps: Benzene, then nitrobenzene, then m-bromonitrobenzene, then m-bromoaniline, then m-bromophenol.

Which named reaction is used to convert benzene to m-bromophenol?

None of the steps has a name. They are substitution and 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 m-bromophenol?

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.

Plan your own conversion