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Organic conversion

Benzaldehyde to benzophenone

2 steps: addition, then oxidation

Class 12, Chapter 8 Aldehydes, Ketones and Carboxylic Acids

  1. OH
    BenzaldehydeC₆H₅CHOAldehyde
  2. Step 1

    (i) C₆H₅MgBr, dry ether (ii) H₂O

    i

    Grignard reagent plus an aromatic aldehyde gives a secondary alcohol.

    HO
    Benzhydrol(C₆H₅)₂CHOHAlcohol
  3. Step 2

    CrO₃

    i

    A secondary alcohol is oxidised to the ketone.

    O
    BenzophenoneC₆H₅COC₆H₅Ketone

Exam answer

  1. Step 1: Benzaldehyde to benzhydrol: (i) C₆H₅MgBr, dry ether (ii) H₂O.
  2. Step 2: Benzhydrol to benzophenone: CrO₃.
Alternative routes (4)
  • Benzaldehyde → Benzoic acid → Benzoyl chloride → Benzophenone
    1. Benzaldehyde to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
    2. Benzoic acid to benzoyl chloride: SOCl₂.
    3. Benzoyl chloride to benzophenone: benzene, anhydrous AlCl₃.
  • Benzaldehyde → Benzyl alcohol → Benzoic acid → Benzoyl chloride → Benzophenone
    1. Benzaldehyde to benzyl alcohol: NaBH₄.
    2. Benzyl alcohol to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
    3. Benzoic acid to benzoyl chloride: SOCl₂.
    4. Benzoyl chloride to benzophenone: benzene, anhydrous AlCl₃.
  • Benzaldehyde → Benzoic acid → Sodium benzoate → Benzene → Benzophenone
    1. Benzaldehyde to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
    2. Benzoic acid to sodium benzoate: NaOH.
    3. Sodium benzoate to benzene: NaOH + CaO (soda lime), heat.
    4. Benzene to benzophenone: C₆H₅COCl, anhydrous AlCl₃.
  • Benzaldehyde → Toluene → Benzoic acid → Benzoyl chloride → Benzophenone
    1. Benzaldehyde to toluene: Zn-Hg, conc. HCl.
    2. Toluene to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
    3. Benzoic acid to benzoyl chloride: SOCl₂.
    4. Benzoyl chloride to benzophenone: benzene, anhydrous AlCl₃.
Why these reagents

Reagent and reason, step by step

  • Step 1: Benzaldehyde to benzhydrol: (i) C₆H₅MgBr, dry ether (ii) H₂O Grignard reagent plus an aromatic aldehyde gives a secondary alcohol.
  • Step 2: Benzhydrol to benzophenone: CrO₃ A secondary alcohol is oxidised to the ketone.
Questions

Benzaldehyde to benzophenone: quick answers

How many steps does it take to convert benzaldehyde to benzophenone?

2 steps: Benzaldehyde, then benzhydrol, then benzophenone.

Which named reaction is used to convert benzaldehyde to benzophenone?

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

What is the reagent for step 1 of benzaldehyde to benzophenone?

Benzaldehyde to benzhydrol: (i) C₆H₅MgBr, dry ether (ii) H₂O. Grignard reagent plus an aromatic aldehyde gives a secondary alcohol.

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