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Organic conversion

Benzaldehyde to benzoic acid

1 step: oxidation

Class 12, Chapter 8 Aldehydes, Ketones and Carboxylic Acids

  1. OH
    BenzaldehydeC₆H₅CHOAldehyde
  2. Step 1

    KMnO₄, KOH, heat; then H₃O⁺

    i

    A strong oxidant takes the aldehyde to the acid; Tollens reagent also works and shows a silver mirror.

    Also written: (i) conc. NaOH (ii) H₃O⁺; Tollens' reagent, [Ag(NH₃)₂]⁺

    OHO
    Benzoic acidC₆H₅COOHCarboxylic acid

Exam answer

  1. Step 1: Benzaldehyde to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
Alternative routes (3)
  • Benzaldehyde → Benzyl alcohol → Benzoic acid
    1. Benzaldehyde to benzyl alcohol: NaBH₄.
    2. Benzyl alcohol to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
  • Benzaldehyde → Toluene → Benzoic acid
    1. Benzaldehyde to toluene: Zn-Hg, conc. HCl.
    2. Toluene to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
  • Benzaldehyde → Toluene → Benzyl chloride → Benzyl alcohol → Benzoic acid
    1. Benzaldehyde to toluene: Zn-Hg, conc. HCl.
    2. Toluene to benzyl chloride: Cl₂, UV light (or heat).
    3. Benzyl chloride to benzyl alcohol: aq. NaOH.
    4. Benzyl alcohol to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺.
Why these reagents

Reagent and reason, step by step

  • Step 1: Benzaldehyde to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺ A strong oxidant takes the aldehyde to the acid; Tollens reagent also works and shows a silver mirror.
Questions

Benzaldehyde to benzoic acid: quick answers

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

1 step: Benzaldehyde, then benzoic acid.

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

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

What is the reagent for step 1 of benzaldehyde to benzoic acid?

Benzaldehyde to benzoic acid: KMnO₄, KOH, heat; then H₃O⁺. A strong oxidant takes the aldehyde to the acid; Tollens reagent also works and shows a silver mirror.

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