Numford
Organic conversion

Ethanol to but-2-enal

2 steps: oxidation, then aldol condensation

Class 12, Chapter 7 Alcohols, Phenols and Ethers; Class 12, Chapter 8 Aldehydes, Ketones and Carboxylic Acids

  1. OH
    EthanolCH₃CH₂OHAlcohol
  2. Step 1

    PCC

    i

    Pyridinium chlorochromate stops at the aldehyde; stronger oxidants go on to the acid.

    Also written: Cu

    OH
    EthanalCH₃CHOAldehyde
  3. Step 2

    dilute NaOH, then heat

    Aldol condensation
    i

    Aldol condensation written as one step: addition followed by loss of water.

    OH
    But-2-enalCH₃CH=CHCHOAldehyde

Exam answer

  1. Step 1: Ethanol to ethanal: PCC.
  2. Step 2: Ethanal to but-2-enal: dilute NaOH, then heat.
Alternative routes (3)
  • Ethanol → Ethanal → 3-Hydroxybutanal → But-2-enal
    1. Ethanol to ethanal: PCC.
    2. Ethanal to 3-hydroxybutanal: dilute NaOH.
    3. 3-Hydroxybutanal to but-2-enal: heat.
  • Ethanol → Ethanoic acid → Ethanoyl chloride → Ethanal → But-2-enal
    1. Ethanol to ethanoic acid: KMnO₄, KOH, heat; then H₃O⁺.
    2. Ethanoic acid to ethanoyl chloride: SOCl₂.
    3. Ethanoyl chloride to ethanal: H₂, Pd/BaSO₄.
    4. Ethanal to but-2-enal: dilute NaOH, then heat.
  • Ethanol → Ethanoic acid → Ethyl ethanoate → Ethanal → But-2-enal
    1. Ethanol to ethanoic acid: KMnO₄, KOH, heat; then H₃O⁺.
    2. Ethanoic acid to ethyl ethanoate: CH₃CH₂OH, conc. H₂SO₄ (catalyst), heat.
    3. Ethyl ethanoate to ethanal: (i) DIBAL-H (ii) H₂O.
    4. Ethanal to but-2-enal: dilute NaOH, then heat.
Why these reagents

Reagent and reason, step by step

  • Step 1: Ethanol to ethanal: PCC Pyridinium chlorochromate stops at the aldehyde; stronger oxidants go on to the acid.
  • Step 2: Ethanal to but-2-enal: dilute NaOH, then heat Aldol condensation written as one step: addition followed by loss of water.
Questions

Ethanol to but-2-enal: quick answers

How many steps does it take to convert ethanol to but-2-enal?

2 steps: Ethanol, then ethanal, then but-2-enal.

Which named reaction is used to convert ethanol to but-2-enal?

Aldol condensation. Aldehydes and ketones with alpha hydrogen, in dilute alkali, form a beta-hydroxy aldehyde or ketone (aldol), which loses water on heating to give an alpha,beta-unsaturated carbonyl compound.

What is the reagent for step 1 of ethanol to but-2-enal?

Ethanol to ethanal: PCC. Pyridinium chlorochromate stops at the aldehyde; stronger oxidants go on to the acid.

Plan your own conversion