Numford
Organic conversion

Ethanol to butane

2 steps: substitution, then Wurtz reaction

Class 12, Chapter 6 Haloalkanes and Haloarenes; Class 11, Chapter 9 Hydrocarbons

  1. OH
    EthanolCH₃CH₂OHAlcohol
  2. Step 1

    red P + Br₂ (PBr₃)

    i

    Phosphorus tribromide formed in situ converts the alcohol to the bromide.

    Br
    BromoethaneCH₃CH₂BrHaloalkane
  3. Step 2

    Na, dry ether

    Wurtz reaction
    i

    Wurtz reaction doubles the alkyl group; only symmetrical alkanes are made cleanly.

    ButaneCH₃CH₂CH₂CH₃Alkane

Exam answer

  1. Step 1: Ethanol to bromoethane: red P + Br₂ (PBr₃).
  2. Step 2: Bromoethane to butane: Na, dry ether.
Alternative routes (4)
  • Ethanol → Ethene → Bromoethane → Butane
    1. Ethanol to ethene: conc. H₂SO₄, 443 K.
    2. Ethene to bromoethane: HBr.
    3. Bromoethane to butane: Na, dry ether.
  • Ethanol → Chloroethane → Ethene → Bromoethane → Butane
    1. Ethanol to chloroethane: SOCl₂.
    2. Chloroethane to ethene: alc. KOH, heat.
    3. Ethene to bromoethane: HBr.
    4. Bromoethane to butane: Na, dry ether.
  • Ethanol → Ethanal → Butan-2-ol → But-2-ene → Butane
    1. Ethanol to ethanal: PCC.
    2. Ethanal to butan-2-ol: (i) C₂H₅MgBr, dry ether (ii) H₂O.
    3. Butan-2-ol to but-2-ene: 85% H₃PO₄, 440 K.
    4. But-2-ene to butane: H₂, Ni (or Pt, Pd).
  • Ethanol → Ethanal → Butan-2-ol → Butanone → Butane
    1. Ethanol to ethanal: PCC.
    2. Ethanal to butan-2-ol: (i) C₂H₅MgBr, dry ether (ii) H₂O.
    3. Butan-2-ol to butanone: CrO₃.
    4. Butanone to butane: Zn-Hg, conc. HCl.
Why these reagents

Reagent and reason, step by step

  • Step 1: Ethanol to bromoethane: red P + Br₂ (PBr₃) Phosphorus tribromide formed in situ converts the alcohol to the bromide.
  • Step 2: Bromoethane to butane: Na, dry ether Wurtz reaction doubles the alkyl group; only symmetrical alkanes are made cleanly.
Questions

Ethanol to butane: quick answers

How many steps does it take to convert ethanol to butane?

2 steps: Ethanol, then bromoethane, then butane.

Which named reaction is used to convert ethanol to butane?

Wurtz reaction. Two molecules of an alkyl halide react with sodium in dry ether to give a higher alkane with double the carbon atoms of the alkyl group.

What is the reagent for step 1 of ethanol to butane?

Ethanol to bromoethane: red P + Br₂ (PBr₃). Phosphorus tribromide formed in situ converts the alcohol to the bromide.

Plan your own conversion