Numford
Organic conversion

Methanol to ethanol

2 steps: oxidation, then addition

Class 12, Chapter 7 Alcohols, Phenols and Ethers

  1. OH
    MethanolCH₃OHAlcohol
  2. Step 1

    Cu

    573 K

    i

    Dehydrogenation of the vapour over copper; this stops at the aldehyde.

    Also written: PCC

    OHH
    MethanalHCHOAldehyde
  3. Step 2

    (i) CH₃MgBr, dry ether (ii) H₂O

    i

    Grignard reagent plus methanal gives a primary alcohol with one more carbon.

    OH
    EthanolCH₃CH₂OHAlcohol

Exam answer

  1. Step 1: Methanol to methanal: Cu, 573 K.
  2. Step 2: Methanal to ethanol: (i) CH₃MgBr, dry ether (ii) H₂O.
Alternative routes (4)
  • Methanol → Chloromethane → Ethanenitrile → Ethanal → Ethanol
    1. Methanol to chloromethane: SOCl₂.
    2. Chloromethane to ethanenitrile: KCN (alcoholic).
    3. Ethanenitrile to ethanal: (i) SnCl₂ + HCl (ii) H₃O⁺.
    4. Ethanal to ethanol: NaBH₄.
  • Methanol → Chloromethane → Ethanenitrile → Ethanoic acid → Ethanol
    1. Methanol to chloromethane: SOCl₂.
    2. Chloromethane to ethanenitrile: KCN (alcoholic).
    3. Ethanenitrile to ethanoic acid: H₃O⁺, heat.
    4. Ethanoic acid to ethanol: (i) LiAlH₄ (ii) H₃O⁺.
  • Methanol → Chloromethane → Ethanenitrile → Ethanamine → Ethanol
    1. Methanol to chloromethane: SOCl₂.
    2. Chloromethane to ethanenitrile: KCN (alcoholic).
    3. Ethanenitrile to ethanamine: H₂, Ni (or LiAlH₄, then H₂O).
    4. Ethanamine to ethanol: NaNO₂ + HCl, 273 to 278 K.
  • Methanol → Bromomethane → Ethane → Chloroethane → Ethanol
    1. Methanol to bromomethane: red P + Br₂ (PBr₃).
    2. Bromomethane to ethane: Na, dry ether.
    3. Ethane to chloroethane: Cl₂, UV light.
    4. Chloroethane to ethanol: aq. NaOH (or aq. KOH).
Why these reagents

Reagent and reason, step by step

  • Step 1: Methanol to methanal: Cu, 573 K Dehydrogenation of the vapour over copper; this stops at the aldehyde.
  • Step 2: Methanal to ethanol: (i) CH₃MgBr, dry ether (ii) H₂O Grignard reagent plus methanal gives a primary alcohol with one more carbon.
Questions

Methanol to ethanol: quick answers

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

2 steps: Methanol, then methanal, then ethanol.

Which named reaction is used to convert methanol to ethanol?

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

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

Methanol to methanal: Cu, 573 K. Dehydrogenation of the vapour over copper; this stops at the aldehyde.

Plan your own conversion