Numford
Organic conversion

Methanol to ethanoic acid

3 steps: substitution, then substitution, then hydrolysis

Class 12, Chapter 6 Haloalkanes and Haloarenes; Class 12, Chapter 8 Aldehydes, Ketones and Carboxylic Acids

  1. OH
    MethanolCH₃OHAlcohol
  2. Step 1

    SOCl₂

    i

    Thionyl chloride is preferred: the by-products SO₂ and HCl escape as gases, so the product is pure.

    Also written: HCl, anhydrous ZnCl₂

    Cl
    ChloromethaneCH₃ClHaloalkane
  3. Step 2

    KCN (alcoholic)

    i

    KCN attacks through carbon, so the nitrile has one more carbon than the halide.

    N
    EthanenitrileCH₃CNNitrile
  4. Step 3

    H₃O⁺, heat

    i

    Complete hydrolysis goes through the amide to the acid.

    OOH
    Ethanoic acidCH₃COOHCarboxylic acid

Exam answer

  1. Step 1: Methanol to chloromethane: SOCl₂.
  2. Step 2: Chloromethane to ethanenitrile: KCN (alcoholic).
  3. Step 3: Ethanenitrile to ethanoic acid: H₃O⁺, heat.
Alternative routes (4)
  • Methanol → Bromomethane → Ethanenitrile → Ethanoic acid
    1. Methanol to bromomethane: red P + Br₂ (PBr₃).
    2. Bromomethane to ethanenitrile: KCN (alcoholic).
    3. Ethanenitrile to ethanoic acid: H₃O⁺, heat.
  • Methanol → Bromomethane → Methylmagnesium bromide → Ethanoic acid
    1. Methanol to bromomethane: red P + Br₂ (PBr₃).
    2. Bromomethane to methylmagnesium bromide: Mg, dry ether.
    3. Methylmagnesium bromide to ethanoic acid: (i) CO₂ (dry ice), dry ether (ii) H₃O⁺.
  • Methanol → Iodomethane → Ethanenitrile → Ethanoic acid
    1. Methanol to iodomethane: red P + I₂ (PI₃).
    2. Iodomethane to ethanenitrile: KCN (alcoholic).
    3. Ethanenitrile to ethanoic acid: H₃O⁺, heat.
  • Methanol → Methanal → Ethanol → Ethanoic acid
    1. Methanol to methanal: Cu, 573 K.
    2. Methanal to ethanol: (i) CH₃MgBr, dry ether (ii) H₂O.
    3. Ethanol to ethanoic acid: KMnO₄, KOH, heat; then H₃O⁺.
Why these reagents

Reagent and reason, step by step

  • Step 1: Methanol to chloromethane: SOCl₂ Thionyl chloride is preferred: the by-products SO₂ and HCl escape as gases, so the product is pure.
  • Step 2: Chloromethane to ethanenitrile: KCN (alcoholic) KCN attacks through carbon, so the nitrile has one more carbon than the halide.
  • Step 3: Ethanenitrile to ethanoic acid: H₃O⁺, heat Complete hydrolysis goes through the amide to the acid.
Questions

Methanol to ethanoic acid: quick answers

How many steps does it take to convert methanol to ethanoic acid?

3 steps: Methanol, then chloromethane, then ethanenitrile, then ethanoic acid.

Which named reaction is used to convert methanol to ethanoic acid?

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

What is the reagent for step 1 of methanol to ethanoic acid?

Methanol to chloromethane: SOCl₂. Thionyl chloride is preferred: the by-products SO₂ and HCl escape as gases, so the product is pure.

Plan your own conversion