Numford
Organic conversion

Ethanamine to methanamine

4 steps: substitution, then oxidation, then condensation, then Hoffmann bromamide degradation

Class 12, Chapter 9 Amines; Class 12, Chapter 7 Alcohols, Phenols and Ethers; Class 12, Chapter 8 Aldehydes, Ketones and Carboxylic Acids

  1. NH2
    EthanamineCH₃CH₂NH₂Amine
  2. Step 1

    NaNO₂ + HCl

    273 to 278 K

    i

    Aliphatic primary amines give an unstable diazonium salt that is hydrolysed at once to the alcohol, with N₂.

    OH
    EthanolCH₃CH₂OHAlcohol
  3. Step 2

    KMnO₄, KOH, heat; then H₃O⁺

    i

    Alkaline KMnO₄ oxidises a primary alcohol all the way to the acid.

    Also written: K₂Cr₂O₇, H₂SO₄

    OOH
    Ethanoic acidCH₃COOHCarboxylic acid
  4. Step 3

    NH₃, then heat

    i

    The acid first forms ammonium ethanoate, which loses water on heating.

    OH2N
    EthanamideCH₃CONH₂Amide
  5. Step 4

    Br₂ + NaOH(aq)

    Hoffmann bromamide degradation
    i

    Hoffmann bromamide degradation: the amine has one carbon less than the amide.

    NH2
    MethanamineCH₃NH₂Amine

Exam answer

  1. Step 1: Ethanamine to ethanol: NaNO₂ + HCl, 273 to 278 K.
  2. Step 2: Ethanol to ethanoic acid: KMnO₄, KOH, heat; then H₃O⁺.
  3. Step 3: Ethanoic acid to ethanamide: NH₃, then heat.
  4. Step 4: Ethanamide to methanamine: Br₂ + NaOH(aq).
Why these reagents

Reagent and reason, step by step

  • Step 1: Ethanamine to ethanol: NaNO₂ + HCl, 273 to 278 K Aliphatic primary amines give an unstable diazonium salt that is hydrolysed at once to the alcohol, with N₂.
  • Step 2: Ethanol to ethanoic acid: KMnO₄, KOH, heat; then H₃O⁺ Alkaline KMnO₄ oxidises a primary alcohol all the way to the acid.
  • Step 3: Ethanoic acid to ethanamide: NH₃, then heat The acid first forms ammonium ethanoate, which loses water on heating.
  • Step 4: Ethanamide to methanamine: Br₂ + NaOH(aq) Hoffmann bromamide degradation: the amine has one carbon less than the amide.
Questions

Ethanamine to methanamine: quick answers

How many steps does it take to convert ethanamine to methanamine?

4 steps: Ethanamine, then ethanol, then ethanoic acid, then ethanamide, then methanamine.

Which named reaction is used to convert ethanamine to methanamine?

Hoffmann bromamide degradation. An amide treated with bromine and aqueous or alcoholic NaOH gives a primary amine with one carbon atom fewer.

What is the reagent for step 1 of ethanamine to methanamine?

Ethanamine to ethanol: NaNO₂ + HCl, 273 to 278 K. Aliphatic primary amines give an unstable diazonium salt that is hydrolysed at once to the alcohol, with N₂.

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