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Amines

Amines from halogenoalkanes and ammonia

  • 3 things to know
  • Component 2

Overview

Why a large excess of ammonia is used, mechanism by which ammonia converts a halogenoalkane into an amine and why the reaction is carried out in a sealed tube.

What you need to know

Answer each one before you reveal it.

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Key term

State the reagent and conditions used to make a primary aliphatic amine from a halogenoalkane.

Key term

Write the equation for the reaction of bromoethane with excess ammonia.

Key term

Explain why a large excess of ammonia is used when an amine is made from a halogenoalkane

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State the reagent and conditions used to make a primary aliphatic amine from a halogenoalkane.

    Model answer

    The halogenoalkane is heated with a large excess of ammonia dissolved in ethanol, in a sealed tube.

  2. 2

    Write the equation for the reaction of bromoethane with excess ammonia.

    Model answer

    CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br.

  3. 3

    Explain why a large excess of ammonia is used.

    Model answer

    The amine produced is itself a nucleophile and attacks more halogenoalkane, so a large excess of ammonia makes it far more likely that a halogenoalkane molecule meets ammonia rather than the amine.

  4. 4

    Name the mechanism by which ammonia converts a halogenoalkane into an amine, and identify the nucleophile.

    Model answer

    It is nucleophilic substitution, and the ammonia molecule is the nucleophile through the lone pair on its nitrogen.

  5. 5

    Describe the part played by the second ammonia molecule when a halogenoalkane is converted into a primary amine.

    Model answer

    The first ammonia molecule bonds to the carbon to give an alkylammonium ion, and a second ammonia molecule then removes a proton from the nitrogen to release the free amine.

  6. 6

    Explain why the reaction is carried out in a sealed tube.

    Model answer

    Ammonia is a gas at room temperature and the mixture must be heated, so a sealed vessel is needed to keep the ammonia in contact with the halogenoalkane under pressure.

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