Making amines from
halogenoalkanes
The halogenoalkane is
heated with a concentrated solution of ammonia in ethanol. The reaction is
carried out in a sealed tube. You couldn't heat this mixture under reflux,
because the ammonia would simply escape up the condenser as a gas
.
We'll talk about the
reaction using 1-bromoethane as a typical halogenoalkane.
You get a mixture of
amines formed together with their salts. The reactions happen one after
another.
Making a primary amine
The reaction happens in
two stages. In the first stage, a salt is formed - in this case, ethylammonium bromide.
This is just like ammonium bromide, except that one of the hydrogens in the
ammonium ion is replaced by an ethyl group.
There is then the
possibility of a reversible reaction between this salt and excess ammonia in
the mixture.
The ammonia removes a
hydrogen ion from the ethylammonium ion to leave a primary amine - ethylamine.
The more ammonia there is
in the mixture, the more the forward reaction is favoured.
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