19.1 Primary amines

Ammonia acts as a nucleophile and replaces the halogen in a halogenoalkane. Heating under pressure in ethanol gives an amine and hydrogen halide, which can react further if ammonia is not in excess.

Use excess ammonia to favour the primary amine and note that detailed amine classification is outside AS scope. The carbon skeleton of the halogenoalkane is retained.

CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br. The second ammonia molecule accepts HBr formed in the substitution.

Ammonia is not simply added across a double bond, and the pressure/solvent conditions are part of the preparation.