Final answer:
Amines can be prepared from halogenoalkanes through an SN2 reaction where the halogen is displaced by an amine group, often using excess ammonia and heating under reflux.
Step-by-step explanation:
Preparation of Amines from Halogenoalkanes
Amines can be prepared from halogenoalkanes through a nucleophilic substitution reaction, commonly known as an SN2 reaction. For example, ethyl bromide, a halogenoalkane, can react with ammonia or amine to form an amine product. In this process, the halide ion is displaced by an amine group. To explain further, the halogen (bromine in the case of ethyl bromide) is replaced with a nitrogen-containing group. This makes use of the alkyl halides that we can produce from alkenes via various methods mentioned, such as the addition of hydrogen halide or free radical reactions with halogens. This synthesis forms the basis for creating a wide range of amine compounds.
A typical reaction involves mixing the halogenoalkane with an excess of ammonia to ensure that the ammonia is the limiting reagent. The resulting mixture is heated under reflux in the presence of a solvent like ethanol. The reaction forms an amine and releases a halide salt as a by-product. For instance, when ammonia reacts with chloroethane, ethylamine and ammonium chloride are produced. This reaction can further continue if there are still reactive halogenoalkane molecules, leading to the formation of secondary and tertiary amines, as well as quaternary ammonium salts.