Why is it difficult topreparepure amines by Hofmann’s ammonolysis?

Explanation

(i) Ammonolysis of alkyl involves the action of ammonia on alkyl halides. Ammonia with its lone pair of electrons acts as a nucleophile and attack the alkyl halide to give a primary amine. As this primary amine also contains a lone pair of electron it further attacks another molecular of alkyl halide to give a secondary amine. This process goes on till the formation of a quaternary ammonium salt takes place. The process stops here as the nitrogen atom in this salt as it does not have a lone pair of electrons.
`underset("Alkyl halide")(RX)underset(-HX)overset(overset(..)NH_(3))rarrunderset(1^(@)"Amine")(Roverset(..)NH_(2))underset(-HX)overset(RX)rarrunderset(2^(@)"Amine")(Roverset(..)NH)underset(-HX)overset(RX)rarrunderset(3^(@)"Amine")(R_(3)overset(..)N)overset(RX)rarrundersetunderset("ammonium salt")("Quaternary")([R_(4)N]^(+)X^(-))`
The separation of this mixture of amines is very difficult. Therefore, it is difficult to prepare pure amines by ammonolysis of alkyl halides.