• The lone pair on the nitrogen atom in amines makes them good?nucleophiles, just like ammonia
• When ammonia reacts with a haloalkane a nucleophilic substitution reaction takes place forming a primary amine
• For example chloromethane reacts with ammonia in two steps to make methylamine and ammonium chloride

CH3Cl?+ NH3?→?[CH3NH3]+Cl?-

[CH3NH3]+Cl?-?+ NH3?→ CH3NH2?+ NH4+Cl?-

• The methylamine is also a good nucleophile so can undergo further substitution with chloromethane to make dimethylamine

CH3Cl? ?+ CH3NH2?→?[(CH3)2NH2]+Cl?-

[(CH3)2NH2]+Cl?-?+ NH3?→?(CH3)2NH?+?NH4+Cl?-

• The dimethylamine can further substitute giving a tertiary amine, trimethylamine

CH3Cl?+?(CH3)2NH?→?[(CH3)3NH]+Cl?-

[(CH3)3NH]+Cl?-?+ NH3?→?(CH3)3N?+?NH4+Cl?-

• The final substitution occurs when the tertiary amine reacts with the chloromethane to make a quaternary ammonium salt

CH3Cl?+?(CH3)3N?→?[(CH3)4N]+Cl?-

• Since all these multiple substitutions occur it is not a very efficient way to synthesise amines
• If you want to just produce the primary amine then a large excess of ammonia is used to ensure it is the dominant nucleophile in the reaction vessel

Mechanism of nucleophilic substitution

The mechanism of nucleophilic substitution between ammonia and a halogenoalkane

• In the first step the ammonia acts as a?nucleophile?and in the second step it acts as a?base