3) Formation of Primary Amines: Aliphatic.
1) Salt Formation: Ammonia has lone pair of electrons on nitrogen so ammonia acts as
nucleophile. Substitution reaction of haloalkane and ammonia, forming ammonium salt.
2) Amine Formation: Ammonium salt reacted with aqueous alkali forms primary amine.
Conditions: Ethanol is used as solvent to prevent substitution of haloalkane with water to
produce alcohols. Excess ammonia also used to reduce further substitution of amine group to
form secondary and tertiary amines, so ammonia acts as nucleophile- minimising a
disadvantage.
In exams just write ‘ethanolic NH3’.
However this method not suitable to make pure primary amine as contains lone pair of electrons
on nitrogen atom that can react further to form secondary amine- see below.
4) Formation of Secondary and Tertiary Amines: Aliphatic.
1) Salt Formation: Primary amine product reacted with haloalkane to form ammonium salt.
2) Amine Formation: Ammonium salt reacted with sodium hydroxide forms secondary amine.
Tertiary Amines: Tertiary amine formed by further reaction of secondary amine- tripropylamine
in this example.
5) Preparation of Aromatic Amines Reduction: Nitrobenzene
C6H5NO2 is heated under reflux with tin and HCl to form ammonium salt, phenylammonium
chloride. Salt then reacted with excess NaOH to produce phenylamine, C6H5NH2 and water.
Nitrobenzene reduced as tin and conc HCl are reducing agents.
In exams, just need to write tin and concentrated HCl as reagents. Remember 6[H] and 2H2O.
Need 2[H] for NH2 and 4[H] for the oxygen substituted out to make 2H2O.