Producing Amines (CIE A Level Chemistry)

• Primary amines are organic compounds that have an -NH₂ functional group attached to an alkyl or aryl group
• Secondary amines have two alkyl or aryl groups attached to an -NH group

Structures of primary and secondary amines

A primary amine has one R-group attached to the nitrogen atom, while a secondary amine has two R-groups attached to the nitrogen atom

• Primary and secondary amines can be prepared from different reactions including:
  • The reaction of halogenoalkanes with ammonia
  • The reaction of halogenoalkanes with primary amines
  • The reduction of amides
  • The reduction of nitriles

Reaction of halogenoalkanes with ammonia

• This is a nucleophilic substitution reaction in which the nitrogen lone pair in ammonia acts as a nucleophile and replaces the halogen in the halogenoalkane
• When a halogenoalkane is reacted with excess, hot ethanolic ammonia under pressure a primary amine is formed

Formation of primary amine

Primary amines can be produced by a nucleophilic substitution of a halogenoalkane with an excess of ammonia

Reaction of halogenoalkanes with primary amine

• This is also a nucleophilic substitution reaction in which the nitrogen in the primary amine acts as a nucleophile and replaces the halogen in the halogenoalkane
• When a halogenoalkane is reacted with a primary amine in ethanol and heated in a sealed tube, under pressure a secondary amine is formed

 Formation of secondary amine

Secondary amines can be produced by a nucleophilic substitution of a halogenoalkane with a primary amine

Reduction of amides

• Amines can also be formed from the reduction of amides by LiAlH₄ in dry ether
• Whether a primary or secondary amine is formed depends on the nature of the amide

Formation of amines from amides

Amides can be reduced by LiAlH₄ to form amines

Reduction of nitriles

• Nitriles contain a -CN functional group which can be reduced to an -NH₂ group
• The nitrile vapour and hydrogen gas are passed over a nickel catalyst or LiAlH₄ in dry ether to form a primary amine

Formation of amines from nitriles

Nitriles can be reduced with LiAlH₄ or H₂ and Ni catalyst