Preparing Aliphatic Amines
Preparing Amines
- Primary amines can be prepared from different reactions including:
- The reaction of halogenoalkanes with ammonia
- 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
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 can be used to form a primary amine
Nitriles can be reduced with LiAlH4 or H2 and Ni catalyst
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
- Tertiary amines can also be formed by further reaction of the secondary amine
- In this example, further substitution would form triethylamine (CH3CH2)N