Reacting halogenoalkanes with ammonia and amines

Aliphatic amines can be produced by reacting a halogenoalkane with ammonia, primary amines, or secondary amines in a nucleophilic substitution reaction.

1. Reaction with ammonia to form primary amines: Primary aliphatic amines can be produced by heating a halogenoalkane with excess ethanolic ammonia.

For example, bromoethane reacts with ammonia to give ethylamine:

CH₃CH₂Br + 2NH₃ ➔ CH₃CH₂NH₂ + NH₄Br

1. Reaction with primary amines to form secondary amines: Secondary aliphatic amines can be produced by reacting a halogenoalkane with a primary amine.

For example, bromoethane reacts with ethylamine to give diethylamine:

CH₃CH₂NH₂ + CH₃CH₂Br ➔ (CH₃CH₂NH₂)₂NH + HBr

1. Reaction with secondary amines to form tertiary amines: Tertiary aliphatic amines can be produced by reacting a halogenoalkane with a secondary amine.

For example, bromoethane reacts with diethylamine to give triethylamine:

(CH₃CH₂)₂NH + CH₃CH₂Br ➔ (CH₃CH₂)₃N + HBr

Mechanism of amine formation

The nucleophilic substitution mechanism for these reactions involves two steps:

1. The nucleophile (ammonia or amine) attacks the halogenoalkane, displacing the halogen and forming an alkylammonium salt.
2. The alkylammonium salt is then deprotonated by a base (e.g., the nucleophile or a separate base) to form the amine product.

For example, the mechanism for the reaction between bromoethane and ammonia is:

Aromatic amines from nitro compounds

Aromatic amines are produced by reducing nitro compounds in a two-step process:

1. The nitro compound is heated under reflux with tin and concentrated HCl to form an ammonium salt.
2. The ammonium salt is then treated with aqueous NaOH to give the free amine.

For example, nitrobenzene is reduced to phenylamine via phenylammonium chloride:

Aromatic amines like this are useful in organic synthesis for making pharmaceuticals, dyes, and other compounds.