3.11 Amines

Give two ways primary aliphatic amines can be prepared.

Primary aliphatic amines can be prepared by the reaction of ammonia with halogenoalkanes and by the reduction of nitriles.

Give two ways the reduction of nitriles can take place.

One way the reduction of nitriles can take place is by using the reducing agent LiAlH₄ in a non-aqueous solvent, followed by dilute acid.
Another cheaper way is using hydrogen gas with a platinum catalyst at a high temperature and pressure, known as catalytic hydrogenation.

How are aromatic amines prepared?

Aromatic amines are prepared by the reduction of nitro compounds.

Describe the first step in the reduction of nitro compounds.

In the first step in the reduction of nitro compounds, a mixture of tin metal, concentrated HCl, and the nitro compound is heated under reflux to form a salt.

Describe the second step in the reduction of nitro compounds.

In the second step in the reduction of nitro compounds, an alkali such as sodium hydroxide is added to produce an aromatic amine.

What are aromatic amines used for?

Aromatic amines are used in the manufacture of dyes.

Fill in the blank.
Amines are weak _____.

Amines are weak bases.

Describe the difference in base strength between ammonia, primary aliphatic and primary aromatic amines.

Primary aliphatic amines have a greater base strength than ammonia, which has a greater base strength than primary aromatic amines.

State how the difference in base strength can be explained.

The difference in base strength can be explained in terms of the availability of the lone pair of electrons on the N atom.

Explain why primary aliphatic amines are stronger bases.

Primary aliphatic amines are stronger bases because the alkyl group donates electrons onto the attached groups, increasing the electron density on the nitrogen atom.
This makes the lone pair more available.

Explain why primary aromatic amines are weaker bases.

Primary aromatic amines are weaker bases because the lone pair on nitrogen becomes partially delocalised onto the benzene ring.
This decreases the electron density on the nitrogen atom, making the lone pair less available.

Fill in the blank.
Amines are ___________.

Amines are nucleophiles.

What do the nucleophilic substitution reactions of ammonia and amines with halogenoalkanes form?

The nucleophilic substitution reactions of ammonia and amines with halogenoalkanes form primary, secondary, tertiary amines and quaternary ammonium salts.

What are quaternary ammonium salts used as?

Quaternary ammonium salts are used as cationic surfactants.

Explain why quaternary ammonium salts are used as cationic surfactants.

Quaternary ammonium salts are used as cationic surfactants because the hydrocarbon tail will bind to non-polar substances such as grease.
The cationic head will dissolve in water and bind to negatively charged surfaces such as hair and fibre.

Name three products where quaternary ammonium salts are used as cationic surfactants.

Three products where quaternary ammonium salts are used as cationic surfactants are fabric cleaners, hair products, and fabric conditioners.