Amines

What is the main property of amines

They act as bases (though weak)

How do amines react with dilute acids, e.g. HCl(aq)?

Amines act as bases, accepting H⁺ to form ammonium salts.

The reaction of phenylamine with nitric acid,

Excess Propylamine reacting with sulfuric acid

Why do amines behave as bases?

Amines are bases because the lone pair of electrons on the nitrogen atom can accept a proton (H⁺).

How to prepare aliphatic amines ( detailed )

Haloalkanes react with excess ammonia in ethanol to produce primary amines.

• Ammonia has a lone pair on the nitrogen that acts as a nucleophile, so a nucleophilic substitution reaction takes place.

• The first step forms an alkylammonium salt, and the second step forms the primary amine.

Note: These are two steps in the mechanism, but can be represented as one overall reaction equation.

and ethanol prevents water reacting with haloalkane → alcohol

When preparing aliphatic amines by substitution of haloalkanes, why do we use excess ammonia

Excess ammonia is used to favour the formation of primary amines and minimise further substitution reactions, reducing the formation of secondary and tertiary amines.

(However, it does not completely prevent further substitution, so a mixture of products may still form)

What is a problem with preparing aliphatic amines by substitution of haloalkanes?

The primary amine produced can also act as a nucleophile and react with more haloalkane, causing further substitution.

This produces a mixture of primary, secondary and tertiary amines, and quaternary ammonium salts, making purification difficult.

How can secondary and tertiary amines and quaternary ammonium salts be prepared from haloalkanes?

• Excess primary amine → Secondary amine.

• Excess secondary amine → Tertiary amine.

• Excess haloalkane → Quaternary ammonium salt.

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How to prepare aromatic amines ( detailed )

Chlorobenzene cannot react with ammonia to form phenylamine because the benzene ring cannot be attacked by nucleophiles.

3,5 EWG