Reactions of amines

How are primary aliphatic amines formed from halogenoalkanes?

Nucleophilic substitution with excess ethanolic ammonia.

Draw the mechanism for the nucleophilic substitution of bromoethane and ammonia (textbook pg. 458).

XXX.

Can the amine product of nucleophilic substitution with a halogenoalkane continue to react?

Yes, as it still has a lone pair on the nitrogen so can still act as a nucleophile.

When does the nucleophilic substitution of halogenoalkanes with ammonia stop?

It stops until a quaternary ammonium salt is produced, which cannot react further as it doesn’t have a lone pair of electrons.

What is another way to produce aliphatic amines?

The reduction of a nitrile to an amine using a strong reducing agent such as LiAlH4/NaBH4 in dry ether, followed by dilute acid.

Why is the reduction of nitriles used to produce amines instead of nucleophilic substitution?

Only one product (primary amine) is produced.

What is an equation for the reduction of a nitrile to produce an amine (ethylamine)?

CH3CN + 4[H] → CH3CH2NH2

How are the conditions for the reduction of nitriles changed in industry and why?

• LiAlH4 is too expensive for industrial use, so industry uses a Pt/Ni catalyst at high temperature and pressure.

• This is called catalytic hydrogenation.

What is an equation for the formation of ethylamine through catalytic hydrogenation?

CH3CN + 2H2 → CH3CH2NH2

How can amines act as nucleophiles?

They can react with acyl chlorides in nucleophilic addition elimination to produce primary amides. The lone pair on the N allows them to act as nucleophiles.

What else is produced when amines react with acyl chlorides?

Toxic HCl gas.

How do amines react with acid anhydrides?

• Acid anhydrides react with primary amines/ammonia to form amides and a carboxylic acid.

• The reaction with primary amines produces an N-substituted amide.

• The reaction with ammonia produces a primary amide.

How can aromatic amines be produced?

• Reduce a nitro(benzene) compound by heating it under reflux with Tin and HCl.

• This makes a salt which can be turned into an aromatic amine by adding an alkali (NaOH).

Why is it important that aromatic amines are produced for industry?

They are used in the manufacture of dyes.