Write an equation for bromoethane with ammonia.

CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br

Why is a large excess of ammonia used?

So the amine formed is less likely to react with more halogenoalkane, which reduces further substitution.

Why is a sealed tube used?

Ammonia and the halogenoalkane are volatile and would escape on heating.

What is the disadvantage of the ammonia route?

A mixture of primary, secondary and tertiary amines and ammonium salts forms, so the yield of primary amine is low.

How is a nitrile converted into a primary amine?

Reduce it with LiAlH₄ in dry ether, or with H₂ and a nickel catalyst.

Write an equation for reducing propanenitrile.

CH₃CH₂CN + 4[H] → CH₃CH₂CH₂NH₂

Why does the nitrile route lengthen the carbon chain?

The nitrile is made from a halogenoalkane and cyanide ions, which adds a carbon atom.

What are the reagents for reducing nitrobenzene?

Tin and concentrated hydrochloric acid, heated under reflux.

Write the equation for the reduction of nitrobenzene.

C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O

Why is sodium hydroxide added after the reduction?

To remove H⁺ from the phenylammonium ion and release free phenylamine.

Preparation of aminesAQA A-Level Chemistry: Flashcards

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How is a primary aliphatic amine made from a halogenoalkane?

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How is a primary aliphatic amine made from a halogenoalkane?: Heat the halogenoalkane with excess ethanolic ammonia in a sealed tube.
Write an equation for bromoethane with ammonia.: CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br
Why is a large excess of ammonia used?: So the amine formed is less likely to react with more halogenoalkane, which reduces further substitution.
Why is a sealed tube used?: Ammonia and the halogenoalkane are volatile and would escape on heating.
What is the disadvantage of the ammonia route?: A mixture of primary, secondary and tertiary amines and ammonium salts forms, so the yield of primary amine is low.
How is a nitrile converted into a primary amine?: Reduce it with LiAlH₄ in dry ether, or with H₂ and a nickel catalyst.
Write an equation for reducing propanenitrile.: CH₃CH₂CN + 4[H] → CH₃CH₂CH₂NH₂
Why does the nitrile route lengthen the carbon chain?: The nitrile is made from a halogenoalkane and cyanide ions, which adds a carbon atom.
What are the reagents for reducing nitrobenzene?: Tin and concentrated hydrochloric acid, heated under reflux.
Write the equation for the reduction of nitrobenzene.: C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O
Why is sodium hydroxide added after the reduction?: To remove H⁺ from the phenylammonium ion and release free phenylamine.
What is phenylamine mainly used to make?: Dyes (azo dyes).

Exam questions on Preparation of amines

A student prepares butylamine, CH₃CH₂CH₂CH₂NH₂, from 1-bromobutane, CH₃CH₂CH₂CH₂Br. The 1-bromobutane is added to a large excess of ammonia dissolved in ethanol, and the mixture is heated in a sealed tube.
Write an equation for the formation of butylamine and explain why two moles of ammonia are needed for each mole of 1-bromobutane.2 marks
Propylamine, CH₃CH₂CH₂NH₂, is prepared in industry from propanenitrile, CH₃CH₂CN. The propanenitrile is itself made by heating bromoethane with potassium cyanide in ethanol. The nitrile is then reduced to the primary amine.
Write an equation for the reduction of propanenitrile using [H] to represent the reducing agent, and suggest one advantage of making a primary amine by this route rather than from a halogenoalkane and ammonia.2 marks
A student reduces nitrobenzene, C₆H₅NO₂ (Mr = 123.0), to phenylamine, C₆H₅NH₂ (Mr = 93.0), by heating it under reflux with tin and concentrated hydrochloric acid. After the reaction the student adds excess sodium hydroxide solution and extracts the phenylamine. From 12.3 g of nitrobenzene the student isolates 6.51 g of phenylamine.
Write an equation for the reduction of nitrobenzene using [H], and explain why sodium hydroxide is added at the end of the reaction.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).