CIE A Level Chemistry (9701) exams from 2022

Revision Notes

7.6.4 Production & Reactions of Phenylamine

Preparation of Phenylamine

  • Phenylamine is an organic compound consisting of a benzene ring and an amine (NH2) functional group
  • It can be produced in a three-step synthesis reaction followed by the separation of phenylamine from the reaction mixture
    • Step 1- Benzene undergoes nitration with concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) at 25 to 60 oC to form nitrobenzene
    • Step 2 – Nitrobenzene is reduced with hot tin (Sn) and concentrated hydrochloric acid (HCl) under reflux to form an acidic mixture that contains the organic product C6H5N+H3
    • Step 3 – Sodium hydroxide (NaOH) is added to the acidic reaction mixture to form phenylamine
    • Step 4 – The phenylamine is separated from the reaction mixture by steam distillation

Nitrogen Compounds - Preparation of Phenylamine Overall, downloadable AS & A Level Chemistry revision notes

The overall reaction of formation of phenylamine from benzene

Nitrogen Compounds - Preparation of Phenylamine (1), downloadable AS & A Level Chemistry revision notes Nitrogen Compounds - Preparation of Phenylamine (2), downloadable AS & A Level Chemistry revision notes

Multi-step synthesis of phenylamine from benzene

Reactions of Phenylamine

  • Both the benzene ring as well as the -NH2 group in phenylamine can take part in chemical reactions
  • These reactions include
    • The bromination of phenylamine
    • Formation of a diazonium salt

Bromination of phenylamine

  • Phenylamines react in electrophilic substitution reactions in a similar way as phenols
  • The lone pair of electrons on the nitrogen atom in phenylamines donate electron density into the benzene ring
    • In phenols, the oxygen atom donates its lone pair of electrons instead
  • The delocalisation of the electrons causes an increased electron density in the benzene ring
  • The benzene ring, therefore, becomes activated and becomes more readily attacked by electrophiles
  • The incoming electrophiles are directed to the 2,4 and 6 positions
  • Phenylamines, therefore, react under milder conditions with aqueous bromine at room temperature to form 2,4,6-tribromophenylamine

Nitrogen Compounds - Bromination of Phenylamine, downloadable AS & A Level Chemistry revision notes

Bromination of phenylamines gives 2,4,6-tribromophenylamine

Formation of diazonium salt

  • Diazonium compounds are very reactive compounds containing an -N2+ group
  • The amine (-NH2) group of phenylamines will react with nitric(III) acid (HNO3) at a temperature below 10 °C to form diazonium salts
    • Since nitric(III) acid is unstable, it has to be made in the test-tube by reacting sodium nitrate (NaNO2) and dilute acid (such as HCl)
  • These diazonium salts are so unstable that they will upon further warming with water to form a phenol

Nitrogen Compounds - Formation of Diazonium Salt from Phenylamine, downloadable AS & A Level Chemistry revision notes

Phenylamine can form an unreactive diazonium salt which thermally decomposes to a phenol

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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