CIE A Level Chemistry (9701) 2019-2021

Revision Notes

7.6.4 Reactions of Phenylamine

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

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