AQA A Level Chemistry复习笔记7.4.2 Nitration of Benzene



  • The electrophilic substitution reaction in arenes consists of three steps:
    • Generation of an electrophile
    • Electrophilic attack
    • Regenerating aromaticity


Mechanism of electrophilic substitution

  • The nitration of benzene is one example of an electrophilic substitution reaction
    • A hydrogen atom is replaced by a nitro (-NO2) group



The overall reaction of nitration of arenes


  • In the first step, the electrophile is generated
    • The electrophile NO2+ ion is generated by reacting concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4)


  • Once the electrophile has been generated, it will carry out an electrophilic attack on the benzene ring
    • The nitrating mixture of HNO3 and H2SO4 is refluxed with the arene at 25 - 60 oC


Nitration of Benzene Mechanism:



Addition reactions of arenes

  • The delocalisation of electrons (also called aromatic stabilisation) in arenes is the main reason why arenes predominantly undergo substitution reactions over addition reactions
  • In substitution reactions,
  • In addition reactions, on the other hand, the aromaticity is not restored and is in some cases completely lost
    • The hydrogenation of arenes is an example of an addition reaction during which the aromatic stabilisation of the arene is completely lost
    • The cyclohexane formed is energetically less stable than the benzene