A2-Level Benzene, Aromatic Chemistry

  • The nitration of an arene (compound with a benzene ring in) is an electrophilic substitution reaction, with a nitronium ion, NO⁺ , acting as the electrophile.

  • The nitronium ion is produced by reacting concentrated nitric acid with concentrated sulfuric acid:




     

  • The reaction is carried out at 55ºC and produces a nitroarene.

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QUICK NOTES

Nitration of Arenes

 

Arenes are compounds that contain a benzene ring. Nitration of an arene means the substitution of a NO  group onto a benzene ring. This reaction requires a temperature of approximately 55ºC, concentrated nitric acid and concentrated sulfuric acid.

 

 

The first thing needed is the electrophile, NO⁺  (nitronium ion). This is produced by the reaction of concentrated nitric acid in the presence of concentrated sulfuric acid, which happens in two stages.

 

 

The nitronium ion (NO⁺  ) is very strong electrophile that will react with benzene. Remember the basic outline for an electrophilic substitution reaction with benzene.

 

An electrophile accepts electrons from the ring of delocalised electrons, forming a new bond with a carbon atom.

 

 

This removes one electron from the delocalised ring and makes it positively charged.

 

 

 

The delocalised ring needs another electron to become stable again. To get this electron, the carbon-hydrogen bond breaks and the electrons go to the ring of delocalised electrons.

 

 

A positive hydrogen ion is released (proton) and the original electrophile is now bonded onto the benzene ring.

 

The hydrogen has been substituted for an electrophile, making the reaction an electrophilic substitution.

 

 

The hydrogen ion that is ‘kicked off’ the benzene ring reacts with the HSO⁻  ion formed at the start and causes H SO  to reform. Therefore, H SO  is a catalyst in this reaction, because it’s reformed at the end of the reaction.

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