Question

What nitrating mixture is used for the nitration of nitrobenzene?

Answer 1

Hint: The mixture consists of nitric acid \[\left( {HN{O_3}} \right)\] and sulphuric acid \[\left( {{H_2}S{O_4}} \right)\]. Both have different roles to play in the nitration of nitrobenzene. The reaction of nitration of nitrobenzene is an electrophilic aromatic substitution reaction. The reaction occurs at warm temperatures.

Complete answer:
Nitrating mixture is the mixture of some acids, used to nitrate aromatic compounds and unsaturated aliphatic compounds, as well as in the production of nitro amino compounds (nitramines) and nitro esters. The nitrating mixture that is used for nitration (conversion of an organic compound into a nitro compound or a nitrate) of nitrobenzene consists of mixture of concentrated nitric acid \[\left( {HN{O_3}} \right)\] and sulphuric acid \[\left( {{H_2}S{O_4}} \right)\]. In the mixture, nitric acid acts as a nitrating agent, and sulphuric acid acts as an acid catalyst. This mixture produces the nitronium ion \[(N{O_2}^ + )\], which is the active species in aromatic nitration. In mixed-acid synthesis, sulfuric acid is not consumed and hence acts as a catalyst as well as an absorbent for water.
In the nitration of benzene, an electrophile is generated to activate nitric acid with sulphuric acid. This produces a strong nucleophile nitronium ion. This nitronium ion is a very good electrophile, which is attacked by benzene to finally produce nitrobenzene. In this reaction, nitric acid is a base. The reaction occurs at a warm temperature not exceeding \[{50^0}{\text{ }}C\]. The reaction is one of the examples of electrophilic aromatic substitution.

Note:
Nitro group in the reaction is electron-withdrawing. It helps to eliminate some of the delocalized electrons from the benzene ring because it has no lone pairs to donate and has electronegative atoms, making it less vulnerable to electrophilic attack. The nitration of nitrobenzene produces three products.