Question

Name the reagent used in the conversion of benzene to nitrobenzene.

• A. Concentrated \(HNO_3\) only
• B. Concentrated \(H_2SO_4\) only
• C. Mixture of concentrated \(HNO_3\) and \(H_2SO_4\)
• D. Dilute \(HNO_3\)

Hint:

In nitration of benzene, concentrated \(H_2SO_4\) helps generate the electrophile \(NO_2^+\) from \(HNO_3\), which then substitutes a hydrogen atom in the benzene ring.

Answer 1

The Correct Option is C

Concept: The conversion of benzene to nitrobenzene occurs through the nitration reaction, which is an electrophilic aromatic substitution reaction. A nitrating mixture consisting of concentrated nitric acid and concentrated sulfuric acid is used.
Step 1: {Formation of the electrophile.} Concentrated sulfuric acid acts as a dehydrating agent and helps generate the nitronium ion: \[ HNO_3 + H_2SO_4 \rightarrow NO_2^+ + HSO_4^- + H_2O \] The \(NO_2^+\) ion is the active electrophile.
Step 2: {Electrophilic substitution on benzene.} The nitronium ion attacks the benzene ring, leading to substitution of a hydrogen atom and formation of nitrobenzene. \[ C_6H_6 + HNO_3 \xrightarrow{H_2SO_4} C_6H_5NO_2 + H_2O \]
Step 3: {Identify the reagent.} Thus, the reagent used is the nitrating mixture: \[ \text{Concentrated } HNO_3 + \text{ Concentrated } H_2SO_4 \]