Nitration of benzene by nitric acid and sulphuric acid is

Options

A. Electrophilic substitution
B. Electrophilic addition
C. Nucleophilic substitution
D. Free radical substitution

Answer

**Step-by-Step Solution:**

1. **Understanding the Reactants:**
The nitration of benzene involves two key reactants: concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4).

2. **Formation of the Electrophile:**
In this reaction, sulfuric acid acts as a catalyst. It donates a proton (H+) to nitric acid, which results in the formation of the nitronium ion (NO2+), the active electrophile in the reaction. The reaction can be represented as follows:
\[ HNO3 + H2SO4 \rightarrow NO2^+ + HSO4^- + H2O \]

3. **Electrophilic Substitution Mechanism:**
Benzene (C6H6) undergoes electrophilic substitution when it reacts with the nitronium ion. The π electrons of the benzene ring attack the nitronium ion, leading to the formation of a sigma complex (also called an arenium ion).

4. **Restoration of Aromaticity:**
The sigma complex is unstable and loses a proton (H+) to restore the aromaticity of the benzene ring. This results in the formation of nitrobenzene (C6H5NO2).

5. **Overall Reaction:**
The overall reaction can be summarized as:
\[ C6H6 + HNO3 \xrightarrow{H2SO4} C6H5NO2 + H2O \]

6. **Conclusion:**
The process described is known as electrophilic substitution, specifically nitration of benzene. Thus, the correct answer to the question is that nitration of benzene by nitric acid and sulfuric acid is an electrophilic substitution reaction.