Nitrobenzenen can be prepared from benzene by using a mixture of conc `HNO_(3)` and conc. `H_(2)SO_(4)` in the nitrating mixture. Nitric acid acts as a

Options

A. base
B. acid
C. reducing agent
D. catalyst

Answer

To determine the role of nitric acid (HNO₃) in the preparation of nitrobenzene from benzene using a nitrating mixture of concentrated HNO₃ and concentrated H₂SO₄, we can analyze the reaction step-by-step.

### Step-by-Step Solution:

1. **Understanding the Reaction Components**:
- The reaction involves benzene (C₆H₆), concentrated nitric acid (HNO₃), and concentrated sulfuric acid (H₂SO₄).
- The purpose of the nitrating mixture is to introduce a nitro group (NO₂) into the benzene ring.

2. **Formation of the Electrophile**:
- In the nitrating mixture, concentrated sulfuric acid acts as a dehydrating agent and protonates nitric acid.
- The reaction can be represented as:
\[ \text{HNO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{NO}_2^+ + \text{HSO}_4^- + \text{H}_2\text{O} \]
- Here, nitric acid donates a proton (H⁺) to sulfuric acid, leading to the formation of the nitronium ion (NO₂⁺), which is the active electrophile in the nitration reaction.

3. **Role of Nitric Acid**:
- In this reaction, nitric acid acts as a proton donor (acid) to sulfuric acid, which accepts the proton.
- The formation of the nitronium ion (NO₂⁺) is crucial for the nitration of benzene.

4. **Nitration of Benzene**:
- The nitronium ion (NO₂⁺) then reacts with benzene (C₆H₆) in an electrophilic aromatic substitution reaction:
\[ \text{C}_6\text{H}_6 + \text{NO}_2^+ \rightarrow \text{C}_6\text{H}_5\text{NO}_2 + \text{H}^+ \]
- This results in the formation of nitrobenzene (C₆H₅NO₂) and a proton (H⁺).

5. **Conclusion**:
- Therefore, in the context of the question, nitric acid (HNO₃) acts as an acid in the nitrating mixture, as it donates a proton to sulfuric acid.

### Final Answer:
Nitric acid (HNO₃) acts as an acid in the nitrating mixture.

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