The attacking reagent in electrophilic sulphonation of benzene is

Options

A. `SO_(4)^(2-)`
B. `SO_(3)^(2-)`
C. `SO_(2)`
D. `SO_(3)`

Answer

To solve the question regarding the attacking reagent in the electrophilic sulphonation of benzene, we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding Electrophilic Sulphonation**:
- Electrophilic sulphonation is a reaction where a sulfonyl group (SO3H) is introduced into a benzene ring. This reaction is typically carried out using sulfuric acid (H2SO4).

2. **Formation of the Electrophile**:
- Sulfuric acid can generate the electrophile needed for the reaction. When sulfuric acid is used, it can dissociate to form H+ ions and the bisulfate ion (HSO4-).
- The key reagent here is sulfur trioxide (SO3), which is generated from sulfuric acid.

3. **Mechanism of Electrophilic Attack**:
- In the presence of sulfuric acid, SO3 can be formed as a reactive electrophile. The mechanism involves the generation of SO3 from the reaction of sulfuric acid.
- The electrophile SO3 is highly reactive and can attack the electron-rich benzene ring.

4. **Identifying the Attacking Reagent**:
- The attacking reagent in the electrophilic sulphonation of benzene is therefore sulfur trioxide (SO3).
- This electrophile can effectively attack the benzene ring, leading to the formation of the sulfonic acid group.

5. **Conclusion**:
- The attacking reagent in the electrophilic sulphonation of benzene is SO3.

### Final Answer:
The attacking reagent in electrophilic sulphonation of benzene is **SO3**.

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