Benzene and other aromatic hydrocarbons, though contain `pi`-bonds, yet they behave as saturated hydrocarbons. They are stable because of delocalisation of cloud. These undergo electrophilic substitution reactions as :
`C_(6)H_(5)-H + YZ to C_(6)H_(5)Y +HZ`
The reactivity of aromatic hydrocarbons towards electrophilic substitution depends upon the electron density in the benzene ring
The electrophile in sulphonation of benzene is

Options

A. `SO_(3)^(+)`
B. `HSO_(4)^(-)`
C. `SO_(3)`
D. `H_(3)SO_(4)^(+)`

Answer

To determine the electrophile in the sulfonation of benzene, we can follow these steps:

### Step 1: Understanding the Reaction
Benzene (C₆H₆) undergoes sulfonation, which is an electrophilic substitution reaction. In this reaction, a hydrogen atom on the benzene ring is replaced by a sulfonyl group (SO₃H).

### Step 2: Identifying the Electrophile
In the sulfonation of benzene, the electrophile is generated from sulfuric acid (H₂SO₄). When sulfuric acid is used, it can produce sulfur trioxide (SO₃) as the active electrophile.

### Step 3: Formation of the Electrophile
The reaction can be summarized as follows:
1. Sulfuric acid can dissociate to form sulfur trioxide (SO₃) and hydronium ions (H₃O⁺).
2. The sulfur trioxide (SO₃) acts as the electrophile in the reaction with benzene.

### Step 4: The Electrophilic Attack
During the reaction, the benzene ring attacks the sulfur trioxide. This leads to the formation of a sigma complex (also known as an arenium ion), where the aromaticity of the benzene ring is temporarily lost.

### Step 5: Regeneration of Aromaticity
After the formation of the sigma complex, a proton is removed from the complex, restoring the aromaticity of the benzene ring and resulting in the formation of the sulfonated product (C₆H₅SO₃H).

### Conclusion
Thus, the electrophile in the sulfonation of benzene is sulfur trioxide (SO₃).

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