In the sulphonation of benzene, the active electrophilic species is

Options

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

Answer

To determine the active electrophilic species in the sulphonation of benzene, we can follow these steps:

### Step 1: Understand the Reaction
The sulphonation of benzene involves the reaction of benzene (C6H6) with concentrated sulfuric acid (H2SO4). The overall reaction can be represented as:
\[ \text{C}_6\text{H}_6 + \text{H}_2\text{SO}_4 \rightarrow \text{C}_6\text{H}_5\text{SO}_3\text{H} + \text{H}_2\text{O} \]

### Step 2: Identify the Electrophile
In this reaction, we need to identify the active electrophile that attacks the benzene ring. The electrophile is typically a positively charged species that can react with the electron-rich benzene.

### Step 3: Formation of the Electrophile
The electrophile in sulphonation is formed from sulfuric acid. When H2SO4 is used, one of the sulfuric acid molecules can donate a proton (H+) to another molecule of sulfuric acid, leading to the formation of the electrophile. The relevant reaction can be summarized as:
\[ \text{H}_2\text{SO}_4 \rightarrow \text{H}^+ + \text{HSO}_3^- \]

### Step 4: Identify the Active Electrophile
The active electrophile in this reaction is the sulfur trioxide (SO3) molecule, which can be represented as:
\[ \text{SO}_3 \]

### Conclusion
Thus, the active electrophilic species in the sulphonation of benzene is sulfur trioxide (SO3).

### Final Answer
The active electrophilic species in the sulphonation of benzene is **SO3**.

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