Sulfonation differs from most of electrophilic aromatic substitution reactions with the fact that the reaction-

Options

A. Is reversible
B. requires Lewis acid as catalyst
C. is explosive
D. takes place at high temperature

Answer

**Step-by-Step Solution:**

1. **Understanding Sulfonation**: Sulfonation is a type of electrophilic aromatic substitution reaction where a sulfonyl group (SO3H) is introduced into an aromatic compound, typically benzene. The key reagent used in this reaction is sulfur trioxide (SO3) or its equivalent, such as fuming sulfuric acid (H2SO4).

2. **Mechanism of Sulfonation**:
- The reaction begins with the generation of the electrophile, sulfur trioxide (SO3), from sulfuric acid (H2SO4).
- The electrophile (SO3) attacks the electron-rich benzene ring, forming a sigma complex (also known as an arenium ion or Wheland intermediate).
- This sigma complex is a resonance-stabilized carbocation where the positive charge is delocalized over the aromatic system.

3. **Equilibrium Steps**:
- The formation of the sigma complex is a slow, rate-determining step.
- The next step involves the loss of a proton (H+) from the sigma complex, which restores aromaticity to the benzene ring and leads to the formation of benzene sulfonic acid (C6H5SO3H).
- Importantly, each step in the sulfonation mechanism is in equilibrium, meaning that the reaction can proceed in both forward and reverse directions.

4. **Reversibility of Sulfonation**:
- Unlike most electrophilic aromatic substitution reactions, which are generally irreversible, sulfonation is unique because it is reversible. This means that the products can revert back to the reactants under certain conditions.
- The reversibility is attributed to the equilibrium nature of the intermediate steps in the reaction mechanism.

5. **Conclusion**:
- Therefore, the key difference of sulfonation from most electrophilic aromatic substitution reactions is that sulfonation is reversible in nature, while other electrophilic substitutions are typically not.

**Final Answer**: Sulfonation differs from most electrophilic aromatic substitution reactions by being reversible in nature.

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