Chorination of benzene is not possible in the following reaction :

Options

A. `C_(6)H_(6) +Cl_(2) overset (FeCl_(3)) to `
B. `C_(6)H_(6) +HOCl overset (H^(+)) to `
C. `C_(6)H_(6) +I - Cl overset (ZnCl_(2)) to `
D. `C_(6)H_(6) +Cl_(2) overset (AlCl_(3)) to `

Answer

To determine why chlorination of benzene is not possible in the given reaction, we need to analyze each option provided in the question step by step.

### Step 1: Understand the Reaction Mechanism
Chlorination of benzene typically requires the generation of a chloronium ion (Cl⁺) which acts as an electrophile. This is usually achieved using chlorine gas (Cl₂) in the presence of a Lewis acid catalyst like FeCl₃.

### Step 2: Analyze Each Option

**Option A: C₆H₆ + Cl₂ + FeCl₃**
- Here, benzene (C₆H₆) reacts with chlorine (Cl₂) in the presence of FeCl₃.
- FeCl₃ acts as a Lewis acid and facilitates the generation of Cl⁺ from Cl₂.
- The reaction will produce chlorobenzene (C₆H₅Cl).
- **Conclusion**: Chlorination is possible in this case.

**Option B: C₆H₆ + OH⁻ + Cl⁺ (in acetic medium)**
- This option suggests that benzene reacts with hydroxide ion (OH⁻) and a positive chlorine ion (Cl⁺).
- The presence of Cl⁺ indicates that chlorination can occur as Cl⁺ is a strong electrophile.
- The reaction will also yield chlorobenzene.
- **Conclusion**: Chlorination is possible in this case as well.

**Option C: C₆H₆ + ICl**
- In this case, benzene reacts with iodine monochloride (ICl).
- ICl can dissociate into I⁻ and Cl⁺, where Cl⁺ can act as an electrophile.
- However, due to the presence of iodine, which is a better nucleophile, the reaction will favor the formation of iodobenzene (C₆H₄I) instead of chlorobenzene.
- **Conclusion**: Chlorination is not favored here, as iodobenzene is formed instead.

**Option D: (not explicitly stated in the transcript)**
- Without specific information about option D, we cannot analyze it. However, based on the previous options, we can conclude that if it involves a similar mechanism that does not generate Cl⁺ or competes with a stronger nucleophile, chlorination may not occur.

### Final Conclusion
The correct answer is **Option C** because chlorination of benzene does not occur when reacting with ICl, as the product formed is iodobenzene instead of chlorobenzene.