which of the following cannot be a catalyst in the electrophilic substitution of arenes ?

Options

A. `FeCl_3`
B. `FeBr_3`
C. `NH_3`
D. `AlCl_3`

Answer

To determine which of the following cannot be a catalyst in the electrophilic substitution of arenes, we need to understand the role of catalysts in this type of reaction. Electrophilic substitution involves the replacement of a hydrogen atom in an aromatic compound (arene) with an electrophile. Catalysts are substances that increase the rate of a reaction without being consumed in the process.

### Step-by-Step Solution:

1. **Identify the Electrophilic Substitution Reaction**:
- In electrophilic substitution reactions of arenes, a strong electrophile attacks the aromatic ring, leading to the substitution of a hydrogen atom.

2. **Understand the Role of Catalysts**:
- Catalysts used in electrophilic substitution reactions are typically Lewis acids. They facilitate the generation of the electrophile or stabilize the transition state.

3. **List Common Catalysts**:
- Common catalysts for electrophilic substitution in arenes include:
- Ferric chloride (FeCl3)
- Aluminum chloride (AlCl3)
- Sulfuric acid (H2SO4)
- These catalysts are Lewis acids that can accept electron pairs.

4. **Evaluate the Given Options**:
- If ammonia (NH3) is given as an option, we need to analyze its role.
- Ammonia is a Lewis base, which means it donates electron pairs rather than accepting them.

5. **Conclusion**:
- Since ammonia acts as a Lewis base and does not facilitate the electrophilic substitution process by acting as a catalyst, it cannot be a catalyst in the electrophilic substitution of arenes.

### Final Answer:
Ammonia (NH3) cannot be a catalyst in the electrophilic substitution of arenes.

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