Which of the following are used as catalyst in Friedel-Crafts reactions ?

Options

A. `AlCl_(3)`
B. `SiCl_(4)`
C. `BF_(3)`
D. `SnCl_(4)`

Explanation

To determine which substances are used as catalysts in Friedel-Crafts reactions, we can follow these steps:

### Step 1: Understand Friedel-Crafts Reactions
Friedel-Crafts reactions are important organic reactions used to introduce alkyl or acyl groups into aromatic compounds. There are two main types: Friedel-Crafts alkylation and Friedel-Crafts acylation.

### Step 2: Identify Common Catalysts
The catalysts commonly used in Friedel-Crafts reactions include:
- **Aluminum chloride (AlCl3)**
- **Boron trifluoride (BF3)**

These catalysts help in generating a more reactive electrophile from the alkyl or acyl halide.

### Step 3: Analyze Other Possible Catalysts
- **Silicon tetrachloride (SiCl4)** is not used as a catalyst in Friedel-Crafts reactions. This is due to the larger size of the chlorine atom, which results in weak interactions with silicon, preventing it from effectively participating in the reaction.

### Step 4: Conclusion
From the analysis, the substances that can act as catalysts in Friedel-Crafts reactions are:
- **AlCl3**
- **BF3**

### Final Answer
The catalysts used in Friedel-Crafts reactions are **AlCl3** and **BF3**.

---