Question

Which of the following reagents are used in Friedel–Crafts alkylation?

• A. \( \text{AlCl}_3 \)
• B. \( \text{FeCl}_3 \)
• C. \( \text{RCOCl} \)
• D. \( \text{H}_2\text{SO}_4 \)

Hint:

Remember the difference: Friedel–Crafts alkylation: Alkyl halide \(+\) \( \text{AlCl}_3 \) Friedel–Crafts acylation: Acyl chloride (\(RCOCl\)) \(+\) \( \text{AlCl}_3 \)

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the standard catalyst or reagent required to perform a Friedel–Crafts alkylation reaction on an aromatic ring.
Step 2: Key Formula or Approach:
Friedel–Crafts alkylation involves the reaction of an aromatic ring with an alkyl halide (\(R-X\)) in the presence of a Lewis acid.
Step 3: Detailed Explanation:
The Lewis acid acts as a catalyst by accepting a lone pair from the halogen of the alkyl halide, thereby generating a carbocation (\(R^+\)) which acts as the electrophile.
\[ R-Cl + AlCl_3 \rightarrow R^+ + [AlCl_4]^- \]
Anhydrous \(AlCl_3\) is the most commonly used Lewis acid for this purpose because of its strong electron-accepting nature.
- \(FeCl_3\) is more common in halogenation.
- \(RCOCl\) is used in Friedel–Crafts acylation.
- \(H_2SO_4\) is used in nitration or sulfonation.
Step 4: Final Answer:
The reagent used in Friedel–Crafts alkylation is \(AlCl_3\).