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

Concept: Friedel–Crafts alkylation is an electrophilic aromatic substitution reaction in which an alkyl group is introduced into an aromatic ring. The reaction generally uses:
• An alkyl halide (\(R-X\))
• A Lewis acid catalyst The most commonly used Lewis acid catalyst is \( \text{AlCl}_3 \).

Step 1: Role of the Lewis acid catalyst. The Lewis acid catalyst \( \text{AlCl}_3 \) helps generate the electrophile from the alkyl halide. Example: \[ R-Cl + AlCl_3 \rightarrow R^+ + AlCl_4^- \] The carbocation \(R^+\) then attacks the aromatic ring.

Step 2: Examine the options.
• \( \text{AlCl}_3 \): Lewis acid catalyst used in Friedel–Crafts alkylation.
• \( \text{FeCl}_3 \): Commonly used in halogenation of benzene.
• \( \text{RCOCl} \): Used in Friedel–Crafts acylation, not alkylation.
• \( \text{H}_2\text{SO}_4 \): Used in nitration and sulfonation reactions.

Step 3: Identify the correct reagent. Thus, the reagent used in Friedel–Crafts alkylation is \[ \boxed{\text{AlCl}_3} \]