Question

The major product 'P' and 'Q' in the above reactions are

• A.
• B.
• C.
• D.

Hint:

Using a simple frame or just bolding for the box
Key Points:
Friedel-Crafts alkylation with primary alkyl halides often involves carbocation rearrangement to more stable secondary or tertiary carbocations before attacking the benzene ring.
1-Chloropropane rearranges to the isopropyl cation, leading to isopropylbenzene (cumene) as the major product.
The reaction sequence starting from cumene involving oxidation to cumene hydroperoxide followed by acid hydrolysis is the industrial Cumene Process for producing phenol and acetone.

Answer 1

The Correct Option is B

This process involves a two-step synthesis. (A) P Formation: Friedel-Crafts Alkylation
Benzene reacts with 1-chloropropane (CH₃CH₂CH₂Cl) using a Lewis acid catalyst (Anhy. AlCl₃). The catalyst generates a carbocation from the alkyl halide. The unstable primary carbocation (propyl cation) rearranges via a 1,2-hydride shift to form a more stable secondary carbocation (isopropyl cation): CH₃CH₂CH₂⁺ → CH₃CH⁺CH₃. This isopropyl carbocation, the electrophile, attacks the benzene ring. The major product P is isopropylbenzene (cumene). (P = Cumene) (B) Q Formation: Cumene Process
Product P (cumene) is oxidized by O₂ (often air), initiated by radicals or heat (Δ), forming cumene hydroperoxide, at the tertiary C-H bond. (Cumene Hydroperoxide) Treatment of cumene hydroperoxide with dilute acid (dil. H₂SO₄) causes rearrangement and cleavage, yielding phenol and acetone. Phenol + Q = Acetone Therefore, product Q is acetone. In summary, P is isopropylbenzene and Q is acetone. This corresponds to options (B) and (C). Based on the selection, (B) is chosen.