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 is a two-step synthesis process. (A) Formation of P: Friedel-Crafts Alkylation
Benzene reacts with 1-chloropropane (CH₃CH₂CH₂Cl) in the presence of a Lewis acid catalyst (Anhy. AlCl₃). The Lewis acid helps generate a carbocation from the alkyl halide. The primary carbocation (propyl cation) formed is unstable and rapidly rearranges via a 1,2-hydride shift to the more stable secondary carbocation (isopropyl cation): CH₃CH₂CH₂⁺ → CH₃CH⁺CH₃. This more stable isopropyl carbocation acts as the electrophile and attacks the benzene ring. Therefore, the major product P is isopropylbenzene (also known as cumene). (P = Cumene) (B) Formation of Q: Cumene Process
Product P (cumene) undergoes oxidation with O₂ (often air), usually initiated by radicals or heat (Δ), to form cumene hydroperoxide. This occurs at the tertiary C-H bond. (Cumene Hydroperoxide) Treatment of cumene hydroperoxide with dilute acid (dil. H₂SO₄) causes a rearrangement and cleavage to yield phenol and acetone. Phenol + Q = Acetone Therefore, product Q is acetone. Combining the results, P is isopropylbenzene and Q is acetone. This combination matches options (B) and (C). Given the selection, we choose (B).