Which of the following is used in the preparation of phenol?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → cumene (isopropylbenzene)
Most phenol is made industrially from cumene (isopropylbenzene), structure 1. Cumene is oxidised by air to cumene hydroperoxide, which is converted by dilute acid into phenol and acetone (a useful by-product):
\( \displaystyle \ce{C6H5CH(CH3)2} \xrightarrow{\ce{O2}} \ce{C6H5C(CH3)2OOH} \)
\( \displaystyle \ce{C6H5C(CH3)2OOH} \xrightarrow{\ce{H+}/\ce{H2O}} \ce{C6H5OH + CH3COCH3} \)
Why the other options are incorrect
Option (2) — Incorrect. 2-ethyltoluene; it is not the starting material of the phenol process.
Option (3) — Incorrect. Propylbenzene has no tertiary hydrogen next to the ring, so it does not form the hydroperoxide that splits into phenol and acetone.
Option (4) — Incorrect. 1-phenylpropene is an alkene; it is not used to make phenol.
NCERT (2026-27 edition):
From Cumene
