Consider the following chemical reaction and identify the reagents required for conversion.
Select the correct option from the below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → CrO2Cl2 in CS2 and H3O+
The reaction converts toluene (methylbenzene) to benzaldehyde: the side-chain –\( \ce{CH3} \) must be oxidised only to the aldehyde stage. Strong oxidants (\( \ce{KMnO4} \)) go on to benzoic acid; chromyl chloride stops at the aldehyde.
So the reagents are CrO2Cl2 in CS2, then H3O+.
Why the other options are incorrect
Option (1) DIBAL-H (Diisobutylaluminium hydride), H2O — Incorrect. This is a reducing agent; it converts nitriles and esters to aldehydes, but cannot oxidise a –\( \ce{CH3} \) group.
Option (2) C5H5NH+CrO3Cl− (PCC) — Incorrect. It oxidises primary alcohols to aldehydes; toluene has no –OH group to oxidise.
Option (3) O3/H2O-Zn dust — Incorrect. ozonolysis cleaves C=C double bonds of alkenes into carbonyl compounds; toluene has no such side-chain double bond.
NCERT (2026-27 edition):
Use of Chromyl Chloride
