Answer the question on the basis of passage given below:
Strong oxidizing agents, oxidize toluene and its derivatives to benzoic acid. However, it is possible to stop the oxidation at the aldehyde stage with suitable reagents that convert methyl group to an intermediate that is difficult to oxidize further.
Conversions that can be done by same reagent are:
A. Benzaldehyde to 2-Nitrobenzaldehyde
B. Propan-1-ol to Propanal
C. Pent-3-en-2-ol to Pent-3-en-2-one
D. Butanal to Butan-1-ol
E. Methanal to Ethanol
Choose the correct answers from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → B and C only
Both B and C are oxidations of an alcohol that must stop at the C=O stage, and one reagent does both: pyridinium chlorochromate (PCC), a complex of \( \ce{CrO3} \) with pyridine and HCl.
(B) \( \ce{CH3CH2CH2OH} \xrightarrow{\text{PCC}} \ce{CH3CH2CHO} \) (a primary alcohol stops at the aldehyde)
(C) \( \ce{CH3CH=CHCH(OH)CH3} \xrightarrow{\text{PCC}} \ce{CH3CH=CHCOCH3} \) (a secondary alcohol gives the ketone, and the C=C bond is not attacked)
The other conversions need different kinds of reagents:
(A) a ring nitration (the –CHO group directs mainly to the meta position): \( \ce{C6H5CHO} \xrightarrow{\text{conc. }\ce{HNO3}\text{ + conc. }\ce{H2SO4}} \text{m-}\ce{O2NC6H4CHO} \)
(D) a reduction: \( \ce{CH3CH2CH2CHO} \xrightarrow{\ce{NaBH4}} \ce{CH3CH2CH2CH2OH} \)
(E) a Grignard reaction followed by hydrolysis: \( \ce{HCHO + CH3MgBr} \xrightarrow{\text{dry ether}} \ce{CH3CH2OMgBr} \xrightarrow{\ce{H3O+}} \ce{CH3CH2OH + Mg(OH)Br} \)
NCERT (2026-27 edition):
Oxidation – …
