NEETChemistryHydrocarbons
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): In the preparation of benzaldehyde from toluene using chromic oxide ( CrO ₃ ), acetic anhydride is used to prevent further oxidation of benzaldehyde to benzoic acid. Reason (R): The intermediate formed, benzylidene diacetate, is resistant to further oxidation and is subsequently hydrolysed to benza
Options
- ABoth Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- BBoth Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
- CAssertion (A) is true but Reason (R) is false.
- DAssertion (A) is false but Reason (R) is true.
Correct answer
A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Step-by-step solution
The use of chromic oxide ( CrO ₃ ) in acetic anhydride converts toluene to benzylidene diacetate. This diacetate intermediate is stable and does not undergo further oxidation to benzoic acid, effectively trapping the oxidation at the aldehyde stage. It is then isolated and hydrolysed with aqueous acid to yield the final product, benzaldehyde. Thus, both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains why acetic anhydride is used to prevent over-oxidation. Answer: Both Assertion (A) and Reas