Question

Which of the following reagents is used in the reaction shown below?
Benzoyl chloride → Benzaldehyde

• A. DIBAI-H
• B. SnCl\(_2\)/HCl
• C. H\(_2\)/Pd – BaSO\(_4\)
• D. Dimethyl cadmium

Hint:

Rosenmund reduction: R–COCl + H\(_2\) \(\xrightarrow{\text{Pd/BaSO}_4}\) R–CHO + HCl. The BaSO\(_4\) and a poison prevent further reduction to R–CH\(_2\)OH.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
Benzoyl chloride (C\(_6\)H\(_5\)COCl) is to be converted to benzaldehyde (C\(_6\)H\(_5\)CHO). This is a reduction of an acid chloride to an aldehyde without over-reduction to the alcohol.

Step 2: Key Formula or Approach:
Selective reduction of acid chlorides to aldehydes is achieved by Rosenmund reduction: H\(_2\) gas with palladium on barium sulfate (Pd/BaSO\(_4\)) poisoned with sulfur or quinoline.

Step 3: Detailed Explanation:
- (A) DIBAI-H (diisobutylaluminium hydride) reduces acid chlorides to aldehydes at low temperatures, but the classic and most common answer in such exams is Rosenmund reduction.
- (B) SnCl\(_2\)/HCl is used for reducing nitro compounds to amines.
- (C) H\(_2\)/Pd – BaSO\(_4\): Correct – Rosenmund reduction.
- (D) Dimethyl cadmium reacts with acid chlorides to give ketones, not aldehydes.
Thus, the reagent used is H\(_2\)/Pd – BaSO\(_4\).

Step 4: Final Answer:
Option (C) is correct.