Question

Which of the following reagents is used in Rosenmund reduction?

• A. Zn/HCl
• B. H$_2$/Pd - BaSO$_4$ (poisoned)
• C. LiAlH$_4$
• D. NaBH$_4$

Hint:

Rosenmund reduction uses Zn/HCl to reduce acyl chlorides to aldehydes, making it different from other reductions.

Answer 1

The Correct Option is B

The Rosenmund reduction selectively converts acyl chlorides into aldehydes. The standard reagents are hydrogen gas (H₂) and a poisoned palladium catalyst (Pd) supported on barium sulfate (BaSO₄). The poisoning of the palladium catalyst prevents over-reduction to an alcohol, ensuring aldehyde formation.

Evaluating the given options:

• H₂/Pd - BaSO₄ (poisoned): This is the specific reagent combination for Rosenmund reduction, achieving selective aldehyde formation.
• Zn/HCl: This reagent set is utilized for reducing nitro compounds and is not applicable to the Rosenmund reduction.
• LiAlH₄: A potent reducing agent that reduces various functional groups to alcohols, but it is not selective for aldehyde synthesis via acyl chloride reduction.
• NaBH₄: Primarily used for reducing aldehydes and ketones to alcohols; it is not employed in the Rosenmund reduction.

Conclusion: The appropriate reagent for the Rosenmund reduction is H₂/Pd - BaSO₄ (poisoned).