Question

Which reagent is typically used in Rosenmund reduction to convert acyl chlorides to aldehydes?

• A. \(LiAlH_4\)
• B. \(H_2 / Pd - BaSO_4\)
• C. \(NaBH_4\)
• D. \(KMnO_4\)

Hint:

Rosenmund Reduction converts: Acyl chloride → Aldehyde Reagent used: \[ H_2 / Pd-BaSO_4 \] The poisoned catalyst prevents further reduction to alcohol.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The Rosenmund reduction is a specific named reaction in organic chemistry used to synthesize aldehydes from acid chlorides. We need to identify the catalyst/reagent system.
Step 2: Key Formula or Approach:
The reaction is: \(R-COCl + H_2 \xrightarrow{\text{catalyst}} R-CHO + HCl\).
A partial reduction is required to prevent the aldehyde from further reducing to a primary alcohol.
Step 3: Detailed Explanation:
1. The reagent used is hydrogen gas (\(H_2\)) over a Palladium (\(Pd\)) catalyst.
2. To stop the reaction at the aldehyde stage, the Palladium is "poisoned" or deactivated with Barium Sulfate (\(BaSO_4\)) and sometimes sulfur or quinoline.
3. Option A and C (\(LiAlH_4\) and \(NaBH_4\)) are too strong or unsuitable for this specific transformation.
4. Option D (\(KMnO_4\)) is an oxidizing agent, not a reducing agent.
Step 4: Final Answer:
The correct reagent is \(H_2 / Pd - BaSO_4\) (B).