Question

Benzoyl chloride can be converted to benzaldehyde by ________.

• A. Rosenmund reduction
• B. Etard reaction
• C. Stephen reaction
• D. Gatterman reaction
• E. Gatterman-Koch reaction

Hint:

$RCOCl \xrightarrow{H_2, Pd/BaSO_4} RCHO$ is always Rosenmund.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
The question asks for the specific named reaction that achieves the synthesis of an aldehyde (benzaldehyde) from an acyl chloride (benzoyl chloride). This is a partial reduction, as complete reduction would yield an alcohol.
Step 2: Detailed Explanation
Let's analyze the transformation and then evaluate the named reactions provided as options.
- Transformation: C\(_6\)H\(_5\)COCl (an acyl chloride) \(\to\) C\(_6\)H\(_5\)CHO (an aldehyde).
Now let's review the reactions:
- (A) Rosenmund reduction: This is the catalytic hydrogenation of an acyl chloride to an aldehyde. The reaction uses H\(_2\) gas and a "poisoned" catalyst, typically palladium on barium sulfate (Pd/BaSO\(_4\)). The catalyst is partially deactivated (poisoned) with a substance like sulfur or quinoline to prevent the aldehyde from being further reduced to an alcohol. This reaction is the classic method for this specific transformation.
\[ \text{C}_6\text{H}_5\text{COCl} + \text{H}_2 \xrightarrow{\text{Pd/BaSO}_4, \text{S}} \text{C}_6\text{H}_5\text{CHO} + \text{HCl} \] - (B) Etard reaction: This reaction oxidizes an alkyl group (specifically a methyl group) on a benzene ring to an aldehyde using chromyl chloride (\(CrO_2Cl_2\)). It converts toluene to benzaldehyde.
- (C) Stephen reaction: This reaction reduces a nitrile (R-C\(\equiv\)N) to an aldehyde using SnCl\(_2\)/HCl followed by hydrolysis.
- (D) Gatterman reaction & (E) Gatterman-Koch reaction: These are reactions that introduce an aldehyde group onto a benzene ring (formylation). They start with benzene, not an acyl chloride.
Based on the analysis, the Rosenmund reduction is the correct named reaction for converting an acyl chloride to an aldehyde.
Step 4: Final Answer
Benzoyl chloride can be converted to benzaldehyde by the Rosenmund reduction.