Question

Benzoyl chloride is converted to benzaldehyde by

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

Hint:

$BaSO_4$ acts as a "poison" to prevent the reduction of the aldehyde to an alcohol.

Answer 1

Answer: (E)

Step 1: Understanding the Concept:
This question asks to identify the specific named reaction that achieves the conversion of an acid chloride (benzoyl chloride) to an aldehyde (benzaldehyde). This is a reduction reaction.
Step 2: Detailed Explanation:
Let's review the named reactions listed: - (A) Etard reaction: This reaction oxidizes a methyl group on a benzene ring (like in toluene) to an aldehyde group using chromyl chloride (CrO\(_2\)Cl\(_2\)). It's an oxidation, not a reduction of an acid chloride. - (B) Stephen reaction: This reaction reduces a nitrile (R-CN) to an aldehyde using tin(II) chloride (SnCl\(_2\)) and HCl, followed by hydrolysis. It's for nitriles, not acid chlorides. - (C) Gatterman reaction: A formylation reaction that introduces an aldehyde group onto an aromatic ring using HCN and HCl (and a Lewis acid catalyst). It starts from an aromatic hydrocarbon, not an acid chloride. - (D) Gatterman - Koch reaction: Another formylation reaction that introduces an aldehyde group onto an aromatic ring using carbon monoxide (CO) and HCl (and a catalyst). It also starts from an aromatic hydrocarbon. - (E) Rosenmund reaction: This is the catalytic hydrogenation of an acid chloride (R-COCl) to an aldehyde (R-CHO). The reaction is carried out using hydrogen gas (H\(_2\)) and a poisoned palladium catalyst (Pd/BaSO\(_4\)). The "poison" (like sulfur or quinoline) is crucial to prevent the over-reduction of the aldehyde to a primary alcohol. The conversion of benzoyl chloride (C\(_6\)H\(_5\)COCl) to benzaldehyde (C\(_6\)H\(_5\)CHO) is a classic example of the Rosenmund reaction. \[ \underset{\text{Benzoyl chloride}}{\text{C}_6\text{H}_5\text{COCl}} + \text{H}_2 \xrightarrow{\text{Pd/BaSO}_4} \underset{\text{Benzaldehyde}}{\text{C}_6\text{H}_5\text{CHO}} + \text{HCl} \] Step 3: Final Answer:
The conversion is achieved by the Rosenmund reaction.