Question:
Which of the following reaction is an example of Rosenmund reduction?
Which of the following reaction is an example of Rosenmund reduction?
Show Hint
To spot the Rosenmund reduction instantly among options, always look for the unique reagent combination of an acid chloride ($\mathrm{-COCl}$) starting material being treated with $\mathrm{Pd/BaSO_4}$.
Updated On: Jun 11, 2026
- $\mathrm{R - CO - R \xrightarrow[NH_2 - NH_2, \Delta]{KOH, \text{ethylene glycol}} R - CH_2 - R}$
- $\mathrm{R - CHO \xrightarrow[\Delta]{Zn - Hg / \text{conc. } HCl} R - CH_3 + H_2O}$
- $\mathrm{R - CO - Cl \xrightarrow[BaSO_4]{Pd - H_2} R - CHO + HCl}$
- $\mathrm{R - CN \xrightarrow[HCl]{SnCl_2 / H_3O^+} R - CHO + NH_4Cl}$
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Question:
The question asks us to identify the standard chemical equation that represents the Rosenmund reduction from the given choices.
Step 2: Key Formula or Approach:
The Rosenmund reduction is a catalytic hydrogenation process used specifically to reduce acyl chlorides (acid chlorides) into their corresponding aldehydes. The reaction uses hydrogen gas ($\mathrm{H_2}$) in the presence of a palladium catalyst supported on barium sulfate ($\mathrm{Pd/BaSO_4}$), which is partially deactivated ("poisoned") by substances like sulfur or quinoline to prevent further reduction of the aldehyde into a primary alcohol.
Step 3: Detailed Explanation:
Let's analyze the nature of each option:
• Option A: Represents the Wolff-Kishner reduction, where a ketone ($\mathrm{R-CO-R}$) is completely reduced to an alkane ($\mathrm{R-CH_2-R}$) using hydrazine and $\mathrm{KOH}$ in ethylene glycol.
• Option B: Represents the Clemmensen reduction, where an aldehyde ($\mathrm{R-CHO}$) is reduced to an alkane ($\mathrm{R-CH_3}$) using zinc amalgam ($\mathrm{Zn-Hg}$) and concentrated $\mathrm{HCl}$.
• Option C: Shows an acyl chloride ($\mathrm{R-CO-Cl}$) reacting with hydrogen in the presence of a poisoned palladium catalyst ($\mathrm{Pd-BaSO_4}$) to yield an aldehyde ($\mathrm{R-CHO}$). This perfectly fits the definition of the Rosenmund reduction.
• Option D: Represents the Stephen reduction, where a nitrile ($\mathrm{R-CN}$) is reduced to an aldehyde using tin(II) chloride ($\mathrm{SnCl_2}$) and $\mathrm{HCl}$ followed by hydrolysis.
Step 4: Final Answer:
The reaction that exemplifies the Rosenmund reduction is shown in option (C).
The question asks us to identify the standard chemical equation that represents the Rosenmund reduction from the given choices.
Step 2: Key Formula or Approach:
The Rosenmund reduction is a catalytic hydrogenation process used specifically to reduce acyl chlorides (acid chlorides) into their corresponding aldehydes. The reaction uses hydrogen gas ($\mathrm{H_2}$) in the presence of a palladium catalyst supported on barium sulfate ($\mathrm{Pd/BaSO_4}$), which is partially deactivated ("poisoned") by substances like sulfur or quinoline to prevent further reduction of the aldehyde into a primary alcohol.
Step 3: Detailed Explanation:
Let's analyze the nature of each option:
• Option A: Represents the Wolff-Kishner reduction, where a ketone ($\mathrm{R-CO-R}$) is completely reduced to an alkane ($\mathrm{R-CH_2-R}$) using hydrazine and $\mathrm{KOH}$ in ethylene glycol.
• Option B: Represents the Clemmensen reduction, where an aldehyde ($\mathrm{R-CHO}$) is reduced to an alkane ($\mathrm{R-CH_3}$) using zinc amalgam ($\mathrm{Zn-Hg}$) and concentrated $\mathrm{HCl}$.
• Option C: Shows an acyl chloride ($\mathrm{R-CO-Cl}$) reacting with hydrogen in the presence of a poisoned palladium catalyst ($\mathrm{Pd-BaSO_4}$) to yield an aldehyde ($\mathrm{R-CHO}$). This perfectly fits the definition of the Rosenmund reduction.
• Option D: Represents the Stephen reduction, where a nitrile ($\mathrm{R-CN}$) is reduced to an aldehyde using tin(II) chloride ($\mathrm{SnCl_2}$) and $\mathrm{HCl}$ followed by hydrolysis.
Step 4: Final Answer:
The reaction that exemplifies the Rosenmund reduction is shown in option (C).
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