Question

Which of the following is Rosenmund reduction?

• A. R=C=N + 2[H] $\xrightarrow{\text{SnCl}_2, \, \text{dil HCl}}$ R-CH=NH.HCl $\xrightarrow{\text{H}_3\text{O}^+}$ R-CHO + NH\(_4\)Cl
• B. R-CHO + H\(_2\)N-NH\(_2\) $\xrightarrow{\text{KOH/ethylene glycol}}$ R-CH=N-NH\(_2\) $\xrightarrow{\Delta}$ RCH\(_3\) + N\(_2\)
• C. Ar-CO-Cl $\xrightarrow{H_2, \, \text{Pd-BaSO}_4}$ Ar-CHO + HCl
• D. R-CO-R + 4[H] $\xrightarrow{\text{Zn-Hg/con. HCl}}$ R-CH\(_2\)-R + H\(_2\)O

Hint:

Rosenmund reduction selectively reduces acyl chlorides to aldehydes using hydrogen and Pd-BaSO\(_4\) as a catalyst.

Answer 1

The Correct Option is C

Step 1: Understanding Rosenmund Reduction.
Rosenmund reduction is a process where acyl chlorides (R-CO-Cl) are reduced to aldehydes (R-CHO) using hydrogen gas in the presence of palladium on barium sulfate (Pd-BaSO\(_4\)) as a catalyst. This reaction selectively reduces the carbonyl group without affecting other parts of the molecule.

Step 2: Analyzing the options.
(A) R=C=N + 2[H] $\xrightarrow{\text{SnCl_2, \, \text{dil HCl}}$ R-CH=NH.HCl $\xrightarrow{\text{H}_3\text{O}^+}$ R-CHO + NH\(_4\)Cl:} Incorrect. This is the reaction for the conversion of an isonitrile to an aldehyde, not Rosenmund reduction.
(B) R-CHO + H\(_2\)N-NH\(_2\) $\xrightarrow{\text{KOH/ethylene glycol}$ R-CH=N-NH\(_2\) $\xrightarrow{\Delta}$ RCH\(_3\) + N\(_2\):} Incorrect. This is a reaction for reducing an aldehyde to a primary amine, not Rosenmund reduction.
(C) Ar-CO-Cl $\xrightarrow{H_2, \, \text{Pd-BaSO_4}$ Ar-CHO + HCl:} Correct. This is the Rosenmund reduction, where acyl chloride is reduced to an aldehyde using hydrogen and Pd-BaSO\(_4\).
(D) R-CO-R + 4[H] $\xrightarrow{\text{Zn-Hg/con. HCl}$ R-CH\(_2\)-R + H\(_2\)O:} Incorrect. This is the Clemmensen reduction, not Rosenmund reduction.

Step 3: Conclusion.
The correct reaction is (C): Ar-CO-Cl $\xrightarrow{H_2, \, \text{Pd-BaSO}_4}$ Ar-CHO + HCl, which is the Rosenmund reduction.