Q43 / 150 · MHT CET 2026 (20 April Shift 1) · Chemistry
Which of the following reaction represents Rosenmund reduction ?
- Correct answerA$\text{R}-\text{CO}-\text{Cl} \xrightarrow[\large{\text{Pd}-\text{BaSO}_4}]{\large{\text{H}_2}} \text{R}-\text{CHO} + \text{HCl}$
- B$\text{R}-\text{CN} \xrightarrow[\large{\text{H}_3\text{O}^+}]{\large{\text{SnCl}_2,\text{HCl}}} \text{R}-\text{CHO} + \text{NH}_4\text{Cl}$
- C$\text{R}-\text{CHO} \xrightarrow[\large{\Delta}]{\large{\text{Zn}-\text{Hg conc.HCl}}} \text{R}-\text{CH}_3 + \text{H}_2\text{O}$
- D$\text{R}-\text{CO}-\text{R} \xrightarrow[\large{\text{ii) KOH, HO}-\text{CH}_2-\text{CH}_2-\text{OH},\ \Delta}]{\large{\text{i) H}_2\text{N}-\text{NH}_2}} \text{R}-\text{CH}_2-\text{R}$
Solution
Rosenmund reduction is the catalytic hydrogenation of an acid chloride to an aldehyde.
The catalyst used is palladium on barium sulfate ($\text{Pd}-\text{BaSO}_4$), which is partially poisoned to prevent further reduction of the aldehyde to an alcohol.
The reaction is given by:
$\text{R}-\text{CO}-\text{Cl} \xrightarrow[\text{Pd}-\text{BaSO}_4]{\text{H}_2} \text{R}-\text{CHO} + \text{HCl}$
The other reactions are:
Stephen reaction: Reduction of nitriles to aldehydes using $\text{SnCl}_2/\text{HCl}$ followed by hydrolysis.
Clemmensen reduction: Reduction of aldehydes or ketones to alkanes using $\text{Zn}-\text{Hg}$ and conc. $\text{HCl}$.
Wolff-Kishner reduction: Reduction of aldehydes or ketones to alkanes using hydrazine and a strong base like $\text{KOH}$ in ethylene glycol.
Answer: $\text{R}-\text{CO}-\text{Cl} \xrightarrow[\large{\text{Pd}-\text{BaSO}_4}]{\large{\text{H}_2}} \text{R}-\text{CHO} + \text{HCl}$
The catalyst used is palladium on barium sulfate ($\text{Pd}-\text{BaSO}_4$), which is partially poisoned to prevent further reduction of the aldehyde to an alcohol.
The reaction is given by:
$\text{R}-\text{CO}-\text{Cl} \xrightarrow[\text{Pd}-\text{BaSO}_4]{\text{H}_2} \text{R}-\text{CHO} + \text{HCl}$
The other reactions are:
Stephen reaction: Reduction of nitriles to aldehydes using $\text{SnCl}_2/\text{HCl}$ followed by hydrolysis.
Clemmensen reduction: Reduction of aldehydes or ketones to alkanes using $\text{Zn}-\text{Hg}$ and conc. $\text{HCl}$.
Wolff-Kishner reduction: Reduction of aldehydes or ketones to alkanes using hydrazine and a strong base like $\text{KOH}$ in ethylene glycol.
Answer: $\text{R}-\text{CO}-\text{Cl} \xrightarrow[\large{\text{Pd}-\text{BaSO}_4}]{\large{\text{H}_2}} \text{R}-\text{CHO} + \text{HCl}$
Hence, the correct answer is option: 'A'.