Which of the following reaction is an example of Rosenmund reduction?

Which of the following reaction is an example of Rosenmund reduction?
  1. $\mathrm{R}-\mathrm{CO}-\mathrm{R} \underset{\mathrm{KOH} \text {,ethylene glycol }}{\stackrel{\mathrm{NH}_2-\mathrm{NH}_2, \mathrm{\Delta}}{\longrightarrow}} \mathrm{R}-\mathrm{CH}_2-\mathrm{R}$
  2. $\mathrm{R}-\mathrm{CHO} \underset{\Delta}{\stackrel{\mathrm{Zn}-\mathrm{Hg} / \text { conc. } \mathrm{HCl}}{\longrightarrow}} \mathrm{R}-\mathrm{CH}_3-\mathrm{H}_2 \mathrm{O}$
  3. $\mathrm{R}-\mathrm{CO}-\mathrm{Cl} \underset{\mathrm{Pd}_2-\mathrm{BaSO}_4}{\stackrel{\mathrm{H}_2}{\longrightarrow}} \mathrm{R}-\mathrm{CHO}+\mathrm{HCl}$
  4. $\mathrm{R}-\mathrm{CN} \underset{\mathrm{H}_3 \mathrm{O}^{+}}{\stackrel{\mathrm{SnCl}_2 / \mathrm{HCl}}{\longrightarrow}} \mathrm{R}-\mathrm{CHO}+\mathrm{NH}_4 \mathrm{Cl}$

Solution

$\mathrm{R}-\mathrm{CO}-\mathrm{Cl} \underset{\mathrm{Pd}_2-\mathrm{BaSO}_4}{\stackrel{\mathrm{H}_2}{\longrightarrow}} \mathrm{R}-\mathrm{CHO}+\mathrm{HCl}$

Asked in: MHT CET 2021 (23 Sep Shift 1)

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