JEE Main · 2025 · 24 Jan 2025 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

Each named reaction converts a specific functional group to an aldehyde:

The Stephen reaction reduces a nitrile with $\mathrm{SnC}{\mathrm{l}}_2/HCl$, and hydrolysis with ${\mathrm{H}}_3{\mathrm{O}}^{+}$ then gives the aldehyde: $\mathrm{RCN}\stackrel{\mathrm{SnC}{\mathrm{l}}_2,\mathrm{HCl}}{\to }\mathrm{RCH}=\mathrm{NH}\cdot \mathrm{HCl}\stackrel{{\mathrm{H}}_3{\mathrm{O}}^{+}}{\to }\mathrm{RCHO}$ — this matches (A).

The Rosenmund reduction hydrogenates an acid chloride over a poisoned $\mathrm{Pd}-\mathrm{BaS}{\mathrm{O}}_4$ catalyst, which stops the reduction at the aldehyde stage rather than proceeding to the alcohol — this matches the acid-chloride-to-aldehyde conversion in (B).

The Etard reaction oxidizes a benzylic methyl group to an aldehyde using $\mathrm{Cr}{\mathrm{O}}_2\mathrm{C}{\mathrm{l}}_2$ in $\mathrm{C}{\mathrm{S}}_2$ followed by hydrolysis — this matches (C).

The Gattermann–Koch reaction formylates an aromatic ring directly using $CO/HCl$ with anhydrous $\mathrm{AlC}{\mathrm{l}}_3/CuCl$ as catalyst — this matches (D).

So (A) is the Stephen reaction, (B) is the Rosenmund reduction, (C) is the Etard reaction, and (D) is the Gattermann–Koch reaction.