JEE Main · 2024 · 30 Jan 2024 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

Etard-type sequence: the toluene methyl group is first protected/activated with $\mathrm{Cr}{\mathrm{O}}_3/(\mathrm{C}{\mathrm{H}}_3\mathrm{CO}{)}_2\mathrm{O}$ (reagent A) to give the benzylidene diacetate, which on hydrolysis (${\mathrm{H}}_3{\mathrm{O}}^{+}$) gives the aldehyde.

In the parallel route, the methyl group is oxidised directly by $\mathrm{Cr}{\mathrm{O}}_2\mathrm{C}{\mathrm{l}}_2$ (reagent B, the Etard reaction) via the chromium complex $\mathrm{CH}[\mathrm{OCrC}{\mathrm{l}}_2(\mathrm{OH}){]}_2$, which on hydrolysis also gives the aldehyde.

So A $=\mathrm{Cr}{\mathrm{O}}_3$ and B $=\mathrm{Cr}{\mathrm{O}}_2\mathrm{C}{\mathrm{l}}_2$.