JEE Main · 2021 · 20 Jul 2021 · Shift 2 · Compounds Containing Nitrogen

Potassium hypobromite is the Hofmann bromamide reagent. It brominates the amide nitrogen, the N-bromoamide loses hydrogen bromide to leave an electron deficient nitrogen, and the aryl group migrates from carbon to that nitrogen; the isocyanate so formed is hydrolysed and the original carbonyl carbon leaves as carbon dioxide, so product A is 3-bromoaniline, one carbon shorter than the amide. Lithium aluminium hydride instead delivers hydride to the amide carbon twice and the oxygen is lost, so the whole $-\mathrm{CON}{\mathrm{H}}_2$ group becomes $-\mathrm{C}{\mathrm{H}}_2\mathrm{N}{\mathrm{H}}_2$ with the carbon count unchanged, and product B is (3-bromophenyl)methanamine. The products are 3-bromoaniline and 3-bromobenzylamine respectively.