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In the Hofmann bromamide degradation reaction, R-CO-NH2 reacts with Br2 and KOH. Which of the following is/are intermediate(s) in this reaction?

1. R-CO-NH-Br
2. R-N=C=O
3. R-NH2
4. R-CNO

Correct answer: R-CO-NH-Br

Solution

The Hofmann bromamide degradation mechanism: Step 1 - R-CO-NH2 + Br2 + KOH -> R-CO-NH-Br (N-bromoamide, intermediate A) + KBr + H2O. Step 2 - R-CO-NH-Br + KOH -> R-CO-N^(-)-Br (anion) -> rearrangement to R-N=C=O (isocyanate, intermediate B). Step 3 - R-N=C=O + H2O -> R-NH2 (product) + CO2. Intermediates: R-CO-NH-Br and R-N=C=O. R-NH2 is the final product. R-CNO is not a real intermediate. So both options A (R-CO-NH-Br) and B (R-N=C=O) are intermediates; since the question may be single-answer, both are correct as intermediates.

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