Hofmann Bromamide Degradation
An amide is treated with bromine and aqueous potassium hydroxide, producing a primary amine that contains one fewer carbon atom than the starting amide; which named reaction explains this carbon loss?
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Solution
Hofmann bromamide degradation
The Hofmann bromamide degradation converts a primary amide into a primary amine having one carbon less than the original amide. The mechanism begins with bromination of the amide nitrogen to give an N-bromoamide, which loses a proton to base to form a bromamide anion. This rearranges by migration of the alkyl or aryl group from carbon to the electron-deficient nitrogen, expelling bromide and generating an isocyanate intermediate. The isocyanate is then hydrolysed by aqueous alkali to a carbamic acid, which decarboxylates to release the amine and carbon dioxide; the lost carbon leaves as that carbon dioxide, explaining the one-carbon reduction in chain length. Gabriel synthesis does not change the carbon count between halide and amine in this way and starts from a halide, not an amide. The Curtius rearrangement also gives amines with one fewer carbon but starts from an acyl azide, not from bromine and KOH treatment of an amide. The Mendius reduction reduces nitriles and adds no such loss. This is the standard NCERT named-reaction question. As a sanity check, the carbon balance confirms exactly one carbon departs as CO2, matching the observed shortening.
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About This Question
- Subject
- chemistry
- Chapter
- organic compounds containing nitrogen
- Topic
- hofmann bromamide degradation
- Difficulty
- Hard
- Year
- 2025
Solution
Correct Answer:
Hofmann bromamide degradation
The Hofmann bromamide degradation converts a primary amide into a primary amine having one carbon less than the original amide. The mechanism begins with bromination of the amide nitrogen to give an N-bromoamide, which loses a proton to base to form a bromamide anion. This rearranges by migration of the alkyl or aryl group from carbon to the electron-deficient nitrogen, expelling bromide and generating an isocyanate intermediate. The isocyanate is then hydrolysed by aqueous alkali to a carbamic acid, which decarboxylates to release the amine and carbon dioxide; the lost carbon leaves as that carbon dioxide, explaining the one-carbon reduction in chain length. Gabriel synthesis does not change the carbon count between halide and amine in this way and starts from a halide, not an amide. The Curtius rearrangement also gives amines with one fewer carbon but starts from an acyl azide, not from bromine and KOH treatment of an amide. The Mendius reduction reduces nitriles and adds no such loss. This is the standard NCERT named-reaction question. As a sanity check, the carbon balance confirms exactly one carbon departs as CO2, matching the observed shortening.
This hard difficulty chemistry question is from the chapter organic compounds containing nitrogen, covering the topic of hofmann bromamide degradation. It appeared in the 2025 exam.
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