Chemistry · Amines · NEET
It REMOVES one carbon. The amide R-CONH2 has the R group plus the carbonyl carbon. That carbonyl carbon leaves as carbonate ion (CO3 2-), so the final amine R-NH2 has one fewer carbon than the starting amide. Example: CH3CONH2 (2 carbons) gives CH3NH2 (1 carbon).
During the mechanism, the R group migrates from the carbonyl carbon to the nitrogen. This forms an isocyanate (R-N=C=O). When the isocyanate is hydrolysed by NaOH, the C=O part is lost as carbonate, leaving only R-NH2. So the carbon that was the C=O carbon is gone from the amine.
The key intermediate is an alkyl (or aryl) ISOCYANATE, R-N=C=O. Steps: (1) base removes an N-H proton, (2) Br adds to N giving N-bromoamide, (3) base removes the second N-H, (4) the R group migrates to N as Br leaves, giving the isocyanate, (5) the isocyanate is hydrolysed to the amine + carbonate.
They are totally different. Hoffmann bromamide degradation (this page) makes a primary amine from an amide using Br2/NaOH and shortens the chain by one carbon. Hofmann elimination is about quaternary ammonium hydroxides losing water to give the LESS substituted alkene (anti-Saytzeff). Do not mix them; NEET sometimes lists both names to confuse you.
Yes. Hoffmann bromamide degradation only works on primary amides (R-CONH2) and always gives a primary amine (R-NH2). It cannot give secondary or tertiary amines, and it cannot be used on secondary amides. This is a common trap in mixed reagent questions.
Bromine (Br2) with aqueous NaOH or KOH. In some books it is written as Br2/KOH or NaOBr (sodium hypobromite). All three phrasings mean the same reaction. If you see amide + Br2/NaOH in NEET, think Hoffmann bromamide degradation and remove one carbon.
Which of the following reactions is appropriate for converting acetamide (CH3CONH2) to methanamine (CH3NH2)?
Identify the major product C: CH3CH2CH2I -> (NaCN) A -> (partial hydrolysis, OH-) B -> (Br2/NaOH) C
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It converts a primary amide R-CONH2 into a primary amine R-NH2 using Br2 and NaOH, removing one carbon atom.
It is a way to shorten a carbon chain by one carbon (a descent of series) while placing an -NH2 group on the next carbon. NEET often puts it in multi-step conversion questions.
Yes. Benzamide (C6H5CONH2) with Br2/KOH gives aniline (C6H5NH2), losing the carbonyl carbon as carbonate.
An isocyanate, R-N=C=O. It forms after the R group migrates to nitrogen, then it is hydrolysed to the amine.
No. It only works on primary amides (R-CONH2) and always gives a primary amine.
