JEE Main · 2021 · 16 Mar 2021 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

Which of the following reaction DOES NOT involve Hoffmann bromamide degradation?

(A)(see structure)
(B)(see structure with reagents: i) Br₂, NaOH/H⁺ ii) NH₃/Δ iii) LiAlH₄/H₂O)
A
B
✓ Correct
(C)(see structure with reagents: i) NH₃, NaOH ii) Br₂, NaOH)
A
B
(D)(see structure with reagents: i) KOH, H₂O ii) Br₂, NaOH)
A
B

Answer: (B)

Solution

Hofmann bromamide degradation acts on a primary amide:

B r_{2}

in aqueous

NaOH

converts

RCON H_{2}

into

RN H_{2}

, an amine with one carbon fewer.
Phenylacetamide with

B r_{2} /NaOH

gives benzylamine directly by this route. Benzoyl chloride first takes up ammonia to give benzamide, and benzonitrile is partially hydrolysed by aqueous KOH to the same benzamide; each is then carried to aniline by

B r_{2} /NaOH

, so both sequences use the degradation as well.
In the remaining sequence the substrate is 1-phenylpropan-2-one, a methyl ketone. Here

B r_{2} /NaOH

brings about the haloform reaction, which cleaves the methyl group and yields phenylacetic acid on acidification; ammonia and heat convert the acid to its amide, and

LiAl H_{4}

reduces that amide to the amine without any loss of carbon. No amide ever meets

B r_{2} /NaOH

in this route.
The sequence that starts from 1-phenylpropan-2-one does not involve Hofmann bromamide degradation.

JEE Main · 2021 · 16 Mar 2021 · Shift 1 · Single correct option

Practise more: all JEE Main PYQs on Aldehydes Ketones and Carboxylic Acids →

JEE Main · 2021 · 16 Mar 2021 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

Solution

More JEE Main questions on Aldehydes Ketones and Carboxylic Acids