Consider the following reactions giving major product. Identify the correct reaction.
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- H3CCH2- O \|C-NH2 + Br2 + 4 KOH (alc) H3CCH2NH2 + 2KBr + K2CO3 + 2H2O
Answer
(4) H3CCH2- O \|C-NH2 + Br2 + 4 KOH (alc) H3CCH2NH2 + 2KBr + K2CO3 + 2H2O
Solution
(1) In benzanilide (C6H5NHCOC6H5) the ring attached to –NH– is activated (lone pair of N), while the ring attached to C=O is deactivated. Nitration therefore occurs at the para position of the ring bonded to N, giving p-O2N-C6H4-NHCOC6H5, not the product shown. Incorrect.
(2) The carbylamine reaction does give benzyl isocyanide, but reduction of an isocyanide gives a secondary amine:
C6H5CH2NC + 4[H] C6H5CH2NHCH3 (N-methylbenzylamine), not benzylamine. Incorrect.
(3) As per NCERT, aromatic primary amines cannot be prepared by Gabriel phthalimide synthesis, because aryl halides do not undergo nucleophilic substitution with the phthalimide anion. Incorrect.
(4) Hoffmann bromamide degradation: the amide is converted into a primary amine with one carbon atom less.
CH3CH2CONH2 + Br2 + 4KOH CH3CH2NH2 + K2CO3 + 2KBr + 2H2O
Propanamide gives ethanamine and the equation is balanced (K: 4 = 2 + 2; O: 1 + 4 = 3 + 2; H: 7 + 4 = 7 + 4). Correct.
Answer: (4)