Consider the following statements about the preparation of amines.
(A) In Hoffmann bromamide degradation, an alkyl or aryl group migrates from the nitrogen atom to the carbonyl carbon of the amide.
(B) The amine formed in Hoffmann bromamide degradation contains one carbon atom less than the amide.
(C) The order of reactivity of alkyl halides with amines is RI > RBr > RCl.
(D) In Gabriel phthalimide synthesis, the potassium salt of phthalimide is heated with an alkyl halide and the product is then hydrolysed with alkali to give the primary amine.
(E) In ammonolysis, an alkyl halide undergoes electrophilic substitution in which the halogen atom is replaced by an amino group.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) and (E) only
In the preparation of amines the key points are what attacks what, and where the groups move.
(A) In Hoffmann bromamide degradation, an alkyl or aryl group migrates from the nitrogen atom to the carbonyl carbon of the amide. — Incorrect statement. The group moves the other way, from the carbonyl carbon to the nitrogen atom.
The carbonyl carbon is then lost as carbonate:
\( \displaystyle \ce{R-CONH2 + Br2 + 4NaOH -> R-NH2 + Na2CO3 + 2NaBr + 2H2O} \)
(B) The amine formed in Hoffmann bromamide degradation contains one carbon atom less than the amide. — Correct statement. Since the carbonyl carbon leaves as Na2CO3, the amine has one carbon less.
(C) The order of reactivity of alkyl halides with amines is RI > RBr > RCl. — Correct statement. The C–I bond is the easiest of the three to break.
(D) In Gabriel phthalimide synthesis, the potassium salt of phthalimide is heated with an alkyl halide and the product is then hydrolysed with alkali to give the primary amine. — Correct statement. The alkyl group goes on to nitrogen, and alkaline hydrolysis then sets the primary amine free.
(E) In ammonolysis, an alkyl halide undergoes electrophilic substitution in which the halogen atom is replaced by an amino group. — Incorrect statement. Ammonia attacks with its unshared electron pair, so it is a nucleophile and the reaction is a nucleophilic substitution:
\( \displaystyle \ce{R-X + NH3} \xrightarrow[\text{373 K}]{\text{ethanol}} \ce{R-NH3^+X^-} \)
NCERT (2026-27 edition):
9.4 Preparation of Amines – “In this degradation reaction, migration of an alkyl or aryl group takes place from carbonyl carbon of the amide to the nitrogen atom. The amine so formed contains one carbon less than that present in the amide.”
“The order of reactivity of halides with amines is RI > RBr >RCl.”
“Phthalimide on treatment with ethanolic potassium hydroxide forms potassium salt of phthalimide which on heating with alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine.”
“…an alkyl or benzyl halide on reaction with an ethanolic solution of ammonia undergoes nucleophilic substitution reaction in which the halogen atom is replaced by an amino (–NH2) group.”