Which statement is/are true for Gabriel Phthalamide synthesis?
A. It is used for the preparation of primary and secondary amines
B. It is only used for the preparation of primary amines
C. Aromatic primary amines cannot be prepared by this method
D. Only tertiary amines can be prepared
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → B, C only
In Gabriel phthalimide synthesis, phthalimide is first converted by ethanolic KOH into potassium phthalimide. This salt is heated with an alkyl halide to give an N-alkylphthalimide, and alkaline hydrolysis then releases the primary amine:
\( \ce{C6H4(CO)2NH + KOH} \xrightarrow{\text{ethanol}} \ce{C6H4(CO)2N^-K^+ + H2O} \)
\( \ce{C6H4(CO)2N^-K^+ + R-X} \xrightarrow{\Delta} \ce{C6H4(CO)2N-R + KX} \)
\( \ce{C6H4(CO)2N-R + 2NaOH(aq)} \xrightarrow{\Delta} \ce{C6H4(COO^-Na^+)2 + R-NH2} \)
(A) It is used for the preparation of primary and secondary amines — False. Secondary amines are not formed. The phthalimide nitrogen carries only one alkyl group, which ends up as \( \ce{RNH2} \).
(B) It is only used for the preparation of primary amines — True. The nitrogen of phthalimide has only one hydrogen to replace, so only one alkyl group can be put on it. Alkaline hydrolysis of the N-alkylphthalimide then gives \( \ce{R-NH2} \), a primary amine, free from secondary and tertiary amines.
(C) Aromatic primary amines cannot be prepared by this method — True. Aryl halides do not undergo nucleophilic substitution with the phthalimide anion, so aniline cannot be made this way.
(D) Only tertiary amines can be prepared — False. A tertiary amine has three alkyl groups on nitrogen. The phthalimide nitrogen can take only one, so tertiary amines are never formed in this synthesis.
NCERT (2026-27 edition):
Gabriel Phthalimide Synthesis
