Why cannot aromatic primary amines be prepared by Gabriel phthalimide synthesis?
Solution and Explanation
Gabriel phthalimide synthesis is used for the preparation of aliphatic primary amines. It involves nucleophilic substitution (SN2) of alkyl halides by the anion formed by the phthalimide.
But aryl halides do not undergo nucleophilic substitution with the anion formed by the phthalimide.
Hence, aromatic primary amines cannot be prepared by this process.
Top Questions on Amines
- How will you convert nitrobenzene to 2, 4, 6-Tribromo aniline?
- (i) The reaction in which an amide is converted into a primary amine by the action of Br2 and alcoholic NaOH is known as ________.
(ii) How is a primary amine distinguished from a secondary amine using the Hinsberg test? - Write the structures of (A), (B), and (C) in the following reaction:
\[ C_6H_5NO_2 \xrightarrow{Fe/HCl} (A) \xrightarrow[\text{273 K}]{NaNO_2 + HCl} (B) \xrightarrow[\Delta]{H_2O/H^+} (C) \] - What happens when aniline reacts with the following:
(A) Bromine water
(B) $(CH_3CO)_2O$ / Pyridine
(C) $HNO_2 + HCl (0^\circ - 5^\circ C)$ - Why is \(-NH_2\) group of aniline acetylated before carrying out nitration?
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Concepts Used:
Preparation of Amines
- Reduction of nitro compounds: Nitro compounds are reduced to amines by reduction with metals in an acidic medium or by passing them through hydrogen gas in the presence of finely divided nickel, palladium, or platinum.
- Ammonolysis of alkyl halides: Alkyl benzyl halide undergoes a nucleophilic substitution reaction while reacting with an ethanolic solution of ammonia where the halogen atom is replaced by an amino group and this process of splitting of the C-X bond by an ammonia molecule is called ammonolysis.
- Reduction of Nitriles: On reduction of nitriles with lithium or aluminum hydride or catalytic hydrogenation are used.
- Reduction of amides: On reduction, the amides with lithium aluminum hydride yield amines.
- Gabriel phthalimide synthesis: Gabriel synthesis is used to prepare primary amines. Phthalimidewhen treated with ethanolic potassium hydroxide, forms potassium salt of phthalimide which when heated with alkyl halide followed by alkaline hydrolysis leads to the formation of the corresponding primary amine.
- Hoffmann bromamide degradation reaction: In the Hoffmann bromamide degradation reaction, the transfer of an alkyl or aryl group takes place from the carbonyl carbon of the amide to the nitrogen atom. The amine so formed, therefore, contains one carbon less than that present in the initial amine.