Account for the following: Gabriel phthalimide synthesis is preferred for synthesizing primary amines.

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Solution

Gabriel phthalimide synthesis is preferred for synthesizing primary amines:
Gabriel's phthalimide reaction is mostly preferred for the synthesis of pure primary amines only, and no $2 ° or 3 °$ Amines are involved in this synthesis.
Gabriel’s Phthalimide synthesis used for the conversion of primary alkyl halide into a primary amine can be given as :
Step 1: Phthalimide reacts with Potassium hydroxide to form N-Alkylphthalimide, which can be shown as
Step 2: The N-Alkylphthalimide formed reacts with sodium hydroxide forming the sodium salt of Phthalic acid and Primary amine, which can be given as:
In this synthesis process, the nucleophile Phthalimide ion attacks the primary Alkyl halide creating an electrophilic alkyl center.
Aromatic amine mostly prefers the electrophilic substitution reaction as the nucleophilic substitution tend to destabilize the resonance of the aromatic compounds.
Hence, Gabriel phthalimide synthesis is known to be preferred for synthesizing primary amines due to the lack of reactivity of aromatic amines.

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Why cannot aromatic primary amines be prepared by Gabriel phthalimide synthesis?

Q. Why can aromatic primary amines not be prepared by Gabriel phthalimide synthesis?

Account for the following

(i) $p K_{b}$ of aniline is more than that of methyl amine.

(ii) Ethylamine is soluble in water whereas aniline is not

(iii) Methyl amine in water reacts with ferric chloride to precipitate hydrated ferric oxide

(iv) Although amino group is o- and p- directing in aromatic electrophilic substitution, aniline on nitration gives a substantial amount of m-nitroaniline

(v) Aniline does not undergo Friedel Crafts reaction

(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines

(vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines

Account for the following:

(i) pK_bof aniline is more than that of methylamine.

(ii) Ethylamine is soluble in water whereas aniline is not.

(iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.

(iv) Although amino group is o, p− directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.

(v) Aniline does not undergo Friedel-Crafts reaction.

(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines.

(vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines.

Q. Account for the following:
(a) Gabriel phthalimide synthesis is not preferred for preparing aromatic primary amines.
(b) On reaction with benzene sulphonyl chloride, primary amine yields product soluble in alkali whereas secondary amine yields product insoluble in alkali.

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