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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Solution

(a) Gabriel phthalimide synthesis involves nucleophilic substitution $(S_{N^{2}})$ 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 and thus aromatic primary amines cannot be prepared by this process.
(b) The reaction of a primary amine with benzene sulphonyl chloride gives a corresponding $N$ -alkyl benzene sulphonylamide. Owing to the presence of strong electron withdrawing sulphonyl group, attached to a nitrogen atom in $N$ -alkyl benzene sulphonylamide is strongly acidic and dissolves in alkali.
On the other hand, a reaction of the secondary amine with benzene sulphonyl chloride gives corresponding $N, N$ -dialkyl benzene sulphonylamide which do not contain acidic hydrogen and hence is insoluble in alkali.

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Similar questions

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

Why cannot aromatic primary amines 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

Q. Gabriel phthalimide synthesis can be used for the synthesis of aromatic 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.

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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.

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.