Explanation:

Gabriel phthalimide synthesis is a method to prepare primary amines from phthalimide. The synthesis involves the conversion of phthalimide to phthalimide anion, which then undergoes nucleophilic substitution with an alkyl halide to form an N-alkylphthalimide. The N-alkylphthalimide is then hydrolyzed under basic conditions to yield the primary amine. However, this method cannot be used to prepare aromatic primary amines.

Reasons:

There are several reasons why aromatic primary amines cannot be prepared by Gabriel phthalimide synthesis:

1. Aromatic amines are less reactive than aliphatic amines towards nucleophilic substitution reactions. This is due to the electron-donating effect of the aromatic ring, which decreases the reactivity of the nitrogen atom towards nucleophiles.

2. Phthalimide anion, which is the key intermediate in Gabriel phthalimide synthesis, is a strong nucleophile. However, it cannot react with aromatic halides due to the low reactivity of the halogen atom in these compounds.

3. Even if an aromatic halide could react with phthalimide anion, the resulting N-arylphthalimide would be unstable and prone to side reactions such as elimination and oxidation.

Alternative methods:

There are several alternative methods for preparing aromatic primary amines, including:

1. Reduction of nitroarenes: Nitroarenes can be reduced to aromatic primary amines using reagents such as iron, zinc, or catalytic hydrogenation.

2. Sandmeyer reaction: This reaction involves the conversion of an aryl diazonium salt to an aryl halide, which can then be converted to an aryl primary amine using nucleophilic substitution.

3. Buchwald-Hartwig reaction: This is a palladium-catalyzed cross-coupling reaction between an aryl halide and an amine, which results in the formation of an aryl primary amine.

Conclusion:

In summary, Gabriel phthalimide synthesis cannot be used to prepare aromatic primary amines due to the low reactivity of the nitrogen atom in aromatic amines and the low reactivity of the halogen atom in aromatic halides. Alternative methods such as reduction of nitroarenes, Sandmeyer reaction, and Buchwald-Hartwig reaction can be used to prepare aromatic primary amines.