The correct statement/statements from the options given below is/are:

(A) Diazonium salts of aromatic amines are less stable than diazonium salts of aliphatic amines.
(B) Ethylamine is insoluble in water.
(C) Gabriel phthalimide synthesis can be used to prepare primary amines.
(D) Beacuse of +R-effect of -NH₂ group, aniline will undergo Friedel-Crafts acylation reaction.

Choose the correct answer from the options given below:

(C)  only

The correct answer is Option (3) → (C) only.

Let us go over each statement in more detail to understand which statement is correct or incorrect.

(A) Diazonium salts of aromatic amines are less stable than diazonium salts of aliphatic amines:

Incorrect: Aromatic diazonium salts (e.g., benzene diazonium chloride) are more stable than aliphatic diazonium salts. This is due to the resonance stabilization provided by the aromatic ring in aromatic diazonium salts, which helps to delocalize the positive charge on the nitrogen atom of the diazonium group. As a result, they are relatively stable at low temperatures.

On the other hand, aliphatic diazonium salts are unstable and tend to decompose rapidly at room temperature, releasing nitrogen gas. They are usually not isolated because they decompose quickly due to the lack of resonance stabilization.

Corrected Statement: Aromatic diazonium salts are more stable than aliphatic diazonium salts.

(B) Ethylamine is insoluble in water:

Incorrect: Ethylamine (Câ‚‚Hâ‚…NHâ‚‚) is actually soluble in water. The reason for this is that ethylamine, being a small molecule with an amino group (-NHâ‚‚), can form hydrogen bonds with water molecules. Hydrogen bonding increases the solubility of ethylamine in water, just as other low molecular weight amines are soluble in water.

Solubility decreases for larger amines because the hydrophobic alkyl chain dominates over the hydrophilic amine group, but ethylamine, with just two carbon atoms, is still quite soluble.

Corrected Statement: Ethylamine is soluble in water.

(C) Gabriel phthalimide synthesis can be used to prepare primary amines:

Correct: The Gabriel phthalimide synthesis is a classical method used to prepare primary amines. The process involves the following steps:

Phthalimide is treated with a base (like KOH) to form a potassium salt, which is then reacted with an alkyl halide.

This produces an N-alkylated phthalimide derivative.

Finally, the phthalimide derivative is hydrolyzed (either through acidic or basic hydrolysis) to yield a primary amine.

This method is specifically designed to produce primary amines without the risk of forming secondary or tertiary amines.

(D) Because of +R-effect of -NHâ‚‚ group, aniline will undergo Friedel-Crafts acylation reaction:

Incorrect: While the -NHâ‚‚ group on aniline exhibits a +R (resonance donating) effect, making the benzene ring electron-rich and more reactive toward electrophiles, aniline does not easily undergo Friedel-Crafts acylation (or alkylation) reactions.

The reason is that the -NH₂ group coordinates with the Lewis acid catalyst (such as AlCl₃) used in the Friedel-Crafts reaction. This coordination deactivates the ring towards electrophilic attack, as the lone pair of electrons on the nitrogen atom is no longer available to donate into the ring, and the reaction is hindered.

Corrected Statement: Aniline does not readily undergo Friedel-Crafts acylation due to the deactivation of the ring by complexation of the -NHâ‚‚ group with the Lewis acid catalyst.

Conclusion:

(A) is incorrect because aromatic diazonium salts are more stable than aliphatic ones.

(B) is incorrect because ethylamine is soluble in water.

(C) is correct because Gabriel phthalimide synthesis is a valid method for making primary amines.

(D) is incorrect because aniline does not undergo Friedel-Crafts acylation easily due to the deactivation by the -NHâ‚‚ group.

Therefore, the correct answer is: (C)  only.