It is because there is double bond character between C\(\rightarrow\)X bond due to which it cannot be broken easily that is why aromatic amines cannot be prepared by Gabriel phthalimide synthesis.

Due to strong electron-donating effect of the -NH₂  group, the electron density increases at the 0-, positions. Further, when aniline is treated with Br₂ the Br⁺ attacks the benzene ring at o- and p-positions to form carbocation intermediates which are stabilized not only by the usual resonance of the Henzene ring. but also by the -NH₂ group as shown below: In case of o-bromination, the carbocation intermediate is stabilized not only by usual resonating structure (I, III and IV) but is also stabilized by resonance structure (II) in which the lone pair of electrons on the N. atom interacts with the positively charged carbon of the ring. Similarly, in case of p-bromination, the carbocation is stabilized not only by the usual resonating structures (V, VI, and VIII) but is also stabilized by the resonance structure (VII) in which the lone pair of electrons on the N-atom interacts with the positively charged carbon of the ring. These additional resonating structures (II and VII) increase the stability of the carbocation to such an extent that bromination occurs instantaneously at the p- and two. o- positions giving 2, 4, 6-tribromoaniline.

(i) Methylamine and dimethylamine can be distinguished by the carbylamine test. Carbylamine test: Aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium hydroxide form foul-smelling isocyanides or carbylamines. Methylamine (being aliphatic primary amine) gives a positive carbylamine test, but dimethylamine does not.
(ii) Secondary and tertiary amines can be distinguished by allowing them to react with Hinsbergs reagent (benzenesulphonyl chloride, C₆H₅SO₂Cl). Secondary amines react with Hinsberg’s reagent to form a product that is insoluble in an alkali. For example, N, N−diethylamine reacts with Hinsberg’s reagent to form N, N−diethylbenzenesulphonamide, which is insoluble in an alkali. Tertiary amines, however, do not react with Hinsberg’s reagent amines, however, do not react with Hinsberg’s reagent.
(iii) Aniline and benzylamine can be distinguished by their reactions with the help of nitrous acid, which is prepared in situ from a mineral acid and sodium nitrite. Benzylamine reacts with nitrous acid to form unstable diazonium salt, which in turn gives alcohol with the evolution of nitrogen gas. 

(i) Gabriel phthalimide synthesis: This reaction is used for the preparation of aliphatic primary amines. In this reaction, phthalimide is first of all treated with ethanolic KOH to form potassium phthalimide. Potassium phthalimide on treatment with alkyl halide gives N-alkyl phthalimide, which on hydrolysis with dilute hydrochloric acid gives a primary amine as the product.

(ii) Coupling reactions: Diazonium salts react with aromatic amines in weakly acidic medium and phenols in weakly alkaline medium to form coloured compounds called azo dyes by coupling at p-position of amines or phenol. The mechanism is basically that of electrophilic aromatic substitutions where the diazonium ion is electrophile.

(iii) Hoffman’s bromamide reaction: When a primary acid amide is heated with an aqueous or ethanolic solution of NaOH or KOH and bromine (i.e., NaOBr or KOBr), it gives a primary amine with one carbon atom less.

amines, i.e., diethylamine reacts with NaNO₂+HCI to give yellow oily nitrosoamine.

Isopropylamine, i.e., (CH)CH-NH is a \({ 1 }^{ \circ }\) amine.

(i) Chemical name of the poisonous vapours is methyl isocynate(MIC)
(ii) It can be prepared by heating methyl amine and phosgene.
(iii) The compound is highly reactive towards group like hydroxyl,amino, thio etc  which are present in enzymes , proteins , carbohydrates , cellular fluids like water present in human system. It destroys the lung tissues and causes acute breathing problems It is also absorbed by the skin and causes its destruction.
(iv) The factories where such chemicals are produced must be installed away from the cities and villages, preferably in remote areas. Proper training must be given to the factories and inspections must be carried out from time to time to ensure that everything is in order.