Give one chemical test to distinguish between the following pairs of compounds .
i. Methylamine and dimethylamine
ii. Secondary and tertiary amines
iii. Ethylamine and aniline
iv. Aniline and benzylamine
v. Aniline and N-methylaniline

Explanation

Methylamine and dimehjthylamine can be disinguished by the carbylamine test. Carbylamine test: Aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium hydroxide from foul-smelling isocyanides or carbylamines. Methylamine (being an aliphatic primary amine) gives a positive carbylamine test, but dimethylamine does not.

Secondary and teritary amines can be distinguished by allowing them to react with Hinsberg's reagent (benzenesulphonyl chloride, `C_(6)H_(5)SO_(2)Cl`).
Secondary amines react with Hinsberg's reagent to from a product that is insoluble in an alkali. For example, N, N-diethylamine reacts with Hinsberg's reagent to from N, N-diethylbezenesulphonamide, which is insoluble in an alkali. Tertiary amines, however, do not react with hinsberg's reagent.

(iii) Ethylamine and aniline can be distiguished using the azo-day test. A day is obtained when aromatic amines react with `HNO_(2)(NaNO_(2)+dil.HCL)"at"0-5^(@)C,` followed by a reaction with the alkaline solution of 2-naphthol. The day is usually yellow, red, or orange in colour. Aliphatic amines give a brisk eddervescence due (to the evolution of `N_(2)` gas) under similar condition.
(iv) Aniline and benzylamine can be distingushed by their reactions with the help of nitrous acid, whihc is prepared in situ from a mineral acid and sodium nitrite. Benzvlamine reacts with nitrous acid to from undtable diazonium salt, whihc in turn givens alcohol with the evolution of nitrogen gas.

On the other hand, aniline reacts with `HNO_(2)` at a low temperature to from stable diazonium salt. Thus, nitrogen gas is not evolved.
`C_(6)H_(5)NH_(2)underset(273-273K)overset(NaNO_(2)+HCl)rarrC_(6)H_(5)-overset(+)N_(2)overset(-)Cl+NaCl+2H_(2)O`
(v) Aniline and N-methylaniline can be distinguished using the Carbylamine test. Primary amines, on heating with chloroform and ethanolic potassium hydroxide, from foul-semlling isocyanides or carbylamines. Aniline, being an aromatic primary amine, gives positive carbylamine test. However, N-methylaniline, being a secondary amine does not.