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

(i) These can be distinguished by the carbylamine test. Methylamine is a primary amine, therefore, it gives carbylamine test, i.e., when heated with an alcoholic solution of KOH and `CHCl_(3)`, it gives offensive smell of methyl isocyanide. In constrast, dimethylamine is a secondary amine and hence does not give this test.
`underset("Methylamine "(1^(@)" Amine"))(CH_(3)NH_(2))+CHCl_(2)+ underset((alc))(3KOH)overset(Delta)to underset("Methyl isocyanide (offensive smell)")(CH_(3)N overset(to)(=)C+3KCl +3H_(2)O`
`underset("Dimethylamine "(2^(@)" Amine"))((CH_(3))_(2)NH) underset(Delta)overset(CHCl_(3)//KOH(alc))to ` No reaction.
(ii) These can be distinguished by Liebermann nitrosoaine test since `2^(@)` amines give Liebermann nitrosoaine test while `3^(@)` amines do not.
`2^(@)` amines on treatment with `HNO_(2)` (generated in situ by the action of dol. HCl on `NaNO_(2)`) gives yellow coloured oily N-nitrosoamines. for example,
`underset("Diethylamine")((CH_(3)CH_(2))_(2)NH)+HO-N=O to underset("N-Nitrosodiethylamine (Yellow colour)")((CH_(3)CH_(2))_(2)N-N=O)+H_(2)O`
N-Nitrosodiethylamine on warming with a crystal of phenol and conc. `H_(2)SO_(4)`, gives a gree solution which when made alkaline with aqueous, NaOH turns deep blue and then red on dilution. Tertiary amines, on th other hand, do not give this test.