Amines

Answer (b) dilute hydrochloric acid

Aliphatic primary amines react with cold nitrous acid to give alcohols with the quantitative evolution of gas.
\underset{\text{Ethylamine}}{ {C2H5NH2}} \underset{\text{Ethanol }}{ {C2H5OH}}

Aromatic tertiary amines undergo electrophilic substitution with nitrosonium ion at p-position of the phenyl ring to form green coloured p-nitrosoamines.

Both aliphatic and aromatic primary amines when warmed with chloroform and an alcoholic solution of KOH produce isocyanides or carbylamines.

A mixture of methylamine (1? amine) and dimethylamine (2? amine) can be separated with the help of and KOH (Hinsberg's method).
Methylamine will form N-methylbenzenesulphonamide which is soluble in KOH. Dimethylamine will form N,N dimcthylbenzene sulphonamide which is insoluble in KOH.

Dimethylamine is a tertiary amine, and tertiary amines do not react with nitrous acid (HNO ) to liberate nitrogen gas. On the other hand, primary and secondary amines react with nitrous acid to form diazonium salts, which then decompose to release nitrogen gas. Thus, Dimethylamine (A) does not liberate nitrogen on reaction with nitrous acid.

The basicity of an amine group (-NH ) is influenced by the substituents on the aromatic ring. The electron-withdrawing groups (such as -NO ) decrease the electron density on the nitrogen, thus reducing the basicity. On the other hand, electron-donating groups (such as -CH ) increase the electron density on the nitrogen, enhancing the basicity. - In option [A] (p-NO -C H NH ), the -NO group is an electron-withdrawing group and thus decreases the basicity of the amine. - In option [B] (C H -CH -NH ), the -CH group is an electron-donating group and increases the basicity of the amine. - In option [C] (m-NO -C H NH ), the -NO group is in the meta position, so it has a lesser effect on the electron density of the amine than when it is in the para position. Thus, the base is stronger than in option [A]. - In option [D] (C H NH ), the amine is attached to a phenyl group, which neither donates nor withdraws electron density significantly, making it weaker than the amine in option [B]. Thus, the strongest base is m-NO -C H NH , which is option [C].