Question

Give a chemical test for differentiating the following couple of compounds: (i) Secondary and Tertiary Amines
(ii) Methyl Amine and Dimethyl Amine
(iii) Ethylamine and Aniline

Hint:

Reactions with nitrous acid, acetic acid, and ferric chloride can help differentiate between various types of amines.

Answer 1

(i) Secondary and Tertiary Amines:
Secondary and tertiary amines can be differentiated by the reaction with nitrous acid. When secondary amines react with nitrous acid, they form a diazonium salt, which can be further tested. Tertiary amines, however, do not form a diazonium salt with nitrous acid. Instead, they produce a different set of products, such as aliphatic products due to the absence of a hydrogen atom attached to nitrogen in tertiary amines.

(ii) Methyl Amine and Dimethyl Amine:
Methyl amine (CH₃NH₂) and dimethyl amine (CH₃NHCH₃) can be differentiated by their reaction with acetic acid. Methyl amine reacts with acetic acid to form methylammonium acetate, while dimethyl amine reacts to form dimethylammonium acetate. The difference in the products can be identified by their physical properties or by further chemical reactions, such as protonation.

(iii) Ethylamine and Aniline:
Ethylamine and aniline can be differentiated by their reaction with ferric chloride. Aniline, being an aromatic amine, reacts with ferric chloride to form a deep red or purple complex, while ethylamine, being an aliphatic amine, does not form such a complex. This is a distinctive test for differentiating aromatic and aliphatic amines.