Organic Compounds Containing Nitrogen - Identification of primary, secondary and tertiary amines
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Amines are classified as primary (), secondary (), or tertiary () based on the number of alkyl or aryl groups attached to the nitrogen atom.
Hinsberg's Test: This is the most important chemical test to distinguish between the three types of amines. It uses Benzenesulfonyl chloride () as the reagent in the presence of an alkali like .
Reaction with Nitrous Acid (): This test differentiates amines based on the nature of the products formed (evolution of gas, formation of yellow oily nitroso compounds, or diazonium salts).
Carbylamine Test: This test is specific ONLY to primary amines (both aliphatic and aromatic). It involves heating the amine with chloroform () and alcoholic to produce foul-smelling isocyanides ().
Azo-dye Test: Used to identify aromatic primary amines (like aniline). It involves the reaction of a diazonium salt with -naphthol in alkaline conditions to form a bright orange/red dye.
Reaction with Mustard Oil (Hofmann Mustard Oil Reaction): Primary amines react with carbon disulfide () and mercuric chloride () to give alkyl isothiocyanates () which have a pungent smell like mustard oil.
📐Formulae
💡Examples
Problem 1:
How can you chemically distinguish between Ethylamine () and Diethylamine ()?
Solution:
Use the Hinsberg's Test or the Carbylamine Test.
Explanation:
- In Hinsberg's Test: Ethylamine (primary) reacts with to form -ethylbenzenesulfonamide, which is soluble in . Diethylamine (secondary) reacts to form -diethylbenzenesulfonamide, which remains insoluble in . 2. In Carbylamine Test: Ethylamine gives a foul smell of ethyl isocyanide () when heated with , while diethylamine does not respond to this test.
Problem 2:
Describe a test to distinguish between Aniline () and -methylaniline ().
Solution:
The Azo-dye test or Carbylamine test can be used.
Explanation:
Aniline is a primary aromatic amine. It undergoes diazotization with at to form a diazonium salt, which then reacts with -naphthol to form a brilliant orange-red dye. -methylaniline is a secondary amine; it does not form a diazonium salt and therefore does not give the azo-dye test. Additionally, Aniline gives the Carbylamine test, while -methylaniline does not.
Problem 3:
What happens when Trimethylamine () is treated with Benzenesulfonyl chloride?
Solution:
No reaction occurs in the presence of alkali.
Explanation:
Tertiary amines like do not have a replaceable hydrogen atom on the nitrogen. While they may form an unstable salt with , the salt is hydrolyzed back in the presence of aqueous alkali (). Thus, practically, no visible reaction is observed.