medium difficulty6 min

Important Reactions and Tests of Amines

Amines undergo reactions based on the nucleophilic lone pair of nitrogen, including acylation, alkylation, carbylamine reaction, Hinsberg test, and reaction with nitrous acid.

In one line: Tests follow class: primary reacts in carbylamine, Hinsberg separates the three classes.

Practice This Concept

Understand it

Primary and secondary amines react with acyl chlorides or acid anhydrides to form substituted amides.
Alkylation can give higher amines and eventually quaternary ammonium salts.
Primary amines give the carbylamine reaction with chloroform and alcoholic KOH, forming isocyanides with an unpleasant odour, while secondary and tertiary amines do not give this test.
Hinsberg reagent helps distinguish primary, secondary, and tertiary amines by their sulphonamide behaviour.
Nitrous acid reactions differ for aliphatic and aromatic amines and for amine class.

Example

Aniline reacts with benzoyl chloride in the presence of base to form N-phenylbenzamide. Methylamine gives a positive carbylamine test, but dimethylamine does not.

Rule to remember

Key patterns: RNH2 + RCOCl gives substituted amide; primary amine + CHCl₃ + alcoholic KOH gives isocyanide; Hinsberg reagent distinguishes amine classes through sulphonamide formation and solubility behaviour.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1Distinguish ethylamine and diethylamine.
2Use carbylamine test: ethylamine is primary and gives isocyanide formation, while diethylamine is secondary and does not give the test.

Method you can reuse

1Identify the amine class.
2Select the reagent: acyl chloride for acylation, alkyl halide for alkylation, CHCl3/KOH for carbylamine, Hinsberg reagent for distinction, or nitrous acid for class-specific products.
3Then write the product and observation if asked.

Visual tip

A decision table for primary, secondary, and tertiary amines with carbylamine and Hinsberg tests is useful.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Which type of amine gives carbylamine reaction?

Think first, then show answer

Only primary amines give carbylamine reaction with chloroform and alcoholic KOH.

Common wrong answer

Writing an isocyanide product for a secondary amine in carbylamine reaction.

Why it loses marks: The reaction requires an N-H pattern of a primary amine.

Don't mix this up

Students often write the carbylamine test for secondary amines, although it is given only by primary amines.

Exam tip

For test-based questions, first identify the class of amine, then apply the correct reagent observation or product.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Questions ask for product prediction, distinguishing tests, named reagent use, completion of reactions, and explanations for selective reactions of primary amines.

1
Enough for 1 mark
Amines undergo reactions based on the nucleophilic lone pair of nitrogen, including acylation, alkylation, carbylamine reaction, Hinsberg test, and reaction with nitrous acid.
2
Add for 2 marks
Example: Aniline reacts with benzoyl chloride in the presence of base to form N-phenylbenzamide. Methylamine gives a positive carbylamine test, but dimethylamine does not.
3
Add for 3 marks
Primary and secondary amines react with acyl chlorides or acid anhydrides to form substituted amides.

MCQ Quiz

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