Question 13 of 20intermediate💡 UnderstandLong Answer5 marks

Describe a method for the identification of primary, secondary and tertiary amines. Also write chemical equations of the reactions involved.

Correct Answer

p-Toluenesulphonyl chloride is used for the identification of primary, secondary and tertiary amines. The influence of the number of hydrogen atoms at the nitrogen atom on the type of reactions and nature of products is responsible for identification and distinction between these amines.

Carbylamine reaction (isocyanide test) is another method for identification. Aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium hydroxide form isocyanides or carbylamines which are foul smelling substances. Secondary and tertiary amines do not show this reaction. This reaction is used as a test for primary amines.

The chemical equation for carbylamine reaction is: R-NH₂ + CHCl₃ + 3KOH → R-NC + 3KCl + 3H₂O

Reaction with nitrous acid is another distinguishing method. Three classes of amines react differently with nitrous acid which is prepared in situ from a mineral acid and sodium nitrite. Primary aliphatic amines react with nitrous acid to form aliphatic diazonium salts which being unstable, liberate nitrogen gas quantitatively and alcohols.

The quantitative evolution of nitrogen is used in estimation of amino acids and proteins.

Exercise: EXERCISES | Q: 9.6 | (Page 21)
For More Understanding

Explanation

The textbook mentions p-Toluenesulphonyl chloride as the primary method for distinguishing between primary, secondary and tertiary amines. Additionally, two other methods are described: the carbylamine reaction (which gives a positive test only for primary amines) and reaction with nitrous acid (where different classes of amines react differently). The chemical equation is explicitly provided only for the carbylamine reaction in the given context.

Solution Steps

  1. Step 1: Identify the methods mentioned in the textbook for distinguishing amines

  2. Step 2: Describe p-Toluenesulphonyl chloride method as the primary identification method

  3. Step 3: Explain carbylamine reaction with its chemical equation

  4. Step 4: Describe reaction with nitrous acid for distinguishing amine classes

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