Experiment 10

Objective

To differentiate between primary, secondary, and tertiary amines by their reactions with nitrous acid (HNO₂).

Introduction

Amines react uniquely with nitrous acid (HNO₂), allowing their classification into primary, secondary, and tertiary forms. Nitrous acid, being unstable, is produced in situ from nitrite salts and hydrochloric acid (HCl).

●      Primary amines react with HNO₂ to produce nitrogen (N₂) gas, observed as bubbles. Initially, a diazonium salt is formed, which subsequently decomposes to release N₂.

●      Secondary amines react to form a nitrosamine, resulting in a yellow, oily liquid.

●      Tertiary amines form trialkyl or alkylphenyl ammonium nitrite salts, which dissolve in the solution.

Materials

Chemicals

●      Nitrous acid (HNO₂)

●      Hydrochloric acid (HCl)

●      Primary amine (e.g., benzylamine)

●      Secondary amine (e.g., diphenylamine)

●      Tertiary amine (e.g., triphenylamine)

Apparatus

●      Three test tubes

●      Three test tube holders

●      White paper (for observation contrast)

Reagents

Prepare a mixture of 2–3 ml of HNO₂ and HCl in each test tube. Add each amine (primary, secondary, tertiary) dropwise to the designated test tube.

Procedure

1.    Place the HNO₂ and HCl mixture in each of the three test tubes.

2.    Add a few drops of each type of amine to the corresponding test tube.

3.    Wait a few minutes to observe any reaction. Shake gently if necessary.

4.    Note the reaction for each type of amine.

Observation

●      Primary amine: N₂ gas is released, visible as bubbles.

●      Secondary amine: A yellow, oily liquid (nitrosamine) forms.

●      Tertiary amine: A soluble salt forms in the solution.

Questions

1.    What is a primary amine?

2.    What is a secondary amine?

3.    What is a tertiary amine?

4.    Describe what occurs when HNO₂ reacts with primary, secondary, and tertiary amines.