Experiment 22

Objective

To differentiate between aliphatic and aromatic amines by observing their reactions with nitrous acid.

Introduction

Amines react with nitrous acid to form diazonium salts, but only aromatic amines, such as aniline, form stable diazonium salts. Aliphatic amines (e.g., methylamine) produce unstable diazonium salts that quickly decompose, releasing nitrogen gas as bubbles.

Reactions:

1.    Aromatic Amine (Aniline):

C6H5​NH2 ​+ HCl + NaNO2​ → C6​H5​N2​Cl + NaCl + H2​O

2.    Aliphatic Amine (Methylamine):

C6​H5NH2 ​+ HCl + NaNO2​ → C6​H5​N2Cl + NaCl + H2​O

Materials

Chemicals

●      Aniline (aromatic amine)

●      Methylamine (aliphatic amine)

●      Hydrochloric acid (HCl)

●      Sodium nitrite (NaNO₂)

Apparatus

●      Two test tubes

●      Two test tube holders

●      Dropper

●      Ice bath

●      Ice

●      Thermometer

Reagents

●      5–6 ml of methylamine and aniline mixture in each test tube

●      3–4 ml of HCl for each test tube

●      Sodium nitrite added dropwise

Procedure

1.    Place the methylamine and aniline mixtures in separate test tubes.

2.    Secure each test tube in a holder.

3.    Add NaNO₂ dropwise to each test tube.

4.    Maintain the temperature between 0–5°C using an ice bath (monitor with a thermometer).

5.    Observe the reactions in each test tube.

Observation

In the aniline test tube, a stable diazonium salt is formed. In the methylamine test tube, nitrogen gas is released as bubbles due to the decomposition of the unstable aliphatic diazonium salt.

Questions

1.    What is a diazonium salt?

2.    Why do aliphatic amines not form stable diazonium salts?

3.    Why can aromatic amines produce stable diazonium salts?