Experiment 105

Objective

To prepare benzene diazonium salt in the laboratory.

Introduction

Benzene diazonium salt is prepared by reacting aniline with hydrochloric acid (HCl) and sodium nitrite (NaNO₂) at a low temperature (0–5°C). This reaction occurs in three steps:

1.    Formation of Nitrous Acid: HCl reacts with sodium nitrite to produce nitrous acid (HNO₂).

2.    Formation of Anilinium Hydrochloride: HCl reacts with aniline to produce anilinium hydrochloride.

3.    Formation of Diazonium Salt: The anilinium hydrochloride then reacts with nitrous acid to produce benzene diazonium chloride.

Overall Reaction:

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

Materials

Chemicals

·       Aniline (Phenylamine)

·       Hydrochloric acid (HCl)

·       Sodium nitrite (NaNO₂)

Apparatus

·       Beaker

·       Ice

·       Ice bath

·       Thermometer

Reagents

·       10 ml of HCl

·       10 ml of aniline in a beaker

·       Sodium nitrite, added dropwise

Procedure

1.    Prepare a mixture of aniline and HCl in a beaker.

2.    Place the beaker in an ice bath to maintain a temperature between 0–5°C (monitor using a thermometer).

3.    Add sodium nitrite dropwise to the mixture, ensuring the temperature remains at 0–5°C.

4.    Stop the reaction once benzene diazonium chloride is formed.

5.    Use the diazonium salt as a solution.

Observation

A clear solution of benzene diazonium salt is obtained.

Questions

1.    What is a diazonium salt?

2.    Why must the temperature be controlled between 0–5°C in diazonium salt preparation?

3.    How is diazonium salt formed?