Experiment 91

Objective

To prepare phenol in the laboratory from aniline through diazotization followed by hydrolysis.

Introduction

Aniline (amino benzene) can be converted to phenol by first forming benzene diazonium chloride in a reaction with nitrous acid and hydrochloric acid at low temperatures (0-5°C). The diazonium salt is then hydrolyzed by heating in water to produce phenol.

Reaction Steps

1.    Formation of Benzene Diazonium Chloride

C6​H5​NH2 ​+ HNO2 ​+ HCl → C6​H5​N2​Cl + 2H2​O

2.    Conversion to Phenol

C6​H5N2​Cl + H2​O → C 6​H5​OH + N2​↑+HCl

Materials

Chemicals

·       Aniline

·       Nitrous acid (HNO₂)

·       Hydrochloric acid (HCl)

·       Distilled water

Apparatus

·       Beaker

·       Thermometer

·       Glass stirrer

·       Bunsen burner

·       Ice bath

Reagents

·       Use 10 mL aniline, 2-3 mL hydrochloric acid, and nitrous acid; add distilled water for the diazonium salt hydrolysis.

Procedure

1.    Preparation of Reaction Solution

o   In a beaker, mix hydrochloric acid (HCl) and nitrous acid (HNO₂) and place the beaker in an ice bath to maintain a temperature of 0-5°C.

2.    Addition of Aniline

o   Using a pipette, add aniline dropwise to the cold solution to form benzene diazonium chloride.

3.    Formation of Phenol

o   Add distilled water to the solution and heat gently to 60°C to hydrolyze the diazonium salt, converting it to phenol.

Observation

Upon hydrolysis, nitrogen gas is released as bubbles, and phenol is produced in the solution.

Questions

1.    What is diazonium chloride?

2.    Why is it essential to maintain a temperature of 0-5°C during diazotization?

3.    Describe the process of phenol production from aniline.