Experiment 90

Objective

To prepare picric acid (2,4,6-trinitrophenol) from chlorobenzene through nitration.

Introduction

Picric acid is synthesized by nitrating chlorobenzene. The reaction involves treating chlorobenzene with a mixture of nitric acid and sulfuric acid to form dinitrochlorobenzene, which, after further nitration and conversion with sodium hydroxide, yields picric acid.

Reaction Steps

1.    Nitration of Chlorobenzene

C6H5​Cl + HNO3​ + H2​SO4 ​→ 2,4 - Dinitrochlorobenzene

2.    Formation of Dinitrophenolz

o   Dinitrochlorobenzene is reacted with NaOH to form 2,4-dinitrophenol.

3.    Final Nitration to Picric Acid

o   Further nitration with HNO₃ and H₂SO₄ converts dinitrophenol into 2,4,6-trinitrophenol (picric acid).

Materials

Chemicals

·       Chlorobenzene

·       Nitric acid (HNO₃)

·       Sulfuric acid (H₂SO₄)

·       Sodium hydroxide (NaOH)

Apparatus

·       Test tube

·       Test tube holder

·       Tissue paper

·       White paper for color observation

Reagents

5-6 mL of chlorobenzene with sulfuric acid and nitric acid, followed by sodium hydroxide.

Procedure

1.    Preparation of Reaction Mixture

o   Place 5-6 mL of chlorobenzene in a test tube.

2.    Addition of Acid Mixture

o   Carefully add a mixture of sulfuric acid and nitric acid to the test tube to initiate the nitration process, producing 2,4-dinitrochlorobenzene.

3.    Conversion to Dinitrophenol

o   Add sodium hydroxide to the dinitrochlorobenzene to convert it into 2,4-dinitrophenol.

4.    Final Nitration

o   Add another portion of sulfuric acid and nitric acid to the dinitrophenol to produce picric acid (2,4,6-trinitrophenol).

Observation

A yellow-colored solution appears, indicating the formation of picric acid.

Questions

1.    What is picric acid?

2.    What are the uses of picric acid?

3.    Why is chlorobenzene used in the production of picric acid?