Experiment 8

Objective

To prepare methyl orange (4-(N,N-Dimethylamino)azobenzene-4-sulphonic acid) from para-sulphobenzene diazonium chloride.

Introduction

Methyl orange, or 4-(N,N-Dimethylamino)azobenzene-4-sulphonic acid, is synthesized by a coupling reaction between para-sulphobenzene diazonium chloride and N,N-dimethyl aniline in an acidic medium. This reaction produces a distinct orange dye known as methyl orange.

Materials

Chemicals

●      Para-sulphobenzene diazonium chloride

●      Hydrochloric acid (HCl)

●      N,N-Dimethyl aniline

Apparatus

●      Test tube

●      Test tube holder

●      Thermometer

●      Dropper

Reagents

●      5–6 ml of N,N-dimethyl aniline and HCl mixture

●      Para-sulphobenzene diazonium chloride, added dropwise

Procedure

1.    Place the N,N-dimethyl aniline and HCl mixture in a test tube.

2.    Add para-sulphobenzene diazonium chloride dropwise to the test tube.

3.    Keep the temperature below 10°C (monitor using a thermometer).

4.    Stop the reaction when the solution turns a distinct orange color, indicating methyl orange formation.

Observation

An orange-colored solution, signifying the formation of methyl orange, is observed in the test tube.

Questions

1.    What is methyl orange?

2.    What is a diazonium salt?

3.    How is diazonium salt formed?

4.    How is methyl orange formed?