Experiment 9

Objective

To prepare methyl red (4-(N,N-Dimethylamino)azobenzene-2-carboxylic acid) from ortho carboxyl diazonium chloride.

Introduction

Methyl red, or 4-(N,N-Dimethylamino)azobenzene-2-carboxylic acid, is synthesized through a coupling reaction between ortho carboxyl diazonium chloride and N,N-dimethyl aniline in an acidic medium. This reaction produces a distinct red dye known as methyl red.

Materials

Chemicals

●      Ortho carboxyl 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

●      Ortho carboxyl diazonium chloride, added dropwise

Procedure

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

2.    Add ortho carboxyl diazonium chloride dropwise to the test tube.

3.    Maintain the temperature below 10°C (use a thermometer to monitor).

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

Observation

A red-colored solution, signifying the formation of methyl red, is observed in the test tube.

Questions

1.    What is methyl red?

2.    What is a diazonium salt?

3.    How is diazonium salt formed?

4.    How is methyl red formed?