Preparation of Aniline Yellow

Aim

To prepare Aniline yellow (also called as para amino azobenzene) from benzene diazonium chloride and aniline.

Apparatus Required

• Aniline

• Sodium nitrite

• Hydrochloric acid

• Distilled water

• Glacial acetic acid

• Bunsen burner

• Round bottom flask

• Stirrer

• Beaker

• Funnel

• Conical flask

• Water bath

Theory

Aniline yellow is an unstable compound that is used as an intermediate for preparing other dyes. Aniline yellow (para amino azobenzene) is prepared by the coupling reaction between benzene diazonium chloride and aniline in an acidic medium. The dye has no industrial significance because it is an acid-sensitive dye.

The Chemical Reaction Involved 

Step 1: When aniline is treated with sodium nitrite in the presence of acid.

Ar-NH2  +  NaNO2  +  HCl    →    Ar-N2+ -Cl-

Aniline     Sodium      Hydrochloric    Benzene

                   Nitrite      Acid               diazonium chloride

Step 2:  Ar-N2+ - Cl- + Ar-NH2  →  Ar-N=N-NH-Ar

Step 3:  Ar-N=N-NH-Ar  →  Ar-N=N-Ar-NH2

            Aniline Yellow

In the first step, aniline acts as a nucleophile and reacts with benzene diazonium chloride to form a C-N bond. The product loses H+ and gives the azo dye.

Procedure

• First of all, take a 10ml concentrated hydrochloric acid (HCl) and 20ml water in a beaker and add4.5ml aniline to the mixture. Dissolve them thoroughly to get a clear solution.

• Cool the solution in an ice bath around 5°C. Mix 4gsodium nitrite with 20ml water and add this sodium nitrite solution to the above mixture by doing the constant stirring.

• After some time, Diazotization will take place and the formation of benzene diazonium will occur.

• Now, Prepare 4ml aniline in 4ml HCl and mix the aniline solution with benzene diazonium chloride solution by slow constant stirring.

• After some time, a yellow precipitate of para amino azobenzene which is also called aniline yellow is formed. Filter the yellow precipitate with a Buchner funnel and dry the crude sample in between the folds of paper.

• The crude sample can be recrystallized by dissolving in carbon tetrachloride to get the pure dye.

Setup

(Image to be added soon)

Observations

Result

Aniline yellow is produced in _____ gm.

Precautions

• Wear lab coats, gloves, and goggles.

• Try to maintain a pH of reaction between 4-5.

• The temperature of the experiment should range between 40°C to 50°C.

• The crude sample should be washed repeatedly by water.

Fun Fact

Preparation of Aniline yellow can be done in the home also. In place of the Buchner funnel, an alternate home-designed suction funnel and plastic bottles can be used.  can be used. To maintain the temperature approx 5°C , ice cubes can be used to settle down the solution.