Preparation of Aniline Yellow: Theory, Procedure & Precautions

Aniline yellow is a volatile chemical that is used as an intermediary in the production of other colors. It is created through a coupling reaction between benzene diazonium chloride and phenylamine, often known as aniline. Aniline works as a nucleophile in the first step, reacting with benzene diazonium chloride to produce a C-N bond. The product loses the H+ to form an aromatic ring, resulting in the azo dye. Aniline yellow (para amino azobenzene) is produced in an acidic medium by the reaction of benzene diazonium chloride with aniline.This dye has no industrial importance because it is an acid-sensitive dye.

Key Terms: Benzene Diazonium chloride, Aniline Yellow, Aniline,Aromatic Ring, Phenylamine, Sodium Nitrate.

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Aim

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

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Theory

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Also known as para amino azobenzene, Aniline yellow is produced when benzenediazonium chloride reacts with aniline in an acidic medium.It is the simplest and first azo dye produced by a coupling reaction between benzene diazonium chloride and phenylamine, often known as aniline. Because it is an acid sensitive dye, this dye has no industrial importance. The first step is the synthesis of benzene diazonium chloride from aniline. 

When aniline is processed in the presence of acid with sodium nitrite, the following chemical reaction is involved.

Step 1: Ar-NH₂ + NaNO₂ + HCl → Ar-N₂ + -Cl- 

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)

The chemical reaction between Diazonium Chloride and Aniline

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Materials Required

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The list of materials required for the preparation of Aniline yellow is mentioned below.

• Aniline
• Hydrochloric acid
• Sodium nitrite
• Glacial acetic acid
• Bunsen burner
• Distilled water
• Round bottom flask
• Beaker
• Stirrer
• Funnel
• Water bath
• Conical flask

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Procedure

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The procedure to prepare Aniline yellow (also called as para amino azobenzene) from benzene diazonium chloride and aniline is mentioned below.

1. In a beaker, take 10ml of concentrated hydrochloric acid and 20ml of water and add 4.5ml of aniline to the mixture.
2. To obtain a clear solution, completely dissolve the mixture.
3. Cool the solution by placing it in an ice bath at 5°C.
4. To 20ml of water, add 4g of sodium nitrite. With continual stirring, add this sodium nitrite solution to the above mixture.
5. Diazotization occurs, resulting in the formation of benzene diazonium.
6. Then in 4ml of hydrochloric acid, prepare 4ml of aniline.
7. Constantly mix the aniline solution into the benzene diazonium chloride solution.
8. It produces a yellow precipitate of para amino azobenzene, often known as aniline yellow.
9. Filter the yellow precipitate through a buchner funnel and dry the crude sample between paper folds.
10. In order to obtain the pure dye, recrystallize the crude sample by dissolving it in carbon tetrachloride.

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Observation

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Observation of the practical is mentioned below.

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Result

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The yield of aniline yellow is _____ gm.

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Precautions

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The following precautions should be kept in mind while preparing aniline yellow.

• Put on a lab coat, gloves, and goggles.
• The experiment's temperature should be between 40°C and 50°C.
• Try to keep the pH of the reaction between 4-5.
• The crude sample should be rinsed many times with water.
• Be careful not to touch the dye otherwise it could stick to your hand.

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Things to Remember

• The temperature in this experiment should not exceed 50°C.
• This dye has no industrial importance because it is an acid sensitive dye.
• Aniline yellow preparation can also be done at home. Instead of the Buchner funnel, a homemade suction funnel and plastic bottles can be utilized. Ice cubes can be used to settle down the solution to keep the temperature around 5°C.