Preparation of 2 Naphthol Aniline Dye

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Preparation of 2 Naphthol Aniline Dye - Practical Experiment

2- Naphthol aniline dye is an azo-compound. It is a red-colored dye. It is mainly used for dyeing textiles. Azo compounds have an extended conjugation scheme and they are also colored and used as colors. These compounds are prepared by a reaction known as the coupling reaction. 2-Aniline naphthol dye is made from aniline. In this article, we will study the preparation of 2 naphthol aniline dye in detail.


Aim

To prepare 2-Naphthol Aniline Dye from aniline, sodium nitrite, hydrochloric acid and alkaline solution of β-naphthol also called 2-naphthol.


Theory

2- Naphthol aniline dye can be prepared by coupling reaction. In the presence of hydrochloric acid, aniline reacts with sodium nitrite and forms benzene diazonium chloride. A bright orange 2-naphthol aniline dye is formed by additional benzene diazonium chloride reacting with 2-naphthol.

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Azo compounds are prepared under alkaline conditions by the reaction of diazonium salts with phenol. To give a diazonium salt, primary aromatic amines react with nitrous acid at 0oC. In exchange, nitrous acid is formed by a sodium nitrite reaction with hydrochloric acid. Nitrous anhydride or dinitrogen trioxide is an active reagent. Nitrous anhydride reacts with aniline to provide an unstable nitroamine derivative and isomerizes to form a diacetic acid, which is converted into a diazonium salt in turn. Finally, in the presence of sodium hydroxide, this diazonium salt reacts with 2-naphthol to give 2-naphthol aniline, which is an aniline dye.


Materials ​Required

  1. Aniline

  2. Sodium nitrite

  3. Hydrochloric acid

  4. 2-Naphthol

  5. Sodium hydroxide solution

  6. Beaker

  7. Test tube

  8. Buchner funnel

  9. Pipette

  10. Capillary tube

  11. Thermometer

  12. Distilled water

  13. Hot air oven

  14. Ice bath


Procedure

  1. 5ml of aniline was dissolved in a mixture of hydrochloric acid and water.

  2. In an ice bath, cool the solution at 0-5 oC.

  3. With constant shaking and monitoring the temperature below 5oC, add a solution of 4gm sodium nitrite in 15ml of water dropwise. 

  4. Take another flask to dissolve 8gm of 2-naphthol in a solution of 5 gm sodium hydroxide solution in 50ml of water.

  5. In the ice bath, cool the solution to 0-5oC. 

  6. Now mix the two cold solutions drop-wise with regular stirring. 

  7. Continue stirring for at least half an hour without rising the temperature above 10oC. 

  8. It is isolated by an orange azo dye called 2-naphthol aniline. 

  9. Filter and wash the crude sample with cold water. 

  10. From ethyl alcohol or glacial acetic acid, dry and recrystallize it.


Observations

Colour of the crystals

Orange crystals

Expected Yield

13gm

Melting Point

131oC


Result

The 2- Naphthol aniline dye yield is ______ gm.


Precautions

  1. It is important to cool the solution to 5oC. Do not let the temperature increase. 

  2. Do not touch the dye as it will stick to your palms.  Do not touch  

  3. Do not touch the concentrated acids as it can cause irritation.

  4. In order to eliminate soluble impurities, wash the crude sample frequently with cold water. 

  5. Keep the pH between 4-5.


Did You Know?

Coupling reaction refers to the class of organic reactions involving the interaction of two chemical species (usually with the help of a metal catalyst). The reaction of an organic halide with an organometallic compound having the general formula R-M that facilitates the formation of a new carbon-carbon bond is an important type of coupling reaction. If the organic halide has the general formula R'-X in this reaction, the compound produced as a result would have the R-R 'formula.


The Coupling Reaction is of Two Types

  1. Homo-coupling reactions

  2. Hetero-coupling reactions (also known as cross-coupling reactions)

FAQ (Frequently Asked Questions)

1. What is the 2 naphthol aniline dye color?

Naphthol aniline dye can be prepared by coupling reaction as a scarlet dye. In the presence of hydrochloric acid, aniline reacts with sodium nitrite and forms benzene diazonium chloride. A bright orange 2-naphthol aniline dye is formed on reacting benzene diazonium chloride with 2-naphthol.

2. Why is the diazotization reaction carried out at low temperatures?

During diazotization and coupling reactions, we must maintain a low temperature since diazonium salts form other materials at high temperatures and provide phenol by reacting with water at high temperatures, which will lead to a major error in the experiments.

3. Why is NaNO2 Used for Diazotization?

HNO2 is a very unstable liquid while sodium nitrite has the advantage of being an easily handled salt. The second primary reagent is a potent mineral acid such as HCl; HCl transforms it into HNO2 if NaNO2 is used.