Preparation of 2 Naphthol Aniline Dye

Dhristi JEE 2022-24

What is a 2 Naphthol Aniline Dye?

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.

 

Preparation of 2 Naphthol Aniline Dye - Practical Experiment

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 dropwise with regular stirring. 

  7. Continue stirring for at least half an hour without raising 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

Color 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)


Importance of Practical Experiments in Chemistry

Chemistry is an experimental science that needs to be understood more in practical terms than theoretical terms. Practical experiments have a significant role to play as the students learn the different chemical compositions through these. All schools and teachers believe in the benefits of practical experience as seeing something makes you more convinced in terms of understanding its concept.  It assists in general evaluation and learning which helps students secure higher marks in their exams. Chemistry is a didactic subject that can only be understood once it is witnessed. Experiments form the core of a subject like Chemistry so that students can pick up whatever they learn in theory faster than usual.

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FAQs (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 by 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.

4. Is Sodium Nitrite required in the formation of Naphthol Aniline Dye?

Yes, sodium nitrite is needed in an experiment that has to do with preparing the naphthol aniline dye. The scientific explanations for each have been provided on Vedantu’s online tutoring platform if the students check out the Preparation of 2 Naphthol Aniline Dye - Chemistry Practicals Report.


This page has logically explained the formation of the dye along with the materials that are needed in its formation. Going through this page will help the students understand all topics in a better manner.

5. What is the colour of the crystals in the experiment on naphthol aniline dye?

The crystals formed are orange in color. The experiment goes on to prove how naphthol aniline dyes are formed. The experiment can be found if the students check out the Preparation of 2 Naphthol Aniline Dye - Chemistry Practicals Report. This page on Vedantu has all the important pointers that one needs to be aware of. Students can read the page and then come to logical conclusions. They can also revise from here before a test that’s on the subject.

6. How can students perform an experiment on the preparation of 2 naphthol aniline dyes?

Students can read from Preparation of 2 Naphthol Aniline Dye - Chemistry Practicals Report on Vedantu and be certain.


The page has explained the entire practical experiment in an elaborate manner. It has been designed by expert Chemistry teachers who are well versed in the subject and extremely reliable. The students can be relieved as the study material is in tandem with the course outlines. Everything that they need to be aware of has been provided here completely free of cost.

7. What are the observations of the 2 naphthol aniline dye experiment?

Observations of the above-mentioned experiment have been provided on Vedantu’s website if the students refer to the Preparation of 2 Naphthol Aniline Dye - Chemistry Practicals Report. This page on Vedantu is free of cost and can be downloaded in PDF mode as well. It has encapsulated all the details of the experiment and has all the relevant bits of information. Students who need to know how to perform this experiment from scratch can read this as this will prove to be quite useful to them. They can also take down notes from it as those pointers might help before an exam.

8. Are there any precautions to be followed before the preparation of 2 Naphthol Aniline dye?

Yes, some of the precautions include keeping the pH between 4 to 5, not touching the highly concentrated acids to avoid corrosion.  Other such precautionary measures have been explained on the Preparation of 2 Naphthol Aniline Dye - Chemistry Practicals Report that’s on Vedantu.


This page has all the information that students need to know before they sit down for a test. All the important reminders that the students need to know before this experiment have been explained well here so that they do not face issues while attempting something similar on their own.

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