[Chemistry Class Notes] on Preparation of 2 Naphthol Aniline Dye Pdf for Exam

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.

 

 

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

 

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 th
eoretical 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.