Preparation of 2 Naphthol Aniline Dye

Introduction

The chemical compound 2-Naphthol is also known as β-Naphthol majorly colourless. However, sometimes it shows a very light yellow coloured texture. It is a solid, used as t dye. It has an isomer of 1-Naphthol, which differs by the position of the Hydroxyl group on the nNphthalene ring.

What is 2-Naphthol Aniline Dye?

The 2-Naphthol aniline dye is a red coloured azo product It can be prepared only with the help of a coupling reaction. The most important use of the compound is in dye textiles. Any kind of azo compounds is part of an extended conjugation scheme that results in colour and can be used as colour. The 2-Naphthol aniline dye is made from Aniline.

Aim

The experiment aims to prepare the 2-Naphthol aniline dye from the Aniline, Sodium Nitrite, Hydrochloric acid, and alkaline solution.

Theory

The term coupling reaction refers to the specific class of organic reaction, where involves two chemical species via coupling reaction. Usually, it happens with the help of the metal catalyst. In simple words, in this reaction, two fragments are joined together with the use of a metal catalyst.

The most common type of coupling reaction is the cross-coupling reaction. In the case of 2-Naphthol aniline dye, when the Aniline reacts with the Sodium Nitrite, in presence of Hydrochloric acid,, Benzene Diazonium Chloride produces. Then, Benzene Diazonium Chloride” reacts with 2-Naphthol and undergoes coupling reaction to produce one bright orange-coloured 2-Naphthol Aniline Dye.

The reaction steps of 2-Naphthol Aniline Dye

Under alkaline conditions, Diazonium salt and Phenol reacts with each other and forms azo compounds. At 0°C, any primary aromatic amines react with the Nitrous acid and form the Diazonium salt. The Nitrous acid is prepared using Sodium Nitrite with Hydrochloric acid. In this case, the active agent is either Nitrous Anhydride or Dinitrogen Trioxide”.

A Nitroamine derivative is produced when the Nitrous Anhydride reacts with Aniline". However, the Nitroamine derivative is unstable by nature and isomerizes to form a Diacetic acid. It helps to transform into the Diazonium salt. In the presence of Sodium Hydroxide, Diazonium salt reacts with the 2-Naphthol and as the result, it produces the 2-Naphthol Aniline, which is an Aniline dye.

Material required

To conduct the reaction, some items are required, such as −

• Aniline

• Sodium Nitrite

• Hydrochloric acid

• 2-Naphthol

• Sodium Hydroxide solution

• Buchner funnel

• Pipette

• Capillary tube

• Hot air oven

• Ice bath

• Beaker

• Test tube

• Thermometer

• Distilled water

Process

In the making of 2 Naphthol Aniline Dye, some steps should be followed −

• 5ml Aniline should be dissolved in the mixture of concentrated Hydrochloric acid and water.

• Left the reaction for cooling in the ice bath and the temperature will be 0 to 5°C.

• In 15 ml water, a 4 gm Sodium Nitrite should be added dropwise and it needs continuous shaking.

• In another flask 8 gm of 2-Naphthol in a solution of 5 gm Sodium hHdroxide solution needs to be dissolved in the water solution and the solution needs to cool down with the help of an ice bath.

• Both solutions need to be mixed dropwise and it needs constant stirring for at least half an hour.

• It will be seen that an orange colour azo dye named 2-Naphthol Aniline separates.

• The crude sample needs to be separated and to be washed with the help of cold water.

• Properly dry it and then recrystallize it from the glacial Acetic acid.

Observation

• Colour of the result- bright orange crystals

• Expected yield- 13 gm

• Melting point- 131°C

Result

The appropriate yield of 2-Naphthol Aniline Dye will be obtained after practical experiments in the labratory.

Precaution

This reaction needs to follow some of the major precautions −

• The temperature cannot be raised and the Solution must be cooled at 5°C.

• The hands should not touch the dye otherwise it will stick to the hands.

• The concentrated acid should not be touched. It can irritate the skin.

• The crude sample needs to be cleaned properly and repeatedly with cold water. It will help to remove the impurities.

• The pH level should be maintained between 4 to5.

Conclusion

2-Naphthol Aniline Dye is a very useful compound that is widely used in the textile industry and it serves the colouring purpose. It is also useful in paper manufacturing and printing units. 2-Naphthol Aniline Dye is a chemical compound that is prepared with the help of a coupling reaction.

FAQs

1. What is the colour of 2-Naphthol Aniline Dye?

2-Naphthol Aniline Dye is prepared as the result of a coupling reaction and it comes out as the scarlet dye. In this reaction, Aniline reacts with the Sodium Nitrate in presence of Hydrochloric acid and forms Benzene Diazonium Chloride. It forms orange 2-Naphthol Aniline Dye after the reaction with 2-Naphthol.

2. Is 2-Naphthol water soluble?

The 2-Naphthol cannot dissolve in the water, which makes it water insoluble and it does not have any affinity to cellulosic.

3. What is the main use of 2-Naphthol?

2-Naphthol is used in many sectors. However, the most common uses are − it can be used in dyes, pigments, fats, oils, in the production of perfume, and can be used as antioxidants rubber.

4. What is the difference between $\mathrm{\alpha\:-\:Naphthol\:and\:\beta\:-\:Naphthol}$ ?

$\mathrm{\alpha\:-\:Naphthol\:and\:\beta\:-\:Naphthol}$ are structural isomers “. They both are chemically known as 1- Naphthol and 2-Naphthol, respectively. They are very useful as biomarkers.