To Prepare a Sample of 2 Naphthol Aniline

2-Naphthol aniline dye has the chemical formula C₁₆H₁₂N₂O, and it is also known as Phenyl-azo-naphthol. It is an orange-red dye. It is a member of a large family of azo compounds. The term "azo compound" refers to any organic chemical compound whose molecular structure includes the azo group (-N=N-). In the structure of 2 naphthol aniline dye, The atomic groups linked to the nitrogen atoms may belong to any organic class. Still, the commercially significant azo compounds that account for more than half of the commercial dyes have the benzene group or its derivatives as the attached groups (aromatic azo compounds).

Orange-Red colour of 2-Naphthol Aniline Dye

Structure of β Beta-Naphthol

It is a fluorescent colourless (or in some cases yellow) crystalline solid. The Melting Point of Beta-Naphthol lies between 120-122 °C. The Structure of β Beta-Naphthol C₁₀H₇OH differs from 1-naphthol where the hydroxyl group is located on the naphthalene ring. In comparison to phenol, the naphthols are more reactive naphthalene homologues. Simple alcohols, ethers, and chloroform all allow the solubility of both isomers. It is also used in the preparation of phenol and the synthesis of dyes and other chemicals. 2-naphthol is a commonly used intermediate in such types of reaction.

Structure of β Beta-Naphthol 

Table of Content

• Aim of the Experiment

• Apparatus Required

• Chemicals Required

• Theory

• Procedure

• Observation

• Result

• Precaution

• Lab Manual Questions

• Viva Questions

• Practical Based Questions

Aim of the Experiment

To prepare the organic compound Beta- Naphthol Aniline from Aniline.

Apparatus Required

•  A 100 mL Conical Flask

• A 100 mL Beaker 

• 250 mL Beaker.

• Water Pump

• An Ice Bath

• A Glass Rod

• Funnel

• Filter Paper

Chemical Required

• Aniline 

• Sodium nitrite (NaNO₂)

• 2-Naphthol 

• Conc. Hydrochloric acid (HCl)

• Glacial acetic acid 

Theory

The preparation of 2-Naphthol aniline dye is carried outusing a coupling reaction. Instead of a straightforward benzene ring, it has a -OH group connected to a naphthalene molecule. Two rings of benzene are fused to form naphthalene.

Aniline and sodium nitrite combine with hydrochloric acid to produce benzene diazonium chloride. Benzene diazonium chloride further interacts with 2-naphthol to give a  deep orange-coloured 2-naphthol aniline dye.

Structure of 2-Naphthol Aniline Dye

Procedure

• Add 4.5 ml of aniline, 10 ml of conc. HCl, and 20 ml of water to a 100 ml conical flask. Put the conical flask in a bath of ice-cold water to cool the solution to 5°C.

• Dissolve 4 g of sodium nitrite in 20 ml of water in a 100 ml beaker, and then cool this mixture to 5°C.

• Now, gradually add sodium nitrite solution to the aniline solution in the cone.

• In a 250 ml beaker, dissolve 7.0 g of 2-naphthol with 60 ml of a 10% NaOH solution. Cool this mixture to 5°C in an ice bath. To facilitate cooling, a little crushed ice may be directly added.

• Now, slowly add the diazotised solution to the naphthol solution while stirring continuously. The phenyl-azo-naphthol quickly separates into orange-red crystals, and the mixed solutions turn red at once.

• Allow the mixture to stand in the ice-salt combination for 30 minutes after the diazo solution has been added, stirring every so often. Under pump suction, filter the mixture using a funnel. 

• After thoroughly cleaning the phenyl-azo-naphthol with water, dry the crystals  obtained by pressing them between the layers of filter paper.

• Re-crystallize the end product from glacial acetic acid. Filter the crystals you got from the pump.

• To get rid of acetic acid, wash with a few ml of ethanol. Orange-red crystals of phenyl-azo-naphthol can be produced. With a melting point of 133°C, a 3 g of product is expected.

Observations

Result

Phenyl-azo-naphthol obtained as orange-red crystals weigh 3 gms.

The melting point of phenyl-azo-naphthalene is 133°C.

Precautions

• Due to the exothermic nature of the reaction, adding sodium nitrite should be done very gradually.

• Aniline hydrochloride solution should be cooled to 5 °C, and this temperature should be maintained while adding sodium nitrite solution.

• Avoid touching the concentrated acids if possible to avoid irritation.

• The pH should be kept between 4-5.

Lab Manual Questions

1. Why is aniline soluble in hydrochloric acid while it is insoluble in water?

Ans.  Due to the presence of highly hydrophobic benzene, aniline does not form hydrogen bonds. Aniline is thus insoluble in water. The amine group in HCl undergoes protonation (-NH₃⁺) and becomes ionic, making it soluble in HCl.

2. Why are the crystals of 2-naphthol obtained washed with ethanol?

Ans. To remove excess Acetic Acid, we wash with a few ml of ethanol. Orange-red crystals of phenyl-azo-naphthol.

3. What do you mean by coupling reaction?

Ans. Coupling reaction refers to the reaction of the diazonium salt with phenols and aromatic amines to produce azo compounds with the general formula Ar−N=N−Ar.

4. Beta naphthol aniline is the derivative of which class of organic compound?

Ans. Beta naphthol aniline is the derivative of Azo-compounds (Naphthol) of organic compounds.

Viva Questions

1. What is the use of Beta Naphthol Aniline Dye?

Ans. It is mostly employed in the dyeing of textiles.

2. Why does the colour of aniline become reddish-brown?

Ans. Due to the +R (electron donating) effect of the NH₂ group, aniline's electron density rises, and because of this, aniline is easily oxidised in air to produce compounds that are coloured. Because of this, aniline turns coloured after spending a lot of time in the air.

3. Which is more acidic: Phenol or Naphthol?

Ans. Since the hydroxyl group is directly linked to the benzene ring, phenols are significantly more acidic than alcohols.

4. Why is the end product re-crystallised from glacial acetic acid?

Ans. Orange-red crystals of phenyl-azo-naphthol are the end product re-crystallize from glacial acetic acid. 

5. What is Diazotization Reaction?

Ans. Diazotisation is the process of turning a primary aromatic amino molecule into a diazonium salt. An excess of primary aromatic amine (such as aniline) in an aqueous sodium nitrite solution is added to this mixture at a temperature below 5 °C.

Practical Based Questions

1. What is the chemical formula of 2- Naphthol Aniline dye?

1.  C₁₆H₁₀N₂O

2.  C₁₆H₁₂N₂O

3. C₁₆H₁₂N₃O

4. C₁₆H₁₁N₂O

Answer. (b)

2. What is the IUPAC name of 2- Naphthol Aniline?

1. 1-Phenylazo-2-naphthol

2.  2- Naphthol

3. Naphthol Azobenzene

4. None of the Above

Answer. (a)

3. What is the colour of 2- Naphthol Aniline?

1. Pink

2. Reddish-brown

3. Yellow

4. Red-Orange

Answer. (d)

4. What is the IUPAC Name of 2- Naphthol?

1. Naphthalen-2-ol

2. Naphthalen-1-ol

3. Naphthalen-2-al

4. None of the above

Answer. (a)

5. What is the Melting Point of Beta Naphthol Aniline?

1. 122 °C

2. 133 °C

3. 123 °C

4. 130 °C

Answer. (b)

6. What is the solution of concentrated nitric acid and sulphuric acid called?

1. Alcoholic Mixture

2. Nitrating Mixture

3. Ethanolic Mixture

4. None of the above

Answer. (b)

7. Which of the following compounds will produce an azo dye when diazotisation and coupling with beta-naphthol are performed?

1. N-Methylaniline

2. p-Toluidine

3. Benzylamine

4. All of the above

Answer. (b)

8. How does Beta Naphthol Aniline smell?

1. Pungent odour

2. Rotten egg odour

3. Sweet, floral-rose odour

4. Odourless

Answer. (c)

9. Is Beta Naphthol Acidic or basic?

1. Weakly Basic

2. Strongly Acidic

3. Weakly Acidic

4. Strongly Basic

Answer.(c) 

10. Which functional group is present in 2- Naphthol Aniline?

1. Hydroxy group

2. Carboxylic group

3. Amide group

4. Halogen group 

Answer. (a)

Conclusion

The azo-compound 2-naphthol aniline dye has a red colour. It is mostly used to colour clothing. Azo compounds are pigmented and utilised as dyes. The coupling reaction is the process used to synthesise these chemical compounds. 2-Naphthol Aniline has a melting point of 133 °C. It is weakly acidic in nature. It is significantly used in dye industries to colour textiles.