"Preparation of p-aminoazobenzene (4-phenylazoaniline) from Aniline"

 

Preparation of p-aminoazobenzene (4-phenylazoaniline) from Aniline

The preparation of p-aminoazobenzene (4-phenylazoaniline) involves two main steps: the synthesis of diazoamino benzene (4-diazoanilinobenzene) and its subsequent conversion to p-aminoazobenzene. Here's a step-by-step outline of the process

Step 1:

Synthesis of Diazoamino Benzene (4-diazoanilinobenzene)

Theory: The synthesis of diazoamino benzene involves the conversion of aniline to its diazonium salt, followed by the reaction of the diazonium salt with an excess of aniline to form the diazoamino compound.

Chemicals Required:

• Aniline (C₆H₅NH₂)
• Concentrated hydrochloric acid (HCl)
• Sodium nitrite (NaNO₂)
• Ice-cold water

Materials Required:

1. Reaction flask
2. Ice bath
3. Stirring apparatus
4. Filtration setup
5. Drying oven

Chemical Reaction:

Mechanism:

Procedure:

• Start by setting up an ice bath and placing a reaction flask in it to keep it cold throughout the process.
• In the reaction flask, add 10 mL of concentrated hydrochloric acid (HCl) and cool the solution in the ice bath.
• In a separate container, dissolve 6.8 g of sodium nitrite (NaNO₂) in 30 mL of water to prepare a sodium nitrite solution.
• Slowly add the sodium nitrite solution dropwise to the cold hydrochloric acid solution in the reaction flask, while stirring continuously. Maintain the temperature below 5°C.
• In another container, prepare a solution of 7.2 g of aniline in 30 mL of water.
• Slowly add the aniline solution to the reaction flask containing the diazonium salt solution, while stirring vigorously.
• Continue stirring the reaction mixture for about 30 minutes to ensure complete reaction.
• Pour the reaction mixture into a large volume of ice-cold water to precipitate the diazoamino benzene.
• Collect the precipitate by filtration and wash it with water to remove impurities.
• Dry the precipitate in a drying oven at a suitable temperature.
• Weigh the dried diazoamino benzene product and record its mass for further calculations.

Calculations:

Aniline (C₆H₅NH₂) = 7.2 g

Sodium nitrite (NaNO₂) = 6.8 g

First, we need to determine the limiting reagent by comparing the moles of aniline and sodium nitrite used:

Molar mass of aniline (C₆H₅NH₂) = 93.13 g/mol

Molar mass of sodium nitrite (NaNO₂) = 69.01 g/mol

Number of moles of aniline: mass / molar mass

Moles = 7.2 g / 93.13 g/mol = 0.0774 mol

Number of moles of sodium nitrite = 6.8 g / 69.01 g/mol = 0.0984 mol

The stoichiometry of the reaction between aniline and sodium nitrite is 1:1. Since the number of moles of aniline is lower than the number of moles of sodium nitrite, aniline is the limiting reagent.

To calculate the theoretical yield of diazoamino benzene, we'll use the moles of aniline and the molar mass of diazoamino benzene:

Molar mass of diazoamino benzene = 181.2 g/mol

Theoretical yield = Moles of limiting reagent × Molar mass of diazoamino benzene

Theoretical yield = 0.0774 mol × 181.2 g/mol

Theoretical yield = 14.04 g

Therefore, the theoretical yield of diazoamino benzene, based on the given quantities, is approximately 14.04 grams.

 

Step 2: Conversion of Diazoamino Benzene to p-Aminoazobenzene

Theory:

The conversion of diazoamino benzene to p-aminoazobenzene involves the reaction of diazoamino benzene with aniline under specific conditions to form the desired product.

Chemicals Required:

1. Diazoamino benzene (from Step 1)
2. Aniline (C₆H₅NH₂)
3. Sodium hydroxide (NaOH)
4. Ethanol (C₂H₅OH)

Materials Required:

1. Reaction flask
2. Ice bath
3. Stirring apparatus
4. Filtration setup
5. Drying oven

Chemical Reaction:

Mechanism:

Procedure:

• Start by setting up an ice bath and placing a reaction flask in it to keep it cold throughout the process.
• In the reaction flask, add the diazoamino benzene obtained from Step 1.
• In a separate container, prepare a solution of 4 g of aniline in 30 mL of ethanol.
• Slowly add the aniline solution to the reaction flask containing diazoamino benzene, while stirring continuously.
• Add a solution of 5 g of sodium hydroxide (NaOH) in 30 mL of water dropwise to the reaction mixture while maintaining the temperature below 10°C.
• Continue stirring the reaction mixture for about 30 minutes.
• Pour the reaction mixture into ice-cold water to precipitate the p-aminoazobenzene.
• Collect the precipitate by filtration and wash it with water to remove impurities.
• Dry the precipitate in a drying oven at a suitable temperature.
• Weigh the dried p-aminoazobenzene product and record its mass for further calculations

Calculations:

Theoretical yield of diazoamino benzene = 14.04 g

The stoichiometry of the reaction between diazoamino benzene and aniline to form p-aminoazobenzene is 1:1. Therefore, the moles of p-aminoazobenzene formed will be equal to the moles of diazoamino benzene used.

Molar mass of p-aminoazobenzene = 197.23 g/mol

Theoretical yield of p-aminoazobenzene = Moles of diazoamino benzene × Molar mass of p-aminoazobenzene

Moles of diazoamino benzene = Theoretical yield of diazoamino benzene / Molar mass of diazoamino benzene Moles of diazoamino benzene

Moles of diazoamino benzene = 14.04 g / 181.2 g/mol = 0.0774 mol

Theoretical yield of p-aminoazobenzene = 0.0774 mol × 197.23 g/mol

Theoretical yield of p-aminoazobenzene = 15.26 g

Therefore, the theoretical yield of p-aminoazobenzene, based on the given quantities, is approximately 15.26 grams.