To prepare a pure sample of Methyl orange from sulphanilic acid.

Aim: To prepare a pure sample of Methyl orange from sulphanilic acid.

Theory:

The method for preparing a pure sample of Methyl orange from sulphanilic acid involves several steps. First, sulphanilic acid is converted into sulphonyl benzene diazonium chloride by treatment with Nitrous acid in the presence of hydrochloric acid at a temperature between 0 - 5 degrees Celsius. Next, the diazonium compound is coupled with dimethyl aniline in an alkaline medium to form methyl orange. The resulting solid product is then separated by filtration through a Buchner funnel, washed with water, and crystallized by boiling.

The materials required for preparing a pure sample of Methyl orange from sulphanilic acid include the following:

Apparatus:

• 250 ml round-bottomed flask
• Beaker
• Buchner funnel
• Filtration flask
• Suction pump

Chemicals:

• Sulphanilic acid (7g)
• Anhydrous sodium carbonate (2g)
• Sodium nitrite (2g)
• Dimethyl aniline (4ml)
• Concentrated hydrochloric acid (8ml)
• Diluted hydrochloric acid (20ml)
• Sodium chloride (8g)
• 20% NaOH solution (30ml) 

Chemical Equations:

Chemical Equations involved in the preparation of Methyl orange:

1. Sulphanilic acid is converted into sulphonyl benzene diazonium chloride by treatment with Nitrous acid in the presence of hydrochloric acid at 0-5 degrees Celsius:

2. Diazonium compound is coupled with dimethyl aniline in an alkaline medium to form methyl orange:

The resulting solid product is then separated by filtration through a Buchner funnel, washed with water, and crystallized by boiling.

Procedure:

1. In a 250 ml round-bottomed flask, dissolve 7.0 g of sulphanilic acid in a solution of 2.0 g of anhydrous sodium carbonate in 50.0 ml of water. Warm the solution until it becomes clear.
2. In a separate container, dissolve 2.0 g of sodium nitrite in 10.0 ml of water, then add it to the sulphanilic acid solution.
3. Cool the resulting solution to 0-5°C in an ice bath.
4. Dilute 8.0 ml of concentrated HCl with 20.0 ml of water and add it dropwise to the reaction mixture, maintaining a temperature below 10°C. Shake the solution to mix thoroughly.
5. In a separate container, dissolve 4.0 ml of dimethyl aniline in 20.0 ml of dilute HCl and cool to 0-5°C. Add this cold solution to the reaction mixture.
6. Shake thoroughly for 10 minutes, and add 30.0 ml of 20% NaOH solution while stirring.
7. Warm the solution to 60°C in a water bath, then add 8.0 g of sodium chloride.
8. Shake and cool the mixture in an ice bath. Separate the product formed through a Buchner funnel and wash it with water.
9. Crystallize the crude product from water.
10. Dry the product in a desiccator and note the weight. Determine the melting point of the pure product.

Result:

• Color: deep orange-red
• Yield: 8.0 g

Note: The above procedure is a general guide, specific details and precautions should be followed as per standard laboratory protocol.

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