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Expt.7: Synthesis of Phenyl-azo-β-Naphthol
AIM :
To synthesize Phenyl-azo-β-Naphthol from Aniline and Calculate its Percentage Yield.
Principale :
2-Naphthol aniline dye or Phenyl-azo-β-naphthol is an orange-red dye. It belongs to a large class of azo-compounds, all of which contain the characteristic grouping. Azo compounds are all coloured compounds. For the preparation of this dye, aniline is diazotized and then diazonium salt thus obtained is subjected to coupling reaction with 2-naphthol.
Requirements :
Chemical :
Aniline 4.5 ml, Sodium nitrite 4g , 2-Naphthol 7g , Con.Hydrochloric acid 10 ml, 10% NaOH 60 ml , Glacial acetic acid 40 ml
Apparatus : One 100 mL conical flask, one 100 mL beaker, one 250 mL beaker, ice-bath,
glass-rod, buchner funnel with water pump.
Procedure:
● Take a 100 ml conical flask and add 4.5 ml of aniline, 10 ml of cone. HCl and 20 ml of water. Cool this solution to 5°C by placing the conical flask in a water bath containing ice- cold water.
● In a 100 ml beaker dissolve 4 g of sodium nitrite in 20 ml of water and cool this solution
also to 5°C.
● Now slowly add sodium nitrite solution to the solution of aniline in con. HCl. ● Dissolve 7.0 g of 2-naphthol in 60 ml of 10% NaOH solution taken in a 250 ml beaker and cool this solution to 5°C by placing it in an ice bath. Some crushed ice may be added directly to facilitate cooling. ● Now add the diazotized solution very slowly to the naphthol solution with constant stirring. The mixed solutions immediately develop a red colour and the phenyl-azo-β- naphthol rapidly separates as orange-red crystals. ● When the addition of diazo solution is complete, allow the mixture to stand in ice-salt mixture for 30 minutes, with occasional stirring. Filter the solution through a buchner funnel under suction from the pump. Wash the phenyl-azo-β-naphthol with water and dry the crystals obtained by pressing between the folds of filter paper.
● Recrystallise the product from glacial acetic acid. Filter the crystals obtained at the
pump. Wash with a few ml of ethanol to remove acetic acid. Phenyl-azo-β-naphthol is obtained as orange-red crystals. Expected yield is 3 g.
Results:
Weight of phenyl-azo-β-naphthol obtained as orange-red crystals = …….g. And % of Yield
is ……….
Calculation:
Molecular formula of Aniline = C 6 H 5 NH 2
