[ps2id id=’background’ target=”/]
BACKGROUND
Phenyl diazonium chloride is obtained first by the diazotization of aniline with nitrous acid as explained earlier, which on coupling with β-naphthol in the presence of NaOH solution yields the desired coupled product phenyl-azo-β-naphthol. A mole of HCl is eliminated which instantly reacts with NaOH from the medium to produce NaCl and H2O. Importantly, both diazotization and coupling reactions are required to be carried out between 0-5°C.1
[ps2id id=’requirements’ target=”/]
REQUIREMENTS
Chemicals: Aniline – 4.0 g
conc. Hydrochloric acid – 12.8 ml
β-Naphthol -6.24 g
10% (w/v) Sodium hydroxide solution – 40 ml
Sodium nitrite – 3.2 g
[ps2id id=’procedure’ target=”/]
PROCEDURE
Dissolve 4.0 g (3.92 ml) aniline in 12.8 ml conc. HCl in a 250 ml beaker and dilute it with 12.8 ml distilled water. Cool the in ice-bath with frequent stirring till it attains a temperature below 5°C. In another beaker, dissolve 3.2 g sodium nitrite in 15 ml water and chill the solution in ice-bath (0–5°C). Add sodium nitrite solution (2) to the aniline solution (1) in small lots (2 ml) at a time in intervals with vigorous stirring with a glass rod taking care that the temperature of the reaction mixture must not exceed beyond 5°C at any cost. After the complete addition of sodium nitrite solution, it is required to test the reaction mixture for the presence of free nitrite by taking out a drop of it and immediately placing it on KI-starch paper that will distinctly turn blue in the presence of free nitrous acid. Dissolve 6.24 g β-naphthol separately in a 250 ml beaker in 40 ml of sodium hydroxide solution, and cool the naphthol-solution in ice-bath (0-5°C). Slowly add the cold diazonium salt solution to the β-naphthol solution with vigorous stirring. Special care must be taken for not allowing the temperature of the reaction mixture rise beyond 5°C. If need be, crushed ice should be added while the coupling-reaction proceeds. A red colour develops and crystals of crude phenylazo-β-naphthol separate out. Allow the reaction mixture to stand for 30-40 minutes with stirring to complete the reaction. Filter the red product in a Büchner funnel using suction, and wash with ice-cold water. Drain the water by pressing with an inverted glass-stopper.
Calculation of Practical Yield: –
93 g of aniline on reacting with 144 g of β-naphthol yields phenylazo-β-naphthol = 258 g
10 g of aniline shall yield phenyl-azo-β-naphthol = (258/ 93) × 10 = 27.74 g
Therefore, Theoretical yield of phenyl-azo-β-naphthol = 27.74 g
If reported Practical yield = 9.5 g
Then, Percentage Practical yield = (Practical yield / Theoretical yield) × 100
= 9.5 / 27.74 × 100 = 34.25 %
[ps2id id=’conclusion’ target=”/]
CONCLUSION
The yield of crude product m.p. 129-130°C is 9.5 g.
[ps2id id=’references’ target=”/]
REFERENCES
- Kar A. Advanced Practical Medicinal Chemistry, New Age International (P) Limited Publication, New Delhi, Page No. – 136.
