PREPARATORY PROBLEM 26 (PRACTICAL) Synthesis of 1-phenyl-azo-2-naphthol (C16H12ON2) Reactions: [VISU — Organic Chemistry Chemistry Question

PREPARATORY PROBLEM 26 (PRACTICAL)
Synthesis of 1-phenyl-azo^-2-naphthol (C₁₆H₁₂ON₂)

Reactions:
[VISUAL]

Chemicals and solutions
Aniline
Concentrated hydrochloric acid
Solid sodium nitrite
β-naphthol
Ethyl alcohol
Urea
Sodium hydroxide

Preparation of diazonium salt
Take 1 cm₃ of aniline in a clean 50 cm₃ beaker. Add approximately 5 cm₃ of distilled water to aniline. Place the beaker in an ice-bath. Slowly add 2.5 cm₃ of conc. HCl. Stir the solution with a glass rod to obtain a clear solution. Cool this solution in the ice-bath.
Weigh accurately 0.5 g of sodium nitrite (NaNO₂) and transfer it quantitatively in a 15 (or 25) cm₃ test tube. Add 5 cm₃ of distilled water (to the test tube) to dissolve NaNO₂. Cool the resulting NaNO₂ solution in an ice-bath.
Allow both the solutions to attain 0 °C temperature. Add sodium nitrite solution in a dropwise manner to the aniline solution with continuous stirring. (During addition, the temperature of the reaction mixture should not rise above 10 °C.)
The presence of excess nitrous acid in the reaction mixture is checked using starch iodide paper.
To decompose the excess nitrous acid formed, add a small portion of solid urea. The solution is then filtered. The filtrate contains the diazonium salt.

Coupling reaction
Weigh 0.75 g of powdered β-naphthol in a 50 cm₃ beaker. Add 5 cm₃ of 10% NaOH solution and 5 cm₃ of distilled water to the beaker. Stir well with glass rod to obtain a clear solution. This solution is also cooled in an ice-bath to 0 °C.
The ice cooled filtrate containing diazotised salt is added dropwise to the ice cooled solution of β-naphthol with constant stirring. At this stage, an orange-red dye will start precipitating. After the addition of the solution is complete, filter the dye using Büchner funnel. Cold water is used for washing the precipitate. Dry the product and record the yield.

Determination of melting point
Recrystallise a small portion of the organic dye prepared using ethyl alcohol. Gently heat the solution in a water bath (careful!) to dissolve the dye. Filter the hot solution. Cool the filtrate and filter the recrystallised product using Büchner funnel and suction.