Question

Write a short note on Libermanns nitroso test.$\left(\mathrm{NaOH}\right)$

Answer 1

Libermanns Nitroso Test

• This test is used for the determination of phenol present in a compound which is a hydroxyl group ${\left(\mathrm{OH}\right)}^{-}$ on an aromatic ring.

Figure: Phenol

Procedure of Libermanns Nitroso Test

• In a clean, dry container, place the sodium nitrite $\left({\mathrm{NaNO}}_2\right)$ crystals.
• To this solution, add 1 mL of phenol.
• Allow the mixture to cool after gently heating it.
• Add 1mL sulphuric acid $\left({\mathrm{H}}_2{\mathrm{SO}}_4\right)$ to it and shake gently.
• Keep an eye on the color of the solution as it changes.
• If the phenolic group i.e. hydroxyl group over the aromatic ring is present, dilute the solution with water until the color of supplied chemical becomes red.
• When we add sodium hydroxide $\left(\mathrm{NaOH}\right)$ solution, a blue or green color solution is obtained.
• The presence of phenol may be seen if the blue-green color solution appears after the test.