Ferric Chloride Test
Dissolve a pinch of organic compound in water or alcohol. A few drops of this solution are mixed with neutral ferric chloride solution. If a red, blue or violet colouration appears, then the presence of phenolic group is confirmed.
For example, red colouration is obtained with phenol while, with o, m- and p-cresol, it is violet. With Resorcinol, gives blue colouration whereas catechol gives green colouration.
The organic compound is mixed with solid sodium nitrite (2-3 crystals) and gently warmed for a few seconds. The mixture is cooled and cone sulphuric acid is added. The solution appears red in colour on dilution with water and the colour changes to blue or green on treatment with sodium hydroxide.
This confirms the presence of phenolic group in the given compound.
How To Perform Experiment
Heat about 50 mg of the organic compound with sodium nitrite (2-3 crystals) gently for 30 seconds in a dry test tube. To the cooled mixture add 1 mL conc. H2SO4.
Add about 2-3 mL water to the mixture. Add NaOH solution to the mixture.