Tests for Organic Compounds having Hydroxyl groups

Alcoholic hydroxyl group

Phenolic hydroxyl group


Liebermann's Nitroso Reaction

Add a crystal of sodium nitrite to 2 mL of concentrated sulfuric acid, and shake until dissolved. Add 0.1 g of the unknown.

Positive Test
A blue color indicates the presence of a phenol. Another indication of the presence of the phenol is the change of color of the solution to red, when it is poured into 20 mL of ice water, and the return of the blue color when the mixture becomes alkaline after the addition of 10% sodium hydroxide solution.

Source:
http://www.chemistry.ccsu.edu/glagovich/teaching/316/qualanal/tests/liebermann.html


REference
Practical Chemistry by O.P. Pandey, D.N. Bejpai, and S.Gir Pub. by S.Chand