FeCl₃ Test for Phenol

Purpose: Used to identify phenols.

Reaction:$$3C_6H_5OH + FeCl_3 \rightarrow Fe(OC_6H_5)_3 + 3HCl$$

Phenol reacts with neutral FeCl₃ to form a ferric phenoxide complex, producing a violet/purple colour.

Observation: Violet colour → Phenol present

JEE/NEET point:
The test is due to formation of a coloured complex, not simply an acid–base reaction.

Example:$$C_6H_5OH \xrightarrow{FeCl_3} \text{violet complex}$$

Note: Some other compounds containing suitable groups can also give colours with FeCl₃, so the test is not absolutely specific for phenol.

Other Tests for Phenol (JEE/NEET)

S. No.	Test	Reagent	Observation
1	Bromine water test	Br2/H2O	Bromine water decolourises and a white precipitate of 2,4,6-tribromophenol forms.
2	Liebermann’s nitroso test	NaNO2+conc.H2SO4	Deep blue/green colour; on dilution, red colour may appear, and on adding alkali, blue/green colour returns.
3	Azo dye test	Benzene diazonium chloride in alkaline medium	An orange/red azo dye forms.
4	Phthalein dye test	Phthalic anhydride + conc. H2SO4 followed by NaOH	Pink colour develops due to formation of phenolphthalein in alkaline medium.
5	Ferric chloride test	Neutral FeCl3 solution	Violet, blue, green or other characteristic colour may develop, depending on the compound.

Important reactions

1. Bromine water test

Product: 2,4,6-tribromophenol (white precipitate).

2. Azo dye test

Phenol reacts with benzene diazonium chloride in alkaline medium to form an orange-red azo dye.

NEET quick revision: Remember FeCl₃ → violet colour, bromine water → white precipitate, and azo dye test → orange/red dye.