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I have read about the neutral FeCl3 test for Phenols, where a positive test is indicated by the colour of the solution which ranges from green to blue to violet. But which specific derivatives of phenol give a specific colour? Or is it random?

Akhil Lasrado
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1 Answers1

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The color of the solution will depend on what substituent is attached to phenol. The following is an excerpt from an e-book:

Ferric Chloride Test: To 2 ml aqueous or alcoholic solution of compound, add 5-6 drops of freshly prepared neutral ferric chloride solution. Colored complexes of phenols are produced

\begin{array}{c|c} \mathbf{Compounds} & \mathbf{Color} \\\hline \text{phenol, resorcinol, o-cresol, p-cresol} & \text{Violet or blue}\\ \text{catechol} & \text{Green} \\ \text{hydroquinone} & \text{Violet or transient blue which changes to yellow on excess addition of FeCl3}\\ \text{pyrogallol} & \text{Blue rapidly changing to red}\end{array}

Aqueous solution of 1 and 2-naphthol however do not give any characteristic coloration but their alcoholic solution give violet-blue and green coloration respectively due to formation of dinaphthols.

Ref.: Systematic Lab Experiments in Organic Chemistry by Arun Sethi, New Age International, 2006

Nilay Ghosh
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