Question

Why phenol turns to a dark Coloured liquid?

Answer 1

Answer:

The phenol is reactive toward oxidation reaction. When phenol is exposed to air it readily undergo oxidation which lead to various di or trihydric phenolic products which are colourful. for example oxidation of phenol leads to the formation of catechol which is feathery brown in colour.

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Answer 2

Explanation:

Phenol turns pink, red or brown on exposure to air and light due to slow oxidation. The colour is due to the formation of p− benzoquinone and phenquinone.