how phenol is oxidised to benzoquionone . write the mechanism ?

Phenol in presence of oxidising agents such as chromic acid (Na₂Cr₂O₇) or silver oxide(Ag₂O) undergoes oxidation to give hydroquinone or catechol depending upon the oxidising agent used which further oxidises to give p-benzoquinone or o-benzoquinone.

For example, Phenol is oxidised to 1,4-benzoquinone with chromic acid in the presence of concentrated sulphuric acid.

Mechanism is as follows:

• In the first step, Deprotonation of phenol leads to phenoxide ion which is transformed into a phenoxy radical by a one-electron oxidation. p-phenoxy adical will transform into hydroquinone.