Initial mushroom tyrosinase-catalysed oxidation product of 4-hydroxyanisole is 4-methoxy-ortho-benzoquinone.

Evidence is presented that the first and major product of the oxidation of 4-hydroxyanisole (4HA) by tyrosinase is 4-methoxy ortho benzoquinone (4-MOB). 4-MOB was synthesized by oxidation of 4HA by potassium nitrodisulphonate and comparisons made between the synthetic quinone and an extract of a reaction mixture in which 4HA had been completely oxidized by mushroom tyrosinase. The chemical species were found to be identical in UV/visible absorption spectrum, 1H-NMR spectrum, and by thin-layer chromatography.