It was found that at neutral pH the hydroxylation reaction rate of phenol w
as accelerated with an increase of the amounts of 1,4-quinone (1,4-BQ), Thi
s acceleration was ascribed to the formation of semiquinone from 1,4-BQ. Th
e semiquinone and 1,4-BQ were suggested to play a role of actual oxidant (e
lectron transfer) in the catalytic cycle. With further reaction, most 1,4-B
Q was converted into 1,4-hydroquinone (HQ) and the corresponding mechanism
was proposed.