Auto-Oxidation of Catechol
Oxidation of Catechol to o-benzoqiunone is free radical mediated, passing through a semiquinone radical.
"The equilibrium potential for the one-electron transfer between catechol and the semiquinone radical (cat.) is 100 mV at pH 7 (Eberson, 1985). For the second electron transfer between the semiquinone radical and the catechol dianion (cat2-), an equilibrium potential of 530 mV, 139 mV and 43 mV for pH 7, pH 11 and pH 13.5 respectively was reported (Steenken and Neta, 1979). As a consequence, under physiological conditions catechol is not auto-oxidized (IronsandSawahata,1985), except in the presence of heavy metals (e.g. copper). Several enzymes in plants, animals and bacteria are able to catalyze oxidation of catechol to benzoqiunone. "
The passage has been extracted from an aricle " Chemical properties of catechols and their modes of toxic action in cells, from microorrganisms to mammals." Environmental Microbiology (2001)3 (2), 81-91