Solvent effect in the kinetics of cobaloxime(II)-catalyzed oxidative dehydrogenation of 3,5-di-tert-butylcatechol by O-2

In the presence of triphenylphosphinecobaloxime(II), 3,5-di-tert-butylcatec hol undergoes catalytic oxidative dehydrogenation to the corresponding 1,2- benzoquinone (DTBQ) at room temperature and atmospheric dioxygen pressure. The semiquinone anion radical (DBSQ(.-)) and its cobaloxime(III) complex Co -III(DBSQ(.-))have been detected as intermediates by ESR spectroscopy. The kinetics were followed in benzene by measuring the dioxygen uptake as a fun ction of time. The reaction is somewhat faster in MeOH which is due to the greater stability of the hydrogen-bonded intermediate (X) formed from super oxocobaloxime ((CoO2)-O-III) and the catechol. H-atom abstraction occurs in the rate-determining decomposition of X. The system investigated is a func tional model of catecholase (oxidase) activity, based an free-radical inter mediates, a possibility recently demonstrated for certain oxidoreductases.