Steric effects of substituents of quinones on the oxygenation of ethylbenzene catalyzed by NHPI/quinone and the catalytic oxidation of ascorbate

The substituents of quinones play an important role in modulating the kinetics of the electron-and proton-transfer reaction. In this paper, the steric effects of substituents of quinones on their catalytic performance were studied in the oxidation of ethylbenzene and ascorbate. The substituents limited the addition of the free radicals to the C=C double bonds of the quinone ring because of the steric hindrance. On the other hand, too many substituents hindered the contact between the active site (C=O) of quinone and the reactant. So, the quinones with two substituents presented better catalytic performance than those with more or less substituents. These results will be helpful in designing the quinone compounds for drugs and in understanding the catalytic behavior of quinones in biochemistry. Copyright (C) 2010 John Wiley & Sons, Ltd.