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

Abstract

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 © 2010 John Wiley & Sons, Ltd.

Metal-free allylic/benzylic oxidation strategies with molecular oxygen: recent advances and future prospects

“…Allylic/benzylic oxidation is of special interest in diverse important processes due to their products from raw materials (Scheme 1) as key intermediates with a variety of commercial applications, such as synthesis of pharmaceuticals, flavor compounds, polyester fibers, and agrochemicals. The transformations from toluenes to benzoic acids, [55][56][57][58][59][60][61] from cumenes to phenols, [62][63][64] from ethylbenzenes to their hydroperoxides or acetophenones, [65][66][67][68][69][70][71][72][73] from isophorones to ketoisophorone, [74][75][76][77][78] and from cholesteryl acetate to 7-keto-cholesteryl acetate 79,80 are examples that are operated industrially on a large scale. These kinds of oxidation always lead to undesired products caused by over-oxidation or side reactions owing to the relatively weak C-H bonds of certain sites in these compounds, which inevitably puts a limit on the selectivity of targeted products.…”

The Proton Trap Technology—Toward High Potential Quinone‐Based Organic Energy Storage

“…This is not surprising as the benzoquinone, particularly at the low current densities employed here, have been shown to be susceptible to side reactions in battery cells. [6f,9a,13] Indeed, applying a constant potential of 0.42 V versus Fc 0/+ (0.1 m TBAPF 6 in MeCN) reveals spectral changes of the electrolyte solution in the UV–vis region (Figure S14a, Supporting Information), indicating degradation products of both side‐groups, something that could be related to instability of the linker unit at high potentials. Additionally, Figure S14b (Supporting Information) reveals additional spectral changes after some hours associated to the PEDOT backbone.…”

Organocatalysis Meets Hydrocarbon Oxyfunctionalization: the Role of N‐Hydroxyimides

“…The same research group further studied the steric effects of substituents of quinones on the catalytic performance of NHPI towards the same oxidation reaction. [34] The authors analyzed the effects of different benzoquinones on the catalytic activity of the proposed system. p-DMQ bearing two substituents demonstrated a higher catalytic activity towards ethylbenzene oxidation among methyl benzoquinones, reaching 26 % of conversion.…”

“…[33] Regarding the reported initiator-free systems, high conversions of cyclohexane. [34] and cumene [48] were achieved, with excellent selectivities to adipic acid and cumene hydroxyperoxide, respectively. The increasing number of metal-free and additive-free systems reported in this context is promising for the development of desirable synthetic approaches towards sustainable selective oxyfunctionalization reactions.…”