Quinone-catalyzed aerobic oxidation reaction

Through subtle modification of the reaction mechanism, the scope of o-quinone-catalyzed aerobic oxidations has been expanded to secondary amines and JV-heterocyclic compounds as well [45-47]. For example, aerobic oxidation of secondary amines and iV-heterocycles has been achieved by using 10-phenanthroline-5,6-dione (phd) as a catalyst (Scheme 14.10a). Using phd and cocatalytic Znl2, a diverse range of iV-heterocyclic compounds undergo... 

Future Developments Selective Aerobic Oxidation Reactions Catalyzed by Quinones 229... 

A semiquinone can be readily oxidized to the parent compormd by molecular oxygen and can then re-enter the reductase-catalyzed reaction. The enzymatic reduction and autoxidation of quinones rmder aerobic conditions generates superoxide anion radicals, and this process is known as redox cycling (Figure 2). Flydroquinones are less prone to transfer electrons to oxygen, because the second-electron potential is often too high. 

Scheme 14.5 Aerobic oxidation of hydroquinone to quinones, a common step in the AO process and in quinone-catalyzed oxidation reactions.

Alternative cocatalysts, such as [Fe(pc)]20 (pc = phthalocyanine) and AIBN, have also been reported for catalytic aerobic DDQ oxidation reactions, though these have seen less widespread application than NO [28]. Aerobic quinone-catalyzed dehydrogenation reactions using less oxidizing quinones, such as chloranil, have been reported using polymer-incarcerated noble metal catalysts reported by Kobayashi and colleagues [29, 30]. 

Figure 18.2 Summary of respiratory energy flows. Foods ate converted into the reduced form of nicotinamide adenine dinucleotide (NADH), a strong reductant, which is the most reducing of the respiratory electron carriers (donors). Respiration can he based on a variety of terminal oxidants, such as O2, nitrate, or fumarate. Of those, O2 is the strongest, so that aerobic respiration extracts the largest amount of free energy from a given amount of food. In aerobic respiration, NADH is not oxidized directly by O2 rather, the reaction proceeds through intermediate electron carriers, such as the quinone/quinol couple and cytochrome c. The most efficient respiratory pathway is based on oxidation of ferrocytochrome c (Fe ) with O2 catalyzed by cytochrome c oxidase (CcO). Of the 550 mV difference between the standard potentials of c)Tochrome c and O2, CcO converts 450 mV into proton-motive force (see the text for further details).

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