Catalytic oxygenation

A direct methanol fuel cell consists of two electrodes—a catalytic methanol anode and a catalytic oxygen cathode—separated by an ionic conduc-... 

Capdevila, J.A., Yadagiri, P., Manna, S. and Falck, J.R. (1986). Absolute configuration of the hydroxyeicosatetraenoic acids (HETEs) formed during catalytic oxygenation of arachidonic acid by microsomal cytochrome P-450. Biochem. Biophys. Res. Commun. 141, 1007-1011. 

Peroxides are compounds of great synthetic interest. Especially, alkyl hydroperoxides and hydrogen peroxide have gained more and more importance as cheap and readily available oxygen donors in catalytic oxygenations. Formerly unsafe oxidation procedures (due to the employment of highly concentrated and therefore explosive peroxide solutions) have been optimized or substituted by other and more effective and safe procedures. Over the last two decades, the need for oxidation technologies with enhanced efficiency... 

These PVP polymers provide a "proximal effect" without addition of free pyridine in the reaction mixture. Different studies have shown that only one pyridine per manganese catalyst is sufficient to enhance the rate of the catalytic oxygen atom transfer from the high-valent metal-oxo species to the organic substrate. The advantage of PVP polymer over a cationic Amberlite resin (see Scheme II for structures) have been recently illustrated in the modeling of ligninase (11). 

Organic compounds can be catalytically oxygenated via various metal oxo or peroxide intermediates. The epoxidation of functionalized and simple olefins can be effected by such complexes. 

Both homogeneous and heterogeneous catalytic oxidations can be divided into the same three categories based on the type of mechanism involved (a) autoxidation, (b) direct oxidation of (coordinated) substrates and (c) catalytic oxygen transfer. 

Interestingly, the first examples of catalytic oxygen transfer involved the so-called Milas reagents,4 formed by mixing heterogeneous metal oxide catalysts with a solution of hydrogen peroxide in tert-butanol. These reagents were used for the vicinal hydroxylation of olefins (reaction 10). 

Finally, both manganese(II) gluconate405 and alkaline solutions of cobalt phthalocyanines406 also promote catalytic oxygen evolution. 

Research on the direct conversion of chemical energy to electricity via fuel cells has received considerable attention in the past decades. Fuel cells are indeed attractive alternatives to combustion engines for electrical power generation in transportation applications and also as promising future power sources, especially for mobile and portable applications. Thus, the search for excellent electrocatalysts for the electro-catalytic oxygen reduction and methanol oxidation reactions, which are the two important cathodic and anodic reactions in fuel cells, is intensively pursued by scientists... 

The kinetic of catalytic oxygen reduction is closely connected with chemical condition of surface nanodispersed diamond. 

Another way to avoid the need for a sacrificial reductant is to use a reduced form of dioxygen, e.g. H202 or R02H, as a single oxygen donor. Such a reaction is referred to as a catalytic oxygen transfer and can be described by the general equation shown in Fig. 4.9. 

XOY = H202, R02H, R3NO, NaOCl, KHSO5, etc. Fig. 4.9 Catalytic oxygen transfer. 

Scheme 30. Mechanism of the catalytic oxygenation of the R group of AcrHR by O2 with a cofacial cobalt porphyrin (177).

The studies of direct heterogeneous electron transfer have been carried out in most cases using cyclic and square wave voltammetry. In these studies the first of the two electrons required for the catalsftic reaction has been transferred although the authors do not see the shift of the reduction potential upon substrate addition as has been reported in Ref. [73] and is known for the reaction in solution. In all cases catalytic oxygen reduction is observed but only rarely could catalytic substrate conversion be achieved. 

Hill, C. L. Catalytic Oxygenation of Unactivated C—H Bonds. Superior Oxo Transfer Catalysts and the Inorganic Porphyrin . In Activation and Functionalization of Alkanes, Hill, C. L., Ed., Wiley New York, 1989 pp 243-279. 

---