Process monooxygenation

Selectivity is among the most important parameters for the partial oxidation, especially in the case of non-02 oxidants. Usually, for 02 oxidations, the selectivity is considered only with respect to the organic reagent. But this approach is not acceptable with monooxygen donors, the cost of which may be of the same order as that of the organic reagent. In this case, selectivity based on the oxidant becomes an equally important parameter for estimating process efficiency. Thus, in the case of... 

Though the investigation of photocatalytic oxygenations performed of the laboratory scale are often motivated by attempts to understand and mimic the catalytic cycle of cytochrome P450 (a natural catalyst of monooxygenation reactions), the results obtained [159, 253, 266] could be applied to industrial processes as well. 

It is obvious from the mechanism (9.1)—(9.7) that oxidation condition variation may direct the process towards selective formation of a definite product. For example, oxygen-containing compounds can be obtained in one highly selective stage (monooxygenation) by the reaction channel (9.7). The comparative simplicity of these reactions is also associated with the fact that metal complexes, representing something like weak acids , coordinate weak bases, such as olefins, N2, CO, etc. with formation of unstable complexes, which provide for catalytic transformation of the substrate [5],... 

Over the past 25 years, biomimetic model systems have been extensively studied and a wide variety of interesting oxidation processes such as the epoxidation of olefins, the hydroxylation of aromatics and alkanes, the oxidation of alcohols to ketones, etc., have been accomplished some of these are also known in enantioselective versions with spectacular ee s. The vast majority of these transformations were obtained using monooxygen donors such as those mentioned above as primary oxidants. The complexity of the catalysts and the practical impossibility to use dioxygen as the terminal oxidant have so far prevented the use of such systems for large industrial applications, but some small applications in the synthesis of chiral intermediates for pharmaceuticals and agrochemicals, are finding their way to market. 

The majority of synthetic reactions in mammalian cells takes place in the cytosol. The intramitochondrial localization of transhydrogenase excludes a direct participation in these anabolic processes. Substrate shuttle mechanisms (176, 177) are required to allow for the interaction between intra- and extramitochondrial nicotinamide nucleotide-dependent reactions. In the first instance transhydrogenase can be regarded to be functionally related to intramitochondrial NADP-linked reactions. A number of studies on isolated mitochondria have elaborated these relationships in some detail, in particular with regard to mitochondrial monooxygenation reactions and to the metabolism of glutamate and isocitrate. 

Because Fe Cfi is an exceptionally strong Lewis acid and electrophilic center, it activates HOOH (which acts as a nucleophile) for the dehydrogenation of a second HOOH. On the basis of the disproportionation process, as well as the monooxygenation and dehydrogenation reactions of Table 11, the activation of HOOH by Fe Cfi probably involves the initial formation of at least two reactive forms (15 and 16) of an Fe Cl3(HOOH) adduct (Scheme 4). 

The disproportionation of HOOH occurs via a concerted transfer of the two hydrogen atoms from a second HOOH to the Fe Cl3(HOOH) adduct. This dehydrogenation of HOOH is a competitive process with the Fe Cfi/substrate/HOOH reactions. The controlled introduction of dilute HOOH into the Fe Cfi/substrate solution limits the concentration of HOOH and ensures that the substrate/HOOH reaction can be competitive with the second-order disproportionation process. The substrate reaction efficiencies in Table 11 are proportional to the relative rates of reaction ( RH/kHoon)-The mode of activation of HOOH by Fe Cls is analogous to that of Fe (MeCN)4 + both are strong electrophiles in ligand-free dry MeCN and induce HOOH to monooxygenate organic substrates. 

The activation of dioxygen for the monooxygenation of saturated hydrocarbons by the methane monooxygenase enzyme systems (MMO hydroxylase/reductase) represents an almost unique biochemical oxygenase, especially for the transformation of methane to methanol. The basic process involves the insertion of an oxygen atom into the C-H bond of the hydrocarbon via the concerted reduction of O2 by the reductase cofactor (equation 120). 

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