Monooxygenation of alkanes

Shteinman, A.A. (2001) The role of metal-oxygen intermediates in biological and chemical monooxygenation of alkanes, Russian Chemical Bulletin 50, 1795-1810. 

The hydroxylation of small alkanes, such as propane and ethane, is particularly attractive to the chemical industry. However, monooxygenation of carbon centers is a reaction that is difficult to achieve chemically as it requires extreme temperatures. An attractive alternative is the use of cytochrome P-450 enzymes (P-450s) that can catalyze such reactions with a high degree of regio- and stereoselectivity. Thus, there has been much work directed toward evolving P-450s with altered substrate specificities that can catalyze hydroxylation of Cl-ClO alkanes. 

Monooxygenation of aromatics, alicyclic and linear alkanes with molecular oxygen is catalyzed by nonheme iron complexes in the anhydrous organic solvents in the presence of hydroquinones as electron and proton donors. Iron complexes are prepared in situ by stirring FeCla, pyrocatechol, and pyridine (mole ratio is 1 1 2) in acetonitrile or in pyridine. Isolated catecholatoiron complex is also used. Catalytic activity is greatly dependent on the kinds of hydroquinone and increases in the order of 2,5-di-t-butyl- t-butyl->methyl->H-hydroquinone. Non-substituted hydroquinone hardly exhibits activity, and the activity is controlled by the oxidation potential and steric effect of hydroquinones. 

Monooxygenation is distributed among a variety of bacteria and several have been examined for their potential to degrade fluorinated alkanes ... 

MePOR species and other complexes in cationic clays can be located at the edges of packed platelets, in the interlamellar space or in the mesopores present (Scheme 10.9). A review of the early data in this area is available.[86] The flat metallo macrocycles under clay synthesis conditions help to induce layer silicate formation, the complexes being intercalated between the layers. Whereas with monooxygen atom donors, alkanes can be oxygenated with significantly enhanced activities compared with the homogeneous case, in every case the expected products (ol/on) were obtained. Competitive oxygenation of adamantane and pentane shows lower... 

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. 

In a base-free medium (dry MeCN), Fe Ch activates HOOH to form a reactive intermediate that oxygenates alkanes, alkenes, and thioethers, and dehydrogenates alcohols and aldehydes. Table 11 summarizes the conversion efficiencies and product distributions for a series of alkene substrates subjected to the Fe Cfi/HOOH/MeCN system. The extent of the Fe Cb-induced monooxygenations is enhanced by higher reaction temperatures and increased concentrations of the reactants (substrate, Fe Cls, and HOOH). For 1-hexene (representative of all of the alkenes), a substantial fraction of the product is the dimer of 1-hexene oxide, a disubstituted dioxane. With other organic substrates (RH), Fe Cb activates HOOH for their monooxygenation the reaction efficiencies and product distributions are summarized in Tables 11(b). In the case of alcohols, ethers, and cyclohexane, a snbstantial fraction of the product is the alkyl chloride, and with aldehydes, for example, PhCHO, the acid chloride represents one-half of the product. In the absence of snbstrate the Fe Cls/MeCN system catalyzes the rapid disproportionation of HOOH to O2 and H2O. 

Role of metal-oxygen intermediates in biological and chemical alkane monooxygenations 01IZV1712. 

Kodera et al. synthesized a rigid (Tf-oxo-di T(-acctalo)diiron(III) complex with l,2-bis[2-di(pyridyl)methyl-6-pyridyl]ethane that is a dinucleating hexa-pyridine ligand. " The complex monooxygenates alkanes (cyclohexane, methylcyclohexane, adamantane) in the presence of m-CPBA with a large turnover frequency and number Radical-rebound mechanism was suggested based... 

The systematic investigation of catalytic alkane hydroxylation has been performed by the use of various (p,-oxo)(ii-carboxylato)diiron(III) with alkylhydroperoxide [95]. When the complex bearing a more electron donating ligand such as TPA is used in the catalytic reaction, monooxygenated products are increased, and byproducts such as dialkylperoxide... 

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