Oxygenation of alkanes

In recent years, oxyfunctionalization of various natural products (steroids, alkaloids) under superacidic conditions have also been explored. In addition, Nafion resins in combination with various oxidizing agents have also been used in the oxygenations. 

The hydrogen peroxonium ion may be considered as an incipient OH+ ion capable of electrophilic hydroxylation of single ( x) bonds in alkanes and, thus, be able to effect reactions similar to such previously described electrophilic reactions as protolysis, alkylation, chlorination (chlorolysis), and nitration (nitrolysis). 

The reaction of branched-chain alkanes with hydrogen peroxide in Magic Acid-S02C1F solution has been carried out with various ratios of alkane and hydrogen peroxide and at different temperatures.602 Some of the results are summarized in Table 5.35. 

The reaction proceeds via a pentacoordinate hydroxycarbonium ion transition state, which cleaves to either fert-butyl alcohol or the tert-butyl cation. Since 1 mol of isobutane requires 2 mol of hydrogen peroxide to complete the reaction, one can conclude that the intermediate alcohol or carbocation reacts with excess hydrogen peroxide, giving fcrt-butyl hydroperoxide. The superacid-induced rearrangement and cleavage of the hydroperoxide results in very rapid formation of the dimethylmethyl-carboxonium ion, which, upon hydrolysis, gives acetone and methyl alcohol. 

When the reaction is carried out at room temperature, by means of passing isobutane into a solution of Magic Acid and excess hydrogen peroxide, the formation 

The most extensive studies of alkane reactions in aqueous media are on the oxygenation reaction. In fact, nature has used monooxygenase (found in mammalian tissue) and other enzymes to catalyze the oxidation of alkanes to give alcohols in aqueous environments at ambient 

Comprehensive Organic Reactions in Aqueous Media, Second Edition, by Chao-Jun 

PPO = poly(propylene oxide TPA = 7n5 [(2-pyridyl)mediyl]amine) 

For transition-metal catalyzed hydroxylation of alkane C-H bonds, the reactions of alkanes with platinum(ll) complexes were the most successful. In an aqueous solution of hexachloroplatinic acid and Na2PtCl4, alkanes were converted into a mixture of isomeric alkyl chlorides, alcohols, and ketones, and the platinum(lV) is reduced to platinum(ll). The kinetics of the reaction with methane as the alkane have been described in detail.  

Two main mechanisms may be proposed for the first step of the alkane interaction with platinum(ll) complexes (1) oxidative addition 

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Oxygenation of alkanes with hydrogen peroxide in homogeneous reactions can be obtained also with Keggin-type iron-substituted polyoxometalates. Evidence against radical reactions has been offered. 

Alkylated carboxonium ions have also been prepared by direct electrophilic oxygenations of alkanes, alcohols, and so on, by ozone or hydrogen peroxide in superacidic media606 [Eq. (3.82)]. 

Zeolite encapsulated complexes catalyse the oxygenation of alkanes with peroxides according to oxo chemistry, following a mechanism very similar to the oxygen-rebound mechanism encountered in monooxygenase enzymes. 

Hill and co-workers have reported that TMSP is effective for the epoxidation of alkenes and the oxygenation of alkanes by use of f-BuOOH and PhIO as oxidants [67]. The characteristics of TMSP in alkene epoxidation, compared with those of metalloporphy-rins, Schiff base complexes, and triflate salts, are as follows [67] ... 

N. Mizumo, C. Nozaki, 1. Kiyoto, M. Misono, Highly efficient utilization of hydrogen peroxide for selective oxygenation of alkanes catalyzed by Diiron-substituted polyoxometalate precursor, J. Am. Chem. Soc. 120 (1998) 9267. 

Recently, we have reported a simple method for the reductive activation of by applying an electrochemical O -Hj cell reaction for the oxygenation of alkanes and aromatics at the cathode [12-14]. With an acidic electrolyte in the Oj-Hj cell, the stoichiometric anode and cathode reactions are written simply as follows. 

Similar to the concept described for the Oj-Hj cell system, the reductive activation of oxygen can be expected at the cathode in the presence of a suitable catalyst. On the basis of this zinc-air battery model, we have designed a number of catalytic systems from mixtures of zinc powder, carboxylic acid and various metal chlorides for oxygenations of alkanes and alkenes. In these catalytic systems, zinc powder works as the reductant as well as the electron conducting medium. The carboxylic acid works as a proton-conducting medium. Oxygen is reductively activated on the metal cations by protons from the carboxylic acid and electrons from zinc powder. 

In addition to the oxidation of propane and propylene, the following mode of oxidation over bismuth-containing mixed catalysts has been reported (i) oxidative coupling of hydrocarbons, (ii) ammo-oxidation of toluene and xylenes, (iii) oxygenation of alkanes and alkenes, (iv) oxidation of alcohols, and (v) oxidative cleavage of carbohydrates. Representative results are summarized in Scheme 5.12. 

To mimic the Cytochrome P450 properties with MePc embedded in zeolites, the oxygenation of alkanes and cycloalkanes has been studied frequently. Occasionally, iodosobenzcnc (PhOI) has been used as oxidant [6] Alternatively, t-butyl hydroperoxide... 

Perhaps of more practical value is the oxygenation of alkanes, and a reaction catalyzed by VO(acac)2 is notable. ... 

N. Mizuno, M. Tateishi, T. Hirose, and M. Iwamoto, Chem. Lett., Oxygenation of Alkanes by... 

Selective Oxygenation of Alkanes Catalyzed by Diiron-Substituted Polyoxometalate Precursor, J. 

The controlled oxygenation of alkanes, alkenes, and aromatic hydrocarbons is one of the most important technologies for the conversion of crude oil and natural gas to valuable commodity chemicals. Biomimetic studies of metalloporpltyrins have led to important advances in practical catalysis, especially with ruthenium porphyrins. Reaction of wj-CPBA, periodate, or iodosylbenzene with Ru(II)(TMP)(CO) produced RuCVIjfTMPXOjj . Remarkably, Ru(VI)(TMP)(0)2 was found to catalyze the aerobic epoxidation of olefins under mild conditions. Thus, for a number of olefins including cyclooctene, norbomene, cis-, and trans- -methyl styrene 16-45 equivalents of epoxide were... 

Grinstaff, M.W., M.G. Hill, J.A. Labinger, and H.B. Gray (1994). Mechanism of catalytic oxygenation of alkanes by halogenated iron porphyrins. Science 264, 1311. 

Scheme IX.8, The mechanism proposed for the FeCli-photocatalyzed oxygenation of alkanes, RH, into alkyl hydroperoxides, ROOH. 

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