Alkan-2-ones, oxidation

The oxyfunctionalization of alkanes with H2O2 on TS-1 has only been reported very recently [113-114]. Linear or branched alkanes are oxidized to secondary and/or tertiary alcohols and ketones, the latter ones being formed by consecutive oxidation of the secondary alcohols. Primary alcohols are not detected. At 50°C maximum turn-overs of n-hexane of 35 mol/mol Ti were reported... 

In 1992, Hari Prasad Rao and Ramaswamy reported on the oxyfunctionalization of alkanes with H2O2 using a vanadium silicate molecular sieve s . With this catalyst acyclic and cyclic alkanes were oxidized to a mixture of the corresponding alcohols (primary and secondary ones), aldehydes and ketones. Unfortunately, most of the early attempts were of rather limited success due to low turnover frequencies and radical producing side reactions as observed, for example, by Mansuy and coworkers in 1988. ... 

Appropriate modification of the ESR spectrometer and generation of free radicals by flash photolysis enables time-resolved (TR) ESR spectroscopy [22]. Spectra observed under these conditions are remarkable for their signal directions and intensities. They can be enhanced as much as one-hundredfold and appear as absorption, emission, or a combination of both. Effects of this type are a result of chemically induced dynamic electron polarization (CIDEP) these spectra indicate the intermediacy of radicals whose sublevel populations deviate substantially from equilibrium populations. Significantly, the splitting pattern characteristic of the spin-density distribution of the intermediate remains unaffected thus, the CIDEP enhancement not only facilitates the detection of short-lived radicals at low concentrations, but also aids their identification. Time-resolved ESR techniques cannot be expected to be of much use for electron-transfer reactions from alkanes, because their oxidation potentials are prohibitively high. Even branched alkanes have oxidation potentials well above the excited-state reduction potential of typical photo-... 

One of the most smdied examples is the mimic of the enzyme cytochrome P-450 in the pores of a faujasite zeolite [196,204,225], The iron-phthalocyanine complex was encapsulated in the FAU supercage and is used as oxidation catalyst for the conversion of cyclohexane and cyclohexanone to adipic acid, an important intermediate in the nylon production. In this case the two step process using homogeneous catalysts could be replaced by a one step process using a heterogeneous catalyst [196]. This allowed better control of the selectivity and inhibited the auto oxidation of the active compound. In order to simulate a catalyst and the reaction conditions which are close to the enzymatic process, the so obtained catalyst was embedded in a polydimethylsiloxane membrane (mimics the phospholipid membrane in the living body) and the membrane was used to limit oxygen availability. With this catalyst alkanes were oxidized at room temperature with rates comparable to those of the enzyme [205]. 

These results question the validity of many previous results on catalytic oxidation of light alkanes. One should reassess the data concerning the relative reactivity of the various alkanes [105] and selectivity. 

Bromide complexes are also efficient in the photooxidation. However, FeBrj photocatalyzes the oxygenation of only alkylbenzenes (Figure IX.2) [60c] and are not effective in the oxidation of alkanes. One can assume that the bromine radical is an active species in this reaction. 

It is essential (though not always done) that the products of combustion be analyzed the assumption of complete combustion is not always an accurate one. Alkane combustion proceeds in a series of steps, in which CO is always predecessor to the final product CO 2- If only 0.1% of the carbon content of an alkane is oxidized only as far as CO, the resulting error in AfH will be 0.07 kcal per C atom. If an equivalent amount of carbon is reduced to graphite (solid soot/graphite is often observed after bomb combustion), the error is 0.1 kcal per C atom. 

One of the problems with the simple mechanism in equation 7 is that, in the oxidation of most alkanes, much less than the stoichiometric amount of hydrogen is observed This has led to the suggestion that when the alkane is oxidized, then... 

One oxidation reaction that is of large industrial relevance is the oxidative dehydrogenation of light alkanes to the corresponding alkene (Scheme 3.20). This reaction has been reported to be promoted by r-GO as catalyst [29]. The importance of this reaction type is particularly high for the industrial preparation of propene from propane and butenes from butanes. Both reactions are carried out industrially in very large scale, because propene is the monomer of polypropene and also the starting material of propylene oxide, acrylonitrile, and other base chemicals. Butenes are mainly used for the preparation of 1,3-butadiene that is one of the major components of rubbers and elastomers. 

Alkenes, Allies, Arenes, and Alkanes. One of the most common apphcations of Oxone in organic synthesis is the in situ formation of dioxiranes fromketones (eq 1). Dioxrrane chemistry has grown significantly in recent years, particularly in the area of enantioselective epoxidation, and a wide variety of chiral ketones have been designed for this purpose. Notably, ketones (5 and 6) derived from fructose and glucose, respectively, have been shown to be effective catalysts for enantioselective epoxida-tions of a variety of trans-, trisubstituted, cis-, and terminal olefins with Oxone as primary oxidant (eqs 38 and 39). ... 

Because, as shown above, in the oxidation catalysis of alkanes, one can replace a transition metal catalyst by a redox-inactive nontransition metal catalyst, the question arises whether it would be possible to go even further and eliminate completely the use of any metal catalyst, thus establishing a metal-free system capable of oxidizing alkanes under mild conditions. 

One of the key aspects in the catal5dic behavior for alkane partial-oxidation catalysts seems to be related to the coordination number (Fig. 24.3), the aggregation degree, and the oxidation state of the vanadium species as active sites. It fact, it has been shown that the V-environment plays an important role in catalytic behavior. 

While alkanes are oxidized by an iodosylbenzene/Fe(TPP) system [43-48], higher valent intermediates observed in these systems are one electron oxidized Fe(IV) complexes such as (MeO)2Fe(IV) and 0=Fe(IV) species [103-107]. Similar 0=Fe(IV) porphyrin complexes are also observable in the peroxidase reactions (so-called compound II) as shown in Scheme 2 [4]. Fe complex of synthetic porphyrin (TPP) was first characterized in the electrochemical oxidation of Fe (TPP)Cl [108]. On the other hand, Phillippi and Goff obtained Fe(III) porphyrin 7C-cation radicals by the electrochemical one-electron oxidation [109]. Balch et al. also prepared 0=Fe(IV) complexes by introducing nitrogen bases into p-peroxo dimmer of Fe(III) porphyrin complexes at low temperature as shown in Scheme 3 [110, 111]. 0=Fe (TPP)(Base) was shown to oxidize triphenylphosphine at -80°C in toluene solution over a period of several hours [112]. 

Respiratory, or oxidative, metaboHsm produces more energy than fermentation. Complete oxidation of one mol of glucose to carbon dioxide and water may produce up to 36 mol ATP in the tricarboxyHc acid (TCA) cycle or related oxidative pathways. More substrates can be respired than fermented, including pentoses (eg, by Candida species), ethanol (eg, by Saccharomjces), methanol (eg, by Hansenu/a species), and alkanes (eg, by Saccharomjces lipoljticd). 

This was also accomplished with BaRu(0)2(OH)3. The same type of conversion, with lower yields (20-30%), has been achieved with the Gif system There are several variations. One consists of pyridine-acetic acid, with H2O2 as oxidizing agent and tris(picolinato)iron(III) as catalyst. Other Gif systems use O2 as oxidizing agent and zinc as a reductant. The selectivity of the Gif systems toward alkyl carbons is CH2 > CH > CH3, which is unusual, and shows that a simple free-radical mechanism (see p. 899) is not involved. ° Another reagent that can oxidize the CH2 of an alkane is methyl(trifluoromethyl)dioxirane, but this produces CH—OH more often than C=0 (see 14-4). ... 

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