Oxidation cycloalkanes

Supercritical CO2 is a non-polar, aprotic solvent and promotes radical mechanisms in oxidation reactions, similar to liquid-phase oxidation. Thus, wall effects might occur as known, e.g. from olefin epoxidation with 02 or H202 which may decrease epoxide selectivities. The literature covers the synthesis of fine chemicals by oxidation either without catalysts (alkene epoxidation, cycloalkane oxidation, " Baeyer-Villiger oxidation of aldehydes and ketones to esters ), or with homogeneous metal complex catalysts (epoxidation with porphyrins, salenes or carbonyls ). Also, the homogeneously catalysed oxidation of typical bulk chemicals like cyclohexane (with acetaldehyde as the sacrificial agent ), toluene (with O2, Co +/NaBr ) or the Wacker oxidation of 1-octene or styrene has been demonstrated. 

Oxidative reactions frequently represent a convenient preparative route to synthetic intermediates and end products This chapter includes oxidations of alkanes and cycloalkanes, alkenes and cycloalkenes, dienes, aromatic fluorocarbons, alcohols, phenols, ethers, aldehydes and ketones, carboxylic acids, nitrogen compounds, and organophosphorus, -sulfur, -selenium, -iodine, and -boron compounds... 

Oxidations of higly fluonnated alkanes and cycloalkanes are rare because of the resistance of these compounds to oxidation agents Reactive centers include C-H and C-I bonds (oxidations of lodo compounds at lodme atom are descnbed in a special part of this chapter)... 

The monofluoromethylene group and difluoromethyl group m 1H perfluoro-alkanes and -cycloalkanes are oxidized at the C-H bond to perfluoroalkyl and perfluorocycloalkyl fluorosulfates by anodic oxidation m fluorosulfonic acid [J, 4] Two modifications of the method are used ox idation by fluorosulfonyl peroxide generated pnor to the reaction [J] (equation 2A) and direct electrolysis m the acid [i, 4] (equabons 2B and 3)... 

Trifluoroacetic acid is a useful medium for a number of oxidation reactions It IS highly resistant to strong oxidants, even to permanganates and chromates For instance, various alkanes, cycloalkanes, and arenes can be oxidized degradatively by potassium permanganate in trifluoroacetic acid under mild conditions [28]... 

In the linear versus cyclic case, n-hexane oxidizes 18.9 times as fast as cyclohexane (see Fig. 6-6) however, under slightly different conditions (same temperature and pressure, acetone solvent) and a slightly different preparation of TS-1, n-hexane oxidizes only 4.8 times as fast as cyclohexane.45 These differences in TOFs between the linear and cyclic isomers are also attributed to the size restrictions of the zeolite. When the channel diameter is increased, as in the Ti-(1 catalyst (-6.5 A), larger cycloalkanes, such as cyclododecane, can be oxidized.45... 

More than three decades ago, skeletal rearrangement processes using alkane or cycloalkane reactants were observed on platinum/charcoal catalysts (105) inasmuch as the charcoal support is inert, this can be taken as probably the first demonstration of the activity of metallic platinum as a catalyst for this type of reaction. At about the same time, similar types of catalytic conversions over chromium oxide catalysts were discovered (106, 107). Distinct from these reactions was the use of various types of acidic catalysts (including the well-known silica-alumina) for effecting skeletal reactions via carbonium ion mechanisms, and these led... 

This article will deal with metal-catalyzed cyclization reactions, with reference to oxide and dual-function catalysts. Product cycles may contain five or six carbon atoms. The respective prefixes C5 and will point to the resulting structure (5). The term dehydrocyclization will be applied to reactions that end up with aromatic products the formation of saturated (cycloalkane) rings will henceforth be called cyclization. ... 

It has been demonstrated that the reaction of azole A -oxides with cycloalkane thiones offers a simple and efficient route to azole-thiones. The described reaction sequence has subsequently been found to constitute a useful synthesis of imidazole-2(3//)-thiones (see Scheme 16). 

Recently, Corma et al. have patented a process of oxidizing cycloalkane with molecular oxygen to produce cycloalkanol and/or cycloalkanone in the presence of hydrotalcite-intercalated heteropoly anion [Co MnCo (H20)039] (M = W or Mo), which comprised one cobalt as a central atom and another as a substitute of a W=0 fragment in the Keggin structure [98]. At 130 °C and 0.5 MPa, 64 and 24% selectivity to cyclohexanone and cyclohexanol, respectively, was achieved at cyclohexane conversion about 5%. This catalytic system could be of practical importance provided a true heterogeneous nature of catalysis and good catalyst recyclability had been proved. Unfortunately, this information was lacking in [98]. 

In the first reports by Ishii and coworkers , catalytic amounts of both HPI and Co(II)acetylacetonate, Co(acac)2, were employed for the oxidation of alkanes in AcOH at 100 °C, dioxygen being the terminal oxidant. The appeal of this procedure for the oxidative transformation of simple hydrocarbons into carbonyl derivatives is clear. Cycloalkanes were converted into a mixture of cyclic ketones plus open-chain a, )-dicarboxylic acids (Table 11), while linear alkanes yielded the corresponding alcohols plus ketones in significant amounts (40-80%), and alkylbenzenes could be oxidized in almost quantitative yields . 

Cyclic ethers can be named simply as oxacycloalkanes, such as oxacyclopropane, oxacyclo-butane, oxacyclopentane, and oxacyclohexane, where the prefix oxa indicates the replacement of CH2 by O in corresponding cycloalkanes. Most cyclic ethers, however, are known by other names. The 3-, 4-, 5-, and 6-membered rings are oxirane, oxetane, oxolane, and oxane, respectively, or ethylene oxide (or epoxide), trimethylene oxide, tetrahydrofuran, and tetrahydropyran. 

Cycloalkanes R R R H and chelating arenes ArH were oxidatively cross-conpled to Ar R R R by [RuClj(p-cymene)]2/TBHP/135°C (the reactants were the solvent) thus 2-phenylpyridine and cyclo-octane were cross-coupled cf. mech. Ch. 1. Other complexes (Ru(acac)3, [RuCl CCOD)] and RuHj(CO)(PPh3)3) also catalysed the reaction [78]. 

Cycloalkane ring-fused 2,4-diaminopyrido[2,3-, pyrimidine 580 was obtained by direct treatment of sulfone 579 with guanidine carbonate in boiling diphenyl ether. Sulfoxide 579 was prepared by perbenzoic acid oxidation of the methylthio derivative <1994T199>. 

The most intriguing difference between the chemical properties of cyclopolysilanes and those of cycloalkanes is the ability of the former to form either anion or cation radicals upon one-electron reduction or oxidation, respectively. For example, the cyclic pentamer (Mc2Si)5 is reduced to the corresponding radical anion by sodium-potassium alloy in diethyl ether [see eqn (4.1) in Section 4.1.3], whereas the hexamer (Me2Si)6 is oxidised by aluminium trichloride in dichlor-omethane to the corresponding cation radical. In both cases the EPR spectra of the radical ions can be interpreted in terms of a-electron delocalisation over the entire polysilane ring (see Section 10.1.4.1). In this respect, the cyclosilanes resemble aromatic hydrocarbons rather than their aliphatic analogues. 

Catalytic reforming has become the most important process for the preparation of aromatics. The two major transformations that lead to aromatics are dehydrogenation of cyclohexanes and dehydrocyclization of alkanes. Additionally, isomerization of other cycloalkanes followed by dehydrogenation (dehydroisomerization) also contributes to aromatic formation. The catalysts that are able to perform these reactions are metal oxides (molybdena, chromia, alumina), noble metals, and zeolites. 

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