Oxidations of alkanes and cycloalkanes

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... 

While examples corresponding to (a), (b) and the deprotonation case of (c) can be counted literally in thousands, the effect of substrate protonation in anodic oxidation is less well documented. However, amines and other nitrogen compounds have been thoroughly investigated on this point (Adams, 1969) and found to behave normally, but some recent work on anodic reactions in superacidic media has revealed a theoretically interesting exception to the rule. This concerns the anodic oxidation of alkanes and cycloalkanes in fluoro-sulphuric acid (Table 4, no. 9) with varying concentrations of added base, potassium fluorosulphate and/or acetic acid (Bertram et al., 1971, 1973). 

Oxidations of alkanes and cycloalkanes are rare and not easy. The rates of oxidation with chromic acid of methyl, methylene, and methine... 

Metalloporphyrin catalyzed oxidation of alkanes and cycloalkanes with 0... 

A further report of the oxidation ability of manganese nodules is that of Nitta.53 Several reactions were carried out with natural manganese oxide nodules including oxidative dehydrogenations of alkanes and cycloalkanes, reduction of NO, total oxidation of CO, and use in the gettering of metal and mixed metal ions. For example, nodules were found to have a tremendous capacity for adsorption of heavy metals and toxic metals like Pb2+, and Hg2+. in addition, nodules have been used to sequester metals that are present in petroleum fractions that can contain metals like V and Ni. These metals can cause degradation of the fluid cracking catalysts even at levels as low as 1 ppm. 

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... 

The reactivity of alkanes and cycloalkanes are very low. Alkenes and alkynes containing double and triple bonds are reactive. The addition reactions follow Markovnikov rule. Conjugated dienes undergo Diels-Alder reactions. The substances that may react violently with unsaturated hydrocarbons are halogens, strong oxidizers, and nitrogen dioxide. Alkynes may form acetylides with certain metals. 

The Co" complex [CoPcFig] have advantageous properties as electrocatalyst for the reduction of oxygen as compared to [CoPc] [39]. The Ru" complex [RuPcF, ] appeared to be an effective catalyst for the room tanperature oxidation of cycloalkanes [9]. Encapsulated in zeolite these species were used for catalytic oxidation of alkanes and alcohols [46]. In photoelectrochemical and (photo)conductivity studies it was shown that [ZnPcFig] behaves as n-type semiconductor in vacuo and photoconductor in the presence of oxygen [37, 47]. Due to its enhanced solubility in different solvents as compared to non-substituted [ZnPc] it has advantages for clinical application in photodynamic tumor therapy [11]. Perfluorinated In ", Ti and Zd phthalocyanines exhibit higher performance as optical limiters than non-fluorinated species [42]. 

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)... 

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 . 

One of the most important applications of vanadium alkoxides is connected with their catalytical action on the reactions of oxidation of hydrocarbons and, in particular, alkanes, cycloalkanes, and so on. [645, 172], Except for VO(OR)3 it was proposed that the complexes already containing the peroxide groups in their composition — such as VO(OBu )2(OOBu ) [1516], VO(OR)(OOH)2, V02(00R) [172], and VIY(OPri)3(OOBu ) [25] — be used. 

The third class of organic donor molecules are a-donors, viz., alkanes and cycloalkanes. These substrates have inherently high ionization and oxidation potentials. Therefore, their radical cations are not readily available by photoinduced electron transfer, but typically require radiolysis and electron impact in the condensed phases or the gas phase, respectively. Thus, radical cations of simple alkanes (methane [206], ethane [207]) or unstrained cycloalkanes (cyclopentane, cyclohexane) [208] were identified and characterized following radiolysis in frozen matrices. In contrast, strained ring compounds have significantly lower oxidation potentials so that the radical cations of appropriate derivatives can be generated by photoinduced electron transfer. 

Recently the Co/Mn/N-hydroxyphthalimide (NHPI) systems of Ishii have been added to the list of aerobic oxidations of hydrocarbons, including both aromatic side chains and alkanes. For example, toluene was oxidized to benzoic acid at 25°C [125] and cyclohexane afforded adipic acid in 73% selectivity at 73% conversion [126], see Fig. 4.46. A related system, employing N-hydroxysac-charine, instead of NHPI was reported for the selective oxidation of large ring cycloalkanes [127]. 

The alkanes and cycloalkanes in diesel fuel are generally not readily metabolized, and are mostly excreted unchanged through the lungs, with a very small fraction excreted in the urine. The aromatic constituents of diesel are subject to oxidative metabolism and are typically excreted in the urine as water-soluble metabolites. 

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