Oxidation of cyclic alkanes

At high temperatures, reaction (15) is the most important radical branching process in combustion at pressures below 1 atm. Emdee et al. [44] missed out many of the reactions that produce H atoms in modelling toluene oxidation at 1200 K, and as a result obtained a value for a factor of about 100 too high. 

Finally it should be realized that quadratic branching may occur where there is no net increase in radicals. Reaction (59) is a key step in determining the second limit of the H2 -I- O2 reaction under conditions where HO2 is inert, so that effectively one active radical gives two active radicals. Similarly reaction (54) is a very important branching reaction in alkane oxidation between 700 and 1000 K. 

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Abstract This chapter covers oxidation of C-H and C-C bonds in alkanes. Section 4.1 concerns oxidation of C-H bonds aldehydes and other CH species (4.1.1), methylene (-CH groups) (4.1.2) and methyl (-CH ) groups (4.1.3). This is followed by the oxidation of cyclic alkanes (4.1.4) and large-scale alkane oxidations (4.1.5). Alkane oxidations not considered here but covered in Chapter 1 are hsted in Section 4.1.6. The final section (4.2) concerns oxidative cleavage of C-C bonds. 

These Pd-Ti systems were active in the oxidation of other substrates such as alkanes, alkenes and alcohols. Hexane was hydroxylated into 2- and 3-hexanols, which were further oxidized in part to the corresponding ketones. In this case the product turnover was sensitive to the concentration of HCl. The addition of MeOH was effective as in the case of oxidation by H, , over TS-1. Finally we note that shape selectivity was found in the oxidation of alkanes and alkenes similarly to what was observed for the oxidation where H2O2 was used as oxidant the rates for oxidation of cyclic alkanes and alkenes were much lower than those of linear alkanes and alkenes. 

One of the first RuO -catalysed alkane oxidations was of cyclic alkanes by RuO / aq. Na(ClO) or Na(IO ) (Table 4.1) [25]. Some of the oxidations with Ru-based catalysts were evaluated using adamantane as a model substrate the common oxidation products are shown in Fig. 4.2. 

A high-valent ruthenium complex is also reported to cleave the sp C-H bond. RuCl3 -3H20 catalyzes the transformation of cyclic alkanes to the corresponding ketones in the presence of peracetic acid, where oxoruthenium species is considered to act as the active species. Alcohol, as a primary product in this oxidation reaction, is obtained as an intermediate in the presence of trifluoroacetic acid (Scheme 14.11) [25]. 

Scheme 34 Proposed mechanism for the iron(II)-catalyzed oxidative alkylation of cyclic alkanes...

The direct oxidation of unfunctionahsed alkanes in an asymmetric fashion is a formidable challenge. However, oxidation of C—H bonds adjacent to suitable functional groups gives a handle on which to operate. In particular, the aUyKc oxidation of cyclic alkenes utilising asymmetric variants of the Kharasch—Sosnovsky reaction has received considerable attention. The reaction is catalysed by copper salts and requires a perester to give the allylic ester as product. 

In conclusion, the COX and COLE kinetic scheme possesses a structure which is reasonably compatible with macroscopic experimental observations relating to the oxidation of alkanes at low temperature. It also gives some indication about the distribution of the families of products formed (alkenes, aldehydes, cyclic ethers) as a function of the operating conditions and especially of the temperature. Its structure can be found in the detailed mechanisms of oxidation of the alkanes which will be discussed in Chapter IX. 

More recently, the electrochemical oxidation of lower alkanes in the HF solvent system has been investigated by Devynck and coworkers over the entire pH range. Classical and cyclic voltammetry show that the oxidation process depends largely on the acidity level. Isopentane (2-methylbutane, M2BH), for example, undergoes two-electron oxidation in HFiSbFs and HFiTaFg solutions (equation 18). ... 

We will follow closely the analysis given by Labingerl . The selective oxidation of cyclic and linear alkanes with O2 over reducible Ma Ali xP04 catalytic materials has been reported under mild conditions. Dugal et al.l l designed Co- and Mn-containing alu-... 

The key initiation step in cationic polymerization of alkenes is the formation of a carbocationic intermediate, which can then interact with excess monomer to start propagation. We studied in some detail the initiation of cationic polymerization under superacidic, stable ion conditions. Carbocations also play a key role, as I found not only in the acid-catalyzed polymerization of alkenes but also in the polycondensation of arenes as well as in the ring opening polymerization of cyclic ethers, sulfides, and nitrogen compounds. Superacidic oxidative condensation of alkanes can even be achieved, including that of methane, as can the co-condensation of alkanes and alkenes. 

The oxidation of primary and secondary alcohols in the presence of 1-naphthylamine, 2-naphthylamine, or phenyl-1-naphthylamine is characterized by the high values of the inhibition coefficient / > 10 [1-7], Alkylperoxyl, a-ketoperoxyl radicals, and (3-hydroxyperoxyl radicals, like the peroxyl radicals derived from tertiary alcohols, appeared to be incapable of reducing the aminyl radicals formed from aromatic amines. For example, when the oxidation of tert-butanol is inhibited by 1-naphthylamine, the coefficient /is equal to 2, which coincides with the value found in the inhibited oxidation of alkanes [3], However, the addition of hydrogen peroxide to the tert-butanol getting oxidized helps to perform the cyclic chain termination mechanism (1-naphthylamine as the inhibitor, T = 393 K, cumyl peroxide as initiator, p02 = 98 kPa [8]). This is due to the participation of the formed hydroperoxyl radical in the chain termination ... 

Davis, J.B. and Raymond, R.L. Oxidation of alkyl-snbstitnted cyclic hydrocarbons by a Nocardia during growth on alkanes, Appl. Microbiol, 9 383-388, 1961. 

This enzyme [EC 1.14.13.25] catalyzes the reaction of methane with NAD(P)H and dioxygen to produce methanol, NAD(P), and water. This enzyme is reported to exhibit a broad specificity. Many alkanes can be hydrox-ylated and alkenes are converted into the corresponding epoxides. Carbon monoxide is oxidized to carbon dioxide, ammonia is oxidized to hydroxylamine, and some aromatic compounds and cyclic alkanes can also be hy-droxylated, albeit not as efficiently. 

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 . 

An electron-deficient manganese(III) porphyrin complex was reported to catalyze the oxidation of alkanes by PhI(OAc)2 in mixed [BMIM]PF6/CH2Cl2 at room temperature (230). Cyclic alkanes were oxidized to secondary alcohols and ketone. A highly active and short-lived intermediate, Mn = O, was observed in the ionic liquid, whereas in CH2CI2 the same reaction gave only a less-active intermediate, Mn " = O. 

Most of the work reported with these complexes has been concerned with kinetic measurements and suggestions of possible mechanisms. The [Ru(HjO)(EDTA)] / aq. HjOj/ascorbate/dioxane system was used for the oxidation of cyclohexanol to cw-l,3-cyclohexanediol and regarded as a model for peroxidase systems kinetic data and rate laws were derived [773], Kinetic data were recorded for the following systems [Ru(Hj0)(EDTA)]702/aq. ascorbate/dioxane/30°C (an analogue of the Udenfriend system cyclohexanol oxidation) [731] [Ru(H20)(EDTA)]70j/water (alkanes and epoxidation of cyclic alkenes - [Ru (0)(EDTA)] may be involved) [774] [Ru(HjO)(EDTA)]702/water-dioxane (epoxidation of styrenes - a metallo-oxetane intermediate was postulated) [775] [Ru(HjO)(EDTA)]7aq. H O /dioxane (ascorbic acid to dehydroascorbic acid and of cyclohexanol to cyclohexanone)... 

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. ... 

The oxidation of organic substances by cyclic peroxides has been intensively studied over the last decades , from both the synthetic and mechanistic points of view. The earliest mechanistic studies have been carried out with cyclic peroxides such as phthaloyl peroxide , and more recently with a-methylene S-peroxy lactones and 1,2-dioxetanes . During the last 20 years, the dioxiranes (remarkable three-membered-ring cyclic peroxides) have acquired invaluable importance as powerful and mild oxidants, especially the epoxidation of electron-rich as well as electron-poor alkenes, heteroatom oxidation and CH insertions into alkanes (cf. the chapter by Adam and Zhao in this volume). The broad scope and general applicability of dioxiranes has rendered them as indispensable oxidizing agents in synthetic chemistry this is amply manifested by their intensive use, most prominently in the oxyfunctionalization of olefinic substrates. 

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