Selective oxidation of alkanes

The selective oxidation of alkanes to ketones using Fe(III)(PA)3 and Fe(III)(PA)2Cl2, Pyr2H (PA = picolinic acid), is performed with BTSP and proceeds by a nonradical mechanism. The Fe -Fe manifold is responsible for the oxidation process (equations 55 and 56). ... 

Selective Oxidation of Alkanes, Alkenes, and Phenol with Aqueous H2O2 on Titanium Silicate Molecular Sieves... 

The selective oxidation of alkanes is cuiTently one of the most widely studied classes of catalytic reactions. This work mainly concentrates on the oxidative dehydrogenation of methane, with some attention paid to the partial oxidation of the product of this reaction, ethane. As regards the latter reaction, higher yields of pai tial oxidation products (acetaldehyde and ethylene) were achieved when N2O was used instead of O2 (1-6). 

The catalysis of the selective oxidation of alkanes is a commercially important process that utilizes cobalt carboxylate catalysts at elevated (165°C, 10 atm air) temperatures and pressures (98). Recently, it has been demonstrated that [Co(NCCH3)4][(PF6)2], prepared in situ from CoCl2 and AgPF6 in acetonitrile, was active in the selective oxidation of alkanes (adamantane and cyclohexane) under somewhat milder conditions (75°C, 3 atm air) (99). Further, under these milder conditions, the commercial catalyst system exhibited no measurable activity. Experiments were reported that indicated that the mechanism of the reaction involves a free radical chain mechanism in which the cobalt complex acts both as a chain initiator and as a hydroperoxide decomposition catalyst. 

Incorporating redox catalytic sites within a zeolite lattice framework should also provide a basis for effecting shape selective oxidations. Indeed, it has recently been reported67 that TS-1 catalyzes the shape selective oxidation of alkanes with 30% H202. Linear alkanes were oxidized much faster than branched or cyclic alkanes, presumably as a result of the molecular sieving action of TS-i. The products were the corresponding alcohols and ketones formed by oxidation at the 2- and 3-positions, e.g.,... 

Use of the urea-hydrogen peroxide complex and /V,/V -bis(TMS) urea provides an improved method126 for the preparation of bis(TMS) peroxide, TMSOOTMS. In the presence of Fe(m)(picolinic acid)3, bis(TMS) peroxide carries out selective oxidation of alkanes to ketones by a non-radical mechanism. The Fe(III)-Fe(IV) manifold is believed to be responsible127. On the other hand, using FeCU in pyridine, alkyl chlorides are formed through a radical mechanism. Here, the Fe(n)-Fe(IV) manifold has been proposed128. 

Selective oxidation of alkanes and benzene derivatives to alcohols and phenols, respectively, are among the most difficult reactions in oxidation catalysis. Therefore, the stoichiometric hydroxylation of alkenes and aromatics performed by a-oxygen at room temperature has aroused great interest as a potential way for developing new steady state catalytic processes for the preparation of these valuable products, similar to the hydroxylation of benzene to phenol. 

The most widespread efforts made towards the achievement of selective oxidation of alkanes are targeted on methane, a principal constituent of natural gas f 6-8]. Activation of the very stable C-H bond of methane is a particularly demanding problem. One example in which this has been achieved on industrial scales is the Degussa process [9], Methane is coupled to ammonia by heterogeneous catalysis in order to produce HCN, an important fundamental material for industrial chemistry. An unsolved problem is the selective oxidation of methane to methanol a reaction that would convert the methane gas into a transportable liquid. In nature, monooxygenases have evolved. These are able to activate molecular oxygen and to... 

In the presence of strong acid activators, such as TFA, cobalt(III) acetate is capable of the selective oxidation of alkanes under mild conditions to alkyl acetates, ketones, or alkyl chlorides, depending on the reagents used.298 For example, the oxidation of n-heptane carried out at 25°C, is illustrated in the following examples ... 

Catalysis of oxidation reactions will continue to be of enormous importance in the future. Areas that continue to be of active interest are the development of efficient methods for the direct epoxidation of olefins, hydroxylation and substitution of aromatics as well as the selective oxidation of alkanes. The application of methods developed for industrial chemicals to the synthesis of more complex molecules is worthy of more attention. A few examples have been discussed in the text. On the whole, however, synthetic chemists have not exploited these methods. 

The selective oxidation of alkanes represents one of the most important and difficult challenges in the chemical industry, and significant recent attention has focused on the use of electrophilic late-transition-metal catalysts to achieve this goal [105-109]. These reactions are often performed in strong-acid solvents that enhance the electrophilicity of the metal center. The use of these solvents also results in formation of alkyl ester products that are deactivated toward further C - H oxidation. 

Prior to this, maleic anhydride had been industrially manufactured by the oxidation of benzene over supported V2O5-M0O3 catalysts. In the late 1970s, when pollution laws that restricted benzene emissions came into effect, industry began to use the -butane route. The reaction is of great importance as it is the only industrial large-scale selective oxidation of alkanes currently in operation. It also involves the functionalization of an alkane, providing a use for this rather unreactive oil fraction. 

Microporous titanium silicate (e.g., TS-1, Ti-(3, Ti-ZSM-12, Ti-mordenite) is an effective molecular-sieve catalyst for the selective oxidation of alkanes, the hydroxyla-tion of phenol, and the epoxidation of alkenes with aqueous H202. The range of organic compounds that can be oxidized is greatly limited, however, by the relatively small pore size (about 0.6 nm) of the host framework. 

Important classes of reactions not included in the above list, because they are not yet used on a commercial scale, are (i) the oxidative dehydrogenation of C2-C5 alkanes, (ii) the selective oxidation of alkanes, such as the synthesis of maleic and phthalic anhydride from n-pentane and methacrolein or methacrylic acid from isobutene, and (iii) propane ammoxidation to acrylonitrile [317-319]. 

The selective oxidation of alkanes is a desirable prospect due to their potentially low environmental impact and the relatively low cost of raw material. Accordingly, the catalysts for such reactions are of great industrial interest. Vanadium-phosphorus oxides are one such group of compounds which have been heavily studied due to their commercial use in the selective oxidation of butane to maleic anhydride. Although the bulk phase of the active commercial catalyst is (V0)2P207, it has been reported that VO(P03)2-containing catalysts are more selective, but less active [1]. Up to a conversion of 8%, the VO(POj)2 catalysts could produce maleic anhydride and fiiran with a combined selectivity of 100%. 

The selective oxidation of alkanes remains a challenge in organic synthesis. The development of economical processes for the functionalization of hydrocarbons is of tremendous technical importance. In nature such reactions are mediated efficiently by various enzymes. The systems related to cytochrome P-450, which for example detoxify lipid-soluble compounds in the human liver, [1] have received the most attention. 

Busch et al. on their search for a cytochrome P450 model useful for the selective oxidation of alkanes investigated the macrobicyclic nickel(II) complex 71 with respect to its inclusion capacity for aliphatic alcohols and phenols. A shift of the host protons in the course of the guest addition (e.g. 1-butanol, phenol) in D O the formation of in-... 

Principles. A photocataiyst is a substance that is activated by a photon. Activation of the semiconductor photocataiyst for reaction is achieved through the absorption of a photon of ultra-band energy, which results in the promotion of electrons from the filled level (i.e. the valence band edge) to the vacant level (i.e. the conduction band edge), generating an electron-hole pair (Figure 1). This electron-hole pair is the primary photoproduct formed upon photoexitation of a semiconductor and has a finite lifetime to allow a separate site for the oxidative and reductive half-reactions to occur. Semiconductor photocatalysis can be more attractive than the more conventional chemical oxidation methods because semiconductors are inexpensive, nontoxic, and capable of repeated use without loss of photoactivity. Therefore, the development of efficient photocatalysis for selective oxidation of alkanes with TiO, is very appealing. 

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