Copper catalysts alkane oxidation

Bobianko and Gorokhovatskil 152) and Roiter, Golodets, and Pyatnit-skii 153) found correlations between the rates of the total oxidation of alkenes and alkanes on copper catalysts and the strength of the C—C bond, which is ruptured in the rate-determining step (series 137, six reactants series 138, seven reactants). 

On the other hand, Tilley et al. have reported a synthesis of a well-defined tris(tert-butoxy)siloxy-iron(lll) complex [13] as well as respective molecular siloxide complexes of cobalt [14] and copper [15], which appear to become precursors for their grafting onto silica and application as catalysts for oxidation of alkanes, alkenes and arenes by hydrogen peroxide. 

Recently, we found that a copper catalyst - as well as ruthenium - is effective for the oxidation of alkanes with molecular oxygen in the presence of acetaldehyde [157]. The catalytic system CUCI2 and 18-crown-6 has proved to be efficient [157cj. Furthermore, we found that specific copper complexes derived from copper salts and acetonitrile are convenient and highly useful catalysts for the aerobic oxidation of unactivated hydrocarbons [158], For example, oxidation of cyclohexane with molecular oxygen (1 atm of O2 diluted with 8 atm of N2) in the presence of acetaldehyde and Cu(OAc)2 catalyst (0.0025 mol%) in CH3CN/CH2CI2 (3 2) at 70°C in an... 

The controlled oxidation of alkanes into alcohols also attracts attention from an industrial point of view. Copper-based catalysts containing Tp ligands have been employed as catalysts for this reaction that led to a very interesting as well as unprecedented transformation with copper. Thus, when cyclohexane was reacted with in the presence of these catalysts, cyclohexane was partially converted into cyclohexanol and cyclohexanone, as expected. However, a certain amount of cyclohexane underwent dehydrogenation affording cyclohexene, in the first example of a copper-mediated alkane dehydrogenation process. Part of the cyclohexene was epoxidized in the reaction... 

Most of the catalysts employed in the chemical technologies are heterogeneous. The chemical reaction takes place on surfaces, and the reactants are introduced as gases or liquids. Homogeneous catalysts, which are frequently metalloorganic molecules or clusters of molecules, also find wide and important applications in the chemical technologies [24]. Some of the important homogeneously catalyzed processes are listed in Table 7.44. Carbonylation, which involves the addition of CO and H2 to a C olefin to produce a + 1 acid, aldehyde, or alcohol, uses rhodium and cobalt complexes. Cobalt, copper, and palladium ions are used for the oxidation of ethylene to acetaldehyde and to acetic acid. Cobalt(II) acetate is used mostly for alkane oxidation to acids, especially butane. The air oxidation of cyclohexane to cyclohexanone and cyclohexanol is also carried out mostly with cobalt salts. Further oxidation to adipic acid uses copper(II) and vanadium(V) salts as catalysts. The... 

The use of mixed-metal catalysts can also dramatically affect the products of autoxidations. An example mentioned earlier is the selective oxidation of acetaldehyde to acetic anhydride in the presence of a mixture of cobalt and copper acetates. Another example is the co-oxidation of alkanes and olefins in the presence of both an autoxidation and an epoxidation catalyst (see Section III.B) ... 

Because oxidations with oxygen are free-radical reactions, free radicals should be good initiators. Indeed, in the presence of hydrogen bromide at high enough temperatures, lower molecular weight alkanes are oxidized to alcohols, ketones, or acids [5 7]. Much more practical are oxidations catalyzed by transition metals, such as platinum [5, 6, 55, 56], or, more often, metal oxides and salts, especially salts soluble in organic solvents (acetates, acetylacetonates, etc.). The favored catalysts are vanadium pent-oxide [3] and chlorides or acetates of copper [2, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66], iron [67], cobalt [68, 69], palladium [60, 70], rhodium [10], iridium [10], and platinum [5, 6, 56, 57]. 

Supported copper-based catalysts are active for a great variety of reactions and there have been many fundamental studies of their catalytic and solid state properties. Among them, the oxidation of hydrocarbons and CO (1), alkanes (2) and alcohols (3) dehydrogenation, hydrogenation of ketones (4), allyl alcohols and a- and 6-unsaturated aldehydes and ketones (5), alcohol amination (6), low temperature water gas shift (7). methanol synthesis (8), oxidative condensation of methanol (9), hydrolysis of acrylonitrile to acrylamide (10), and removal of NOx pollutants (11). 

Introduction.—The oxidative dehydrogenation of alcohols to aldehydes and ketones over various catalysts, including copper and particularly silver, is a well-established industrial process. The conversion of methanol to formaldehyde over silver catalysts is the most common process, with reaction at 750—900 K under conditions of excess methanol and at high oxygen conversion selectivities are in the region 80—95%. Isopropanol and isobutanol are also oxidized commercially in a similar manner. By-products from these reactions include carbon dioxide, carbon monoxide, hydrogen, carboxylic acids, alkenes, and alkanes. 

The applications reported for polymer-supported, soluble oxidation catalysts are the use of poly(vinylbenzyl)trimethylammonium chloride for the autooxidation of 2,6-di-tert-butylphenol [8], of copper polyaniline nanocomposites for the Wacker oxidation reaction [9], of cationic polymers containing cobalt(II) phthalocyanate for the autooxidation of 2-mercaptoethanol [10] and oxidation of olefins [11], of polymer-bound phthalocyanines for oxidative decomposition of polychlorophenols [12], and of a norbornene-based polymer with polymer-fixed manganese(IV) complexes for the catalytic oxidation of alkanes [13], Noncatalytic processes can also be found, such as the use of soluble polystyrene-based sulfoxide reagents for Swern oxidation [14], The reactions listed above will be described in more detail in the following paragraphs. 

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