As catalyst for oxidation

Catalysts. Silver and silver compounds are widely used in research and industry as catalysts for oxidation, reduction, and polymerization reactions. Silver nitrate has been reported as a catalyst for the preparation of propylene oxide (qv) from propylene (qv) (58), and silver acetate has been reported as being a suitable catalyst for the production of ethylene oxide (qv) from ethylene (qv) (59). The solubiUty of silver perchlorate in organic solvents makes it a possible catalyst for polymerization reactions, such as the production of butyl acrylate polymers in dimethylformamide (60) or the polymerization of methacrylamide (61). Similarly, the solubiUty of silver tetrafiuoroborate in organic solvents has enhanced its use in the synthesis of 3-pyrrolines by the cyclization of aHenic amines (62). 

NR is c/ s -1,4-polyisoprcnc, of molecular weight 200,000-500,000, but it also contains a small level of highly important non-rubber constituents. Of these, the most important are the proteins, sugars and fatty acids which are antioxidants and activators of cure. Trace elements present include potassium, manganese, phosphorus, copper and iron which can act as catalysts for oxidation. 

We showed that the application of PEG/CO2 biphasic catalysis is also possible in aerobic oxidations of alcohols [15]. With regard to environmental aspects it is important to develop sustainable catalytic technologies for oxidations with molecular oxygen in fine chemicals synthesis, as conventional reactions often generate large amoimts of heavy metal and solvent waste. In the biphasic system, palladium nanoparticles can be used as catalysts for oxidation reactions because the PEG phase both stabilises the catalyst particles and enables product extraction with SCCO2. 

Cobalt salts and their complexes have been widely used as homogeneous oxidation catalysts in organic syntheses as well as in the chemical industry [19]. Various complexes of cobalt are useful as catalysts for oxidative organic transformations [20-25]. In view of the ability of cobalt to cycle between the commonly encountered II and III oxidation states, complexes of cobalt find application as catalysts in the oxidation of a variety of substrates... 

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. 

The calcined iron-grafted materials exhibit high selectivity as catalysts for oxidations of alkanes, alkenes and arenes with H2O2 as the oxidants [13a]. A similar method has been used by Tilley et al. to prepare a pseudotetrahedral (Co(II) [Co(4,4 -di Bu-bipy) OSi(0 Bu)3 2]) complex grafted onto the SBA-15 surface and subsequently use it in catalytic oxidation of alkylaromatic substrates with tert-butyl hydroperoxide [14]. Unfortunately, neither iron nor cobalt surface organometaUic compounds have been tested in the recycled catalytic system. 

It has been reported that Mo-P oxides show a good performance in oxidation of butenes to maleic anhydride [26]. On the other hand, Bordes et al. [27] have reported that U-Mo oxides with Mo-rich compositions are effective as catalysts for oxidation of butenes to maleic anhydride. These findings suggest that the functions required for oxidation of toluene are similar to those required for oxidation of butenes to maleic anhydride. However, the V-P oxides are not effective for toluene oxidation. Possibly, the consecutive oxidation of benzaldehyde cannot be suppressed with V Og-containing catalysts. Even over the Mo-P and U-Mo oxides, benzaldehyde is degraded, to a certain extent. 

Carbides of transition metals as catalysts for oxidation reactions... 

Boutevin et al. [177-180] treated different types of wastes of polyolefins (more often low density polyethylene) with a mixture air/ozone. They focused their studies on the quantification of the formed oxygenated species based on colorimetric titration using stable radicals such as diphenylpicryl-hydrazyl. They investigated the influence of mineral compounds (iron oxide, for example) used as catalysts for oxidative reactions. The ozonized polymers have been used as binders for composites materials containing mineral materials (sand, stones, etc.). 

In spite of the fact that this classification makes things look quite complicated, it is a dangerously simplified one, and the real situation is much more involved. Therefore it is not surprising that many organic materials have been reported as catalysts for oxidation, but that the explanations given for their activity are often contradictory. Pyrolized polyacrylonitrile and polyphenylacetylene are reported to inhibit the oxidation of cumene 56X This may be connected with the reported quinonic structure of these polymers, which makes them active towards free radicals. 

Fig. 4.58 Ruthenium salts in ionic liquids as catalysts for oxidation of alcohols.

Cesium fluoride—Celite as catalyst for oxidation by atmospheric oxygen 789... 

The formation of undesirable flavors in soybean oil is accelerated by the presence of 0.01 ppm copper and 0.1 ppm iron, which act as catalysts for oxidation this can be minimized by the addition of chelating agents. 

Many other metal ions have been reported as catalysts for oxidations of paraffins or intermediates. Some of the more frequently mentioned ones include cerium, vanadium, molybdenum, nickel, titanium, and ruthenium [21, 77, 105, 106]. These are employed singly or in various combinations, including combinations with cobalt and/or manganese. Activators such as aldehydes or ketones are frequently used. The oxo forms of vanadium and molybdenum may very well have the heterolytic oxidation capability to catalyze the conversion of alcohols or hydroperoxides to carbonyl compounds (see the discussion of chromium, above). There is reported evidence that Ce can oxidize carbonyl compounds via an enol mechanism [107] (see discussion of manganese, above). Although little is reported about the effectiveness of these other catalysts for oxidation of paraffins to acetic acid, tests conducted by Hoechst Celanese have indicated that cerium salts are usable catalysts in liquid-phase oxidation of butane [108]. 

Challa, G., Meinders, H. C. Copper-polymer complexes as catalysts for oxidative coupling reactions. J. Mol. Catal. 1977, 3,185-190. 

Copper-Polymer Complexes as Catalysts for Oxidative Coupling Reactions... 

Neumann, R. Mixed Addenda Phosphomolybdovanadates as Catalysts for Oxidations with Dioxygen and Hydrogen Peroxide. In Polyoxometalates from Platonic Solids to Anti-retroviral Activity Pope, M. T., Muller, A., Eds. Kluwer Academic Publishers Dordrecht, 1994 pp 307-313. 

In a mixture of water and water-miscible solvents such as acetone, 1,4-dioxane, and methanol, peroxidase could act as catalyst for oxidative polymerization of various phenol derivatives, yielding a new class of polyaromatics.4 The polymerization proceeds at room temperature, and during the polymerization, powdery polymers are often precipitated, which are readily collected after the polymerization. 

To follow the environmental law and to remove small but sometimes persistent concentrations of pollutants activated carbons seem to be the media of choice. They are relatively inexpensive, easily to obtain, and owing to their enormously high surface area and pore volume, they are able to remove and retain even traces of air and water pollutants. Activated carbons, due to their unique surface chemistry act not only as adsorbents but also as catalysts for oxidation of inorganic and organic species. Moreover, their surface can be modified and tailored toward desired applications. 

Heteropolyacids and their salts have been studied as catalysts for oxidation both in the liquid and in the gas phase of several organic saturated and unsaturated substrates (44-50). The main features of these systems, which make them suitable for application as heterogeneous catalysts, can be summarized as follows (51-53) ... 

In living cells, various oxidoreductases play an important role in maintaining the metabolism of living systems. Most of oxidoreductases contain low valent metals as their catalytic center. In vitro enzymatic oxidoreductions have afforded functional organic materials. Some oxidoreductases such as peroxidase, laccase, and polyphenol oxidase have received much attention as catalysts for oxidative polymerizations of phenol derivatives to produce novel polyaromatics [1-10], This chapter deals with enzymatic oxidative polymerization of phenolic compounds. 

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