Homogeneous oxidation reactions

Propylene oxide is also produced in Hquid-phase homogeneous oxidation reactions using various molybdenum-containing catalysts (209,210), cuprous oxide (211), rhenium compounds (212), or an organomonovalent gold(I) complex (213). Whereas gas-phase oxidation of propylene on silver catalysts results primarily in propylene oxide, water, and carbon dioxide as products, the Hquid-phase oxidation of propylene results in an array of oxidation products, such as propylene oxide, acrolein, propylene glycol, acetone, acetaldehyde, and others. 

Another aspect of the gas-phase homogeneous oxidation reaction at high temperatures is that the major reaction of the alkyl radicals (ethyl and propyl) is their reaction with molecular oxygen to form alkene and 02H radical ... 

As is evident from the above said, all S -compounds in Table 1 will be oxidized in air. The principal process is a homogeneous oxidation reaction, usually comprising several steps before the end product H2SO4 is arrived at. The main role in this reaction is played by the hydroxy radical. In the troposphere this one is formed according to the following reaction ... 

A thorough investigation of possible atmospheric homogeneous oxidation reaction has been carried out by Calvert et al. [3] and possible atmospheric processes in the gas phase are listed in table I. 

The kinetics of the homogeneous oxidation reaction of iron(II) under conditions typical of natural waters is well established (Stumm and Lee, 1961 Singer and Stumm, 1970). Flic rate constant, ktvd, of the photochemical reductive... 

A similar degradation mechanism was proposed for homogeneous oxidation reactions involving hydroxyl radicals (14-20). Therefore, one would intuitively expect to find similar reaction intermediates in heterogeneous oxi- ... 

On occasion, a reaction takes place in more than one phase of a multiphase reactor. An example is the so-called catalytic combustion. If the temperature is high enough, a hydrocarbon fuel such as propane can be oxidized catalyticaUy, on the surface of a heterogeneous catalyst, at the same time that a homogeneous oxidation reaction takes place in the gas phase. This situation calls for two separate definitions of the reaction rate, one for the gas phase and the other for the heterogeneous catalyst. 

The most common situation studied is that of a film reacting with some species in solution in the substrate, such as in the case of the hydrolysis of ester monolayers and of the oxidation of an unsaturated long-chain acid by aqueous permanganate. As a result of the reaction, the film species may be altered to the extent that its area per molecule is different or may be fragmented so that the products are soluble. One may thus follow the change in area at constant film pressure or the change in film pressure at constant area (much as with homogeneous gas reactions) in either case concomitant measurements may be made of the surface potential. 

Copper—cadmium and zinc—chromium oxides seem to provide most selectivity (38—42). Copper chromite catalysts are not selective. Reduction of red oil-grade oleic acid has been accompHshed in 60—70% yield and with high selectivity with Cr—Zn—Cd, Cr—Zn—Cd—Al, or Zn—Cd—A1 oxides (43). The reduction may be a homogeneously catalyzed reaction as the result of the formation of copper or cadmium soaps (44). 

Homogeneous Oxidation Catalysts. Cobalt(II) carboxylates, such as the oleate, acetate, and naphthenate, are used in the Hquid-phase oxidations of -xylene to terephthaUc acid, cyclohexane to adipic acid, acetaldehyde (qv) to acetic acid, and cumene (qv) to cumene hydroperoxide. These reactions each involve a free-radical mechanism that for the cyclohexane oxidation can be written as... 

Homogeneous reactions. Homogeneous noncatalytic reactions are normally carried out in a fluidized bed to achieve mixing of the gases and temperature control. The sohds of the bed act as a heat sink or source and facihtate heat transfer from or to the gas or from or to heat-exchange surfaces. Reaclious of this type include chlorination of hydrocarbons or oxidation of gaseous fuels. 

If iron metal would oxidize to form a homogenous oxide layer without flaking off, draw a diagram showing the reaction conditions, the phase boundary formed and the diffusion conditions likely to prevail in the solid state reaction. 

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