Oxidation reaction scenario

Many scenarios involving spontaneous combustion involve a combination of materials exposed to sufficient air, often in an insulating situation that prevents heat from a slow oxidation reaction from dissipating, which results in a self-heating situation. 

In subsequent research, it turned out that two-state reactivity can also provide a concept for the understanding of oxidation reactions way beyond the scope of gas-phase ion chemistry and can actually resolve a number of existing mechanistic puzzles. In enzymatic oxidations involving cytochrome P450, for example, changes in spin multiplicity appear to act as a kind of mechanistic distributor for product formation [27-29], and in the case of manganese-catalyzed epoxidation reactions, two-state scenarios have been put forward to account for the experimentally observed stereoselectivities [30-32], Two-state reactivity is not restricted to oxidation reactions, and similar scenarios have been proposed for a number of other experimentally studied reactions of 3d metal compounds [33-37]. Moreover, two-state scenarios have recently also been involved in the chemistry of main group elements [38]. The concept of two-state reactivity developed from the four-atomic system FeO /H2... 

The reactivity of the molecular fullerene solid resembles the expected pattern for a homogeneous material. Only a small prereactivity at 700 K indicates that a fullcrcne-oxygen complex [12] is formed as an intermediate stoichiometric compound [15, 105], At 723 K the formation of this compound and the complete oxidation are in a steady state [12, 106, 107] with the consequence of a stable rate of oxidation which is nearly independent of the bum-off of the fullerene solid. This solid transforms prior to oxidation into a disordered polymeric material. The process is an example of the alternative reaction scenario sketched above for the graphite oxidation reaction. The simultaneous oxidation of many individual fullerene molecules. leaving behind open cages with radical centers, is the reason for the polymerization. 

The molecular nature of this carbon allows the spectroscopic identification [15, 108] of this intermediate and several oxocomplexes serving as precursor compounds [105, 109, 110]. On this basis the reactivity of fullerenes in oxidation is now understood in detail and the reaction scenario is secured by experimental verification [106, 107, 111]. 

Figure 23 Various reaction scenarios for the passive corrosion of titanium alloys (A) linear oxide film growth due to film recrystallization (B) linear Him growth kinetics maintained by film dissolution.

Oxide catalysts are known to be effective for oxidation reactions. In this study, we wanted to produce carbon monoxide through partial oxidation of the biomass, as this could be expected to lead to a conversion of carbon monoxide into hydrogen via the water-gas shift reaction. An oxidization of the tarry product is also expected. By these two effects, improvement of the efficiency of the gasification is expected. Oxide catalyst is expected to enhance the oxidation reaction needed for this scenario. Since oxide catalyst is considerably cheaper than nickel catalyst, its use would make the whole gasification process more economical. Hence, we decided to examine the effect of oxide catalysts on gasification with partial oxidation using cellulose as a model compound. 

The complexity of the methanol-oxide surface interaction is responsible for the still inconsistent picture about this reaction which may well proceed via several pathways on the same bulk oxide. The reaction scenario in Scheme 3 is a... 

After the removal of water a transient CO species is obtained which is then oxidized to the final stable product CO2. An important point in this reaction scenario is whether or not the C-O bond of the methanol molecule is actually cleaved. 

In the EK-PRB treatment system, the removal mechanism for Cr(VI) can be illustrated by Fig. 23.7. Since the removal is believed to involve the reduction of Cr(VI) to Cr(III) by the oxidation of Fe° to Fe(II)/Fe(III) and the accumulation of Cr(VI) in the reservoirs, two simple removal paths are sketched. The first path is reduction of Cr(VI) due to the corrosion of the acid front passing through the barrier and bringing the dissolved Fe°/Fe + ions into the EO flow. The second path is the migration of Cr(VI) ions directly into a PBR reacting with the ZVI. The reaction scenarios of this reductive precipitation mechanism are described as below. 

Our initial approach centered on the use of a strategic Wessely oxidation reaction to transform an appropriately decorated resorcinol precursor into a tricyclic cage architecture formed by an in situ intramolecular Diels-Alder cycloaddition reaction (Scheme 1). From there we envisioned a 6-exo-type cyclization to form the tetracyclic core, which in the best case scenario would also set the C9-methyl stereocenter. Manipulation of the functional groups on the tetracyclic core would then be followed by a late-stage C—C bond fragmentation reaction to access the vinigrol core. Conversion of the exocyclic methyl ketone group was expected to afford the desired isopropyl moiety. 

The application of techniques of pulse radiolysis offers the potential to determine rates of primary radiolysis induced reaction processes. This knowledge can be of great value in the determination of redox processes of Pu ions occurring in a wide variety of aqueous solutions. As a matter of fact, such information is essential to a prediction of the Pu oxidation states to be expected in breached repository scenarios. For an... 

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