Multi oxidation steps

Natural multi-step processes, where oxidation steps are involved in metaboUc pathways. 

In principle, multi -phase surface layers may be expected on pure metals whenever the metal ion can occur in several valancies, such as in the sulfuridation or oxidation of iron, where the surface layers consist of FeS and FeS2 or FeO, Fe O and Fe20g. The mechanism of surface layer formation can be described quantitatively under the assumption of a preferred parallel stratification of the individual oxides in the surface layer, the lowest oxidation step being located near the metal and the highest being in equilibrium with the gas atmosphere. 

Very long chain fatty acids are initially oxidized in the peroxisome where the initial oxidation step is catalyzed by acyl-CoA oxidase and the subsequent steps in fS-oxidation are catalyzed by a multi-enzyme complex with hydratase, dehydo-genase, and thiolase activities. Unsaturated fatty acids require additional enzymatic activities, including enoyl-CoA isomerase and dienoyl-CoA reductase. Readers are directed to Vance and Vance (2) for additional details regarding fi-oxidation, including the details of the metabolic reactions. 

A further development of the Mopac process led to the KWU Cord process (Chemical—Oxidation—Reduction-Decontamination), a multi-cycle, low-concentration process which proved to be especially suitable for the decontamination of subsystems and full reactor systems (Wille and Sato, 1994). The principles of this process are shown in Fig. 4.52. A CoRD decontamination cycle starts with an oxidation step, using a dilute solution of permanganic acid the excess Mn04 is then reduced by addition of a dicarboxylic acid, thereby generating CO2. By further addition of the dicarboxylic acid up to a concentration of about 0.2%, dissolution of the oxides starts and the metal ions are retained in the solution as complex compounds. The whole process is conducted at about 95 C it does not require a fixed number of cycles, but can be repeated according to the final radiation dose... 

Plutonium pyrochemical processes are now the principal tools at Los Alamos for producing large amounts of high purity plutonium metal from impure metal and oxide scrap. Pyrochemical processing was selected because of its cost effectiveness. The processes are highly compact and require little floor space and manpower to operate. The processes are also operationally efficient in that one or two steps can be used to supplant multi-step operations found in the classical aqueous chemistry flow streams. The... 

Phenol is the starting material for numerous intermediates and finished products. About 90% of the worldwide production of phenol is by Hock process (cumene oxidation process) and the rest by toluene oxidation process. Both the commercial processes for phenol production are multi step processes and thereby inherently unclean [1]. Therefore, there is need for a cleaner production method for phenol, which is economically and environmentally viable. There is great interest amongst researchers to develop a new method for the synthesis of phenol in a one step process [2]. Activated carbon materials, which have large surface areas, have been used as adsorbents, catalysts and catalyst supports [3,4], Activated carbons also have favorable hydrophobicity/ hydrophilicity, which make them suitable for the benzene hydroxylation. Transition metals have been widely used as catalytically active materials for the oxidation/hydroxylation of various aromatic compounds. 

Some companies are successfully integrating chemo- and biocatalytic transformations in multi-step syntheses. An elegant example is the Lonza nicotinamide process mentioned earlier (.see Fig. 2.34). The raw material, 2-methylpentane-1,5-diamine, is produced by hydrogenation of 2-methylglutaronitrile, a byproduct of the manufacture of nylon-6,6 intermediates by hydrocyanation of butadiene. The process involves a zeolite-catalysed cyciization in the vapour phase, followed by palladium-catalysed dehydrogenation, vapour-pha.se ammoxidation with NH3/O2 over an oxide catalyst, and, finally, enzymatic hydrolysis of a nitrile to an amide. 

Fine and specialty chemicals can be obtained from renewable resonrces via multi-step catalytic conversion from platform molecules obtained by fermentation. An alternative method decreasing the processing cost is to carry out one-pot catalytic conversion to final product without intermediate product recovery. This latter option is illustrated by an iimovative oxidation method developed in our laboratory to oxidize native polysaccharides to obtain valuable hydrophilic end-products useful for various technical applications. 

The presence of two types of catalytic centers (e.g., oxidative and reductive) in the same material can give rise to the possibility of multi-step photocatalysis in a one-pot procedure. C-C coupling, for example, is a field of great interest and a recent very good review was published [221]. C-N coupling reactions are also of interest. 

The tautomerism of furoxan (l,2,5-oxadiazole-2-oxide) has been investigated by different computational methods comprising modern density functions as well as single-reference and multi-reference ab initio methods. The ring-opening process to 1,2-dinitrosoethylene is the most critical step of the reaction and cannot be treated reliably by low-level computations (Scheme 2). The existence of cis-cis-trans- 1,2-dinitrosoethylene as a stable intermediate is advocated by perturbational methods, but high-level coupled-cluster calculations identify this as an artifact <2001JA7326>. 

Mechanism [5] was based on the results obtained from multi-step sequential pyrolysis experiments in an inert atmosphere (23). This mechanism [5] differs from [3], primarily in that [5] was proposed to be surface catalytic in nature, and that the reaction between the oxide particle surface and the organohalogen was considered only as the first step, initiating the process leading to the eventual formation of volatile antimony species. 

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