Oxygen donors hydrogen peroxide

When cells such as neutrophils undertake phagocytosis, the process is associated with a metabolic burst in which NADPH oxidase catalyzes the divalent reduction of oxygen to hydrogen peroxide, with NADPH as the hydrogen donor. The source of the donor is the pentose phosphate pathway. Activation of phagocytic cells can be caused artificially by chemicals such as phorbol-12-myristate-13-acetate... 

The oxidation of hydrocarbons by molecular oxygen in the absence of metal complexes has been discussed in Chapter II. The oxidation of hydrocarbons with molecular oxygen, as well as with donors of an oxygen atom (hydrogen peroxide, alkyl hydroperoxides and some other compounds), is a very important field since many industrial processes are based on these reactions [1], In many cases, chain radical non-catalyzed autoxidation of samrated hydrocarbons is not very selective and the yields of valuable products are often low. The use of salts and complexes of transition metals creates great possibilities for solving problems of selective oxidation, as has been demonstrated for a number of important processes. 

Determination of the level of total sulfur in a rubber can give information on the type of cure system used, for example, elemental sulfur plus accelerator or sulfur donor system, etc. The ISO 6528-1 1992 method — Rubber — Determination of total sulfur content — Part 1 Oxygen combustion flask method is often employed. The principle of the method is oxidation by ignition in an atmosphere of oxygen in the presence of hydrogen peroxide, conversion of sulfur to sulfuric acid and determination of the sulfate by titration with barium perchlorate. The method is... 

Peroxides are compounds of great synthetic interest. Especially, alkyl hydroperoxides and hydrogen peroxide have gained more and more importance as cheap and readily available oxygen donors in catalytic oxygenations. Formerly unsafe oxidation procedures (due to the employment of highly concentrated and therefore explosive peroxide solutions) have been optimized or substituted by other and more effective and safe procedures. Over the last two decades, the need for oxidation technologies with enhanced efficiency... 

Besides a variety of other methods, phenols can be prepared by metal-catalyzed oxidation of aromatic compounds with hydrogen peroxide. Often, however, the selectivity of this reaction is rather poor since phenol is more reactive toward oxidation than benzene itself, and substantial overoxidation occurs. In 1990/91 Kumar and coworkers reported on the hydroxylation of some aromatic compounds using titanium silicate TS-2 as catalyst and hydrogen peroxide as oxygen donor (equation 72) . Conversions ranged from 54% to 81% with substituted aromatic compounds being mainly transformed into the ortho-and para-products. With benzene as substrate, phenol as the monohydroxylated product... 

The greater effectiveness of hydrogen peroxide is also shown in the reactions of the pentacoordinated complexes [M(A -L )(cod)] supported by N-donor hgands (L = dpa-R [72,79], Cn [79], PysSs [81]) (Fig. 5). While these complexes are unreactive with molecular oxygen, they react with H2O2 to systematically give the l-hydroxy-2-metalla (5,6,7)-allyl derivatives (Scheme 12) as the thermodynamic products. 

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