Hydrogen peroxide mechanisms

Not all aspects of biooxidation with the hydrogen peroxide mechanism in the presence of catalase are clear yet. The following mechanism is accepted in the biochemical literature [82], which illustrates formal iron valences in catalase and peroxidase reactions ... 

Very stable intermediates reside near the equihbrium potential for adsorbed oxygen and hydroxyl, and coupled proton/electron transfer to and dominates the overall reaction kinetics. In step 3 of Eq. (4), hydrogen peroxide may also form instead of water, and this "associative" hydrogen peroxide mechanism is believed to dominate for most noble metals. 

Method(B). Add3g. (3ml.)ofbenzonitrileto50ml.of lo-volumes hydrogen peroxide in a beaker, stir mechanically and add i ml. of 10% aqueous sodium hydroxide solution. Warm the stirred mixture at 40° until the oily suspension of the nitrile has been completely replaced by the crystalline benzamide (45-60 minutes). Cool the solution until crystallisation of the benzamide is complete, and then filter at the pump and recrystallise as above. One recrystallisation gives the pure benza-mide, m.p. 129-130° yield of purified material, 2-2-5 S ... 

In a 500 ml. three-necked flask, equipped with a mechanical stirrer, thermometer and dropping funnel, place 300 ml. of 88-90 per cent, formic acid and add 70 ml. of 30 per cent, hydrogen peroxide. Then introduce slowly 41 g. (51 ml.) of freshly distilled cyclohexene (Section 111,12) over a period of 20-30 minutes maintain the temperature of the reaction mixture between 40° and 45° by cooling with an ice bath and controlling the rate of addition. Keep the reaction mixture at 40° for 1 hour after all the cyclohexene has been added and then allow to stand overnight at room temperature. Remove most of the formic acid and water by distillation from a water bath under reduced pressure. Add an ice-cold solution of 40 g. of sodium hydroxide in 75 ml. of water in small portions to the residual mixture of the diol and its formate take care that the tempera... 

The mechanism of this reaction involves an activation of the ammonia and hydrogen peroxide because these compounds do not themselves react (118—121). It appears that acetamide functions as an oxygen transfer agent, possibly as the iminoperacetic acid (41) which then oxidizes the transient Schiff base formed between MEK and ammonia (40) to give the oxaziridine (42), with regeneration of acetamide ... 

Hydrogen peroxide may react directiy or after it has first ionized or dissociated into free radicals. Often, the reaction mechanism is extremely complex and may involve catalysis or be dependent on the environment. Enhancement of the relatively mild oxidizing action of hydrogen peroxide is accompHshed in the presence of certain metal catalysts (4). The redox system Fe(II)—Fe(III) is the most widely used catalyst, which, in combination with hydrogen peroxide, is known as Fenton s reagent (5). 

The mechanism and rate of hydrogen peroxide decomposition depend on many factors, including temperature, pH, presence or absence of a catalyst (7—10), such as metal ions, oxides, and hydroxides etc. Some common metal ions that actively support homogeneous catalysis of the decomposition include ferrous, ferric, cuprous, cupric, chromate, dichromate, molybdate, tungstate, and vanadate. For combinations, such as iron and... 

Oxidation. Hydrogen peroxide is a strong oxidant. Most of its uses and those of its derivatives depend on this property. Hydrogen peroxide oxidizes a wide variety of organic and inorganic compounds, ranging from iodide ions to the various color bodies of unknown stmcture in ceUulosic fibers. The rate of these reactions may be quite slow or so fast that the reaction occurs on a reactive shock wave. The mechanisms of these reactions are varied and dependent on the reductive substrate, the reaction environment, and catalysis. Specific reactions are discussed in a number of general and other references (4,5,32—35). 

Although considered an active participant in the process cycle, the tetrahydroaLkylanthraquinone (10) may not be a significant part of the catalytic hydrogenation because, dependent on the concentration in the working solution, these could all be converted to the hydroquinone by the labile shift per equation 17 and not be available to participate. None of the other first- or second-generation anthraquinone derivatives produce hydrogen peroxide, but most are susceptible to further reaction by oxidative or reductive mechanisms. 

Most of the hydrogen peroxide use in Canada is at more recendy constmcted large chemithermal mechanical pulp (CTMP) mills. These modem mills can consume 5000 10,000 t/yr of hydrogen peroxide. 

Peroxyoxalate. The chemical activation of a fluorescer by the reactions of hydrogen peroxide, a catalyst, and an oxalate ester has been the object of several mechanism studies. It was first proposed in 1967 that peroxyoxalate (26) was converted to dioxetanedione (27), a highly unstable intermediate which served as the chemical activator of the fluorescer (fir) (6,9). 

Certain chemical treatments can be employed during the TMP process to achieve improved strength. Sodium sulfite and hydrogen peroxide have been used either for chip pre- or post-treatment of the TMP pulp such pulp is called chemithermomechanical pulp (CTMP). The strength improvements, which may be 50%, are obtained at some sacrifice to yield and opacity. The yields of mechanical pulps are 90—95% the lower yields are associated with chemical treatment. No principal commercial pulps are produced in the next lower yield range, ie, 80—90%. 

Quantum, by contrast, converted an ethylene—carbon monoxide polymer into a polyester-containing terpolymer by treatment with acidic hydrogen peroxide, the Baeyer-Villiger reaction (eq. 11). Depending on the degree of conversion to polyester, the polymer is totally or partially degraded by a biological mechanism. 

In the Talalay process, the froth is produced by chemical rather than mechanical means. Hydrogen peroxide and an enzyme decomposition catalyst are mixed iato the latex and the mixture placed ia the mold. Decomposition of the peroxide by the added enzyme results ia the Hberation of oxygen which causes the latex mix to foam and fill the mold. The foam is then rapidly chilled and CO2 is iatroduced to gel the latex. The gelled foam is then handled ia a manner similar to that used ia the Dunlop process. 

Etch Mechanisms. Most wet etches for the compound semiconductors employ oxidation of the semiconductor followed by dissolution of the oxide. For this reason, many wet etches contain the oxidant hydrogen peroxide, although nitric acid can also be used. One advantage of wet etching over dry is the absence of subsurface damage that is common with dry etching. Metal contacts placed on wet-etched surfaces exhibit more ideal characteristics than dry-etched surfaces. 

A smaller but important use for sulfur dioxide is for stabilization of pulp (qv) brightness after hydrogen peroxide bleaching of mechanical pulps. Sulfur dioxide neutralizes the alkalinity and destroys any excess hydrogen peroxide, which if left in the pulp would cause it to lose brightness. 

A. Preparation of hydroperoxide. In a 2-1. three-necked round-bottomed flask, equipped with a mechanical stirrer (Note 1), a dropping funnel, and a thermometer, is placed 800 g. of 30% hydrogen peroxide (Note 2). The flask is surrounded by an ice bath and rapid stirring is started. In the meantime, 800 g. of 95-96% sulfuric acid is added to 310 g. of cracked ice and the solution is cooled to 10°. When the temperature of the hydrogen peroxide reaches 5-10°, the cold sulfuric acid is added slowly from the dropping funnel during a period of about 20 minutes (Note 3). The temperature of the solution should not exceed 20° during the... 

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