Peroxide formation

Drier Mechanism. Oxidative cross-linking may also be described as an autoxidation proceeding through four basic steps induction, peroxide formation, peroxide decomposition, and polymerization (5). The metals used as driers are categorized as active or auxiUary. However, these categories are arbitrary and a considerable amount of overlap exists between them. Drier systems generally contain two or three metals but can contain as many as five or more metals to obtain the desired drying performance. 

A.ctive driers promote oxygen uptake, peroxide formation, and peroxide decomposition. At an elevated temperature several other metals display this catalytic activity but are ineffective at ambient temperature. Active driers include cobalt, manganese, iron, cerium, vanadium, and lead. 

Peroxide Formation. Except for the methyl alkyl ethers, most ethers tend to absorb and react with oxygen from the air to form unstable peroxides that may detonate with extreme violence when concentrated by evaporation or distillation, when combined with other compounds that give a detonable mixture, or when disturbed by heat, shock, or friction. Appreciable quantities of crystalline soHds have been observed as gross evidence for the formation of peroxides, and peroxides may form a viscous Hquid in the bottom of ether-fiHed containers. If viscous Hquids or crystalline soHds are observed in ethers, no further tests for the detection of peroxides are recommended. Several chemical and physical methods for detecting and estimating peroxide concentrations have been described. Most of the quaHtative tests for peroxides are readily performed and strongly recommended when any doubt is present (20). 

A refined grade of MTBE is used ia the solvents and pharmaceutical iadustries. The main advantage over other ethers is its uniquely stable stmctural framework that contains no secondary or tertiary hydrogen atoms, which makes it very resistive to oxidation and peroxide formation. In addition, its higher autoignition temperature and narrower flammabihty range also make it relatively safer to use compared to other ethers (see Table 3). 

Another purpose of inerting is to control oxygen concentrations where process materials are subject to peroxide formation or oxidation to form unstable compounds (acetylides, etc.) or where materials in the process are degraded by atmospheric oxygen. An inert gas supply of sufficient capacity must be ensured. The supply pressure must be monitored continuously. 

Shaken with aq 5% Na2C03, dried with MgS04 and stored with chromatographic alumina to prevent peroxide formation. 

Metbyl-l-pentene [763-29-1] M 84.2, b 61.5-62", d 0.680, n 1.395. Water was removed, and peroxide formation prevented by several vacuum distns from sodium, followed by storage with sodium-potassium alloy. 

Inhibited THF is problematic for semipreparative separations. Because small quantities of polymer are being collected along with larger volumes of solvent, more inhibitor, usually butylated hydroxytoluene (BHT), than sample is often collected in each fraction. Thus, one must carefully consider if the BHT will cause a problem in the subsequent analysis of the isolated fractions. If it does, uninhibited THF or other alternate solvents should be used. It must be remember that if uninhibited THF is used, the analyst must pay careful attention to the inevitable peroxide formation in the solvent/fractions. 

Applications of peroxide formation are underrepresented in chiral synthetic chemistry, most likely owing to the limited stability of such intermediates. Lipoxygenases, as prototype biocatalysts for such reactions, display rather limited substrate specificity. However, interesting functionalizations at allylic positions of unsaturated fatty acids can be realized in high regio- and stereoselectivity, when the enzymatic oxidation is coupled to a chemical or enzymatic reduction process. While early work focused on derivatives of arachidonic acid chemical modifications to the carboxylate moiety are possible, provided that a sufficiently hydrophilic functionality remained. By means of this strategy, chiral diendiols are accessible after hydroperoxide reduction (Scheme 9.12) [103,104]. 

Kitada, M., Igarashi, K., Hirose, S. Kitagawa, H. (1979). Inhibition by polyamines of lipid peroxide formation in rat liver microsomes. Biochemical Biophysical Research Communications, 87, 388-92. 

Two major pathways exist for this reaction, one bypassing hydrogen peroxide (first pathway) and the other involving intermediate peroxide formation via reaction (15.21) (second pathway). The peroxide formed is either electrochemically reduced to water via reaction (15.22) or decomposed catalytically on the electrode surface via reaction (15.23), in which case half of the oxygen consumed to form it reemerges [in both cases the overall reaction corresponds to Eq. (15.20)]. 

The beneficial effect of deprenyl in Parkinson s disease was su ested to be in part due to its effect on increasing the levels of SOD activity in several brain regions (Carrillo et al., 1993). Deprenyl is known to inhibit monoamine oxidase type B, which results in a reduction in hydrogen peroxide formation by blockade of the oxidative deamination of dopamine. That is believed to be the major mechanism of action of this drug in inhibiting the progression of Parkinson s disease. 

Wills, E.D. (1969). Lipid peroxide formation in microsomes the role of non-heme iron. Biochem. J. 113, 325-332. 

Frenkel, K. and Chrzan, K. (1987). Hydrogen peroxide formation and DNA base modification by tumor promoter-activated polymorphonuclear leukocytes. Carcinogenesis 8, 455-460. 

Oxatomide (l- 3- [4-(diphenylmethyl)-l-piperazinyl] propyl)-l,3-dihydro-2H-benzimidazol-2-one) is an antiallergy drug. Akamatsu has reported that oxatomide decreases neutrophil-generated superoxide anion and hydrogen peroxide formation in a dose-dependent manner. The authors hypothesize that the drug is inhibiting NADPH-dependent oxygen metabolism within the neutrophil (Akamatsu et al., 1993). 

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