Promoters peroxidation

Kharasch called this the peroxide effect and demonstrated that it could occur even if peroxides were not deliberately added to the reaction mixture Unless alkenes are pro tected from atmospheric oxygen they become contaminated with small amounts of alkyl hydroperoxides compounds of the type ROOH These alkyl hydroperoxides act m the same way as deliberately added peroxides promoting addition m the direction opposite to that predicted by Markovmkov s rule... 

Similarly, satisfactory results can be obtained with high molecular weight fatty acids by exchange deuteration with a metal catalyst in the presence of alkali and a suitable-peroxide promoter. ... 

The potency of a chain-breaking antioxidant, which scavenges peroxyl radicals, will decrease as the concentration of lipid peroxides in the LDL particle increases (Scheme 2.2). This is illustrated in the experiment shown in Fig. 2.3 in which the antioxidant potency of a peroxyl radical scavenger (BHT) decreases as a function of added exogenous hpid hydroperoxide. If the endogenous lipid peroxide content of LDL were to vary between individuals, this could explain the observed diferences in the effectiveness of a-tocopherol in suppressing lipid peroxidation promoted by copper. 

S. Campestrini, M. Carraro, U. Tonellato, M. Pagliaro and R. Ciriminna, Alcohols oxidation with hydrogen peroxide promoted by TPAP-doped ormosils, Tetrahedron Lett., 2004, 45, 7283. 

Tzoganakis, C., Vlachopoulos, J., and Hamielec, A.E., Production of Controlled-Rheol-ogy Polypropylene Resins hy Peroxide Promoted Degradation During Extrusion, Polym. Eng. Set, 28, 170 (1988)... 

Benzoyl peroxide promotes the shedding of keratinised epithelial cells on the skin and is therefore a keratolytic agent. In the treatment of acne it is indicated as a first-line agent in the form of topical preparations. Benzoyl peroxide is mildly irritant, particularly during the early stages of treatment and hence a low strength is chosen to initiate treatment. Moreover aqueous preparations are preferred over alcoholic preparations, to avoid irritation. 

These compounds are relatively unstable, and treatment with hydrogen peroxide promotes telluroxide elimination to give the corresponding a-methylene ketones. 

Castro GD, Diaz-Gomez Ml, Castro JA. 1990. Biotransformation of carbon tetrachloride and lipid peroxidation promotion by liver nuclear preparations from different animal species. Cancer Lett 53 9-15. 

Schweizer, J., Loehrke, H., Elder. L. Goerttler, K. (1987) Benzoyl peroxide promotes the formation of melanotic tumors in the skin of 7,12-dimethylbenz[a]anthracene-initiated Syrian golden hamsters. Carcinogenesis. 8. 479-482... 

Rivas, F., Kolaczkowski, S., Beltran, F., and McLurgh, D., Hydrogen peroxide promoted wet air oxidation of phenol influence of operating conditions and homogeneous metal catalysts, ]. Chem. Technol. Biotechnol., 74(5), 390-398, 1999. 

Experimental results on conjugated ethylbenzene dehydrogenation with hydrogen peroxide, shown in Table 4.2 (experiments 1 and 2), indicate that the use of 15% aqueous hydrogen peroxide promotes high yields of styrene for both the missed and the converted ethylbenzene 36.3% and 90%, respectively1. 

C. Tzoganakis, J. Vlachopoulos, and A. E. Hamielec, Production of Controlled-rheology Polypropylene Resins by Peroxide Promoted Degradation during Extrusion, Polym. Eng. Sci., 28, 170-180 (1988). 

Mechanisms whereby superoxide and hydrogen peroxide promote cell growth or growth responses... 

The rearrangement products derived from aromatic and non-aromatic heterocyclic amines crystallize readily from the lower alcohols. Unlike those of many of the A-substituted glycosylamines, the crystals are not solvated. On the other hand, the ketose derivatives of aralkyl- and alkyl-amines, such as 2-phenylethylamine, ethanolamine, diethanolamine, glycine ethyl ester, and phenylalanine (see Table II), are hydrated or alcoholated, or both, and are difficult to isolate in pure crystalline form. The crystals which have been isolated were hygroscopic. Alcohols, aqueous alcohols, and water are the most commonly used solvents for crystallization. Acetone, ether, or benzene have been added to the alcoholic media in order to increase the yield of crystalline compound. The use of solvents that contain peroxides promotes decomposition of the crystals during storage. ... 

Yu, G.X., Lu, S.X., Chen, H., and Zhu, Z.N. Diesel fuel desulfurization with hydrogen peroxide promoted by formic acid and catalyzed by activated carbon. Carbon, 2005, 43, 2285. 

C. W. Smith investigated oxidations by hydrogen peroxide promoted by a purely catalytic amount of selenium dioxide. Acrolein is oxidized smoothly to monomeric acrylic acid with a 15% solution of hydrogen peroxide in t-butanol in the presence of 5 g. of selenium dioxide per mole of peroxide. Curiously, the same... 

This trend was rather surprising, since it had been generally accepted that a transition metal or metal complex catalyzed hydrosilylation of alkynes proceeded through exclusive ds-addition2. The stereoselectivity observed in this reaction resembles that obtained in the peroxide-promoted reaction of trichlorosilane with alkynes63,37. 

Free radical cyclization Dibenzoyl peroxide promotes the isomerization of -iodoalkyl propynoates to a-(iodomethylene)- y-lactones in refluxing benzene. 

The only fact not clearly compatible with this mechanism is the observation (192,193) that benzoyl peroxide promotes the formation of telomers between phosphite and methacrylic acid. Other catalysts such as sodium methoxide, triethyl amine, and isoamyl iodide are less effective. 

There is more than one correct cure cycle for EVA. Like most polymers with peroxide promoters, it is good practice to raise the bond-line temperature rapidly to avoid peroxide decomposition before an adequate cure has been obtained. One cycle that has been proven uses two steps, one at 100 C for evacuation and adhesion, the other at 150°C for long-term oven cure. This cycle provides a high throughput with only one laminator. 

The peroxidation of P,6-triketones with an ethereal solution of hydrogen peroxide promoted by phosphomolybdic acid (PMA) in the presence of acetonitrile is substrate-controlled unsubstituted triketones, or those containing aliphatic substituents, produce only tricyclic monoperoxides 32 triketones containing benzyl substituents afford tricyclic monoperoxides 32, bridged tetraoxanes 33, and stereoisomeric ozonides 34 and 35 (Scheme 85) (14CEJ10160). 

Conjugated dienes react with radicals by both 1,2- and 1,4-addition. Write a detailed mechanism to account for this fact using the peroxide-promoted addition of one molar equivalent of HBr to 1,3-butadiene as an illustration. 

The catalysts required by plastics may be classified as (1) strong add catalysts (e.g., sulfuric acid, hydrochloric acid, and phosphoric acid alone or in combination with modifiers), (2) latent acid catalysts (e.g., ammonium salts of strong acids such as ammonium chloride generally useful in accelerating the setting of urea or melamine resins), (3) aldehydic catalysts (e.g., catalysts peculiar to phenol-formaldehyde and urea-formaldehyde resins such as paraformaldehyde and hexamethylenetetramine often used in urea and resorcinol adhesives), and (4) peroxide catalysts (e.g., benzoyl peroxide and dicumyl peroxide promote polymerization of polyesters through a free radical mechanism). 

The free radical addition process is used to polymerize the resin. The catalyst (organic peroxides) becomes the source for the free radicals, and with elevated temperature the heat decomposes the peroxide, producing the free radicals. Peroxyester and benzoyl peroxide are the organic peroxides primarily used at elevated temperatures. (See peroxide.) Promoters used singularly or in combination and retarders complete the cnre system. 

Based on the 2,2-dimethylbenzopyran template, a family of chalcones 152, which includes the Cube resin components lonchocarpin, 4-hydroxylonchocarpin, 4-hydroxy-3-melhoxy-lonchocarpin, and paratocarpin, ° with important biological activities was synthesized. Condensation of a variety of 11 aldehydes 151 with a set of resin-bound benzopyrans bearing a methyl ketone substituent 150 followed by cleavage from the resin by hydrogen-peroxide-promoted selenoxide elimination gave chalcones 152 (Figure 11.76). ... 

Berzin, F. Vergnes, B. Delamare L. (2001). Rheological behaviour of controlled-rheology polypropylenes by peroxide-promoted degradation during extrusion comparison... 

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