Methyl radical reaction with molecular oxygen

The C-centered radicals of nucleic acid bases generated via hydrogen atom abstraction and addition of hydroxyl or other oxyl radicals to the double bonds also decay rapidly via bimolecular reactions with molecular oxygen. For instance, the rate constant for the reaction of 02 with the C-centered 5-(2 -deoxyuridinyl) methyl radical (U- CH2) derived by hydrogen atom abstraction from the methyl group of thymidine was estimated as 2.2 x 109 M 1 s 1 [61]. The radicals produced by the addition of OH radicals to the C8 position of dG (8-1 IO-dC) also rapidly... 

The major products were ethyl formate and formaldehyde and the minor products were ethyl acetate, acetaldehyde, peroxyacetyl nitrate, and methyl and ethyl nitrates. The products arise from the decomposition reactions of the 1-ethoxyethoxy radical and from its reaction with molecular oxygen ... 

However, several complications arise in hydroxyl chemistry when one considers the ultimate fate of the hydrogen and methyl radicals formed in these two reactions. Both radicals combine rapidly with molecular oxygen to form hydroperoxyl radicals (i.e. HO2 and CH3O2). But the hydroperoxyl radical can regenerate OH ... 

The oxidation of methyl radical with molecular oxygen is a complicated process that involves different competing reactions. The first step of CH3 oxidation is the formation, without energy barrier, of the methylperoxy radical that is a common intermediate for the subsequent reactions. In the pathway that give CH2O + OH as final products, the existence of a CH300 >CH200H isomerization process is postulated to occur. Because of the well known difficulties in the theoretical characterization of radical reactions and the importance of the role that these reactions plays in the combustion processes, we have undertaken the study of the entire reaction profile with both HF-CI and DF methods. The localization of the transition state for the above mentioned isomerization at ab-initio HF level is possible only when the correlation is considered [49]. 

These NSAIDs are photolabUe and are known to exhibit phototoxicity, causing a number of side effects such as dizziness, drowsiness, nausea, and gastrointestinal tract irritation. Many of them can also induce skin photosensitivity in some patients. In addition, ketoprofen, one of the commonly prescribed NSAIDs, produces photohemolytic activity toward red blood cells and is also capable of causing photocleavage of DNA. - The photosensitization of NSAIDs can be traced to their photochemistry and, upon excitation, decarboxylation is the major reaction pathway. " The aryl methyl radical can then react with molecular oxygen to yield a peroxide radical. It can also undergo coupling and other related radical reactions. 

There are examples in which base radicals undergo reaction with adjacent base residues. The 5-(2 -deoxyuridinyl)methyl radical (63, Scheme 8.30) can forge an intrastrand cross-link with adjacent purine residues. Cross-link formation is favored with a guanine residue on the 5 -side of the pyrimidine radical and occurs under low-oxygen conditions. A mechanism was not proposed for this process, but presumably the reaction involves addition of the nucleobase alkyl radical to the C8-position of the adjacent purine residue. Molecular oxygen likely inhibits crosslink formation by trapping the radical 63, as shown in Scheme 8.24. The radical intermediate 89 must undergo oxidation to yield the final cross-linked product 90,... 

Washida, N., and K. D. Bayes. The reactions of methyl radicals with atomic and molecular oxygen. Int. J. Chem. Kinetics 8 777-794, 1976. 

The fact that functionalization of polymers and small molecules is observed to occur predominately on terminal (methyl) carbon atoms does not imply that the oxyfluorination reaction is truly selective. Although the reaction mechanism has not been studied in detail, it is undoubtedly a free-radical process. Molecular oxygen reacts spontaneously with the fluorocarbon—hydrogen radicals generated by fluorine during the fluorination process. Acid fluorides are retained on terminal carbon atoms because they are stable in 1 atm of elemental fluorine. Hypofluorites, which may be short-lived intermediates of oxygen reactions with methylene radical sites along the carbon chain, are not observed in the functionalized polymers. It is probable that, if they are intermediates, they are cleaved and removed by the excess elemental fluorine. 

Cobalt complexes derived from Schiff bases 388 catalyzed the hydroxyacylation of electron-deficient alkenes (Fig. 90) [431, 432]. Thus, methyl acrylate 387 reacted with aliphatic aldehydes 386 in the presence of 5 mol% of the in situ generated catalyst, molecular oxygen, and acetic anhydride to 2-acyloxy-4-oxoesters 389 in 56-77% yield. When acetic anhydride was omitted, the yields of products were lower and mixtures of the free hydroxy compounds and acylated compounds resulting from Tishchenko reactions were obtained. Electron-rich alkenes did not undergo the transformation, since the addition of the acyl radical is much slower. The acylcobalt species inserts oxygen instead and acts as an epoxidation catalyst. 

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