Oxygen as a radical

Allylstannanes are stable towards allylic rearrangements up to ca. 100 °C in non-polar solvents, or at rather lower temperature in polar solvents.30-31 Photolytic sigmatropic rearrangement occurs in competition with homolysis, and, in the presence of oxygen as a radical trap, cinnamyltriphenylstannane gives a 1 9 mixture with the a-stannyl isomer.32... 

Tritiated methane (13.9%) and propane (14.6%) are the major products in the reaction of ions with propane. Smaller amounts of ethane (4.7%), ethylene (4.5%) and traces of butane have also been produced. The above yields are insensitive to the addition of 2 mol% of oxygen as a radical scavenger and to a decrease in pressure from 760 to 20 torr (except for an increase in the methane yield from 14 to 18%). These results have been... 

The unique chemical behavior of KO2 is a result of its dual character as a radical anion and a strong oxidizing agent (68). The reactivity and solubiHty of KO2 is gready enhanced by a crown ether (69). Its usefiilness in furnishing oxygen anions is demonstrated by its appHcations in SN2-type reactions to displace methanesulfonate and bromine groups (70,71), the oxidation of benzyHc methylene compounds to ketones (72), and the syntheses of a-hydroxyketones from ketones (73). 

Watanabe et al,25-5 52s applied AMS dimer (116) as a radical trap to examine the reactions of oxygen-centered radicals (e.g. r-butoxy, cumyloxy, benzoyloxy). AMS dimer (116) is an addition fragmentation chain transfer agent (see 6.2.3.4) and reacts as shown in Scheme 3,96. The reaction products are macromonomers and may potentially react further. The reactivity of oxygen centered radicals towards 116 appears to be similar to that of S.2 1 Cumyl radicals are formed as a byproduct of trapping and are said to decay mainly by combination and disproportionation. 

This oxidative process has been successful with ketones,244 esters,245 and lactones.246 Hydrogen peroxide can also be used as the oxidant, in which case the alcohol is formed directly.247 The mechanisms for the oxidation of enolates by oxygen is a radical chain autoxidation in which the propagation step involves electron transfer from the carbanion to a hydroperoxy radical.248... 

The luminol dianion Lum2< > does not exist in appreciable quantities in aqueous solvents hydrogen peroxide and a catalyst such as hemin are required. Thus another mechanism seems to be at work here. Perhaps a hydrogen atom is abstracted from the luminol monoanion Lum( > to yield a luminol radical anion 55 which then reacts with oxygen or a radical ion derived from hydrogen peroxide according to 3,4,109)... 

Aerobic aerobic microorganisms utilize oxygen as a terminal electron acceptor and possess superoxide dismutase or catalase enzymes which are capable of degrading peroxide radicals. 

Special interest has been devoted to the reaction of oxygen on carbanionic sites.- It has been established that triplet oxygen acts as an electron acceptor, and that the reaction may yield either terminal hydroperoxy or alcohol functions. Depending on the reaction conditions, the latter group which originates from a disproportionation process between a hydro-peroxidate and a carbanlon may be observed. By choosing proper conditions one can get polymers terminated quantitatively with hydroperoxide groups. The latter can be used in a later step as a radical initiator to prepare new block copolymers. 

It is essential that the oxidation of the glycol groupings in the polysaccharide be complete, and that no overoxidation occurs. The latter is excluded by performing the reaction with the exclusion of light, at low temperature, and at a pH of 3-3.5, as described by Bobbitt.73 The use of oxygen-free water and the addition of propyl alcohol, as a radical scavenger, also lessen radical-induced depolymerization during oxidation.75... 

Radical inhibitors and electron acceptors prevent the formation of the substituent product. Oxygen drastically retards the substitution but facilitates p-nitrocumyl peroxide formation. Photoirradiation accelerates the reaction. Consequently, the reaction belongs to the ion radical type. The nucleophile (PhS ) is sufficiently active as an electron donor and as a radical interceptor. 

Chan FIWS, Levett G, Matthew JA (1978) Thermal isomerisation of methyl linoleate hydroperoxides. Evidence of molecular oxygen as a leaving group in a radical rearrangement. J Chem Soc Chem Commun 756-757... 

Martinez GR, Medeiros MHG, Ravanat J-L, Cadet J, Di Mascio P (2002) [0ls]-Labeled singlet oxygen as a tool for mechanistic studies of 8-oxo-7,8-dihydroguanine oxidative damage detection of spiroiminodihydantoin, imidazolone and oxazolone derivatives. Biol Chem 383 607-617 Martini M, Termini J (1997) Peroxy radical oxidation of thymidine. Chem Res Toxicol 10 234-241 Merenyi G, Lind J, Shen X (1988) Electron transfer from indoles, phenol, and sulfite (S032T to chlorine dioxide (CICV). J Phys Chem 92 134-137... 

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