Alkylperoxy radical, generation

Reaction of the alkylperoxy radical generated in (30) with NO followed by decomposition will generate the CFC12 radical ... 

As the temperature is increased through the NTC zone, the contribution of alkylperoxy radicals falls. Littie alkyl hydroperoxide is made and hydrogen peroxide decomposition makes a greater contribution to radical generation. Eventually the rate goes through a minimum. At this point, reaction 2 is highly displaced to the left and alkyl radicals are the dominant radical species. 

Eurther reactions of the alkylperoxy radical (ROO-) depend on the environment but generally cause generation of other radicals that can attack undecomposed hydrosend peroxide, thus perpetuating the induced decomposition chain. Radicals also can attack undecomposed peroxide by radical displacement on the oxygen—oxygen bond ... 

Oxygen-centered radicals are arguably the most common of initiator-derived species generated during initiation of polymerization and many studies have dealt with these species. The class includes alkoxy, hydroxy and aeyloxy radicals and tire sulfate radical anion (formed as primary radicals by homolysis of peroxides or hyponitrites) and alkylperoxy radicals (produced by the interaction of carbon-centered radicals with molecular oxygen or by the induced decomposition of hydroperoxides). 

Alkylperoxy radicals are generated by the reactions of carbon-centered radicals with oxygen and in the induced decomposition of hydroperoxides (Scheme 3.82). Their reactions have been reviewed by Howard452 and rate constants for their self reaction and for their reaction with a variety of substrates including various inhibitors have been tabulated.453... 

Alkyl radicals generated from azoalkanes as in (7) react with oxygen added to argon matrices giving alkylperoxy radicals. In this manner radicals... 

Furimsky E, Howard JA, Selwyn J (1980) Absolute rate constants for hydrocarbon autoxidation. 28. A low temperature kinetic electron spin resonance study of the self- reactions of isopropylperoxy and related secondary alkylperoxy radicals in solution. Can J Chem 58 677-680 Gebicki JM, Allen AO (1969) Relationship between critical micelle concentration and rate of radiolysis of aqueous sodium linolenate. J Phys Chem 73 2443-2445 Gebicki JM, Bielski BHJ (1981) Comparison of the capacities of the perhydroxyl and the superoxide radicals to initiate chain oxidation of linoleic acid. J Am Chem Soc 103 7020-7022 Gilbert BC, Holmes RGG, Laue HAH, Norman ROC (1976) Electron spin resonance studies, part L. Reactions of alkoxyl radicals generated from alkylhydroperoxidesand titanium(lll) ion in aqueous solution. J Chem Soc Perkin Trans 2 1047-1052... 

Only one-third of the RH is consumed by alkylperoxy radicals under these conditions. Thus, the chain lengths are short, and substantial amounts of RH are attacked by alkoxy and hydroxy radicals generated from the thermolysis of the hydroperoxide. 

Contrary to our results, other workers (4, 9, 20, 36) state that in the stabilization of carotene, paraffin wax, and lard the activity of pyrocatechol is favorably affected by substitution at position 4, not only by normal but by tertiary alkyl groups as well. Disparate influences of substitution are not surprising when comparing the activity in different substrates owing to the possibility of directive influences in the process of inhibited oxidation. The participation of phenolic antioxidants in the inhibition of autoxidation can be demonstrated (1, 2, 3) simply as a reaction between the molecule of antioxidant AH and the alkylperoxy radical ROO formed duririg the autoxidation of the substrate RH. During this process, an aryloxy radical (A ) is first generated. 

The mechanism of radical generation initially occurs via UV irradiation of the oxide producing surface trapped holes, O". Electron transfer from the adsorbed ketone to the surface trapped hole occurs, producing an adsorbed cation radical. This quickly deprotonates by H transfer to the surface oxide, forming an intermediate radical which subsequently reacts with molecular oxygen to form the adsorbed alkylperoxy radical observable by EPR [48]. 

One aspect which sets oxidation apart from other reactions, e.g. hydrogenation and carbonylation is the fact that there is almost always a reaction (free radical chain autoxidation) in the absence of the catalyst (Reactions 1-3). Moreover, (transition) metal ions which readily imdergo a reversible one-electron valence change, e.g. manganese, cobalt, iron, chromium, and copper, catalyze this process by generating alkoxy and alkylperoxy radicals from RO2H (Reactions 4-6). 

The photodissociation of N02 is the only definitely established process for the formation of ozone in the troposphere and must be held responsible also for the generation of ozone in photochemical smog. The reaction of alkylperoxy radicals with oxygen, ROO + 02— R0 + 03 has occasionally been invoked—for example, by Cadle and Allen (1970)—but according to... 

Hydroxyl radicals react with alkenes mainly by addition to the double bond. This generates a new reaction site at the neighboring carbon atom where oxygen is added. The resulting hydroxy-alkylperoxy radical reacts with NO in a manner similar to that of alkylperoxy radicals to produce hydroxy-alkoxy radicals, for example, in the case of propene... 

The propagation reactions by peroxy radicals should generate mostly radical (3.56), since a tertiary C—H bond is about 25 times more reactive than a secondary C—H bond toward alkylperoxy radicals at 25°C [771, 2182] so that the main oxidation products of poly(vinyl chloride) are assumed... 

In 1968 Fish [119] proposed an alkylperoxy isomerization theory that explains the temperature dependence of the ignition delays and the complex spectrum of products that can be obtained in hydrocarbon oxidation. Once formed the ROO radical can under go an internal isomerization. Cleavage of the resulting R OOH (or QOOH) radical is a chain propagating step leading to generation of a number of different products and an OH radical. Alternatively at low temperatures the addition of O2 can compete with unimolecular dissociation. 

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