Peroxy radical formation

A similar statement could probably be made concerning ketones. These compounds are commonly used as solvents, and they are known to form fi radicals when photolyzed. Many chlorinated hydrocarbons, which are also widely used as solvents, can be attacked by hydroxyl radicals and thus contribute to peroxy radical formation. 

Metal ions and particularly heavy metal ions tend to sensitize peroxy radical formation, and hence, the presence of metal scavenging or chelating species can offset this effect. This form of stabilization is particularly important for polymers in which metal-containing polymerization catalyst residues are present, such as polyolefins. While simple additives like calcium stearate may be used, more sophisticated ones based on bifunctional chelating species also are available commercially. 

The variation in A+ with [O2] arises from the complex interplay between reactions (60-62). At high [O2], decomposition of the alkyl radical cannot compete with the addition of oxygen and peroxy radical formation is fast and irreversible (/c6i[02] 5> k-(,i). The concentration of oxygen required to achieve this condition will increase with temperature as both k o and A 6i depend sensitively on temperature. Under these conditions k(,2 is the... 

Once formed, polyunsaturated fatty acids (PUFA) can undergo double bond rearrangement to produce a diene conjugated molecule, which enhances stability of the radical intermediate. In the presence of oxygen, chain propagation can occur via lipid peroxy radical formation (LOO ), and initiation of an autocatalytic cycle as outlined below in Eqs. 11 to Eq. 13 [76] ... 

For measuring the steady-state concentration of organic peroxy radicals (ROO ) produced in sunlit natural waters series of antioxidants, such as poly-methylphenols, have been successfully applied as selective probe compounds (Faust and Hoigne, 1987). The rates of transformation have shown that the steady-state concentration of the apparent photooxidants increases with the amount of light absorbed by the DOM. The sink for ROO has not been identified, but kinetic evidence is that DOM, even when the DOC amounts up to 5 mgL"1, does not control the lifetime of the peroxy radicals. The following reaction scheme summarizes the results of the kinetic analysis for peroxy radical formation ... 

Under thermal conditions, hydroxylamine ethers can reversibly decompose (Reaction 15). The radicals formed disproportionate to eliminate olefins and yield hydroxylamine (Reaction 16). In the presence of sufficiently effective acceptors of alkyl radicals (e.g., oxygen), the reaction rate of peroxy radical formation is much higher than that of hydroxylamine formation. Thus, in the process of polymer photooxidation, nitroxyl radicals regenerate and can break multiple oxidative chains. 

These facts indicated that the ethyleneglycol segments should probably be the oxidation sites. The initial high CL emission, which decreases with UV degradation time, must be due to the cyclohexanedimethylene units. Hydroperoxides formed in these aliphatic segments are responsible for this difference with the homopolymer PET. Two possibilities of different peroxy radical formation were postulated, in the ethylene units, as it was observed for PET, and in the cyclohexanedimethylene units. 

Figure I. Electron spin resonance spectra of peroxy radical formation at room temperature (5.0 Mrads). (a) Primary radical R under vacuum,...

A general review of pulse radiolysis studies on electron transfer in solution is presented together with some recent unpublished data. Electron transfer processes occurring in irradiated solutions of metal ions, inorganic anions, and various aliphatic and aromatic organic compounds are discussed with respect to general redox phenomena in radiation and free radical chemistry. Specific topics include the measurement of peroxy radical formation, the use of nitrous oxide in alkaline radiation chemistry, and cascade electron transfer processes. Some implications of the kinetics of electron transfer are discussed briefly. 

Electron transfer to ferricyanide is being used as a reference system for studying and measuring reactions involving peroxy radical formation of the type... 

Kuzuya M, Kondo S, Sugito M, Yamashiro T. Peroxy radical formation from plasma-induced surface free radicals of polyethylene as studied by electron spin resonance. Macromolecules 1998 31 3230-34. 

Klotz et al. (1995) showed that f-butenedial, glyoxal, CH2O, and CO are major products of the OH-initiated oxidation of both E-,Z- 2,4-hexadienedial and E-Js- 2,4-hexadienedial. A mechanism was proposed involving only addition of OH to the double bonds, followed by fragmentation of the alkoxy radical formed following peroxy radical formation and reaction with NO. 

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