Peroxy compounds, 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. 

Peroxides decompose when heated to produce active free radicals which in turn react with the mbber to produce cross-links. The rate of peroxide cure is controlled by temperature and selection of the specific peroxide, based on half-life considerations (see Initiators, free-radical Peroxy compounds, organic). Although some chemicals, such as bismaleimides, triallyl isocyanurate, and diallyl phthalate, act as coagents in peroxide cures, they are not vulcanization accelerators. Instead they act to improve cross-link efficiency (cross-linking vs scission), but not rate of cross-link formation. 

The ditellurium compounds, in which a Te —Te group joins two carbonyl groups, can be considered to be the tellurium analogs of peroxy compounds derived from carbonic acid or benzoic acids (e.g. benzoyl peroxides). Only a few of these compounds are known. During the reduction of aromatic nitro compounds with disodium telluride in dimethylfor-mamide, bis[dimethylaminocarbonyl] ditellurium was formed as a by-product in yields from 5 to 15%. The formation of this compound was attributed to the capture of the dimethylaminocarbonyl radical by the telluride anion and subsequent oxidation of the tellurocarbamoyl species4. 

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 ... 

A general review of pulse radiolysis studies on electron transfer in solution is presented together with some recent unpublished data.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. 

These reaction pathways are in parallel with those for alkanes mentioned in Sect, 7.2.2, and the reactions (7.7, 7.8 and 7.9) after CH3 radicals are formed in reaction (7.43) are the same as those in the oxidation processes of methane described in Sect. 7.1. The specific feature of oxidation reactions of aldehydes is the formation of a metastable peroxy acyl nitrates from the reaction of peroxy acyl radicals with NO2 by reaction (7.41). In the case of acetaldehyde, peroxy acetyl nitrate, CH3C(0)00N02, is formed. This compound is called PAN (Peroxy Acetyl Nitrate), and is known to have much stronger toxicity to plants than ozone. A group of peroxy acyl nitrates are collectively called PANs. 

Laser flash photolysis of model compounds of diphenylmethane-4,4 -diisocyanate based polyurethane low molecular weight model compounds, such as mono- and bis-carbamates, exhibits the formation of diarylmethyl radicals which readily react with oxygen. The formed polymer peroxy (PO2) radicals abstract hydrogen and yield polymer hydroperoxides (POOH) [1000, 1001, 1003, 1006, 1007]. 

Ethylene-propylene and silicone rubbers are crosslinked by compounding with a peroxide such as dicumyl peroxide or di-t-butyl peroxide and then heating the mixture. Peroxide cross-linking involves the formation of polymer radicals via hydrogen abstraction by the peroxy radicals formed from the decomposition of the peroxide. Crosslinks are formed by coupling of the polymer radicals... 

The interplay of HO, peroxy radicals, VOCs, and NO , species has substantial implications for tropospheric air quality. For instance, VOCs, NO , , and sunlight result in poor visibility from ozone and aerosol formation, together denoted as photochemical smog, which can lead to adverse health effects in sensitive individuals. Normally, we think of minimizing either class of compounds as beneficial to the atmosphere. However, minimizing VOC emissions only impacts ozone concentration in high-NO , areas. Moreover, in VOC-sensitive areas, reductions in NO , may lead to the overproduction of ozone. We can examine a simplified scheme for ozone production ... 

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