0-Scission hydroperoxides

PC Bisphenol A, stilbenes, water, some organic pigments Chain scissions, crosslinks, free radicals, hydroxyl groups, ethers, unsaturations Chain scissions, hydroperoxides, free radicals, carbonyl groups... 

Products of degradation photo-Fries rearrangement, yellowing, chains scission, hydroperoxides, carbonyls ... 

Properly end-capped acetal resins, substantially free of ionic impurities, are relatively thermally stable. However, the methylene groups in the polymer backbone are sites for peroxidation or hydroperoxidation reactions which ultimately lead to scission and depolymerisation. Thus antioxidants (qv), especially hindered phenols, are included in most commercially available acetal resins for optimal thermal oxidative stabiUty. 

Two secondary propagating reactions often accompany the initial peroxide decomposition radical-induced decompositions and -scission reactions. Both reactions affect the reactivity and efficiency of the initiation process. Peroxydicarbonates and hydroperoxides are particularly susceptible to radical-induced decompositions. In radical-induced decomposition, a radical in the system reacts with undecomposed peroxide, eg ... 

Although primary and secondary alkyl hydroperoxides are attacked by free radicals, as in equations 8 and 9, such reactions are not chain scission reactions since the alkylperoxy radicals terminate by disproportionation without forming the new radicals needed to continue the chain (53). Overall decomposition rates are faster than the tme first-order rates if radical-induced decompositions are not suppressed. 

Alkoxy radicals from hydroperoxides can undergo a -scission reaction (eq. 2) to yield an alkyl radical and a ketone. The higher stabiUty of the generated alkyl radical compared to that of the parent alkoxy radical provides the driving force for this reaction, and the R group involved is the one that forms the most stable alkyl radical. 

As with other hydroperoxides, hydroxyaLkyl hydroperoxides are decomposed by transition-metal ions in an electron-transfer process. This is tme even for those hydroxyaLkyl hydroperoxides that only exist in equiUbrium. For example, those hydroperoxides from cycHc ketones (R, R = alkylene) form an oxygen-centered radical initially which then undergoes ring-opening -scission forming an intermediate carboxyalkyl radical (124) ... 

Primary and secondary hydroperoxides are also susceptible to induced decomposition through loss of an a-hydrogen. The radical formed is usually not stable and undergoes (3-scission to give a carbonyl compound and hydroxy radical.2"3 It is reported that these hydroperoxides may also undergo non-radical decomposition with evolution of hydrogen.137... 

Hydroperoxide groups react with NO to give only nitrates as the dominant products, with only traces (< 5%) of nitrite in both oxidized polyolefins and in concentrated solutions of model hydroperoxides (-OOH levels from iodometry -ONO and -ON02 levels by IR). As reported by Shelton and Kopczewski we have confirmed that both nitrate and nitrite result from NO reaction with dilute hydroperoxide solutions (24). Rather than the NO-induced 0-0 scission proposed by these authors, our evidence points to hydrogen abstraction by NO (reaction 4). (A similar scheme may explain nitrite formation from alcohols.) Both e.s.r. and FTIR evidence is... 

To perform the dissociation of the hydrocarbon to alkyl radicals with C—C bond scission, a hydrocarbon molecule should absorb light with the wavelength 270-370 nm. However, alkanes do not absorb light with such wavelength. Therefore, photosensitizers are used for free radical initiation in hydrocarbons. Mercury vapor has been used as a sensitizer for the generation of free radicals in the oxidized hydrocarbon [206-212], Nalbandyan [212-214] was the first to study the photooxidation of methane, ethane, and propane using Hg vapor as photosensitizer. Hydroperoxide was isolated as the product of propane oxidation at room temperature. The quantum yield of hydroperoxide was found to be >2, that is, oxidation occurs with short chains. The following scheme of propane photoxidation was proposed [117] ... 

The bleomycins (50) are hardly simple amines, but they do have two NH2 groups and a CONH2 group at the N-terminal domain, as well as potential donor nitrogens in pyrimidine and imidazole, which can complex metal ions." " The complexing of iron to bleomycin" " " has a significant effect on bleomycin-DNA interactions—metal complexes can mediate strand scission—and on alkene oxidation. Both may involve hydroperoxide intermediates." " " " ... 

The mechanism of this reaction involves free radical oxidation of butane to butane hydroperoxide, which decomposes to acetaldehyde via P scissions. It is similar to the oxidation of cyclohexane to cyclohexanol and cyclohexanone, which will be discussed in Chapter 11, Section 4. 

The cyclohexane hydroperoxide then undergoes a one-electron transfer with cobalt or manganese (II). Chain transfer of the cyclohexyloxyl radical gives cyclohexanol or P-scission gives cyclohexanone. 

Tertiary hydroperoxides derived from tetrasubstituted olefins containing allylic H atoms undergo scission on acid treatment at the site of the original double bond, yielding... 

---