Hydroperoxide groups from carbonyl group

The gas phase enthalpy of reaction 6 for bis(hydroxymethyl) peroxide is — 192 kJ mol , which deviates from the other hydrate-producing peroxides by nearly 89 kJ mol . The enthalpy of reaction 8, 145 kJmol, is likewise discrepant by some 120 kJmol from that for diethyl peroxide, ca 26 kJ mol. From the high-level calculations reported in Reference 28, the reaction enthalpy for the addition of H2O2 to formaldehyde is —59 kJ mol. A similar reaction is equation 10 for the gas phase addition of tert-butyl hydroperoxide to a carbonyl group. 

Important initiating chromophores include carbonyl and hydroperoxide groups (from oxidations during polymerization and extrusion, and O3 or singlet oxygen, Ag attack) and residues from the polymerization catalyst (Ti and possibly also A1 compounds)... 

Radiation cross-linking of PVC in the absence of additives has been reported by several authors [20,21,267,268]. PVC by itself is not readily cross-linkable by EB radiation. In the study of radiation chemistry of PVC, it is known that the oxidation takes place in the presence of atmospheric oxygen during irradiation [269] and hydroperoxide groups are produced on oxidation. The formation of carbonyl group along with the elimination of HCl from PVC on irradiation in air has also been reported [270,271]. 

The quality of the polymer, its photo-oxidation and thermo-oxidation history expressed in concentration of hydroperoxides, carbonyl groups or of other oxidized structures and terminal groups. The rate of an oxidative attack may then be related to the average molar mass and to its distribution, and to the ratio of amorphous/crystalline structures. Polymers cannot be simply ordered according to the intensity of light emission at a given temperature. The chemiluminescence-time patterns are related with the rate of sample oxidation, but they may differ from one to the next polymer. 

Aldehyde Formation. Several investigators observed a marked dominance of hexanal in the volatile products of low-temperature oxidation. At the higher temperatures, however, 2,4-decadienal was the major aldehyde formed (19,20,21). Both aldehydes are typical scission products of linoleate hydroperoxides. Swoboda and Lea (20) explained this difference on the basis of a selective further oxidation of the dienal at the higher temperature, while Kimoto and Gaddis (19) speculated that the carbon-carbon bond between the carbonyl group and the double bond (Type B) is the most vulnerable to cleavage under moderate conditions of autoxidation, while scission at the carbon-carbon bond away from the olefinic linkage (Type A) is favored under stress such as heat or alkali. 

Fig. 1. a-Oxidation of amino acids. Hydroxyl radical (or other reactive radical) abstracts hydrogen atom from the a-carbon. The C-centered free radical formed may react with other amino acid residues or dimerize in the absence of oxygen, which leads to protein aggregation. In die presence of oxygen the carbon-centered radical forms peroxyl radical. Reduction of peroxyl radical leads to protein hydroperoxide. Decomposition of hydroperoxide leads to formation of carbonyl compounds via either oxidative deamination or oxidative decarboxylation. Oxidation of the new carbonyl group forms a carboxyl group. 

Benzeneseleninic anhydride, C5HjSe(0)0(0)SeC5Hs, which is prepared in situ from diphenyldiselenide and tert-hniyX hydroperoxide, is used for the oxidation of alcohols to aldehydes or ketones [525]. This reagent is a suitable dehydrogenating agent for the introduction of double bonds a to carbonyl groups [526] and the regeneration of ketones from their oximes, semicarbazones, and phenylhydrazones [527]. 

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