Peroxide-like species

In one scenario,the dissolution of magnetite entails formation of an unstable iron-deficient oxide phase produced by the more rapid migration of iron ions out of the oxide matrix the reaction rate is governed by decomposition of this peroxide-like species. Gorichev et al. ° determined a value for j of 2.2 0.2 in HaS04, but it was apparent that the fit of the data was poor. The Erofeev reaction does not appear to be suitable for the treatment of data prior to the induction period. 

The free radical polymerization is probably initiated by the reaction of the peroxide with a metal—carbon bond which has been modified through complexation, solvation, or even chemical interaction with a proper monomer. This "site is interacted with the peroxide molecule, which is then decomposed in a metal-catalyzed manner to form a free radical terminus on the polymer chain along with an inert metal—peroxide interaction product. Whether the metal in question is aluminum, titanium, or a complex of the two is uncertain since the mechanism of Ziegler type reactions is still uncertain and since all three have been found in separate studies to promote the polymerization of methyl methacrylate in the presence of peroxides. However, the complex between AlEt>Cl and TiCl3 has been observed to have a much greater effect in accelerating the polymerization of methyl methacrylate than either component by itself hence, the complex appears to be the most likely species. 

Dialkyl peroxides, like diacyl peroxides and peroxyesters, are characterized by homolysis of the 0-0 bond, which is promoted thermally, photochemically or by transition metal catalysis. The combination of steric factors, and the poor leaving group ability makes simple dialkyl peroxides (ROOR) almost unreactive in heterolytic oxygen atom transfer.128 Consequently, no further mention of these species will be made. 

Fade The polymers are not photostable without the use of stabilizers. Their degradation mechanism involves the breaking of the double bond and the subsequent oxidation. This results in the formation of large quantities of species like peroxides. These species can have significantly different refractive indices than the PVC, causing scatter at the interface. If enough interferences are present, the resulting scatter will appear as a whitish haze [1,2],... 

The P-B Pair. Partly to assess the reliability of the experimental tensors for M-B, we determined D and g tensors for the analogous phenyl-benzoyloxy pair (P-B) in photolyzed dibenzoyl peroxide. This species, like M-P, was first reported by Lebedev. (15) We used perdeuterated crystals to remove phenyl hfs from the highly overlapped spectra of four symmetry-related versions of each radical pair (there would have been eight, each corresponding to loss of one of the CO2 groups in the cell, if it were not for an approximate, non-crystallographic... 

Most likely singlet oxygen is also responsible for the red chemiluminescence observed in the reaction of pyrogaHol with formaldehyde and hydrogen peroxide in aqueous alkaU (152). It is also involved in chemiluminescence from the decomposition of secondary dialkyl peroxides and hydroperoxides (153), although triplet carbonyl products appear to be the emitting species (132). 

This last result bears also on the mode of conversion of the adduct to the final substitution product. As written in Eq. (10), a hydrogen atom is eliminated from the adduct, but it is more likely that it is abstracted from the adduct by a second radical. In dilute solutions of the radical-producing species, this second radical may be the adduct itself, as in Eq. (12) but when more concentrated solutions of dibenzoyl peroxide are employed, the hydrogen atom is removed by a benzoyloxy radical, for in the arylation of deuterated aromatic compounds the deuterium lost from the aromatic nucleus appears as deuterated benzoic acid, Eq. (13).The over-all reaction for the phenylation of benzene by dibenzoyl peroxide may therefore be written as in Eq, (14). 

Lipid peroxidation (see Fig. 17.2) is a chain reaction that can be attacked in many ways. The chain reaction can be inhibited by use of radical scavengers (chain termination). Initiation of the chain reaction can be blocked by either inhibiting synthesis. of reactive oxygen species (ROS) or by use of antioxidant enzymes like superoxide dismutase (SOD), complexes of SOD and catalase. Finally, agents that chelate iron can remove free iron and thus reduce Flaber-Weiss-mediated iron/oxygen injury. 

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