Alkyl peroxyl radicals

Irg 1076, AO-3 (CB), are used in combination with metal dithiolates, e.g., NiDEC, AO-30 (PD), due to the sensitized photoxidation of dithiolates by the oxidation products of phenols, particularly stilbenequinones (SQ, see reaction 9C) (Table 3). Hindered piperidines exhibit a complex behavior when present in combination with other antioxidants and stabilizers they have to be oxidized initially to the corresponding nitroxyl radical before becoming effective. Consequently, both CB-D and PD antioxidants, which remove alkyl peroxyl radicals and hydroperoxides, respectively, antagonise the UV stabilizing action of this class of compounds (e.g.. Table 3, NiDEC 4- Tin 770). However, since the hindered piperidines themselves are neither melt- nor heat-stabilizers for polymers, they have to be used with conventional antioxidants and stabilizers. 

Chain propagation proceeds in ester oxidation via the reaction of the ester peroxyl radical with weakest C—H bond of the ester. Is the activity of the ester peroxyl radical same as alkyl peroxyl radical Let us compare the rate constants of two different peroxyl radicals reactions with the same ester group, namely, RCH2C(0)0CH2R. 

The role and influence of polar interaction in reactions of alkyl peroxyl radicals with esters can be studied within the scope of the IPM (see Chapter 7). The increment of polar interaction in activation energy of peroxyl radical with polar compound can be calculated from parameters hrc (Equation (6.33)). The results of the calculation of AEy are presented in Table 9.17. 

The values of rate constants, activation energies, and geometric parameters of secondary alkyl peroxyl radical reaction with several aromatic amines are presented in Table 15.7. 

We present the enthalpies of disproportionation of aminyl radicals with hydroxyalkyl and alkyl peroxyl radicals in Table 16.2 [22-24],... 

Polyphenols can act as antioxidants by a number of potential pathways. The most important is likely to be by free radical scavenging, in which the polyphenol can break the radical chain reaction. Polyphenols are effective antioxidants in a wide range of chemical oxidation systems, being capable of scavenging peroxyl radicals, alkyl peroxyl radicals, superoxide, hydroxyl radicals, nitric oxide and peroxynitrate in aqueous and organic environments [121]. This activity is due to the ability of donating an H atom from an aromatic hydroxyl group to a free radical, and the major ability of an aromatic structure to support an unpaired electron by delocalization around the 7i-electron system. Phenolic acids... 

Alfassi ZB, Mosseri S, Neta P (1987) Halogenated alkyl peroxyl radicals as oxidants effects of solvents and of substituents on rates of electron transfer. J Phys Chem 91 -.3383-3385 Alfassi ZB, Marguet S, Neta P (1994) Formation and reactivity of phenyl peroxyl radicals in aqueous solutions. J Phys Chem 98 8019-8023... 

A common feature of fragmentation reactions of alkyl peroxyl radicals is the fact that the peroxide group decomposes into an inactive compound and only one free radical is formed per one free radical consumed. Thus the overall number of free radicals potentially available for initiation reaction is reduced. 

A particular type of fragmentation is assumed for secondary alkyl peroxyl radicals [88],... 

Og r r h-oh o2 (tert. alkyl peroxyl radicals) ( sec. alkyl peroxyl radicals)... 

Formation and reaction of peroiqrl radicals Except for fluorinated organic conqxiunds, the radical species (alkyl, phenyl) generated on dissociative electron ciqiture process have absorption bands at X < 300 nm. The peroxyl radicals gennated on addition of oxygen also have absorption bands at X < 300 nm except for phenyl peroxyl radicals which show absorption band in 400 - 600 nm region [89-92]. Phenyl peroxyl radicals (1%00, E° 0.7 V vs NHE) are much more reactive than alkyl peroxyl radicals... 

Hindered amine stabilizers are transparent to visible and terrestrial UV light (300-400 nm). In polymeric matrices, they are oxidized in a sacrificial reaction by way of a not yet fully understood mechanism to stable nitroxyl (aminoxyl) radicals >N-0. A mechanism based on the reaction of HASs with alkyl hydroperoxides and alkyl peroxyl radicals is presented in Scheme 9.14 [87]. 

Scheme 9.14 Schematic illustration of the oxidation of hindered amine stabilizers by alkyl hydroperoxides and alkyl peroxyl radicals [87].

We found that the reaction of alkyl hydroperoxide (ROOM) (a model of oxidized lipid) with heme-iron generates alkyl peroxyl radical (ROO ) rather than alkoxyl radical (RO ) or alkyl radical (R ) (6-8). Instead the reaction with... 

Anti-Tumor-Promoter Effect and Alkyl Peroxyl Radical Scavenging Activity of Boiled Vegetables Soup Compared with Cold Water-Extracts of Fresh Vegetabies... 

Table ID. The Activities of Scavei ng Alkyl Peroxyl Radical and Suppressing EA Formation of Cold- and Hot-Water-Extracts of...

Figure 7. Correlation between alkyl peroxyl radical-scavenging effect (IPOX50) and anti-tumor promoter effect (IEA50), Data were reproduced from reference...

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