Oxidation by radicals

The reaction probabilities for O and OH with soot particles have been measured by Roth and co-workers in a series of shock tube experiments [58-60], They have found that both radicals react with soot particles with a collision efficiency of between 0.10 and 0.20. In contrast, the reaction probability with 02 is at least an order of magnitude lower [55], Of course, at lower temperatures and sufficiently lean mixtures, soot oxidation by radical species becomes small and oxidation by 02 is important (though slow). Consequently, soot that passes through or avoids the primary reaction zone of a flame (e.g., due to local flame quenching) may experience oxidation from 02 in the post-flame gases. Analysis of soot oxidation rates in flames [54-57] has supported the approximate value of the OH collision efficiency determined by Roth and co-workers. 

Unfortunately, OH and O concentrations in flames are determined by detailed chemical kinetics and cannot be accurately predicted from simple equilibrium at the local temperature and stoichiometry. This is particularly true when active soot oxidation is occurring and the local temperature is decreasing with flame residence time [59], As a consequence, most attempts to model soot oxidation in flames have by necessity used a relation based on oxidation by 02 and then applied a correction factor to augment the rate to approximate the effect of oxidation by radicals. The two most commonly applied rate equations for soot oxidation by 02 are those developed by Lee el al. [61] and Nagle and Strickland-Constable [62],... 

The oxides of sulfur create global pollution problems because they have longer lifetimes in the atmosphere than the oxides of nitrogen. Some of the SO2 and SO3 in the air originates from biological processes and from volcanoes, but much comes from the oxidation of sulfur in petroleum and in coal burned for fuel. If the sulfur is not removed from the fuel or the exhaust gas, SO2 enters the atmosphere as a stable but reactive pollutant. Further oxidation by radicals leads to sulfur trioxide ... 

Figure 4. Postulated mechanism of amino acid oxidation by radical attack of a-...

M. Kamachi, H. Q. Guo, and A. Kajiwara. Block copolymer synthesis of V-vinylcarbazole and cyclohexene oxide by radical/cation transformation polymerization. A/acwmt)/. Chem. Phys., 203(7) 991-997, May 2002. 

The mechanism of the reactions of aryl halides cannot occur by the common S 2 patii for the oxidative addition of methyl halides, and most aryl halides lack substituents that would make them sufficiently electrophilic to react by nucleophilic aromatic substitution pathways. As presented in the section on radical pathways for oxidative addition, aryl halides react with metal complexes that readUy imdergo one-electron oxidation by radical mechanisms. However, metal complexes that do not readily undergo one-electron processes tend to react by two-electron mechanisms. Thus, aryl halides typically react with tP" palladium(O) complexes by concerted pathways through three-centered transition states. No strong data for a radical pathway has been gained during the many studies on the oxidative addition of aryl halides to Pd(0). In contrast, evidence that oxidative addition of aryl halides to P, iridium, Vaska-t)q)e complexes occurs by a radical pathway has been published. ... 

The radical scavenging antioxidants are non-enzymatic and are found in plasma, lipoproteins and membranes. It is these types of antioxidant reactions that this Chapter will concentrate on, since many of these antioxidants can be increased by dietary supplementation and, therefore, could be used medicinally to prevent oxidation by radicals and other reactive oxygen species. 

Figure 7. Unsaturatedfatty acid oxidation by radical pathway and crosslinking...

A. Alaaeddine, C. Negrell and B. Ameduri, Recent Advances on New Fluorinated Copolymers Based on Carbonate and 01igo(Ethylene Oxide) by Radical Copolymerization, in Advances in Fluorine-Containing Polymers, ed. 

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