Cyclic mechanisms of chain termination

Inhibition Coefficients f and Rate Constants k for the Reactions of Peroxyl Radicals with Aromatic Amines in Systems with a Cyclic Mechanism of Chain Termination (Experimental Data)... 

A new cyclic mechanism of chain termination by nitroxyl radicals, including the formation of aminyl radicals as intermediate species, has been proposed by Korcek and coworkers [42,43]. It was shown that the addition of 4,4 -dioctyldiphenylnitroxyl radical to the hexa-decane that is oxidized (T = 433 K) leads to the formation of the corresponding diphenyl-amine as an intermediate compound during its transformations. The following cyclic mechanism of chain termination was suggested ... 

Thus, nitroxyl radicals can participate in various cyclic mechanisms of chain termination. Additional information about cyclic chain termination is described in Chapter 19. 

Cyclic mechanisms of Chain Termination in the Liquid-Phase Oxidation of Organic Compounds... 

Nitroxyl radicals are formed as intermediates in reactions of polymer stabilization by steri-cally hindered amines as light stabilizers (HALS) [30,34,39,59]. The very important peculiarity of nitroxyl radicals as antioxidants of polymer degradation is their ability to participate in cyclic mechanisms of chain termination. This mechanism involves alternation of reactions involving alkyl and peroxyl radicals with regeneration of nitroxyl radical [60 64],... 

Therefore, such alkyl radical acceptors as quinones, nitroxyl radicals, and nitro compounds retard the oxidation of PP according to the following cyclic mechanism of chain termination ... 

In this system the nitroxyl and acid act as catalysts and H2O2 is consumed. A similar cyclic mechanism of chain termination takes place when the system alcohol + nitroxyl + acid or the system hydrogen peroxide + quinonimine + acid are introduced into oxidized hydrocarbon. 

Alkyl radicals and halogen atoms formed in these reactions do not branch and do not propagate chains therefore, reactions of this type result in chain termination. In some cases, cyclic mechanisms of chain termination appear, as in the case of HBr,... 

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