Aroxyl radicals

Dimroth, K. Arylated Phenols, Aroxyl Radicals and Aryloxenium Ions Syntheses and Properties. /29, 99-172 (1985). 

Rate Constants, Equilibrium Constants, Enthalpies, and Entropies of Aroxyl Radicals Dimerization in Hexane at T = 293 K... 

The mechanism of inhibitory action of aryl phosphites seems to be relatively complex. Phosphites reduce hydroperoxide and thus decrease chain autoinitiation. The formed peroxyl and alkoxyl radicals react with phosphites to form aroxyl radicals. The latter terminates the chains by reaction with peroxyl radicals. On the other hand, phosphites are hydrolyzed with... 

There seems to be a ratio of one free radical per quinone oxygen. Donnet et al. (101) concluded that either paraquinones or aroxylic radicals were present, which would react according to the following schemes. 

The procedure for preparing 2,4,6-triphenylphenoxyl is based on the method described by Dimroth and co-workers. This method represents the commonly used preparation of aroxyl radicals by oxidation of the corresponding phenol. The chemistry of stable phenoxyl radicals has been reviewed. ... 

Other aroxyl radicals, especially those with i-butyl groups at the phenyl ring, are described by Cook and by Miiller. ... 

When coniferyl alcohol is dehydrogenated, it loses its phenolic hydrogen atom to form first an aroxyl radical Ra (XI), which is in eflFect also present as the mesomeric radicals Rb (XII), Rc (XIII), and Rd (XIV). Of these limiting structures, Rb is the most favored. The existence of the radicals in these forms is recognized by their reaction products. In very dilute dioxane-water solution (1 1 vol.), the half-life of the radicals is about 45 seconds 13). 

The reactions between free radicals and flavonoids (or polyphenols) are assumed to form aroxyl radicals (PO) (reaction 8). The stability of these secondary radical species is an important element to be considered in their antioxidant actions. Flavonoids with similar reduction potentials can originate radicals with very different reactivity toward other molecules present in biological systems. While a stable and relatively nonreactive PO is also nonreactive to propagate the chain reaction, a high reactive PO would propagate rather than interrupt a chain reaction. 

To compare the stability of aroxyl radicals derived from different flavonoids, the rate constants for the disproportionation reaction between two PO to render nonradical species (reaction 15) can be used ... 

When a series of flavonoids were compared through the analysis of the second-order rate constants (ko), it was concluded that (i) ko values differ considerably, ranging from 105 M-1 s 1 (the most stable) to 10s M 1 s 1 (the less stable), and (ii) these data, together with the spectral characteristics of transient aroxyl radicals, were used to establish the structural requirements for... 

Arylated Phenols, Aroxyl Radicals and Aryloxenium Ions... 

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