Hydroxyl radical disproportionate

Generation of superoxide radical under physiological conditions ultimately leads to the production of hydroxyl radical through a cascade of redox reactions. Initially, sn-peroxide disproportionates to generate hydrogen peroxide (Eq. 3, Scheme 8.36) Superoxide radical exists in equilibrium with its protonated form (H02, = 5). 

The first step in this sequence is the hydroxyl radical attack on chlorobenzene (reaction 2), which likely results in the formation of chlorohydroxycy-clohexadienyl (C1HCD) radical I (Dorfman et al., 1962). This may initiate one of several possible further reactions. In the absence of strong oxidants, two predominant reactions are dimerization, to produce dichlorobiphenyls (reaction 3), and bimolecular disproportionation, to produce chlorophenol and chlorobenzene (reaction 4). Both reactions showed the stoichiometry of 2 mol... 

Hydrogen abstraction by RH02 could also participate in the process of initiating a chain of thermal oxidation reactions (pathy). In aqueous systems, cations will further react by solvolysis, and superoxide anion will readily disproportionate to yield H202 (path i). This is in contrast to the fate of superoxide anions in ozonation advanced oxidation processes (AOPs), where they react primarily with ozone to produce hydroxyl radical. This description of the chemical pathways of UV/H202 oxidation of organics illustrates that, when oxygen is present, the major paths directly or indirectly create more... 

Biaglow JE, Kachur AV (1997) The generation of hydroxyl radicals in the reaction of molecular oxygen with polyphosphate complexes of ferrous ion. Radiat Res 148 181-187 Biaglow JE, Field KD, Manevich Y, Tuttle S, Kachur A, Uckun F (1996) Role of guanosine triphosphate in ferric ion-linked Fenton chemistry. Radiat Res 145 554-562 Bielski BHJ (1991) Studies of hypervalent iron. Free Radical Res Commun 12/13 469-477 Bielski BHJ, Allen AO, Schwarz HA (1981) Mechanism of disproportionation of ascorbate radicals. J Am Chem Soc 103 3516-3518... 

The primary quantum yields ranged between 5 x 10 3 and 8 x 10 3 [11], In oxygenated media solvated electrons (eaq) are mainly trapped by molecular oxygen, generating hydrogen peroxyl radicals and superoxide anions this disproportionation is a source of hydrogen peroxide and thereby hydroxyl radicals. 

This scheme of interrelated primary photochemical and subsequent radical reactions is comphcated by the back reaction of hydrogen atoms and hydroxyl radicals with formation of water (Fig. 7-16, reaction 2) or the dimerization of the latter with formation of hydrogen peroxide (Fig. 7-16, reaction 3). Furthermore, hydroxyl radicals are scavenged by hydroperoxyl radicals with formation of oxygen and water (Fig. 7-16, reaction 5) or by hydrogen peroxide to yield hydroperoxyl radicals and water (Fig. 7-16, reaction 4). In addition, hydroxymethyl radicals (HOCH ) formed by reaction 1 (Fig. 7-16) are able to dimerize with formation of 1,2-ethane-diole (Fig. 7-16, reaction 7) or they disproportionate to yield methanol and formaldehyde (Fig. 7-16, reaction 8). 

Here, M stands for monomer, as usual. The oligomers produced by reaction (8-7) could meet several fates. If such a radical encounters another radical in the aqueous phase it may undergo termination by combination or disproportionation (Section 6.3.3) to yield a molecule with one or two sulfate ion ends, respectively. The end groups may also reflect whether the second reactant in the termination reaction is a hydroxyl radical (reaction 8-2) or sulfate ion radical (reaction 8-10), or results from hydrolysis, as in ... 

Reaction (50) has been supported by Vaughn and co-workers as a four-center reaction, and they confirmed the disproportionation reaction (51). By means of flash spectroscopy (and in systems with a substantial temperature rise), hydroxyl radicals have been observed in the photooxidation of methyl iodide. Thus the second set of reactions is ... 

It has been shown recently that a hydroxyl radical may partition from the gaseous to the aqueous phase, or may be formed directly in the aqueous phase, and there effect the oxidation of sulfur dioxide. Sulfur dioxide can also be oxidized inside raindrops by hydrogen peroxide, H2O2, which is a minor atmospheric species formed principally by the disproportionation of HO2 radicals... 

The radioprotectant activity of Cu(II)(3,5-DIPS)2 may not be solely due to its disproportionation of superoxide, k = (1-2) X 10 M s [517], but may also be related to its reactivity with hydroxyl radical, hydroperoxyl radical, hydrated electrons, and hydrogen atoms according to the following reactions at biological pH values [324, 462, 518-520] ... 

---