OH-Adducts

Gilbert and co workers42 found the same behavior of OH radicals with other aliphatic sulfoxides. In many of these cases the OH adduct is decomposed to the sulfonyl radical. 

Steenken, S. (1989). Purine bases, nucleosides and nucleotides aqueous solution redox chemistry and transformation reactions of their radical cations and e" and OH adducts. Chem. Rev. 89, 503-520. 

The scavenging ability toward O2 can also be measured by using electron spin resonance (ESR) spectrometry. The 02 anion is trapped with 5,5-dimethyl-1-pyrroline TV-oxidc (DMPO), and the resultant DMPO-OH adduct is detected by ESR using manganese oxide as internal standard. Noda and others (1997) used this technique to evaluate antioxidant activities of pomegranate fruit extract and its anthocyanidins (delphinidin, cyanidin, and pelargonidin). 

Conflicting data were also received for the reactions of LA and DHLA with hydroxyl radicals and superoxide. Suzuki et al. [206] found that both LA and DHLA inhibited the formation of DMPO-OH adducts formed in the Fenton reaction. However, Scott et al. [207] concluded that only LA is a powerful scavenger of hydroxyl radicals while DHLA accelerated iron-catalyzed hydroxyl radical formation and lipid peroxidation. 

The yields of 6-hydroxycyclohex-3-en-l-one and 4,5-dihydroxycyclohexene are about equal (0.13 and 0.11 pmols-1, respectively), in accordance with this mechanism. Their yields account for more that 80% of their precursor — the peroxyl radical of the OH adduct (G = 0.29 pmolJ-1). Both the cis and tram isomers of 4,5-dihydroxycyclohexene are formed with the latter being predominant (ca 64%). 

The slow, rate-limiting step is almost certainly the migration of phenyl that occurs in the initial OH adduct (135). This is essentially the analogue for 1,2-diketones of the intramolecular Cannizzaro reaction on the 1,2-dialdehyde glyoxal, OHCCHO (p. 217). In the latter... 

OH addition leads to the OH adduct HO-Y (Eq. 23). In order for this adduct to yield electron transfer products, heterolysis of the bond joining HO and Y has to occur. However, due to the fact that OH is a very bad leaving group (as evidenced by the high pK (15.7) of its conjugate acid, H2O), the rate of the spontaneous heterolysis, kh (Eq. 23a), is very low (very often, 10 s ). As... 

Reactions (24) and (25) are examples for the general phenomenon of redox inversion [38] by dehydration of OH adducts. 

This number is based on the observation that in the reaction with SO], k(observed) for formation of optical density at 340 nm (where the OH adduct of benzonitrile absorbs) is proportional to [benzonitrile] up to the saturation limit ( a 20 mM, k(observed) = 5 x 10 s" ), as shown by 248 nm laser experiments... 

The oxidative degradations of binuclear azaarenes (quinoline, isoquinoline, and benzodrazines) by hydroxyl and sulfate radicals and halogen radicals have been studied under both photochemical and dark-reaction conditions. A shift from oxidation of the benzene moiety to the pyridine moiety was observed in the quinoline and isoquinoline systems upon changing the reaction from the dark to photochemical conditions. The results were interpreted using frontier-orbital calculations. The reaction of OH with the dye 3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-(l,8)(2//,5//)-acridinedione has been studied, and the transient absorption bands assigned in neutral solution.The redox potential (and also the pA a of the transient species) was determined. Hydroxyl radicals have been found to react with thioanisole via both electron transfer to give radical cations (73%) and OH-adduct formation (23%). The bimolec-ular rate constant was determined (3.5 x lO lmoU s ). " ... 

The solute benzene radical cation was formed on pulse radiolysis of an acidic aqueous solution of benzene. The transient optical absorption bands (A-max = 310, 350-500 nm) were assigned to the solute benzene radical cation which is formed on acid-catalysed dehydration of the OH adduct. The radical cation is able to undergo an electron-transfer reaction with Br and was found to be a strong electron oxidant. Pulse radiolysis has been used to study the complex reaction that follows electron addition to hydroxybenzophenones (HOBPs). The various radical species involved have been characterized spectrally and their p/fa values evaluated. The differences... 

For example, Klotz et al. (1997, 1998) have shown that benzene oxide/oxepin photolyzes in sunlight to give phenol with a yield of 43.2 + 4.5%. This reaction mechanism is therefore feasible for the formation of phenol in the benzene-OH reaction. However, photolysis of toluene l,2-oxide/2-methyloxepin gave o-cresol only in small yields, 2.7 + 2.2% (Klotz et al., 1998) this suggests that cresols formed in the OH-toluene reaction come primarily from the direct reaction (63) of the OH adduct with 02, in contrast to the conclusions of Moschonas et al. (1999). 

OH adduct radical (e.g., see Atkinson, 1994, and Chapter 6.G). However, in the presence of sufficient NOz, 2-nitrofluoranthene and 2-nitropyrene are formed and subsequently condense out on particle surfaces (see Pitts, 1987, Atkinson and Arey, 1994, Arey, 1998a, and references therein). 

Xylene and more reactive aromatics XYL Aromatic-OH adduct from TOL ADDT... 

Criegee biradical (H2COO ) CRIG Isoprene OH-adduct IS03... 

Excited formic acid HOTA Methylvinyl ketone OH-adduct MV1... 

Excited acetic acid HTMA Methylvinyl ketone OH-adduct MV2... 

Nitrated organic peroxy radical PN02 Methacrolein OH-adduct MAC1... 

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