Radical formation from

In the absence of an initiator, alcohols are oxidized with self-acceleration [7-9]. As in the oxidation of hydrocarbons, the increase in the reaction rate is due to the formation of peroxides initiating the chains. The kinetics of radical formation from peroxides was studied for the oxidation of isopropyl alcohol [58] and cyclohexanol [59,60]. 

Benzene was also oxidized by O2 to dehydroxybenzenes and/or polyphenylene hydrocarbons on high silica zeolites [127]. Fe3+ impurities and Lewis-acid sites in the catalyst participate in the reaction through cation-radical formation from benzene. 

I. primary initiation (free radical formation from organic peroxides) ... 

Nirofuran compounds are also effective anti-parasitic drugs. Nifurtimox, for example, is used to treat Chagas disease (caused by Trypansoma cruzi) but has side effects. In exploring the use of alternatives to nifurtimox, Olea-Azar et al. have examined radical formation from two analogues. Radical anions were observed upon electrolytic reduction of the compounds and a nitroxide, believed to be the glutathionyl radical-adduct, was detected upon electrolysis in the presence of DMPO and GSH. Radical adducts were also detected upon incubation of one of the analogues with microsomes from T. Cruzi.m A novel endo-peroxide reductase has been isolated from T. Cruzi. Whereas the flavoenzyme was found to reduce quinones to their semiquinones, nifurtimox underwent a direct, two-electron reduction, without the formation of radicals.129... 

Since water is required for the reaction, the primary photochemical product is thought to be a surface bound hydroxy radical. The observed chemoselectivity for radical formation from the adsorbed ether, however, is thought to be governed by adsorption phenomena since a free hydroxyl radical in homogeneous solution is much less selective than the photoirradiated catalyst system. 

Measured Values of Isotope Effect on the Relative Rates of Priipfiry Radical Formation from Propanes and Isobutanes... 

The phenomena enumerated in Section 2.4 do not, of course, fully describe all the differences between chemical and electrode processes of ion radical formation. From time to time, effects are found that cannot be clearly interpreted and categorized. For instance, one paper should be mentioned. It bears the symbolic title ir- and a-Diazo Radical Cations Electronic and Molecular Structure of a Chemical Chameleon (Bally et al. 1999). In this work, diphenyldiazomethane and its 15N2, 13C, and Di0 isotopomers, as well as the CH2-CH2 bridged derivative, 5-diazo-10,ll-dihydro-5H-dibenzo[a,d]cycloheptene, were ionized via one-electron electrolytic or chemical oxidation. Both reactions were performed in the same solvent (dichloromethane). Tetra-n-butylammonium tetrafluoroborate served as the supporting salt in the electrolysis. The chemical oxidation was carried out with tris(4-bromophenyl)-or tris(2,4-dibromophenyl)ammoniumyl hexachloroantimonates. Two distinct cation radicals that corresponded to it- and a-types were observed in both types of one-electron oxidation. These electromers are depicted in Scheme 2-28 for the case of diphenyldiazomethane. 

Scheme 10.18 illustrates the key features of the intramolecular reaction in general and also the specific radical intermediates in the mechanistic study [18]. After initial radical formation from a suitable halide precursor, in the vast majority of cases using Bu3SnH and... 

Hanna PM, Mason RP. Direct evidence for inhibition of free radical formation from Cu(I) and hydrogen peroxide by glutathione and other potential ligands using the EPR spin-trapping technique. Arch Biochem Biophys 1992 295 205-213. 

Fe2+. Because peroxide decomposition was slowest under the same conditions at which benzoic acid decomposition was highest, it is important to consider the efficiency of hydroxyl radical formation from peroxide decomposition. With the surface catalyst, either hydroxyl radical is not readily available to benzoic acid and is scavenged by other species, or the mineral-catalyzed decomposition of hydrogen peroxide involves additional, nonhydroxyl radical-forming pathways for peroxide decomposition. 

Ferrihydrite catalysis of hydroxyl radical formation from peroxide has also shown experimental results consistent with a surface reaction [57]. The yield of hydroxyl radical formation was lower for ferrihydrite than for dissolved iron, resulting in a higher peroxide demand to degrade a given amount of pollutant. As mentioned above, although ferrihydrite exhibited a faster rate of peroxide decomposition than goethite or hematite, the rate of 2-chlorophenol degradation with these catalysts was fastest for hematite [55], In other studies, quinoline oxidation by peroxide was not observed when ferrihydrite was used as catalyst [53]. 

As previously discussed, the concentration of Fe2+ is an important factor in the rate of hydroxyl radical formation from hydrogen peroxide. Consequently, any process that can speed the reduction of Fe3+ to Fe2+ will increase the formation rate of hydroxyl radical. UV or visible radiation can play this role by photoreducing iron. However, the photo-Fenton process involves three additional mechanisms that can contribute to pollutant degradation (a) direct photolysis of H202 to yield two hydroxyl radicals (Eq. (22)) (b) photolysis of Fe(OH)2+ to form hydroxyl radical (Eq. (23)) and (c) degradation of pollutants by direct photolysis (i.e., absorption of a photon by the pollutant molecule followed by decomposition of the photoexcited pollutant molecule). 

Lopes GKB, Schulman FIM, Flermes-Lima M. Polyphenol tannic acid inhibits hydroxyl radical formation from Fenton reaction by complexing ferrous ions. Biochim Biophys Acta 1999 1472 142-152. 

Another significant reaction on BDD anodes is the generation of ozone from OH (Babak et al. 1994 Michaud et al. 2003). Reduced solubility and high reactivity are responsible for the rare detection of ozone in the liquid phase. If ozone quickly disappears, radical formation from H202 and ozone in the bulk electrolyte [(7.52) and (7.53)] is negligible. 

The rate of oxidation can be determined by measuring the oxygen uptake at a certain temperature. Such measurements have shown that the oxidation at 140 °C of low-density polyethylene increases exponentially after an induction period of 2 h. It can be concluded from this result that the thermal oxidation, like photo-oxidation, is caused by autoxidation, the difference merely being that the radical formation from the hydro peroxide is now activated by heat. 

Photodissociation of the dimer [2-2] to the pyridinyl radical (2 ) occurs readily in thin films at low temperatures or in acetonitrile solutions. Although excitation spectra could not be obtained from these experiments a new technique was used 1) the wavelength dependence of radical formation from dimer generated electro-chemically in small amounts, 2) the measurement of the radical produced by a rapid jump to a potential at which reoxidation of the radical takes place. Since the photodissociation spectra of dimers may well determine their practical use, a convenient procedure is useful. 

Brimfield, A.A., Novak, M.J., Mancebo, A.M., Gallagher, B.S., Arroyo, M. (2006). The detection of free radical formation from the interaction of sulfur mustard with NADPH-cytochrome P450 reductase. Toxicologist 90 391. 

The pH (or pD in D2O) was found to have a great effect on sugar radical formation from excited states of one-electron oxidized guanine (in dGuo) but not for one electron oxidized dAdo and its... 

Free radical formation from triazoles has been little studied. Oxidation of triazolidinediones to triazolinones may afford a free radical if dehydrogenation is blocked as in Scheme 35 (74ja333s). The resulting radical is stable in solution and is isolated as its dimer. 

The evidence for radical formation from the cyanine borates is the following ... 

---