Peroxide radical ions

Maximum production of butadiene occurs around Q0 = 50. In some cases such as Sn02 the reoxidation by 02 of the reduced surface causes the surface to become more strongly oxidizing. This is ascribed to the formation of peroxide radical ions. 

When light is absorbed by the zinc oxide, the initial reaction may be a transfer of an electron from zinc to O2 absorbed on the surface, and the resulting -02 is a radical ion. Organic additives undergo oxidation, either by transfer of electrons to the photopositive surface of the zinc oxide after loss of a photo-excited electron by the crystal to O2 or by hydrogen abstraction by the peroxide radical ion to form HO2 . 

Hydrogen peroxide greatly accelerates the decomposition of ozone in alkaline solutions because of formation of HOg, which reacts rapidly with ozone to form the radical ion (25). When the concentration of H2O2 exceeds 10 Af, the decomposition of ozone is initiated faster by HOg than by... 

At 70—140°C, peroxide is vaporised. Peroxide vapor has been reported to rapidly inactivate pathogenic bacteria, yeast, and bacterial spores in very low concentrations (133). Experiments using peroxide vapor for space decontamination of rooms and biologic safety cabinets hold promise (134). The use of peroxide vapor and a plasma generated by radio frequency energy releasing free radicals, ions, excited atoms, and excited molecules in a sterilising chamber has been patented (135). 

Indeed, when present in concentrations sufficient to overwhelm normal antioxidant defences, ROS may be the principal mediators of lung injury (Said and Foda, 1989). These species, arising from the sequential one-electron reductions of oxygen, include the superoxide anion radical, hydrogen peroxide, hypochlorous ions and the hydroxyl radical. The latter species is thought to be formed either from superoxide in the ptesence of iron ions (Haber-Weiss reaction Junod, 1986) or from hydrogen peroxide, also catalysed by ferric ions (Fenton catalysis Kennedy et al., 1989). 

The luminol dianion Lum2< > does not exist in appreciable quantities in aqueous solvents hydrogen peroxide and a catalyst such as hemin are required. Thus another mechanism seems to be at work here. Perhaps a hydrogen atom is abstracted from the luminol monoanion Lum( > to yield a luminol radical anion 55 which then reacts with oxygen or a radical ion derived from hydrogen peroxide according to 3,4,109)... 

That a bridged peroxide 68 (for a more detailed discussion, see 1>, p. 84) arises from the intermediate open-chain peroxide formed either by recombination of hydrazide radical ion with. 02( > radical ion, such as 66, or by nucleophilic attack of ion on a carbonyl group of a diazaquinone, such as 67, appears to be very plausible. One of the most important experimental reasons for this assumption has been put forward by E. H. White and M. M. Bursey 106> who, on oxidation of luminol with... 

The importance of radical ions and electron-transfer reactions has been pointed out in the preceding sections (see also p. 128). Thus, in linear hydrazide chemiluminescence (p. 103) or acridine aldehyde or ketone chemiluminescence, the excitation steps consist in an electron transfer from a donor of appropriate reduction potential to an acceptor in such a way that the electron first occupies the lowest antibonding orbital, as in the reaction of 9-anthranoyl peroxide 96 with naphthalene radical anion 97 142> ... 

As in the case with catalytic decomposition of hydrogen peroxide, radical generation by the reaction of metal ions with hydroperoxide consists of several steps. In an aqueous solution, first ROOH is substituted in the internal coordination sphere of the ion followed by the transfer of an electron from the ion to ROOH accompanied by the subsequent cleavage of hydroperoxide to RO and OH, for example,... 

The influence of substituents on the rates of degradation of arylazo reactive dyes based on H acid, caused by the action of hydrogen peroxide in aqueous solution and on cellulose, has been investigated [43]. The results suggested that the oxidative mechanism involves attack of the dissociated form of the o-hydroxyazo grouping by the perhydroxyl radical ion [ OOH]. The mechanism of oxidation of sulphonated amino- and hydroxyarylazo dyes in sodium percarbonate solution at pH 10.6 and various temperatures has also been examined. The initial rate and apparent activation energy of these reactions were determined. The ketohydrazone form of such dyes is more susceptible to attack than the hydroxyazo tautomer [44]. 

The oxidative behaviour of glycolaldehyde towards hexacyanoferrate(III) in alkaline media has been investigated and a mechanism proposed, which involves an intermediate alkoxide ion. Reactions of tetranitromethane with the luminol and luminol-peroxide radical anions have been shown to contribute substantially to the tetranitromethane reduction in luminol oxidation with hexacyanoferrate(III) in aerated aqueous alkali solutions. The retarding effect of crown ethers on the oxidation of triethylamine by hexacyanoferrate(III) ion has been noted. The influence of ionic strength on the rate constant of oxidation of ascorbic acid by hexacyanofer-rate(III) in acidic media has been investigated. The oxidations of CH2=CHX (where X = CN, CONH2, and C02 ) by alkaline hexacyanoferrate(III) to diols have been studied. ... 

The reaction of superoxide ion with carbon tetrachloride is important for olefin epoxidations. This reaction includes the formation of the trichloromethyl peroxide radical Oj" + CCI4 —> Cl + CI3COO. The trichloromethyl peroxide radicals formed oxidize electron-rich olefins. The latter gives the corresponding epoxides. This peroxide radical is a stronger oxidizing agent than the superoxide ion itself (Yamamoto et al. 1986). 

Other detection methods have been used in optical MIP sensing systems. An MIP-based chemiluminescent flow-through sensor was developed for the detection of 1,10-phenanthroline (Lin and Yamada 2001). A metal complex was used to catalyze the decomposition of hydrogen peroxide and form the superoxide radical ion that can... 

This mechanism has been formulated in analogy to the known electrochemiluminescence, in which radical-ion annihilation generated at opposite electrodes leads to the formation of the electronically excited state (Scheme 2) . The difference between the CIEEL mechanism and electrochemiluminescence is that, in the former, the radical ions—whose annihilation is responsible for the formation of the excited state—are formed chemically by electron transfer to high-energy peroxides and subsequent bond cleavage or rearrangements. 

Radical cations can be generated by many chemical oxidizing reagents, including Brpnsted and Lewis acids, the halogens, peroxide anions or radical anions, metal ions or oxides, nitrosonium and dioxygenyl ions, stable aminium radical cations, semiconductor surfaces, and suitable zeolites. In principle, it is possible to choose a reagent with a one-electron redox potential sufficient for oxidation-reduction, and a two-electron potential insufficient for oxidation-reduction of the radical ion. 

Hexakis(benzylthio)benzene acts as a rather efficient electron donor. The ESR spectrum obtained with in situ electrolysis indicates a pattern corresponding to the twelve equivalent protons in the benzyl positions. However, cyclovoltammet-ric measurements reveal that the radical cation exists in a complicated equilibrium with the dication and the parent neutral precursor53. Radical ions generated from C60 have been the subject of several publications and discussions within the last years. Several authors have postulated that C6o + can be observed in solid C60. However it could be demonstrated that this signal has to be ascribed to C6a peroxide or its decomposition products54. 

This chemoluminescence results from interaction of 156 (generated from 155 under thermal conditions) and 1,3-DIBF (formed in a minor amount from 156). The first step is the formation of an encounter complex. Electron transfer generates a peroxide radical anion of 156 and a radical cation of 1,3-DIBF. Cleavage of the 0-0 bond in the radical anion of 156 forms an o-dibenzoylbenzene radical anion. Annihilation of the oppositely charged ions gives an excited singlet of 1,3-DIBF (with subsequent fluorescence) (82JA1041). 

Chemiluminescence can occur when a thermal (dark) reaction is so exothermic that its energy exceeds that of the electronically excited state of one of the product molecules. The major pathway for these reactions is the decomposition of cyclic peroxides, and this is at the basis of most bioluminescence processes. There are some other physico-chemical processes which can lead to the formation of excited states and thereby to the emission of light these are based on the bimolecular recombination of high-energy species such as free radicals and radical ions. 

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