Superoxide ions

Such a proton-driven disproportionation process means that 02 can deprotonate acids much weaker than water ( pATa = 23).13 

The standard potential of the 02/02 pair is equal to -0.15 V in water and -0.60 V in DMF. Usually, dioxygen easily captures two electrons in the stepwise reaction O2 + e — O2 , then O2 + e 02 . In DMSO, dioxygen reductions into the superoxide ion and then into the dioxygen dianion are characterized by Ey2 = -0.5 V and Ey = -1.5 V in regard to the saturated calomel electrode (Sawyer and Gibian 1979). The superoxide ion occupies an intermediate position in the following redox triad O2 — 02 — In accordance with such a position, the superoxide ion 

According to a widespread opinion, the superoxide ion possesses expressed oxidative properties. Thermodynamically, however, it must be a weak oxidant and a moderate strong reductant (Sawyer and Gibian 1979). This statement refers, of course, to aprotic mediums in which the superoxide ion is stable. In the presence of proton donors, the superoxide ion undergoes disproportionation 

Protonation enhances the electron affinity of the superoxide ion and it easily transforms into hydrogen peroxide HOO + H+ — H2O2 (Costentin et al. 2007). 

The reaction of 1-hydroxy- or 1-aminonaphthoquinone with O2 shows a significant feature of the superoxide ion formation. The superoxide ion forms a van der Waals complex with another product of this reaction, a semiquinone. Hydrogen bonds are formed between Oj and the OH and NH2 groups of the corresponding semiquinone. As a result, the reaction equilibrium is shifted to the right (Liwo et al. 1997). 

---

Erythrocuprein, which contains about 60 wt % of the erythrocyte copper, hepatocuprein, and cerebrocuprein act as superoxide dismutases. Each contains two atoms of copper per molecule, having mol wt ca 34,000. The superoxide ion, O", and peroxide, two main toxic by-products of... 

Contents Introduction and Principles. - The Reaction of Dichlorocarbene With Olefins. - Reactions of Dichlorocarbene With Non-Olefinic Substrates. -Dibromocarbene and Other Carbenes. - Synthesis of Ethers. - Synthesis of Esters. - Reactions of Cyanide Ion. - Reactions of Superoxide Ions. - Reactions of Other Nucleophiles. - Alkylation Reactions. - Oxidation Reactions. - Reduction Techniques. - Preparation and Reactions of Sulfur Containing Substrates. -Ylids. - Altered Reactivity. - Addendum Recent Developments in Phase Transfer Catalysis. 

Peroxide and superoxide ions have recently been identified in molten systems. These ions are formed by the oxidation of oxide ions by oxygen or oxy-anions such as nitrate (see Reference 11). 

Write the Lewis structure of each of the following species and indicate which are radicals (a) the superoxide ion, Oz ... 

The principal product of the reaction of the alkali metals with oxygen varies systematically down the group (Fig. 14.15). Ionic compounds formed from cations and anions of similar radius are commonly found to he more stable than those formed from ions with markedly different radii. Such is the case here. Lithium forms mainly the oxide, Li20. Sodium, which has a larger cation, forms predominantly the very pale yellow sodium peroxide, Na202. Potassium, with an even bigger cation, forms mainly the superoxide, K02, which contains the superoxide ion, O,. ... 

It should be noted that the superoxide ion O2 and peroxide ion 0 " are different,... 

Nanni, E.J., Stallings, M.D. and Sawyer, D.T. (1980). Does superoxide ion oxidised catechal, tocopherol and ascorbic acid by direct electron transfer. J. Am. Chem Soc. 102, 448. 

Starke, P.E., and Farber, J.L. (1985). Ferric iron and superoxide ions are required for the killing of cultured hepatocytes by hydrogen peroxide. Evidence for the participation of hydroxyl radicals formed by an iron catalyzed Haber-Weiss reaction. J. Biol. Chem. 260, 10099-10104. 

It should be noted that dissociation of surface complexes of oxygen in polar solvents on semireduced ZnO films is presumably justified from the thermodynamic point of view as oxygen adsorption heat on ZnO and electron work function are [58] 1 and approximately 5 eV respectively while the energies of affinity of oxygen molecules to electron, to solvation of superoxide ion and surface unit charge zinc dope ions are 0.87, 3.5, and higher than 3 eV, respectively [43]. 

Although the g tensor provides evidence for the identification of a particular spectrum, one should never really be certain until hyperfine structure confirms the identification. The spectrum of the superoxide ion affords a beautiful example of the application of hyperfine structure to establish... 

Hyperfine interaction has also been used to study adsorption sites on several catalysts. One paramagnetic probe is the same superoxide ion formed from oxygen-16, which has no nuclear magnetic moment. Examination of the spectrum shown in Fig. 5 shows that the adsorbed molecule ion reacts rather strongly with one aluminum atom in a decationated zeolite (S3). The spectrum can be resolved into three sets of six hyperfine lines. Each set of lines represents the hyperfine interaction with WA1 (I = f) along one of the three principal axes. The fairly uniform splitting in the three directions indicates that the impaired electron is mixing with an... 

The existence of a variety of adsorption sites in the cationic form of Y-type zeolites is also evident from ESR spectra of the superoxide ion as shown in Fig. 28. Here, only the low-field maxima are shown. At least... 

The state of the superoxide ion has been summarized by Naceache et al. 22). It appears probable that an ionic model is most suitable for the adsorbed species since the hyperfine interaction with the adjacent cation is relatively small. Furthermore, the equivalent 170 hyperfine interaction suggests that the ion is adsorbed with its internuclear axis parallel to the plane of the surface and perpendicular to the axis of symmetry of the adsorption site. Hence, the covalent structures suggested by several investigators have not been verified by ESR data. 

The role of Os" in the oxidation of various reactants, including hydrocarbons, has been briefly investigated but no definitive data has been obtained. In most of the studies the ESR spectra have been observed following addition of a reactant to a surface which has the superoxide ion. The ESR spectrum of the superoxide ion remains essentially unperturbed upon addition of hydrogen, methane, carbon monoxide or ethylene how-... 

At temperatures near 100° Horiguchi and associates (117) have shown that CO reacts with the superoxide ion on ZnO, but the Or spectrum remained at a fixed level following the addition of a mixture of CO and 02. Hydrogen did not react with 02- at that temperature. Upon addition of nitric oxide at room temperature the Oi signal instantaneously disappeared. 

This mode of hyperfine interaction will become important only when the impaired electron is able to partially occupy a low-lying excited state (AE small), and the ground state has orbital angular momentum (L 0). The adsorbed nitric oxide molecule and the superoxide ion with 170 are typical examples where hyperfine coupling via spin-orbit interaction may be observed. 

M.E. Poever and B.S. White, Electrolytic reduction of oxygen in aprotic solvents the superoxide ion. Electrochim. Acta. 11, 1061-1067 (1966). 

D.T. Sawyer and J.L. Roberts, Electrochemistry of oxygen and superoxide ion in dimethyl sulfoxide at platinum, gold, and mercury electrodes. J. Electroanal. Chem. 12, 90-101 (1966). 

J. Chevalet, F. Roulle, L. Gierst, and J.P. Lambert, Electrogeneration and some properties of the superoxide ion in aqueous solutions. J. Electroanal. Chem. Interfacial Electrochem. 390, 201-216 (1972). 

P.F. Knowles, J.F. Gibson, F.M. Pick, and R.C. Bray, Electron-spin-resonance evidence for enzymic reduction of oxygen to a free radical, the superoxide ion. Biochem. J. Ill, 53-58 (1969). 

F. Matsumoto, K. Tokuda, and T. Ohsaka, Electrogeneration of superoxide ion at mercury electrodes with a hydrophobic adsorption film in aqueous media. Electroanalysis. 8, 648-653 (1996). 

T. Ohsaka, F. Matsumoto, and K. Tokuda, An electrochemical approach to dismutation of superoxide ion using a biological model system with a hydrophobic/hydrophilic interface, in Frontiers of Reactive Oxygen Species in Biological and Medicine (K. Asaka and T. Yoshikawa, eds), pp. 91—93. Elsevier Science B.V. Oxford (1994). 

T. Ohsaka, Y. Tian, M. Shioda, S. Kasahara, and T. Okajima, A superoxide dismutase-modified electrode that detects superoxide ion. Chem. Comnum. 990-991 (2002). 

Although this reaction shows the formation of 02 +, it is also possible to add one electron to the 02 molecule to produce (),, the superoxide ion, or two electrons to form O/, the peroxide ion. In each case, the electrons are added to the antibonding 7r orbitals, which reduces the bond order from the value of 2 in the 02 molecule. For ()2 the bond order is 1.5, and it is only 1 for 022-, the peroxide ion. The 0-0 bond energy in the peroxide ion has a strength of only 142k) moT1 and, as expected, most peroxides are very reactive compounds. The superoxide ion is produced by the reaction... 

The 02 ion is known as the superoxide ion, and it is produced when oxygen reacts with potassium, rubidium, and cesium. 

---