Peroxides and Superoxides

Compounds containing O — O bonds and oxygen in the —1 oxidation state are 

Because of this reaction, potassium superoxide is used as an oxygen source in masks worn by rescue workers ( FIGURE 22.15). For proper breathing in toxic environments, oxygen must be generated in the mask and exhaled carbon dioxide in the mask must be eliminated. Moisture in the breath causes the KO2 to decompose to O2 and KOH, and the KOH removes CO2 from the exhaled breath  

Hydrogen peroxide ( FIGURE 22.16) is the most familiar and commercially important peroxide. Pure hydrogen peroxide is a clear, syrupy liquid that melts at —0.4 °C. Concentrated hydrogen peroxide is dangerously reactive because the decomposition to Water and oxygen is very exothermic  

This is another example of a disproportionation reaction, in which an element is simultaneously oxidized and reduced. The oxidation number of oxygen changes from — 1 to —2 and 0. 

Hydrogen peroxide is marketed as a chemical reagent in aqueous solutions of up to about 30% by mass. A solution containing about 3% H2O2 by mass is sold in drugstores and used as a mild antiseptic. Somewhat more concentrated solutions are used to bleach fabrics. 

The peroxide ion is a by-product of metabolism that results from the reduction of O2. 

The body disposes of this reactive ion with enzymes such as peroxidase and catalase. 

The other group 6A elements are sulfur, selenium, tellurium, and polonium. In this section, we will survey the properties of the group as a whole and then examine the chemistry of sulfur, selenium, and tellurium. We will not discuss polonium, which has no stable isotopes and is found only in minute quantities in radium-containing minerals. 

We have already seen that the alkali metals do not all give usual or normal oxides when they react with excess oxygen. In a deficiency of oxygen, however, the oxides (containing O2-) are obtained. Peroxides accept protons from water to give H202  

Peroxides are also strong oxidizing agents. Moreover, the 022- ion is a base, so peroxides have the ability to react with acidic oxides. For example, CO and C02 react with Na202 as represented by the following equations  

Hydrogen peroxide is relatively unstable and decomposes to give water and oxygen as shown in the following equation  

H202 marketed in retail stores is used as a bleach and disinfectant. The structure of the H202 molecule can be shown as follows  

Many of these compounds that contain peroxide linkages are dangerous explosives, but they can be hydrolyzed to produce hydrogen peroxide. Finally, H2O2 can be prepared by the action of acids on Ba02  

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The relevant properties of peroxide and superoxide salts are given in Table 4 (see Peroxides and peroxide compounds, inorganic). Potassium peroxide is difficult to prepare and lithium superoxide is very unstable. The ozonides, MO3, of the alkah metals contain a very high percentage of oxygen, but are only stable below room temperature (see Ozone). 

Analytical Methods. Analysis of fresh and spent peroxides and superoxides is done by adding the material to water. Approximately 0.1 wt % permanganate is used in the water to decompose the peroxide ion which otherwise forms. The evolved oxygen is measured volumetricaHy. If the material is spent, the base strength is titrated to a phenolphthalein end point, acidified further, and the carbon dioxide is deterrnined volumetricaHy. 

Peroxides, superoxides, and chlorates are oxidising compounds and should not contact organic materials, eg, oil, greases, etc. This is especially tme while oxygen is being produced. Caustic residues that may remain after use of peroxides and superoxides require disposal appropriate to alkaH metal hydroxides. Spent candles containing barium may require special disposal considerations. 

Dusts associated with these oxidising compounds produce caustic irritation of skin, eyes, and nasal membranes. Appropriate protection should be worn when handling. Skin contact should be treated as for any caustic material, ie, flush with water and neutralize. Toxicity is low to moderate and is the same as for the hydroxides. Toxicity of the chlorate is greater than for the peroxides and superoxides, and the chlorate material also causes local irritation. 

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). 

Reduced flavoproteins and complex III may undergo side reactions directly with dioxygen, to a limited extent, forming highly reactive and toxic products, hydrogen peroxide, and superoxide. 

The same goes for peroxides and superoxides. Thus, tin powdered which was in contact with sodium peroxide in a carbon dioxide atmosphere in the presence of water traces glowed before combusting. With potassium superoxide there is an immediate incandescence of the mixture. 

The heart has a relatively low catalase activity, which, together with the superoxide dismutase (SOD) system, acts to remove hydrogen peroxide and superoxide radicals. In addition, in man, dietary vitamin C plays an important role in the reduction of vitamin E, an intrinsic antioxidant component of biological membranes (Chen and Thacker, 1986 Niki, 1987). Both vitamins C and E can also react directly with hydroxyl and superoxide radicals (HalliwcU and Gutteridge, 1989 Meister, 1992). 

Porras, A.G., Olson, J.S. and Palmer, G. (1981). The reaction of reduced xanthine oxidase with oxygen kinetics of peroxide and superoxide formation. J. Biol. Chem. 256, 9096-9103. 

Nonaka, A., Manabe, T., Tamura, K., Asano, N., Imanishi, K. and Tobe, T. (1989b). Changes of xanthine oxidase, lipid peroxide and superoxide dismutase in mouse acute pancreatitis. Digestion 43, 41-46. 

Sostaric et al. [67] also found that dissolution of CdS could be achieved through sonochemical reduction of the sulphur by hydroxyl radicals, hydrogen peroxide and superoxide ... 

The oxidation number of oxygen in its compounds is -2 except in peroxides (where it is -1), superoxides (where it is - ), or in OF2 and 02F2 (where it is positive). The peroxides and superoxides generally occur only with other elements in their maximum oxidation states. You will be able to recognize peroxides or superoxides by the presence of pairs of oxygen atoms and by the fact that if the compounds were normal oxides, the other element present would have too high an oxidation number (Sec. 13.3). 

Baranenko, V.V. (2001). Pea chloroplasts under clino-rotation lipid peroxidation and superoxide dismutase activity. Advances in Space Research 27 973-976. Bhowmik, P.C. and Inderjit (2003). Challenges and opportunities in implementing allelopathy for natural weed management. Crop Protection 22 661-671. 

Li and Mg form normal oxides, Li20 and MgO, when oxidized in air at 1 atm pressure, while the other members of Group 1A form peroxides and superoxides. 

To study the effects of iron overloading on inflammatory cells, Muntane et al. [186] investigated the effect of iron dcxtran administration on the acute and chronic phases of carrageenan-induced glanuloma. It was found that iron dcxtran increased the iron content in plasma and stores, and enhanced lipid peroxidation and superoxide production by inflammatory cells. At the same time, iron dcxtran had a beneficial effect on recovery from the anemia of inflammation. It has been suggested that iron overload may affect nitric oxide production in animals. For example, alveolar macrophages from iron-overloaded rats stimulated with LPS or interferon-7 diminished NO release compared to normal rats [187]. 

In addition to OH (aq), 02(g) is formed in the case of peroxide and superoxide. The resulting equations are balanced by inspection if one pays attention to charge balance. 

Hni HAO, Tew DG (1987) Dioxygen, Peroxide and Superoxide. In Wilkinson G, Gillard RD, McCleverty JA (eds) Comprehensive Coordination Chemistry, vol 2, chap 15.2. Pergamon Press, Oxford, p 315... 

The majority of the published electrochemical studies involving hydroxides have been conducted in the NaOH-KOH eutectic (49.0-51.0 mol%, mp = 170°C). This eutectic mixture can be used at temperatures considerably below those of the individual salts pure NaOH and KOH melt at 318 and 400°C, respectively. Water, oxygen, and carbon dioxide are the major impurities in molten hydroxides. The various procedures for removing these contaminants have been summarized [34]. Water can be eliminated by passing dry inert gas over the melt when it is heated to about 450 or 500°C heating the melt to these temperatures also leads to the thermal decomposition of peroxide and superoxide contaminants [34] ... 

It seems reasonable that the pathway for production of dioxygen would involve the formation of a bridged peroxide and superoxide. Oxidation could involve transient formation of Mn111. Various mechanisms have been put forward387 and reviewed.379,384... 

Binary oxygen-containing compounds can be classified on the basis of oxygen s oxidation state. Binary compounds with oxygen in the —2 oxidation state are called oxides, compounds with oxygen in the —1 oxidation state are peroxides, and compounds with oxygen in the —1/2 oxidation state are superoxides. We ll look first at oxides and then consider peroxides and superoxides in Section 14.10. 

Schmidt K. N., Amstad P., Cerutti P., and Baeuerle P. A. (1995). The roles of hydrogen peroxide and superoxide as messengers in the activation of transcription factor NF-kB. Chemistry Biology 2 13-22. 

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