Superoxide reaction with carbonate

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). 

Cesium reacts with water in ways similar to potassium and rubidium metals. In addition to hydrogen, it forms what is known as superoxides, which are identified with the general formula CsO When these superoxides react with carbon dioxide, they release oxygen gas, which makes this reaction useful for self-contained breathing devices used by firemen and others exposed to toxic environments. 

AH the peroxides are colorless and diamagnetic when pure. Traces of the superoxide in technical-grade sodium peroxide impart a yellow color. Storage containers must be sealed to prevent reaction with atmospheric carbon dioxide and water vapor. 

Some moisture must be present to promote these reactions. Dry carbon dioxide does not react with the superoxides. One mole of MO2 yields 1.5 mol oxygen and then absorbs one mole of carbon dioxide to form carbonate, or two moles to form bicarbonate. Thus, if only carbonate is formed, an RQ of 0.67 is reached if only bicarbonate is formed, an RQ of 1.33 results. The required stoichiometry for an RQ of 0.82 is. 

In this type of spin traps, 5,5-dimethyl-l-pyrroline-Af-oxide (DMPO) deserves particular mention. DMPO is widely employed as a spin trap in the detection of transient radicals or ion-radicals in chemical and biological systems (see, e.g., Siraki et al. 2007). Characteristic ESR spectra arising from the formation of spin adducts are used for identification of specific spin species. In common opinion, such identification is unambiguous. However, in reactions with superoxide ion (Villamena et al. 2004, 2007b), carbon dioxide anion-radical (Villamena et al. 2006), or carbonate anion-radical (Villamena et al. 2007a), this spin trap gives rise to two adducts. Let us consider the case of carbonate anion-radical. The first trapped product arises from direct addition of carbonate anion-radical, second adduct arises from partial decarboxylation of the first one. Scheme 4.25 illustrates such reactions based on the example of carbonate anion-radical. 

Reaction of carbon tetrachloride with superoxide in vitro reaction rates, products formed role in toxi ci ty. 

Guanine is the most easily oxidizable natural nucleic acid base [8] and many oxidants can selectively oxidize guanine in DNA [95]. Here, we focus on the site-selective oxidation of guanine by the carbonate radical anion, COs , one of the important emerging free radicals in biological systems [96]. The mechanism of COs generation in vivo can involve one-electron oxidation of HCOs at the active site of copper-zinc superoxide dismutase [97, 98], and homolysis of the nitrosoperoxycarbonate anion (0N00C02 ) formed by the reaction of peroxynitrite with carbon dioxide [99-102]. 

The reaction of alkyl isothiocyanates, RNCS, with diphenylphosphinic hydrazide (338) in benzene has been reported.308 The bis(diethylamino)[(methylthio)thiocarbon-yl]carbenium salts (339 X = I or BF4) display ambident reactivity and can react either at carbenium carbon (hard nucleophiles) or at the thiocarbonyl sulfur atom (soft nucleophiles).309 Electrochemically generated superoxide reacts with dithioic S,S -diesters (dicarbothiolates) (340 Ar = C5H3N or C6H4) to give the monocarboxylate anions in 100% yield before giving the dicarboxylate anions.310... 

Fig. 3 Formation of peroxynitrite from nitric oxide and superoxide anion and reaction products with carbon dioxide...

Another plausible route for the creation of a reactive radical might be the carbonic anhydrase catalyzed addition of superoxide ion to carbon dioxide (Eq. 37). An enzymatic reaction is consistent with the variable response of different individuals to paraquat exposure. There are at least two common genetic variants of carbonic anhydrase, and additional variation can occur through posttranslational modification of the protein... 

Combination of superoxide ion with the cation radical (MV+0 of methyl viologen (l,T-dimethyl-4,4 -bipyridinium ion, Paraqnat) is one of the best-documented examples of a stoichiometric 02 - radical coupling reaction. The initial addition to give an unstable diamagnetic product is assumed to be at a-carbon atoms (which possess the maximum unpaired spin density in the cation radical), followed by formation of a dioxetane-like intermediate that decomposes to a complex mixture of products (Scheme 13). This process may provide a means to explain the mechanism of Paraquat toxicity. Several other reports have proposed direct coupling of 02 - to cation radicals. ... 

The superoxides release oxygen gas in reactions with water or carbon dioxide ... 

The reactions of CCI4 with HO" and Oi"- are complex multistep reactions and the nature of the primary step is not well understood. The initial reaction is followed by even faster secondary reactions that ultimately result in the almost complete oxygenation of the carbon and the release of the chlorine as chloride ion. The overall reaction for superoxide ion with CCI4 (followed by dilution with water),... 

Gas masks used by firefighters often contain potassium superoxide, KO2. KO2 reacts with carbon dioxide and water in exhaled breath to produce oxygen by the following reaction ... 

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