Reactions of Superoxide Ions

Superoxide salts like potassium and sodium superoxide are virtually insoluble in nonpolar media, and although they are somewhat more soluble in hydroxylic media, they are not stable in these solvents [1]. Potassium superoxide is only sparingly soluble in the dipolar aprotic solvent DMSO [2]. As a result of these solubility problems and the inaccessibility of electrochemically generated superoxide [3] in most laboratories, the chemistry of this potentially interesting nucleophile was little studied until recently. 

It has been shown in the past few years that 18-crown-6 and dicyclohexyl-18-crown-6 will complex and solubilize potassium superoxide in such solvents as di-methylsulfoxide, benzene, tetrahydrofuran, dimethylformamide, dimethoxyethane, and even diethyl ether [4]. The interest in the biological role of superoxide and its ready availability in solution has made it the focus of considerable recent attention, some of which is recorded in this chapter. 

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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. 

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). 

Anderson, R. F. Flavin-oxygen complex formed on the reaction of superoxide ions with flavo-semiquinone radicals. In Flavins and flavoproteins (Massey, V., Williams, C. H. eds.) pp. 278-283, New York, Elsevier North Holland 1982... 

The reaction continuum for HO can be subdivided into three discrete categories that are outlined in Scheme 14 (a) displacement reactions in which the leaving group departs with an electron supplied by HO (polar-group transfer), (b) addition reactions in which a covalent bond is formed (polar-group addition), and (c) simple electron-transfer reactions in which HO acts as an electron donor (single-electron transfer). This view of the chemistry of HO also applies to the reactions of superoxide ion (O2 ) and other nucleophilic oxyanions (Table 16). 

The reaction of superoxide ion (02 )> radical anion, with water also can be viewed as a polar-group transfer reaction (equation 168). The product HOO- is a radical that reacts btmolecularly to form hydrogen peroxide and dioxygen (equation 169). 

Moro-Oka YC, Pyoimg J, Arakawa H, Ikawa T. Chemistry of superoxide ion. Reaction of superoxide ion with substrates having labile hydrogens. Chem Lett 1976 11 1293-1296. 

Scheme 5. Electrochemically detectaUe reactions of superoxide ion in the first steps of silanone formation. The bimolecular reaction with k is rate determining.

R. F. Anderson, Flavin-Oxygen Complex Formed on the Reaction of Superoxide Ions with Flavosemiquinone Radicals. In Flavins and Fiavoproteins) V. Massey, C. H. Williams, Eds. Elsevier North-Holland New York, 1982 pp 278-283. 

The reaction of superoxide ion with alkyl halides produces a radical in the primary step, because the spin angular... 

Danen, W. C., and R. J. Warner The Remarkable Nucleophlicity of Superoxide Anion Radical. Rate Constants for Reaction of Superoxide Ion with Aliphatic Bromides. Tetrahedron Letts 1977, 989. 

Oxidation is a reaction which can obviously assume many appearances. The conversion of an alcohol to a ketone or an aldehyde to an acid is unquestionably an oxidation, but the conversion of a primary amine to a nitrile or a bromide to an alcohol is just as much an oxidation process although it may be less obviously so. Included in this chapter are a wide variety of substrates and oxidizing reagents. A notable exception is the superoxide ion which can effect both displacement and oxidation. The reactions of superoxide ion in two-phase systems are treated separately in Chap. 8. 

Formation of superoxide ion attached to iron is probable when iron is in the ferrous state or has a ferrous character. Thus, reactivity of superoxide ion has attracted attention in the mechanistic studies of the enzymatic reactions. Reaction of superoxide ion was studied in some details by Moro-oka and Foote in 1976 [13]. Both types of intra- and extra-diol oxygenation products are formed from 1 as shown in Scheme 3. Products 5 and 13-15 are also formed. Since the same products are formed also from the quinone 6, the common intermediate is assumed for both the reactions of catechol and quinone. The product formation is explained by the O2 attack to the activated catecholate anion radical forming a peroxide ion. The initial step forming a radical species is similar to that in... 

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