Reactivity of superoxide ion

Rate constants for superoxide ion (02 ) and its conjugate acid HOz as oxidant, reductant, and nucleophile have been measured in several solvents (Hendry and Schuetzle, 1976 Sawyer et al., 1978 Bielski et al., 1985), but few SARs have been developed. Moreover, the reactivity of superoxide ion generally is too low for the oxidant to be important in surface waters. Solvated electrons (e Aq) also form on insolation of DOM (Fischer et. al., 1985 Zepp et. al., 1988), but its concentration is very low, and target compounds are too few to make e (Aq) an important redox agent in surface waters (Buxton et al., 1988). One possible exception is nitroaromatics such as 2,4,6-trinitrotoluene (TNT), which exhibit strong acceleration of photolysis rates in the presence of DOM (Mabey et al., 1983). 

Merritt MV, Sawyer DT (1970) Electrochemical studies of the reactivity of superoxide ion with several alkyl halides in dimethyl sulfoxide. J Org Chem 35(7) 2157-2159... 

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... 

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. 

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). 

Table 2 The reactivity of complexes [M(triphos)(catecholate)J+ (M=Co, Rh, Ir) with molecular oxygen as a function of the catecholate/ semiquinone oxidation potential. I=no reactivity 11= the oxygenated complex regenerates the initial complex in the quinone form by release of superoxide ion III = the oxygenated complex regenerates the initial complex in the quinone form by release of molecular oxygen...

The reaction products of superoxide ions are believed to be partly responsible for the removal and destruction of bacteria and damaged cells [1]. In view of its low reactivity it is unlikely that superoxide itself is responsible for killing the invading material, but the hydrogen peroxide formed from dismutation by superoxide dismutase can kill some strains of bacteria. Once the phagocytic... 

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... 

The preceding section describes the primary reaction chemistry of superoxide ion (02 -) to be that of (a) a Bronsted base (proton transfer from substrate), (b) a nucleophile (via displacement or addition), (c) a one-electron reductant, and (d) a dehydrogenase of secondary amine groups. The chemistry is characteristic of all oxyanions (H0 (R0 ), HOO (ROO ), and 02 -)> but the relative reactivity for each is determined by its pXa and one-electron oxidation potential, which are strongly affected by the anionic solvation energy of the solvent matrix. The present focus is on the reactivity of hydroxide ion (HO ), but the principles apply to all oxyanions and permit assessments of their relative reactivity. 

The apparent nonreactivity of frflMs-l,2-dichloroethene (and of Dieldrin and Aldrin) is not immediately explained by this mechanism in view of the facile reactivity of cis-l,2-dichloroethene. Steric effects may account for the differential reactivities of cis- and trfl s-l,2-dichloroethene addition of superoxide ion would be expected to relieve steric strain between the two chlorines in the cis isomer. However, this reactivity pattern also is consistent with base-catalyzed elimination reactions of these systems.32... 

A. Mechanism. Alkyl halides undoubtedly represent the most well-tested functional group for nucleophilic reactivity. That superoxide ion reacts with alkyl haldies by an S 2 mechanism has been demonstrated. Dietz, et al., (J) y observed a relative reactivity which fell in the series n-BuBr > sec-BuBr > -BuBr > jt-BuBr for variation of alkyl group structure and in the series n -BuBr > n-BuOTs > n-BuCl for variation of leaving group. The former order is consistent with a Sj 2 reaction mechanism and the latter order suggests that superoxide anion radical is a strong nucleophile. 

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