Carbon dioxide radical anion, reactions

Bonifacic M, Schafer K, Mockel H, Asmus K-D (1975b) Primary steps in the reactions of organic disulfides with hydroxyl radicals in aqueous solution. J Phys Chem 79 1496-1502 Bonifacic M, Armstrong DA, Carmichael I, Asmus K-D (2000a) p-Fragmentation and other reactions involving aminyl radicals from amino acids. J Phys Chem B 104 643-649 Bonifacic M, Hug GL, Schoneich C (2000b) Kinetics of the reactions between sulfide radical cation complexes,[S.. S]+ and [S. N]+, and superoxide or carbon dioxide radical anions. J Phys Chem A 104 1240-1245... 

Triorganyl-sulfonium, -selenonium and -telluronium salts are reduced by carbon dioxide radical anions/solvated electrons produced in aqueous solution by radiolysis. The radical expulsion accompanying reduction occurred with the expected leaving group propensities, i.e. benzyl > secondary alkyl > primary alkyl > methyl > phenyl. Much higher product yields in the reduction of selenonium and telluronium compounds have been accounted for in terms of a chain reaction with carbon-centred radicals, with formate serving as the chain transfer agent.282... 

The oxalyl radical anion decomposes to a carbon dioxide radical anion and to carbon dioxide according to Eq. 5-14. Again, the CO radical anion is able to reduce ferrioxalate with formation of ferrous ions (Eq. 5-15). The correct reaction stoichiometry of the photolysis of ferrioxalate in aqueous solution is given by Eq. 5-16 (Hislop and Bolton, 1999). 

Radiat. Phys. Chem. 11 225, cited in Rosso 1 A, Bertolotti S G, Braun A M, Martire D O, Gonzalez M C (2001) Reactions of Carbon Dioxide Radical Anion with Substituted Benzenes, I. Phys. Org. Chem. 14 ... 

Early workers [103] detected benzilic acid formed during the reduction of benzophenone in dimethylformamide in the presence of carbon dioxide. The carbon dioxide radical anion system is known to have E" = —2.2V (vs. SCE) [104] and will thus not be formed in preference to the ketone radical anion. Reaction occurs through trapping of aromatic carbonyl radical anions by carbon dioxide, and this has been developed into a convenient synthesis of aryllactic acids. The modern technological process uses constant current conditions. On a small scale, a divided cell with mercury cathode has been used to obtain benzilic acids from substituted benzophenones and carbon dioxide in 70-90% yields [105] and to convert 4-isopropylacetophenone to the corresponding phenyllactic acid in 85% yield [106]. On a technical scale, these reactions are best carried out in an undivided cell using a lead cathode and a sacrificial aluminum anode with dimethylformamide as solvent... 

Bonifacic M., Hug G.L., Schoeneich C., Kinetics of the reaction between sulfide raducal cation complexes [SS]-i- and [SN]-i- and superoxide or carbon dioxide radical anion, J. Phys. Chem. A, 2000,104,1240-1245. 

The superoxide radical and its conjugate acid, the hydroperoxyl radical, rapidly equilibrate with PK45 = 4.9, The hydroxyl radical center is transferred to a superoxide radical in a two-step process HO abstracts a hydrogen atom from the formate ion, producing the carbon dioxide radical anion, which then transfers an electron to oxygen (reactions 46 and 47). 

Reactions of carbon dioxide radical anion with substituted benzenes... 

Carbon dioxide radical anions, C02 , are commonly used in aqueous chemistry as a reducing agent for metalloporphyrins or as intermediate in the formation of superoxide anion. COf has been reported to undergo efficient electron transfer reactions with methyl violo-gen, quinones, alkyl halides, fumarates, nitro and nitrosobenzenes and chlorinated benzaldehydes. With nitrobenzenes and chlorinated benzaldehydes, electron attachment occurs on the nitro and aldehyde groups, respectively. CO2 radicals have also been reported to add to some unsaturated compounds such as acrylamide and pyridin-3-ol. Efficient hydrogen abstraction from mercaptobenzenes have also been reported. 

Bonifacio M, Hug GL, Schoneich C (2000) Kinetics of the reactions between sulfide radical cation complexes, [S.. .. S]" and [S.. N], and superoxide or carbon dioxide radical anions. J Phys Chem A 104 1240-1245... 

Upon reaction of (1010) with Nil2, trinuclear [Ni3(/r3-I)2(dppm)3] (1012) is formed. The latter can also be obtained directly from [Ni(cod)2], Nil2 and dppm. (1012) photoreduces carbon dioxide to its radical anion, which can be trapped by cyclohexene.2455... 

Dietz and Peover examined the electrochemical reduction of cis and trans stilbene (114) in DMF containing carbon dioxide, 9>. The first electron transfer to trans-114 affords a planar radical anion (115) which then undergoes rapid reaction with carbon dioxide to produce, ultimately, 2,3-diphenylsuc-cinic acid (116) in... 

Carbon dioxide, CO2, is a typical component of the gaseous environment for reactions in air or in the presence of air traces. Therefore, both interactions between CO2 and organic ion-radicals as well as reactions of 62 with uncharged molecules of organic compounds should be considered. Interaction of CO2 with organic anion-radicals leads, as a rule, to carboxylic acids COj" anion-radicals are not formed. Even such a one-electron reductant as the superoxide ion (in aprotic medium) simply adds to carbon dioxide CO2 + O2 -> 00-C02. The additional product accepts an electron ... 

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. 

For anion-radicals, air (i.e., oxygen, carbon dioxide, and water [moisture]), on the whole, is an active component of the medium and so it should be removed before conducting reactions. Understandably, air inhibits anion-radical reactions The anion-radicals primarily formed are consumed at the expense of oxidation, carboxylation, and protonation. Certainly, oxidation can take place only if the acceptor organic molecule possesses a lower affinity for an electron than oxygen does or if one-electron oxidation of the anion-radical by oxygen proceeds more rapidly than the anion-radical decomposition into a radical and an anion (RX R + X ). 

The radical-anions from from alkenes with electron withdrawing substituents will add to carbon dioxide [28]. This process involves the alkene radical-anion, which transfers an electron to carbon dioxide for which E° = -2.21 V vs. see [29]. Further reaction then occurs by combination of carbon dioxide and alkene radcal-anions [30]. The carbanion centre formed in this union may either be protonated or react with another molecule of carbon dioxide. If there is a suitable Michael acceptor group present, this carbanion undergoes an intramolecular addition reaction... 

Aromatic radical-anions will react with carbon dioxide. The redox process for carbon dioxide has E° = -2.2 V vr. see [108], so the high yield reactions with the... 

The reaction involves the transfer of an electron from the alkali metal to naphthalene. The radical nature of the anion-radical has been established from electron spin resonance spectroscopy and the carbanion nature by their reaction with carbon dioxide to form the carboxylic acid derivative. The equilibrium in Eq. 5-65 depends on the electron affinity of the hydrocarbon and the donor properties of the solvent. Biphenyl is less useful than naphthalene since its equilibrium is far less toward the anion-radical than for naphthalene. Anthracene is also less useful even though it easily forms the anion-radical. The anthracene anion-radical is too stable to initiate polymerization. Polar solvents are needed to stabilize the anion-radical, primarily via solvation of the cation. Sodium naphthalene is formed quantitatively in tetrahy-drofuran (THF), but dilution with hydrocarbons results in precipitation of sodium and regeneration of naphthalene. For the less electropositive alkaline-earth metals, an even more polar solent than THF [e.g., hexamethylphosphoramide (HMPA)] is needed. 

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]. 

---