Carbon Dioxide Anion-Radical

Subsequent studies (63,64) suggested that the nature of the chemical activation process was a one-electron oxidation of the fluorescer by (27) followed by decomposition of the dioxetanedione radical anion to a carbon dioxide radical anion. Back electron transfer to the radical cation of the fluorescer produced the excited state which emitted the luminescence characteristic of the fluorescent state of the emitter. The chemical activation mechanism was patterned after the CIEEL mechanism proposed for dioxetanones and dioxetanes discussed earher (65). Additional support for the CIEEL mechanism, was furnished by demonstration (66) that a linear correlation existed between the singlet excitation energy of the fluorescer and the chemiluminescence intensity which had been shown earher with dimethyl dioxetanone (67). 

The authors propose that an initial abstraction of a hydrogen atom produces a complex containing bound carbon dioxide radical-anion. This complex could break down in two ways... 

Janzen EG, Towner RA, Brauer M. 1988. Factors influencing the formation of the carbon dioxide radical anion (CO2-) spin adduct of PBN in the rat liver metabolism of halocarbons. Free Radic Res Common 4 35-369. 

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... 

V3. Vasquez-Vivar, J., Denicola, A., Radi, R., and Augusto, O., Peroxynitrite-mediated decarboxylation of pyruvate to both carbon dioxide and carbon dioxide radical anion. Chem. Res. Toxicol. 10, 786-794 (1997). 

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 ... 

H atom, carbon dioxide radical anion and even HO2 and have low molar absorptivities and absorption bands in the region where the protein itself has a large absorbance, making optical detection a challenge. Competition kinetics has proven very useful, using a competitor with a well-defined chromophore. Both direct observation and competition kinetics have been used with great success to understand the chemistry that ensues upon radiolysis of proteins in water. 

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). 

In the example shown in Eig. 2.11 [29] the paramagnetic species is the carbon dioxide radical anion, CO2, in an X-irradiated lithium formate crystal. ENDOR lines from several Li nuclei (/ = 3/2) at different lattice positions occur. The principal values and directions of the hyperfine coupling tensors provide a means to obtain the geometric arrangement of the ions about CO2. The analysis is based on the point dipolar approximation, in which the maximum value, bmax, in MHz of the dipolar coupling is given by... 

Approximate axial g-tensors are frequently observed for transition metal ion complexes. Inorganic radicals can also have appreciable axial g-anisotropy. This property is of value for the assignment of ESR powder spectra in applied studies. Carbon dioxide radical anions, CO2, and related species contribute for instance to the ESR signal used for geological dating [21] see Chapter 9. The ESR spectrum of this anion has also been employed as an indicator that a certain foodstuff has been irradiated, for dosimetric purposes in certain carboxylic acid salts, and as a component in tooth enamel samples used in retrospective dosimetry. 

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

KEYWORDS carbon dioxide radical anion vacuum ultraviolet irradiation electron transfer radical addition phenol toluene benzene chlorobenzene benzaldehyde benzoic acid... 

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. 

Radiolytic production of 02 is achieved in oxygen saturated aqueous solutions containing formate. Of the primary radicals produced upon water radiolysis, both the hydrated electron and the hydrogen atom react rapidly with oxygen to produce 02. The hydroxyl radicals (and the hydrogen atom) react with the formate to produce the carbon dioxide radical anion and this radical anion reacts with oxygen generating further 0 [46],... 

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... 

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