Carbon dioxide radical cation

The carbon dioxide anion-radical was used for one-electron reductions of nitrobenzene diazo-nium cations, nitrobenzene itself, quinones, aliphatic nitro compounds, acetaldehyde, acetone and other carbonyl compounds, maleimide, riboflavin, and certain dyes (Morkovnik and Okhlobystin 1979). The double bonds in maleate and fumarate are reduced by CO2. The reduced products, on being protonated, give rise to succinate (Schutz and Meyerstein 2006). The carbon dioxide anion-radical reduces organic complexes of Co and Ru into appropriate complexes of the metals(II) (Morkovnik and Okhlobystin 1979). In particular, after the electron transfer from this anion radical to the pentammino-p-nitrobenzoato-cobalt(III) complex, the Co(III) complex with thep-nitrophenyl anion-radical fragment is initially formed. The intermediate complex transforms into the final Co(II) complex with the p-nitrobenzoate ligand. 

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). 

Mechanisms depending on carbanionic propagating centers for these polymerizations are indicated by various pieces of evidence (1) the nature of the catalysts which are effective, (2) the intense colors that often develop during polymerization, (3) the prompt cessation of sodium-catalyzed polymerization upon the introduction of carbon dioxide and the failure of -butylcatechol to cause inhibition, (4) the conversion of triphenylmethane to triphenylmethylsodium in the zone of polymerization of isoprene under the influence of metallic sodium, (5) the structures of the diene polymers obtained (see Chap. VI), which differ. both from the radical and the cationic polymers, and (6)... 

As evident from Scheme 4.9, one-electron oxidation of 1,4-dimethoxybenzene produces cation-radical. The cation-radical, being more active than the initial substrate, recombines with benzoyloxy radical before the latter decomposes into phenyl radical and carbon dioxide. The process ends in the formation of a stable substitution product. 

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. 

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... 

Manganese(III) has been employed for the oxidation of aldoses, and a general mechanism for the oxidation has been proposed.167 The oxidation of hexoses, pentoses, hexitols, and pentitols by Mn(III), as well as by other cations, was proposed to proceed via a free-radical mechanism,168 as shown in Scheme 26. Oxidation of alditols produces the corresponding aldoses, which are further oxidized in the presence of an excess of oxidant to the lower monosaccharides and thence to formaldehyde, formic acid, and even carbon dioxide. The kinetics for the oxidation of aldoses and ketoses by Mn(III) in sulfuric acid medium have been reported.169... 

Bonifadc 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 zmons. J Phys Chem A 104 1240-1245. 

The reduction of carbon dioxide to formate in the presence of FDH represents a photochemical C02-fixation process. In addition to MV+, the enzyme recognizes other electron carriers such as 2,2 -bipyridinium radical cations [184]. Reduction of nitrate (N03 ) to nitrite (NO2 ) and subsequently the reduction of nitrite to ammonia in the presence of NitraR and NitriR, respectively, allows the sequential 8e ... 

The a-exomethylene-y-lactone framework has been successfully constructed via two electrosynthetic pathways, that is, both by the direct and by the concerted decarboxylation processes as mentioned earlier [Eq. (45)] [151]. The electrodecarboxylation of XCa is probably initiated by a one-electron oxidation of the sulfur atom, giving first the cation radical (XCb) and subsequently a concerted elimination of the thiyl radical and carbon dioxide to LXXXIX. On the other hand, the electrochemical decarboxylation of LXXXVIIIa involves an El-type elimination of a proton from the cation intermediate (LXXXVIIIb) generated from direct two-electron oxidation of the carboxyl group. The latter method generally requires a higher oxidation potential than that required for the concerted method. Therefore, the concerted electrodecarboxylation method becomes more advantageous, especially when the substrates or products are unstable under oxidative conditions. 

In a preliminary study (284) on the photolysis of the t-butyl methyl ether-02 CT-complex some products have been identified and their quantum yields determined. They are peroxidic compounds (4i = 0.15), t-butyl formate (cj) = 0.21), t-butanol ((j> = 0.035), 2-methoxy-2-methylpropionaldehyde ( = 0.03), formaldehyde ((j> = 0.04), water (iji = 0.3), and carbon dioxide (cj) = 0.007). It was noted (284) that deprotonation of the t-butyl methyl ether radical cation, although it largely occurs at the methyl group next to the oxygen (product, t-butyl formate), is also possible at the 8-posltlon (product, 2-methoxy-2-methylpropionaldehyde). 

Danforth and Dix [75] compared the behaviours of both zinc and magnesiimi (see below) oxalates. Kinetic measurements were made by independent determinations of the yields of carbon monoxide and of carbon dioxide at appropriate reaction times. The kinetics of reaction of the zinc salt were fitted by the Prout-Tompkins equation (620 to 645 K) and i , = 196 kJ mol. The activation step was identified as the formation of the radical ion 204, following the transfer of an electron to a cation. The decomposition of this activated species was then accelerated by the product zinc oxide. The term accelerated rather than catalysed was preferred because the magnitude of was not decreased by the presence of the oxide product. 

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