Reactions of carbon dioxide radical anion with substituted benzenes

Abstract

We report mechanistic studies on the reactivity of CO 2 .À radicals towards substituted benzenes, XPh, with X = NO 2 , COOH, COH, CH 3 , H, Cl and HO. Vacuum ultraviolet (VUV, 172 nm) irradiation of aqueous solutions containing formate was used as a method of CO 2 .À radical generation for the study of the reaction products, which were determined by gas chromatography-mass spectrometry and high-performance liquid chromatography. The nature of some of the reaction intermediates was studied by laser flash photolysis of aqueous solutions of peroxodisulfate in the presence of formate. The observed products and intermediates of reaction are discussed and rationalized by a dual reactivity of the CO 2 .À radical anion with substituted benzenes: a one-electron reduction and radical addition to the aromatic ring. For substituted benzenes with X = NO 2 , COOH and COH, the observed products support an electron transfer from CO 2 .À to the substrates as the primary reaction channel, while the reactions with toluene follow the channel of radical addition. Benzene and chlorobenzene react with CO 2 .À by both routes, electron transfer and radical addition. Our experimental results indicate that H abstraction by the CO 2 .À radical is negligible under the chosen experimental conditions.

Alloxan-dialuric acid cycling: A complex redox mechanism

“…Peroxodisulphate photolysis in Ar-saturated solutions containing formate yields CO 2 + ( radical anions, reaction R4 [15], which were reported to reduce A.H 2 O to AH + radicals, R12 [11,17]. In the presence of molecular oxygen, CO 2 + ( efficiently reacts with O 2 to yield superoxide radical anions, O 2 + ( , R6, which are also reported to reduce A.H 2 O to AH + radicals, R13a [18].…”

“…These radicals efficiently react with formate ions to yield carbon dioxide radical anions (CO 2 + ( ), which in the presence of molecular oxygen are quantitatively converted into O 2 + ( [15].…”

Benzene depletion by Fe2+-catalyzed sodium percarbonate in aqueous solution

“…It has been documented that the carbonate radical (CO 2 ÅÀ ) can be generated from HCO 4 À [30]. In addition, it has been reported that CO 2 ÅÀ can degrade benzene by both addition and H-abstraction mechanisms [31]. Hence, we speculate that a large number of other active species (such as HCO 4 À and CO 2 ÅÀ ) make the contribution of the apparent expediting effect when the HCO 3 À concentration is increased from 10 to 100 mM.…”

The chemical effects of CO2 addition to methane on aromatic chemistry

“…In spite of all our efforts, we could not find any studies considering the effects of CO 2 -addition to benzene during the combustion of the latter. Rosso et al [71] investigated the reaction of carbon dioxide radical anion with substituted benzenes in aqueous solutions. There does not appear to be any direct connections between their results and our main concerns in this article.…”