Reactions of fluorinated benzenes with hydrated electrons and hydroxyl radicals in aqueous solutions

Abstract

Publication cost assisted by Hahn-Meitner-lnstitut fur KerntorschungThe reactions of fluorinated benzenes with hydrated electrons and hydroxyl radicals in aqueous solutions have been investigated by pulse radiolysis and 7-irradiation experiments. One fluoride ion per attacking eaq" is eliminated from the higher fluorinated compounds via a dissociative electron capture process.The yields of F_ ions are lower in the reaction of eaq~w ith mono-, o-di-, and p-difluorobenzene. The majority of electrons here interact with the aromatic ring, and the molecular anions thus formed are neutralized to yield fluorocyclohexadienyl radicals. The oxidation of fluorinated., benzenes by hydroxyl radicals occurs via addition of the OHto any of the six carbon atoms with alihost equal probability. If the attacked carbon atom carries a hydrogen atom a fluorohydroxycyclohexadienyl radical is produced. The addition to a carbon atom carrying a fluorine atom leads to the elimination of hydrogen fluoride. Rate constants have been determined for the reactions of the fluorinated benzenes with eaq-~a nd OHand for the reactions of transient species produced from these processes. Radicals and stable products have also been characterized by their optical absorption spectra. Mechanistic details of the reduction and oxidation reactions are discussed.

Investigation of the cross-reaction mechanism of C6H5F-HNO2 aqueous solution irradiated at 355 nm by transient absorbance spectrum technique

“…When the relationship of the C 6 H 5 F concentration with k obs was investigated, the second-order reaction rate constant for Rea1 could be determined to be k 1 = (5.83±0.17)×10 9 L·mol −1 ·s −1 , which is close to the value of 5.7×10 9 and 8.0×10 9 L·mol −1 · s −1 reported earlier by Köster [11] and Mohan [12] respectively using pulse radiolysis instrument to study the reaction of C 6 H 5 F with OH radical.…”

“…The transient absorbance spectrum of C 6 H 5 F···OH adduct was also obtained by Köster in the reaction investigation of C 6 H 5 F and OH radical employing pulse radiolysis technique [11] . In comparison to Figure 3a, the spectrum indicates the same absorption characteristics except for the absorption peak at 310 nm with a red shift and at 300 nm in the sample solution.…”

“…which had the absorption peaks at 270 and 300 nm. Mohan [12] and Köster [11] had separately reported that C 6 H 5 F···OH adduct was observed to decay by secondorder kinetics with the bimolecular rate constants of 1.1×10 9 and 9.0×10 8 L·mol −1 ·s −1 respectively when they investigated the reaction of C 6 H 5 F with OH radical by pulse radiolysis means. The concentration of OH radical is about (4-5)×10 −6 mol·L −1 in the sample solution.…”

“…Monofluorobenzene is one of the most valuable fluorinated organics due to its distinct physical and chemical properties showing in the wide range of industrial and commercial applications, involving the nitration, chlorination, bromination, alkylation, acylation and reduction reactions to form different kinds of medicines, pesticides, dyestuff, polymer fluoroplastic intermediations. Despite the reported reactions of C 6 H 5 F with OH free radical investigated by Köster [11] and Mohan [12] using pulse radiolysis instrument, the photochemical cross-reaction mechanism between C 6 H 5 F and HONO is not well known.…”

Decomposition of halophenols in room-temperature ionic liquids by ionizing radiation

“…The reaction rates of halogenated organic compounds (HOCs) with the solvated electrons are generally fast in water, and their reaction mechanisms have been investigated in many previous studies (Arbon and Mincher, 1996;Koster and Asmus, 1973;Solar, 1986, 1988;Glowa and Mezyk, 1998;Mohan et al, 1992;Winarno and Getoff, 2002;Zona et al, 1999). HOCs, therefore, are good probes to study reactions involving solvated electrons in RTILs.…”