71815-46-8Relevant articles and documents
Radical-mediated degradation mechanisms of tribromo- and other trihalogenated acetic acids in oxygen-free solutions as studied by radiation chemistry methods
Fliount, Roman,Makogon, Oksana,Guldi, Dirk M.,Asmus, Klaus-Dieter
, p. 1535 - 1545 (2007/10/03)
.CBr2CO2- and .CCl2CO2- radicals, generated upon one electron reduction of tribromo- and trichloroacetic acids and .CF2CO2- radicals produced from difluoroacetic acid by reaction with .OH, exhibit optical absorptions in the UV with λmax at 290 nm (ε = 2580 dm3 mol-1 cim-1), 330 nm (ε = 3000 dm3 mol-1 cm-1) and 310 nm (ε ≈ 660 dm3 mol-1 cm-1), respectively. Mechanistically, the present report focuses on the free-radical-induced degradation of tribromoacetic acid. Absolute rate constants have been determined for the reactions of CBr3CO2- with eaq-, H., CO2. , .CH2OH, CH3.CHOH, (CH3)2.COH and .CH3 radicals to be k = 1.8 × 1010, 1.5 × 1010, 2.8 × 109, 1.6 × 109, 2.3 × 109, 3.0 × 109 and 3.0 × 107 dm3 mol-1 s-1, respectively. The major fate of .CBr2CO2- is self-termination to yield tetrabromosuccinic acid which, however, is unstable and thermally decomposes to HBr, CO2 and tribromoacrylic acid. Dibromofumaric acid, dibromomaleic acid and carbon monoxide were found as minor secondary products, formation of which is explained by a small yield of reductive decomposition of the transient tetrabromosuccinic acid. A complete and mechanistically satisfying material balance is provided for several systems in which CBr3CO2- has been degraded via a variety of radicals under various conditions. .OH Radicals do not react directly with CBr3CO2-. They have been shown, however, to contribute indirectly to the degradation of this acid via their reaction with reductively liberated bromide ions. The Br. atoms formed in this process are considered to abstract a bromine atom from CBr3CO2- or oxidize the carboxyl function in a one-electron transfer process. The formation of free Br. atoms has been recognized by pulse radiolysis through their conjugate dimer radical anions Br2.-. With respect to the other trihalogenated acids it is noteworthy that CCl3CO2- is efficiently reduced by CO2.- radicals and that CF3CO2- exhibits a high stability toward γ-irradiation and practically resists any reductive attack.
