- Decomposition of tetrachloro-1,4-benzoquinone (p-Chloranil) in aqueous solution
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p-Chloranil (2,3,5,6-tetrachloro-2,5-cyclohexadiene-1,4-dione; tetrachloro-1,4-benzoquinone) has been observed as an oxidation product in processes used to oxidize pentachlorophenol (PCP), has known biocidal properties, and has been implicated in genotoxic effects associated with PCP. Chloranil undergoes displacement of chloride by hydroxide under highly alkaline conditions, but no previous work on chloranil decomposition has been conducted at environmentally relevant pH. Electrospray mass spectrometry was used in this study to confirm the two-step hydrolysis of chloranil to yield chloranilic acid (2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone), and the kinetics of each step were quantified as a function of pH. The half-life of chloranil at pH 7 is estimated to be slightly over 1 h, while that of its first hydrolysis product (trichlorohydroxyquinone) is about 21 d, Chloranil also reacts with hydrogen peroxide in a pH-dependent manner at rates substantially greater than the rate of spontaneous hydrolysis. The low yield of chloranilic acid from this reaction suggests that other, as yet unidentified, products are formed. Chloranilic acid has lower acute toxicity (BS measured in the Microtox screening assay) than does chloranil, so that promoting the accelerated hydrolysis of chloranil may be advantageous in waste treatment or remediation processes in which it is formed.
- Sarr,Kazunga,Charles,Pavlovich,Aitken
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- Analytical and toxicity characterization of halo-hydroxyl-benzoquinones as stable halobenzoquinone disinfection byproducts in treated water
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Exposure to chlorination disinfection byproducts (DBPs) is potentially associated with an increased risk of bladder cancer. Four halobenzoquinones (HBQs) have been detected in treated drinking water and have shown potency in producing reactive oxygen species and inducing damage to cellular DNA and proteins. These HBQs are unstable in drinking water. The fate and behavior of these HBQs in drinking water distribution systems is unclear. Here we report the high-resolution mass spectrometry identification of the transformation products of HBQs as halo-hydroxyl-benzoquinones (OH-HBQs) in water under realistic conditions. To further examine the kinetics of transformation, we developed a solid-phase extraction with ultrahigh-performance liquid chromatography tandem mass spectrometry (SPE-UHPLC-MS/MS) method to determine both the HBQs and OH-HBQs. The method provides reproducible retention times (SD 50 of HBQs and OH-HBQs ranging from 15.9 to 72.9 μM. While HBQs are 2-fold more toxic than OH-HBQs, both HBQs and OH-HBQs are substantially more toxic than the regulated DBPs.
- Wang, Wei,Qian, Yichao,Li, Jinhua,Moe, Birget,Huang, Rongfu,Zhang, Hongquan,Hrudey, Steve E.,Li, Xing-Fang
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p. 4982 - 4988
(2014/06/09)
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- The reaction of the OH radical with pentafluoro-, pentachloro-, pentabromo- and 2,4,6-triiodophenol in water: Electron transfer vs. addition to the ring
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The OH-radical-induced dehalogenation of pentafluorophenol (F5C6OH), pentachlorophenol (Cl5C6OH), pentabromophenol (Br5C6OH) and 2,4,6-triiodophenol (I3H2C6OH) in water has been studied by pulse radiolysis in basic solution where these compounds are deprotonated and hence slightly water soluble. Hydroxyl radicals react with these phenolates both by electron transfer and by addition. Electron transfer yields hydroxide ions and the corresponding phenoxyl radicals (X5C6O and I3H2C6O); these were also generated independently, to the exclusion of OH-adduct radicals, by reacting the phenolates with N3 radicals [k(N3 + F5C6O-) = 4.9 × 109 dm3 mol-1 s-1, λmax(F5C6O) = 395 nm; k(N3 + Cl5C6O-) = 5.7 × 109 dm3 mol-1 s-1, λmax(Cl5C6O) = 452 nm; k(N3 + Br5C6O-) = 6.5 × 109 dm3 mol-1 s-1, λmax(Br5C6O) = 476 nm; k(N3 + I3H2C6O-) = 5.6 × 109 dm3 mol-1 s-1, λmax(I3H2C6O) = 540 nm]. Hydroxyl radical addition to the pentahalophenolates is followed by rapid halide elimination, giving rise to hydroxytetrahalophenoxyl radical anions (X4O-C6O). The latter exhibit absorption maxima near those of the pentahalophenoxyl radicals. This prevents a proper determination of the relative importance of the two processes by optical detection. However, these two processes distinguish themselves by their behaviour with respect to the stoichiometry and kinetics of the production of ionic conducting species. In basic solution, electron transfer causes a conductivity increase due to the formation of OH- whereas addition followed by HX elimination and deprotonation of the X4OHC6O radical results in a conductivity drop. The evaluation of the conductivity change at 8 μs after the radiolytic pulse has ended, reveals that about 27%, 53%, 73%, and 97% of the OH radicals react by electron transfer with F5C6O-, Cl5C6O-, Br5C6O- and I3H2C6O-, respectively. Further conductivity change occurs during the bimolecular termination of the halophenol-derived radicals (t1/2 9 and 4 × 109 dm3 mol-1 s-1) and continues into progressively longer times, owing to the hydrolysis of unstable HX-releasing products, on account of the replacement of OH- by halide/halophenolate ions. Additionally, further halide is released on a time scale of minutes and hours. The rates of the conductivity change in the time range from a few ms to several tens of seconds are proportional to the OH- concentration.
- Fang, Xingwang,Schuchmann, Heinz-Peter,Von Sonntag, Clemens
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p. 1391 - 1398
(2007/10/03)
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- Conversion of pentahalogenated phenols by microperoxidase-8/H2O2 to benzoquinone-type products
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This study reports the microperoxidase-8 (MP8)/H2O2-catalyzed dehalogenation of pentafluorophenol and pentachlorophenol, compounds whose toxic effects and persistence in the environment are well documented. The primary products of this dehalogenation reaction appear to be the corresponding tetrahalo-p-benzoquinones. Under the conditions used, the fluorinated phenol and its intermediate products are more susceptible to degradation than the corresponding chlorinated analogue and its products. The main degradation products of tetrachloro-p-benzoquinone and tetrafluoro-p- benzoquinone were identified as trichlorohydroxyp-benzoquinone and trifluorohydroxy-p-benzoquinone, respectively. This secondary conversion of tetrafluoro-p-benzoquinone and tetrachloro-p-benzoquinone was not mediated by MP8, but was driven by H2O2. Evidence is presented for a mechanism where H2O2 molecules and not hydroxide anions are the reactive nucleophilic species attacking the tetrahalo-p-benzoquinones. In addition to the formation of the trihalohydroxy-p-benzoquinones, the formation of adducts of the tetrahalo-p-benzoquinone products with ethanol, present in the incubation medium, was observed. The adduct from the reaction of tetrachloro-p- benzoquinone with ethanol was isolated and identified as trichloroethoxyquinone. Thus, the present paper describes a system in which the formation of tetrahalo-p-benzoquinone-type products by an oxidative heme- based catalyst could be unequivocally demonstrated.
- Osman, Ahmed M.,Posthumus, Maarten A.,Veeger, Cees,Van Bladeren, Peter J.,Laane, Colja,Rietjens, Ivonne M.C.M.
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p. 1319 - 1325
(2007/10/03)
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- Photoreactivity of some 2-alkoxy/phenoxy-3,5,6-tri-chloro/bromo-1,4-benzoquinones
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We report the reaction between 2,3,5,6-tetrachloro/bromo-1,4-benzoquinones (5A/B) with deprotonated alkoholes/phenoles 7a-e to give yellow 2-alkoxy/phenoxy-3,5,6-trichloro/bromo-1,4-benzoquinones 9A/Ba-e. These reaction products are probably photodegraded yielding the corresponding 2-hydroxy-3,5,6-trichloro/bromo-1,4-benzoquinones 15A/B. The quinones 9A/B are not O-conjugated dehydrated, and the quinones 9Ba-e are not C-3-debrominated. These reactions are observed by photodegradation from 2-dialkylamino-3,5,6-trichloro/bromo-1,4-benzoquinones.
- Kallmayer,Fritzen
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p. 235 - 238
(2007/10/02)
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