- Dechlorination of pentachlorophenol by zero valent iron and modified zero valent irons
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The disappearance of pentachlorophenol (PCP) from aqueous solutions in contact with zero valent metals (ZVMs) may be due to dechlorination reactions or sorption to ZVM-related surfaces. Previously reported results on PCP and zero valent iron measured only PCP loss from aqueous solutions and attributed this loss to reaction. In this study, the total amount of unreacted PCP, both that in aqueous solution and that sorbed to ZVM-related surfaces, was measured using a modified extraction method. PCP dechlorination was confirmed by following the appearance of tetrachlorophenol isomers. The results indicate that the rate of dechlorination is much slower than previously reported. In our experiments, electrolytic zero valent iron with a surface area of 0.12 m2/g resulted in an observed first-order rate constant (±95% confidence limits) of 3.9 (±0.7) x 10-3 h-1 or a half-life of approximately 7.4 days. Normalized to surface area, the rate constant (k(SA)) is 3.2 (±0.6) x 10-4 L m-2 h-1. Four amended irons prepared by coating iron with palladium (Pd/Fe), platinum (Pt/Fe), nickel (Ni/Fe), and copper (Cu/Fe) were also used and showed slower removal rates as compared to unamended iron (estimated half-lives of 36-43 days). Slower reaction rates obtained with amended irons as compared to iron have not been previously reported. Overall, this study conclusively demonstrates PCP dechlorination by iron and several bimetallic ZVMs and indicates that it is essential to separate reaction and sorption processes. The disappearance of pentachlorophenol (PCP) from aqueous solutions in contact with zero valent metals (ZVMs) may be due to dechlorination reactions or sorption to ZVM-related surfaces. Previously reported results on PCP and zero valent iron measured only PCP loss from aqueous solutions and attributed this loss to reaction. In this study, the total amount of unreacted PCP, both that in aqueous solution and that sorbed to ZVM-related surfaces, was measured using a modified extraction method. PCP dechlorination was confirmed by following the appearance of tetrachlorophenol isomers. The results indicate that the rate of dechlorination is much slower than previously reported. In our experiments, electrolytic zero valent iron with a surface area of 0.12 m2/g resulted in an observed first-order rate constant (±95% confidence limits) of 3.9 (±0.7) × 10-3 h-1 or a half-life of approximately 7.4 days. Normalized to surface area, the rate constant (kSA) is 3.2 (±0.6) × 10-4 L m-2 h-1. Four amended irons prepared by coating iron with palladium (Pd/Fe), platinum (Pt/Fe), nickel (Ni/Fe), and copper (Cu/Fe) were also used and showed slower removal rates as compared to unamended iron (estimated half-lives of 36-43 days). Slower reaction rates obtained with amended irons as compared to iron have not been previously reported. Overall, this study conclusively demonstrates PCP dechlorination by iron and several bimetallic ZVMs and indicates that it is essential to separate reaction and sorption processes.
- Kim, Young-Hun,Carraway, Elizabeth R.
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- SYNTHESIS OF CLAY-TEMPLATED SUBNANO-SIZED ZERO VALENT IRON (ZVI) PARTICLES, CLAYS CONTAINING SAME, AND USE OF BOTH IN CONTAMINANT TREATMENTS
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A clay comprising a 2:1 aluminosilicate clay having negative charge sites, the 2:1 aluminosilicate clay containing subnano-sized zero valent iron (ZVI) particles distributed on clay surfaces is provided. In one embodiment, at least some or all of the particles have a cross-section of five (5) angstroms or less. Methods of synthesizing and the novel clays and the clay-templated subnano-scale ZVI particles themselves are also described. Such novel products are useful in a variety of remediation applications, including for reduction and dechlorination reactions.
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Page/Page column 7-8
(2011/06/23)
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- Removal of dioxins and related aromatic hydrocarbons from flue gas streams by adsorption and catalytic destruction
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The dioxin removing capacity of the shell dedioxin system (SDDS a - Ti/V oxidative type catalyst) has been tested using the Umefa lab-scale incinerator over the temperature range 100 -230°C and at space velocities of 8000 and 40,000 h-1. Other analogous organic compounds, such as PCBs, PAHs, chlorobenzenes and chlorophenols have also been investigated. Results show a high degree of dioxin removal already at 100°C (82%), which occurs mainly by adsorption. When the temperature is raised a transition towards destruction is seen and at 150°C, gas hour space velocity (GHSV) 8000 and at 230°C, GHSV 40,000 virtually all removal is by destruction. High PCDD/F destruction efficiencies are reported (> 99.9%, based on I-TEQ); the other dioxin-related species and PAHs are also removed and destroyed to a significant extent. The SDDS has proved to be an effective means of destroying organic compounds in the gas phase, particularly dioxins, at temperatures as low as 150°C.
- Liljelind, Per,Unsworth, John,Maaskant, Onno,Marklund, Stellan
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p. 615 - 623
(2007/10/03)
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- Identification of surrogate compounds for the emission of PCDD/F (I-TEQ value) and evaluation of their on-line realtime detectability in flue gases of waste incineration plants by REMPI-TOFMS mass spectrometry
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Correlations between products of incomplete combustion (PIC), e.g., chloroaromatic compounds, can be used to characterise the emissions from combustion processes, like municipal or hazardous waste incineration. A possible application of such relationships may be the on-line real-time monitoring of a characteristic surrogate, e.g., with Resonance-Enhanced Multiphoton Ionization-Time-of-Flight Mass Spectrometry (REMPI-TOFMS). In this paper, we report the relationships of homologues and individual congeners of chlorinated benzenes (PCBz), dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) and phenols (PCPh) to the International Toxicity Equivalent (I-TEQ) of the PCDD/F (I-TEQ value) in the flue gas and stack gas of a 22 MW hazardous waste incinerator (HWI). As the REMPI detection sensitivity is decreasing with the increase of the degree of chlorination, this study focuses on the lower chlorinated species of the compounds mentioned above. Lower chlorinated species, e.g., chlorobenzene (MCBz), 1,4-dichlorobenzene, 2,4,6-trichlorodibenzofuran or 2,4-dichlorophenol, were identified as I-TEQ surrogates in the flue gas. In contrast to the higher chlorinated phenols, the lower chlorinated phenols (degree of chlorination 4) were not reliable as surrogates in the stack gas. The identified surrogates are evaluated in terms of their detectability by REMPI-TOFMS laser mass spectrometry. The outcome is that MCBz is the best suited surrogate for (indirect) on-line measuring of the I-TEQ value in the flue gas by REMPI-TOFMS. The correlation coefficient r of the MCBz concentration to the I-TEQ in the flue gas was 0.85.
- Blumenstock,Zimmermann,Schramm,Kettrup
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p. 507 - 518
(2007/10/03)
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- Natural formation of chlorinated phenols, dibenzo-p-dioxins, and dibenzofurans in soil of a Douglas fir forest
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The natural formation of 4-MCP, 24/25- and 26-DCP, and 245-TrCP was detected in four selected areas of a rural Douglas fir forest where the humic layer was spiked in situ with a solution of Na37Cl and covered by an enclosure, after 1 year of incubation. Chlorinated phenols (CP) can be formed naturally from organic matter and inorganic chloride by either de novo synthesis or chloroperoxidase (CPO)-catalyzed chlorination. The natural CP congeners were found to be present in high concentrations in soil compared to the other congeners, except for 245-TrCP which was present in a relatively low concentration. This study did not reveal which source, natural or anthropogenic, caused the observed concentrations. Some 20 chlorinated dibenzo-p-dioxins and dibenzofurans (CDD/F) were found to be formed naturally in soil of the Douglas fir forest; the formation of three 2,3,7,8-substituted congeners, 2378-TeCDD, 12378-PeCDD, and 123789-HxCDD, deserves special attention. A formation mechanism has been proposed which starts from naturally formed CP congeners and which probably involves peroxidase mediation. Chlorination of CDD/F congeners by the CPO-mediated reaction cannot be ruled out, but seems to be less likely due to the absence of several predicted congeners. The natural formation of 4-MCP, 24/25- and 26-DCP, and 245-TrCP was detected in four selected areas of a rural Douglas fir forest where the humic layer was spiked in situ with a solution of Na37Cl and covered by an enclosure, after 1 year of incubation. Chlorinated phenols (CP) can be formed naturally from organic matter and inorganic chloride by either de novo synthesis or chloroperoxidase (CPO)-catalyzed chlorination. The natural CP congeners were found to be present in high concentrations in soil compared to the other congeners, except for 245-TrCP which was present in a relatively low concentration. This study did not reveal which source, natural or anthropogenic, caused the observed concentrations. Some 20 chlorinated dibenzo-p-dioxins and dibenzofurans (CDD/F) were found to be formed naturally in soil of the Douglas fir forest; the formation of three 2,3,7,8-substituted congeners, 2378-TeCDD, 12378-PeCDD, and 123789-HxCDD, deserves special attention. A formation mechanism has been proposed which starts from naturally formed CP congeners and which probably involves peroxidase mediation. Chlorination of CDD/F congeners by the CPO-mediated reaction cannot be ruled out, but seems to be less likely due to the absence of several predicted congeners.
- Hoekstra, Eddo J.,De Weerd, Henk,De Leer, Ed W. B.,Brinkman, Udo A.Th.
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p. 2543 - 2549
(2007/10/03)
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- Aryne formation from 1-(3′-Carboxyaryl)-3,3-dim ethyl trianzenes
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A study of the decomposition of 1-(2′-carboxyphenyl)-3,3-dimethyltriazene and the tetrabromoand tetrachloro- analogues showed that the arenediazonium-2-carboxylates were intermediates in the formation of the corresponding arynes: the 1-(2′-carboxyteirahalophenyl)-3,3-dimethyltriazenes are stable precursors that enable cycloaddition reactions of the tetrahalobenzynes to be carried out in acceptable yields using substrates such as N-methylpyrrole,p-xylene and m-dimethoxybenzene.
- Christopher Buxton,Heaney, Harry
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p. 3929 - 3938
(2007/10/02)
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- Agent for protecting sawn timber
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The present invention relates to an agent or concentrate for protecting sawn timber against wood-discolouring fungi, containing a fungicide on phenol basis and a fungicide on organo-iodine basis, optionally fungicides and insecticides, dissolved in an organochemical solvent or solvent mixture or in a mixture of water and organochemical solvent or solvent mixture and at least one emulsifier.
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- Crown Ethers from o-Quinone Diazides and Oxetane
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The carbenes 11, generated by photolysis of the di- and tetrachloro-o-quinone diazides 10, react with oxetane in a 1:3 ratio to give the 15-membered crown ethers 19.In the presence of methanol, the oxonium ions 12 are trapped with formation of 1-(aryloxy)-3-methoxypropanes (13).In the absence of additional nucleophiles, 12 react with oxetane until the chain length is appropriate for inverting intramolecular attack of the aryl oxide at the α-carbon atom of the oxonium ion (18 -> 19). Key Words: Carbonyl carbenes/ Oxygen ylides/ Displacement, nucleophilic, intramolecular/ Carbenes/ Ylides
- Kirmse, Wolfgang,Lelgemann, Rudolf
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p. 1865 - 1866
(2007/10/02)
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- PYROLYSIS-GAS CHROMATOGRAPHY-MASS SPECTROMETRY OF POLYCHLOROPHENOLS AND POLYCHLOROPHENATES
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Pentachlorophenol, 1, its sodium salt and the sodium salts of 2,3,4,5-tetrachlorophenol, 2, and 2,4,6-trichlorophenol, 3, have been submitted to pyrolysis-gas chromatography-mass spectrometry for 20 s at 990 deg C and at 500 deg C.Polychlorophenols (PCPs) and polychlorodibenzodioxins (PCDDs) were formed at the lower temperature.PCPs, PCCDs and polychlorobenzenes (PCBzs) were formed at the higher temperature.Compounds derived from loss of one or two carbon atoms were also formed from the sodium salt of 1 at the higher temperature.A mechanism based on the formation of ketocarbenes and arynes is suggested.
- Bassoli, Angela,Parrilli, Daniele,Rindone, Bruno,Pitea, Demetrio,Siniscalco, Falco
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p. 333 - 339
(2007/10/02)
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- Rate and Equilibrium Studies of the Reaction of Oxyanions with 2-Phenyloxazol-5(4H)-one
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Equilibrium constants for the reaction of phenoxide ions with 2-phenyloxazol-5(4H)-one at 25 deg C and 1M ionic strength obey a Broensted relationship (log kOH/kArO = log K' = -173pKArOH - 15.81) and are not subject to steric effects from ortho-substituents.Both forward and reverse rate parameters exhibit steric effects, and the Broensted equations for meta- and para-substituted species are log kOH = -0.81 pKArOH + 9.75, and log kArO = 0.95pKArOH - 6.40.There is no break in the Broensted line in the region of pKArOH 5-11, consistent with a single transition-state.An upward deviation exists for oxyanions with low basicity (pKXOH 5); one of these oxyanions, betaine, has a solvent deuterium oxide isotope effect for its reaction with the oxazolone greater than 2, consistent with a general base mechanism for attack for these species.The results for nucleophilic attack of phenolate anions are in agreement with a concerted displacement at the carbonyl group.
- Chrystiuk, Edwin,Jusoh, Adelina,Santafianos, Dino,Williams, Andrew
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p. 163 - 168
(2007/10/02)
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- Photochemistry of Polyhaloarenes. 4. Phototransformations of Perchloro-o-phenoxyphenol in Basic Media
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Irradiation of the sodium salt of the conjugate base of perchloro-o-phenoxyphenol (PreD-Na+) in methanol (300 nm) in the presence of sensitizer m-methoxyacetophenone generates ether cleavage products and mono- and di-dechlorination with no cycliozation to OCDD.In the presence of sensitizer and excess triethylamine, irradiation of perchloro-o-phenoxyphenol leads to OCDD as a major product with ether cleavage and dechlorination products representing important reaction pathways.Photodecomposition of the conjugate base of perchloro-o-phenoxyphenol in methanol reveals a small amount of cyclization, while irradiation in methanol in the presence of a 10-fold excess of triethylamine increases the quantum yield for cyclization 17-fold.The photolytic transformations of the conjugate base of perchloro-o-phenoxyphenol in the presence of excess triethylamine are dependent upon solvent polarity with the quantum yield for cyclization increasing strongly in methanol or water/acetonitrile (70:30) relative to that in dibutyl ether.These results are interpreted in terms of electron transfer to PreD- to form a radical dianion.
- Freeman, Peter K.,Srinivasa, Remanujan
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p. 3939 - 3942
(2007/10/02)
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- Photochemistry of halogenated benzene derivatives. Part VI. Photoreactions of tetra- and pentachlorophenols in water-acetonitrile mixtures
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Laboratory photochemical studies of aqueous acetonitrile solution of some polychlorinated phenols (PCPs) such as 2,3,4,5-tetrachlorophenol (2,3,4,5-Cl4-Pn)(1), 2,3,4,6-Cl4-Pn(2), 2,3,5,6-Cl4-Pn(3), and pentachlorophenol (Cl5-Pn)(4) at λ>285 nm have been carried out for 6 and 24 h exposure times.All the investigated PCPs underwent reductive dechlorination.This process was dependent not only upon the position of OH group but also upon the relative positions of the Cl substituents on the benzene ring.The Cl4-Pn 2 (and 3) and Cl5-Pn (4) also yielded photoproducts of molecular formulae C8H4Cl3NO(M+.=235) and C8H3Cl4NO(M+.=269), respectively.Furthermore, phenol 3 is unique amongst the investigated PCPs; in addition to the above mentioned photoproducts, it yielded hexa-, hepta-, and octachlorodihydroxybiphenyl(s) as well as heptachlorohydroxydiphenyl ether.
- Choudhry, Ghulam Ghaus,Wielen, Frans W. M. van der,Webster, G. R. Barrie,Hutzinger, Otto
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p. 469 - 475
(2007/10/02)
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- Participation of Oligochlorobenzenes in the Base-Catalyzed Halogen Dance
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The three trichlorobenzenes fail to participate in the base-catalyzed halogen dance even on treatment with the favorable base/solvent combination potassium tert-butoxide in hexamethylphosphoric triamide.However, 1,2,3,5- and 1,2,4,5-tetrachlorobenzenes undergo disproportionation to penta- and trichlorobenzenes as well as interconversion into each other.Pentachlorobenzene disproportionates to hexa- and tetrachlorobenzenes, but further reactions of C6Cl6 form pentachlorophenol.Substitution reactions to form aryl tert-butyl ethers are observed as side reactions and are believed to occur by the SNAr mechanism.The phenols produced in several reactions apparently result from E2 cleavage of these ethers.These observations are possibly relevant to the mechanism of formation of 2,3,7,8-tetrachlorodibenzo-p-dioxin from 1,2,4,5-tetrachlorobenzene.
- Mach, Martin H.,Bunnett, Joseph F.
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p. 4660 - 4666
(2007/10/02)
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