- Photocatalytic degradation of dichloroacetyl chloride adsorbed on TiO 2
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Dichloroacetyl chloride (DCAC) attracted our attention as an intermediate product of the photocatalytic degradation of trichloroethylene (TCE). The adsorption and photocatalytic reaction of DCAC on TiO2 have been investigated by FTIR spectroscopy. The influence of the surface structure of several TiO2s on the reaction mechanism was discussed in order to understand the complete degradation mechanism of TCE as well as DCAC. DCAC was transformed into dichloroacetic acid (DCAA) on the relatively hydrophobic TiO2 surface by the small amount of the water molecules weakly adsorbed on the surface. This DCAA was degraded to phosgene, CO2, and CO during UV irradiation. For the hydrophilic TiO2, DCAC was mainly transformed into the dichloroacetate anion. UV irradiation allowed this species to produce chloroform in addition to phosgene, CO2, and CO. It is suggested that DCAC easily reacts with the Ti-OH group on the hydrophilic TiO2 and forms the bidentate titanium chelate of dichloroacetate, which efficiently degrades into chloroform.
- Nishikiori, Hiromasa,Tagahara, Makoto,Mukoyama, Leo,Fujii, Tsuneo
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- Role of humic acids in the TiO2-photocatalyzed degradation of tetrachloroethene in water
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The effect of humic acids on the TiO2-mediated photocatalytic degradation of tetrachloroethene (PCE) was kinetically investigated at different pH and initial substrate concentrations. The process occurs through two parallel paths: a major oxidative route leading to mineralization and a reductive route leading to the formation of dichloroacetic acid (DCAA), also undergoing photodegradation. The rate of PCE decomposition was found to decrease in the presence of humic acids adsorbed on the semiconductor surface, while the concentration of the intermediate dichloroacetic acid increased. This is a consequence of the scavenging action of humic acids toward photoproduced surface oxidant species, which makes conduction band electrons more easily available for interface reactions. Kinetic studies on the effect of humic acids in the TiO2-mediated photodegradation of dichloroacetic acid showed that the progressively greater accumulation of this highly toxic intermediate, observed with increasing humic acids content, was a consequence of both an increase in the rare of its production from PCE and a decrease in the rate of its oxidative photodegradation. The effect of humic acids on the TiO2-mediated photocatalytic degradation of tetrachloroethene (PCE) was kinetically investigated at different pH and initial substrate concentrations. The process occurs through two parallel paths: a major oxidative route leading to mineralization and a reductive route leading to the formation of dichloroacetic acid (DCAA), also undergoing photodegradation. The rate of PCE decomposition was found to decrease in the presence of humic acids adsorbed on the semiconductor surface, while the concentration of the intermediate dichloroacetic acid increased. This is a consequence of the scavenging action of humic acids toward photoproduced surface oxidant species, which makes conduction band electrons more easily available for interface reactions. Kinetic studies on the effect of humic acids in the TiO2-mediated photodegradation of dichloroacetic acid showed that the progressively greater accumulation of this highly toxic intermediate, observed with increasing humic acids content, was a consequence of both an increase in the rate of its production from PCE and a decrease in the rate of its oxidative photodegradation.
- Selli, Elena,Baglio, Daniela,Montanarella, Luca,Bidoglio, Giovanni
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- Correlation of molecular and morphologic effects of thermoembolization in a swine model using mass spectrometry imaging
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Hepatocellular carcinoma is a growing worldwide problem with a high mortality rate. This malignancy does not respond well to chemotherapy, and most patients present late in their disease at which time surgery is no longer an option. Over the past three decades, minimally invasive methods have evolved to treat unresectable disease and prolong survival. Intra-arterial embolization techniques are used for large or multiple tumors but have distressingly high levels of local recurrence and can be costly to implement. A new method called thermoembolization was recently reported, which destroys target tissue by combining reactive exothermic chemistry with an extreme local change in pH and ischemia. Described herein are experiments performed using this technique in vivo in a swine model. A microcatheter was advanced under fluoroscopic guidance into a branch of the hepatic artery to deliver a targeted dose of dichloroacetyl chloride dissolved in ethiodized oil into the liver. The following day, the animals were imaged by computed tomography and euthanized. Assessing the reaction product distribution and establishing a correlation with the effects are important for understanding the effects. This presented a significant challenge, however, as the reagent used does not contain a chromophore and is not otherwise readily detectable. Mass spectrometry imaging was employed to determine spatial distribution in treated samples. Additional insights on the biology were obtained by correlating the results with histology, immunohistochemistry, and immunofluorescence. The results are encouraging and may lead to a therapy with less local recurrence and improved overall survival for patients with this disease.
- Guo, Chunxiao,Baluya, Dodge L.,Thompson, Emily A.,Whitley, Elizabeth M.,Cressman, Erik N.K.
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- Ionic liquid-hemoglobin-carbon paste composite bioelectrode and its electrocatalytic activity
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Anew carbon ionic liquid paste bioelectrode was fabricated by mixing hemoglobin (Hb) with graphite powder, ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) and liquid paraffin homogeneously. Nafion film was cast on the electrode surface to improve the stability of bioelectrode. Direct electrochemistry of Hb in the bioelectrode was carefully investigated. Cyclic voltammetric results indicated that a pair of well-defined and quasi-reversible electrochemical responses appeared in pH 7.0 phosphate buffer solution (PBS), indicating that direct electron transfer of Hb was realized in themodified electrode. The formal potential (E0') was calculated as -0.316 V (vs. SCE), which was the typical characteristic of the electrochemical reaction of heme Fe(III)/Fe(II) redox couple. Based on the cyclic voltammetric results the electrochemical parameters of the electrode reaction were calculated. This bioelectrode showed high electrocatalytic activity towards the reduction of trichloroacetic acid (TCA) with good stability and reproducibility.
- Xuan, Zong-Wei,Sun, Xiao-Ying,Jiao, Guo-Song,Zhai, Zi-Qin,Sun, Wei,Lu, Lu-De
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- TiO2 MEDIATED PHOTOOXIDATION OF TRICHLOROETHYLENE AND TOLUENE DISSOLVED IN FLUOROCARBON SOLVENTS
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Titanium dioxide mediated photodegradation of trichloroethylene (TCE) and toluene dissolved in a fluorocarbon solvent (Galden HT110) was demonstrated. The photodegradation of TCE yielded dichloroacetic acid as a major intermediate. The TCE reaction kinetics and high photoefficiency suggest autocatalysis and/or a radical chain reaction mechanism. Photooxidation of toluene is a first-order reaction. Membrane-assisted solvent extraction of TCE from water to the fluorocarbon solvent was demonstrated, and the combination of photooxidation and extraction from the basis for a novel two-stage process for the removal and destruction of organic contaminants from water.
- Sun, Yunfu,Brown, Gilbert M.,Moyer, Bruce A.
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- Photocatalytic degradation of gaseous trichloroethylene on porous titanium dioxide pellets modified with copper(II) under visible light irradiation
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Porous titanium dioxide pellets modified with copper(II) ion (Cu-TiO2) were synthesized by sol-gel method with dialysis for photocatalytic degradation of gaseous trichloroethylene (TCE) under visible light (VL) irradiation. TCE was completely degraded by passing the gas stream (mole fractions of oxygen and TCE were 0.2 and 1.75 × 10?4, respectively) at the flow rate of 25 mL min?1 through 0.2 g of the Cu-TiO2 pellets (Cu content: 0.1 atom%) calcined at 200 °C. TCE was converted mainly to carbon dioxide, dichloroacetic acid (DCAA), and inorganic chlorine species. Relatively small quantities of pentachloroethane (PCA) and trichloroacetaldehyde (TCAH) were detected as products on the Cu-TiO2 surface. Comparison with porous TiO2 pellets under ultraviolet irradiation revealed that more chlorinated products and less carbon dioxide were formed on Cu-TiO2 under VL irradiation. The mineralization of TCE to carbon dioxide was calculated to be only ca. 30.0%. It is noted that DCAA, PCA and TCAH were accumulated on the surface and were extracted with ethyl acetate. The porous Cu-TiO2 pellets show promise as the photocatalyst acting under VL irradiation for converting TCE gas to chlorinated compounds which can be used in industries.
- Tashiro, Keigo,Tanimura, Toshifumi,Yamazaki, Suzuko
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p. 228 - 235
(2019/04/17)
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- A Straightforward Homologation of Carbon Dioxide with Magnesium Carbenoids en Route to α-Halocarboxylic Acids
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The homologation of carbon dioxide with stable, (enantiopure) magnesium carbenoids constitutes a valuable method for preparing α-halo acid derivatives. The tactic features a high level of chemocontrol, thus enabling the synthesis of variously functionalized analogues. The flexibility to generate magnesium carbenoids through sulfoxide-, halogen- or proton- Mg exchange accounts for the wide scope of the reaction. (Figure presented.).
- Monticelli, Serena,Urban, Ernst,Langer, Thierry,Holzer, Wolfgang,Pace, Vittorio
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supporting information
p. 1001 - 1006
(2019/01/30)
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- Effect of dissolved oxygen concentration on iron efficiency: Removal of three chloroacetic acids
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The monochloroacetic, dichloroacetic and trichloroacetic acid (MCAA, DCAA and TCAA) removed by metallic iron under controlled dissolved oxygen conditions (0, 0.75, 1.52, 2.59, 3.47 or 7.09mg/L DO) was investigated in well-mixed batch systems. The removal of CAAs increased first and then decreased with increasing DO concentration. Compared with anoxic condition, the reduction of MCAA and DCAA was substantially enhanced in the presence of O2, while TCAA reduction was significantly inhibited above 2.59mg/L. The 1.52mg/L DO was optimum for the formation of final product, acetic acid. Chlorine mass balances were 69-102%, and carbon mass balances were 92-105%. With sufficient mass transfer from bulk to the particle surface, the degradation of CAAs was limited by their reduction or migration rate within iron particles, which were dependent on the change of reducing agents and corrosion coatings. Under anoxic conditions, the reduction of CAAs was mainly inhibited by the available reducing agents in the conductive layer. Under low oxic conditions, the increasing reducing agents and thin lepidocrocite layer were favorable for CAA dechlorination. Under high oxic conditions, the redundant oxygen competing for reducing agents and significant lepidocrocite growth became the major restricting factors. Various CAA removal mechanisms could be potentially applied to explaining the effect of DO concentration on iron efficiency for contaminant reduction in water and wastewater treatment.
- Tang, Shun,Wang, Xiao-mao,Mao, Yu-qin,Zhao, Yu,Yang, Hong-wei,Xie, Yuefeng F.
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p. 342 - 352
(2015/03/04)
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- Thermodynamically leveraged tandem catalysis for ester RC(O)O-R′ bond hydrogenolysis. scope and mechanism
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Rapid and selective formal hydrogenolysis of aliphatic ester RC(O)O-R′ linkages is achieved by a tandem homogeneous metal triflate + supported palladium catalytic system. The triflate catalyzes the mildly exothermic, turnover-limiting O-R′ cleavage process, whereas the exothermic hydrogenation of the intermediate alkene further drives the overall reaction to completion.
- Lohr, Tracy L.,Li, Zhi,Assary, Rajeev S.,Curtiss, Larry A.,Marks, Tobin J.
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p. 3675 - 3679
(2015/06/16)
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- The electrochemical studies of cytochrome c incorporated in 3D porous calcium alginate films on glassy carbon electrodes
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In this work, the cytochrome c (Cyt c) was incorporated in three-dimension (3D) porous calcium alginate (CA) films prepared by using sodium alginate, calcium chloride and polyethylene glycol, and formed the electroactive porous Cyt c-CA composite films. The stable composite films were characterized by means of scanning electron microscopy (SEM), UV-vis absorption, cyclic voltammetry (CV) and square-wave voltammetry (SWV) techniques. UV-vis experiments demonstrated that Cyt c assembled in the 3D porous CA films retains its near native conformation at medium pH. The Cyt c-CA films modified on glassy carbon electrodes showed a pair of well-defined and nearly reversible cyclic voltammetry peaks at about -0.352 V vs. SCE in protein-free buffer, which originated from heme FeIII/II redox couples within Cyt c. The electrochemical parameters such as apparent heterogeneous electron transfer rate constant (ks) and formal potential (Eo') were estimated by fitting the data of SWV with nonlinear regression analysis. The Cyt c-CA films showed the electrocatalytic activity toward dioxygen, hydrogen peroxide, nitrite and trichloroacetic acid with significant decreases in the electrode potential required. Experimental data demonstrated that the porous film can provide a favorable microenvironment for the protein to directly transfer electrons with the underlying electrode and possess good stability and reproducibility, showing the possible future application of the films for biosensors and biocatalysis.
- Jian, Shan,Liu, Xingchao,Sun, Hong,Hou, Shifeng
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p. 6165 - 6172
(2014/01/23)
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- Nucleofugality of aliphatic carboxylates in mixtures of aprotic solvents and water
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The leaving group ability (nucleofugality) of fluoroacetate, chloroacetate, bromoacetate, dichloroacetate, trifluoroacetate, trichloroacetate, heptafluorobutyrate, formate, isobutyrate, and pivalate have been derived from the solvolysis rate constants of the corresponding X,Y-substituted benzhydryl carboxylates in 60 % and 80 % aqueous acetonitrile and 60 % aqueous acetone, applying the LFER equation: log k = sf(Ef + Nf). The experimental barriers (ΔG?,exp) for solvolyses of 11 reference dianisylmethyl carboxylates in these solvents correlate very well (r = 0.994 in all solvents) with ΔG?,model of the model σ-assisted heterolytic displacement reaction of cis-2,3-dihydroxycyclopropyl trans-carboxylates calculated earlier. Linear correlation observed between the log k for the reference dianisylmethyl carboxylates and the sf values enables estimation of the reaction constant (sfestim). Using the ΔG?,exp vs. ΔG?,model correlation, and taking the estimated sfestim, the nucleofugality parameters for other 34 aliphatic carboxylates have been determined in 60 % and 80 % aqueous acetonitrile and 60 % aqueous acetone. The most important variable that determines the reactivity of aliphatic carboxylates in aprotic solvent/water mixtures is the inductive effect of the group(s) attached onto the carboxylate moiety.
- Mati, Mirela,Denegri, Bernard,Kronja, Olga
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p. 375 - 384
(2015/10/12)
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- Microwave synthesis of chloroacetic acid with various cocatalysts in acetic anhydride catalyzing method
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In this paper, we introduce a method of synthesizing chloroacetic acid using acetyl chloride as catalyst and anhydrous ferric chloride, ferric chloride hexahydrate, zinc chloride and concentrated sulfuric acid (98 % H 2SO4) as cocatalysts respectively with a variable frequency microwave oven as heater. From investigating the influences of cocatalysts in reaction, we draw a optimal condition that the yield and selectivity of chloroacetic acid are 98.11 and 98.58 % respectively when adding 0.4 g FeCl3 in mixture after reacting 3.5 h and in comparable with the corresponding percentages, 96.9 and 96.87 %, with 0.7 g ZnCl2 adding, the adding amount of 1.5 g 98 % H2SO4 result in a little lower percentages of 95.71 and 95.61 % correspondingly. We have speculated the cocatalytic mechanisms in chlorination.
- Song, Guo-Qiang,Wang, Li-Sheng,Li, Fu-Xiang
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p. 3923 - 3926
(2014/08/05)
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- Study on Gas-phase mechanism of chloroacetic acid synthesis by catalysis and chlorination of acetic acid
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The process of acetic acid catalysis and chlorination for synthesizing chloroacetic acid can exist in not only gas phase but also liquid phase. In this paper, the gas-phase reaction mechanism of the synthesis of chloroacetic acid was studied. Due to the high concentration of acetic acid and the better reaction mass transfer in the liquid-phase reaction, the generation amount of the dichloroacetic acid was higher than that in the gas-phase reaction. Under the solution distillation, the concentration of acetyl chloride, whose boiling point is very low, was very high in the gas phase, sometimes even up to 99 %, which would cause the acetyl chloride to escape rapidly with the hydrogen chloride exhaust, so that the reaction slowed down. Therefore, series reactions occured easily in the gas-phase reaction causing the amount of the dichloroacetic acid to increase.
- Xue, Jian-Wei,Zhang, Jian-Peng,Wu, Bo,Li, Fu-Xiang,Lv, Zhi-Ping
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p. 475 - 480
(2014/06/09)
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- Photocatalytic degradation of chlorinated ethanes in the gas phase on the porous TiO2 pellets: Effect of surface acidity
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The photocatalytic degradation of chlorinated ethanes was studied in a tubular photoreactor packed with TiO2 pellets prepared by sol-gel method. The steady-state condition was not obtained, but the deterioration in the photocatalytic activity was observed during the irradiation. Effects of mole fractions of water vapor, O2, and C2H5Cl or C2H4Cl2 and reaction temperature on the photodegradation of C2H5Cl or C2H 4Cl2 were examined, and these data were compared with those obtained by the photodegradation of chlorinated ethylenes. On the basis of the products detected with and without oxygen in the reactant's gas stream, we proposed the degradation mechanism. Measurement of diffuse reflectance infrared Fourier transform spectroscopy of pyridine adsorbed on the catalysts showed that decrease in the conversion for the photodegradation of C2H 5Cl was attributable to the formation of Bronsted acid sites. Comparison of the data obtained with the TiO2 and the sulfated TiO2 (SO42-/TiO2) pellets indicated that the photodegradation of C2H5Cl was suppressed by the presence of the Bronsted sites, but that of trichloroethylene was not affected. Such a difference is attributable to the adsorption process of these reactants on the acid sites on the catalyst surface.
- Yamazaki, Suzuko,Ichikawa, Keiko,Saeki, Atsue,Tanimura, Toshifumi,Adachi, Kenta
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experimental part
p. 5092 - 5098
(2010/08/05)
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- An efficient and practical system for the catalytic oxidation of alcohols, aldehydes, and α,β-unsaturated carboxylic acids
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(Chemical Equation Presented) Upon exposure to commercial bleach (～5% aqueous sodium hypochlorite), nickel(II) chloride or nickel(II) acetate is transformed quantitatively into an insoluble nickel species, nickel oxide hydroxide. This material consists of high surface area nanoparticles (ca. 4 nm) and is a useful heterogeneous catalyst for the oxidation of many organic compounds. The oxidation of primary alcohols to carboxylic acids, secondary alcohols to ketones, aldehydes to carboxylic acids, and α,β- unsaturated carboxylic acids to epoxy acids is demonstrated using 2.5 mol % of nickel catalyst and commercial bleach as the terminal oxidant. We demonstrate the controlled and selective oxidation of several organic substrates using this system affording 70-95% isolated yields and 90-100% purity. In most cases, the oxidations can be performed without an organic solvent, making this approach attractive as a "greener" alternative to conventional oxidations.
- Grill, Joseph M.,Ogle, James W.,Miller, Stephen A.
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p. 9291 - 9296
(2007/10/03)
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- Kinetics of hydrolysis of 4-methoxyphenyl-2,2-dichloroethanoate in binary water-cosolvent mixtures; the role of solvent activity and solute-solute interactions
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Rate constants are reported for the pH-independent hydrolysis of 4-methoxyphenyl-2,2-dichloroethanoate in aqueous solution as a function of the concentration of added cyanomethane (acetonitrile), polyethylene glycol (PEG 400) and tetrahydrofuran (THF). The concentration of water was varied between ca. 25 and 55.5 M. It was found that the variation in water activity yields only a minor contribution to the observed variation in rate constants. Interestingly, for both cyanomethane and PEG 400 log(k) varies approximately linearly with the molar concentration of water. Medium effects in highly aqueous solutions ([H2O] > 50 M) of ethanol, 1-propanol, 2-propanol, 1-butanol and 2-methyl-2-propanol have also been determined. Unexpectedly, in this concentration range the alcohols induce significantly smaller effects per unit volume than cyanomethane. The present results are discussed in terms of pairwise interaction parameters. Isobaric activation parameters have been determined and reveal remarkable differences in the nature of the induced medium effects.
- Rispens, Theo,Cabaleiro-Lago, Celia,Engberts, Jan B. F. N.
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p. 597 - 602
(2007/10/03)
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- A PROCESS FOR THE PREPARATION OF MONOCHLOROACETIC ACID
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The invention pertains to a process for the production of monochloroacetic acid from chlorine and acetic acid in the presence of a catalyst by reactive distillation. The process and the required reactive distillation apparatus is much less complex than conventional reactors and yields a monochloroacetic acid product having a low content of over-chlorinated products.
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- Aqueous solutions that model the cytosol: Studies on polarity, chemical reactivity and enzyme kinetics
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Concentrated solutions of a series of organic compounds have been prepared and the effects of these solutes on the properties of the solvent system assessed as a function of their concentration and nature. Polarity, as measured by Reichardt's ET/sub
- Asaad, Nabil,Otter, Marie Jetta Den,Engberts, Jan B. F. N.
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p. 1404 - 1412
(2007/10/03)
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- Novel photoacid generators for photodirected oligonucleotide synthesis
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Photodirected oligonucleotide synthesis uses either direct or indirect light-dependent 5′-deprotection. Both have been reported to give lower stepwise synthetic yields than conventional methods. The deficiency appears to be due to incomplete deprotection at the oligonucleotide 5′-position and, additionally in the case where photodirection is indirect and uses photogenerated photoacid to effect 5′-detritylation, the depurinating effects of strong acid. We have developed novel photosensitive-2-nitrobenzyl esters that on irradiation with near UV light generate α-chloro-substituted acetic acids, such as trichloroacetic acid, which are widely and successfully used in conventional solid-phase oligonucleotide synthesis. α-Phenyl-4,5-dimethoxy-2-nitrobenzyltrichloroacetate and α-phenyl-4,5-dimethoxy-2,6-dinitrobenzyltrichloroacetate showed appropriate photochemical characteristics and were used for photodirected synthesis of a variety of oligonucleotides, including (T)5, TATAT, TGTGT, (T)10, (AT)5, (CT)5 (GT)5 and (TGCAT)2 on a modified Millipore Expedite DNA synthesizer. The outcomes were compared with those obtained by use of directly added trichloroacetic acid (conventional synthesis). The stepwise yields for the two methods were essentially identical.
- Serafinowski, Pawel J.,Garland, Peter B.
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p. 962 - 965
(2007/10/03)
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- Microsomal oxidation of tribromoethylene and reactions of tribromoethylene oxide.
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Halogenated olefins are of interest because of their widespread use in industry and their potential toxicity to humans. Epoxides are among the enzymatic oxidation products and have been studied in regard to their toxicity. Most of the attention has been given to chlorinated epoxides, and we have previously studied the reactions of the mono-, di-, tri-, and tetrachloroethylene oxides. To further test some hypotheses concerning the reactivity of these compounds, we prepared tribromoethylene (TBE) oxide and compared it to trichloroethylene (TCE) oxide and other chlorinated epoxides. TBE oxide reacted with H(2)O about 3 times faster than did TCE oxide. Several hydrolysis products of TBE oxide were the same as formed from TCE oxide, i.e., glyoxylic acid, CO, and HCO(2)H. Br(2)CHCO(2)H was formed from TBE oxide; the yield was higher than for Cl(2)CHCO(2)H formed in the hydrolysis of TCE oxide. The yield of tribromoacetaldehyde was 0.4% in aqueous buffer (pH 7.4). In rat liver microsomal incubations containing TBE and NADPH, Br(2)CHCO(2)H was a major product, and tribromoacetaldehyde was a minor product. These results are consistent with schemes previously developed for halogenated epoxides, with migration of bromine being more favorable than for chlorine. Reaction of TBE oxide with lysine yielded relatively more N-dihaloacetyllysine and less N-formyllysine than in the case of TCE oxide. This same pattern was observed in the products of the reaction of TBE oxide with the lysine residues in bovine serum albumin. We conclude that the proposed scheme of hydrolysis of halogenated epoxides follows the expected halide order and that this can be used to rationalize patterns of hydrolysis and reactivity of other halogenated epoxides.
- Yoshioka, Tadao,Krauser, Joel A,Guengerich, F Peter
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p. 1414 - 1420
(2007/10/03)
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- Degradation pathways of trichloroethylene and 1,1,1-trichloroethane by Mycobacterium sp. TA27
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We analyzed the kinetics and metabolic pathways of trichloroethylene and 1,1,1-trichloroethane degradation by the ethane-utilizing Mycobacterium sp. TA27. The apparent Vmax and Km of trichloroethylene were 9.8 nmol min-1 m
- Hashimoto, Akiko,Iwasaki, Kazuhiro,Nakasugi, Naou,Nakajima, Mutsuyasu,Yagi, Osami
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p. 385 - 390
(2007/10/03)
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- Reduction of haloacetic acids by Fe0: Implications for treatment and fate
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To predict the fate of haloacetic acids (HAAs) in natural or engineered systems, information is needed concerning the types of reactions that these compounds undergo, the rates of those reactions, and the products that are formed. Given that many drinking water distribution systems consist of unlined cast iron pipe, reactions of HAAs with elemental iron (Fe0) may play a role in determining the fate of HAAs in these systems. In addition, zerovalent iron may prove to be an effective treatment technology for the removal of HAAs from chlorinated drinking water and wastewater. Thus, batch experiments were used to investigate reactions of four trihaloacetic acids, trichloroacetic acid (TCAA), tribromoacetic acid (TBAA), chlorodibromoacetic acid (CDBAA), and bromodichloroacetic acid (BDCAA), with Fe0. All compounds readily reacted with Fe0, and investigation of product formation and subsequent disappearance revealed that the reactions proceeded via sequential hydrogenolysis. Bromine was preferentially removed over chlorine, and TBAA was the only compound completely dehalogenated to acetic acid. In compounds containing chlorine, the final product of reactions with Fe0 was monochloroacetic acid. Halogen mass balances were 95-112%, and carbon mass balances were 62.6-112%. The pseudo-first-order rate constants for trihaloacetic acid degradation were as follows: BDCAA (10.6 ± 3.1 h-1) > CDBAA (1.43 ± 0.32 h-1) ≈ TBAA (1.41 ± 0.28 h--1) ? TCAA (0.08 ± 0.02 h-1).
- Hozalski, Raymond M.,Zhang, Li,Arnold, William A.
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p. 2258 - 2263
(2007/10/03)
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- Hydrolytic removal of the chlorinated products from the oxidative free-radical-induced degradation of chloroethylenes: Acid chlorides and chlorinated acetic acids
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Progressive hydrolytic decomposition of acyl chlorides, among them the chlorinated acetyl chlorides, which are produced in the gas-phase oxidation of chlorinated ethylenes, permits the complete mineralization of organically bound chlorine to chloride anion. Hydrolysis rate constants (100% water) have been determined for the following acyl chlorides: acetyl (350 s-1), chloroacetyl (5.5 s-1), dichloroacetyl (300 s-1), trichloroacetyl (>350 s-1), and oxalyl dichloride (>350 s-1). The chlorinated acetyl chlorides thereby give rise to the chloroacetates whose decomposition has also been studied and the kinetic parameters determined. Mono- and dichloroacetate anion undergo hydrolytic dechlorination (kobs = ko + kOH- × [OH-]; ClCH2C(O)O-: Ao 6.4 × 1015 s-1, Eo 148 kJ mol-1, AOH- 1.6 × 109 dm3 mol-1 s-1, EOH- 86 kJ mol-1. Cl2CHC(O)O-: Ao 3.2 × 1016 s-1, Eo 156 kJ mol-1, AOH- 3.2 × 1010 dm3 mol-1 s-1, EOH- 104 kJ mol-1). Trichloroacetate anion decomposes by another mechanism, undergoing decarboxylation which is base-uncatalyzed: Ao 2.1 × 1017 s-1, Eo 146 kJ mol-1. Procedures on a pilot-plant scale are pointed out that allow the elimination of these compounds upon oxidation of the strip-gas produced when contaminated water is freed from chlorinated ethylenes by air-stripping.
- Prager, Lutz,Dowideit, Peter,Langguth, Helmut,Schuchmann, Heinz-Peter,Von Sonntag, Clemens
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p. 1641 - 1647
(2007/10/03)
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- Effects of bromide on the formation of THMs and HAAs
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The role of bromide in the formation and speciation of disinfection by-products (DBPs) during chlorination was investigated. The molar ratio of applied chlorine to bromide is an important factor in the formation and speciation of trihalomethanes (THMs) and halogenacetic acids (HAAs). A good relationship exists between the molar fractions of THMs and the bromide incorporation factor. The halogen substitution ability of HOBr and HOCl during the formation of THMs and HAAs can be determined based on probability theory. The formation of HAAs, and their respective concentrations, can also be estimated through use of the developed model.
- Chang,Lin,Chiang
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p. 1029 - 1034
(2007/10/03)
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- The formation and control of disinfection by-products using chlorine dioxide
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In this study, chlorine dioxide (ClO2) was used as an alternative disinfectant with vanillic acid, p-hydroxybenzoic acid, and humic acid as the organic precursors in a natural aquatic environment. The primary disinfection by-products (DBPs) formed were trihalomethanes (THMs) and haloacetic acids (HAAs). Under neutral conditions (pH = 7) for vanillic acid, more total haloacetic acids (THAAs) than total trihalomethanes (TTHMs) were found, with a substantial increase during the later stages of the reaction. In the case of p-hydroxybenzoic acid, the amount of THAAs produced was minimal. Raising the concentration of ClO2 was not favorable for the control of THAAs in low concentrations of vanillic acid. ClO2 could reduce the total amount of TTHMs and THAAs for higher concentration of vanillic acid. It was found that the humic acid treatment dosage was not significant. Under alkaline conditions (pH = 9), the control of TTHMs and THAAs for the treatment of vanillic acid was better and more economical, however, an appreciable amount of inorganic by-products were observed. Under the same alkaline condition, the control of THAA for the treatment of p-hydroxybenzoic acid was not beneficial and for the treatment of humic acid was not significant. (C) 2000 Elsevier Science Ltd.
- Chang, Chen-Yu,Hsieh, Yung-Hsu,Shih, I-Chen,Hsu, Shen-Sheng,Wang, Kuo-Hua
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p. 1181 - 1186
(2007/10/03)
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- Pairwise Gibbs energies of interaction involving N-alkyl-2- pyrrolidinones and related compounds in aqueous solution obtained from kinetic medium effects
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Kinetic solvent effects of N-alkyl-2-pyrrolidinones and structurally related compounds on the water-catalyzed hydrolysis reactions of p- methoxyphenyl dichloroacetate (MPDA), 1-benzoyl-3-phenyl-1,2,4-triazole (BPhT), and 1-benzoyl-1,2,4-triazole (BT) in highly dilute aqueous solutions at pH 4 and 298.15 K have been determined by UV/vis spectroscopy. Using a thermodynamic description of solute-solute interactions in aqueous solutions, the kinetic results have been analyzed in terms of pairwise Gibbs energy interaction parameters: G(c) values. These are negative, indicating that hydrophobic interactions in the initial state dominate the medium effects. The interaction parameters increase in the order MPDABT>BPhT. However, when differences in reactivity and transition state effects are taken into account, it appears that BPhT is more successful in establishing hydrophobic interactions with the cosolutes than are MPDA and BT. Using the SWAG-approach for additivity of group interactions, additivity is observed for the first three consecutive CH2 groups in the cosolute in all three hydrolysis reactions. Larger alkyl substituents cause larger retardations than anticipated on basis of this additivity. The results are explained by intramolecular destructive overlap of the polar hydration shell of the amide functionality and the apolar (hydrophobic) hydration shell of the alkyl group, which extends to the third CH2 group in the N-alkyl group of the cosolute molecule. The inner apolar groups, therefore, have a reduced apparent hydrophobicity. More remote CH2 groups develop independent hydrophobic hydration shells. The effect of the position of a CH2 group in the cosolute molecule is also considered. Kinetic solvent effects with structurally related esters show that amide-amide, ester-ester, and amide- ester group interactions affect the transition state in different ways. Finally, the effects of PVP polymers on the three hydrolysis reactions have been examined. The data presented enhance the understanding of pairwise hydrophobic interactions in aqueous solutions. In addition the results provide insights into the interactions between hydrophobic and hydrophilic hydration shells as well as into the energetics of amide hydration and interactions involving amides in aqueous solution, both playing important roles in protein stabilization.
- Apperloo, Joke J.,Streefland, Lisette,Engberts, Jan B. F. N.,Blandamer, Michael J.
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p. 411 - 418
(2007/10/03)
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- Formation of the haloacetic acids during ozonation and chlorination of water in warsaw waterworks (Poland)
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The results of the study of the HAAs formation in Water Works in Warsaw, Poland are presented. Water taken from Zegrzynskie Lake is characterized by elevated content of humic substances and algae bloom in hot seasons. The water is ozonated and chlorinated
- Dojlido, Jan,Zbiec, Edward,Swietlik, Ryszard
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p. 3111 - 3118
(2007/10/03)
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- Evidence for an additional oxidant in the photoassisted Fenton reaction
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The photo-Fenton reaction (Fe3+ + H2O2 + UV) has potential applications in wastewater treatment. This reaction was compared to H2O2 photolysis and other reactions that produce only hydroxyl radicals (OH·) in order to probe for additional or alternative intermediates that may contribute to the recognized potency of photo-Fenton as an oxidant of organic compounds. Distinct differences were found between photo-Fenton and genuine OH· reactions. The kinetic deuterium isotope effect (KDIE) for cyclohexane in the photo-Fenton reaction increases from 1.2 to 1.4 with increasing concentration of OH· scavenger, tert-butyl alcohol; whereas the KDIE in genuine OH· reactions (H2O2/UV, Fe3+/UV, and Fe2+ + H2O2) is 1.1 and unchanged in the presence of tert-butyl alcohol. Photo-Fenton catalyzed the epoxidation of cyclohexene at a much greater rate than H2O2/UV. The relative yields of chlorinated organic acids from 1,1,2-trichloroethane, trichloroethene, and tetrachloroethene oxidation were markedly affected by the presence of iron. Time-resolved laser flash photolysis spectroscopy in the absence of organics revealed a transient, seen only in Fe3+ + H2O2 solutions, with broad absorbance in the visible and a lifetime of ~100 ns. The results suggest the participation of a high-valent oxoiron complex (ferryl) in addition to OH· in organic compound oxidations. Hydrogen peroxide forms a complex with iron, Fe(O2H)2+ (K15 = 1.15 x 10-2), that absorbs in the visible region and could be the precursor of the ferryl complex. The photo-Fenton reaction (Fe3+ + H2O2 + UV) has potential applications in wastewater treatment. This reaction was compared to H2O2 photolysis and other reactions that produce only hydroxyl radicals (OH·) in order to probe for additional or alternative intermediates that may contribute to the recognized potency of photo-Fenton as an oxidant of organic compounds. Distinct differences were found between photo-Fenton and genuine OH· reactions. The kinetic deuterium isotope effect (KDIE) for cyclohexane in the photo-Fenton reaction increases from 1.2 to 1.4 with increasing concentration of OH· scavenger, tert-butyl alcohol; whereas the KDIE in genuine OH· reactions (H2O2/UV, Fe3+/UV, and Fe2+ + H2O2) is 1.1 and unchanged in the presence of tert-butyl alcohol. Photo-Fenton catalyzed the epoxidation of cyclohexene at a much greater rate than H2O2/UV. The relative yields of chlorinated organic acids from 1,1,2-trichloroethane, trichloroethene, and tetrachloroethene oxidation were markedly affected by the presence of iron. Time-resolved laser flash photolysis spectroscopy in the absence of organics revealed a transient, seen only in Fe3+ + H2O2 solutions, with broad absorbance in the visible and a lifetime of approx. 100 ns. The results suggest the participation of a high-valent oxoiron complex (ferryl) in addition to OH· in organic compound oxidations. Hydrogen peroxide forms a complex with iron, Fe(O2H)2+ (K15 = 1.15 × 10-2), that absorbs in the visible region and could be the precursor of the ferryl complex.
- Pignatello, Joseph J.,Liu, Di,Huston, Patrick
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p. 1832 - 1839
(2007/10/03)
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- Correlation analysis of carbonyl carbon 13C NMR chemical shifts, IR absorption frequencies and rate coefficients of nucleophilic acyl substitutions. A novel explanation for the substituent dependence of reactivity
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Rate coefficients of nucleophilic acyl substitutions, carboxylate carbon 13C NMR chemical shift values and v(C=O) frequencies of several series of aryl and acyl substituted aryl acetates or alkyl benzoates have been investigated. An increasing electron-withdrawal by the acyl or aryl substituents results in higher reaction rates, upfield 13C NMR chemical shifts and higher frequencies of the C=O stretching. Good correlations are observed for the log k versus δC(C=O) plots. The increase of the reaction rate with increased electron density at the C=O carbon (as proved by 13C NMR shifts) contradicts the previous concept of increased electrophilicity of the carbonyl carbon by electron-withdrawing substituents. The rate increase is now attributed to the decrease of the ester ground state resonance stabilization caused by electron-withdrawing substituents. The use of log k versus δc(C=O) correlations is presented as a practical method to evaluate rate coefficients especially for compounds for which Hammett type correlations cannot be used.
- Neuvonen, Helmi,Neuvonen, Kari
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p. 1497 - 1502
(2007/10/03)
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- 2,2-Dichloroalkanecarboxylic acids, processes for their production and pharmaceutical agents containing these
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Pharmaceutical agents for treating diabetus mellitus which contain a compound of formula I STR1 as the active substance, in which A, B, A' and W have the meanings stated in the claims, new compounds of formula I as well as processes for their production.
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- Mechanism of aqueous decomposition of trichloroethylene oxide
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The aqueous decomposition of trichloroethylene (TCE) oxide is shown to involve both pH-independent and hydronium ion-dependent regions. C-C bond scission is a major reaction at all pH values. Disappearance of TCE oxide is the rate-determining step for the formation of CO under the conditions studied. The product distribution of CO and three carboxylic acids (HCO2H, Cl2CHCO2H, and glyoxylic acid) did not change considerably over the pH range of -1.5-14, in general, even though the hydrolysis mechanism changes from hydronium ion-dependent to pH-independent. Mechanisms for the hydronium ion-dependent and pH-independent hydrolysis of TCE oxide were elucidated on the basis of the results of H218O and H incorporation and identification of products of the reaction of TCE oxide with lysine in both H216O and H218O. In the pH-independent hydrolysis, a zwitterionic intermediate could be formed and undergo an intramolecular rearrangement (Cl- shift) to generate dichloroacetyl chloride, which would subsequently decompose to Cl2CHCO2H. The zwitterionic intermediate could also hydrolyze at the less sterically hindered methylene to give a glycol anion, which would dehydrohalogenate to form an oxoacetyl chloride intermediate. The oxoacetyl chloride could hydrolyze to generate either glyoxylic acid, as a final product, or an anionic intermediate, which could go through a concerted mechanism to generate CO, HCO2H, and chloride. A mechanism proposed for the hydronium ion-dependent hydrolysis is very similar to that for the pH-independent hydrolysis except for the first step, which involves hydronium ion attack on TCE oxide to form a TCE-oxide cation intermediate. The lysine amide adducts were characterized by HPLC and mass spectrometry as those resulting from reaction with the postulated acyl chlorides.
- Cai, Hongliang,Guengerich, F. Peter
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p. 11656 - 11663
(2007/10/03)
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- Electrochemical incineration of 4-chlorophenol and the identification of products and intermediates by mass spectrometry
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This report summarizes results obtained as part of a larger effort to demonstrate the applicability of electrolytic procedures for the direct anodic (oxidative) degradation of toxic organic wastes. We refer to this process as "electrochemical incineration" (ECI) because the ultimate degradation products, e.g., carbon dioxide, are equivalent to those achieved by thermal incineration processes. In this work, the ECI of 4-chlorophenol is achieved in an aqueous medium using a platinum anode coated with a quaternary metal oxide film containing Ti, Ru, Sn, and Sb oxides. The electrode is stable and active when used with a solid Nafion membrane without the addition of soluble supporting electrolyte. Liquid chromatography (LC), including reverse phase and ion exchange chromatography, is coupled with electrospray mass spectrometry (ES-MS) and used, along with gas chromatography-mass spectrometry (GC-MS) and measurements of pH, chemical oxygen demand (COD), and total organic carbon (TOC), to study the reaction and identify the intermediate products from the ECI of 4-chlorophenol. Twenty-six intermediate products are identified and reported. The most abundant of these products are benzoquinone, 4-chlorocatechol, maleic acid, succinic acid, malonic acid, and the inorganic anions chloride, chlorate, and perchlorate. After 24 h of ECI, a solution that initially contained 108 ppm 4-chlorophenol yields only 1 ppm TOC with 98% of the original chlorine remaining in the specified inorganic forms. LC-ES-MS and direct infusion ES-MS detection limits are between 80 ppb and 4 ppm for these intermediate products. Elemental analysis of the electrolyzed solutions by inductively coupled plasma mass spectrometry ICP-MS showed that only trace amounts (25 ppb) of the metallic elements comprising the metal oxide film were present in the solution.
- Johnson, Steve K.,Houk, Linda L.,Feng, Jianren,Houk,Johnson, Dennis C.
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p. 2638 - 2644
(2007/10/03)
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- Halogen atom transfer radical cyclization of N-allyl-N-benzyl-2,2-dihaloamides to 2-pyrrolidinones, promoted by Fe0-FeCl3 or CuCl-TMEDA
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The halogen atom transfer radical cyclization of a N-allyl-N-benzyl-2,2-dihaloamides to 2-pyrrolidinones has been carried out in high yields under mild conditions, in a reaction promoted by CuCl-TMEDA or Fe0-FeCl3 in acetonitrile or N,N-dimethylformamide, respectively.
- Benedetti, Miriam,Forti, Luca,Ghelfi, Franco,Pagnoni, Ugo Maria,Ronzoni, Roberto
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p. 14031 - 14042
(2007/10/03)
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- On the of Relative Leaving Groyp Abilities of Imidazole and the Subsituted Phenoxide Ions. the Effect of the Acyl Group
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Rate coefficients for the imidazole-catalysed hydrolysis of substituted phenyl acetates, chloroacetates and dichloroaeetates have been determined in 40% (v/v) acetonitrile-water. It is shown that the increasing iiectror,withdrawai by the acyl group makes the general base-cataiysed nucleophilic reaction of imidazoie detectable beside the uncatalysed nucleophilic attack of the amine. This is attributed to the acyl group-induced change of the partitioning ratio of imidazoie and the ester leaving group. A kinetic evidence is obtained of a change in the rate-limiting step with increasing imidazoie concentration for the imidazole-catalysed reactions of 4-chloro- and 4-methoxyphenyl dichloroacetates. VCH Verlagsgesellschaf; mbH, 1996.
- Nenvonen, Helmi
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p. 1231 - 1236
(2007/10/03)
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- Neutral hydrolysis and imidazole-catalysed decomposition of bis(4-nitrophenyl) oxalate. 1,1'-Oxalyldiimidazole as an intermediate
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Neutral hydrolysis and imidazole-catalysed decomposition of a peroxyoxalate chemiluminescence reagent type compound, bis(4-nitrophenyl) oxalate (4-NPO), have been studied in acetonitrile and in acetonitrile-water mixtures.For comparison, the rate coeffici
- Neuvonen, Helmi
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p. 945 - 950
(2007/10/02)
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- Process for the reaction of a low-molecular hydroxyl compound with a carboxylic acid halide
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In a process for reacting a low molecular weight hydroxy compound with a carboxylic acid halide, a small amount of the acid halide is introduced into the reaction vessel and the remainder of the acid halide and the hydroxy compound are added gradually in an approximately stoichiometric ratio. The hydrogen halide formed is thus prevented from dissolving in the reaction medium. The heat of reaction to be dissipated is negligible.
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- Reaction of the OH Radical with Tetrachloroethene and Trichloroacetaldehyde (Hydrate) in Oxygen-free Aqueous Solution
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Hydroxyl radicals are generated radiolytically in NO2-saturated aqueous solutions and are reacted with either tetrachloroethene or trichloroacetaldehyde hydrate.The primary products after irradiation are tetrachlorosuccinic acid (G = 2.3*10-7 mol J-1 and 2.7*10-7 mol J-1, respectively) and chloride ions (G = 11.6*10-7 mol J-1 and 7.3*10-7 mol J-1, respectively).The former decomposes into trichloroacrylic acid and carbon dioxide (Ea = 115 kJ mol-1).From tetrachloroethene some dichloroacetic acid is also formed (G = 0.2*10-7 mol J-1).Trichloroacetic acid is not among the products.Kinetic studies were carried out by pulse radiolysis.In the case of trichloroacetaldehyde hydrate there is a jump in conductivity increase of G(H+) ca. 2*G((OH(radical)) within not greater than 5 μs and no further increase in conductivity at later times.It is concluded that the OH-radicals abstract the carbon-bound H-atom and the resulting CCl3C(OH)2 radicals rapidly eliminate HCl forming CCl2CO2H radicals which dissociate and dimerize yielding tetrachlorosuccinic acid.In the case of the reaction of the OH-radical with tetrachloroethene the conductivity build-up is biphasic.In the first step one equivalent H+ is formed when the primary CCl2CCl2OH radical eliminates HCl yielding the CCl2C(O)Cl radical (k > 7*105 s-1).Upon dimerization (2 k = 6.9*108 dm3 mol-1 s-1) Cl(O)CCCl2CCl2C(O)Cl is formed which hydrolyses (k = 5 s-1).Only one conductivity equivalent is liberated, and it is concluded that the ensuing monoanion rapidly eliminates a chlorine ion (no conductivity change) yielding tetrachlorosuccinic anhydride.It subsequently hydrolyses at a later stage, not resolved by pulse radiolysis, to tetrachlorosuccinic acid.
- Mertens, Ralf,Sonntag, Clemens von
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p. 2181 - 2186
(2007/10/02)
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- Ozonides of Acyclic Olefins Having Mono- and Dichloro-Substituted Double Bonds
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Ozonolyses of acyclic olefins containing 1,2-dichloro-substituted (4a,b) and monochloro-substituted double bonds (7a, b, 12) as well as two (4a, b, 7a, b) or one halomethyl group (12) attached to the double bond afford the corresponding ozonides as the first representatives of monocyclic chlorinated ozonides.Their stability decreases in order 5a, 5b > 8a, 8b > 13. - Key Words: Ozonides/ 1,2,4-Trioxolanes, 3-chloro-, 3,5-dichloro- / Polyethylene
- Griesbaum, Karl,Schlindwein, Konrad,Hilss, Michael
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p. 1843 - 1848
(2007/10/02)
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- Kinetics of Uncatalysed Hydrolysis of 1-Benzoyl-3-phenyl-1,2,4-triazole and p-Methoxyphenyl Dichloroethanoate in Aqueous Solution Containing Ureas, Carboxamides, Sulfonamides, Sulfones and Sulfoxides
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Rate contants are reported for the hydrolysis of 1-benzoyl-3-phenyl-1,2,4-triazole and p-methoxyphenyl dichloroethanoate in aqueous solutions containing formamide, acetamide, propionamide, isobutyramide, N-methylformamide, N,N-dimethylformamide, n-butyramide, N-methylacetamide, N,N-dimethylacetamide, urea, 1,3-dimethylurea, 1,1,3,3-tetramethylurea, methanesulfonamide, N-methylmethanesulfonamide, dimethylsulfonamide, dimethyl sulfone, tetramethylene sulfone, diethyl sulfone, DMSO, tetramethylene sulfoxide or diethyl sulfoxide.The data are analysed to yield quantitiesdefined as G(c) which describe Gibbs energies for substrate added solute interactions.The G(c) parameters are used to calculate group interaction parameters.Trends in derived G(c) parameters can be understood in terms of additivity of group interactions following the patern described by Savage and Wood for pairwise solute-solute interactions in aqueous solutions.
- Kerstholt, Rene P. V.,Engberts, Jan B. F. N.,Blandamer, Michael J.
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- Influence of TiO2 Surface on 1,2-Chlorine Shift in β-Chlorine Substituted Radicals As Studied by Radiation Chemistry and Photocatalysis
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The influence of surface-specific parameters on the photocatalytically induced oxidative degradation of halogenated hydrocarbons in aqueous TiO2 suspensions has been evaluated by comparing the results obtained in this heterogeneous system with those from γ-irradiated homogeneous aqueous solutions.A 1,2-chlorine shift known to occur in β-chlorinated alkyl radicals and the products obtained upon degradation of these radicals (particularly various chloroacetic acids) have been used as markers in these investigations.The results indicated that this chlorine shift, e.g., the rearrangement of CCl3-CH2(.) -> (.)CCl2-CH2Cl, occurs much slower (k in the order of 106 s-1) at the TiO2 surface than the homogeneous solution, where the present data confirm earlier rate constants of >/=108 s-1.This slowdown of the rearrangement process is attributed to steric hindrance in the surface-adsorbed state of the radicals.In the heterogeneous systems the rearrangement can, in fact, be interfered with by peroxidation of the unrearranged radical in the presence of molecular oxygen while such a competition cannot be achieved in the homogeneous solution even at high O2 concentrations.Experimentally, this has been demonstrated, for example, by the fate of the (.)CHCl-CCl3 radical generated upon oxidative C-H cleavage from 1,1,1,2-tetrachloroethane.Direct oxygen addition to this species yields the (.)OOCHCl-CCl3 peroxyl radical which eventually degrades into CCl3COOH.After rearrangement ((.)CHCl-CCl3 -> CHCl2-CCl2(.)) and subsequent peroxidation the then formed CHCl2-CCl2OO(.) peroxyl radical ends up in a completely different acid, namely, CHCl2COOH.It could further be deduced that the 1,2-chlorine shift occurs via a bridged mechanism without transient liberation of the chlorine atom, thereby rendering an alternatively possible chlorine elimination/readdition mechanism an unlikely event.Finally, a marked pH dependence of the product distribution in both the γ-radiolytic and photocatalytic systems is suggested to reflect acid/base catalyzed hydrolysis processes en route of the radical degradation to their final products.
- Mao, Yun,Schoeneich, Christian,Asmus, Klaus-Dieter
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p. 8522 - 8529
(2007/10/02)
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- Identification of Organic Acids and Other Intermediates in Oxidative Degradation of Chlorinated Ethanes on TiO2 Surfaces en Route to Mineralization. A Combined Photocatalytic and Radiation Chemical Study
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The oxidative degradation of chlorinated ethanes proceeds practically via the same mechanism in γ-radiolysis and photocatalysis at TiO2 surfaces, respectively.C-centered radicals generated via hydroxyl radical induced C-H bond cleavage and peroxyl radicals derived therefrom after oxygen addition are the key radical intermediates in these processes.The main molecular products identified and isolated in both the γ-radiolytic and photocatalytic experiments are organic (mostly chlorinated) acids, HCl, and CO2.Other products formed in minor yields are aldehydes and HCOOH.Photocatalytic degradation of these product acids and nonionic substrates leads eventually to complete mineralization.The results strongly suggest that the photocatalytic degradation is initiated by an oxidation of the chlorinated compounds through TiO2-surface-adsorbed hydroxyl radicals.Only some acids, like trichloroacetic acid and oxalic acid, seem to be oxidized primarily by valence band holes via a photo-Kolbe process.Several rate constants are reported on the oxidation of chlorinated ethanes and acids by free and surface-adsorbed hydroxyl radicals and on the overall photocatalytic degradation of the chlorinated compounds.The paper also includes a discussion of the material balance.The study demonstrates the value of radiation chemical investigations for the understanding of the details in the photocatalytic mineralization process of halogenated organic compounds.
- Mao, Yun,Schoeneich, Christian,Asmus, Klaus-Dieter
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p. 10080 - 10089
(2007/10/02)
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- NEUTRAL HYDROLYSIS OF ESTERS
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The study of the kinetics of hydrolysis of acyl-activated esters in binary mixtures of water and organic solvents and in concentrated aqueous solutions of strong electrolytes showed that the reaction rate is a function of the concentration or activity of the water in the system and is described by an equation of the type kobs = n, where n varies from 2 to 5.A mechanism of the reaction whose transition state includes n molecules of water was proposed based on the data obtained.
- Neverov, A. A.,Deiko, S. A.,Yatsimirskii, A. K.
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p. 1107 - 1115
(2007/10/02)
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- Proton transfers among oxygen and nitrogen acids and bases in DMSO solution
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Rate constants for the proton-transfer reactions between conjugate acids and bases of several amines, phenols, carboxylic acids, and the solvated proton in DMSO-d6 at 20 °C have been determined by the use of NMR line-shape analysis. Equilibrium constants for the same reactions are obtained from the pKa's of the acids in dimethyl sulfoxide, some of which have been reported in earlier work and the rest obtained in the present work by use of Bordwell's indicator techniques. All of the reactions have rale constants considerably below expected diffusion-controlled limits for the proton transfers in the thermodynamically favorable direction, and several of the reactions, including the identity reactions of carboxylic acids, have kinetic deuterium isotope effects, kH/kD, between 0.8 and 1.3. For reactions of N,N-dimethylbenzylammonium ion with several phenoxides, carboxylates, and solvent, the rate constants for transfers in the unfavorable directions show a reasonable Bronsted correlation with β ≈ 1 and a reasonably constant reverse rate constant of ≈3 × 106 M-1 s-1. The data clearly indicate that the proton-transfer step is not rate-limiting in these reactions. Most likely, desolvation is involved in the rate-limiting steps, but the rate constants are not simple functions of acidities as might have been expected if hydrogen bonding of acid to solvent were the major factor involved in the solvation Other factors, particularly dispersion interactions of solvent with solutes, are discussed. We suggest that the formation of an acid-base complex with proper orientation to allow contact between the proton and the basic site is rate-determining and involves desolvation along with detailed steric interactions of the acid-base pair.
- Ritchie, Calvin D.,Lu, Shanzheng
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p. 7748 - 7756
(2007/10/02)
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- SYNTHESIS OF DICHLOROKETENE ACETALS UNDER CONDITIONS OF PHASE-TRANSFER CATALYSIS AND THEIR REACTIONS WITH SULFUR-CONTAINING ELECTROPHILES
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A method was developed for the production of dichloroketene acetals by the dehydrochlorination of chloral acetals in DMFA in the presence of triethylbenzylammonium chloride as phase-transfer catalyst.Sulfur monochloride, sulfur dichloride, and benzene sulfenyl chloride react with dichloroketene acetals with the formation of adducts (alkoxycarbonyldichloromethanesulfenyl chloride ClSCCl2COOR, alkoxycarbonyldichloromethanethiosulfenyl chloride ClSSCCl2COOR, and butyl phenylthiodichloroacetate C6H5SCCl2COOR respectively).The action of secondary amines on butoxycarbonyldichloromethanesulfenyl chloride gave sulfenamides R1R2NSCCl2COOBu.The reactions of butoxycarbonyldichloromethanethiosulfenyl chloride and butyl phenylthiodichloroacetate with secondary amines under various conditions led to degradation products.
- Guseva, S. A.,Mirskova, A. N.,Levkovskaya, G. G.,Kalikhman, I. D.,Voronkov, M. G.
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p. 261 - 268
(2007/10/02)
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- CHEMICAL CONVERSIONS OF TRICHLOROETHYLENE.
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The purpose of this work is to study the causes of decomposition of trichloroethylene under production conditions, and to investigate the products formed. Experimental results show that among the high-boiling impurities in technical trichloroethylene, dichloroacetic acid, dichloroacetyl chloride, and hexachlorobutene were isolated. Formation of hexachlorobutene in trichloroethylene on heating is initiated by peroxides present as impurities in trichloroethylene. Decrease of pH of the aqueous extract when trichloroethylene is heated presumably occurs mainly as the result of hydrolysis of dichloroacetyl chloride present in trichloroethylene or formed from intermediate products of trichloroethylene oxidation.
- Kolesnikov,Efremov,Danov,Putova,Sukhotin
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p. 1312 - 1314
(2007/10/02)
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- Kinetics and Mechanisms of the Neutral and Acid-catalysed Hydrolyses of Chloro-substituted Alkyl Acetates in Aqueous Solutions of Constant Ionic Strength
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The simultaneous neutral and acid-catalysed hydrolyses of different chloro-substituted alkyl acetates in water and in aqueous acetone solutions have been studied using electrolyte solutions of constant ionic strength.The mechanism of the acid-catalysed hydrolyses of monochloroesters is AAC2.When an ester has two chloro-substituents the acid-catalysed hydrolysis takes place simultaneously by the AAC2 and A-BAC3 mechanisms and in the case of trihalogenated esters the mechanism is A-BAC3, a mechanism with an unsymmetrically catalysed partition of the intermediate formed from the water-catalysed addition of water to the carbonyl group of the ester.Structural and solvent effects of these reactions are discussed.
- Euranto, Erkki K.,Kanerva, Liisa T.,Cleve, Nils J.
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p. 2085 - 2092
(2007/10/02)
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- Inhibition of Water-Catalyzed Ester Hydrilysis in Hydrophobic Microdomains of Poly(methacrylic acid) Hypercoils
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The water-catalyzed hydrolysis of p-methoxyphenyl dichloroacetate (1) and 2,2-dichloropropionate (2) in aqueous solution at 25 deg C is strongly retarded by neutral atactic (at) and syndiotactic (st) poly(methacrylic acid) (PMAA), but not by poly(acrylic acid) and poly(N-vinylpyrrolidone).The rates and thermodynamic activation parameters are consistent with binding of the substrates to hydrophobic microdomains within the PMAA hypercoil.A conformational transition of PMAA to an extended coil leads to disappearance of the rate inhibition.This transition is induced either by ionization of PMAA or, at constant pH (ca. 3), by addition of urea and can be monitored by potentiometric titrations.Solubility measurements employing the water-insoluble dye Orange OT further established hydrophobic bonding to neutral at-PMAA.Whereas inhibition of the hydrolysis of 1 and 2 in water in the presence of hydrophobic cosolvents or micelles is characterized by initial-state stabilization, it appears that the inhibition by at- and st-PMAA primarily involves destabilization of the transition state.The effect of PMAA may be explained in terms of a lack of water penetration into the hydrophobic microdomains.
- Jager, Jan,Engberts, Jan B. F. N.
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p. 3331 - 3334
(2007/10/02)
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