- Kinetic Study and Mechanism Hydrolysis of 4-Bromo-3,5 dimethylphenyl?N-methylcarbamate in Aqueous Media
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Degradation via hydrolysis is among the main transformation pathways and particularly for N-methylcarbamates. Carbamate pesticide hydrolysis is known to proceed through alkaline catalysis, with reaction of the hydroxide ion with the carbonyl function or with abstraction of hydrogen in the α position with respect to the carbonyl. This reaction leads to the formation of methylamine and corresponding phenol. In this respect, the reaction kinetics of 4-bromo-3,5-dimethylphenyl?N-methylcarbamate (BDMC) hydrolysis have been investigated in alkaline solution using a spectrophotometric technique and reversed phase liquid chromatography. The kinetic constants were determined following a proposed pseudo–first-order kinetic model. The positive activation entropy ΔS≠ = +35.73 J mol?1 K?1 and the absence of general base catalysis indicated an unimolecular elimination conjugate base (E1cB) hydrolytic mechanism involving the formation of methyl isocyanate. This result was confirmed by the fact that BDMC fits well into br?nsted and Hammett lines, obtained for a series of substituted N-methylcarbamate whose decomposition in aqueous media was established to follow an E1cB mechanism.
- Attig, Jihène Ben,Ouertani, Randa,Megriche, Adel,Hamida, Néjib Ben,El Atrache, Latifa Latrous
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- Regioselective monobromination of phenols with KBr and ZnAl–BrO3?–layered double hydroxides
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The regioselective mono-bromination of phenols has been successfully developed with KBr and ZnAl–BrO3?–layered double hydroxides (abbreviated as ZnAl–BrO3?–LDHs) as brominating reagents. The para site is much favorable and the ortho site takes the priority if para site is occupied. This reaction featured with excellent regioselectivity, cheap brominating reagents, mild reaction condition, high atom economy, broad substrate scope, and provided an efficient method to synthesize bromophenols.
- Wang, Ligeng,Feng, Chun,Zhang, Yan,Hu, Jun
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supporting information
(2020/02/22)
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- IPSO-hydroxylation of boronic acid via ozonolysis: A metal-, ligand-, and base-free method
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Here, we have developed a simple, efficient, and metal-, ligand-, and base-free method for the synthesis of functionalized aryl and alicyclic alcohols via ozonolysis of corresponding boronic acids in aqueous ethanol. The procedure is compatible with a variety of functional groups and can be utilized as an alternative method for the synthesis of hydroxy arenes and alicyclic alcohols.
- Bommegowda, Yadaganahalli K.,Mallesha, Ningegowda,Vinayaka, Ajjampura C.,Sadashiva, Maralinganadoddi P.
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supporting information
p. 268 - 270
(2016/05/02)
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- The synthesis of 1,2-ethanediylbis(triphenylphosphonium) ditribromide as a new brominating agent in the presence of solvents and under solvent-free conditions
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Abstract: 1,2-Ethanediylbis(triphenylphosphonium) ditribromide was quantitatively prepared and used for the bromination of anilines and phenols in the presence of a mixed solvent system (DCM/MeOH 2:1) and also under solvent-free conditions. This new ionic liquid has advantages over similar brominating agents in terms of short reaction time, simple workup, regioselectivity and high yields. Single-crystal X-ray analysis of title salt revealed that the bistriphenylphosphonium cation is organized around an inversion center located at the center of the –CH2–CH2– bridge and the two triphenylphosphine segments are anti with respect to one another. All the tribromide anions adopt a linear geometry with different Br–Br–Br bond angles for each anion. Graphical Abstract: [Figure not available: see fulltext.]
- Salmasi, Reihaneh,Gholizadeh, Mostafa,Salimi, Alireza,Garrison, Jered C.
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p. 2019 - 2028
(2016/09/16)
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- Compound and application thereof
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The invention discloses a compound and application thereof. The compound is the compound shown in the formula (I) or a stereoisomer or a pharmaceutical acceptable salt or solvate or a prodrug of the compound shown in the formula (I). The compound can restrain tumor cell proliferation through the effect RRM2, and restrain tumor stem cell regeneration, thereby being effectively used for preparing medicine for preventing or treating proliferative diseases and particularly anti-cancer medicine.
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Paragraph 0709
(2016/10/09)
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- Synthesis of deuterated benzopyran derivatives as selective COX-2 inhibitors with improved pharmacokinetic properties
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We designed a series of specifically deuterated benzopyran analogues as new COX-2 inhibitors with the aim of improving their pharmacokinetic properties. As expected, the deuterated compounds retained potency and selectivity for COX-2. The new molecules possess improved pharmacokinetic profiles in rats compared to their nondeuterated congeners. Most importantly, the new compounds showed pharmacodynamic efficacy in several murine models of inflammation and pain. The benzopyran derivatives were separated into their enantiomers, and the activity was found to reside with the S-isomers. To streamline the synthesis of the desired S-isomers, an organocatalytic asymmetric domino oxa-Michael/aldol condensation reaction was developed for their preparation.
- Zhang, Yanmei,Tortorella, Micky D.,Wang, Yican,Liu, Jianqi,Tu, Zhengchao,Liu, Xiaorong,Bai, Yang,Wen, Dingsheng,Lu, Xin,Lu, Yongzhi,Talley, John J.
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p. 1162 - 1166
(2014/12/10)
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- Lewis acid promoted construction of chromen-4-one and isoflavone scaffolds via regio- and chemoselective domino Friedel-Crafts acylation/Allan-Robinson reaction
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A facile and efficient synthesis of chromen-4-one and isoflavone frameworks is achieved by the domino C-acylation/O-acylation/aldolization sequence. This operationally simple one-pot elegant strategy provides structurally unique chromen-4-ones and isoflavones directly from phenols via concomitant formation of multiple C-C and C-O bonds in a single operation. The outcomes of the buttressing effect, substituent dependence, and catalyst and solvent specificity during the course of the Friedel-Crafts acylation reactions are demonstrated and supported by fitting experiments.
- Chanda, Tanmoy,Chowdhury, Sushobhan,Koley, Suvajit,Anand, Namrata,Singh, Maya Shankar
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supporting information
p. 9216 - 9222
(2014/12/11)
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- Selectivity enhancement of aromatic halogenation reactions at the micellar interface: Effect of highly ionic media
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Halogenation (iodination and bromination) of various aromatic compounds has been studied in micellar media in order to observe the effect on regioselectivity and conversion of the reaction. The addition of surfactant causes a change in the chemical shifts of the aromatic proton resonance of phenol which proves the orientation of the aromatic compound on the micellar surface. However, increase in ionic strength of the reaction media affects the selectivity of reaction by disturbing this spatial orientation of the aromatic compound in the micelle. Selectivity towards particular isomers is dependent on the concentration of the surfactant. In bromination of chlorobenzene (deactivated aromatic compound) enhancement in selectivity and conversion towards the para isomer has been observed.
- Samant, Bhupesh S.,Bhagwat, Sunil S.
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scheme or table
p. 1039 - 1044
(2012/10/18)
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- Bifunctional Aryloxylate Esters as potential oxidatively cleavable linkers
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Selectively cleavable linkers are essential parts in environmentally responsive materials. Here, we introduce aryl oxalate esters (AOE) as one of the first examples for oxidatively cleavable linkers. To this end a series of novel AOEs was synthesized and explored regarding the H2O 2-dependent degradation. All AOEs were cleaved selectively at the oxalate group. The degradation rate was clearly dependent on the substituents. Further, it was found that the H2O2 based degradation undergoes an autocatalysis mechanism.
- Czarnecki,Kampert,Barbe,Tiller
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scheme or table
p. 3551 - 3554
(2011/07/29)
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- Aerobic oxybromination of phenols catalyzed by sodium nitrite under mild conditions
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An efficient catalytic system for oxybromination of phenols under mild conditions has been developed, which utilizes sodium nitrite as the catalyst, dioxygen or air as the terminal oxidant, aqueous hydrobromic acid or molecular bromine as the bromine resource. From both the atom-economic and environmental points of view, the developed protocol is expected to provide a valuable synthetic method for practical applications in laboratory or industry. Georg Thieme Verlag Stuttgart - New York.
- Xu, Li,Wang, Yong,Wen, Xin,Ding, Chengrong,Zhang, Guofu,Liang, Xinmiao
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supporting information; experimental part
p. 2265 - 2269
(2011/10/31)
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- Chemo-and regioselective bromination of aromatic compounds in the presence of γ-picolinium bromochromate (γ-PBC)/CH3CN
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Regioselective oxidative bromination of activated aromatic compounds has been studied using γ-Picolinium bromochromate in either CH3COOH or CH3CN is reported. The results obtained revealed excellent yields of monobromo compounds at para-position under thermal condition especially in methyl cyanide.
- Mahmoodi,Yazdanbakhsh,Hassanzadeh
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experimental part
p. 429 - 434
(2012/04/04)
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- Synthesis of arylbromides from arenes and Nbromosuccinimide bromosuccinimide (NBS) in acetonitrile - A convenient method for aromatic bromination
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Regioselective and chemoselective electrophilic bromination of a wide series of activated arenes using N-bromosuccinimide (NBS) in acetonitrile occurs readily. Environmentally friendly conditions, large substrate scope, and ease of synthesis enhance the utility of this method over other electrophilic bromination conditions.
- Zysman-Colman, Eli,Arias, Karla,Siegel, Jay S.
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experimental part
p. 440 - 447
(2009/12/01)
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- First synthesis of nitro-substituted 2,2-diphenyl-2H-1-benzopyrans via the ipso-nitration reaction
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The first synthesis of a series of nitro-substituted 2,2-diphenyl-2H-1-benzopyrans is reported. Our synthetic approach is based on a linear synthesis in two steps from appropriate brominated 2,2-diphenyl-2H-1-benzopyrans 12-17, which requires the preliminary preparation of bromophenols 7-11. These latter were easily obtained by the reaction of phenols 1-5 with a mild and selective brominating agent tetrabutylammonium tribromide (TBA·Br3). The key intermediates 12-17 were efficiently elaborated through an univocal classic chromenization between the commercially available 1,1-diphenyl-2-yn-1-ol and the brominated phenols 6-11. The compounds 12-17 so obtained were converted into arylboronic acids 18-23 by a metalation/boronylation sequence, followed by acid hydrolysis. From advanced building blocks 18-23, the introduction of nitro group, which constitutes the ultimate step of our strategy, was achieved by an ipso-nitration reaction using the Crivello's reagent. This highly selective method provides only the ipso-nitrated products 24-29 in moderate to high yield.
- Bougdid, Lahoussine,Heynderickx, Arnault,Delbaere, Stéphanie,Moustrou, Corinne
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p. 8242 - 8249
(2008/02/05)
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- SOLVENT CONTAINING 1,2,5-THIADIAZOLE COMPOUND, AND METHOD FOR EXTRACTING AN ORGANIC COMPOUND USING THE SOLVENT
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The object of the present invention is to provide a solvent which is free from the risk of destroying the ozone layer surrounding the Earth, hardly toxic, and free from the risk of causing environment pollution problems by polluting underground water or air. The solvent contains at least one chosen from 1,2,5-thiadiazole compounds represented by formula (1) below: (where R1 and R2 each represent hydrogen or methyl group).
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Page/Page column 11-12
(2010/11/25)
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- Application of the Suzuki reaction as the key step in the synthesis of a novel atropisomeric biphenyl derivative for use as a liquid crystal dopant
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A heavily functionalized atropisomeric biphenyl derivative (4), which is designed to possess a large lateral dipole moment, has been synthesized with use of a Suzuki coupling as the key step and resolved by chiral HPLC. The final coupling reaction is complicated by rapid hydrolytic deboronation of the sterically hindered, electron poor boronate 22. Rigorously anhydrous conditions are therefore necessary to achieve the coupling.
- Cammidge, Andrew N.,Crepy, Karen V. L.
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p. 6832 - 6835
(2007/10/03)
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- Bromide ions and methyltrioxorhenium as cocatalysts for hydrogen peroxide oxidations and brominations
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Oxidation of alcohols by hydrogen peroxide is negligible; even when catalyzed by methyltrioxorhenium (MTO), the process requires a long reaction time. The addition of a catalytic quantity of bromide ions, as HBr or NaBr, greatly enhances the rate. Some of the reactions were carried out on a larger scale in glacial acetic acid, and others at kinetic concentrations. The data establish that Br2 is the active oxidizing agent in the system, because the catalytic rates under suitable circumstances match those for the independently measured Br2 reaction with alcohol (benzyl alcohol, in particular). At much lower levels of MTO, however, Br2 formation plays a role in the kinetics. Certain other reluctant transformations are conveniently carried out with the MTO/H2O2/Br- combination: aldehydes to methyl esters; 1,3-dioxolanes to glycol monoesters; and ethers (with cleavage) to ketones (mostly), but in fair yield only. When Br- was used in stoichiometric quantity, certain bromination reactions occur. Thus, phenyl acetylenes (PhC2R, R = H, Me, Ph) are converted to dibromoalkenes that are entirely or largely formed as the trans isomer, and phenols are brominated. The latter reaction shows the preference para > ortho > meta. Kinetic studies of benzyl alcohol oxidation with MTO/H2O2Br- were carried out in aqueous solution. With sufficient (normal) levels of MTO, the rate constant for the formation of benzaldehyde agreed with the independently determined value for Br2 + PhCH2OH, k = 4.3 x 10-3 L mol-1 s-1 at 25.0 °C; for sec- phenethyl alcohol, k = (9.8 ± 0.4) x 10-3 L mol-1 s-1. Bromine is formed from the known oxidation of Br- with H2O2, catalyzed by MTO. This reaction results in BrO-/HBOr, which is then rapidly converted to Br2. However, with substantially lower concentrations of MTO, the buildup of benzaldehyde is ca. 4-fold slower, reflecting the diminished rate of Br- oxidation.
- Espenson,Zhu,Zauche
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p. 1191 - 1196
(2007/10/03)
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- N-substituted aminotriphenylphosphonium tribromides as novel brominating agents
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A number of N-substituted aminotriphenylphosphonium tribromides were investigated for their brominating ability of substituted phenols. It was found that t-butylaminotriphenylphosphonium tribromide, I, exhibits a good and a rather high regiospecificity in comparison with the commonly used bromine.
- Amer, Adel,Mayer, Andrea,Conroy, Gary M.,Zimmer, Hans
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p. 245 - 248
(2007/10/03)
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- Solid-state Nuclear Bromination of Some Phenols by N-Bromosuccinimide
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Treatment of crystalline dimethylphenols and hydroquinones with N-bromosuccinimide leads rapidly and regioselectively to ring-substituted products.
- Goud, B. Satish,Desiraju, Gautam R.
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p. 244 - 245
(2007/10/03)
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- Hindered organoboron groups in organic chemistry. 27. Preparations and some properties of alkylbis(2,6-dimethyl-4-methoxyphenyl)boranes ((DMP)2BR)
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Akylbis(2,6-dimethyl-4-methoxyphenyl)boranes ((DMP)2BR) have been synthesized in an attempt to overcome the limitations of the steric hindrance approach to the production of boron stabilised carbanions. Anion production from (DMP)2BR, followed by alkylations and condensations with aldehydes are reported. Reduction of (DMP)2F with potassium hydride yields the corresponding hydroborate. Attempts to isolate (DMP)2BH were unsuccessful but the borane was readily trapped with alkynes, yielding alkenylboranes. The allyl derivative, (DMP)2BAllyl, was made and some of its reactions were investigated.
- Pelter, Andrew,Drake, Robert
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p. 13775 - 13800
(2007/10/02)
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- Selective para-Bromination of Phenols via a Regenerable Polymer-bound Tetraalkylammonium Tribromide
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Amberlyst-A26 resin in its tribromide form effects para-bromination of phenols with high yields and selectivity; the resin is easily recovered by filtration and can be reconverted into the tribromide form by addition of bromine.
- Smith, Keith,James, D. Martin,Matthews, Ian,Bye, Martin R.
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p. 1877 - 1878
(2007/10/02)
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- Halogenation Using Quaternary Ammonium Polyhalides. IV. Selective Bromination of Phenols by Use of Tetraalkylammonium Tribromides
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Reaction of phenols with calculated amounts of benzyltrimethylammonium tribromide or tetrabutylammonium tribromide in dichloromethane-methanol for 0.5-1 h under mild conditions gave, selectively, the objective mono-, di-, or tribromophenols in good yields.
- Kajigaeshi, Shoji,Kakinami, Takaaki,Okamoto, Tsuyoshi,Nakamura, Hiroko,Fujikawa, Masahiro
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p. 4187 - 4189
(2007/10/02)
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- Observation of Transient Cyclohexadienones during the Aqueous Bromination of Phenols
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Transient 4-bromo-2,5-cyclohexadienone intermediates have been observed during the aqueous bromination of phenol and several methylated derivatives.They enolize to the corresponding p-bromophenols by both acid-catalyzed and water-catalyzed pathways in the pH range 0-6.Studies carried out in buffers also indicate both general acid catalysis (α ca 0.0) and general base catalysis (β=0.54).The latter is ascribed to simple rate-limiting proton abstraction, but the former is not so easily rationalized.The very low α is attributed to a termolecular transition state (water, substrate, and general acid) in which the dienone becomes more anion-like than cation like.This seemingly anomalous behaviour can be explained by the very large enol/keto ratio (ca. 1011) for phenol.
- Tee, Oswald S.,Iyengar, N. Rani
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p. 455 - 459
(2007/10/02)
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- Vinyl Cation Intermediates in Solvolytic and Electrophilic Reactions. 1. Solvolysis of α-Arylvinyl Derivatives
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The solvolysis of 16 α-arylvinyl tosylates, bromides, and chlorides has been investigated in various alcohol-water mixtures and in acetic acid at several temperatures.All substrates were substituted with either 2-methyl or 2,6-dimethyl groups to accelerate the rates of reaction.The major or exclusive product isolated in most cases was the acetophenone arising from hydrolysis of the expected enol ethers or acetates during workup.The kinetics were simple first order in the vast majority of cases, with excess base added to prevent side reactions.Leaving group effects, Winstein-Grunwald m values, Schleyer Q values, and effects of solvent nucleophilicity all point to a limiting SN1 ionization generating a vinyl cation intermediate, in which there is little rear-side nucleophilic assistance by solvent.Substituent effects led to ρ values in the range -3.9 to -5.3 vs. ?+.Activation parameters are typical for an SN1 process, and ΔS% is insensitive to the presence of zero, one, or two o-methyl groups, as are the effects of solvent polarity on the rates.The results should therefore be directly comparable with other solvolytic or electrophilic reactions generating formally similar vinyl cation intermediates.
- Yates, Keith,Mandrapilias, George
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p. 3892 - 3902
(2007/10/02)
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