- Characterization of chlorinated adducts of hemoglobin and albumin following administration of pentachlorophenol to rats
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Five cysteinyl adducts (including one with multiple isomeric forms) of hemoglobin (Hb) and albumin (Alb) have been characterized in the blood of Sprague-Dawley rats following administration of pentachlorophenol (PCP). Three of these adducts were formed by multiple substitution reactions of tetrachloro-1,4-benzoquinone (Cl4-1,4-BQ) and its products, and two arose from reactions of tetrachloro-1,4-benzosemiquinone (Cl4-1,4-SQ) and tetrachloro-1,2-benzosemiquinone (Cl4-1,2-SQ). Adducts of tetrachloro-1,2- benzoquinone (Cl4-1,2-BQ) were not observed. Regarding adducts of Cl4-1,4- BQ and its products, specific structures were assigned to monosubstituted, disubstituted, and trisubstituted adducts of Hb and Alb following modification of rat blood with Cl4-1,4-BQ (0-45 μM) in vitro and after metabolism of PCP (0-40 mg/kg body weight) in Sprague-Dawley rats, in vivo. The formation of all adducts was linear over the ranges tested, with Alb adducts being more abundant than Hb adducts. The levels of the adducts measured were in the following order: monosubstituted > disubstituted > trisubstituted. The observation that Cl4-1,4-BQ can produce multisubstituted adducts with proteins suggests that protein-protein cross links may be formed, with inherent toxicological implications. Regarding adducts of the semiquinones (detected only in vivo), linear production of Hb and Alb adducts was observed with increasing dosage of PCP for adducts of both Cl41,4-SQ and Cl4-1,2-SQ. Higher levels of the semiquinone adducts were observed in Hb than in Alb, in contrast to the results with the quinone adducts. In a separate in vivo experiment (20 mg PCP/kg body weight), where animals were sacrificed at intervals up to 336 h postadministration, adducts were eliminated at rates which were comparable among the different adducts of a given protein.
- Waidyanatha, Suramya,Lin, Po-Hsiung,Rappaport, Stephen M.
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- Photoaccelerated oxidation of chlorinated phenols
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Exposure to visible light increases the rate of oxidation of chlorinated phenols by hydrogen peroxide in aqueous solution in either the presence or the absence of iron-based catalysts, which may be explained by the aqueous photoreactions of chloroquinone intermediates.
- Lente, Gabor,Espenson, James H.
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- Chlorine atom substitution influences radical scavenging activity of 6-chromanol
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Synthetic 6-chromanol derivatives were prepared with several chlorine substitutions, which conferred both electron-withdrawing inductive effects and electron-donating resonance effects. A trichlorinated compound (2), a dichlorinated compound (3), and three monochlorinated compounds (4, 5, and 6) were synthesized; compounds 2, 3, and 6 were novel. The antioxidant activities of the compounds, evaluated in terms of their capacities to scavenge galvinoxyl radical, were associated with the number and positioning of chlorine atoms in the aromatic ring of 6-chromanol. The activity of compound 1 (2,2-dimethyl-6-chromanol) was slightly higher than the activities of compounds 2 (2,2-dimethyl-5,7-dichloro-6-chromanol) or 3 (2,2-dimethyl-5,7,8-trichloro-6- chromanol), in which the chlorine atoms were ortho to the phenolic hydroxyl group of 6-chromanol. The scavenging activity of compound 3 was slightly higher than that of 2, which contained an additional chlorine substituted in the 8 position. The activities of polychlorinated compounds 2 and 3 were higher than the activities of any of the monochlorinated compounds (4-6). Compound 6, in which a chlorine was substituted in the 8 position, exhibited the lowest activity. Substitution of a chlorine atom meta to the hydroxyl group of 6-chromanol (compounds 2 and 6) decreased galvinoxyl radical scavenging activity, owing to the electron-withdrawing inductive effect of chlorine. Positioning the chloro group ortho to the hydroxyl group (compounds 4 and 5) retained antioxidant activity because the intermediate radical was stabilized by the electron-donating resonance effect of chlorine in spite of the electron-withdrawing inductive effect of chlorine. Antioxidant activities of the synthesized compounds were evaluated for correlations with the O-H bond dissociation energies (BDEs) and the ionization potentials. The BDEs correlated with the second-order rate constants (k) in the reaction between galvinoxyl radical and the chlorinated 6-chromanol derivatives in acetonitrile. This indicated that the antioxidant mechanism of the synthesized compounds consisted of a one-step hydrogen atom transfer from the phenolic OH group rather than an electron transfer followed by a proton transfer. The synthesized compounds also exhibited hydroxyl radical scavenging capacities in aqueous solution.
- Inami, Keiko,Iizuka, Yuko,Furukawa, Miyuki,Nakanishi, Ikuo,Ohkubo, Kei,Fukuhara, Kiyoshi,Fukuzumi, Shunichi,Mochizuki, Masataka
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- Light induced elimination of mono- and polychlorinated phenols from aqueous solutions by PW12O403-. The case of 2,4,6-trichlorophenol
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PW12O403- was used as catalyst in the photodegradation of polychlorinated phenols (2,4-dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6-DCP), 3,4-dichlorophenol (3,4-DCP), 3,5-dichlorophenol (3,5-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP)). Photolysis in 270-290 nm led to the photodecomposition of chlorophenols while the addition of PW12O403- to oxygenated solutions accelerated the photodecomposition. Chlorination of phenol generally enhanced photodecomposition rates while the effect of chlorine substituents in the ortho position was less pronounced. A detailed study of 2,4,6-TCP photodecomposition showed that the major reactions involved hydroxylation of the aromatic ring, substitution of chlorine by OH, oxidation of chlorinated HQ to the corresponding quinone, and breaking of the aromatic ring to produce carboxylic acids, such as maleic, oxalic, acetic and formic acids. The ultimate products were CO2, H2O and Cl-.
- Papaconstantinou,Androulaki,Minero,Androulaki,Dimotikali,Pelizzetti,Hiskia
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- Geometrically specific hydrogen transfer in the reaction of terminally alkyl-substituted 1,3-dienes with 1,4-quinones
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Reaction of certain geometrically defined 1,1-dioxy-4-alkyl- and -4,4-dialkyl-substituted buta-l,3-dienes with halogenated quinones does not involve Diels-Alder or Michael addition chemistry. Instead, rapid competitive oxidation of the dienes to give 2,4-dienoate esters was observed. This new reaction involves strong spatial association between diene and quinone, hydrogen being transferred specifically from the (4E)-alkyl group. Its scope is compared with addition of the same terminally substituted dienes towards the reactive non-quinonoid dienophile tetracyanoethylene. CSIRO 2000.
- Cameron, Donald W.,Heisey, Ross M.
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- Photochemical transformations of 2, 6-dichlorophenol and 2-chlorophenol with superoxide ions in the atmospheric aqueous phase
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The possible photochemical transformation pathways of chlorophenols (2, 6-dichlorophenol and 2-chlorophenol) with superoxide anion radical (O2·?) were studied by steady-state irradiation and 355 nm laser flash photolysis technique. O
- Dong, Linchang,Hu, Shuheng,Lu, Jun,Peng, Shuchuan,Zhu, Chengzhu,Zhu, Mengyu
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- Electrochemical oxidation of diclofenac on CNT and M/CNT modified electrodes
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The electrochemical oxidation of diclofenac (DCF), a non-steroidal anti-inflammatory drug considered as an emerging pollutant (frequently detected in wastewater), was investigated on CNT, Pt/CNT and Ru/CNT modified electrodes based on Carbon Toray in aqueous media. The electroreactivity of DCF on these modified electrodes was studied using cyclic voltammetry and the kinetic parameters were calculated from the scan rate study. Cyclic voltammograms show several oxidation processes, which confirm the interaction between DCF and the catalyst surface necessary for direct oxidation processes. Constant potential electrolysis of DCF was carried out on carbon nanotubes (CNT) and metal supported CNT (M/CNT) modified electrodes, in 0.1 M NaOH and 0.1 M Na2CO3/NaHCO3buffer media. The highest DCF conversion (88% after 8 h of electrolysis) was found in carbonate buffer medium, for Ru/CNT, while the best carbon mineralization efficiency (corresponding to 48% of the oxidized DCF) was obtained on Pt/CNT modified electrode in 0.1 M NaOH medium. The products of the electrolyses were identified and quantified by HPLC-MS, GC-MS, HPLC-UV-RID and IC. The results show the presence of some low molecular weight carboxylic acids, confirming the cleavage of the aromatic rings during the oxidation process.
- Ferreira, M.,Figueiredo, J. L.,Fonseca, A. M.,Güney, S.,Ku?niarska-Biernacka, I.,Neves, I. C.,Parpot, P.,Pereira, M. F. R.,Soares, O. S. G. P.
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p. 12622 - 12633
(2021/07/25)
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- TiO2-modified MALDI target for in vitro modeling of the oxidative biotransformation of diclofenac
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The UV-induced photocatalytic oxidation in the presence of TiO2 nanoparticles (UV/TiO2-PCO) is a more adequate approach than electrochemical oxidation to simulate the oxidative metabolism of diclofenac based on the comparative analysis of oxidation products using high-resolution tandem mass spectrometry. A simple and fast high-throughput technique is proposed for modeling the oxidative metabolism, which involves UV/TiO2-PCO performed directly on a MALDI target and subsequent analysis by matrix-assisted laser desorption/ionization mass spectrometry. The ranges and yields of diclofenac oxidation products obtained by the conventional bulk UV/TiO2-PCO and the proposed on-target version are in excellent agreement.
- Babakov, Vladimir N.,Bardin, Alexander A.,Gorbunov, Alexander Yu.,Keltsieva, Olga A.,Krasnov, Konstantin A.,Podolskaya, Ekaterina P.
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p. 220 - 222
(2020/05/25)
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- Catalytic Electrophilic Alkylation of p-Quinones through a Redox Chain Reaction
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Allylation and benzylation of p-quinones was achieved through an unusual redox chain reaction. Mechanistic studies suggest that the existence of trace hydroquinone initiates a redox chain reaction that consists of a Lewis acid catalyzed Friedel–Crafts alkylation and a subsequent redox equilibrium that regenerates hydroquinone. The electrophiles could be various allylic and benzylic esters. The addition of Hantzsch ester as an initiator improves the efficiency of the reaction.
- Xu, Xiao-Long,Li, Zhi
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supporting information
p. 8196 - 8200
(2017/06/30)
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- Kinetic mechanism of the dechlorinating flavin-dependent monooxygenase HadA
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The accumulation of chlorophenols (CPs) in the environment, due to their wide use as agrochemicals, has become a serious environmental problem. These organic halides can be degraded by aerobic microorganisms, where the initial steps of various biodegradation pathways include an oxidative dechlorinating process in which chloride is replaced by a hydroxyl substituent. Harnessing these dechlorinating processes could provide an opportunity for environmental remediation, but detailed catalytic mechanisms for these enzymes are not yet known. To close this gap, we now report transient kinetics and product analysis of the dechlorinating flavin-dependent monooxygenase, HadA, from the aerobic organism Ralstonia pickettii DTP0602, identifying several mechanistic properties that differ from other enzymes in the same class. We first overexpressed and purified HadA to homogeneity. Analyses of the products from single and multiple turnover reactions demonstrated thatHadAprefers 4-CP and 2-CP over CPs with multiple substituents. Stopped-flow and rapid-quench flow experiments of HadA with 4-CP show the involvement of specific intermediates (C4a-hydroperoxy-FAD and C4a-hydroxy-FAD) in the reaction, define rate constants and the order of substrate binding, and demonstrate that the hydroxylation step occurs prior to chloride elimination. The data also identify the non-productive and productive paths of the HadA reactions and demonstrate that product formation is the rate-limiting step. This is the first elucidation of the kinetic mechanism of a two-component flavin-dependent monooxygenase that can catalyze oxidative dechlorination of various CPs, and as such it will serve as the basis for future investigation of enzyme variants that will be useful for applications in detoxifying chemicals hazardous to human health.
- Pimviriyakul, Panu,Thotsaporn, Kittisak,Sucharitakul, Jeerus,Chaiyen, Pimchai
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p. 4818 - 4832
(2017/04/03)
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- A detailed kinetic study of the direct photooxidation of 2,4,6-trichlorophenol
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The direct photodegradation of 2,4,6-trichlorophenol (TCP) by UV–vis light was studied in aqueous solution in order to analyze the mechanism of the photochemical process and to determine the kinetic parameters including the quantum yield. Based on initial rate studies at different overall volumes and illumination patterns, it was proved that the rate of the process is directly proportional to the intensity of irradiating light. A significant, but moderate acceleration of the reaction rate with increasing temperature was revealed between 5.0 and 35.0?°C, which could be interpreted readily by assuming that the excited state of TCP is involved in two competing processes. High pressure liquid chromatography and mass spectrometry provided us information on the nature of the intermediates and the products formed. 2,6-Dichloro-1,4-benzoquinone, 3,5-dichloro-2-hydroxy-1,4-benzoquinone and 2,6-dihclorohydroxyquinone were detected as products and/or intermediates, and there were also hints of the formation of 3,5-dichlorobenzene-1,2-diol and 3,5-dichloro-1,2-benzoquinone. A possible degradation mechanism is proposed to interpret the kinetic findings.
- Pino-Chamorro, Jose ángel,Ditrói, Tamás,Lente, Gábor,Fábián, István
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- Cycloacylation of chloro-substituted hydroquinone dimethyl ethers with dichloromaleic anhydride
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Under the drastic conditions of Zahn—Ochwat cycloacylation of 2-chloroand 2,3-dichlorohydroquinones with dichloromaleic anhydride (a melt of anhydrous AlCl3 and NaCl, 185—195 °C), the substrates undergo various degrees of disproportionation, which reduces the yields of the target triand tetrachloronaphthazarins. Quantum chemical calculations showed that the cycloacylation in question proceeds as a double aromatic electrophilic substitution of the vicinal protons with the corresponding oxocarbenium ions (acylium cations).
- Novikov,Balaneva,Shestak,Anufriev, V. Ph.,Glazunov
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p. 993 - 1003
(2017/01/11)
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- Halogenated volatiles from the fungus Geniculosporium and the actinomycete Streptomyces chartreusis
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Two unidentified chlorinated volatiles X and Y were detected in headspace extracts of the fungus Geniculosporium. Their mass spectra pointed to the structures of a chlorodimethoxybenzene for X and a dichlorodimethoxybenzene for Y. The mass spectra of some constitutional isomers for X and Y were included in our databases and proved to be very similar, thus preventing a full structural assignment. For unambiguous structure elucidation all possible constitutional isomers for X and Y were obtained by synthesis or from commercial suppliers. Comparison of mass spectra and GC retention times rigorously established the structures of the two chlorinated volatiles. Chlorinated volatiles are not very widespread, but brominated or even iodinated volatiles are even more rare. Surprisingly, headspace extracts from Streptomyces chartreusis contained methyl 2-iodobenzoate, a new natural product that adds to the small family of iodinated natural products.
- Wang, Tao,Rabe, Patrick,Citron, Christian A.,Dickschat, Jeroen S.
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supporting information
p. 2767 - 2777
(2014/01/06)
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- PROCESS FOR THE PREPARATION OF HYDROQUINONES
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The invention relates to a process for the preparation of a hydroquinone compound of formula (I) wherein R2, R3, R5 and R6 have the meaning according to claim 1, with the steps of formylating a substituted phenol and oxidising the resulting substituted 4-hydroxy- benzaldehyde under acidic conditions to the corresponding hydroquinone of formula (I). Another object of the invention concerns the intermediate 2,3,5-trimethyl-4-hydroxy- benzaldehyde for synthesis of 2,3,5-trimethyl-hydroquinone (TMHQ) and (dl)cc-tocopherol.
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Page/Page column 14
(2011/11/01)
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- Substrate specificity of Sphingobium chlorophenolicum 2,6- dichlorohydroquinone 1,2-dioxygenase
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PcpA is an aromatic ring-cleaving dioxygenase that is homologous to the well-characterized Fe(II)-dependent catechol extradiol dioxygenases. This enzyme catalyzes the oxidative cleavage of 2,6-dichlorohydroquinone in the catabolism of pentachlorophenol by Sphingobium chlorophenolicum ATCC 39723. 1H NMR and steady-state kinetics were used to determine the regiospecificity of ring cleavage and the substrate specificity of the enzyme. PcpA exhibits a high degree of substrate specificity for 2,6-disubstituted hydroquinones, with halogens greatly preferred at those positions. Notably, the kcat app/KmAapp of 2,6-dichlorohydroquinone is ~40-fold higher than that of 2,6-dimethylhydroquinone. The asymmetric substrate 2-chloro-6-methylhydroquinone yields a mixture of 1,2- and 1,6-cleavage products. These two modes of cleavage have different K mO2app values (21 and 260 μM, respectively), consistent with a mechanism in which the substrate binds in two catalytically productive orientations. In contrast, monosubstituted hydroquinones show a limited amount of ring cleavage but rapidly inactivate the enzyme in an O2-dependent fashion, suggesting that oxidation of the Fe(II) may be the cause. Potent inhibitors of PcpA include ortho-disubstituted phenols and 3-bromocatechol. 2,6-Dibromophenol is the strongest competitive inhibitor, consistent with PcpA's substrate specificity. Several factors that could yield this specificity for halogen substituents are discussed. Interestingly, 3-bromocatechol also inactivates the enzyme, while 2,6-dihalophenols do not, indicating a requirement for two hydroxyl groups for ring cleavage and for enzyme inactivation. These results provide mechanistic insights into the hydroquinone dioxygenases.
- MacHonkin, Timothy E.,Doerner, Amy E.
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body text
p. 8899 - 8913
(2012/05/05)
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- Characterization of chlorophenol 4-monooxygenase (TftD) and NADH:FAD oxidoreductase (TftC) of burkholderia cepacia AC1100
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Burkholderia cepacia AC1100 completely degrades 2,4,5-trichlorophenol, in which an FADH2-dependent monooxygenase (TftD) and an NADH:FAD oxidoreductase (TftC) catalyze the initial steps. TftD oxidizes 2,4,5-trichlorophenol (2,4,5-TCP) to 2,5-dichloro-p-benzoquinone, which is chemically reduced to 2,5-dichloro-p-hydroquinone (2,5-DiCHQ). Then, TftD oxidizes the latter to 5-chloro-2-hydroxy-p-benzoquinone. In those processes, TftC provides all the required FADH2. We have determined the crystal structures of dimeric TftC and tetrameric TftD at 2.0 and 2.5 A resolution, respectively. The structure of TftC was similar to those of related flavin reductases. The stacked nicotinamide:isoalloxazine rings in TftC and sequential reaction kinetics suggest that the reduced FAD leaves TftC after NADH oxidation. The structure of TftD was also similar to the known structures of FADH2-dependent monooxygenases. Its His-289 residue in the re-side of the isoalloxazine ring is within hydrogen bonding distance with a hydroxyl group of 2,5-Di-CHQ.AnH289Amutation resulted in the complete loss of activity toward 2,5-DiCHQ and a significant decrease in catalytic efficiency toward 2,4,5-TCP. Thus, His-289 plays different roles in the catalysis of 2,4,5-TCP and 2,5-DiCHQ. The results support that free FADH2 is generated by TftC, and TftD uses FADH2 to separately transform 2,4,5-TCP and 2,5-DiCHQ. Additional experimental data also support the diffusion of FADH2 between TftC and TftD without direct physical interaction between the two enzymes.
- Webb, Brian N.,Ballinger, Jordan W.,Kim, Eunjung,Belchik, Sara M.,Lam, Ka-Sum,Youn, Buhyun,Nissen, Mark S.,Xun, Luying,Kang, Chulhee
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scheme or table
p. 2014 - 2027
(2011/02/22)
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- Process for the synthesis of phenols from arenes
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A process to synthesize substituted phenols such as those of the general formula RR′R″Ar(OH) wherein R, R′, and R″ are each independently hydrogen or any group which does not interfere in the process for synthesizing the substituted phenol including, but not limited to, halo, alkyl, alkoxy, carboxylic ester, amine, amide; and Ar is any variety of aryl or hetroaryl by means of oxidation of substituted arylboronic esters is described. In particular, a metal-catalyzed C—H activation/borylation reaction is described, which when followed by direct oxidation in a single or separate reaction vessel affords phenols without the need for any intermediate manipulations. More particularly, a process wherein Ir-catalyzed borylation of arenes using pinacolborane (HBPin) followed by oxidation of the intermediate arylboronic ester by OXONE is described.
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(2008/06/13)
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- C-H activation/borylation/oxidation: A one-pot unified route to meta-substituted phenols bearing ortho-/para-directing groups
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An efficient one-pot C-H activation/borylation/oxidation protocol for the preparation of phenols is described. This method is particularly attractive for the generation of meta-substituted phenols bearing ortho-/para-directing groups, as such substrates are difficult to access by other phenol syntheses. Copyright
- Maleczka Jr., Robert E.,Shi, Feng,Holmes, Daniel,Smith III, Milton R.
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p. 7792 - 7793
(2007/10/03)
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- Chemistry of L-ascorbic acid. Part 3.1 Photoreduction of quinones with 5,6-O-isopropylidene-L-ascorbic acid
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Upon irradiation with UV light, instead of undergoing the Paterno-Buechi reaction, 5,6-O-isopropyIidene-L-ascorbic acid reduced quinones quite efficiently and rapidly to the corresponding hydroquinones. The Royal Society of Chemistry 2000.
- Kulkarni, Mukund G.,Kate, Sandesh D.
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p. 4242 - 4244
(2007/10/03)
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- First total syntheses of cytotoxic substances russuphelins A-C
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Russuphelins (A-C) are synthesized from 2,4,6-trichlorophenol, using Michael type nucleophilic displacement of halides on 2,6-dihaloquinone followed by simple chemical manipulations.
- Reddy, K. Laxma,Vittal
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p. 107 - 118
(2007/10/03)
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- Properties of chlorinated dihydroxybenzenes - components of pulp bleaching effluents
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Gas chromatography and mass spectrometry data are given for the chlorodihydroxybenzenes which are components of wood pulp bleaching effluents and biologically-treated effluents, and are proposed intermediates in the chlorination of humic acids. The chlorohydroxybenzenes include the nine chlorocatechols, the six chlorohydroquinones and the seven known chlororesorcinols. The 22 chlorinated compounds were generally well separated on a phenyl methyl silicone column with the exception of three dichloro compounds. The chloro compounds with the same level of chlorine substitution were not able to be distinguished on the basis of their electron impact mass spectra.
- Smith, Terrence J.,Wearne, Ross H.,Wallis, Adrian F. A.
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p. 1555 - 1560
(2007/10/03)
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- PHOTOSENSITIZED DIMERIZATION OF PHENOL IN PORPHYRIN-QUINONE-PHENOL SYSTEM
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Photosensitized dimerization of 4-methoxyphenol was observed upon irradiation of porphyrin in the presence of quinone.Quantum yield for dimer was depended upon the concentration and reduction potential of quinones used.Free radical coupling mechanism was confirmed by means of ESR and CIDNP techniques.
- Maruyama, Kazuhiro,Furuta, Hiroyuki
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p. 243 - 246
(2007/10/02)
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- Reduction of Quinones by Hydride Meisenheimer Adducts
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Hydride Meisenheimer adducts, prepared by the reaction of 1,3,5-trinitrobenzene or 2,4-dinitroaniline with tetrahydridoborate ions, can transfer hydride to a range of quinones in dimethyl sulphoxide solution.Rate constants are reported for the 1,3,5-trinitrobenzene adduct and tetrachloro-1,4-benzoquinone, tetrabromo-1,4-benzoquinone, and 2,6-dichloro-1,4-benzoquinone, and for the 2,4-dinitroaniline adduct with 1,4-benzoquinone.The rates increase with increasing reduction potential of the quinone.In all cases the hydroquinones formed are slowly oxidised back to quinones.There are indications that the formation of the products of the hydride transfer is preceded by formation of a species having a low-intensity absorption maximum at > 700 nm, which is tentatively ascribed to a charge-transfer complex. 4-Nitrobenzaldehyde reacts with the hydride adduct of 1,3,5-trinitrobenzene at a much lower rate.All the ractions observed are characterised by low energies of activation (in the range 36-51 kJ mol-1) and large negative entropies of activation.
- Atkins, Paul J.,Gold, Victor,Wassef, Wasfy N.
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p. 463 - 466
(2007/10/02)
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- Mechanism of the Oxidation of NADH by Quinones. Energetics of One-Electron and Hydride Routes
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The kinetics of NADH oxidation by 7 o-benzoquinones and 14 p-benzoquinones were studied by using buffered aqueous solutions and UV/vis spectroscopy.For each quinone the rate law was first order in NADH and first order in quinone.The rate constants varied from 0.0745 to 9220 M-1s-1.Variation of the pH from 6 to 8 gave no change in rate.The use of 4-D and 4,4-D2NADH revealed kinetic isotope effects.The dideutero data gave kH/kD in the range 1.6-3.1 for p-quinones and 4.2 for 3,5-di-tert-butyl-o-quinone.When p-quinones were used, the log k was a linear function of Eo for the quinone/hydroquinone monoanion (Q/QH(1-)) couple with a slope of 16.9 V-1. o-Quinones reacted about 100 times more rapidly, but the same linear relationship with a slope of 16.4 V-1 was observed.Comparisons to data for one-electron-transfer reactions indicate that such mechanisms are not involved.A hydride-transfer mechanism accommodates all the data, and rate-limiting hydrogen atom transfer followed by electron transfer cannot be ruled out.
- Carlson, Brian W.,Miller, Larry L.
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p. 479 - 485
(2007/10/02)
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- ON THE 1,6-ADDITION OF ALKYLALUMINIUM COMPOUNDS TO para-QUINONES
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Ethyl, n-butyl and i-butylaluminium dichlorides undergo 1,6-addition to a conjugated bond system O=C-C=C-C=O of para-quinones.Methylaluminium dichloride is inactive in this addition, and triethylaluminium gives low yields.The reactivities of the quinones vary with their electron affinities, and the highest yields of 1,6-addition are obtained in the reactions of chlorine derivatives of 1,4-benzoquinone.The results are discussed in terms of a radical mechanism involving a homolytic cleavage of the Al-C bond in the donor-acceptor complex formed between the reactants followed by combination of alkyl radicals and aluminium derivatives of semiquinone within a cage.The stable donor-acceptor complexes and aluminium derivative of semiquinone were isolated and characterized from the reactions of aluminium trichloride with 2,3,5,6-tetramethyl-1,4-benzoquinone and 2,3,5,6-tetrachloro-1,4-benzoquinone, respectively.
- Florjanczyk, Zbigniew,Szymanska-Zachara, Ewa
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p. 127 - 138
(2007/10/02)
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