- Photochemistry of Semiconductor Particles. Part 4. - Effects of Surface Condition on the Photodegradation of 2,4-Dichlorophenol catalysed by TiO2 Suspensions
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The photocatalysed degradation of 2,4-dichlorophenol (DCP) has been investigated in aqueous suspensions of TiO2.A possible reaction scheme has been proposed for the degradation, in which chlorobenzoquinone (CBQ) was detected as a predominant intermediate present in the reaction solution.Kinetic details for the degradation steps have been analysed based on the experimental results.The essential role of oxygen was considered to be the capturing of the photogenerated electron to form the oxidizing species, such as H2O2, HO2(.) and OH(.).In anaerobic conditions, the photodegradation rate was quite low even with the adsorbed Cu(2+) ion on the TiO2 powder as an alternative electron scavenger.This is due to the rapid indirect recombination of the photogenerated electron and hole, which is mediated by the short-circuiting reaction of Cu(2+).However, in aerobic conditions, oxygen takes up the photogenerated electron trapped at the adsorbed Cu(2+) ion to prevent it from recombining with the photogenerated hole.As a result, the hole has sufficient opportunity to participate in the oxidizing reactions.The degradation rate was dependent to some extent on the surface charge of the TiO2 particles.Positive charge always promotes the photodegradation, whereas negative change is detrimental.This was attributed to the effects of surface charge on the migration of electrons from the interior of the TiO2 particles to the surface.
- Zang, Ling,Liu, Chun-Yan,Ren, Xin-Min
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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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- Iron-catalyzed arene C-H hydroxylation
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The sustainable, undirected, and selective catalytic hydroxylation of arenes remains an ongoing research challenge because of the relative inertness of aryl carbon-hydrogen bonds, the higher reactivity of the phenolic products leading to over-oxidized by-products, and the frequently insufficient regioselectivity. We report that iron coordinated by a bioinspired L-cystine-derived ligand can catalyze undirected arene carbon-hydrogen hydroxylation with hydrogen peroxide as the terminal oxidant. The reaction is distinguished by its broad substrate scope, excellent selectivity, and good yields, and it showcases compatibility with oxidation-sensitive functional groups, such as alcohols, polyphenols, aldehydes, and even a boronic acid. This method is well suited for the synthesis of polyphenols through multiple carbon-hydrogen hydroxylations, as well as the late-stage functionalization of natural products and drug molecules.
- Cheng, Lu,Wang, Huihui,Cai, Hengrui,Zhang, Jie,Gong, Xu,Han, Wei
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- Preparation method of sesamol
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The invention belongs to the technical field of compound synthesis, and particularly relates to a preparation method of sesamol, which firstly prepares 2 -chloro -1, 4 -diphenol, and then 2 - chlorine -1, 4 -biphenol and sodium hydroxide in an aqueous solution to obtain the sesamol, namely 1 2, 1 2 4 - 4 -triphenol and dichloromethane. The invention provides a new method for preparing the sesame phenol, and the yield of the sesamol is remarkably improved.
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Paragraph 0022; 0026; 0028-0029
(2021/11/21)
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- Can Donor Ligands Make Pd(OAc)2a Stronger Oxidant? Access to Elusive Palladium(II) Reduction Potentials and Effects of Ancillary Ligands via Palladium(II)/Hydroquinone Redox Equilibria
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Palladium(II)-catalyzed oxidation reactions represent an important class of methods for selective modification and functionalization of organic molecules. This field has benefitted greatly from the discovery of ancillary ligands that expand the scope, reactivity, and selectivity in these reactions; however, ancillary ligands also commonly poison these reactions. The different influences of ligands in these reactions remain poorly understood. For example, over the 60-year history of this field, the PdII/0 redox potentials for catalytically relevant Pd complexes have never been determined. Here, we report the unexpected discovery of (L)PdII(OAc)2-mediated oxidation of hydroquinones, the microscopic reverse of quinone-mediated oxidation of Pd0 commonly employed in PdII-catalyzed oxidation reactions. Analysis of redox equilibria arising from the reaction of (L)Pd(OAc)2 and hydroquinones (L = bathocuproine, 4,5-diazafluoren-9-one), generating reduced (L)Pd species and benzoquinones, provides the basis for determination of (L)PdII(OAc)2 reduction potentials. Experimental results are complemented by density functional theory calculations to show how a series of nitrogen-based ligands modulate the (L)PdII(OAc)2 reduction potential, thereby tuning the ability of PdII to serve as an effective oxidant of organic molecules in catalytic reactions.
- Bruns, David L.,Musaev, Djamaladdin G.,Stahl, Shannon S.
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supporting information
p. 19678 - 19688
(2020/12/18)
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- Preparation method of 2,5-dimethoxychlorobenzene
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The invention relates to a preparation method of 2,5-dimethoxychlorobenzene, which comprises the following steps: 1) one-pot oxidatiion and chlorination: dissolving phenol in a solvent, putting a formed solution into a high-pressure reaction kettle, adding a copper salt catalyst, conducting stirring to conduct reaction at a temperature range of room temperature to 50 DEG C under the oxygen pressure of 0.5-3 MPa, introducing 0.1-2 MPa dry HCl gas into the solution after the reaction is completed, and conducting stirring to conduct reaction at room temperature, and after the reaction is completed, conducting decompressing and rectifying to obtain a 2-chlorohydroquinone intermediate; and 2) methylation: adding 2-chlorohydroquinone into a high-pressure reaction kettle, conducting dissolving, introducing 0.1-2MPa of chloromethane gas under an alkaline condition, maintaining the pressure, conducting reacting at 50-120 DEG C until the raw materials are completely consumed, conducting filtering and desolventizing, and carrying out reduced pressure distillation to obtain the product 2,5-dimethoxychlorobenzene. Compared with a traditional preparation method, the method has the advantages ofless emission of three wastes, low cost, environmental friendliness and the like.
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Paragraph 0029-0031; 0034-0037
(2020/12/15)
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- Reductive Electrochemical Activation of Molecular Oxygen Catalyzed by an Iron-Tungstate Oxide Capsule: Reactivity Studies Consistent with Compound i Type Oxidants
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The reductive activation of molecular oxygen catalyzed by iron-based enzymes toward its use as an oxygen donor is paradigmatic for oxygen transfer reactions in nature. Mechanistic studies on these enzymes and related biomimetic coordination compounds designed to form reactive intermediates, almost invariably using various "shunt" pathways, have shown that high-valent Fe(V)=O and the formally isoelectronic Fe(IV) =O porphyrin cation radical intermediates are often thought to be the active species in alkane and arene hydroxylation and alkene epoxidation reactions. Although this four decade long research effort has yielded a massive amount of spectroscopic data, reactivity studies, and a detailed, but still incomplete, mechanistic understanding, the actual reductive activation of molecular oxygen coupled with efficient catalytic transformations has rarely been experimentally studied. Recently, we found that a completely inorganic iron-tungsten oxide capsule with a keplerate structure, noted as {Fe30W72}, is an effective electrocatalyst for the cathodic activation of molecular oxygen in water leading to the oxidation of light alkanes and alkenes. The present report deals with extensive reactivity studies of these {Fe30W72} electrocatalytic reactions showing (1) arene hydroxylation including kinetic isotope effects and migration of the ipso substituent to the adjacent carbon atom ("NIH shift"); (2) a high kinetic isotope effect for alkyl C - H bond activation; (3) dealkylation of alkylamines and alkylsulfides; (4) desaturation reactions; (5) retention of stereochemistry in cis-alkene epoxidation; and (6) unusual regioselectivity in the oxidation of cyclic and acyclic ketones, alcohols, and carboxylic acids where reactivity is not correlated to the bond disassociation energy; the regioselectivity obtained is attributable to polar effects and/or entropic contributions. Collectively these results also support the conclusion that the active intermediate species formed in the catalytic cycle is consistent with a compound I type oxidant. The activity of {Fe30W72} in cathodic aerobic oxidation reactions shows it to be an inorganic functional analogue of iron-based monooxygenases.
- Bugnola, Marco,Shen, Kaiji,Haviv, Eynat,Neumann, Ronny
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p. 4227 - 4237
(2020/05/05)
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- Pompon Dahlia-like Cu2O/rGO Nanostructures for Visible Light Photocatalytic H2 Production and 4-Chlorophenol Degradation
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Hierarchical Cu2O nanospheres with a Pompon Dahlia-like morphology were prepared by a one-pot synthesis employing electrostatic self-assembly. Nanocomposite analogues were also prepared in the presence of reduced graphene oxide (rGO). Photophysical properties of the hierarchical Cu2O nanospheres and Cu2O/rGO nanocomposite were determined, and their photocatalytic applications evaluated for photocatalytic 4-chlorophenol (4-CP) degradation and H2 production. Introduction of trace (2O for H2 production from 2.23 % to 3.35 %, giving an increase of evolution rate from 234 μmol.g?1.h?1 to 352 μmol.g?1.h?1 respectively. The AQE for 4-CP degradation also increases from 52 % to 59 %, with the removal efficiency reaching 95 % of 10 ppm 4-CP within 1 h. Superior performance of the hierarchical Cu2O/rGO nanocomposite is attributable to increased visible light absorption, reflected in a greater photocurrent density. Excellent catalyst photostability for >6 h continuous reaction is observed.
- Karthikeyan, Sekar,Ahmed, Kassam,Osatiashtiani, Amin,Lee, Adam F.,Wilson, Karen,Sasaki, Keiko,Coulson, Ben,Swansborough-Aston, Will,Douthwaite, Richard E.,Li, Wei
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p. 1699 - 1709
(2020/02/11)
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- Heterogeneous Nitrogen-doped Graphene Catalysed HOO? Generation via a Non-radical Mechanism for Base-free Dakin Reaction
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A heterogeneous nitrogen-doped graphene catalytic pathway for H2O2 activation to generate alkaline hydrogen peroxide (HOO?) through a non-radical mechanism was reported. Remarkably, the heterogeneous catalytic procedure has been used for the evergreen and environmentally Dakin reaction without using any transition metals, homogeneous bases, ligands, additives or promoters, completely. The study of catalyst structure and catalytic activities indicate that the most active sites are created by the graphitic N atoms at zig-zag edges of the sheets. In addition, N as dopant element changes the reactivity of the neighbour C atoms, and leads to the formation of carbon-hydroperoxide (C?(HOOH)) and C?O* (C?O?) transition state species on the graphene surface in catalytic the reaction. (Figure presented.).
- Sun, Wei,Gao, Lingfeng,Sun, Xu,Yang, Hua,Zheng, Gengxiu
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supporting information
p. 5210 - 5216
(2019/11/03)
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- Rate enhancements due to ultrasound in isoquinolinium dichromate and isoquinolinium chlorochromate catalyzed chlorination of aromatic compounds in presence of KHSO4/KCl
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Chlorination of aromatic compounds underwent magnificent rate accelerations in isoquinolinium dichromate and isoquinolinium chlorochromate catalyzed chlorination of aromatic hydrocarbons in the presence of KCl and KHSO4. Reaction times reduced highly significantly from 4-5 h in conventional protocol to 30-40 min under sonication, followed by high yields of monochloro derivatives as products with high regioselectivity.
- Rajanna,Rao, A. Sambashiva,Chakravarthi,Reddy, K. Rajendar
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p. 167 - 170
(2017/12/26)
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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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- 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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- A dinuclear iron(II) complex bearing multidentate pyridinyl ligand: Synthesis, characterization and its catalysis on the hydroxylation of aromatic compounds
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A dinuclear iron(II) complex Fe2L2(μ2-Cl)2Cl2 (L = N,N-bis(pyridin-2-ylmethyl)prop-2-yn-1-amine) was prepared and fully characterized by UV–Vis spectroscopy, elemental analysis, electrochemical analysis and X-ray single crystal diffraction analysis. The catalytic activity of the complex was assessed for the hydroxylation of aromatic compounds by using aqueous H2O2 as an oxidant in acetonitrile. The catalytic system was applicable in a wide range of substrates including aromatic compounds with both electron-donating and electron-withdrawing substituents and showed moderate to good catalytic activity and selectivity in the oxidation reactions. Particularly, in the case of benzene the selectivity of phenol achieve to 74% with the reaction conversion of 24.8%.
- Gu, Erxing,Zhong, Wei,Ma, Hongxia,Xu, Beibei,Wang, Hailong,Liu, Xiaoming
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p. 159 - 165
(2018/03/29)
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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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- Biocatalytic One-Pot Synthesis of l-Tyrosine Derivatives from Monosubstituted Benzenes, Pyruvate, and Ammonia
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l-Tyrosine derivatives were obtained in >97% ee via a biocatalytic one-pot two-step cascade using substituted benzenes, pyruvate, and NH3 as starting materials. In the first step, monosubstituted arenes were regioselectively hydroxylated in the o-position by monooxygenase P450 BM3 (using O2 as oxidant with NADPH-recycling) to yield the corresponding phenols, which subsequently underwent C-C coupling and simultaneous asymmetric amination with pyruvate and NH3 using tyrosine phenol lyase to furnish l-DOPA surrogates in up to 5.2 g L-1. Instead of analytically pure arenes, crude aromatic gasoline blends containing toluene were used to yield 3-methyl-l-tyrosine in excellent yield (2 g L-1) and >97% ee.
- Dennig, Alexander,Busto, Eduardo,Kroutil, Wolfgang,Faber, Kurt
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p. 7503 - 7506
(2015/12/11)
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- Candida antarctica lipase B-catalyzed regioselective deacylation of dihydroxybenzenes acylated at both phenolic hydroxy groups
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Candida antarctica lipase B proved to be highly active in the deacylation of substituted hydroquinones and resorcinols acylated at both phenolic hydroxy groups. The deacylation reactions were much faster than the corresponding direct acylations of these dihydroxybenzenes catalyzed by the same lipase. More importantly, they took place generally in a markedly regioselective manner: the acyloxy group remote from the substituent was preferentially cleaved. The main or exclusive products obtained were the regioisomers of those produced through the direct acylation of the dihydroxybenzenes. In the case of alkyl-substituted hydroquinone derivatives, the regioselectivity increased with an increase in the bulk of the substituent. In the case of 4-substituted diacylated resorcinols, the 3-O-monoacyl derivatives were obtained generally as the sole products. Quite interestingly, some secondary alcohols proved to act as better acyl acceptors than the corresponding primary alcohols in these enzymatic deacylations.
- Miyazawa, Toshifumi,Hamada, Manabu,Morimoto, Ryohei
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- Enzymatic removal of chlorophenols using horseradish peroxidase immobilized on superparamagnetic Fe3O4/graphene oxide nanocomposite
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Magnetic Fe3O4 nanoparticles were successfully deposited on graphene oxide sheets by ultrasound-assisted coprecipitation. The nanoparticles were characterized using transmission electron microscopy, vibrating sample magnetometry, and X-ray photoelectron spectroscopy. The synthesized material was used as a support for the immobilization of horseradish peroxidase (HRP). The removals of 2-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol using the immobilized HRP were investigated. Batch degradation studies were used to determine the effects of the initial solution pH values, reaction temperature, reaction time, H2O2 and chlorophenol concentrations, and immobilized enzyme dosage on the removal of chlorophenols. The different numbers and positions of electron-withdrawing substituents affected the chlorophenol removal efficiency; the order of the removal efficiencies was 2-chlorophenol 4-chlorophenol 2,4-dichlorophenol. The oxidation products formed during chlorophenol degradation were identified using gas chromatography-mass spectrometry. The biochemical properties of the immobilized HRP were investigated; the results indicated that the storage stability and tolerance to changes in pH and temperature of the immobilized HRP were better than those of free HRP. The nanoparticles were recovered using an external magnetic field, and the immobilized HRP retained 66% of its initial activity for the first four cycles, showing that the immobilized HRP had moderate stability. These results suggest that the immobilized enzyme has potential application in wastewater treatment.
- Chang, Qing,Jiang, Guodong,Tang, Heqing,Li, Na,Huang, Jia,Wu, Laiyan
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p. 961 - 968
(2015/07/01)
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- Efficient photocatalytic dechlorination of chlorophenols over a nonlinear optical material Na3VO2B6O11 under UV-visible light irradiation
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One type of nonlinear optical crystal Na3VO2B6O11 (NVB) with noncentrosymmetry was synthesized and shows extraordinary UV-visible light driven photocatalytic activity in the dechlorination of 2,4-DCP under UV-vis (λ > 320 nm) light irradiation. The obtained dechlorination efficiency is 90 times higher than that of the commercial P25 TiO2 catalyst under the same conditions. The noncentrosymmetric structure of NVB gives rise to an intrinsic large polarization effect as evidenced by Kelvin probe force microscopy, and the polarization promotes separation of photogenerated electron-hole pairs, leading to efficient cleavage of chlorophenols into phenol series fragments and dissociative Cl- anions. A possible reaction pathway for 2,4-DCP dechlorination by NVB upon UV-vis light irradiation is proposed. Hydrodechlorination was found to be the major reaction pathway for 2,4-DCP dechlorination which could react with hydroxyl radicals to produce 1,4-benzoquinone and ocatechol. This work further advances the understanding of nonlinear optical materials, which opens up a new route to the design and synthesis of highly efficient photocatalysts by using nonlinear optical materials.
- Fan, Xiaoyun,Lai, Kangrong,Wang, Lichang,Qiu, Hengshan,Yin, Jiao,Zhao, Pengjun,Pan, Shilie,Xu, Jinbao,Wang, Chuanyi
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supporting information
p. 12179 - 12187
(2015/06/17)
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- Synthesis of nitrogen-doped ZnO by sol-gel method: Characterization and its application on visible photocatalytic degradation of 2,4-D and picloram herbicides
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In this work, nitrogen-doped ZnO material was synthesized by the sol-gel method using zinc acetate as the precursor and urea as the nitrogen source (15, 20, 25 and 30% wt.). For comparative purposes, bare ZnO was also prepared. The influence of N doping on structural, morphological, optical and photocatalytic properties was investigated. The synthesized catalysts were characterized by XRD, SEM-EDS, diffuse reflectance UV-Vis spectroscopy, BET and XPS analysis. The photocatalytic activity of N-doped ZnO catalysts was evaluated during the degradation of a mixture of herbicides (2,4-D and picloram) under visible radiation ≥400 nm. The photo-absorption wavelength range of the N-doped ZnO samples was shifted to longer wavelength compared to those of the unmodified ZnO. Among different amounts of dopant agent, the 30% N-doped ZnO material showed higher visible-light activity compared with pure ZnO. Several degradation by-products were identified by using HPLC and ESI-MS/MS. The enhancement of visible photocatalytic activity of the N-doped ZnO semiconductor could be mainly due to their capability in reducing the electron-hole pair recombination. This journal is
- Macías-Sánchez,Hinojosa-Reyes,Caballero-Quintero,De La Cruz,Ruiz-Ruiz,Hernández-Ramírez,Guzmán-Mar
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p. 536 - 542
(2015/03/14)
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- Hydroxyl radical reactions with 2-chlorophenol as a model for oxidation in supercritical water
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To determine the detailed mechanism of 2-chlorophenol (2-CP) oxidation in supercritical water, both the experiments and theoretical calculations were conducted in this paper. A set of experiments was performed to oxidize 2-CP in supercritical water under temperatures of 380-420 °C, pressure of 25 MPa, residence times of 0-60 s, and H2O2 as oxidant. By determining the molar yields of products, the primary single-ring products were identified as chlorohydroquinone, 2,4-dichlorophenol (2,4-DCP), 2,6-DCP, and 4-CP. The trends for the molar yields of the four products were analyzed at various temperatures and residence times. And built upon the trends, the possible reaction pathways were conjectured. Subsequently, the reaction mechanism was further verified by theoretical calculations, in which density functional theory was adopted as the computational method. The calculated results have well illustrated the experimental results and ascertained the reaction paths we proposed. Springer Science+Business Media Dordrecht 2013.
- Zhang, Jiaming,Ma, Chunyuan,Sun, Youmin,Ren, Xiaohua
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p. 973 - 990
(2014/05/06)
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- A convenient road to 1-chloropentacycloundecanes - A joint experimental and computational investigation
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An efficient synthetic strategy to obtain 1-chloro-Cs- trishomocubane and 1-chloro-D3-trishomocubane is described. 1-Chloro-Cs-trishomocubane is synthesized by a regioselective Diels-Alder reaction, and B3PW91/6-31G(d,p) calculations offer a plausible explanation of the reaction mechanism. Surprisingly, 1-chloro-C s-trishomocubane does not undergo an acid-catalyzed rearrangement to form 1-chloro-D3-trishomocubane and was obtained by chlorosulfation of Cookson's diketone. A possible mechanism of the reaction involving the formation of Cs- and D3-trishomocubane nonclassical cations was proposed on the basis of a mechanistic [B3PW91/6-31G(d,p) and MP2/cc-pVDZ] study. An efficient method to prepare 1-substituted pentacycloundecanes is described. Simple modification of the starting material for the Diels-Alder reaction gives 1-Cs-trishomocubane derivatives readily. Chlorosulfation of Cookson's diketone in four steps gives 1-chloro-D3-trishomocubane in good yields. The proposed mechanism of the reactions is explained by DFT and MP2 calculations. Copyright
- Sharapa, Dmitry I.,Gayday, Alexander V.,Mitlenko, Alena G.,Levandovskiy, Igor A.,Shubina, Tatyana E.
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scheme or table
p. 2554 - 2561
(2011/06/10)
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- Bioconversion of aromatic compounds by Escherichia coli that expresses cytochrome P450 CYP153A13a gene isolated from an alkane-assimilating marine bacterium Alcanivorax borkumensis
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The cytochrome P450 CYP153 family has been isolated from alkane-assimilating bacteria. CYP153 has been shown to mediate terminal hydroxylations of linear alkanes or alkyl aromatics. We here performed the biotransformation of various aromatic compounds by Escherichia coli cells that expressed the CYP153A13a (P450balk) gene, which was isolated from an alkane-degading marine bacterium Alcanivorax borkumensis. Aromatic compounds including a short alkyl moiety or methyl ether moiety, and phenolic compounds were converted to their respective hydroxylated products, whose structures were determined by HRMS and NMR analyses. The present study revealed that the catalytic function of CYP153A13a is multifunctional, i.e., it can hydroxylate not only the terminal of short alkyl groups that attached to aromatic rings but also the p-position of phenolic compounds substituted with a halogen or the acetyl group. CYP153A13a was also shown to demethylate methylether-including aromatic compounds.
- Otomatsu, Toshihiko,Bai, Liming,Fujita, Naoya,Shindo, Kazutoshi,Shimizu, Keiko,Misawa, Norihiko
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experimental part
p. 234 - 240
(2011/01/03)
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- Influence of activated carbons on the kinetics and mechanisms of aromatic molecules ozonation
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Companies have been looking for new methods for treating toxic or refractory wastewaters; which can mainly be used prior to or after or in connexion with biological treatment processes. This paper compares conventional ozone oxidation with activated carbon (AC) promoted ozone oxidation, which helps developing a mechanism involving HO{radical dot} radical. For a compound which is quite easy to oxidise, like 2,4-dichlorophenol (2,4-DCP) conventional ozonation is efficient enough to remove the initial molecule. The mechanism involved mainly consists of an electrophilic attack on the aromatic ring, which is activated by the donor effect of the -OH group, then followed by a 1,3 dipolar cycloaddition (Criegee mechanism) that leads to aliphatic species, mainly carboxylic acids. Yet, the addition of AC, through the presence of HO{radical dot} radical, enhances the removal of these species which are more refractory. For a refractory compound like nitrobenzene (NB), with a de-activated aromatic ring because of the attractive effect of -NO2, conventional ozonation is inefficient. On the contrary, this molecule can be quite easily removed with AC promoted oxidation and it is found that the mechanism (electrophilic attack followed by a 1,3 dipolar cycloaddition) is quite similar to the one corresponding to conventional ozonation, but with less selectivity. For both molecules, a mass balance has established that the by-products accounting for more than 75% of the remaining COD can be quantified. A significant part is composed of carboxylic acids (acetic, oxalic, etc.), which could afterwards be easily removed in an industrial wastewater treatment process followed by a final biological treatment step.
- Merle,Pic,Manero,Mathé,Debellefontaine
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experimental part
p. 166 - 172
(2010/08/20)
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- PROCESS FOR CONVERSION OF PHENOL TO HYDROQUINONE AND QUINONES
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The present invention relates to a process for the conversion of phenol to hydroquinone and quinones. More particularly this invention relates to a process for the oxidation of phenol to a mixture of 1,4-benzoquinone and hydroquinone using an oxidant in the presence of titanium superoxide as a reusable catalyst in a liquid phase condition.
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Page/Page column 8; Table 1
(2008/06/13)
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- Photoreduction of p-Benzoquinones: Effects of Alcohols and Amines on the Intermediates and Reactivities in Solution
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The photochemistry of 1,4-benzoquinone (BQ) and alkyl-, Cl- and related derivatives, e.g. methyl-, 2,6-dimethyl-, chloro-, 2,5-dichloro-1,4-benzoquinone, duroquinone and chloranil, was studied in nonaqueous solvents by UV-vis spectroscopy using nanosecond laser pulses at 308 nm. The reactivity of the triplet state (3Q*) of the quinones with 2-propanol in the absence of water is largest for BQ and depends mainly on the quinone structure, whereas the rate constant of electron transfer from amines, such as triethylamine (TEA) or 1,4-diazabicyclo[2.2.2]octane, is close to the diffusion-controlled limit for BQ and most derivatives. Photoinduced charge separation after electron transfer from amines to 3Q* and the subsequent charge recombination or neutralization are supported by time-resolved conductivity measurements. The half-life of the decay kinetics of the semiquinone radical (.QH/Q.-) depends significantly on the donor and the medium. The photoconversion into the hydroquinones was measured under various conditions, the quantum yield, λirr = 254 nm, increases with increasing 2-propanol and TEA concentrations. The effects of quenching of 3Q*, the .QH/Q.- radicals and the photoconversion are outlined. The mechanisms of photoreduction of quinones in acetonitrile by 2-propanol are compared with those by TEA in benzene and acetonitrile, and the specific properties of substitution are discussed.
- Goerner, Helmut
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p. 440 - 448
(2007/10/03)
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- Sonolysis of 2,4-dichlorophenoxyacetic acid in aqueous solutions. Evidence for 'OH-radical-mediated degradation
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2,4-dichlorophenoxyacetic acid (2,4-D) undergoes efficient degradation when an U2- or Ar-saturated aqueous solution is subjected to high-frequency (640 kHz) sonolysis. 2,4-dichlorophenol, hydroquinone, and catechol are major reaction intermediates common
- Peller, Julie,Wiest, Olaf,Kamat, Prashant V.
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p. 3176 - 3181
(2007/10/03)
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- Kinetics of heterogeneous photocatalytic decomposition of 2,4-dichlorophenoxyacetic acid over titanium dioxide and zinc oxide in aqueous solution
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The photocatalytic transformation of 2,4-D in aqueous solution containing a suspension of titanium dioxide or zinc oxide leads to the formation of intermediates which are totally mineralised to carbon dioxide and hydrogen chloride (2,4-dichlorophenol and chlorohydroquinone are the major intermediates). The products at the initial stage of the reaction were 2,4-dichlorophenol (2,4-DCP), chlorohydroquinone, 4-chloropyrocatechol, 2,4-dichloro-pyrocatechol and 1.4-chlorobenzoquinone. The initial rate of photodegradation was studied as a function of the initial concentration of reactants by the linearised form of the Langmuir-Hinshelwood equation, by which rate constants κ and equilibrium adsorption constants K were evaluated. These constants were calculated at different temperatures between 25 and 60°C. The photodegradation rate increased with increase of pH. The photocatalytic transformation of 2,4-D over titanium dioxide or zinc oxide in solution containing hydrogen peroxide was studied. The latter accelerated the reaction rate of 2,4-D significantly. It was found that chloride or bicarbonate ions slowed down the photo-degradation rate of 2,4-D by scavenging hydroxyl radicals. Partial inhibition by ethanol is attributed to scavenging of the OH radicals involved in the first step of the reaction.
- Djebbar,Sehili
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p. 269 - 276
(2007/10/03)
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- Ultrasonic and photochemical degradation of chlorpropham and 3-chloroaniline in aqueous solution
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Sonolysis and photolysis are compared for the transformation of chlorpropham, a systemic herbicide belonging to the carbamate group, and 3-chloroaniline, the main intermediate often observed in the degradation of chlorpropham. In both cases the ultrasonic degradation is much more efficient at 482 kHz than at 20 kHz. The main identified sonoproducts formed in the degradation of chlorpropham are 3-chloroaniline, formic acid, carbon monoxide and dioxide and chloride ions. The degradation of 3-chloroaniline also leads to Cl-, CO and CO2 but chlorohydroquine was also detected as an intermediate. Two different mechanisms are involved in the ultrasonic transformation: pyrolysis resulting from the implosion of cavitation microbubbles and oxidation by hydroxyl radicals formed by sonolysis of water. Photolysis is more specific: 3-chloroaniline is initially quantitatively transformed into 3-aminophenol. A heterolytic mechanism is suggested. Resorcinol and some unidentified photoproducts are formed in a second stage. The same type of reaction is involved in the photo-transformation of chlorpropham, but the reaction is not so specific. In both cases the photolysis at 254 nm leads to a complete disappearance of phenolic and quinonic compounds. Sonolysis and photolysis are compared for the transformation of chlorpropham, a systemic herbicide belonging to the carbamate group, and 3-chloroaniline, the main intermediate often observed in the degradation of chlorpropham. In both cases the ultrasonic degradation is much more efficient at 482 kHz than at 20 kHz. The main identified sonoproducts formed in the degradation of chlorpropham are 3-chloroaniline, formic acid, carbon monoxide and dioxide and chloride ions. The degradation of 3-chloroaniline also leads to Cl-, CO and CO2 but chlorohydroquine was also detected as an intermediate. Two different mechanisms are involved in the ultrasonic transformation: pyrolysis resulting from the implosion of cavitation microbubbles and oxidation by hydroxyl radicals formed by sonolysis of water. Photolysis is more specific: 3-chloroaniline is initially quantitatively transformed into 3-amino-phenol. A heterolytic mechanism is suggested. Resorcinol and some unidentified photoproducts are formed in a second stage. The same type of reaction is involved in the photo-transformation of chlorpropham, but the reaction is not so specific. In both cases the photolysis at 254 nm leads to a complete disappearance of phenolic and quinonic compounds.
- David,Lhote,Faure,Boule
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p. 2451 - 2461
(2007/10/03)
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- Redox reactions of phenylhydroquinone with quinones in water
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The reversible reaction of hydrogen transfer between phenylhydroquinone and quinones (p-benzo-quinone, chlorobenzoquinone, and methylbenzoquinone) was studied as depending on water pH and composition and the procedure for water pretreatment. A spectrophotometric technique for measuring low concentrations of phenylbenzoquinone produced in the reaction was developed, and the rate constants for the forward and back reactions and the equilibrium constants were calculated. The reaction rate increased drastically (by more than 4 orders of magnitude) as pH grew from 4 to 8. The dependence of the reaction rate in water on pH was explained by the formation of hydroquinone anions in the alkaline region. These anions are strong electron donors and readily react with quinone molecules. The mechanism of the redox reaction in the hydroquinone-p-benzoquinone system is considered in quantum-chemical terms.
- Kalnin'sh,Pavlova
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p. 1596 - 1600
(2007/10/03)
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- ELECTROCHEMICAL BEHAVIOUR OF SUBSTITUTED HYDROQUINONES
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The oxidation potentials of thirteen hydroquinones substituted by chlorine, pyrazol-1-yl and 3,5-dimethylpyrazol-1-yl groups were experimentally determined by cyclic voltammetry.The estimated half-wave potentials E1/2 have been discussed taking into account the inductive and conjugative substituent effects.Key words: Cyclic voltammetry, Hydroquinones, Redox, Pyrazoles
- Claramunt, R. M.,Escolastico, C.,Maria, M. D. Santa,Lopez, V.
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p. 368 - 371
(2007/10/02)
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- Sodium Percarbonate: A Convenient Reagent for the Dakin Reaction
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Sodium percarbonate, a readily available, inexpensive and easy to handle reagent efficiently oxidizes hydroxylated benzaldehydes and hydroxylated acetophenones to hydroxyphenols.
- Kabalka, G. W.,Reddy, N. K.,Narayana, C.
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p. 865 - 866
(2007/10/02)
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- REACTION OF PHOSPHORUS PENTACHLORIDE WITH QUINONES
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Phosphorus pentachloride reacts with 1,4-benzoquinone and 2-chloro-1,4-benzoquinone at room temperature.The basic products are dichlorophosphoranes (1a, b).Intermediates have been ascertained.The scheme of the process has been confirmed by model reactions.Key words: Quinones; Phosphorus pentachloride; Mechanism; Infrared; Dimethylaniline; Mass spectra.
- Kutyrew, A. A.,Fomin, S. G.,Moskva, V. V.
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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 carbonyl compounds promoted by silicon hydrides under the influence of trimethylsilyl-based reagents
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The synthetic utility of hydrosilanes under the influence of trimethylsilyl-based reagents as new reducing systems is described. 1,1,3,3-Tetramethyldisiloxane (TMDS) reagent in combination with iodotrimethylsilane or bromotrimethylsilane produces alkyl halides from aldehydes in good to excellent yields.Polymethylhydrosiloxane (PMS) in the presence of iodotrimethylsilane also produces benzyl iodides in excellent yields.On the contrary, PMS reagent was found unsuitable for the synthesis of benzyl bromides.Similary, TMDS reagent in combination with trimethylsilyl triflate produces symmetrical ethers from aldehydes without concomitant formation of competitive products.Under similar conditions, PMS reagent failed to provide the expected symmetrical ethers and Friedel-Crafts products were formed.Reduction of quinones to hydroquinones is also described.
- Aizpurua, Jesus M.,Lecea, Begona,Palomo, Claudio
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p. 2342 - 2347
(2007/10/02)
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- The Thermal Addition Reactions of Cycloheptatriene with Aromatic p-Quinones
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Thermal addition reactions of cycloheptatriene with several aromatic p-quinones gave the Diels-Alder adducts as minor products; the most characteristic feature was the formation of the vic-ditropylation products.The mechanism of their formation was clarified to be a sequential ene-reaction and dehydrogenation by means of chemical conversion from the isolated intermediates.Several new other additions, e.g., successive Diels-Alder reactions, were also noted.
- Mori, Akira,Mametsuka, Hiroaki,Takeshita, Hitoshi
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p. 2072 - 2077
(2007/10/02)
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- REAGENTS AND SYNTHETIC METHODS 52. SILANE REDUCTION OF CARBONYL COMPOUNDS IN THE PRESENCE OF IODINE.
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Synthetic utility of 1,1,3,3,-tetramethyldisiloxane (TMDS) reagent under the influence of iodine is described.TMDS reagent in combination with iodine produces alkyl iodides from carbonyl compounds and oxiranes in good to excellent yields.Reduction of quinones into hydroquinones is also described.The mentioned transformations are explained from mechanistic points of view.
- Lecea, B.,Aizpurua, J. M.,Palomo, C.
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p. 4657 - 4666
(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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- Hydroxy and ether containing phenothiazine derivatives
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Phenothiazine derivatives of the formula: SPC1 Wherein X represents methylthio, methylsulphonyl or dimethylsulphamoyl, R represents hydrogen, alkyl of 1 through 10 carbon atoms, phenylalkyl containing 1 through 4 carbon atoms in the alkyl part, or tetrahydropyranyl, A represents --(CH2)3 -- or --CH2 --CH(CH3)--CH2 --, and R1 represents hydrogen, alkanoyl containing 1 through 16 carbon atoms in the alkyl part or alkenoyl containing 2 through 16 carbon atoms in the alkenyl part, are new compounds possessing pharmacodynamic properties; they are particularly active as anti-emetic agents.
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- Enzyme-activated oxidative process for coloring hair
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An enzyme-based oxidative process for coloring hair wherein the hair is exposed to a solution having a pH of about 4 to about 10 and containing hydrogen peroxide, soybean peroxidase enzyme and one or more oxidation dye precursors.
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- Process for preparing chlorohydroquinone
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Preparation of chlorohydroquinone by adding hydrogen chloride to p-benzoquinone, wherein a 1 to 20 % by weight solution of p-benzoquinone in benzene is treated discontinuously or continuously with hydrogen chloride at a hydrogen chloride pressure of from 1 to 6 atmospheres gauge, at a temperature of from 40° to 80°C, the residence time being from 1 to 4 hours and the chlorohydroquinone is isolated in known manner.
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