- Hydroxyl Radicals quantification by UV spectrophotometry
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Hydroxilation of aromatic compounds is an oxidative process that has been employed as indirect method to quantify the produced hydroxyl radicals during an advanced oxidation process (a-OH). This is usually complicated by the radical high reactivity and short life time and therefore a scavenging agent such as salicylic acid is commonly employed. This usually implies a rather sophisticated analytical method such as chromatography. In this work, however, a relatively simple and low cost method is proposed to achieve the aforementioned objective. This method is based on UV-Vis spectrophotometry and was employed to quantify the hydroxyl radicals produced during the electrochemical oxidation of water when employing a platinum anode in a galvanostatic type process. Salicylic acid was employed as a-OH scavenger. The concentration of the hydroxilated resulting products, 2,3-dihidroxybenzoic Acid and 2,5-dihydroxibenzoic Acid, was determined by UV-Vis Spectroscopy and utilized to quantify the hydroxyl radicals. In addition, mineralization was followed by Chemical Oxygen Demmand measurements.
- Peralta,Roa,Hernandez-Servin,Romero,Balderas,Natividad
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- PHOTOCHEMICAL HYDROXYLATION OF SALICYLIC ACID DERIVATIVES WITH HYDROGEN PEROXIDE, CATALYZED WITH Fe(III) AND SENSITIZED WITH METHYLENE BLUE
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Substitution of hydrogen in the carboxy or hydroxy group of a salicylic acid molecule with a methyl group, which hinders the coordination of Fe(III), results in a pronounced reduction of photocatalytic effects.The complex of Fe(III) with salicylic acid is the precursor of the thermal catalyst arising on irradiation.
- Lunak, Stanislav,Muzart, Jacques,Brodilova, Jirina
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- Gentisides A and B, two new neuritogenic compounds from the traditional Chinese medicine Gentiana rigescens Franch
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Two new alkyl 2,3-dihydroxybenzoates, gentisides A and B, were isolated from the traditional Chinese medicine Gentiana rigescens Franch. Their structures and stereochemistry were elucidated by spectroscopic methods and chemical derivatization. These compounds showed a significant neuritogenic activity at 30 μM against PC12 cells that was comparable to that seen for the best nerve growth factor (NGF) concentration of 40 ng/mL. Gentisides A and B showed parallel activity, indicating that the observed structural difference at the end of their alkyl chain did not affect neuritogenic activity.
- Gao, Lijuan,Li, Jinyou,Qi, Jianhua
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- Photochemical hydroxylation of salicylic acid with hydrogen peroxide; mechanistic study of substrate sensitized reaction
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The photochemical hydroxylation of salicylic acid (SA) by hydrogen peroxide proceeds via the same intermediate independently of the excited reactant (i.e. SA or H2O2). This conclusion is supported by the similar effect of pH on the quantum yields and on the isomer ratio of formed products: 2,3-dihydroxybenzoic acid (2,3-DHB) and 2,5-dihydroxybenzoic acid (2,5-DHB). The product ratio ([2,3-DHB]/[2,5-DHB]) is not affected by H2O2 concentration.
- Lang, Kamil,Brodilova, Jirina,Lunak, Stanislav
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- Aromatic hydroxylation of salicylic acid and aspirin by human cytochromes P450
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Aspirin (acetylsalicylic acid) is a well-known and widely-used analgesic. It is rapidly deacetylated to salicylic acid, which forms two hippuric acids - salicyluric acid and gentisuric acid - and two glucuronides. The oxidation of aspirin and salicylic acid has been reported with human liver microsomes, but data on individual cytochromes P450 involved in oxidation is lacking. In this study we monitored oxidation of these compounds by human liver microsomes and cytochrome P450 (P450) using UPLC with fluorescence detection. Microsomal oxidation of salicylic acid was much faster than aspirin. The two oxidation products were 2,5-dihydroxybenzoic acid (gentisic acid, documented by its UV and mass spectrum) and 2,3-dihydroxybenzoic acid. Formation of neither product was inhibited by desferrioxamine, suggesting a lack of contribution of oxygen radicals under these conditions. Although more liphophilic, aspirin was oxidized less efficiently, primarily to the 2,5-dihydroxy product. Recombinant human P450s 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4 all catalyzed the 5-hydroxylation of salicylic acid. Inhibitor studies with human liver microsomes indicated that all six of the previously mentioned P450s could contribute to both the 5- and 3-hydroxylation of salicylic acid and that P450s 2A6 and 2B6 have contributions to 5-hydroxylation. Inhibitor studies indicated that the major human P450 involved in both 3- and 5-hydroxylation of salicylic acid is P450 2E1.
- Boji?, Mirza,Sedgeman, Carl A.,Nagy, Leslie D.,Guengerich, F. Peter
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- Black TiO2 nanotube arrays decorated with Ag nanoparticles for enhanced visible-light photocatalytic oxidation of salicylic acid
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Novel forms of black TiO2 nanotubes-based photocatalysts for water purification were prepared. Two features were combined: decoration of TiO2 nanotube arrays with Ag nanoparticles (sample TiO2-NT's@Ag) and further hydrogenation of this material (TiO2-NT's@Ag-HA). Obtained photocatalysts show high efficiency for degradation of salicylic acid, a typical water-borne pollutant. The photocatalysts considerably exceed the photocatalytic properties of TiO2 nanotubes and commercial TiO2 P25 taken as a reference for modeling of the photocatalytic process. The comparison of photocatalytic activities between novel photocatalyst was based on a numerical approach supported by the complex kinetic model. This model allowed a separate study of different contributions on overall degradation rate. The contributions include: salicylic acid photolysis, photocatalysis in UVB, UVA and in the visible part of applied simulated solar irradiation. The superior photocatalytic performance of the photocatalyst TiO2-NT's@Ag-HA, particularly under visible irradiation, was explained by the combined effect of a local surface plasmon resonance (LSPR) due to Ag nanoparticles and creation of additional energy levels in band-gap of TiO2 due to Ti3+ states at nanotube surfaces. The presence of Ag also positively influence charge separation of created electron-holes pairs. The synergy of several effects was quantified by a complex kinetic model through the factor of synergy, fSyn. Stability testing indicated that the catalysts were stable for at least 20 h. The novel design of catalysts, attached on Ti foils, presents a solid base for the development of more efficient photocatalytic reactors for large-scale with a long-term activity.
- Plodinec, Milivoj,Gr?i?, Ivana,Willinger, Marc G.,Hammud, Adnan,Huang, Xing,Pan?i?, Ivana,Gajovi?, Andreja
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p. 883 - 896
(2018/11/10)
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- HPLC study on Fenton-reaction initiated oxidation of salicylic acid. Biological relevance of the reaction in intestinal biotransformation of salicylic acid
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Fenton-reaction initiated in vitro oxidation and in vivo oxidative biotransformation of salicylic acid was investigated by HPLC-UV-Vis method. By means of the developed high performance liquid chromatography (HPLC) method salicylic acid, catechol, and all the possible monohydroxylated derivatives of salicylic acid can be separated. Fenton oxidations were performed in acidic medium (pH 3.0) with two reagent molar ratios: (1) salicylic acid: iron: hydrogen peroxide 1:3:1 and (2) 1:0.3:1. The incubation samples were analysed at different time points of the reactions. The biological effect of elevated reactive oxygen species concentration on the intestinal metabolism of salicylic acid was investigated by an experimental diabetic rat model. HPLC-MS analysis of the in vitro samples revealed presence of 2,3- and 2,5-dihydroxybenzoic acids. The results give evidence for nonenzyme catalysed intestinal hydroxylation of xenobiotics.
- Nyúl, Eszter,Kuzma, Mónika,Mayer, Mátyás,Lakatos, Sándor,Almási, Attila,Perjési, Pál
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p. 1040 - 1051
(2018/10/24)
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- Evidence for the electrochemical production of persulfate at TiO2 nanotubes decorated with PbO2
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It is well known that PbO2-based electrodes are considered to be non-active anodes, producing higher concentrations of hydroxyl radicals in aqueous solutions, and consequently, favouring the electrochemical degradation of organic pollutants. However, no evidence has been reported on the production of persulfates using this kind of electrode in sulphate aqueous solutions. For this reason, the aim of this work is to prepare (by an electrochemical procedure (anodization and electrodeposition)) and characterize (by X-ray diffraction, scanning electron microscopy, and potentiodynamic measurements) Ti/TiO2-nanotubes/PbO2 disk electrodes (with a geometrical area of 65 cm2) in order to evaluate the electrochemical production of persulfate using Na2SO4 solution as the support electrolyte and applying current densities of 7.5 and 60 mA cm-2, as well as the influence of the electrosynthesis of hydroxyl radicals, in concomitance. The results clearly showed that significant production of hydroxyl radicals and persulfate is achieved at the Ti/TiO2-nanotubes/PbO2 surface, but this depends on the current density. The production of OH at the Ti/TiO2-nanotubes/PbO2 surface in Na2SO4 solution was confirmed by a RNO spin trapping reaction. The results were compared with those of a Ti/Pt electrode in order to understand the effect when a lower amount of OH is produced at the active anode surface. Based on the results, the Ti/TiO2-nanotubes/PbO2 anode could exhibit good electrocatalytic properties for environmental applications involving persulfate oxidants.
- Santos, José Eudes L.,Antonio Quiroz, Marco,Cerro-Lopez, Monica,De Moura, Dayanne Chianca,Martínez-Huitle, Carlos A.
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p. 5523 - 5531
(2018/04/02)
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- Biocatalytic carboxylation of phenol derivatives: Kinetics and thermodynamics of the biological Kolbe-Schmitt synthesis
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Microbial decarboxylases, which catalyse the reversible regioselective ortho-carboxylation of phenolic derivatives in anaerobic detoxification pathways, have been studied for their reverse carboxylation activities on electron-rich aromatic substrates. Ortho-hydroxybenzoic acids are important building blocks in the chemical and pharmaceutical industries and are currently produced via the Kolbe-Schmitt process, which requires elevated pressures and temperatures (≥ 5 bar, ≥ 100 °C) and often shows incomplete regioselectivities. In order to resolve bottlenecks in view of preparative-scale applications, we studied the kinetic parameters for 2,6-dihydroxybenzoic acid decarboxylase from Rhizobium sp. in the carboxylation- and decarboxylation-direction using 1,2-dihydroxybenzene (catechol) as starting material. The catalytic properties (Km, Vmax) are correlated with the overall thermodynamic equilibrium via the Haldane equation, according to a reversible random bi-uni mechanism. The model was subsequently verified by comparing experimental results with simulations. This study provides insights into the catalytic behaviour of a nonoxidative aromatic decarboxylase and reveals key limitations (e.g. substrate oxidation, CO2 pressure, enzyme deactivation, low turnover frequency) in view of the employment of this system as a 'green' alternative to the Kolbe-Schmitt processes. Microbial decarboxylases are known to catalyze the reversible regioselective ortho-carboxylation of phenolic derivatives in anaerobic detoxification pathways. In order to get new insights into the catalytic action and to resolve bottlenecks in view applications, we studied the kinetics of 2,6-dihydroxybenzoic acid decarboxylase from Rhizobium sp. in the carboxylation- and decarboxylation-direction, correlating the data according to a reversible random bi-uni mechanism.
- Pesci, Lorenzo,Glueck, Silvia M.,Gurikov, Pavel,Smirnova, Irina,Faber, Kurt,Liese, Andreas
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p. 1334 - 1345
(2015/04/14)
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- IMPROVED PROCESS FOR PREPARATION OF 2,3-DIHYDROXY BENZONITRILE
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Disclosed is one pot process of the preparation of 2,3-dihydroxy benzonitrile from 2,3-dialkoxy benzoic acid without prior isolation of the intermediates. Further disclosed is the preparation of 2,3-dihydroxy benzonitrile by dealkylation of 2,3-dialkoxy benzonitrile using suitable aluminum salt-amine complex.
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- Regioselective ortho-carboxylation of phenols catalyzed by benzoic acid decarboxylases: A biocatalytic equivalent to the Kolbe-Schmitt reaction
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The enzyme catalyzed carboxylation of electron-rich phenol derivatives employing recombinant benzoic acid decarboxylases at the expense of bicarbonate as CO2 source is reported. In contrast to the classic Kolbe-Schmitt reaction, the biocatalytic equivalent proceeded in a highly regioselective fashion exclusively at the ortho-position of the phenolic directing group in up to 80% conversion. Several enzymes were identified, which displayed a remarkably broad substrate scope encompassing alkyl, alkoxy, halo and amino- functionalities. Based on the crystal structure and molecular docking simulations, a mechanistic proposal for 2,6-dihydroxybenzoic acid decarboxylase is presented.
- Wuensch, Christiane,Gross, Johannes,Steinkellner, Georg,Lyskowski, Andrzej,Gruber, Karl,Glueck, Silvia M.,Faber, Kurt
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p. 9673 - 9679
(2014/03/21)
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- Inclusion complex containing epoxy resin composition for semiconductor encapsulation
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The invention is an epoxy resin composition for sealing a semiconductor, including (A) an epoxy resin and (B) a clathrate complex. The clathrate complex is one of (b1) an aromatic carboxylic acid compound, and (b2) at least one imidazole compound represented by formula (II): wherein R2 represents a hydrogen atom, C1-C10 alkyl group, phenyl group, benzyl group or cyanoethyl group, and R3 to R5 represent a hydrogen atom, nitro group, halogen atom, C1-C20 alkyl group, phenyl group, benzyl group, hydroxymethyl group or C1-C20 acyl group. The composition has improved storage stability, retains flowability when sealing, and achieves an effective curing rate applicable for sealing delicate semiconductors.
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- Regioselective enzymatic carboxylation of phenols and hydroxystyrene derivatives
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The enzymatic carboxylation of phenol and styrene derivatives using (de)carboxylases in carbonate buffer proceeded in a highly regioselective fashion: Benzoic acid (de)carboxylases selectively formed o-hydroxybenzoic acid derivatives, phenolic acid (de)carboxylases selectively acted at the β-carbon atom of styrenes forming (E)-cinnamic acids.
- Wuensch, Christiane,Glueck, Silvia M.,Gross, Johannes,Koszelewski, Dominik,Schober, Markus,Faber, Kurt
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supporting information; experimental part
p. 1974 - 1977
(2012/06/15)
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- Electrochemical behavior of triflusal, aspirin and their metabolites at glassy carbon and boron doped diamond electrodes
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The electrochemical behavior of triflusal (TRF) and aspirin (ASA), before and after hydrolysis in water and in alkaline medium using two different electrode surfaces, glassy carbon and boron doped diamond, was studied by differential pulse voltammetry over a wide pH range. The hydrolysis products were 2-(hydroxyl)-4-(trifluoromethyl)-benzoic acid (HTB) for triflusal and salicylic acid (SA) for aspirin, which in vivo represent their main metabolites. The hydrolysis processes were also followed by spectrophotometry. The UV results showed complete hydrolysis after one hour for TRF and after two hours for ASA in alkaline solution. The glassy carbon electrode enables only indirect determination of TRF and ASA through the electrochemical detection of their hydrolysis products HTB and SA, respectively. The oxidation processes of HTB and SA are pH dependent and involve different numbers of electrons and protons. Moreover, the difference between the oxidation peak potential of SA and HTB was equal to 100 mV in the studied pH range from 1 to 8 due to the CF3 of the aromatic ring of HTB molecule. Due to its wider oxidation potential range, the boron doped diamond electrode was used to study the direct oxidation of TRF and ASA, as well as of their respective metabolites HTB and SA.
- Enache, Teodor Adrian,Fatibello-Filho, Orlando,Oliveira-Brett, Ana Maria
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scheme or table
p. 569 - 577
(2010/12/25)
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- Enzymatic Kolbe-Schmitt reaction to form salicylic acid from phenol: Enzymatic characterization and gene identification of a novel enzyme, Trichosporon moniliiforme salicylic acid decarboxylase
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Salicylic acid decarboxylase (Sdc) can produce salicylic acid from phenol; it was found in the yeast Trichosporon moniliiforme WU-0401 and was for the first time enzymatically characterized, with the sdc gene heterologously expressed. Sdc catalyzed both reactions: decarboxylation of salicylic acid to phenol and the carboxylation of phenol to form salicylic acid without any byproducts. Both reactions were detected without the addition of any cofactors and occurred even in the presence of oxygen, suggesting that this Sdc is reversible, nonoxidative, and oxygen insensitive. Therefore, it is readily applicable in the selective production of salicylic acid from phenol, the enzymatic Kolbe-Schmitt reaction. The deduced amino acid sequence of the gene, sdc, encoding Sdc comprises 350 amino acid residues corresponding to a 40-kDa protein. The recombinant Escherichia coli BL21(DE3) expressing sdc converted phenol to salicylic acid with a 27% (mol/mol) yield at 30 °C for 9 h.
- Kirimura, Kohtaro,Gunji, Hiroaki,Wakayama, Rumiko,Hattori, Takasumi,Ishii, Yoshitaka
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experimental part
p. 279 - 284
(2011/11/14)
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- Polyvinylpyrrolidone-supported hydroperoxide for selective oxidation of aldehydes to carboxylic acids and sulfides to sulfoxides
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The facile immobilization of hydroperoxide on the cross-linked poly(vinylpyrrolidone) is described by treatment of a poly(vinylpyrrolidone)- Vilsmeier adduct with (35%) hydrogen peroxide. The in situ-generated poly(vinyl pyrrolidone)-supported hydroperoxide reagent showed very good performance in chemoselective oxidation of aldehydes to carboxylic acids as well as sulfides to sulfoxides. Supplemental materials are available for this article. Go to the publishers online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. Taylor & Francis Group, LLC.
- Lakouraj, Moslem Mansour,Aghajani, Bahareh,Mokhtary, Masoud
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experimental part
p. 2393 - 2401
(2011/03/17)
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- Application of advanced oxidation processes for removing salicylic acid from synthetic wastewaters
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In this study, advanced oxidation processes (AOPs) such as anodic oxidation (AO), UV/H2O2 and Fenton processes (FP) were investigated for the degradation of salicylic acid (SA) in lab-scale experiments. Boron-doped diamond (BDD) film electrodes using Ta as substrates were employed for AO of SA. In the case of FP and UV/H2O2, most favorable experimental conditions were determined for each process and these were used for comparing with AO process. The study showed that the FP was the most effective process under acidic conditions, leading to the highest rate of SA degradation in a very short time interval. However, the results showed that Ta/BDD films had high electrocatalytic activity for complete degradation of SA; even if it employs more time for complete elimination of the SA respect to FP. Additionally, AO led to a sixfold acceleration of the oxidation rate compared with the UV/H2O2 process. Finally a rough comparison of the specific energy consumption shows that AO process reduced the energy consumption by at least 90% compared with the UV/H2O2 process.
- Chen, Xue Ming,da Silva, Djalma Ribeiro,Martínez-Huitle, Carlos A.
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experimental part
p. 101 - 104
(2010/11/17)
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- PROCESS FOR STRAIGHTENING KERATIN FIBRES WITH A HEATING MEANS AND DENATURING AGENTS
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The invention relates to a process for straightening keratin fibres, comprising: (i) a step in which a straightening composition containing at least two denaturing agents is applied to the keratin fibres, (ii) a step in which the temperature of the keratin fibres is raised, using a heating means, to a temperature of between 110 and 250° C.
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- Catechuic acid and ethyl 2,4,5-trihydroxybenzoate from d-glucose
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Synthesis of catechuic acid (1) and ethyl 2,4,5-trihydroxybenzoate (2) from d-glucose-derived β-ketoester is described. The polyhydroxylated β-ketoester obtained from the hydrolysis of sugar β-ketoester 3 was subjected to an aldol-type condensation to get
- Bhujbal, Namdeo N.,Bande, Omprakash P.,Dhavale, Dilip D.
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experimental part
p. 734 - 738
(2009/06/08)
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- Aluminium(III) adsorption: A soft and simple method to prevent TiO 2 deactivation during salicylic acid photodegradation
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Deposition of poisoning species on TiO2 during salicylic acid photodegradation can be halted when Al(III) has been previously adsorbed on the catalyst surface; this widens the application of photocatalysis to more concentrated solutions. The Royal Society of Chemistry 2005.
- Franch, Maria Isabel,Peral, Jose,Domenech, Xavier,Ayllon, Jose A.
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p. 1851 - 1853
(2007/10/03)
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- Water-soluble cyclopalladated aryl oxime: A potent 'green' catalyst
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Orthopalladated aryl oxime with a 15-crown-5 motif is prepared in a 72% yield by the exchange of cyclopalladated ligands from oxime of 4′-acetylbenzo-15-crown-5 and orthometalated N,N-dimethylbenzylamine, [Pd(o-C6H4CH2NMe2)Cl]2. Its solubility in water is more than ten times higher than that of the related complex without the crown fragment and increases further in the presence of magnesium(II) salts. Potential applications of the newly synthesized palladacycle in catalysis is demonstrated by the example of biomimetic hydrolysis of 4-nitrophenyl 2,3-dihydroxybenzoate. It has been demonstrated that a 120-fold rate increase is achieved by realization of the intramolecular general base mechanism.
- Bezsoudnova, Ekaterina Yu.,Ryabov, Alexander D.
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- Demethoxylation and hydroxylation of methoxy- and hydroxybenzoic acids by OH-radicals. Processes of potential importance for food irradiation
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The hydroxylation process for methoxy- and hydroxy-benzoic acids (MBA, HBA) induced by γ-radiation is compared. 2-, 3-, and 4-methoxybenzoic acid as well as 3-hydroxybenzoic acid have been irradiated in N2O and aerated solutions up to 1.5 kGy. The products were analyzed by HPLC. The results for 2- and 4-HBA have been taken from literature data. The OH·-adduct distribution is generally the same for the hydroxy- as well as for the methoxy-benzoic acid isomers. With both 4-HBA and 4-MBA more than 65% C3-adducts and about 15% C4-adducts are formed, which could be proved by their reactions with K3 Fe(CN)6. Oxidation of the nonipso-adducts of 3-HBA and 3-MBA results in 84 and 87% of the corresponding phenols. Whereas in N2O-saturated solutions only part of the OH·-radicals leads to substrate decomposition, in the presence of air, the degradation of both kinds of compounds is equivalent to [OH·]. The nonipso OH·-adducts of the HBAs are converted into 68-77% hydroxylation products. With the MBAs, the hydroxylation process is ≤10%. This is attributed to different decay pathways of the peroxyl radicals, intermediates formed by O2 addition to the OH·-adducts. The hydroxyperoxycyclohexadienyl radicals of the HBAs decay mainly by HO2· elimination to the corresponding phenols, those of the MBAs decay predominantly by fragmentation of the benzene ring, yielding to nonidentified aliphatic products. The replacement of -OCH3 by -OH is practically not influenced by the presence of oxygen, it increases in the sequence 3-MBA 4-MBA 2-MBA. For 2-MBA, yields of more than 15% are obtained. Both processes, hydroxylation as well as demethoxylation, might be of importance for the recognition of radiolytical changes in foodstuff.
- Gaisberger,Solar
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p. 394 - 404
(2007/10/03)
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- Hydroxylation by Electrochemically Generated OH. Radicals. Mono- and Polyhydroxylation of Benzoic Acid: Products and Isomers' Distribution
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The electrochemical Fenton reaction (simultaneous reduction of dioxygen and ferric ions) permits a controlled production of OH. radicals.These are used for the stepwise hydroxylation of benzoic acid to mono- and polyhydroxylated products.The quantitative distribution of all the hydroxylated products is achieved by use of HPLC.The overall reaction scheme is established and the rate constants of the individual steps are measured.
- Oturan, Mehmet A.,Pinson, Jean
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p. 13948 - 13954
(2007/10/02)
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- Degradation of Phenol and Salicylic Acid by Ultraviolet Radiation/Hydrogen Peroxide/Oxygen
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Based on the oxidation reactions of u.v. radiation/hydrogen peroxide/oxygen with either phenol or salicylic acid a spectra library was established. The reaction products contain hydroxylated phenols, benzoquinone and aliphatic acids with up to six carbon atoms. Many of the substances have been identified by means of chromatography and spectra comparison. From the observed concentrations of the substances and the known reaction mechanisms the following course of reaction has been postulated. The first reaction step is the hydroxylation of the aromatic ring. Further oxidation occurs via abstraction of a hydrogen atom to form 1,2-benzoquinone which is cleaved to form muconic acid. The cleavage of the muconic acid by u.v. radiation/hydrogen peroxide/oxygen leads to maleic acid, fumaric acid and oxalic acid. The degradation of oxalic acid leads to formic acid and finally to carbon dioxide. The hydroxylation of the double bond of the maleic or fumaric acid and the abstraction of a hydrogen atom produces malic acid. The reactions can be seen as essential step in the photochemical transformation of refractory substances into biodegradable ones.
- Scheck, Christoph K.,Frimmel, Fritz H.
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p. 2346 - 2352
(2007/10/03)
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- Hydroxybenzoic acids from Boreava orientalis
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A new guaiacylglycerol ether, threo-guaiacylglycerol-8'-vanillic acid ether, pyrocatechuic acid, pyrocatechuic acid 3-O-β-D-glucoside, gentisic acid, gentisic acid 5-O-β-D-glucoside, vanillic acid and vanillic acid 4-O-β-D-glucoside were identified from fruits of Boreava orientalis.Structural elucidation was carried out on the basis of UV, mass, 1H and 13C NMR spectral data, including 2D shift-correlation and selective INEPT experiments.
- Sakushima, Akiyo,Coskun, Maksut,Maoka, Takashi
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p. 257 - 262
(2007/10/02)
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- The Photoinduced Fenton Reaction; Mechanism of Photosensitized Catalyst Generation
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Laser flash-photolytic studies along with determination of the hydroxylation kinetics of salicylic acid under continuous irradiation (λirr = 589 nm) have shown that the active species inducing the photoreduction of Fe(III) salicylate (i.e. the photogeneration of the catalyst) is the excited singlet state of methylene blue, 1MB(+).The hydroxylation products are 2,3- and 2,5-dihydroxybenzoic acid.Binuclear complexes containing iron in various oxidation states (i.e.Fe(II) and Fe(III)) seem to be effective hydroxylation catalysts. - Keywords: Methylene blue / Hydrogen peroxide / Photosensitization / Hydroxylation
- Lang, Kamil,Lunak, Stanislav,Sedlak, Petr,Kubat, Pavel,Brodilova, Jirina
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p. 203 - 210
(2007/10/02)
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- Quantitation of the hydroxyl radical adducts of salicylic acid by micellar electrokinetic capillary chromatography: Oxidizing species formed by a Fenton reaction
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There has been controversy concerning the products formed by a Fenton reaction. We determined the hydroxyl radical (.OH) generated in a Fenton reaction system with no iron chelator using micellar electrokinetic capillary chromatography (MECC). The hydroxyl radical generated in this Fenton system attacked salicylic acid to produce major products of 2,3- and 2,5-dihydroxybenzoic acid (DHB), 2,3-DHB being prominent. Hydroxyl radical scavengers, such as mannitol, ethanol, thiourea and a ferric chelator, Desferal, significantly diminished the peaks for DHBs, showing production of .OH. We compared the MECC method with the electron paramagnetic resonance (EPR) spin trapping technique. The quantity of DHBs obtained by MECC increased dose-dependently up to 1 μM Fe2+ at a fixed concentration of H2O2, whereas that of the spin adduct by EPR showed a bell-shaped curve. This quantitation of .OH adducts by MECC supports the proposal that the oxidizing species formed by a Fenton reaction with no chelator is .OH. The EPR spin trapping method appears to be erroneous, particularly when iron is present at a higher concentration than hydrogen peroxide. The application of this method to the paraquat effect in vitro is demonstrated, and the possibility for analysis of .OH in vivo is also discussed.
- Tomita,Okuyama,Watanabe,Watanabe
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p. 428 - 433
(2007/10/03)
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- THE ROLE OF HYDROGEN PEROXIDE IN DIOXYGEN INDUCED HYDROXYLATION OF SALICYLIC ACID
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The photochemically initiated oxidation of salicylic acid by molecular oxygen in the presence of 3- leads to a mixture of 2,3- and 2,5-dihydroxybenzoic acids.Iron(II) generated by the photoreduction is reoxidized by dioxygen.Hydrogen peroxide formed in this reaction takes part in the Fenton reaction in the presence of Fe(II).Experiments with OH* radical scavengers document the role of radicals in the photochemical and thermal hydroxylation of salicylic acid.
- Lang, Kamil,Wagnerova, Dana M.,Brodilova, Jirina
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p. 2447 - 2453
(2007/10/02)
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- LIFETIME OF THE TRIPLET STATE OF METHYLENE BLUE IN THE PRESENCE OF SALICYLIC ACID
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A break the lifetime of MBH2+ (T1) vs. salicylic acid concentration plot occurs at around 6x10 E(-5) M (corresponding to pH of the solution 4.3).This pH is close to pK1 of leucomethylene blue.The quantum yields of 2,3-dihydroxybenzoic acid increase with increasing salicylic acid concentration over the whole range investigated (9x10 E(-6) - 3x10 E(-4)M); the growth of the quantum yields becomes more pronounced for pH 4.35, too.
- Sedlak, Petr,Vidoczy, Tamas,Lunak, Stanislav
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p. 987 - 988
(2007/10/02)
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- Kinetics and mechanism of the oxidation of 2,3-dihydroxybenzoic acid by iron(III)
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The kinetics of the oxidation of 2,-3-dihydroxybenzoic acid (DHB) by aqueous iron(III) have been studied in aqueous acid with [Fe(III)] ? [DHB]. The initial complexation reaction of Fe(OH2)63+ and DHB was studied previously. The iron(III)-DHB complex is oxidized by iron(III) with a rate law that is first order in iron(III) and has terms that are inverse first order in [H+] and inverse second order in [Fe(OH2)62+]. It is shown that the oxidation does not proceed by simple intramolecular electron transfer within the iron(III)-DHB complex. A mechanism is proposed in which the latter complex reacts first by substitution on free iron(III) followed by two reversible electron-transfer steps to give the quinone product.
- Xu, Jinhuang,Jordan
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p. 4563 - 4566
(2008/10/08)
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- On the Oxygenation of Several Aromatic and Aliphatic Compounds with Aqueous Ferrous Ion-molecular Oxygen
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Hydroxylation was shown to occur readily in the reactions of aromatic compounds siuch as benzoic acid, nitrobenzene, acetanilide, and phenol with ferrous ion-molecular oxygen in 0.5M phosphate buffer (pH 6.8) at 40 deg C for 3 h.The yields of hydroxylated products were higher than those obtained with other reported hydroxylation systems of transition metal-molecular oxygen.The NIH shift was not observed in the title reactions of C(4)-deuterioacetanilide and C(4)-deuteriobenzoic acid.This system was also demonstrated to oxygenate caproic acid to give a mixture of 3-, 4-, and 5-oxocaproic acids in 67percent total yield. Keywords ---- hydroxylation of aromatic compound; ferrous ion; molecular oxygen; benzoic acid; nitrobenzene; acetanilide; phenol; NIH shift; oxygenation of caproic acid; GC-MS of methyl oxocaproate
- Miura, Toshiaki,Shibata, Kunihiko,Adachi, Kenichi,Sawaya, Takuji,Kimura, Michiya
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p. 100 - 105
(2007/10/02)
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- STERIC EFFECTS IN THE METALLATION OF ALKOXY- AND DIALKOXY-BENZENES
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With the aim of examining the role of steric factors in determining the position of metallation, the reaction of n-butyllithium with a series of 1,2-dialkoxy-, 1,2-alkylthio-, 1,4-dialkoxy-, and 2-t-butyl-1-alkoxy-benzenes has been studied in the presence and in the absence of N,N,N',N'-tetramethylethylenediamine (TMEDA).Steric factors are particularly relevant in the case of 2-t-butyl-alkoxybenzenes where the yields of metallation dramatically decrease passing from the methoxy to the isopropoxy derivative, while with the t-butoxy derivative only cleavage of the ether bond occurs.
- Bernard, Angela Maria,Piras, Pier Paolo,Plumitallo, Antonio,Melis, Stefana,Sotgiu, Francesca
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p. 443 - 446
(2007/10/02)
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