- Metal-free Transformations of Nitrogen-Oxyanions to Ammonia via Oxoammonium Salt
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Transformations of nitrogen-oxyanions (NOx?) to ammonia impart pivotal roles in sustainable biogeochemical processes. While metal-mediated reductions of NOx? are relatively well known, this report illustrates proton-assisted transformations of NOx? anions in the presence of electron-rich aromatics such as 1,3,5-trimethoxybenzene (TMB?H, 1 a) leading to the formation of diaryl oxoammonium salt [(TMB)2N+=O][NO3?] (2 a) via the intermediacy of nitrosonium cation (NO+). Detailed characterizations including UV/Vis, multinuclear NMR, FT-IR, HRMS, X-ray analyses on a set of closely related metastable diaryl oxoammonium [Ar2N+=O] species disclose unambiguous structural and spectroscopic signatures. Oxoammonium salt 2 a exhibits 2 e? oxidative reactivity in the presence of oxidizable substrates such as benzylamine, thiol, and ferrocene. Intriguingly, reaction of 2 a with water affords ammonia. Perhaps of broader significance, this work reveals a new metal-free route germane to the conversion of NOx to NH3.
- Anju, Balakrishnan S.,Kundu, Subrata,Mondal, Aditesh,Sahana, Tuhin
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supporting information
p. 20661 - 20665
(2021/08/25)
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- Oxidative Dearomatization of Phenols and Polycyclic Aromatics with Hydrogen Peroxide Triggered by Heterogeneous Sulfonic Acids
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We report herein a method for the oxidative dearomatization of phenols and bare polycyclic arenes into the corresponding quinoid derivatives using hydrogen peroxide. The reaction is catalyzed by sulfonic acids and best results were achieved using heterogenized species. The best results using phenols were achieved using a hybrid material, namely a perfluorinated polymer functionalized with sulfonic acid groups supported on silica. The dearomatization of polycyclic aromatic hydrocarbons performed better using the polymeric acid catalyst. These methods operate under mild conditions, using mild and benign oxidants and thus minimizing the formation of waste.
- Pancrazzi, Francesco,Maestri, Giovanni,Maggi, Raimondo,Viscardi, Rosanna
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supporting information
p. 5407 - 5414
(2021/10/25)
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- Polyoxometalate-based supramolecular porous frameworks with dual-active centers towards highly efficient synthesis of functionalized: P -benzoquinones
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Selective oxidation of substituted phenols is an ideal method for preparing functionalized p-benzoquinones (p-BQs), which serve as versatile raw materials for the synthesis of a variety of biologically active compounds. Herein, two new polyoxometalate-based supramolecular porous frameworks, K3(H2O)4[Cu(tza)2(H2O)]2[Cu(Htza)2(H2O)2][BW12O40]·6H2O (1) and H3K3(H2O)3[Cu(Htza)2(H2O)]3[SiW12O44]·14H2O (2) (Htza = tetrazol-1-ylacetic acid), were synthesized and structurally characterized by elemental analysis, infrared spectroscopy, thermal analysis, UV-vis diffuse reflectance spectroscopy, and single-crystal X-ray and powder diffraction. The single-crystal X-ray diffraction analysis indicates that both compounds possess unique petal-like twelve-nucleated Cu-organic units composed of triangular and hexagonal metal-organic loops. In 1, the Cu-organic units are isolated and [BW12O40]5- polyoxoanions are sandwiched between staggered adjacent triangular channels in the structure. However in 2, the Cu-organic units extend into a two-dimensional layered structure, and the [SiW12O44]12- polyoxoanions occupy the larger hexagonal channels in the stacked structure. Both compounds as heterogeneous catalysts can catalyze the selective oxidation of substituted phenols to high value-added p-BQs under mild conditions (60 °C) with TBHP as the oxidant, particularly in the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone (TMBQ, key intermediate in vitamin E production). Within 8-10 min, the yield of TMBQ is close to 100%, and oxidant utilization efficiency is up to 94.2% for 1 and 90.9% for 2. The turnover frequencies of 1 and 2 are as high as 5000 and 4000 h-1, respectively. No obvious decrease in the yield of TMBQ was observed after five cycles, which indicates the excellent sustainability of both compounds. Our study of the catalytic mechanism suggests that there is a two-site synergetic effect: (i) the copper ion acts as the catalytic site of the homolytic radical pathway; and (ii) the polyoxoanion acts as the active center of the heterolytic oxygen atom transfer pathway. This journal is
- An, Haiyan,Chang, Shenzhen,Chen, Yanhong,Huang, Yaohui,Luo, Huiyun,Zhu, Qingshan
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p. 8591 - 8603
(2021/11/17)
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- Polycarboxylated compounds and compositions containing same
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Methods of selectively modifying lignin, polycarboxylated products thereof, and methods of deriving aromatic compounds therefrom. The methods comprise electrochemically oxidizing lignin using stable nitroxyl radicals to selectively oxidize primary hydroxyls on β-O-4 phenylpropanoid units to corresponding carboxylic acids while leaving the secondary hydroxyls unchanged. The oxidation results in polycarboxylated lignin in the form of a polymeric β-hydroxy acid. The polymeric β-hydroxy acid has a high loading of carboxylic acid and can be isolated in acid form, deprotonated, and/or converted to a salt. The β-hydroxy acid, anion, or salt can also be subjected to acidolysis to generate various aromatic monomers or oligomers. The initial oxidation of lignin to the polycarboxylated form renders the lignin more susceptible to acidolysis and thereby enhances the yield of aromatic monomers and oligomers obtained through acidolysis.
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Page/Page column 17-22
(2021/06/09)
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- Photocatalytic Chemoselective C-C Bond Cleavage at Room Temperature in Dye-Sensitized Photoelectrochemical Cells
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Selective cleavage of C-C bonds can be a valuable tool for various applications including polymer degradation and biomass utilization. Performing chemical transformations involving C-C bond cleavage steps under mild conditions and ambient temperature remains challenging due to the high dissociation energies of the C-C bond. This fundamental challenge can be solved by coupling a dye-sensitized photoelectrochemical cell (DSPEC) system, that generally targets the water splitting reaction, with a hydrogen atom transfer (HAT) mediator (HAT-DSPEC). Here, we report the solar-driven selective cleavage of the C(aryl)-C(alkyl) σ-bond in lignin at ambient temperature using an HAT-DSPEC under redox-neutral conditions. The photocatalyst (bis-2,2′-bipyridine)(2,2′-bipyridine-4,4′-dicarboxylic acid)Ru(II) (RuC) adsorbed onto a TiO2 nanorod array with the length of ~1.6 μm and a rod diameter of 100 nm atop fluorine-doped tin oxide (FTO|TiO2 NRAs|RuC) film was prepared and investigated with an HAT mediator, 4-acetamido 2,2,6,6-tetramethylpiperidine-1-oxyl (ACT), in solution. Photophysical and electrochemical studies of RuC and ACT with a lignin model compound, 1-(4-hydroxy-3,5-dimethoxyphenyl)-2-(2-methoxyphenoxy) propane-1,3-diol (LMC) reveal that the metal-to-ligand charge transfer (MLCT) excited states from the RuC are efficiently quenched in the presence of ACT with LMC. The HAT-DSPEC photoanode, containing the surface-bound photocatalyst RuC at the photoanode with ACT and LMC in solution, sustained an excellent photocurrent density, significantly outperforming that with the photocatalyst RuC alone. Moreover, the chemoselective cleavage of the C(aryl)-C(alkyl) bond in the LMC at the ambient temperature was demonstrated in the HAT-DSPEC system with a remarkable photocatalytic turnover number (>3000) leading to excellent selectivity (>90%) of C-C bond cleavage under AM1.5G irradiation (1 sun, 100 mW cm-2). These results were obtained over short reaction times and mild, redox-neutral reaction conditions without the need for extended reaction time (e.g., >24 h) or high temperature that is typical of homogeneous catalytic systems. This is the first report to demonstrate that an HAT-DSPEC can serve as a viable method for performing visible-light-driven selective C-C bond cleavage at ambient temperature.
- Li, Shuya,Kim, Saerona,Davis, Andrew H.,Zhuang, Jingshun,Shuler, Eric Wolfgang,Willinger, Debora,Lee, Jae-Joon,Zheng, Weiwei,Sherman, Benjamin D.,Yoo, Chang Geun,Leem, Gyu
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p. 3771 - 3781
(2021/04/07)
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- Differences in the Mechanisms of MnO2Oxidation between Lignin Model Compounds with the p-Hydroxyphenyl, Guaiacyl, and Syringyl Nuclei
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The purpose of this study was to examine how the rate and mechanism of MnO2 oxidation differ between the p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) types of simple nonphenolic lignin model compounds as well as the p-ethylphenyl (E) type compounds. The oxidation was conducted using an excess amount of MnO2 in a sulfate buffer solution at a pH value of 1.5 at room temperature. MnO2 oxidized at least the G and S nuclei, although it commonly oxidizes alcohols present at the benzyl position. The oxidation rates of the benzyl alcohol derivatives were in the order of G- > S- ? H- > E-type, which suggests that the rates are determined by the electronic effects of their methoxy and ethyl functional groups on not only their benzyl positions but also their aromatic π-electron systems. The kinetic isotope effect was observed in the MnO2 oxidations of the same derivatives deuterated at their benzyl hydroxymethyl groups. The observed magnitudes were in the order of E- ? H- > G- ? S-type, suggesting that the contribution of oxidation of their aromatic nuclei, which is another reaction mode of the oxidation of their benzyl positions, increases in the reverse order.
- Sun, Shirong,Akiyama, Takuya,Yokoyama, Tomoya,Matsumoto, Yuji
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p. 6819 - 6825
(2020/07/02)
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- Oxidation of Electron-Rich Arenes Using HFIP-UHP System
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The straightforward oxidation of electron-rich arenes, namely, phenols, naphthols, and anisole derivatives, under mild reaction conditions, is described by means of the use of an environmentally benign HFIP-UHP system. The corresponding quinones or hydroxylated arenes were obtained in moderate to good yields.
- Llopis, Natalia,Baeza, Alejandro
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p. 6159 - 6164
(2020/05/20)
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- Regiodivergent oxidation of alkoxyarenes by hypervalent iodine/oxone system
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We have found that the combination of Oxone with an organoiodine compound, i.e., 2-iodobenzoic acid (2-IB), selectively yields p-quinones from monomethoxyarenes under mild conditions. In this reaction system, an organoiodine compound is immediately oxidized by Oxone to generate cyclic hypervalent iodine (III) species in situ, which serves as the specific mediator for the selective p-quinone synthesis, preventing o-quinone formation.
- China, Hideyasu,Tanihara, Kokoro,Sasa, Hirotaka,Kikushima, Kotaro,Dohi, Toshifumi
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- Improved Pd/Ru metal supported graphene oxide nano-catalysts for hydrodeoxygenation (HDO) of vanillyl alcohol, vanillin and lignin
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Pd and Ru nanoparticles supported on graphene oxide (GO) [Pd?GO and Ru?GO] and bimetallic [Pd/Ru?GO] were prepared and well characterized by XRD, FT-IR, EDS, TEM, XPS and ICP-AES analyses. The prepared nano-catalysts were tested for hydrodeoxygenation (HDO) of lignin monomer molecules-vanillyl alcohol and vanillin. In comparison with previously reported methods, Ru?GO and bimetallic Pd/Ru?GO catalysts showed high activity and selectivity, under milder conditions, at room temperature and 145 psi H2 pressure, for the formation of p-creosol, a value added product, as a potential future biofuel with antibacterial and anti-insecticidal properties. The multifold advantages of both these catalysts are in terms of reduced catalyst loading with a lower metal content and ambient temperture conditions resulting in higher conversion of the starting material. Furthermore, the efficacy of the developed methodology using Ru?GO and bimetallic Pd/Ru?GO catalysts under the optimized conditions was tested on the phenolic components of commercial lignin obtained by photo-catalytic fragmentation using TiO2, to obtain a mixture after HDO which contained vanillyl alcohol and p-creosol among others, as indicated by HPLC-MS analysis.
- Arora, Shalini,Gupta, Neeraj,Singh, Vasundhara
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supporting information
p. 2018 - 2027
(2020/04/07)
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- Steric effects of bulky tethered arylpiperazines on the reactivity of Co-Schiff base oxidation catalysts—a synthetic and computational study
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New C2-symmetric and C2-asymmetric Co-Schiff base catalysts tethered to arylpiperazine units were synthesized and used to oxidize phenolic lignin models to para-benzoquinones. Synthetic approaches to these catalysts were optimized to include fewer steps and broaden the types of catalyst structures available. In contrast to conventional Co-Schiff base catalysts, these systems induce phenolic oxidation in the absence of an external axial base, simplifying the process. Asymmetric catalysts bearing a phenylethylene or diphenylmethyl piperazine substituent display the highest catalytic activity observed to date for the conversion of S-models to 2,6-dimethoxybenzoquinone (DMBQ). Computational analysis shows that more reactive catalysts populate conformations that favor oxidation in preference to non-productive decomposition routes. This balance between catalyst reactivity and catalyst deactivation is optimized by inclusion of sufficient steric bulk around the periphery of the Schiff base ligand, reducing catalyst deactivation and allowing oxidations to proceed in the absence of an added axial ligand.
- Key, Rebecca E.,Elder, Thomas,Bozell, Joseph J.
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p. 3118 - 3127
(2019/05/10)
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- Investigating homogeneous Co/Br-/H2O2 catalysed oxidation of lignin model compounds in acetic acid
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Oxidation of α-O-4, β-O-4 and monomeric lignin model compounds by Co/Br-/H2O2 in acetic acid at 70 °C was investigated. Co and Br- were introduced as cobalt acetate tetrahydrate and KBr respectively. The degree of methoxylation of the substrate was found to affect its reactivity. For the α-O-4 model compounds, increased methoxylation of the benzyl moiety influenced product selectivity, while increased methoxylation of the phenolic moiety increased substrate conversion. The β-O-4 model compounds exhibited similar conversions to the α-O-4 models, but afforded a lesser amount of monomeric products. The formation of phenol and guaiacol from α-O-4 bond cleavage inhibited substrate conversion and sequestered oxidation products due to the formation of phenoxy radicals and polyguaiacols. Similar to the α-O-4 model compounds, increased methoxylation of the monomers changed the types of products formed, from polyphenols (phenol and guaiacol) to quinones (syringol). The behaviour of syringol was explored extensively, revealing that the corresponding 1,4-hydroquinone strongly inhibited syringol oxidation, and the syringol oxidation product, 4,4′-diphenoquinone, was susceptible to over-oxidation. The deleterious effects of phenols on oxidation of an α-O-4 model could be reduced by substitution of the Br- co-catalyst with N-hydroxyphthalimide (NHPI), improving substrate conversion and product selectivity.
- Clatworthy, Edwin B.,Picone-Murray, Julia L.,Yuen, Alexander K. L.,Maschmeyer, Richard T.,Masters, Anthony F.,Maschmeyer, Thomas
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p. 384 - 397
(2019/01/28)
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- Electrochemical Aminoxyl-Mediated Oxidation of Primary Alcohols in Lignin to Carboxylic Acids: Polymer Modification and Depolymerization
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An electrochemical process has been developed for chemoselective oxidation of primary alcohols in lignin to the corresponding carboxylic acids. The electrochemical oxidation reactions proceed under mildly basic conditions and employ 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) and 4-acetamidoO (ACT) as catalytic mediators. Lignin model compounds and related alcohols are used to conduct structure-reactivity studies that provide insights into the origin of the reaction selectivity. The method is applied to the oxidation of lignin extracted from poplar wood chips via a mild acidolysis method, and the reaction affords a novel polyelectrolyte material. Gel permeation chromatography data for the oxidized lignin shows that this material has a molecular weight and molecular weight distribution very similar to that of the extracted lignin, but notable differences are also evident. Base titration reveals a significant increase in the acid content, and the oxidized lignin has much higher water solubility relative to the extracted lignin. Treatment of the oxidized lignin under acidic conditions results in depolymerization of the material into characterized aromatic monomers in nearly 30 wt% yield.
- Rafiee, Mohammad,Alherech, Manar,Karlen, Steven D.,Stahl, Shannon S.
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supporting information
p. 15266 - 15276
(2019/10/19)
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- Stepwise degradation of hydroxyl compounds to aldehydes: Via successive C-C bond cleavage
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Stepwise degradation of hydroxyl compounds to aldehydes via successive cleavage of C-C bonds was achieved by using a bimetallic catalytic system (PdCl2 + CuCl) without any ligands and additives. The broad applicability is expanded to a diverse range of aromatic, aliphatic, primary and secondary alcohols, as well as lignin model compounds.
- Liu, Mingyang,Zhang, Zhanrong,Shen, Xiaojun,Liu, Huizhen,Zhang, Pei,Chen, Bingfeng,Han, Buxing
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supporting information
p. 925 - 928
(2019/01/24)
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- Selective synthesis of benzoquinones over Cu(ii)-containing propylsalicylaldimine functionalized mesoporous solid catalysts
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The major product, 2,3,5-trimethyl-1,4-benzophenone (TMBO), was synthesised by an eco-friendly liquid-phase oxidation of 2,3,6-trimethylphenol (TMP-OH) over Cu(ii)-containing propylsalicylaldimine (CSA) functionalized mesoporous solid catalysts, namely, CSASBA-15(0.2), CSASBA-15(0.1) and CSAMCM-41(0.2), synthesized using various amounts of copper in a simple post-grafting method using different mesoporous silica materials, e.g., thick-silica walled SBA-15 and thin-silica walled MCM-41. The benzoquinones, i.e., 2,6-disubstituted p-benzoquinones (DSBQs), were also synthesised by the slurry-phase oxidation of di/tri-substituted phenols using the prepared catalysts. A promising chemical treatment was used for the removal of extra-framework copper species from the active surface of CSASBA-15(0.2), and the catalytic activity of the recovered catalyst, i.e. green mesoporous CSASBA-15(0.2) or W-CSASBA-15(0.2), was evaluated. Various reaction parameters, oxidants and solvents were used in this catalytic oxidation. To confirm the catalytic stability, recyclability and hot-catalytic filtration experiments were performed. On the basis of all catalytic results, it is worth noting that the mesoporous CSASBA-15(0.2) is an outstanding and a promising heterogeneous catalyst for the selective synthesis of TMBO and DSBQs, and produces 98% TMBO selectivity with 100% TMP-OH conversion at 353 K for 40 min and 97-99% DSBQ selectivity with 98-100% di/tri-substituted phenols conversion at 330 K for 1-3 h. The green mesoporous catalyst has unprecedented catalytic activity compared with that of other CSA functionalized mesoporous solid catalysts.
- Selvaraj, Manickam,Assiri, Mohammed A.
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supporting information
p. 3291 - 3299
(2019/03/13)
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- Reactions between 5-Nitroso-1,3-diphenyltetrazolium salts and electron-rich arenes, amines, thiophenol, sulfoxides, and thioanisole
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A series of reactions between 5-nitroso-1,3-diphenyltetrazo-lium tetrafluoroborate and methoxybenzenes, amines, thiols, sulfoxides, and sulfides, most of which are generally accepted as being inert to nitroso groups, is reported here. The tetrazolium-activated nitroso functionality is capable of oxidizing the aforementioned substrates to give the corresponding oxidized products, and the nitroso tetrazolium itself is transformed into the corresponding amide or hydroxyamide, depending on the nature of the reaction partners. In the case of thioanisole, an addition product was obtained.
- Matsukawa, Yuta,Hirashita, Tsunehisa,Araki, Shuki
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supporting information
p. 540 - 544
(2019/04/05)
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- Au-Pd alloy cooperates with covalent triazine frameworks for the catalytic oxidative cleavage of β-O-4 linkages
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To design highly efficient catalysts for the cleavage of the C-O/C-C bond is the key task in the depolymerization of lignin. Bimetallic alloy catalysts Au-Pd-CTFs were developed to be effective in the oxidative cleavage of β-O-4 lignin model compounds with O2. Au-Pd nanoparticles with an Au/Pd molar ratio between 1?:?1 and 1?:?1.5 showed the highest cleavage efficiency. The kinetics of the reaction process revealed that a synergistic effect between Au and Pd played a crucial role in the oxidation of Cα-OH into CαO, which was the rate-determining step for the whole oxidative cleavage process. Further insight revealed that the cooperative effect between Au-Pd nanoparticles and the support covalent triazine frameworks (CTFs) facilitated the cleavage of the formed β-O-4 ketone compound to the corresponding aromatics. In addition, Au-Pd-CTF catalysts also showed efficiency in the oxidative transformation of the organosolv lignin. This catalytic system will provide guidance in the oxidative cleavage of β-O-4 linkages in lignin.
- Zhao, Li,Shi, Song,Zhu, Guozhi,Liu, Meng,Gao, Jin,Xu, Jie
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p. 6707 - 6716
(2019/12/26)
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- Activating molecular oxygen with Au/CeO2 for the conversion of lignin model compounds and organosolv lignin
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Au/CeO2 was demonstrated to be a high efficiency catalyst for the conversion of 2-phenoxyacetophenol (PP-ol) employing O2 as an oxidant and methyl alcohol as the solvent without using an erosive strong base or acid. Mechanistic investigations, including emission quenching experiments, electron spin-resonance (ESR) and intermediate verification experiments, were carried out. The results verified that the superoxide anion activated by Au/CeO2 from molecular oxygen plays a vital role in the oxidation of lignin model compounds, and the cleavage of both the β-O-4 and Cα-Cβ linkages was involved. Au/CeO2 also performed well in the oxidative conversion of organosolv lignin under mild conditions (453 K), producing vanillin (10.5 wt%), methyl vanillate (6.8 wt%), methylene syringate (3.4 wt%) and a ring-opened product. Based on the detailed characterization data and mechanistic results, Au/CeO2 was confirmed to be a promising catalytic system.
- Song, Wu-Lin,Dong, Qingmeng,Hong, Liang,Tian, Zhou-Qi,Tang, Li-Na,Hao, Wenli,Zhang, Hongxi
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p. 31070 - 31077
(2019/10/28)
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- Oxidative cleavage of β-O-4 bonds in lignin model compounds with a single-atom Co catalyst
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Single-atom catalysts are emerging as primary catalysts for many reactions due to their 100% utilization of active metal centers leading to high catalytic efficiencies. Herein, we report the use of a single-atom Co catalyst for the oxidative cleavage of the β-O-4 bonds of lignin model compounds at a low oxygen pressure. Under the optimized reaction conditions, the conversion of 2-(2-methoxyphenoxy)-1-phenylethanol up to 95% with high selectivities was achieved with a variety of substrates investigated. The reusability of the Co catalyst with a high catalytic efficiency indicates its potential application in the oxidative cleavage of C-O bonds.
- Liu, Sijie,Bai, Lichen,Van Muyden, Antoine P.,Huang, Zhangjun,Cui, Xinjiang,Fei, Zhaofu,Li, Xuehui,Hu, Xile,Dyson, Paul J.
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supporting information
p. 1974 - 1981
(2019/04/29)
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- Rhodium-catalyzed C-H bond activation for the synthesis of quinonoid compounds: Significant Anti-Trypanosoma cruzi activities and electrochemical studies of functionalized quinones
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Thirty four halogen and selenium-containing quinones, synthesized by rhodium-catalyzed C-H bond activation and palladium-catalyzed cross-coupling reactions, were evaluated against bloodstream trypomastigotes of T.?cruzi. We have identified fifteen compounds with IC50/24?h values of less than 2?μM. Electrochemical studies on A-ring functionalized naphthoquinones were also performed aiming to correlate redox properties with trypanocidal activity. For instance, (E)-5-styryl-1,4-naphthoquinone 59 and 5,8-diiodo-1,4-naphthoquinone 3, which are around fifty fold more active than the standard drug benznidazole, are potential derivatives for further investigation. These compounds represent powerful new agents useful in Chagas disease therapy.
- Jardim, Guilherme A.M.,Silva, Thaissa L.,Goulart, Marilia O.F.,de Simone, Carlos A.,Barbosa, Juliana M.C.,Salom?o, Kelly,de Castro, Solange L.,Bower, John F.,da Silva Júnior, Eufranio N.
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supporting information
p. 406 - 419
(2017/05/19)
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- An alternative synthesis of 2,6-dimethoxyl-1,4-benzoquinone
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An economic four-step synthesis of 2,6-dimethoxy-1,4-benzoquinone was achieved in 68 % overall yield starting from aniline. The reaction sequence involved conversion to1,3,5-tribromoaniline, deamination, methoxylation, and oxidation. The procedure is operationally simple and amenable to scale-up production.
- Wang, Qian,Yang, Jian,Zheng, Yang,Liao, Xiali
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p. 193 - 194
(2017/06/20)
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- Synthesis of coenzyme Q0 through divanadium-catalyzed oxidation of 3,4,5-trimethoxytoluene with hydrogen peroxide
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The selective oxidation of methoxy/methyl-substituted arenes to the corresponding benzoquinones has been first realized using aqueous hydrogen peroxide as a green oxidant, acid tetrabutylammonium salts of the γ-Keggin divanadium-substituted phosphotungstate [γ-PW10O38V2(μ-O)2]5- (I) as a catalyst, and MeCN as a solvent. The presence of the dioxovanadium core in the catalyst is crucial for the catalytic performance. The reaction requires an acid co-catalyst or, alternatively, a highly protonated form of I can be prepared and employed. The industrially relevant oxidation of 3,4,5-trimethoxytoluene gives 2,3-dimethoxy-5-methyl-1,4-benzoquinone (ubiquinone 0 or coenzyme Q0, the key intermediate for coenzyme Q10 and other essential biologically active compounds) with 73% selectivity at 76% arene conversion. The catalyst retains its structure under turnover conditions and can be easily recycled and reused without significant loss of activity and selectivity.
- Zalomaeva, Olga V.,Evtushok, Vasilii Yu.,Maksimov, Gennadii M.,Maksimovskaya, Raisa I.,Kholdeeva, Oxana A.
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p. 5202 - 5209
(2017/04/27)
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- Molecular and biochemical characterization of a new thermostable bacterial laccase from Meiothermus ruber DSM 1279
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A new laccase gene (mrlac) from Meiothermus ruber DSM 1279 was successfully overexpressed to produce a laccase (Mrlac) in soluble form in Escherichia coli during simultaneous overexpression of a chaperone protein (GroEL/ES). Without the GroEL/ES protein, the Mrlac overexpressed in E. coli constituted a huge amount of the total cellular protein, but the enzyme was localized in the insoluble fraction with no activity in the soluble fraction. Co-expression of the Mrlac with the E. coli GroEL/ES drastically improved proper folding and expression of active Mrlac in the soluble fraction. Spectroscopic analysis of the purified enzyme by UV/visible and electron paramagnetic resonance spectroscopy confirmed that the Mrlac was a multicopper oxidase. The Mrlac had a molecular weight of ~50 kDa and exhibited activity towards the canonical laccase substrates 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), syringaldazine (SGZ), and 2,6-dimethoxyphenol (2,6-DMP). Kinetic constants Km and kcat were 27.3 μM and 325 min-1 on ABTS, 4.2 μM and 106 min-1 on SGZ, and 3.01 μM and 115 min-1 on 2,6-DMP, respectively. Maximal enzyme activity was achieved at 70°C with ABTS as substrate. In addition, Mrlac exhibited a half-life for deactivation at 70°C and 75°C of about 120 min and 67 min, respectively, indicating that the Mrlac is intrinsically thermostable. Finally, Mrlac was efficient in catalyzing the removal of 2,4-dichlorophene (DCP) in aqueous solution, a trait which makes the enzyme potentially useful for environmentally friendly applications.
- Kalyani,Munk,Mikkelsen,Meyer
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p. 3910 - 3918
(2016/01/20)
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- ONO-pincer ruthenium complex-bound norvaline for efficient catalytic oxidation of methoxybenzenes with hydrogen peroxide
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The enhanced catalytic activity of ruthenium complex-bound norvaline Boc-l-[Ru]Nva-OMe 1, in which the ONO-pincer ruthenium complex Ru(pydc)(terpy) 2 is tethered to the α-side chain of norvaline, has been demonstrated for the oxidation of methoxybenzenes to p-benzoquinones with a wide scope of substrates and unique chemoselectivity.
- Yoshida, Ryota,Isozaki, Katsuhiro,Yokoi, Tomoya,Yasuda, Nobuhiro,Sadakane, Koichiro,Iwamoto, Takahiro,Takaya, Hikaru,Nakamura, Masaharu
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supporting information
p. 7468 - 7479
(2016/08/16)
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- Total synthesis of evelynin B and taccabulin D
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Concise total syntheses of biosynthetic retro-dihydrochalones evelynin B and taccabulin D isolated from roots and rhizomes of Tacca chantrieri and T. integrifolia, have been achieved from pyrogallol trimethylether in six steps and 1,3,5-trimethoxybenzene in three steps, respectively. A condensation between aldehyde and acetophenone was applied to form chalcone as a key step.
- Huang, Yu,Gan, Haifeng,Guo, Kai
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p. 458 - 461
(2015/11/03)
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- Synthesis of enantiomerically pure lignin dimer models for catalytic selectivity studies
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A series of highly enantioselective transformations, such as the Sharpless asymmetric epoxidation and Jacobsen hydrolytic kinetic resolution, were utilized to achieve the complete stereoselective synthesis of β-O-4 lignin dimer models containing the S, G, and H subunits with excellent ee (>99%) and moderate to high yields. This unprecedented synthetic method can be exploited for enzymatic, microbial, and chemical investigations into lignins degradation and depolymerization as related to its stereochemical constitution. Preliminary degradation studies using enantiopure Co(salen) catalysts are also reported.
- Njiojob, Costyl N.,Rhinehart, Jennifer L.,Bozell, Joseph J.,Long, Brian K.
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p. 1771 - 1780
(2015/02/19)
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- Divergent and concise total syntheses of dihydrochalcones and 5-deoxyflavones recently isolated from Tacca species and Mimosa diplotricha
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Dihydrochalcones and 5-deoxyflavones are types of compounds possessing various biologically interesting properties. Herein, we report the concise and divergent total syntheses of several naturally occurring dihydrochalcones and 5-deoxyflavones from readily available starting materials. The divergent strategy is based around manipulation of a common chalcone scaffold and features application of Algar-Flynn-Oyamada oxidation and benzoquinone C-H activation methodologies. These are the first reported total syntheses of these biologically interesting compounds and the concise and flexible route should be readily amenable to future analogue generation. Furthermore, this work provides an illustration of the utility of divergent synthesis for the expedient and step-economical preparation of natural product libraries.
- Sum, Tze Han,Sum, Tze Jing,Stokes, Jamie E.,Galloway, Warren R.J.D.,Spring, David R.
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p. 4557 - 4564
(2015/06/08)
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- Steric effects in the design of Co-Schiff base complexes for the catalytic oxidation of lignin models to para-benzoquinones
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New Co-Schiff base complexes that incorporate a sterically hindered ligand and an intramolecular bulky piperazine base in close proximity to the Co center are synthesized. Their utility as catalysts for the oxidation of para-substituted lignin model phenols with molecular oxygen is examined. Syringyl and guaiacyl alcohol, as models of S and G units in lignin, are oxidized in good yield using a catalyst bearing an N-benzylpiperazinyl substituent, with the catalysts displaying improved reactivity for G oxidation. Computational evaluation of the catalysts shows that the piperazinyl substituent is within bonding distance of the Co center. The increased steric interference is suggested as the source of increased G reactivity. This journal is the Partner Organisations 2014.
- Biannic, Berenger,Bozell, Joseph J.,Elder, Thomas
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supporting information
p. 3635 - 3642
(2014/07/08)
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- Highly active and green mesostructured titanosilicate catalysts synthesized for selective synthesis of benzoquinones
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Two-dimensional hexagonal thick-walled mesoporous titanosilicate catalysts synthesized using various amounts of titanium were used for the synthesis of 2,3,5-trimethyl-1,4-benzoquinone (TMBO) by liquid-phase oxidation of 2,3,6-trimethylphenol (TMP-OH). These catalysts were also used for the oxidation of di-/tri-substituted phenols to produce 2,6-disubstituted p-benzoquinones (DSBQs). A promising chemical treatment method, for the preparation of green mesoporous TiSBA-15(6) or Washed TiSBA-15(6), was used for removal of non-framework TiO2 nanoparticle species from the active surface, and the catalytic activity of the recovered mesoporous TiSBA-15(6) catalyst has been evaluated. To confirm the green aspects, recyclability and hot-catalytic filtration experiments were performed. Based on the experimental results, it was found that the green mesoporous TiSBA-15(6) is a highly active, recyclable, and promising heterogeneous catalyst for the selective synthesis of TMBO and DSBQs and produces >99% TMBO selectivity with 100% TMP-OH conversion at 353 K for 60 min and 90-100% DSBQs selectivity with 83-99% phenol conversion at 330 K for 1-5 h.
- Selvaraj
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p. 2674 - 2684
(2014/07/22)
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- Copper catalysts for selective C-C bond cleavage of β-O-4 lignin model compounds
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The reactivity of homogeneous copper catalysts towards the selective C-C bond cleavage of both phenolic and non-phenolic arylglycerol β-aryl ether lignin model compounds has been explored. Several copper precursors, nitrogen ligands, and solvents were evaluated in order to optimize the catalyst system. Using the optimized catalyst system, copper(I) trifluoromethanesulfonate [CuACHTUNGTRENUNG(OTf)]/L/ TEMPO (L=2,6-lutidine, TEMPO=2,2,6,6-tetramethyl- piperidin-1-yl-oxyl), aerobic oxidation of the non-phenolic β-O-4 lignin model compound proceeded with good selectivity for Cα-Cβ bond cleavage, affording 3,5-dimethoxybenzaldehyde as the major product. Aerobic oxidation of the corresponding phenolic β-O-4 lignin model proceeded with different selectivity, affording 2,6-dimethoxybenzoquinone and a,β-unsaturated aldehyde products resulting from cleavage of the Ca-Caryl bond. At low catalyst concentrations, however, a change in selectivity was observed as oxidation of the benzylic secondary alcohol predominated with both substrates.
- Sedai, Baburam,Baker, R. Tom
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p. 3563 - 3574
(2015/02/19)
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- Copper catalysts for selective c-c bond cleavage of b-o-4 lignin model compounds
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The reactivity of homogeneous copper catalysts towards the selective C-C bond cleavage of both phenolic and non-phenolic arylglycerol b-aryl ether lignin model compounds has been explored. Several copper precursors, nitrogen ligands, and solvents were evaluated in order to optimize the catalyst system. Using the optimized catalyst system, copper(I) trifluoromethanesulfonate [CuACHTUNGTRENUNG(OTf)]/L/TEMPO (L=2,6-lutidine, TEMPO=2,2,6,6-tetramethyl-piperidin-1-yl-oxyl), aerobic oxidation of the non-phenolic b-O-4 lignin model compound proceeded with good selectivity for Ca-Cb bond cleavage, affording 3,5-dimethoxybenzaldehyde as the major product. Aerobic oxidation of the corresponding phenolic b-O-4 lignin model proceeded with different selectivity, affording 2,6-dimethoxybenzoquinone and a,b-unsaturated aldehyde products resulting from cleavage of the CaCaryl bond. At low catalyst concentrations, however, a change in selectivity was observed as oxidation of the benzylic secondary alcohol predominated with both substrates.
- Sedai, Baburam,Tom Baker
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supporting information
p. 3563 - 3574
(2015/01/09)
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- A metal-free, carbon-based catalytic system for the oxidation of lignin model compounds and lignin
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Nitrogen-containing graphene material (LCN) has been identified as an effective catalyst for the oxidation of β-O-4 and α-O-4 types of lignin model compounds in the presence of tert-butyl hydroperoxide, to provide aromatic aldehydes, acids and other organic chemicals in high yield. The transformations of five lignin model compounds over LCN were investigated systematically. Instrumentation analysis, kinetic study and radical trapping experiments highlight the mechanistic features of the reaction, including: 1) the reaction pathway starts by benzylic C-H or C-OH bond activation, followed by Cα-Cβ or Cα-O bond cleavage, and finally further oxidation of intermediate aromatics; and 2) the reaction follows a free-radical mechanism with all the key steps involving radical species. In addition, the LCN proved to be a highly stable catalyst; no significant activity decrease was observed for four consecutive runs, and X-ray photoelectron spectroscopy analysis indicates negligible decrease in the content of the active nitrogen species in the catalyst. Notably, this new catalytic system can be extended to the oxidative depolymerisation of real lignin, to produce a significant portion of liquefied, low-molecular-mass products. Low mass, high conversion: Nitrogen-containing graphene-based carbon material has been used to establish a metal-free catalytic system for the oxidation of α-O-4 and β-O-4 types of lignin model compounds in the presence of tert-butyl hydroperoxide (see figure). In the oxidative depolymerization of organosolv lignin, a significant portion of liquefied, low-molecular-mass product is produced. Copyright
- Gao, Yongjun,Zhang, Jiaguang,Chen, Xi,Ma, Ding,Yan, Ning
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p. 825 - 834
(2014/07/08)
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- A green mesostructured vanadosilicate catalyst and its unprecedented catalytic activity for the selective synthesis of 2,6-disubstituted p-benzoquinones
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We have developed a green method for the production of 2,6-disubstituted p-benzoquinones (DSBQs) by liquid-phase oxidations of di/tri-substituted phenols using two-dimensional hexagonally thick-walled mesoporous vanadosilicate catalysts. In particular, 2,6-di-tert-butyl-p-benzoquinone was synthesized by the oxidation of 2,6-di-tert-butylphenol, using various reaction parameters, over mesoporous VSBA-15 catalysts synthesized with various vanadium contents. A promising chemical treatment method for the preparation of green mesoporous VSBA-15(5) or W-VSBA-15(5) (W: washed) catalysts was successfully used in the presence of ammonium acetate solution to remove moderately toxic non-framework V2O5 crystallite species from the active surface, and the catalytic activity of the recovered green mesoporous VSBA-15(5) catalyst was determined. To confirm the green aspects, recyclability and hot-catalytic filtration experiments were performed. The combined results show that the green mesoporous VSBA-15(5) is a highly active, recyclable, and promising heterogeneous catalyst for the selective synthesis of DSBQs (98-100%), and has unprecedented catalytic activity compared with other mesoporous vanadosilicate catalysts. The Royal Society of Chemistry 2014.
- Selvaraj,Park,Kim
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p. 958 - 966
(2014/01/06)
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- Efficient cobalt-catalyzed oxidative conversion of lignin models to benzoquinones
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Phenolic lignin model monomers and dimers representing the primary substructural units of lignin were successfully oxidized to benzoquinones in high yield with molecular oxygen using new Co-Schiff base catalysts bearing a bulky heterocyclic nitrogen base as a substituent. This is the first example of a catalytic system able to convert both S and G lignin model phenols in high yield, a process necessary for effective use of lignin as a chemical feedstock.
- Biannic, Berenger,Bozell, Joseph J.
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supporting information
p. 2730 - 2733
(2013/07/26)
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- Differing selectivities in mechanochemical versus conventional solution oxidation using Oxone
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A mechanochemical oxidation of methoxylated aromatic chemicals is described, providing an example of a very different selectivity as compared to solution-based chemistry. Oxone was shown to react with 1,2,3-trimethoxybenzene to yield predominantly 2,6-dimethoxybenzoquinone in the solid state or 2,3,4-trimethoxyphenol in solution. The difference in effective acidity of the reaction conditions was not apparently responsible for the observed selectivity. The mechanochemical method described is simple, reproducible, and gave higher yield at higher conversion of substrate compared to solution conditions.
- Collom,Anastas,Beach,Crabtree,Hazari,Sommer
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supporting information
p. 2344 - 2347
(2013/06/27)
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- Laccase catalysed modification of lignin subunits and coupling to p-aminobenzoic acid
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Laccase catalysed oxidation of syringyl and guaiacyl subunits of lignin and their modification with an aromatic amine, p-aminobenzoic acid (PABA) were investigated. Laccase from Galerina sp. HC1 isolated earlier by us was used as the main catalyst, and Trametes versicolor laccase was used for comparison. Among the syringyl compounds, syringic acid and syringaldehyde were oxidised to 2,6-dimethoxy-1,4-benzoquinone, and in the presence of PABA yielded a cross-coupling imine product. The reaction with methyl syringol resulted in several products whose structures were determined. The possible oxidative coupling pathways were proposed for the formation of the identified products. Oxidation of syringol and the guaiacyl compounds resulted mainly in homooligomers by free radical mechanism, with a negligible tendency of reaction with the nucleophilic group of PABA. Similar treatment of Eucalyptus Kraft lignin, which is rich in syringyl moieties, showed the presence of identical products obtained with syringic acid and syringaldehyde.
- Ibrahim, Victor,Volkova, Natalia,Pyo, Sang-Hyun,Mamo, Gashaw,Hatti-Kaul, Rajni
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- Synthesis of 3-O-methylgallic acid a powerful antioxidant by electrochemical conversion of syringic acid
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Background A kinetic study of the electrochemical oxidation of syringic acid (3,5-dimethoxy-4-hydroxybenzoic acid) by cyclic voltammetry at treated gold disk was combined with results of electrolyses at Ta/PbO2 anode in order to convert it into potentially high-added-value product. Methods The electrochemical oxidation of syringic acid was carried out in order to convert this compound to 3-O-methylgallic acid. This latter was identified by mass spectrophotometry using LC-MS/MS apparatus. The 3-O-methylgallic acid synthesis was controlled by cyclic volammetry, Ortho-diphenolicdeterminations and DPPH radical-scavenging activity. Results The proposed mechanism is based on the hypothesis of a bielectronic discharge of syringic acid molecule under free and adsorbed form involving two intermediate cation mesomers. Hydrolysis of the more stable of this last one leads to the formation of the 3,4-dihydroxy-5- methoxybenzoic acid (3-O-methylgallic acid) as a major product. The latter aromatic compound was synthesized by anodic oxidation of syringic acid at PbO2 electrode. The cyclic voltammogram of the electrolysis bath of syringic acid shows that the anodic peak potential of 3-O-methylgallic acid was lower (E pa = 128 mV) than that of SA (Epa = 320 mV). And the strongest antiradical activity was detected when the 3-O-methylgallic acid concentration was higher . Conclusion The electrochemical oxidation using PbO2 anode is a rapid, simple and efficient method tool for a conversion of SA into 3-O-methylgallic acid, a potent antioxidant derivative General Significance The electrochemical process consists in a simple transformation of the syringic acid into 3-O-methylgallic acid having a better antioxidant capacity. This result has been justified by cyclic voltametry which shows that anodic peak of 3-O-methylgallic acid is reversible. Furthermore, its potential is lower than that of the irreversible anodic peak of syringic acid to 3-O-methylgallic acid.
- Gargouri, Olfa Dridi,Gargouri, Boutheina,Trabelsi, Souhel Kallel,Bouaziz, Mohamed,Abdelhédi, Ridha
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p. 3643 - 3649
(2013/08/25)
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- Aerobic oxidation of β-1 lignin model compounds with copper and oxovanadium catalysts
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The reactivity of homogeneous oxovanadium and copper catalysts toward aerobic oxidation of phenolic and nonphenolic β-1 lignin model compounds has been investigated. Aerobic oxidation of diastereomeric, nonphenolic β-1 lignin models (1T, 1E) using the six-coordinate vanadium complex (HQ) 2VV(O)(OiPr) (HQ = 8-oxyquinolinate) as a precatalyst in pyridine afforded ketone (3) and dehydrated ketone (4) derived from oxidation of the secondary alcohol. In contrast, using CuOTf/2,6-lutidine/ TEMPO (OTf = trifluoromethanesulfonate, TEMPO = 2,2,6,6-tetramethyl-piperidin-1- yl-oxyl) in toluene for the same reaction afforded 3,5-dimethoxybenzaldehyde (5) and 4-methoxybenzaldehyde (6) as major products resulting from C α-Cβ bond cleavage. Reactions of the corresponding phenolic lignin model compounds (2T, 2E) with 10 mol % CuOTf/2,6-lutidine/TEMPO gave ketone (9) as the major product, whereas 10 mol % (HQ)2VV(O)(OiPr) or a stoichiometric amount of CuOTf/2,6-lutidine/TEMPO yielded 2,6-dimethoxybenzoquinone (10) as the major product, arising from cleavage of the Caryl-Cα bond. Different selectivity was observed in the oxidation of 2T, 2E using the five-coordinate complex (dipic)VV(O)(OiPr) (dipic = dipicolinate), with α,β-unsaturated aldehyde (14) as the major product (formed from oxidation of the primary alcohol and dehydration). The key differences in chemoselectivity between the vanadium and copper catalysts in the oxidations of these phenolic and nonphenolic β-1 lignin models are discussed.
- Sedai, Baburam,Diaz-Urrutia, Christian,Baker, R. Tom,Wu, Ruilian,Silks, L. A. Pete,Hanson, Susan K.
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p. 3111 - 3122
(2014/01/06)
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- Activated zeolites and heteropolyacids: An efficient catalysts for the synthesis of triacetoxyaromatic precursors of hydroxyquinones
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The Thiele-Winter reaction is of interest for synthesis of triacetoxyaromatic precursors of hydroquinones. Liquid acid such as, chlorosulfonic acid and solid acids like heteropolyacids have an efficient catalyst can effectively replace sulfuric acid in acetoxylation reaction of quinones without use of organic solvent at room temperature.
- Hadjila, Dokari,Mohamed, Hammadi
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p. 6112 - 6116
(2013/07/26)
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- Improved manganese-oxidizing activity of DypB, a peroxidase from a lignolytic bacterium
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DypB, a dye-decolorizing peroxidase from the lignolytic soil bacterium Rhodococcus jostii RHA1, catalyzes the peroxide-dependent oxidation of divalent manganese (Mn2+), albeit less efficiently than fungal manganese peroxidases. Substitution of Asn246, a distal heme residue, with alanine increased the enzyme's apparent kcat and kcat/K m values for Mn2+ by 80- and 15-fold, respectively. A 2.2 A resolution X-ray crystal structure of the N246A variant revealed the Mn2+ to be bound within a pocket of acidic residues at the heme edge, reminiscent of the binding site in fungal manganese peroxidase and very different from that of another bacterial Mn2+-oxidizing peroxidase. The first coordination sphere was entirely composed of solvent, consistent with the variant's high Km for Mn2+ (17 ± 2 mM). N246A catalyzed the manganese-dependent transformation of hard wood kraft lignin and its solvent-extracted fractions. Two of the major degradation products were identified as 2,6-dimethoxybenzoquinone and 4-hydroxy-3,5-dimethoxybenzaldehyde, respectively. These results highlight the potential of bacterial enzymes as biocatalysts to transform lignin.
- Singh, Rahul,Grigg, Jason C.,Qin, Wei,Kadla, John F.,Murphy, Michael E. P.,Eltis, Lindsay D.
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p. 700 - 706
(2013/06/27)
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- μ-oxo-bridged hypervalent iodine(III) compound as an extreme oxidant for aqueous oxidations
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We have found that in aqueous oxidations the -oxo-bridged hypervalent iodine trifluoroacetate reagent 1 {[(PhI(OCOCF]} is generally more reactive than the corresponding monomeric reagent, especially toward phenolic substrates. -Oxo-bridged 1 in aqueous media thus provided dearomatized quinones 3 in excellent yields in most cases compared to conventional phenyliodine(III) diacetate and bis(trifluoroacetate), as a result of the rapid oxidation of both phenols and naphthols 2. Furthermore, the oxidation reactions proceeded even in water using water-soluble -oxo oxidant 1, which has promise for -oxo-bridged reagent 1 to become the favored reagent over hydrophobic phenyliodine(III) diacetate and bis(trifluoroacetate). Georg Thieme Verlag Stuttgart New York.
- Dohi, Toshifumi,Nakae, Tomofumi,Takenaga, Naoko,Uchiyama, Teruyoshi,Fukushima, Kei-Ichiro,Fujioka, Hiromichi,Kita, Yasuyuki
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experimental part
p. 1183 - 1189
(2012/05/19)
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- Catalytic oxidation of para-substituted phenols with cobalt-Schiff base complexes/O2 - Selective conversion of syringyl and guaiacyl lignin models to benzoquinones
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Models of guaiacyl (G) and syringyl (S) subunits in lignin have been catalytically oxidized to their corresponding p-quinones in the presence of molecular oxygen. The oxidation of syringyl-like phenols readily occurred with 5-coordinate cobalt catalysts on which one of the ligands is a monodentate pyridine or imidazole base that coordinates axially to the metal. Formation of p-quinones with this system depends on the coordination of the axial base to the metal as influenced by its pKa and its size. The yield of p-quinones from guaiacyl models was markedly improved by the addition of a sterically hindered aliphatic nitrogen base that does not coordinate to the catalyst. A mechanism involving deprotonation of the phenol substrate by the bulky base is proposed.
- Cedeno, Diana,Bozell, Joseph J.
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supporting information; experimental part
p. 2380 - 2383
(2012/06/01)
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- Supported sulfonic acids: Metal-free catalysts for the oxidation of hydroquinones to benzoquinones with hydrogen peroxide
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Some silica- and polystyrene-supported sulfonic acids, prepared by tethering or sol-gel techniques, were employed as metal-free heterogeneous catalysts in the oxidation of hydroquinones to the corresponding 1,4-benzoquinones, carried out with 30% aqueous hydrogen peroxide. The activity of these catalysts was tested in the model oxidation of methylhydroquinone under batch conditions: high yield and selectivity at room temperature and under environmentally friendly conditions can be achieved in the presence of SiO 2-(CH2)3-SO3H. The heterogeneous catalyst, that can be easily recovered by simply filtration, can be used for at least three cycles affording the same good results (~80% yield, ~91% selectivity).
- Maggi, Raimondo,Piscopo, Calogero G.,Sartori, Giovanni,Storaro, Loretta,Moretti, Elisa
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experimental part
p. 146 - 152
(2012/02/04)
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- C-C or C-O bond cleavage in a phenolic lignin model compound: Selectivity depends on vanadium catalyst
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The aerobic oxidation of a phenolic lignin model compound with a vanadium catalyst results in the oxidative cleavage of the C-C bond between the aryl ring and the adjacent hydroxy-substituted carbon atom (see scheme). Labeling experiments indicate key mechanistic differences to a previously reported related C-O bond cleavage reaction. The selectivity in C-C versus C-O bond cleavage depends on the choice of the vanadium catalyst. Copyright
- Hanson, Susan K.,Wu, Ruilian,Silks, Louis A. Pete
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supporting information; experimental part
p. 3410 - 3413
(2012/06/30)
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- The first total synthesis of tarennane, a potent antioxidant chalcone constituent from tarenna attenuate or Magnolia officinalis
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The convergent total synthesis of tarennane has been accomplished in six steps starting from commercially available phloroglucinol and guaiacol; the key step of the synthesis relies on a highly regioselective Heck reaction applying iodophenol and PdCl2(PPh3)2.
- Yang, Jincheng,Yang, Tao,Luo, Youfu,He, Jun,Shi, Jianyou,Peng, Aihua
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experimental part
p. 258 - 263
(2012/04/18)
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- Oxidation of hydroquinones to benzoquinones with hydrogen peroxide using catalytic amount of silver oxide under batch and continuous-flow conditions
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Silver oxide (Ag2O) can be utilized as heterogeneous catalyst in the oxidation of hydroquinones to the corresponding benzoquinones with 30% aq. H2O2. The catalytic properties of Ag2O have been explored in the model reaction of methylhydroquinone with H2O2 performed under batch conditions. Results show that the reaction can be carried out in high yield and selectivity at room temperature under environmentally friendly conditions. The truly heterogeneous catalyst can be recovered by filtration and reused for at least five times, giving the same excellent results (~95% yield, ~98% selectivity). The catalyst can be packed in a tubular reactor and utilized under continuous-flow conditions giving similar good results.
- Derikvand, Fatemeh,Bigi, Franca,Maggi, Raimondo,Piscopo, Calogero Giancarlo,Sartori, Giovanni
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experimental part
p. 99 - 103
(2010/06/17)
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- Oxidative depolymerization of lignin in ionic liquids
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Beech lignin was oxidatively cleaved in ionic liquids to give phenols, unsaturated propylaromatics, and aromatic aldehydes. A multiparallel batch reactor system was used to screen different ionic liquids and metal catalysts. Mn(NO3)2 in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMIM][CF3SO3] proved to be the most effective reaction system. A larger scale batch reaction with this system in a 300mL autoclave (11g lignin starting material) resulted in a maximum conversion of 66.3% (24h at 100 °C, 84 × 105 Pa air). By adjusting the reaction conditions and catalyst loading, the selectivity of the process could be shifted from syringaldehyde as the predominant product to 2,6-dimethoxy-1,4-benzoquinone (DMBQ). Surprisingly, the latter could be isolated as a pure substance in 11.5 wt% overall yield by a simple extraction/crystallization process.
- St?rk, Kerstin,Taccardi, Nicola,B?smann, Andreas,Wasserscheid, Peter
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experimental part
p. 719 - 723
(2011/12/21)
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- On the reactions of two fungal laceases differing in their redox potential with lignin model compounds: products and their rate of formation
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Laceases (EC 1.10.3.2) are multicopper oxidases able to oxidize phenolic compounds such as lignin-related polyphenols. Since the discovery that so-called mediators effectively extend the family of lacease substrates, direct interactions between lignin-like materials and lacease have gained much less attention. In this work, the aim was to characterize oxidation products formed in direct laccase-catalyzed oxidation of different guaiacylic and syringylic lignin model compounds with two different laceases: a low redox potential Melanocarpus alborneces lacease and a high redox potential Trametes hirsuta lacease. By following the formation of different, mainly biphenylic (5-5) and benzylic oxidation products, it was found that although both of these enzymes generated practically the same pattern of products with particular types of syringyl and guaiacyl compounds, in some cases a clear difference in the rates of their formation was observed. The results also confirm further to the suggestions that syringylic compounds are able to act as mediators in their own oxidation reactions and also that in some instances acetylation of phenolic material may produce altered, unexpected structures.
- Maarit, Lahtinen,Kristiina, Kruus,Petri, Heinonen,Jussi, Sipilae
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experimental part
p. 8357 - 8365
(2010/08/19)
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- Synthesis of 2,5-Diaminoquinones by one-pot copper-catalyzed aerobic oxidation of hydroquinones and addition reaction of amines
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The aerobic oxidation of various hydroquinones was achieved by using copper nanoparticles entrapped in aluminum oxyhydroxide [Cu/ AlO(OH)] at room temperature. Furthermore, 2,5diamino-1,4-benzoquinones were synthesized directly from hydroquinone and amines by a one-pot procedure consisting of the copper-catalyzed aerobic oxidation of hydroquinones and the double addition of amines to the resulting quinones.
- Kim, Sungjin,Kim, Daehwan,Park, Jaiwook
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experimental part
p. 2573 - 2578
(2009/12/29)
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- t-butyl hydroperoxide oxidative dealkylation of hydroquinone ethers to 1,4-quinones
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Various organoselenium compounds (diselenides, benzisoselenazol-3(2H)-ones, and 1,3,2-thiaselenazolones) are effective catalysts for oxidative dealkylation of hydroquinone ethers with t -butyl hydroperoxide to 1,4-quinones. The reactions is most efficient when t -butyl hydroperoxide in the presence of poly(bis-1,2-phenyl) diselenide is used as an oxidizing agent. In this way 1,4-benzo and 1,4-naphthoquinones are produced in good to high yields. Copyright Taylor & Francis Group, LLC.
- Wojtowicz, Halina,Mlochowski, Jacek,Syper, Ludwik,Yadav, Hardeo
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p. 1991 - 2000
(2007/10/03)
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- Synthesis of methoxy-substituted phenols by peracid oxidation of the aromatic ring
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A novel benign protocol for the preparation of hydroxy-methoxybenzene derivatives is disclosed. By utilizing this protocol, activated aromatic compounds such as l,3-dimethoxy-2-methyl-benzene and 1-(2,6-dimethoxyphenyl) ethanone are smoothly converted to the corresponding monohydroxylated compound. The reaction can be considered to be a normal aromatic electrophilic substitution reaction, and the regioselectivity for the reaction thus follows the similar rules as for electrophilic substitutions. The protocol is composed by benign reagents, namely, hydogenperoxide, acetic acid, and p-toluene sulfonic acid, which lead to the production of ethaneperoxoic acid in situ. The ethaneperoxoic acid operates as the hydroxylating reagent. The hydroxylation reaction is completed within a short period and requires moreover only mild experimental conditions, which make this novel protocol a green, cheap, and rapid process leading to hydroxy-methoxybenzene derivatives. The proposed reaction mechanism is supported by density functional theory and NMR spectroscopy experiments. The mechanism is constituted by two discrete steps: (a) addition of OH+ to the most nucleophilic carbon atom of the aromatic ring, which is the rate-determining step, and (b) the loss of the proton from the aromatic ring.
- Bjorsvik, Hans-Rene,Occhipinti, Giovanni,Gambarotti, Cristian,Cerasino, Leonardo,Jensen, Vidar R.
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p. 7290 - 7296
(2007/10/03)
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