- Cu(i)-Catalyzed asymmetric intramolecular addition of aryl pinacolboronic esters to unactivated ketones: Enantioselective synthesis of 2,3-dihydrobenzofuran-3-ol derivatives
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An (S,S)-QuinoxP?-supported Cu(i) catalyst has been disclosed for highly enantioselective intramolecular addition of aryl pinacolboronic esters to unactivated ketones under mild reaction conditions. This protocol showcases a broad substrate tolerance and allows access to various chiral 2,3-dihydrobenzofuran-3-ol derivatives in generally good yields with excellent enantioselectivities.
- Ni, Chunjie,Gao, Jihui,Fang, Xianjie
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- Catalytic C–O bond cleavage in a β-O-4 lignin model through intermolecular hydrogen transfer
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A base-free and redox neutral approach for the selective breaking of aryl ether bond (C–O) contained by a lignin model compound mimicking a β-O-4 linkage is reported. A palladium loaded metal-organic framework (MOF) was used as a catalyst for this purpose. The reaction proceeds through dehydrogenation of benzylic alcohol moiety followed by the hydrogenolysis of the ether bonds. Therefore, no external hydrogen source is required for the reaction to take place.
- Ahsan Usman, Muhammad,Naeem, Maham,Saeed, Muhammad,Zaheer, Muhammad
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- Atomically Dispersed Pt-N3C1Sites Enabling Efficient and Selective Electrocatalytic C-C Bond Cleavage in Lignin Models under Ambient Conditions
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Selective cleavage of C-C linkages is the key and a challenge for lignin degradation to harvest value-added aromatic compounds. To this end, electrocatalytic oxidation presents a promising technique by virtue of mild reaction conditions and strong sustainability. However, the existing electrocatalysts (traditional bulk metal and metal oxides) for C-C bond oxidative cleavage suffer from poor selectivity and low product yields. We show for the first time that atomically dispersed Pt-N3C1sites planted on nitrogen-doped carbon nanotubes (Pt1/N-CNTs), constructed via a stepwise polymerization-carbonization-electrostatic adsorption strategy, are highly active and selective toward Cα-Cβbond cleavage in β-O-4 model compounds under ambient conditions. Pt1/N-CNTs exhibits 99% substrate conversion with 81% yield of benzaldehyde, which is exceptional and unprecedented compared with previously reported electrocatalysts. Moreover, Pt1/N-CNTs using only 0.41 wt % Pt achieved a much higher benzaldehyde yield than those of the state-of-the-art bulk Pt electrode (100 wt % Pt) and commercial Pt/C catalyst (20 wt % Pt). Systematic experimental investigation together with density functional theory (DFT) calculation suggests that the superior performance of Pt1/N-CNTs arises from the atomically dispersed Pt-N3C1sites facilitating the formation of a key Cβradical intermediate, further inducing a radical/radical cross-coupling path to break the Cα-Cβbond. This work opens up opportunities in lignin valorization via a green and sustainable electrochemical route with ultralow noble metal usage.
- Cui, Tingting,Ma, Lina,Wang, Shibin,Ye, Chenliang,Liang, Xiao,Zhang, Zedong,Meng, Ge,Zheng, Lirong,Hu, Han-Shi,Zhang, Jiangwei,Duan, Haohong,Wang, Dingsheng,Li, Yadong
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supporting information
p. 9429 - 9439
(2021/07/19)
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- 1,3-Dibromo-5,5-dimethylhydantoin (DBH)/DMSO mediated oxidative difunctionalization of styrenes: Microfluidic synthesis of pentafluorophenoxy ketone
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A practical and mild synthesis of pentafluorophenoxy ketone in a continuous flow microfluidic reactor has been developed through 1,3-Dibromo-5,5-dimethylhydantoin (DBH)/DMSO mediated oxidative coupling of styrenes with pentafluorophenol. Moreover, a series of pentafluorophenoxy ketone products were provided in moderate to good yields under metal-free conditions. A magnifying continuous flow system was erected to verify the appliance of this method.
- Xu, Jia,Hua, Jiawei,Bian, Mixue,Li, Yuguang,He, Wei,Yang, Zhao,Liu, Chengkou,Fang, Zheng,Guo, Kai
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- Mild selective oxidative cleavage of lignin C-C bonds over a copper catalyst in water
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The conversion of lignin into aromatics as commodity chemicals and high-quality fuels is a highly desirable goal for biorefineries. However, the presence of robust inter-unit carbon-carbon (C-C) bonds in natural lignin seriously impedes this process. Herein, for the first time, we report the selective cleavage of C-C bonds in β-O-4 and β-1 linkages catalyzed by cheap copper and a base to yield aromatic acids and phenols in excellent yields in water at 30 °C under air without the need for additional complex ligands. Isotope-labeling experiments show that a base-mediated Cβ-H bond cleavage is the rate-determining step for Cα-Cβ bond cleavage. Density functional theory (DFT) calculations suggest that the oxidation of β-O-4 ketone to a key intermediate, i.e., a peroxide, by copper and O2 lowers the Cα-Cβ bond dissociation energy and facilitates its subsequent cleavage. In addition, the catalytic system could be successfully applied to the depolymerization of various authentic lignin feedstocks, affording excellent yields of aromatic compounds and high selectivity of a single monomer. This study offers the potential to economically produce aromatic chemicals from biomass.
- Hu, Yuzhen,Li, Song,Ma, Longlong,Wang, Chenguang,Yan, Long,Zhang, Qi,Zhang, Xinghua,Zhao, Xuelai
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p. 7030 - 7040
(2021/09/28)
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- Nickel-Mediated Photoreductive Cross Coupling of Carboxylic Acid Derivatives for Ketone Synthesis**
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A simple visible light photochemical, nickel-catalyzed synthesis of ketones from carboxylic acid-derived precursors is presented. Hantzsch ester (HE) functions as a cheap, green and strong photoreductant to facilitate radical generation and also engages in the Ni-catalytic cycle to restore the reactive species. With this dual role, HE allows for the coupling of a large variety of radicals (1°,2°, benzylic, α-oxy & α-amino) with aroyl and alkanoyl moieties, a new feature in reactions of this type. With both precursors deriving from abundant carboxylic acids, this protocol is a welcome addition to the organic chemistry toolbox. The reaction proceeds under mild conditions without the need for toxic metal reagents or bases and shows a wide scope, including pharmaceuticals and complex molecular architectures.
- Brauer, Jan,Quraishi, Elisabeth,Kammer, Lisa Marie,Opatz, Till
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p. 18168 - 18174
(2021/11/30)
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- Alkylation of monomeric, dimeric, and polymeric lignin models through carbon-hydrogen activation using Ru-catalyzed Murai reaction
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In this study, we have assessed directed carbon-hydrogen activation (CHA) for alkylation of monomeric, dimeric, and polymeric lignin models using Murai's catalyst [RuH2(CO)(PPh3)3]. Based on related work from our laboratory showing that isolated organosolv lignin bears benzylic directing groups ideal for CHA reactions, this approach could offer new methodology for the valorization of biorefinery lignin. Monomeric and dimeric models bearing a keto group at the benzylic position undergo Ru-catalyzed alkylation in good to excellent yield. Similarly, models bearing a benzylic OH group also undergo alkylation via a tandem oxidation/alkylation process enabled by the Ru catalyst. Polymeric models show low levels of functionalization as a result of the poor solubility of the starting polymer. With unsymmetrical models, functionalization occurs first at the least sterically hindered ortho-site, but a subsequent alkylation, leading to disubstituted products can occur at the more sterically hindered site, leading to hexasubstituted arenes. The reaction shows sensitivity to free phenolic OH groups, which appears to reduce the yield in some reactions, and is also a contributing factor to the low yields observed with polymeric lignin models. Combining CHA methodology with lignin isolation technology able to introduce appropriate directing groups for catalytic functionalization will form the basis for improved conversion of lignin to high value chemical products.
- Zuleta, Ernesto C.,Bozell, Joseph J.
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- Cleavage∕cross-coupling strategy for converting β-O-4 linkage lignin model compounds into high valued benzyl amines via dual C–O bond cleavage
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Lignin is the most recalcitrant of the three components of lignocellulosic biomass. The strength and stability of the linkages have long been a great challenge for the degradation and valorization of lignin biomass to obtain bio-fuels and commercial chemicals. Up to now, the selective cleavage of C–O linkages of lignin to afford chemicals contains only C, H and O atoms. Our group has developed a cleavage/cross-coupling strategy for converting 4-O-5 linkage lignin model compounds into high value-added compounds. Herein, we present a palladium-catalyzed cleavage/cross-coupling of the β-O-4 lignin model compounds with amines via dual C–O bond cleavage for the preparation of benzyl amine compounds and phenols.
- Jia, Le,Li, Chao-Jun,Zeng, Huiying
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supporting information
(2021/10/29)
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- Synthesis of Cyclobutanones by Gold(I)-Catalyzed [2 + 2] Cycloaddition of Ynol Ethers with Alkenes
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A broad scope synthesis of cyclobutanones by gold(I)-catalyzed [2 + 2] cycloaddition of ynol ethers with alkenes has been developed. We also found that internal aryl ynol ethers can undergo (4 + 2) cycloaddition reaction with alkenes leading to the corres
- Zanini, Margherita,Cataffo, Andrea,Echavarren, Antonio M.
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supporting information
p. 8989 - 8993
(2021/11/20)
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- Alternative ball-milling synthesis of vanadium-substituted polyoxometalates as catalysts for the aerobic cleavage of C-C and C-O bonds
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Vanadium-substituted phosphomolybdic acids (H3+x[PMo12-xVxO40], denoted as Vx) are well-known oxidation catalysts that are generally prepared by the hydrothermal treatment of MoO3 and V2O5 in the presence of H3PO4. This synthesis procedure is highly energy consuming and the Vx yields are not always acceptable. In the present work, an alternative hybrid mechanochemical/hydrothermal synthesis of Vx is proposed, comprising the ball-milling of MoO3 and V2O5, followed by a hydrothermal attack. The resulting materials, with 2 ≤ x ≤ 3, obtained from this new route were compared, in terms of yield, energy consumption and catalytic activity, with a reference V3 sample prepared through a conventional hydrothermal treatment. The ball-milling step proved to lead not only to a shorter and far more energy-saving synthesis procedure, but also to high yields of Vx. Moreover, Vx from this alternative route proved to be generally more active than the conventionally prepared V3 in the aerobic oxidative cleavage of C-O and C-C bonds in 2-phenoxyacetophenone, used herein as a lignin model compound.
- Al-Hussaini, Louay,Gálvez, Maria Elena,Launay, Franck,Valange, Sabine
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supporting information
p. 12850 - 12859
(2021/10/12)
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- Enhancing Photocatalytic β-O-4 Bond Cleavage in Lignin Model Compounds by Silver-Exchanged Cadmium Sulfide
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Photocatalytic conversion of lignocellulose to valuable aromatics has significant potential for applications in biorefineries. The photocatalyst efficiency of lignocellulose conversion is typically limited by the buffering redox system in combination with oxidation and reduction of the photoexcited holes and electrons, respectively, which ensures high charge-recombination rates. Herein, Ag+-exchanged CdS is employed for easy photoexcited electron transfer to the oxidized intermediate, which results in a marked increase in the conversion yield with high product selectivity under mild reaction conditions without any additives. The conversion yield of the lignin model compound under 6 W blue LED illumination is nearly 100% and only cleaved aromatic compounds are formed. The efficient photoredox CdS catalyst obtained via photoexcited electron-hole coupled transfer derived from an appropriate Ag+ exchange affords a promising method for lignocellulose conversion with reduced energy consumption.
- Cha, Hyun Gil,Cho, Soyoung,Kim, Hyun Sung,Lee, Hangil,Lee, Jehee,Lee, Min-Woo,Lee, Sunggyu,Yoo, Hyeonji
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p. 8465 - 8475
(2020/09/18)
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- Visible-light-induced oxidative lignin c-c bond cleavage to aldehydes using vanadium catalysts
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Lignin is the largest carrier of aromatics on earth, and its depolymerization can afford value-Added aromatic products. Direct cleavage of the C-C bonds in lignin linkages is significant, but it is challenging to obtain low-molecular-weight aromatic monomers. Herein, using vanadium catalysts under visible light, we selectively cleave the C-C bonds in β-1 and β-O-4 interlinkages occluded in lignin models and extracts by an oxidative protocol. Visible light irradiation triggered single electron transfer between the substrate and the catalyst, which further induced the selective Cα-Cβ bond cleavage and generated the final aromatic products through radical intermediates. Using this photocatalytic chemistry, the reactivity of lignin models and the selectivity of Cα-Cβ bond cleavage were significantly improved. More importantly, this protocol affords aromatic monomers through the fragmentation of organosolv lignins even at room temperature, indicating the potential of photocatalytic C-C bond cleavage of lignin linkages under ambient conditions.
- Liu, Huifang,Li, Hongji,Luo, Nengchao,Wang, Feng
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p. 632 - 643
(2020/01/02)
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- An alternative route for boron phenoxide preparation from arylboronic acid and its application for C[sbnd]O bond formation
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An efficient synthetic route to benzyl phenyl ether preparation has been successfully developed via a one-pot synthetic protocol utilizing a combination of arylboronic acids, hydrogen peroxide (H2O2), and benzyl halides. The whole procedure consists of two consecutive reactions, formation of boron phenoxide from arylboronic acids and its nucleophilic attack. A simple operation under mild conditions such as room-temperature ionic liquid (choline hydroxide), aerobic environment, and absence of metal- and base-catalysts has been employed. Expansion to utilize benzyl surrogates was also successfully accomplished.
- Joo, Seong-Ryu,Kim, Seung-Hoi,Lim, In-Kyun
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- Synthesis and in vitro anti-Toxoplasma gondii activity of a new series of aryloxyacetophenone thiosemicarbazones
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Abstract: A new series of aryloxyacetophenone thiosemicarbazones 4a–q have been synthesized as anti-Toxoplasma gondii agents. All compounds showed significant inhibitory activity against T. gondii-infected cells (IC50 values 1.09–25.19?μg/mL). The 4-fluorophenoxy derivative (4l) was the most potent compound with the highest selectivity toward host cells (SI = 19), being better than standard drug pyrimethamine. SAR study indicated that the concurrence of proper substituents on both aryl ring of phenoxyacetophenone is important for potency and safety profile. Further in vitro experiments with the representative compounds 4l and 4p revealed that these compounds at the concentration of 5?μg/mL can significantly reduce the viability of T. gondii tachyzoites, as well as their infectivity rate and intracellular proliferation, comparable to those of pyrimethamine. Graphic abstract: [Figure not available: see fulltext.]
- Ansari, Mahsa,Montazeri, Mahbobeh,Daryani, Ahmad,Farshadfar, Kaveh,Emami, Saeed
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p. 1223 - 1234
(2019/09/09)
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- Sulfuryl Fluoride Mediated Synthesis of Amides and Amidines from Ketoximes via Beckmann Rearrangement
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A metal-free and redox-neutral method for Beckmann rearrangement employing inexpensive and readily available SO2F2 gas is described. The reported transformation proceeds at ambient temperature and is compatible with a wide range of sterically and electronically diverse aromatic, heteroaromatic, aliphatic and lignin-like oximes providing amides in good to excellent yields. The reaction proceeds through the formation of an imidoyl fluoride intermediate that can also be used for the synthesis of amidines.
- Gurjar, Jitendra,Fokin, Valery V.
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p. 10402 - 10405
(2020/07/25)
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- Palladium-Catalyzed Cascade Reactions of 2-(Cyanomethoxy)chalcones with Arylboronic Acids: Selective Synthesis of Emissive Benzofuro[2,3- c]pyridines
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The Pd(II)-catalyzed cascade reactions of 2-(cyanomethoxy)chalcones with arylboronic acids were demonstrated, allowing the rapid construction of benzofuro[2,3-c]pyridine skeletons with excellent selectivity. These transformations involve the domino-style formation of C-C/C-C/C-N bonds through nitrile carbopalladation, intramolecular Michael addition, cyclization, and aromatization. This chemistry allows for the reactions of 2-(cyanomethoxy)chalcones with thiophen-3-ylboronic acid, providing 3-aryl-1-(thiophen-3-yl)benzofuro[2,3-c]pyridines in moderate to good yields. In addition, the resulting products represent a new class of emissive fluorophores.
- Xiong, Wenzhang,Hu, Kun,Lei, Yunxiang,Zhen, Qianqian,Zhao, Zhiwei,Shao, Yinlin,Li, Renhao,Zhang, Yetong,Chen, Jiuxi
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supporting information
p. 1239 - 1243
(2020/01/11)
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- Metal Catalyst-Free Oxidative C?C Bond Cleavage of a Lignin Model Compound by H2O2 in Formic acid
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Selective cleavage of the β-O-4 ether bond of lignin to produce aromatics is one of the most important topics for the sustainable production of chemicals from biomass. A simple system has been developed for Cα?Cβ bond cleavage of a β-O-4 ketone-structured lignin model compound (LMC) by H2O2 in formic acid under metal catalyst-free conditions. By using this simple system, with H2O2, formic acid, and mineral acid catalyst, over 90 % product yield is achieved in 6 h at room temperature. The reaction proceeds through the classic Baeyer–Villiger oxidation and in situ-generated performic acid serves as the key oxidant. The cleavage of alcoholic LMCs by using the presented method in a two-step process is also demonstrated.
- Li, Xiukai,Zhang, Yugen
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p. 1740 - 1745
(2020/03/23)
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- A multicentre synergistic polyoxometalate-based metal-organic framework for one-step selective oxidative cleavage of β-: O -4 lignin model compounds
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A novel mixed-valence polyoxovanadate-based copper-organic framework, [CuI(bbi)]2{[CuI(bbi)]2VIV2VV8O26}·2H2O (NENU-MV-5, bbi = 1,1′-(1,4-butanediyl)bis(imidazole)), was facilely synthesized from routine reagents under mild hydrothermal conditions. Using NENU-MV-5 as a heterogeneous catalyst without any co-catalyst, one-step oxidative cleavage of β-O-4 lignin into phenols and aromatic acids with high catalytic activity and selectivity was realized under an oxygen atmosphere. No obvious decrease in activity was observed after five cycles, which indicates the excellent stability and sustainability of NENU-MV-5. The perfect catalytic performance of NENU-MV-5 can be attributed to the multi-site synergistic effect of the mixed-valence VV-O-VIV sites on polyoxovanadate for the oxidation of β-O-4 alcohol to β-O-4 ketone and the Cu(i) sites on the framework for the rapid cleavage of the Cα-Cβ bond of β-O-4 ketone. This system represented the first co-catalyst-free example for the one-step selective degradation of lignin catalyzed by a well-defined crystalline catalyst with definite composition and structure in a single solvent.
- Tian, Hong-Rui,Liu, Yi-Wei,Zhang, Zhong,Liu, Shu-Mei,Dang, Tian-Yi,Li, Xiao-Hui,Sun, Xiu-Wei,Lu, Ying,Liu, Shu-Xia
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p. 248 - 255
(2020/01/13)
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- Synergistic Activation of Amides and Hydrocarbons for Direct C(sp3)–H Acylation Enabled by Metallaphotoredox Catalysis
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The utilizations of omnipresent, thermodynamically stable amides and aliphatic C(sp3)?H bonds for various functionalizations are ongoing challenges in catalysis. In particular, the direct coupling between the two functional groups has not been realized. Here, we report the synergistic activation of the two challenging bonds, the amide C?N and unactivated aliphatic C(sp3)?H, via metallaphotoredox catalysis to directly acylate aliphatic C?H bonds utilizing amides as stable and readily accessible acyl surrogates. N-acylsuccinimides served as efficient acyl reagents for the streamlined synthesis of synthetically useful ketones from simple C(sp3)?H substrates. Detailed mechanistic investigations using both computational and experimental mechanistic studies were performed to construct a detailed and complete catalytic cycle. The origin of the superior reactivity of the N-acylsuccinimides over other more reactive acyl sources such as acyl chlorides was found to be an uncommon reaction pathway which commences with C?H activation prior to oxidative addition of the acyl substrate.
- Baik, Mu-Hyun,Choi, Seulhui,Hong, Soon Hyeok,Lee, Geun Seok,Won, Joonghee
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p. 16933 - 16942
(2020/08/03)
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- Multiple Mechanisms Mapped in Aryl Alkyl Ether Cleavage via Aqueous Electrocatalytic Hydrogenation over Skeletal Nickel
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We present here detailed mechanistic studies of electrocatalytic hydrogenation (ECH) in aqueous solution over skeletal nickel cathodes to probe the various paths of reductive catalytic C-O bond cleavage among functionalized aryl ethers relevant to energy science. Heterogeneous catalytic hydrogenolysis of aryl ethers is important both in hydrodeoxygenation of fossil fuels and in upgrading of lignin from biomass. The presence or absence of simple functionalities such as carbonyl, hydroxyl, methyl, or methoxyl groups is known to cause dramatic shifts in reactivity and cleavage selectivity between sp3 C-O and sp2 C-O bonds. Specifically, reported hydrogenolysis studies with Ni and other catalysts have hinted at different cleavage mechanisms for the C-O ether bonds in α-keto and α-hydroxy β-O-4 type aryl ether linkages of lignin. Our new rate, selectivity, and isotopic labeling results from ECH reactions confirm that these aryl ethers undergo C-O cleavage via distinct paths. For the simple 2-phenoxy-1-phenylethane or its alcohol congener, 2-phenoxy-1-phenylethanol, the benzylic site is activated via Ni C-H insertion, followed by beta elimination of the phenoxide leaving group. But in the case of the ketone, 2-phenoxyacetophenone, the polarized carbonyl πsystem apparently binds directly with the electron rich Ni cathode surface without breaking the aromaticity of the neighboring phenyl ring, leading to rapid cleavage. Substituent steric and electronic perturbations across a broad range of β-O-4 type ethers create a hierarchy of cleavage rates that supports these mechanistic ideas while offering guidance to allow rational design of the catalytic method. On the basis of the new insights, the usage of cosolvent acetone is shown to enable control of product selectivity.
- Hegg, Eric L.,Jackson, James E.,Klinger, Grace E.,Saffron, Christopher M.,Zhou, Yuting
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p. 4037 - 4050
(2020/03/10)
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- Cobalt-Catalyzed Reductive C-O Bond Cleavage of Lignin β-O-4 Ketone Models via in Situ Generation of the Cobalt-Boryl Species
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An efficient and mild method for reductive C-O bond cleavage of lignin β-O-4 ketone models was developed to afford the corresponding ketones and phenols with PDI-CoCl2 as the precatalyst and diboron reagent as the reductant. The synthetic utility of the methodology was demonstrated by depolymerization of a polymeric model and gram-scale transformation. Mechanistic studies suggested that this transformation involves steps of carbonyl insertion, 1,2-Brook type rearrangement, β-oxygen elimination, and rate-limiting regeneration of the catalytic active Co-B species.
- Gao, Kecheng,Xu, Man,Cai, Cheng,Ding, Yanghao,Chen, Jianhui,Liu, Bosheng,Xia, Yuanzhi
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supporting information
p. 6055 - 6060
(2020/08/12)
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- Tandem Acid/Pd-Catalyzed Reductive Rearrangement of Glycol Derivatives
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Herein, we describe the acid/Pd-tandem-catalyzed transformation of glycol derivatives into terminal formic esters. Mechanistic investigations show that the substrate undergoes rearrangement to an aldehyde under [1,2] hydrogen migration and cleavage of an oxygen-based leaving group. The leaving group is trapped as its formic ester, and the aldehyde is reduced and subsequently esterified to a formate. Whereas the rearrangement to the aldehyde is catalyzed by sulfonic acids, the reduction step requires a unique catalyst system comprising a PdII or Pd0 precursor in loadings as low as 0.75 mol % and α,α′-bis(di-tert-butylphosphino)-o-xylene as ligand. The reduction step makes use of formic acid as an easy-to-handle transfer reductant. The substrate scope of the transformation encompasses both aromatic and aliphatic substrates and a variety of leaving groups.
- Ciszek, Benjamin,Fleischer, Ivana,Kathe, Prasad,Schmidt, Tanno A.
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supporting information
p. 3641 - 3646
(2020/03/25)
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- Synthesis of benzofurans from the cyclodehydration of α-phenoxy ketones mediated by Eaton’s reagent
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Cyclodehydration of α-phenoxy ketones promoted by Eaton’s reagent (phosphorus pentoxide–methanesulfonic acid) is used to prepare 3-substituted or 2,3-disubstituted benzofurans with moderate to excellent yields under mild conditions. The method provides a facile access to benzofurans from readily available starting materials such as phenols and α-bromo ketones. The reaction is highly efficient, which is attributed to the good reactivity and fluidity of Eaton’s reagent. The reaction can be applied to prepare naphthofurans, furanocoumarins, benzothiophenes, and benzopyrans.
- Ma, Lin,Ma, Zhanwei,Zhang, Min,Zhou, Min
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p. 426 - 436
(2020/03/23)
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- Lewis-acid-mediated intramolecular trifluoromethylthiolation of alkenes with phenols: Access to SCF3-containing chromane and dihydrobenzofuran compounds
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A Lewis-acid-mediated intramolecular trifluoromethylthiolation of alkenes with phenols that can offer direct access to SCF3-containing chromane and dihydrobenzofuran compounds was disclosed for the first time. Numerous SCF3-containing chromanes were obtai
- Song, Xu-Feng,Ding, Tong-Mei,Zhu, Deng,Huang, Jie,Chen, Zhi-Min
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supporting information
p. 7052 - 7056
(2020/09/15)
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- Visible-light-induced C-C bond cleavage of lignin model compounds with cyanobenziodoxolone
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The catalytic degradation of lignin to value-added chemicals has received considerable attention over the past decade. Photocatalysis provides promising approaches to enable previously inaccessible transformations. However, examples of the visible-light promoted degradation of lignin are still limited. In this work, the visible-light-induced selective C-C bond cleavage of β-O-4 lignin model compounds has been disclosed via β-scission of in situ generated alkoxy radical intermediates. With cyanobenziodoxolone as the oxidant, a variety of substrates could be transformed into aldehydes in moderate to good yields. In addition, unexpected acetal esters which could conveniently furnish formaldehyde and phenols by alcoholysis were observed.
- Zheng, Ming,Huang, Yan,Zhan, Le-Wu,Hou, Jing,Li, Bin-Dong
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supporting information
(2020/10/02)
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- Highly Selective Photocatalytic Valorization of Lignin Model Compounds Using Ultrathin Metal/CdS
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Depolymerization of recalcitrant lignin is a crucial step in realizing the full potential of transforming biomass to value-added small organic molecules. Herein, we report a photocatalytic system consisting of ultrathin CdS nanosheets decorated with first-row transition metals (M/CdS) for the direct photocleavage of lignin model compounds to small aromatic products. In the meantime, the reducing power of M/CdS is utilized to simultaneously generate another valuable product, H2, hence eliminating the necessity of sacrificial reagents and maximizing the energy conversion efficiency. We further demonstrate that, by judiciously modulating the photocatalytic conditions, it is feasible to yield different products with very high selectivity using the same catalyst of Ni/CdS. A series of control experiments were performed to investigate the mechanistic steps of each reaction and highlight the important roles played by both solvent and base in the photocleavage of the β-O-4 bond in lignin valorization.
- Han, Guanqun,Yan, Tao,Zhang, Wei,Zhang, Yi C.,Lee, David Y.,Cao, Zhi,Sun, Yujie
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p. 11341 - 11349
(2019/11/21)
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- Visible-Light-Driven Cleavage of C?O Linkage for Lignin Valorization to Functionalized Aromatics
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Lignin is the most abundant source of renewable aromatics. Catalytic valorization of lignin into functionalized aromatics is attractive but challenging. Photocatalysis is a promising sustainable approach. The strategies for designing well-performing photocatalysts are desired but remain limited. Herein, a facile energy band engineering strategy for promoting the photocatalytic activity of zinc–indium–sulfide (ZnmIn2Sm+3) for cleavage of the lignol β-O-4 bond under mild conditions was developed. The energy band structure of ZnmIn2Sm+3 could be tuned by controlling the atomic ratio of Zn/In. It was found that Zn4In2S7 performed best for cleavage of the β-O-4 bond under visible-light irradiation, owing to its appropriate energy band structure for offering adequate visible-light absorption and suitable redox capability. Functionalized aromatic monomers with near 18.4 wt % yield could be obtained from organosolv birch lignin. Mechanistic studies revealed that the β-O-4 bond was efficiently cleaved mainly through a one-step redox-neutral pathway via a Cα radical intermediate. The thiol groups on the surface of Zn4In2S7 played a key role in cleavage of the β-O-4 bond.
- Lin, Jinchi,Wu, Xuejiao,Xie, Shunji,Chen, Liangyi,Zhang, Qinghong,Deng, Weiping,Wang, Ye
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p. 5023 - 5031
(2019/12/02)
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- Visible light induced redox neutral fragmentation of 1,2-diol derivatives
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A homogeneous, redox-neutral photo fragmentation of diol derivatives was developed. Under photo/hydrogen atom transfer (HAT) dual catalysis, diol derivatives such as lignin model compounds and diol monoesters undergo selective β C(sp3)-O bond cleavage to afford ketones, phenols and acids effectively.
- Chen, Kang,Schwarz, Johanna,Karl, Tobias A.,Chatterjee, Anamitra,K?nig, Burkhard
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p. 13144 - 13147
(2019/11/11)
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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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- 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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p. 1974 - 1981
(2019/04/29)
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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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- Selective Cα Alcohol Oxidation of Lignin Substrates Featuring a β-O-4 Linkage by a Dinuclear Oxovanadium Catalyst via Two-Electron Redox Processes
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Developing highly efficient catalyst systems to transform lignin biomass into value-added chemical feedstocks is imperative for utilizing lignin as renewable alternatives to fossil fuels. Recently, the pre-activated strategy involving the selective oxidat
- Tsai, Yan-Ting,Chen, Chih-Yao,Hsieh, Yi-Ju,Tsai, Ming-Li
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p. 4637 - 4646
(2019/11/16)
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- Transfer-dehydrogenation of secondary alcohols catalyzed by manganese NNN-pincer complexes
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Novel catalytic systems based on pentacarbonylmanganese bromide and stable NNN-pincer ligands are presented for the transfer-dehydrogenation of secondary alcohols to give the corresponding ketones in good to excellent isolated yields. Best results are obtained using di-picolylamine derivatives as ligands and acetone as an inexpensive hydrogen acceptor. Besides high activity for benzylic substrates, aliphatic alcohols, as well as steroid derivatives, are readily oxidized in the presence of the optimal phosphorus-free catalyst.
- Budweg, Svenja,Junge, Kathrin,Beller, Matthias
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supporting information
p. 14143 - 14146
(2019/12/02)
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- Controlled Photocatalytic Hydrocarbon Oxidation by Uranyl Complexes
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Controlled, photocatalytic C?H bond activations are key reactions in the toolkits of the modern synthetic chemist. While it is known that the uranyl(VI) ion, [UVIO2]2+, the environmentally dominant form of uranium, is photoactive, most literature examines its luminescent properties, neglecting its potential synthetic utility for photocatalytic C?H bond cleavage. Here, we synthesise and fully characterise an air-stable and hydrocarbon-soluble uranyl phenanthroline complex, [UVIO2(NO3)2(Ph2phen)], UPh2phen, and demonstrate that it can catalytically abstract hydrogen atoms from a variety of organic substrates under visible light irradiation. We show that the commercially available parent complex, uranyl nitrate ([UVIO2(NO3)2(OH2)2]?4H2O; UNO3), is also competent, but from electronic spectroscopy we attribute the higher rates and selectivity of UPh2phen to ligand-mediated electronic effects. Ketones are selectively formed over other oxygenated products (alcohols, etc.), and the catalytic oxidation of substrates containing a benzylic C?H position is particularly improved for UPh2phen. We also show uranyl-mediated photocatalytic C?C bond cleavage in a model lignin compound for the first time.
- Arnold, Polly L.,Purkis, Jamie M.,Rutkauskaite, Ryte,Kovacs, Daniel,Love, Jason B.,Austin, Jonathan
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p. 3786 - 3790
(2019/03/07)
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- Lignin oxidation by MnO2 under the irradiation of blue light
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Traditionally, conventional heat has been required for a large proportion of the oxidation and degradation process to utilise lignin from biomass. A photocatalysis system which is considered as a novel and green strategy for chemical reactions has been ap
- Dai, Jinhuo,Patti, Antonio F.,Styles, Gavin N.,Nanayakkara, Sepa,Spiccia, Leone,Arena, Francesco,Italiano, Cristina,Saito, Kei
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p. 2005 - 2014
(2019/04/27)
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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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- Photocatalytic Cleavage of C-C Bond in Lignin Models under Visible Light on Mesoporous Graphitic Carbon Nitride through π-π Stacking Interaction
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Photocatalysis is a potentially promising approach to harvest aromatic compounds from lignin. However, the development of an active and selective solid photocatalyst is still challenging for lignin transformation under ambient conditions. We herein report a mild photocatalytic oxidative strategy for C-C bond cleavage of lignin β-O-4 and β-1 linkages using a mesoporous graphitic carbon nitride catalyst. Identifications by solid-state NMR techniques and density functional theory (DFT) calculations indicate that π-π stacking interactions are most likely present between the flexible carbon nitride surface and lignin model molecule. Besides, low charge recombination efficiency and high specific surface area (206.5 m2 g-1) of the catalyst also contribute to its high catalytic activity. Mechanistic investigations reveal that photogenerated holes, as the main active species, trigger the oxidation and C-C bond cleavage of lignin models. This study sheds light on the interaction between complex lignin structures and the catalyst surface and provides a new strategy of photocatalytic cleavage of lignin models with heterogeneous photocatalysts.
- Liu, Huifang,Li, Hongji,Lu, Jianmin,Zeng, Shu,Wang, Min,Luo, Nengchao,Xu, Shutao,Wang, Feng
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p. 4761 - 4771
(2018/05/14)
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- Method for synthesizing β - O - 4 lignin dimers model compounds (by machine translation)
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The invention belongs to the field of biological chemical and biological-based material, and in particular relates to a synthetic β - O - 4 lignin dimers model compounds. The phenolic material with the alkali is dissolved in the acetone in magnetic stirring and mixing, [...] ketone material under protection of inert gas in the room temperature to 60 °C reaction 16 - 48 h, filtering the filtrate after reaction is rotary evaporated to obtain crude product, crude after excessive polar organic solvent, washing the collection after dissolving the organic phase, dried and filtered, concentrated in vacuo, re-crystallization, dried under vacuum to get β - O - 4 lignin dimers model compound. The invention synthetic method and the conventional method compared with the universality is relatively strong, mild reaction conditions, the operation is simple, one-step synthesis output is high, and high purity, can reach 98% or more. (by machine translation)
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Page/Page column 5-7
(2019/01/08)
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- Electronic and bite angle effects in catalytic C-O bond cleavage of a lignin model compound using ruthenium Xantphos complexes
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Bite angle and electronic effects on the ruthenium-diphosphine catalysed ether bond cleavage of the lignin β-O-4 model compound 2-phenoxy-1-phenylethanol were tested. Enhanced conversion of the substrate was observed with increasing σ-donor capacity of the ligands. Kinetic and thermodynamic data suggest oxidative addition of the dehydrogenated model compound to the diphosphine Ru(0) complex to be rate-limiting.
- Shaw, Luke,Somisara, D. M. Upulani K.,How, Rebecca C.,Westwood, Nicholas J.,Bruijnincx, Pieter C. A.,Weckhuysen, Bert M.,Kamer, Paul C. J.
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p. 619 - 626
(2017/08/14)
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- Self-hydrogen transfer hydrogenolysis of β-O-4 linkages in lignin catalyzed by MIL-100(Fe) supported Pd-Ni BMNPs
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A MIL-100(Fe) supported Pd-Ni BMNP catalyst has been fabricated, and the catalyst exhibits superior catalytic performance toward the intramolecular transfer hydrogenolysis of lignin model compounds and organosolv lignin. Alcoholic groups (CαH-OH) of lignin were exploited as the hydrogen source, and selective cleavage of β-O-4 linkages in lignin was realized without an extra hydrogen donor. This protocol was suitable for organosolv lignin as well as model compounds; several phenols and functionalized acetophenones were detected when extracted lignin was treated in our system. The catalyst exhibits outstanding catalytic stability during the reaction process, which can be ascribed to the porous structure and the strong water stability of MIL-100(Fe). The excellent catalytic performance of Pd1Ni4/MIL-100(Fe) highlights the "synergistic effect" between the BMNPs and the functional synergy between MNPs and MOFs, and our work shows the bright future of BMNPs and MOFs in the development of catalysts for sustainable chemistry.
- Zhang, Jia-Wei,Lu, Guo-Ping,Cai, Chun
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supporting information
p. 4538 - 4543
(2017/10/13)
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- Visible-Light-Driven Self-Hydrogen Transfer Hydrogenolysis of Lignin Models and Extracts into Phenolic Products
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Obtaining high selectivity of aromatic monomers from renewable lignin has been extensively pursued but is still unsuccessful, hampered by the need to efficiently cleave C-O/C-C bonds and inhibit lignin proliferation reactions. Herein, we report a transfer hydrogenolysis protocol using a heterogeneous ZnIn2S4 catalyst driven by visible light. In this process, alcoholic groups (CαH-OH) of lignin act as hydrogen donors. Proliferation of phenolic products to dark substances is suppressed under visible light illumination at low temperature (below 50 °C); formation of a light and transparent reaction solution allows visible light to be absorbed by the catalyst. With this strategy, 71-91% yields of phenols in the conversion of lignin β-O-4 models and a 10% yield of p-hydroxyl acetophenone derivatives from organosolv lignin are achieved. Mechanistic studies reveal that CαH-OH groups of lignin β-O-4 linkage are initially dehydrogenated on ZnIn2S4 to form a "hydrogen pool", and the adjacent Cβ-O bond is subsequently hydrogenolytically cleaved to two monomers by the "hydrogen pool". Thus, the dehydrogenation and hydrogenolysis reaction are integrated in one-pot with lignin itself as a hydrogen donor. This study shows a promising way of supplying phenolic compounds by taking advantages of both renewable biomass feedstocks and photoenergy.
- Luo, Nengchao,Wang, Min,Li, Hongji,Zhang, Jian,Hou, Tingting,Chen, Haijun,Zhang, Xiaochen,Lu, Jianmin,Wang, Feng
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p. 4571 - 4580
(2017/07/24)
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- The selective hydrogenolysis of C-O bonds in lignin model compounds by Pd-Ni bimetallic nanoparticles in ionic liquids
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β-O-4 and α-O-4 linkages can be selectively cleaved by Pd-Ni bimetallic nanoparticles in ionic liquids using hydrogen gas as the hydrogen donor under ambient pressure and neutral conditions. No hydrogenation of the benzene ring takes place in the catalytic system. An obvious improvement in activity is found compared with single nickel and palladium catalysts based on the results of experiments and characterization. After the reaction, the catalytic system still remains in the reactor by simple extraction, which can be reused without further treatment.
- Sun, Kang-Kang,Lu, Guo-Ping,Zhang, Jia-Wei,Cai, Chun
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p. 11884 - 11889
(2017/09/18)
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- Promoting Lignin Depolymerization and Restraining the Condensation via an Oxidation-Hydrogenation Strategy
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For lignin valorization, simultaneously achieving the efficient cleavage of ether bonds and restraining the condensation of the formed fragments represents a challenge thus far. Herein, we report a two-step oxidation-hydrogenation strategy to achieve this goal. In the oxidation step, the O2/NaNO2/DDQ/NHPI system selectively oxidizes CαH-OH to Cα=O within the β-O-4 structure. In the subsequent hydrogenation step, the α-O-4 and the preoxidized β-O-4 structures are further hydrogenated over a NiMo sulfide catalyst, leading to the cleavage of Cβ-OPh and Cα-OPh bonds. Besides the transformation of lignin model compounds, the yield of phenolic monomers from birch wood is up to 32% by using this two-step strategy. The preoxidation of CαH-OH to Cα=O not only weakens the Cβ-OPh ether bond but also avoids the condensation reactions caused by the presence of Cα+ from dehydroxylation of CαH-OH. Furthermore, the NiMo sulfide prefers to catalyze the hydrogenative cleavage of the Cβ-OPh bond connecting with a Cα=O rather than catalyze the hydrogenation of Cα=O back to the original CαH-OH, which further ensures and utilizes the advantages of preoxidation.
- Zhang, Chaofeng,Li, Hongji,Lu, Jianmin,Zhang, Xiaochen,Macarthur, Katherine E.,Heggen, Marc,Wang, Feng
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p. 3419 - 3429
(2017/06/09)
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- Acid promoted C-C bond oxidative cleavage of β-O-4 and β-1 lignin models to esters over a copper catalyst
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Depolymerisation of lignin to aromatics is a challenging task. We herein report that a Cu(OAc)2/BF3·OEt2 catalyst is effective in simultaneously cleaving C-C bonds in β-1 and β-O-4 ketones, yielding esters and phenols. In-depth studies show that C-H bond activation is the rate determining step for C-C bond cleavage. BF3·OEt2 promotes the reaction via activating the β-C-H bond. This study offers the potential to obtain aromatic esters from lignin.
- Wang,Li,Lu,Li,Zhang,Liu,Luo,Wang
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supporting information
p. 702 - 706
(2017/08/15)
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- Ionic liquid [OMIm][OAc] directly inducing oxidation cleavage of the β-O-4 bond of lignin model compounds
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We explored the oxidation reactions of lignin model compounds directly induced by ionic liquids under metal-free conditions. In this work, it was found that ionic liquid 1-octyl-3-methylimidazolium acetate as a solvent could promote the aerobic oxidation of lignin model compound 2-phenoxyacetophenone (1) and the yields of phenol and benzoic acid from 1 could be as high as 96% and 86%, respectively. A possible reaction pathway was proposed based on a series of control experiments. An acetate anion from the ionic liquid attacked the hydrogen from the β-carbon thereby inducing the cleavage of the C-O bond of the aromatic ether. Furthermore, it was found that 2-(2-methoxyphenoxy)-1-phenylethanone (4) with a methoxyl group could also be transformed into aromatic products in this simple reaction system and the yields of phenol and benzoic acid from 4 could be as high as 98% and 85%, respectively. This work provides a simple way for efficient transformation of lignin model compounds.
- Yang, Yingying,Fan, Honglei,Meng, Qinglei,Zhang, Zhaofu,Yang, Guanying,Han, Buxing
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supporting information
p. 8850 - 8853
(2017/08/10)
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- New protocol of copper-catalyzed oxidative C(CO)[sbnd]C bond cleavage of aryl and aliphatic ketones to organic acids using O2 as the terminal oxidant
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Catalytic oxidation of C[sbnd]C bond is a key technology to transform petroleum-based as well as sustainable biomass feedstock into more valuable oxygenates. We herein describe a convenient and useful oxidation strategy of converting ketones into carboxylic acids using homogeneous copper catalyst without additives and with O2as the terminal oxidant. A wide range of aryl and aliphatic ketones as well as β–O–4 lignin models were selectively oxidized to acids via C[sbnd]C bond cleavage. Mechanism studies by EPR and in situ NMR elucidate the principles of Cu/O2reactivity that involves C[sbnd]H bond and O2activation via a peroxide species. This provides an important foundation for expanding the scope of useful aerobic oxidation reactions using copper catalysts.
- Liu, Huifang,Wang, Min,Li, Hongji,Luo, Nengchao,Xu, Shutao,Wang, Feng
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p. 170 - 179
(2017/01/22)
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- Degradation of β-O-4 model lignin species by vanadium Schiff-base catalysts: Influence of catalyst structure and reaction conditions on activity and selectivity
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In the pursuit of value-added products from the degradation of the abundant aromatic biopolymer lignin, homogeneous catalysis has the potential to provide a mild, selective route to monomeric phenols. Homogeneous vanadium catalysts have previously been shown to effectively cleave dimeric β-O-4 model lignin compounds, with selectivity for C-C or C-O cleavage, or benzylic oxidation, depending on the ligand structure and oxidation state of the metal. In this study, a systematic kinetic investigation was undertaken in order to gain further understanding of the role of ligand structure and reaction conditions on the activity of vanadium Schiff-base catalysts towards a non-phenolic β-O-4 model lignin dimer, and the selectivity of these species towards C-O bond cleavage. Catalytic activity was found to be increased by the addition of bulky, alkyl substituents at the 3′-position of the phenolate ring, whereas electron-withdrawing substituents were found to dramatically reduce activity irrespective of their size. Selective depolymerization of a phenolic β-O-4 dimer was also achieved.
- Parker, Heather J.,Chuck, Christopher J.,Woodman, Timothy,Jones, Matthew D.
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- Facile and selective hydrogenolysis of β-O-4 linkages in lignin catalyzed by Pd-Ni bimetallic nanoparticles supported on ZrO2
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The β-O-4 linkage in lignin can be selectively cleaved by Pd-Ni bimetallic nanoparticles supported on ZrO2 using hydrogen gas as the hydrogen donor under ambient pressure and neutral conditions. Conspicuous enhancement in activity is observed compared with single nickel and palladium catalysts based on the results of experiments and characterization. Moreover, hydrogenation of the produced phenols is tuned by adjusting the amount of NaBH4. The catalyst can be reused over ten times in the model reaction and over five times in the hydrogenolysis of lignin without an obvious change in activity and selectivity.
- Zhang, Jia-Wei,Cai, Yao,Lu, Guo-Ping,Cai, Chun
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p. 6229 - 6235
(2016/12/03)
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- A comparison of the oxidation of lignin model compounds in conventional and ionic liquid solvents and application to the oxidation of lignin
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The oxidation of lignin model compounds was studied in conventional solvents in parallel with oxidations in ionic liquid solvents. Catalyst systems were investigated in ionic liquid solvents to determine how reaction rates and the selectivity for benzylic carbon oxidation were affected. Oxidation rates were often lower in ionic liquids than in conventional solvents-as indicated by lower conversion in a standard reaction time-likely due, at least in part, to the higher viscosity of ionic liquids. Selectivity of the TPPFeCl/t-BuOOH catalyst system for oxidation of the benzylic C-OH versus benzylic C-H was higher in the ionic liquids tested than in conventional solvents.
- Yao, Soledad G.,Meier, Mark S.,Pace, Robert B.,Crocker, Mark
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p. 104742 - 104753
(2016/11/17)
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- Chemoselective oxidant-free dehydrogenation of alcohols in lignin using Cp?Ir catalysts
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A remarkably effective method of chemoselective dehydrogenation of alcohols in lignin has been developed with an iridium catalyst. An additional operation of Zn/NH4Cl via a two-step one pot process could further promote the cleavage of the C-O bond in β-O-4 units in lignin. And this reaction system was also applicable to native lignin as the molecular weight of native lignin decreased obviously as detected by gel permeation chromatography (GPC). Additionally, this is the first to date generation of the by-product H2 from native lignin and the by-product was straightforwardly captured by 1-decene. A probable mechanistic pathway was also proposed with the help of density functional theory (DFT) calculations.
- Zhu, Rui,Wang, Bing,Cui, Minshu,Deng, Jin,Li, Xinglong,Ma, Yingbo,Fu, Yao
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supporting information
p. 2029 - 2036
(2016/04/19)
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