- 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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- 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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- 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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- Highly efficient Meerwein-Ponndorf-Verley reductions over a robust zirconium-organoboronic acid hybrid
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The Meerwein-Ponndorf-Verley (MPV) reaction is an attractive approach to selectively reduce carbonyl groups, and the design of advanced catalysts is the key for these kinds of interesting reactions. Herein, we fabricated a novel zirconium organoborate using 1,4-benzenediboronic acid (BDB) as the precursor for MPV reduction. The prepared Zr-BDB had excellent catalytic performance for the MPV reduction of various biomass-derived carbonyl compounds (i.e., levulinate esters, aldehydes and ketones). More importantly, the number of borate groups on the ligands significantly affected the catalytic activity of the Zr-organic ligand hybrids, owing to the activation role of borate groups on hydroxyl groups in the hydrogen source. Detailed investigations revealed that the excellent performance of Zr-BDB was contributed by the synergetic effect of Zr4+and borate. Notably, this is the first work to enhance the activity of Zr-based catalysts in MPV reactions using borate groups.
- Song, Jinliang,Hua, Manli,Huang, Xin,Visa, Aurelia,Wu, Tianbin,Fan, Honglei,Hou, Minqiang,Zhang, Zhaofu,Han, Buxing
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p. 1259 - 1265
(2021/02/26)
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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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- Coupling Reaction between Aldehydes and Non-Activated Hydrocarbons via the Reductive Radical-Polar Crossover Pathway
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Herein, we describe the generation of an organochromium-type carbanion species from a non-activated C-H bond and its nucleophilic addition to aldehydes. The catalytic carbanion generation occurred through formal deprotonation of a non-activated C-H bond under mild conditions and did not need the prefunctionalization or anion stabilizing group. Carbon radical intermediates generated by decatungstate photocatalyst-mediated hydrogen abstraction were captured by a chromium salt with the reductive radical-polar crossover reaction to produce organochromium carbanions.
- Yahata, Kenzo,Sakurai, Shu,Hori, Shuhei,Yoshioka, Shin,Kaneko, Yuki,Hasegawa, Kai,Akai, Shuji
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supporting information
p. 1199 - 1203
(2020/02/04)
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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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- 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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supporting information
p. 4037 - 4050
(2020/03/10)
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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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supporting information
p. 248 - 255
(2020/01/13)
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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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- Nickel-Catalyzed Asymmetric Addition of Aromatic Halides to Ketones: Highly Enantioselective Synthesis of Chiral 2,3-Dihydrobenzofurans Containing a Tertiary Alcohol
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A highly enantioselective and straightforward synthetic procedure to chiral 3-hydroxy-2,3-dihydrobenzofurans has been developed by nickel/bisoxazoline-catalyzed intramolecular asymmetric addition of aryl halides to unactivated ketones, giving 2,3-dihydrobenzofurans with a chiral tertiary alcohol at the C-3 position in good yields and excellent enantioselectivities (up to 92percent yield and 98percent ee). The gram-scale reaction also proceeded smoothly without a loss of yield and enantioselectivity.
- Li, Ying,Li, Wendian,Tian, Jiangyan,Huang, Guozheng,Lv, Hui
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p. 5353 - 5357
(2020/07/14)
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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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supporting information
p. 4637 - 4646
(2019/11/16)
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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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supporting information
p. 13144 - 13147
(2019/11/11)
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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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- 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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supporting information
p. 6707 - 6716
(2019/12/26)
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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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- 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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- 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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supporting information
p. 11884 - 11889
(2017/09/18)
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- Decomposition of a Β-O-4 lignin model compound over solid Cs-substituted polyoxometalates in anhydrous ethanol: acidity or redox property dependence?
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Production of aromatics from lignin has attracted much attention. Because of the coexistence of C–O and C–C bonds and their complex combinations in the lignin macromolecular network, a plausible roadmap for developing a lignin catalytic decomposition process could be developed by exploring the transformation mechanisms of various model compounds. Herein, decomposition of a lignin model compound, 2-phenoxyacetophenone (2-PAP), was investigated over several cesium-exchanged polyoxometalate (Cs-POM) catalysts. Decomposition of 2-PAP can follow two different mechanisms: an active hydrogen transfer mechanism or an oxonium cation mechanism. The mechanism for most reactions depends on the competition between the acidity and redox properties of the catalysts. The catalysts of POMs perform the following functions: promoting active hydrogen liberated from ethanol and causing formation of and then temporarily stabilizing oxonium cations from 2-PAP. The use of Cs-PMo, which with strong redox ability, enhances hydrogen liberation and promotes liberated hydrogen transfer to the reaction intermediates. As a consequence, complete conversion of 2-PAP (>99%) with excellent selectivities to the desired products (98.6% for phenol and 91.1% for acetophenone) can be achieved.
- Wu, Xuezhong,Jiao, Wenqian,Li, Bing-Zheng,Li, Yanming,Zhang, Yahong,Wang, Quanrui,Tang, Yi
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p. 1216 - 1228
(2017/07/10)
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- Investigation on the cleavage of Β-O-4 linkage in dimeric lignin model compound over nickel catalysts supported on ZnO-Al2O3 composite oxides with varying Zn/Al ratios
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Catalytic depolymerization of lignin is still a challenge due to its low conversion and repolymerization of the reactive intermediates. Reductive depolymerization over supported nickel catalysts with probable surface acidic and basic properties is a very promising process. It is therefore very important to investigate the effect of acidity and basicity of the supports on catalytic reactivity. In this paper, we synthesized a series of nickel based catalysts supported on ZnO-Al2O3 composites with varying Zn/Al atom ratios (Zn/Al = 2, 3, 5, ∞) and tested their catalytic performances over a model compound 2-phenoxy-1-phenylethanone containing β-O-4 bond. All these catalysts showed 100% conversion by reacting at 250 °C for 2 h under 2 MPa of H2. Higher selectivity towards ethylcyclohexane could be obtained over the catalyst Ni/ZnO-Al2O3-5. The possible cleavage pathways of selective oxidized β-O-4 ether linkage have been proposed.
- Xu, Chen,Tang, Si-Fu,Sun, Xianyong,Sun, Yuanyuan,Li, Guangci,Qi, Jingbo,Li, Xiaoyu,Li, Xuebing
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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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supporting information
p. 6229 - 6235
(2016/12/03)
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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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- Lignin Depolymerization with Nitrate-Intercalated Hydrotalcite Catalysts
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Hydrotalcites (HTCs) exhibit multiple adjustable parameters to tune catalytic activity, including interlayer anion composition, metal hydroxide layer composition, and catalyst preparation methods. Here, we report the influence of several of these parameters on β-O-4 bond scission in a lignin model dimer, 2-phenoxy-1-phenethanol (PE), to yield phenol and acetophenone. We find that the presence of both basic and NO3- anions in the interlayer increases the catalyst activity by 2-3-fold. In contrast, other anions or transition metals do not enhance catalytic activity in comparison to blank HTC. The catalyst is not active for C-C bond cleavage on lignin model dimers and has no effect on dimers without an α-OH group. Most importantly, the catalyst is highly active in the depolymerization of two process-relevant lignin substrates, producing a significant amount of low-molecular-weight aromatic species. The catalyst can be recycled until the NO3- anions are depleted, after which the activity can be restored by replenishing the NO3- reservoir and regenerating the hydrated HTC structure. These results demonstrate a route to selective lignin depolymerization in a heterogeneous system with an inexpensive, earth-abundant, commercially relevant, and easily regenerated catalyst.
- Kruger, Jacob S.,Cleveland, Nicholas S.,Zhang, Shuting,Katahira, Rui,Black, Brenna A.,Chupka, Gina M.,Lammens, Tijs,Hamilton, Phillip G.,Biddy, Mary J.,Beckham, Gregg T.
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p. 1316 - 1328
(2016/02/18)
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- HYDROXIDE CATALYSTS FOR LIGNIN DEPOLYMERIZATION
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Solid base catalysts and their use for the base-catalyzed depolymerization (BCD) of lignin to compounds such as aromatics are presented herein. Exemplary catalysts include layered double hydroxides (LDHs) as recyclable, heterogeneous catalysts for BCD of
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Paragraph 0101
(2016/05/02)
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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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- Cleavage of the lignin β-O-4 ether bond: Via a dehydroxylation-hydrogenation strategy over a NiMo sulfide catalyst
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The efficient cleavage of lignin β-O-4 ether bonds to produce aromatics is a challenging and attractive topic. Recently a growing number of studies have revealed that the initial oxidation of CαHOH to CαO can decrease the β-O-4 bond dissociation energy (BDE) from 274.0 kJ mol-1 to 227.8 kJ mol-1, and thus the β-O-4 bond is more readily cleaved in the subsequent transfer hydrogenation, or acidolysis. Here we show that the first reaction step, except in the above-mentioned pre-oxidation methods, can be a Cα-OH bond dehydroxylation to form a radical intermediate on the acid-redox site of a NiMo sulfide catalyst. The formation of a Cα radical greatly decreases the Cβ-OPh BDE from 274.0 kJ mol-1 to 66.9 kJ mol-1 thereby facilitating its cleavage to styrene, phenols and ethers with H2 and an alcohol solvent. This is supported by control experiments using several reaction intermediates as reactants, analysis of product generation and by radical trap with TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) as well as by density functional theory (DFT) calculations. The dehydroxylation-hydrogenation reaction is conducted under non-oxidative conditions, which are beneficial for stabilizing phenol products.
- Zhang, Chaofeng,Lu, Jianmin,Zhang, Xiaochen,Macarthur, Katherine,Heggen, Marc,Li, Hongji,Wang, Feng
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supporting information
p. 6545 - 6555
(2018/06/06)
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- Mapping reactivities of aromatic models with a lignin disassembly catalyst. Steps toward controlling product selectivity
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Copper-doped porous metal oxides catalyze the one-pot disassembly of biomass-derived lignin via C-O bond hydrogenolysis and hydrodeoxygenation in supercritical methanol. This catalytic system cleanly converts lignin as well as lignocellulose composites, such as sawdust, to organic liquids with little or no formation of intractable tars or chars. However, this catalyst based on Earth-abundant components also catalyzes less desirable aromatic ring hydrogenations and various methylations that contribute to the diversity of products. In this context, we undertook a quantitative experimental and computational evaluation of model reactions relevant to the reductive disassembly of lignin by this catalyst system in order to determine quantitatively the rates of desirable and less desirable chemical steps that define the overall product selectivities. Global fitting analysis methods were used to map the temporal evolution of key intermediates and products and to elucidate networks that provide guidelines regarding the eventual fates of reactive intermediates in this catalysis system. Phenolic compounds display multiple reaction pathways, but substrates such as benzene, toluene, and alkyl- and alkoxy-substituted aromatics are considerably more stable under these conditions. These results indicate that modifying this catalytic system in a way that controls and channels the reactivity of phenolic intermediates should improve selectivity toward producing valuable aromatic chemicals from biomass-derived lignin. To this end we demonstrate that the O-methylating agent dimethyl carbonate can intercept the phenol intermediate formed from hydrogenolysis of the model compound benzyl phenyl ether. Trapping the phenol as anisole thus gave much higher selectivity towards aromatic products.
- Bernt, Christopher M.,Bottari, Giovanni,Barrett, Jacob A.,Scott, Susannah L.,Barta, Katalin,Ford, Peter C.
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p. 2984 - 2994
(2016/05/24)
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- Well-defined epoxide-containing styrenic polymers and their functionalization with alcohols
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Polymers containing electrophilic moieties, such as activated esters, epoxides, and alkyl halides, can be readily modified with a variety of nucleophiles to produce useful functional materials. The modification of epoxide-containing polymers with amines and other strong nucleophiles is well-documented, but there are no reports on the modification of such polymers with alcohols. Using phenyloxirane and glycidyl butyrate as low molecular weight model compounds, it was determined that the acid-catalyzed ring-opening of aryl-substituted epoxides by alcohols to form β-hydroxy ether products was significantly more efficient than that of alkyl-substituted epoxides. An aryl epoxide-type styrenic monomer, 4-vinylphenyloxirane (4VPO), was synthesized in high yield using an improved procedure and then polymerized in a controlled manner under reversible addition-fragmentation chain-transfer (RAFT) polymerization conditions. A successful chain extension with styrene proved the high degree of chain-end functionalization of the poly4VPO-based macro chain transfer agent. Poly4VPO was modified with a library of alcohols and phenols, some of which contained reactive functionalities, e.g., azide, alkyne, allyl, etc., using either CBr4 (in PhCN at 90°C for 2-3 days) or BF3 (in CH2Cl2 at ambient temperature over 30 min) as the catalyst. The resulting β-hydroxy ether-functionalized homopolymers were characterized using size exclusion chromatography, 1H NMR and IR spectroscopy, and thermal gravimetric analysis.
- McLeod, David C.,Tsarevsky, Nicolay V.
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p. 1132 - 1144
(2016/03/12)
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- Free radical reaction promoted by ionic liquid: A route for metal-free oxidation depolymerization of lignin model compound and lignin
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Ionic liquid 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BnMIm][NTf2]) can promote the generation of the OOH free radical and thereby efficiently transformed the β-O-4 lignin model compound 2-phenoxyacetophenone into benzoic acid and phenol using O2 as the oxidant. Furthermore, the IL-based metal-free catalytic system can also depolymerize other lignin model compounds and organosolv lignin effectively. This journal is
- Yang, Yingying,Fan, Honglei,Song, Jinliang,Meng, Qinglei,Zhou, Huacong,Wu, Lingqiao,Yang, Guanying,Han, Buxing
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supporting information
p. 4028 - 4031
(2015/03/30)
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- Reductive cleavage of inert aryl C-O bonds to produce arenes
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Reductive cleavage of the aryl C-O bonds in various phenolic compounds and aryl ethers was achieved using LiAlH4 combined with KOtBu and without any other catalysts or additives, solely producing arenes in high yields.
- Xu, Huanjun,Yu, Bo,Zhang, Hongye,Zhao, Yanfei,Yang, Zhenzhen,Xu, Jilei,Han, Buxing,Liu, Zhimin
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supporting information
p. 12212 - 12215
(2015/07/27)
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- Oxidative conversion of lignin and lignin model compounds catalyzed by CeO2-supported Pd nanoparticles
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The oxidative transformation of lignin into aromatic compounds is an attractive route for chemical utilization of lignocellulosic biomass. Unlike hydrogenolysis, no consumption of expensive hydrogen is required for the oxidative transformation. However, only limited success has been achieved for the oxidative conversion of lignin. Here, we report that cerium oxide-supported palladium nanoparticles (Pd/ CeO2) can efficiently catalyze the one-pot oxidative conversion of 2-phenoxy-1-phenylethanol, a lignin model compound containing a β-O-4 bond and a Cα-hydroxyl group, in methanol in the presence of O2, producing phenol, acetophenone and methyl benzoate as the major products. Pd nanoparticles played a pivotal role in the oxidation of a Cα-hydroxyl group into a Cα-ketonic group, which was crucial for the transformation of the model compound. The presence of the Cα-ketonic group activated the β-O-4 bond, which was subsequently cleaved over the Pd/CeO2 catalyst, affording phenol and acetophenone. At the same time, the Cα-Cβ bond also underwent oxidative cleavage catalyzed by CeO2, producing benzoic acid and further methyl benzoate. The Pd/CeO2 catalyst could also catalyze the oxidative conversion of organosolv lignin under mild conditions (458 K), producing vanillin, guaiacol and 4-hydroxybenzaldehyde.
- Deng, Weiping,Zhang, Hongxi,Wu, Xuejiao,Li, Rongsheng,Zhang, Qinghong,Wang, Ye
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p. 5009 - 5018
(2015/11/17)
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- Microwave-assisted fast conversion of lignin model compounds and organosolv lignin over methyltrioxorhenium in ionic liquids
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Conversion of a series of lignin β-O-4 model compounds 2-aryloxy-1-arylethanols and organosolv lignin to aromatic chemicals over methyltrioxorhenium (MTO) in ionic liquids without any oxidant and reducing agent under mild conditions was developed. Microwave irradiation accelerates the cleavage of aryl ether bonds and shortens the reaction time to 2 min.
- Zhang, Bo,Li, Changzhi,Dai, Tao,Huber, George W.,Wang, Aiqin,Zhang, Tao
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p. 84967 - 84973
(2015/10/28)
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- Highly efficient, NiAu-catalyzed hydrogenolysis of lignin into phenolic chemicals
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A highly efficient, stable NiAu catalyst that exhibits unprecedented low temperature activity in lignin hydrogenolysis was for the first time developed, leading to the formation of 14 wt% aromatic monomers from organosolv lignin at 170 °C in pure water. the Partner Organisations 2014.
- Zhang, Jiaguang,Asakura, Hiroyuki,Van Rijn, Jeaphianne,Yang, Jun,Duchesne, Paul,Zhang, Bin,Chen, Xi,Zhang, Peng,Saeys, Mark,Yan, Ning
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supporting information
p. 2432 - 2437
(2014/05/06)
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- In situ slow release of isocyanates: Synthesis and organocatalytic application of N-acylureas
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A novel, efficient, and operationally simple one-pot synthesis of both, symmetrical and unsymmetrical N-acylureas from carboxamides and in situ generated isocyanates (from N,N-dibromo-p-toluenesulfonamide) in the presence of a mild base at rt is reported. The protocol avoids the tedious isolation and purification steps of hazardous isocyanates. The first application of these acylureas to the catalysis through hydrogen bonding is also demonstrated.
- Singh, Atul K.,Chawla, Ruchi,Yadav, Lal Dhar S.
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p. 5099 - 5102
(2013/09/02)
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- Efficient Ring opening reaction of epoxides with oxygen nucleophiles catalyzed by quaternary onium salt
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Ring opening reactions of epoxides with oxygen nucleophiles catalyzed by a variety of quaternary onium salt, such as ammonium or phosphonium salt were explored. The results showed that tetrabutylphosphonium bromide (TBPB) among salts serves as the most ef
- Kim, Jin Won,Cho, Dae Won,Park, Gyoosoon,Kim, Sung Hong,Ra, Choon Sup
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p. 2286 - 2290
(2013/09/24)
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- Catalytic cleavage of lignin β-O-4 link mimics using copper on alumina and magnesia-alumina
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Copper on γ-alumina and on mixed magnesia-alumina, Cu/MgO-Al 2O3, catalyse the hydrodeoxygenation (HDO) of β-O-4 lignin-type dimers, giving valuable aromatics. The typical selectivity to phenol is as high as 20%. By changing the support's acidity we can modify the dispersion of copper. Interestingly, more HDO occurs with larger copper agglomerates than with finely dispersed particles. The presence of copper also increases the selectivity of the HDO cleavage. Three different pathways are hypothesized for the reaction on the catalyst surface. Thus, copper activates ketones more and especially more selective towards cleavage than their corresponding alcohols. DFT calculations of bond dissociation energies correlate well with this experimental observation. Excitingly, ethylbenzene is formed in proportional amounts to phenol, showing that these catalysts can reduce the oxygen content of lignin-type product streams. Considering its low price and ready availability, we conclude that copper on alumina is a promising alternative catalyst for lignin depolymerization.
- Strassberger, Zea,Alberts, Albert H.,Louwerse, Manuel J.,Tanase, Stefania,Rothenberg, Gadi
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p. 768 - 774
(2013/03/29)
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- Chiral epoxides via borane reduction of 2-haloketones catalyzed by spiroborate ester: Application to the synthesis of optically pure 1,2-hydroxy ethers and 1,2-azido alcohols
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An enantioselective borane-mediated reduction of a variety of 2-haloketones with 10% spiroaminoborate ester 1 as catalyst is described. By a simple basic workup of 2-halohydrins, optically active epoxides are obtained in high yield and with excellent enantiopurity (up to 99% ee). Ring-opening of oxiranes with phenoxides or sodium azide is investigated under different reaction conditions affording nonracemic 1,2-hydroxy ethers and 1,2-azido alcohols with excellent enantioselectivity (99% ee) and in good to high chemical yield. 2011 American Chemical Society.
- Huang, Kun,Wang, Haiyang,Stepanenko, Viatcheslav,De Jesus, Melvin,Torruellas, Carilyn,Correa, Wildeliz,Ortiz-Marciales, Margarita
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supporting information; scheme or table
p. 1883 - 1886
(2011/06/20)
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- CATALYTIC DISPROPORTIONATION AND CATALYTIC REDUCTION OF CARBON-CARBON AND CARBON-OXYGEN BONDS OF LIGNIN AND OTHER ORGANIC SUBSTRATES
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The present invention provides methods and catalyst compositions for the catalytic reduction of carbon-oxygen bonds of organic substrates and the catalytic disproportionation of carbon-oxygen or carbon-carbon bonds of organic substrates. These methods and catalyst compositions may be used to depolymerize lignin. The disproportionation of carbon-oxygen or carbon-carbon bonds of organic substrates or lignin is carried out by cleaving a carbon-oxygen bond or a carbon-carbon bond in a catalytic disproportionation reaction. The catalysts may be formed from a metal precursor such as ruthenium or vanadium and a bidentate ligand The catalytic reduction of carbon-oxygen bonds of organic substrates such as lignin is carried out by cleaving a carbon-oxygen bond in the presence of a hydrogen atom source. Lignin fragments produced following depolymerization by such methods may be further processed into fuels.
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Page/Page column 93
(2011/02/24)
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- Catalytic C-O bond cleavage of 2-aryloxy-1-arylethanols and its application to the depolymerization of lignin-related polymers
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A ruthenium-catalyzed, redox neutral C-O bond cleavage of 2-aryloxy-1-arylethanols was developed that yields cleavage products in 62-98% isolated yield. This reaction is applicable to breaking the key ethereal bond found in lignin-related polymers. The bond transformation proceeds by a tandem dehydrogenation/reductive ether cleavage. Initial mechanistic investigations indicate that the ether cleavage is most likely an organometallic C-O activation. A catalytic depolymerization of a lignin-related polymer quantitatively yields the corresponding monomer with no added reagent.
- Nichols, Jason M.,Bishop, Lee M.,Bergman, Robert G.,Ellman, Jonathan A.
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supporting information; experimental part
p. 12554 - 12555
(2010/12/19)
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- Enantioselective reduction of α-substituted ketones mediated by the boronate ester TarB-NO2
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A facile and mild reduction procedure is reported for the preparation of chiral secondary alcohols prepared from α-substituted ketones using sodium borohydride and the chiral boronate ester (l)-TarB-NO2. Direct reduction of substituted ketones bearing Lewis basic heteroatoms generally provided secondary alcohols of only modest enantiomeric excess likely due to either competition between the target carbonyl and the functionalized sidechains at the Lewis acidic boron atom in TarB-NO2 or the added steric bulk of the α-sidechain. As an alternative method, these substrates were synthesized using TarB-NO2 via a two-step procedure involving the reduction of an α-halo ketone to a chiral terminal epoxide, followed by regioselective/regiospecific epoxide opening by various nucleophiles. This procedure provides access to a variety of functionalized secondary alcohols including β-hydroxy ethers, thioethers, nitriles, and amines with enantiomeric excesses of 94% and yields up to 98%.
- Eagon, Scott,Ball-Jones, Nicholas,Haddenham, Dustin,Saavedra, Jaime,Delieto, Cassandra,Buckman, Matthew,Singaram, Bakthan
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supporting information; experimental part
p. 6418 - 6421
(2010/12/30)
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- 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2- diazaphosphorine supported on polystyrene (PS-BEMP) as an efficient recoverable and reusable catalyst for the phenolysis of epoxides under solvent-free conditions
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2-tert-Butylimino-2-diethylamino-1,3-dimethylperhydro-1,3, 2-diazaphosphorine supported on polystyrene (PS-BEMP) is an efficient catalyst for the ring-opening of epoxides with phenols (1.0 equiv.). Excellent yields have been obtained and in most of the cases the final products have been isolated in pure form without any additional purification step. E-factors associated to this protocol are small and further improvements were obtained by setting a cyclic continuous-flow reactor operating under solvent-free conditions (SolFC) that allowed us to minimize waste and reduce the E-factor by 95% compared to batch conditions. In addition the representative synthesis of a 2,3-dihydrobenzo[1,4]dioxepin-5-one has been realized. Optimization of this process was achieved by setting up an automated multi-step continuous-flow reactor based on a phenolysis process and a subsequent lactonization by thermal treatment of the reaction mixture. 3-Phenoxymethyl-2,3-dihydrobenzo[e][1,4] dioxepin-5-one was isolated in pure form and on a multi-gram scale in a very satisfactory 86% overall yield and an E-factor of 1.47.
- Zvagulis, Artis,Bonollo, Simona,Lanari, Daniela,Pizzo, Ferdinando,Vaccaro, Luigi
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supporting information; scheme or table
p. 2489 - 2496
(2010/12/29)
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- Biomimetic transfer hydrogenation of 2-alkoxy- and 2-aryloxyketones with iron-porphyrin catalysts
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In situ generated iron porphyrins are applied as homogeneous catalysts in the transfer hydrogenation of α-substituted ketones. Using 2-propanol as hydrogen donor various protected 1,2-hydroxyketones are reduced to the corresponding mono-substituted 1,2-di
- Enthaler, Stephan,Spilker, Bj?rn,Erre, Giulia,Junge, Kathrin,Tse, Man Kin,Beller, Matthias
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p. 3867 - 3876
(2008/09/20)
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- An efficient catalyst-free regio- and stereoselective ring-opening of epoxides with phenoxides using polyethylene glycol as the reaction medium
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A catalyst-free regio- and stereoselective ring-opening of epoxides with phenoxides has been carried out efficiently using polyethylene glycol as the reaction medium to form the corresponding β-aryloxyalcohols in high yields at room temperature.
- Das, Biswanath,Krishnaiah, Maddeboina,Thirupathi, Ponnaboina,Laxminarayana, Keetha
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p. 4263 - 4265
(2008/02/12)
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- ANTI-INFECTIVE AGENTS AND METHODS OF USE
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The present invention provides compounds and methods of using of the compounds as anti-infective agents. In a preferred embodiment, the present invention provides wherein R1 is not H when R2 is H and R2 is not H when R1 is H, further wherein R1 is CH(2n+1)O, wherein n is 1-10; wherein R2 is OH or CH(2n+1)O, wherein n is 1-10; and wherein A, B and R1, R2, R5, R6, and R7 are independently selected from a group consisting of H, alkyl and aryl groups and R11 is an alkyl or an aryl group.
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Page/Page column 11
(2008/06/13)
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- The "reverse-tethered" ruthenium (II) catalyst for asymmetric transfer hydrogenation: Further applications
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The attachment of a tethering group from the basic nitrogen atom to the arene ligand of a ruthenium(II) catalyst greatly improves its ability to catalyze asymmetric transfer hydrogenation (ATH) reactions. In this paper, we describe further applications of this versatile system to an extended substrate range.
- Morris, David J.,Hayes, Aidan M.,Wills, Martin
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p. 7035 - 7044
(2007/10/03)
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- Hydrophobic amplification of noncovalent organocatalysis
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The effects of hydrogen-bonding organocatalysts and water for the acceleration of epoxide openings with a variety of nucleophiles are additive and lead to excellent yields of the catalyzed reactions in water. The Royal Society of Chemistry 2006.
- Kleiner, Christian M.,Schreiner, Peter R.
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p. 4315 - 4317
(2007/10/03)
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- Highly regioselective ring opening of epoxides with polymer supported phenoxide and naphthoxide anions
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Amberlite IRA-400 supported phenoxide and naphthoxide anions are easily prepared. These polymer supported reagents that are highly air stable are used for the regioselective ring opening reactions of different epoxides to give aryl ether alcohols in high yields under mild reaction conditions.
- Tamami,Iranpoor,Rezaei
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p. 2789 - 2795
(2007/10/03)
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- Highly regioselective ring opening of oxiranes with phenoxides in the presence of β-cyclodextrin in water
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Highly regioselective ring opening of oxiranes to β-hydroxy ethers with phenoxides has been achieved in impressive yields in the presence of β-cyclodextrin as catalyst and water as solvent.
- Surendra,Krishnaveni, N. Srilakshmi,Nageswar,Rao, K. Rama
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p. 4994 - 4995
(2007/10/03)
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- Efficient ring-opening reaction of epoxides and aziridines promoted by tributylphosphine in water
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Tributylphosphine was found to be an effective promoting reagent for the ring-opening reaction of various epoxides and aziridines with nucleophile to produce corresponding anti-bifunctional products in moderate to excellent yields in water.
- Fan, Ren-Hua,Hou, Xue-Long
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p. 726 - 730
(2007/10/03)
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- Model compound studies of the beta-O-4 linkage in lignin: absolute rate expressions for beta-scission of phenoxyl radical from 1-phenyl-2-phenoxyethanol-1-yl radical.
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Arrhenius rate expressions were determined for beta-scission of phenoxyl radical from 1-phenyl-2-phenoxyethanol-1-yl, PhC*(OH)CH2OPh (V). Ketyl radical V was competitively trapped by thiophenol to yield PhCH(OH)CH2OPh in competition with beta-scission to yield phenoxyl radical and acetophenone. A basis rate expression for hydrogen atom abstraction by sec-phenethyl alcohol, PhC*(OH)CH3, from thiophenol, log(k(abs)/M(-1) s(-1)) = (8.88 +/- 0.24) - (6.07 +/- 0.34)/theta, theta = 2.303RT, was determined by competing hydrogen atom abstraction with radical self-termination. Self-termination rates for PhC*(OH)CH3 were calculated using the Smoluchowski equation employing experimental diffusion coefficients of the parent alcohol, PhCH(OH)CH3, as a model for the radical. The hydrogen abstraction basis reaction was employed to determine the activation barrier for the beta-scission of phenoxyl from 1-phenyl-2-phenoxyethanol-1-yl (V): log(k beta)/s(-1)) = (12.85 +/- 0.22) - (15.06 +/- 0.38)/theta, k beta (298 K) ca. (64.0 s(-1) in benzene), and log(k beta /s(-1)) = (12.50 +/- 0.18) - (14.46 +/- 0.30)/theta, k beta (298 K) = 78.7 s(-1) in benzene containing 0.8 M 2-propanol. B3LYP/cc-PVTZ electronic structure calculations predict that intramolecular hydrogen bonding between the alpha-OH and the -OPh leaving group of ketyl radical (V) stabilizes both ground- and transition-state structures. The computed activation barrier, 14.9 kcal/mol, is in good agreement with the experimental activation barrier.
- Kandanarachchi, Pramod H,Autrey, Tom,Franz, James A
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p. 7937 - 7945
(2007/10/03)
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