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One-Pot Transformation of Lignin and Lignin Model Compounds into Benzimidazoles
It is a challenging task to simultaneously achieve selective depolymerization and valorization of lignin due to their complex structure and relatively stable bonds. We herein report an efficient depolymerization strategy that employs 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidant/catalyst to selectively convert different oxidized lignin models to a wide variety of 2-phenylbenzimidazole-based compounds in up to 94 % yields, by reacting with o-phenylenediamines with varied substituents. This method could take full advantage of both Cβ and/or Cγ atom in lignin structure to furnish the desirable products instead of forming byproducts, thus exhibiting high atom economy. Furthermore, this strategy can effectively transform both the oxidized hardwood (birch) and softwood (pine) lignin into the corresponding degradation products in up to 45 wt% and 30 wt%, respectively. Through a “one-pot” process, we have successfully realized the oxidation/depolymerization/valorization of natural birch lignin at the same time and produced the benzimidazole derivatives in up to 67 wt% total yields.
Guo, Tao,He, Jianghua,Liu, Tianwei,Zhang, Yuetao
supporting information

(2022/02/07)

Application of tungsten oxide supported monatomic catalyst in preparation of aromatic compound by hydrogenolysis of lignin
The invention provides application of a tungsten oxide supported monatomic catalyst in preparation of aromatic compounds by hydrogenolysis of lignin. According to the method, various beta-O-4 model molecules, organic lignin, lignosulfonate and alkali lignin are taken as raw materials, and high-selectivity cracking of aryl ether bonds is realized in a hydrogen atmosphere at the temperature of 150-240 DEG C and the pressure of 0.7-3.0 MPa to obtain the aromatic compound. Compared with the prior art, the method has the advantages that when renewable natural biomass is used as the raw material and different lignin is used as the raw material for conversion, the highest yield of the aromatic bio-oil is 72%. Raw materials are cheap and wide in source; inorganic acid and alkali are not needed, and generation of a large amount of alkali liquor in traditional lignin catalysis is avoided; the method has the characteristics of cheap tungsten-based catalyst, green reaction process, atom economy and the like, and also has the characteristics of mild reaction conditions, high activity and selectivity, environment-friendly reaction process and the like.
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Paragraph 0044-0051

(2021/05/22)

Eco-friendly preparation of ultrathin biomass-derived Ni3S2-doped carbon nanosheets for selective hydrogenolysis of lignin model compounds in the absence of hydrogen
Lignin is an abundant source of aromatics, and the depolymerization of lignin provides significant potential for producing high-value chemicals. Selective hydrogenolysis of the C-O ether bond in lignin is an important strategy for the production of fuels and chemical feedstocks. In our study, catalytic hydrogenolysis of lignin model compounds (β-O-4, α-O-4 and 4-O-5 model compounds) over Ni3S2-CS catalysts was investigated. Hence, an array of 2D carbon nanostructure Ni3S2-CSs-X-Yderived catalysts were produced using different compositions at different temperatures (X= 0 mg, 0.2 mg, 0.4 mg, 0.6 mg, and 0.8 mg; Y = 600 °C, 700 °C, 800 °C, and 900 °C) were prepared and applied for hydrogenolysis of lignin model compounds and depolymerization of alkaline lignin. The highest conversion of lignin model compounds (β-O-4 model compound) was up to 100% and the yield of the obtained corresponding ethylbenzene and phenol could achieve 92% and 86%, respectively, over the optimal Ni3S2-CSs-0.4-700 catalyst in iPrOH at 260 °C without external H2. The 2D carbon nanostructure catalysts performed a good dispersion on the surface of the carbon nanosheets, which facilitated the cleavage of the lignin ether bonds. The physicochemical characterization studies were carried out by means of XRD, SEM, TEM, H2-TPR, NH3-TPD, Raman and XPS analyses. Based on the optimal reaction conditions (260 °C, 4 h, 2.0 MPa N2), various model compounds (β-O-4, α-O-4 and 4-O-5 model compounds) could also be effectively hydrotreated to produce the corresponding aromatic products. Furthermore, the optimal Ni3S2-CSs-0.4-700 catalyst could be carried out in the next five consecutive cycle experiments with a slight decrease in the transformation of lignin model compounds.
Chen, Changzhou,Jiang, Jianchun,Li, Jing,Liu, Peng,Wu, Dichao,Xia, Haihong,Zhou, Minghao
p. 3090 - 3103
(2021/05/07)

Electro-reductive Fragmentation of Oxidized Lignin Models
Lignin provides a potential sustainable source for production of electron-rich aromatic compounds. Recently, electrochemical lignin degradation via an oxidation/reduction sequence under mild conditions has garnered much attention within the lignin community, as electrochemistry simplifies redox reactions and offers an electron source/sink for synthesis without using stoichiometric oxidants or reductants. This paper describes a fundamental approach for the electrochemical fragmentation of the primary connection in native lignin, β-O-4. Potential-controlled electrolysis enables selective reduction and provides fragmentation products and/or coupling products in isolated yields of 59-92%.
Yang, Cheng,Magallanes, Gabriel,Maldonado, Stephen,Stephenson, Corey R. J.
p. 15927 - 15934
(2021/06/30)

The graphite-catalyzed: ipso -functionalization of arylboronic acids in an aqueous medium: metal-free access to phenols, anilines, nitroarenes, and haloarenes
An efficient, metal-free, and sustainable strategy has been described for the ipso-functionalization of phenylboronic acids using air as an oxidant in an aqueous medium. A range of carbon materials has been tested as carbocatalysts. To our surprise, graphite was found to be the best catalyst in terms of the turnover frequency. A broad range of valuable substituted aromatic compounds, i.e., phenols, anilines, nitroarenes, and haloarenes, has been prepared via the functionalization of the C-B bond into C-N, C-O, and many other C-X bonds. The vital role of the aromatic π-conjugation system of graphite in this protocol has been established and was observed via numerous analytic techniques. The heterogeneous nature of graphite facilitates the high recyclability of the carbocatalyst. This effective and easy system provides a multipurpose approach for the production of valuable substituted aromatic compounds without using any metals, ligands, bases, or harsh oxidants.
Badgoti, Ranveer Singh,Dandia, Anshu,Parewa, Vijay,Rathore, Kuldeep S.,Saini, Pratibha,Sharma, Ruchi
p. 18040 - 18049
(2021/05/29)

Catalytic C(β)-O Bond Cleavage of Lignin in a One-Step Reaction Enabled by a Spin-Center Shift
A challenge to the utilization of lignin as a feedstock for aromatic fine chemicals lies in selective cleavage of copious β-O-4 linkages. A photocatalytic strategy for the selective cleavage of the C(β)-O bonds of model substrates and natural lignin extracts is achieved by a redox-neutral, catalytic cycle that does not require stoichiometric reagents. Mechanistic studies reveal the generation of a thiyl radical, which is derived from a cystine-derived H-atom transfer catalyst, initiates a spin-center shift (SCS) that leads to C(β)-O bond cleavage. The SCS reactivity is reminiscent of the C(β)-O bond cleavage chemistry that occurs in the active site of ribonucleotide reductase.
Zhu, Qilei,Nocera, Daniel G.
p. 14181 - 14187
(2021/11/27)

Sustainable Production of Benzylamines from Lignin
Catalytic conversion of lignin into heteroatom functionalized chemicals is of great importance to bring the biorefinery concept into reality. Herein, a new strategy was designed for direct transformation of lignin β-O-4 model compounds into benzylamines and phenols in moderate to excellent yields in the presence of organic amines. The transformation involves dehydrogenation of Cα?OH, hydrogenolysis of the Cβ?O bond and reductive amination in the presence of Pd/C catalyst. Experimental data suggest that the dehydrogenation reaction proceeds over the other two reactions and secondary amines serve as both reducing agents and amine sources in the transformation. Moreover, the concept of “lignin to benzylamines” was demonstrated by a two-step process. This work represents a first example of synthesis of benzylamines from lignin, thus providing a new opportunity for the sustainable synthesis of benzylamines from renewable biomass, and expanding the products pool of biomass conversion to meet future biorefinery demands.
Guo, Tenglong,Kühn, Fritz E.,Li, Changzhi,Liu, Yuxuan,Wang, Chao,Xiao, Jianliang,Zhang, Bo,Zhang, Tao,Zhao, Zongbao K.
supporting information
p. 20666 - 20671
(2021/08/25)

Thio-assisted reductive electrolytic cleavage of lignin β-O-4 models and authentic lignin
Avoiding the use of expensive catalysts and harsh conditions such as elevated temperatures and high pressures is a critical goal in lignin depolymerization and valorization. In this study, we present a thio-assisted electrocatalytic reductive approach using inexpensive reticulated vitreous carbon (RVC) as the working cathode to cleave the β-O-4-type linkages in keto aryl ethers. In the presence of a pre-electrolyzed disulfide (2,2′-dithiodiethanol) and a radical inhibitor (BHT) at room temperature at a current density of 2.5 mA cm-2, cathodic reduction of nonphenolic β-O-4 dimers afforded over 90% of the corresponding monomeric C-O cleavage products in only 1.5 h. Extended to DDQ-oxidized poplar lignin, this combination of electric current and disulfide, applied over 6 h, released 36 wt% of ethyl acetate soluble fragments and 26 wt% of aqueous soluble fragments, leaving only 38 wt% of insoluble residue. These findings represent a significant improvement over the current alone values (24 wt% ethyl acetate soluble; 22 wt% aqueous soluble; 54 wt% insoluble residue) and represent an important next step in our efforts to develop a mild electrochemical method for reductive lignin deconstruction.
Fang, Zhen,Flynn, Michael G.,Jackson, James E.,Hegg, Eric L.
p. 412 - 421
(2021/01/28)

Oxygen-Free Regioselective Biocatalytic Demethylation of Methyl-phenyl Ethers via Methyltransfer Employing Veratrol- O-demethylase
The cleavage of aryl methyl ethers is a common reaction in chemistry requiring rather harsh conditions; consequently, it is prone to undesired reactions and lacks regioselectivity. Nevertheless, O-demethylation of aryl methyl ethers is a tool to valorize natural and pharmaceutical compounds by deprotecting reactive hydroxyl moieties. Various oxidative enzymes are known to catalyze this reaction at the expense of molecular oxygen, which may lead in the case of phenols/catechols to undesired side reactions (e.g., oxidation, polymerization). Here an oxygen-independent demethylation via methyl transfer is presented employing a cobalamin-dependent veratrol-O-demethylase (vdmB). The biocatalytic demethylation transforms a variety of aryl methyl ethers with two functional methoxy moieties either in 1,2-position or in 1,3-position. Biocatalytic reactions enabled, for instance, the regioselective monodemethylation of substituted 3,4-dimethoxy phenol as well as the monodemethylation of 1,3,5-trimethoxybenzene. The methyltransferase vdmB was also successfully applied for the regioselective demethylation of natural compounds such as papaverine and rac-yatein. The approach presented here represents an alternative to chemical and enzymatic demethylation concepts and allows performing regioselective demethylation in the absence of oxygen under mild conditions, representing a valuable extension of the synthetic repertoire to modify pharmaceuticals and diversify natural products.
Grimm, Christopher,Lazzarotto, Mattia,Pompei, Simona,Schichler, Johanna,Richter, Nina,Farnberger, Judith E.,Fuchs, Michael,Kroutil, Wolfgang
p. 10375 - 10380
(2020/10/02)

Method for preparing alcohol and phenol through aerobic hydroxylation reaction of boric acid derivative in absence of photocatalyst
The invention discloses a method for preparing alcohol and phenol through aerobic hydroxylation reaction of a boric acid derivative in the absence of a photocatalyst, wherein the boric acid derivativeis aryl boronic acid or alkyl boronic acid, and the corresponding target compounds are respectively a phenol-based compound and an alcohol-based compound. According to the method, by using a boric acid derivative as a reaction substrate, an additive is added under a solvent condition, and a hydroxylation reaction is performed under aerobic and illumination conditions to obtain a corresponding target compound. According to the invention, the new strategy is provided for the synthesis of phenols through aerobic hydroxylation of aryl boronic acid without a photocatalyst; the catalyst-free aerobic hydroxylation method for photocatalysis of aryl boronic acid or alkyl boronic acid by using triethylamine as an additive is firstly disclosed; and the new method has advantages of photocatalyst-freecondition, wide substrate range and good functional group compatibility.
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Paragraph 0025-0028; 0030-0032

(2020/01/25)

Amine-Mediated Bond Cleavage in Oxidized Lignin Models
Introducing amines/ammonia into lignin cracking will allow novel bond cleavage pathways. Herein, a method of amines/ammonia-mediated bond cleavage in oxidized lignin β-O-4 models was studied using a copper catalyst at room temperature, demonstrating the effect of the amine source on the selectivity of products. For primary and secondary aliphatic amines, lignin ketone models underwent oxidative Cα?Cβ bond cleavage and Cα?N bond formation to generate aromatic amides. For ammonia, the competition between oxygen and ammonia determined the selectivity between Cα?N and Cβ?N bond formation, generating amides and α-keto amides, respectively. For tertiary amines, the lignin models underwent oxidative Cα?Cβ bond cleavage to benzoic acids. Control experiments indicated that amines act as nucleophiles attacking at the Cα or Cβ position of the oxidized β-O-4 linkage to be cleaved. This study represents a novel example that the breakage of oxidized lignin model can be regulated by amines with a copper catalyst.
Li, Hongji,Liu, Meijiang,Liu, Huifang,Luo, Nengchao,Zhang, Chaofeng,Wang, Feng
p. 4660 - 4665
(2020/07/04)

Synthesis method of 1-(4-hydroxy-3,5-dimethoxyphenyl)ethan-1-one
The invention relates to a synthesis method of 1-(4-hydroxy-3,5-dimethoxyphenyl)ethan-1-one. The synthesis method is characterized by comprising the following steps: removing a 2-methyl group from 1,2,3-trimethoxybenzene serving as an initial raw material to obtain 2,6-dimethoxyphenol; then carrying out a reaction on 2,6-dimethoxyphenol and an acetyl group to obtain 2,6-dimethoxyphenylacetate; andfinally, rearranging 2,6-dimethoxyphenol to obtain the 1-(4-hydroxy-3,5-dimethoxyphenyl)ethan-1-one. Compared with the prior art, the method adopts non-toxic and environment-friendly materials as rawmaterials, is simple to operate and mild in reaction, does not cause environmental pollution or harm to operators, and is suitable for large-scale production.
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Paragraph 0019-0021; 0028-0029; 0034-0035

(2020/05/30)

Method for selective depolymerization of non-noble metal catalytic lignin
The invention relates to a method for preparing an aromatic compound by catalyzing lignin to select depolymerization. The method comprises the following steps: taking an M(mpo)n complex (M=Fe, Co, n=3; M=Ni, n=2) as a catalyst, taking various beta-O-4 model molecules, organic lignin, lignosulfonate and alkali lignin as raw materials, and realizing high-selectivity catalytic cracking aryl-ether bands in a nitrogen atmosphere of 0.1 MPa at the temperature of 80 to 200 DEG C so as to obtain a phenolic compound. The conversion rate of the beta-O-4 model molecules reaches 100% at most, the productive rate of guaiacol reaches 95% at most, and the yield of styrene reaches 71% at most; when different lignins are used as raw materials for conversion, the yield of aromatic biological oil is 34% to 71%. The method has the characteristics of mild reaction conditions, no consumption of hydrogen source, high activity and selectivity, environment-friendly reaction process and the like.
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Paragraph 0037-0052

(2020/09/25)

Rhodium-terpyridine catalyzed redox-neutral depolymerization of lignin in water
Simple rhodium terpyridine complexes were found to be suitable catalysts for the redox neutral cleavage of lignin in water. Apart from cleaving lignin model compounds into ketones and phenols, the catalytic system could also be applied to depolymerize dioxasolv lignin and lignocellulose, affording aromatic ketones as the major monomer products. The (hemi)cellulose components in the lignocellulose sample remain almost intact during lignin depolymerization, providing an example of a "lignin-first" process under mild conditions. Mechanistic studies suggest that the reaction proceeds via a rhodium catalyzed hydrogen autotransfer process.
Liu, Yuxuan,Li, Changzhi,Miao, Wang,Tang, Weijun,Xue, Dong,Xiao, Jianliang,Zhang, Tao,Wang, Chao
supporting information
p. 33 - 38
(2020/01/13)

Organocatalytic Approach to Photochemical Lignin Fragmentation
Herein, an organocatalytic method for photochemical C-O bond cleavage of lignin systems is reported. The use of photochemistry enabled fragmentation of the β-O-4 linkage, the primary linkage in lignin, provides the fragmentation products in good to high yields. The approach was merged with reported oxidation conditions in a one-pot, two-step platform without any intermediary purification, suggesting its high fidelity. The future utility of the organocatalytic method was illustrated by applying the visible light-mediated protocol to continuous flow processing.
Yang, Cheng,K?rk?s, Markus D.,Magallanes, Gabriel,Chan, Kimberly,Stephenson, Corey R. J.
supporting information
p. 8082 - 8085
(2020/11/02)

A scalable and green one-minute synthesis of substituted phenols
A mild, green and highly efficient protocol was developed for the synthesis of substituted phenols via ipso-hydroxylation of arylboronic acids in ethanol. The method utilizes the combination of aqueous hydrogen peroxide as the oxidant and H2O2/HBr as the reagent under unprecedentedly simple and convenient conditions. A wide range of arylboronic acids were smoothly transformed into substituted phenols in very good to excellent yields without chromatographic purification. The reaction is scalable up to at least 5 grams at room temperature with one-minute reaction time and can be combined in a one-pot sequence with bromination and Pd-catalyzed cross-coupling to generate more diverse, highly substituted phenols.
Elumalai, Vijayaragavan,Hansen, J?rn H.
p. 40582 - 40587
(2020/11/18)

Structural features and antioxidant activities of Chinese quince (Chaenomeles sinensis) fruits lignin during auto-catalyzed ethanol organosolv pretreatment
Chinese quince fruits (Chaenomeles sinensis) have an abundance of lignins with antioxidant activities. To facilitate the utilization of Chinese quince fruits, lignin was isolated from it by auto-catalyzed ethanol organosolv pretreatment. The effects of three processing conditions (temperature, time, and ethanol concentration) on yield, structural features and antioxidant activities of the auto-catalyzed ethanol organosolv lignin samples were assessed individually. Results showed the pretreatment temperature was the most significant factor; it affected the molecular weight, S/G ratio, number of β-O-4′ linkages, thermal stability, and antioxidant activities of lignin samples. According to the GPC analyses, the molecular weight of lignin samples had a negative correlation with pretreatment temperature. 2D-HSQC NMR and Py-GC/MS results revealed that the S/G ratios of lignin samples increased with temperature, while total phenolic hydroxyl content of lignin samples decreased. The structural characterization clearly indicated that the various pretreatment conditions affected the structures of organosolv lignin, which further resulted in differences in the antioxidant activities of the lignin samples. These results can be helpful for controlling and optimizing delignification during auto-catalyzed ethanol organosolv pretreatment, and they provide theoretical support for the potential applications of Chinese quince fruits lignin as a natural antioxidant in the food industry.
Cheng, Xi-Chuang,Guo, Xin-Ran,Liu, Hua-Min,Liu, Yu-Lan,Qin, Zhao,Wang, Xue-De
p. 4348 - 4358
(2020/09/22)

Catalytic Activation of Carbon-Hydrogen Bonds in Lignin Linkages over Strong-Base-Modified Covalent Triazine Frameworks for Lignin Oxidative Cleavage
The design of highly efficient catalysts for the cleavage of various lignin linkages is the key step in the depolymerization of lignin. In this paper, strong-base-modified covalent triazine frameworks (CTFs) were reported to be effective in the cleavage o
Gao, Jin,Liu, Meng,Shi, Song,Xu, Jie,Zhao, Li,Zhu, Guozhi
p. 7526 - 7534
(2020/08/21)

Mechanochemical cleavage of lignin models and ligninviaoxidation and a subsequent base-catalyzed strategy
Mechanochemical cleavage of lignin dimer model compounds to phenolic monomers has been developedviaa two-step strategy under milling conditions. In the first step of this process, the secondary benzylic alcohol of lignin β-O-4 linkages was selectively oxidized to the corresponding ketones over a 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)/NaNO2catalytic system under milling conditions. In the subsequent step, mechanochemical selective cleavage of the Cβ-O bonds and Cα-Cβbonds of lignin β-O-4 ketones to acids and phenols was promoted by NaOH-catalyzed depolymerization. In addition, this two-step strategy was performed to depolymerize organosolv birch lignin, giving aromatic monomers with good selectivity for syringate. This approach provides an efficient method to convert the β-O-4 linkages of lignin to valuable aromatic monomers under mild reaction conditions.
Dushkin, Alexandr V.,Su, Weike,Sun, Chen,Xu, Wenhao,Zheng, Lei
p. 3489 - 3494
(2020/07/30)

Profiling of the formation of lignin-derived monomers and dimers from: Eucalyptus alkali lignin
Lignin is a renewable and the most abundant aromatic source that can be used for extensive chemicals and materials. Although approximately 50 million tons of lignin are produced annually as a by-product of the pulp and paper industry, it is currently underutilized. It is important to know the structural features of technical lignin when considering its application. In this work, we have demonstrated the formation of low-molecular-weight constituents from hardwood (Eucalyptus) lignin, which produces much more low-molecular-weight constituents than softwood (spruce) lignin, after a chemical pulping process, and analyzed the micromolecular compositions in the alkali lignin after fractionation by dichloromethane (DCM) extraction. By applying analytical methods (gel-permeation chromatography, 2D NMR and GC-MS) with the aid of evidence from authenticated compounds, a great treasure trove of lignin-derived phenolic compounds from Eucalyptus alkali lignin were disclosed. Except for some common monomeric products, as many as 15 new lignin-derived monomers and dimers including syringaglycerol, diarylmethane, 1,2-diarylethanes, 1,2-diarylethenes, (arylvinyl ether)-linked arylglycerol dimers and isomeric syringaresinols were identified in the DCM-soluble fraction. Regarding the formation and evolution of the Cα-condensed β-aryl ether structure, a novel route that is potentially responsible for the high content of β-1 diarylethenes and diarylethanes in the lignin low-molecular-weight fraction, in addition to the β-1 (spirodienone) pathway, was proposed. This work not only provides novel insights into the chemical transformation of S-G lignin during the alkali pulping process, but also discovered lignin-derived phenolic monomers and dimers that can potentially be used as raw materials in the chemical or pharmaceutical industries. This journal is
Hu, Zhenhua,Li, Suxiang,Lu, Fachuang,Shi, Lanlan,Wang, Chen,Yue, Fengxia,Zhang, Han,Zhao, Chengke
supporting information
p. 7366 - 7375
(2020/11/18)

Mild Redox-Neutral Depolymerization of Lignin with a Binuclear Rh Complex in Water
A mild redox-neutral lignin depolymerization system featuring a water-soluble binuclear Rh complex has been developed. The catalytic system could be successfully applied to the depolymerization of a lignin-like polymer, alkaline lignin, as well as raw lignocellulose samples to produce aromatic ketones, providing a homogeneous catalytic system for "lignin-first" biorefinery in water. Mechanistic studies on the model substrate suggest that the reaction proceeds via a metal-catalyzed dehydrogenation step to afford a carbonyl intermediate, followed by C-O bond cleavage to afford ketone and phenol products. Deuterium labeling study shows that the hydrogen used for cleavage of the C-O bond originates from the alcohol moiety in the substrate.
Liu, Yuxuan,Li, Changzhi,Miao, Wang,Tang, Weijun,Xue, Dong,Li, Chaoqun,Zhang, Bo,Xiao, Jianliang,Wang, Aiqin,Zhang, Tao,Wang, Chao
p. 4441 - 4447
(2019/05/14)

A room temperature next amine control lignin model molecular breaking method
The invention relates to a room temperature next amine control lignin model molecular breaking method. The method adopts the 1 - aryl - 2 - [...] as lignin β - O - 4 model molecule, in under the action of the copper salt and an amine, is oxidized and broken C - C/C - O key; wherein a primary and secondary aliphatic amine control into aromatic amide and a phenolic compound, inorganic ammonia control generating α - one amide and phenolic compound, tertiary amine control into aromatic acid and phenol compounds. The testing process are as follows: the 1 - aryl - 2 - [...], amine compound with a copper salt in dimethyl sulfoxide in mixed, put in the pressure container, the charge air or oxygen after the replacement is closed, at room temperature, stirring the reaction 8 - 12 is H, can occur model molecular C - C/C - O bond breaking, to obtain aromatic amide, α - one amide, aromatic acid and phenol compounds. The mild conditions, cheap catalyst and oxidizing agent, various controllable reaction product, the reaction process is simple and easy to operate.
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Paragraph 0044; 0045; 0070; 0072

(2019/06/30)

Cleavage of lignin model compounds and ligninox using aqueous oxalic acid
Aqueous oxalic acid cleaves oxidised β-O-4 lignin model compounds by two distinct mechanisms that are dependent on the presence of the hydroxymethyl substituent. Various β-O-4 phenoxyacetophenones that do not contain the hydroxymethyl substituent undergo oxidative cleavage upon exposure to aqueous oxalic acid in the presence of air, likely through concerted ring opening of a dioxetane intermediate to give the corresponding benzoic acid and phenyl formate. Importantly, detrimental side reactions arising from singlet oxygen and hydroperoxy radicals (from both O2 and oxalic acid) are minimal when the cleavage is run under air compared to neat oxygen. When oxidised β-O-4 lignin model compounds bearing the hydroxymethyl group are cleaved by aqueous oxalic acid, the resulting diketone and phenol products arise from a redox neutral cleavage that is analogous to the formic acid-sodium formate mediated lignin cleavage process reported by Stahl. Aqueous oxalic acid also cleaves lignin itself, with oxidised milled wood lignin (MWLox) from Pinus radiata giving a 14% yield of ethyl acetate soluble aromatics with good selectivity for vanillin. Aqueous oxalic acid appears to be a promising lignin cleavage system given the benign, bio-based reagents, absence of metals and organic solvents and a simple extraction procedure that enables oxalic acid recycling.
Lindsay, Ashley C.,Kudo, Shinji,Sperry, Jonathan
p. 7408 - 7415
(2019/08/15)

Visible light induced redox neutral fragmentation of 1,2-diol derivatives
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
supporting information
p. 13144 - 13147
(2019/11/11)

Photoinduced hydroxylation of arylboronic acids with molecular oxygen under photocatalyst-free conditions
Photoinduced hydroxylation of boronic acids with molecular oxygen under photocatalyst-free conditions is reported, providing a green entry to a variety of phenols and aliphatic alcohols in a highly concise fashion. This new protocol features photocatalyst-free conditions, wide substrate scope and excellent functional group compatibility.
Xu, Yu-Ting,Li, Chen-Yuan,Huang, Xiao-Bo,Gao, Wen-Xia,Zhou, Yun-Bing,Liu, Miao-Chang,Wu, Hua-Yue
supporting information
p. 4971 - 4975
(2019/09/30)

A Green Alternative for the Conversion of Arylboronic Acids/Esters into Phenols Promoted by a Reducing Agent, Sodium Sulfite
Hydroxylation of arylboronic acids and arylboronic esters using sodium sulfite and oxygen as the source of ultimate oxidant proceeds rapidly in water under transition metal-free conditions. This remarkable mild and environmentally benign protocol represents a green alternative to synthesize phenols using inexpensive starting materials in a simple methodology. This new application for sodium sulfite shows a wide tolerance of functional groups, and it is compatible with oxidizable functionalities.
Castro-Godoy, Willber D.,Schmidt, Luciana C.,Argüello, Juan E.
p. 3035 - 3039
(2019/05/15)

Au-Pd alloy cooperates with covalent triazine frameworks for the catalytic oxidative cleavage of β-O-4 linkages
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
p. 6707 - 6716
(2019/12/26)

Cleavage of lignin C-O bonds over a heterogeneous rhenium catalyst through hydrogen transfer reactions
Hydrogenolysis is one of the most popular strategies applied in the depolymerization of lignin for the production of aromatic chemicals. Currently, this strategy is mainly conducted under high hydrogen pressure, which can pose safety risks and is not sustainable and economical. Herein, we reported that heterogeneous rhenium oxide supported on active carbon (ReOx/AC) exhibited excellent activity in the selective cleavage of lignin C-O bonds in isopropanol. High yields of monophenols (up to 99.0%) from various lignin model compounds and aromatic liquid oils (>50%) from lignin feedstock were obtained under mild conditions in the absence of H2. The characterization of the catalyst by X-ray absorption fine structure, X-ray photoelectron spectroscopy and H2-temperature-programed reduction suggested that the activity of ReOx/AC could be attributed to the presence of ReIV-VI. The interaction between the surface oxygen groups of the active carbon and rhenium oxide could also play an important role in the cleavage of the C-O bonds. Notably, an ReOx/AC-catalyzed C-O bond cleavage pathway beyond a typical deoxydehydration mechanism was disclosed. More importantly, 2D-HSQC-NMR and GPC characterizations showed that ReOx/AC exhibited high activity not only in β-O-4 cleavage, but also in the deconstruction of more resistant β-5 and β-β linkages in lignin without destroying the aromatic ring. This study paves the way for the development of rhenium-based catalysts for the controlled reductive valorization of realistic lignin materials through a hydrogen transfer pathway.
Zhang, Bo,Qi, Zaojuan,Li, Xinxin,Ji, Jianwei,Zhang, Leilei,Wang, Hua,Liu, Xiaoyan,Li, Changzhi
supporting information
p. 5556 - 5564
(2019/10/28)

Method for converting lignin into isoxazole and aromatic nitrile
The present invention relates to a method for obtaining isoxazole and aromatic nitrile from a lignin model and pre-oxidized birch lignin. The method is characterized in that hydroxylamine hydrochloride and a beta-O-4 model compound containing ketone in the benzyl position, which are used as reaction substrates, undergo oximation condensation Cbeta-O bond fracture under the action of magnesium andother additives to prepare the isoxazole compound, and undergo oximation rearrangement Calpha-Cbeta bond fracture the action of magnesium and other additives to prepare the fragrant nitrile compound.The method can be applied to the conversion of pre-oxidized lignin into the isoxazole and aromatic nitrile. The preparation method comprises the following steps: mixing the beta-O-4 model compound orpre-oxidized birch lignin, hydroxylamine hydrochloride and the additives in an alcohol solvent, adding the obtained mixture into a pressure-resistant container, replacing air in the container with nitrogen, sealing the container, and stirring the mixture at 120 DEG C for 8-12 h to obtain the products isoxazole and aromatic nitrile. The method realizes the obtaining of nitrogen-containing compoundssuch as isoxazole and aromatic nitrile from lignin for the first time, and the reaction process is simple and controllable, and is easy to operate.
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Paragraph 0053; 0054; 0064

(2019/07/04)

METHOD OF SELECTIVELY OXIDIZING LIGNIN
A method of selectively reacting lignin or a lignin-derived reactant to yield an aromatic product. The method includes the step of reacting lignin or a lignin-derived reactant with a molybdenum-containing catalyst, in a solvent, and optionally in the presence of an oxidant, for a time and a temperature wherein at least a portion of the lignin or lignin-derived reactant is selectively converted into an aromatic product, preferably coniferaldehyde and/or sinapaldehyde.
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Paragraph 0022

(2019/06/20)

Lignin Valorization by Cobalt-Catalyzed Fractionation of Lignocellulose to Yield Monophenolic Compounds
Herein, a catalytic reductive fractionation of lignocellulose is presented using a heterogeneous cobalt catalyst and formic acid or formate as a hydrogen donor. The catalytic reductive fractionation of untreated birch wood yields monophenolic compounds in up to 34 wt % yield of total lignin, which corresponds to 76 % of the theoretical maximum yield. Model compound studies revealed that the main role of the cobalt catalyst is to stabilize the reactive intermediates formed during the organosolv pulping by transfer hydrogenation and hydrogenolysis reactions. Additionally, the cobalt catalyst is responsible for depolymerization reactions of lignin fragments through transfer hydrogenolysis reactions, which target the β-O-4′ bond. The catalyst could be recycled three times with only negligible decrease in efficiency, showing the robustness of the system.
Rautiainen, Sari,Di Francesco, Davide,Katea, Sarmad Naim,Westin, Gunnar,Tungasmita, Duangamol N.,Samec, Joseph S. M.
p. 404 - 408
(2019/01/04)

Selective C-O Bond Cleavage of Lignin Systems and Polymers Enabled by Sequential Palladium-Catalyzed Aerobic Oxidation and Visible-Light Photoredox Catalysis
Lignin, which is a highly cross-linked and irregular biopolymer, is nature's most abundant source of aromatic compounds and constitutes an attractive renewable resource for the production of aromatic commodity chemicals. Herein, we demonstrate a practical and operationally simple two-step degradation approach involving Pd-catalyzed aerobic oxidation and visible-light photoredox-catalyzed reductive fragmentation for the chemoselective cleavage of the β-O-4 linkage - the predominant linkage in lignin - for the generation of lower-molecular-weight aromatic building blocks. The developed strategy affords the β-O-4 bond cleaved products with high chemoselectivity and in high yields, is amenable to continuous flow processing, operates at ambient temperature and pressure, and is moisture- and oxygen-tolerant.
Magallanes, Gabriel,K?rk?s, Markus D.,Bosque, Irene,Lee, Sudarat,Maldonado, Stephen,Stephenson, Corey R. J.
p. 2252 - 2260
(2019/02/19)

Selective Cleavage of C?O Bonds in Lignin Catalyzed by Rhenium(VII) Oxide (Re2O7)
The selective cleavage of C?O bonds in typical model lignin β-O-4 compounds and deconstruction of a realistic lignin feedstock catalyzed by Re2O7 is described. High yields of C?O cleavage products (up to 97.8 %) from model compounds and oils (76.3 %) from organosolv pinewood lignin were obtained under mild conditions. Evidence for the pathway of this catalytic process is also provided.
Qi, Zaojuan,Zhang, Bo,Ji, Jianwei,Li, Xinxin,Dai, Tao,Guo, Haiwei,Wang, Aiqin,Lu, Lican,Li, Changzhi
p. 500 - 505
(2018/03/27)

Dealkylation of Lignin to Phenol via Oxidation-Hydrogenation Strategy
Lignin is a renewable and abundant aromatic polymer found in plants. We herein propose a "cutting tail" methodology to produce phenol from lignin, which is achieved by combining Ru/CeO2 catalyst and CuCl2 oxidant via an oxidation-hydrogenation route. Phenol was obtained from separated poplar lignin with 13 wt % yield. Even raw biomass, such as poplar, birch, pine, peanut, bamboo willow, and straw, could be converted into phenol in 1-33 mg per gram of biomass.
Wang, Min,Liu, Meijiang,Li, Hongji,Zhao, Zhitong,Zhang, Xiaochen,Wang, Feng
p. 6837 - 6843
(2018/06/25)

Efficient dealkylation of aryl alkyl ethers catalyzed by Cu2O
An efficient protocol for dealkylation of aryl alkyl ethers under the catalysis of inexpensive and easily reusable Cu2O has been described. The phenol products were obtained in high yields, and a range of functional groups were well tolerated. The choice of solvent is critical to the catalysis, and CH3OH proved to be the optimal choice. Mechanistic investigations showed that this reaction possibly proceeds via a single-electron transfer (SET) process.
Liu, Lingxian,Li, Zengguang,Chen, Changjun,Li, Huanrong,Xu, Lijin,Yu, Zhiyong
supporting information
p. 2447 - 2453
(2018/04/11)

Transition-metal-free conversion of lignin model compounds to high-value aromatics: Scope and chemoselectivity
An efficient and straightforward reaction protocol for the conversion of lignin model compounds was developed based on a simple system consisting of a base, oxygen, and a green solvent under mild conditions in the absence of metals. This protocol was successfully applied to the cleavage of both 'β-O-4' dimeric and trimeric compounds, and a controlled selective degradation was achieved depending on the bond type. The feasibility of this method to provide aromatic compounds in high yields from lignin by a sequential oxidative dehomologation reaction was clearly demonstrated.
Lee, Tae Woo,Yang, Jung Woon
p. 3761 - 3771
(2018/08/21)

Efficient cleavage of aryl ether C-O linkages by Rh-Ni and Ru-Ni nanoscale catalysts operating in water
Bimetallic Ru-Ni and Rh-Ni nanocatalysts coated with a phase transfer agent efficiently cleave aryl ether C-O linkages in water in the presence of hydrogen. For dimeric substrates with weaker C-O linkages, i.e. α-O-4 and β-O-4 bonds, low loadings of the precious metal (Rh or Ru) in the nanocatalysts quantitatively afford monomers, whereas for the stronger 4-O-5 linkage higher amounts of the precious metal are required to achieve complete conversion. Under the optimized, relatively mild operating conditions, the C-O bonds in a range of substituted ether compounds are efficiently cleaved, and mechanistic insights into the reaction pathways are provided. This work paves the way to sustainable approaches for the hydrogenolysis of C-O bonds.
Bulut, Safak,Siankevich, Sviatlana,Van Muyden, Antoine P.,Alexander, Duncan T. L.,Savoglidis, Georgios,Zhang, Jiaguang,Hatzimanikatis, Vassily,Yan, Ning,Dyson, Paul J.
p. 5530 - 5535
(2018/07/06)

Selective reductive cleavage of C–O bond in lignin model compounds over nitrogen-doped carbon-supported iron catalysts
Lignin has recently attracted much attention as a promising resource to produce fuels and aromatic chemicals. The selective cleavage of C–O bond while preserving the aromatic nature has become one of the major challenges in the catalytic valorization of lignin to aromatic chemicals. In this work, we report that the selective reductive cleavage of C–O bond in lignin model compounds can be successfully achieved through heterogeneous iron catalysis. The hydrogenolysis of α-O-4 model linkage shows that the iron catalyst prepared by the simultaneous pyrolysis of iron acetate and 1,10-phenanthroline on activated carbon at 800 °C is the most active iron catalyst, affording phenol and toluene with yields of 95% and 90%, respectively. This aromatics selectivity is found to be much higher than that obtained over noble metal catalysts. The presence of N?Fe species as the active center of heterogeneous iron catalyst was confirmed by various technologies especially XPS and H2-TPR. For the β-O-4 model linkage, the vicinal –OH group was essential for the iron-catalyzed hydrogenolysis of ether linkage. The oxidation of the α-carbon in the β-O-4 model compounds can significantly decrease the bond dissociation energy of ether linkage, giving depolymerization products in moderate to excellent yields.
Li, Jiang,Sun, Hui,Liu, Jia-xing,Zhang, Jun-jie,Li, Zhen-xing,Fu, Yao
p. 36 - 45
(2018/04/10)

Selective oxidation of lignin model compounds
Lignin, the planet’s most abundant renewable source of aromatic compounds, is difficult to degrade efficiently to well-defined aromatics. We developed a microwave-assisted catalytic Swern oxidation system using an easily prepared catalyst, MoO2Cl2(DMSO)2, and DMSO as the solvent and oxidant. It demonstrated high efficiency in transforming lignin model compounds containing the units and functional groups found in native lignins. The aromatic ring substituents strongly influenced the selectivity of β-ether phenolic dimer cleavage to generate sinapaldehyde and coniferaldehyde, monomers not usually produced by oxidative methods. Time-course studies on two key intermediates provided insight into the reaction pathway. Owing to the broad scope of this oxidation system and the insight gleaned with regard to its mechanism, this strategy could be adapted and applied in a general sense to the production of useful aromatic chemicals from phenolics and lignin.
Gao, Ruili,Li, Yanding,Kim, Hoon,Mobley, Justin K.,Ralph, John
p. , 2045
(2018/10/20)

Method for preparing carboxylic acid compound by oxidatively breaking carbon-carbon bond of ketone compound
The invention relates to a method for directly preparing a carboxylic acid compound by oxidatively breaking a carbon-carbon bond of a ketone compound. The method comprises adding a ketone compound anda catalyst into an organic solvent, putting the solution into a pressure container, sealing the container, and feeding oxygen source gas under a certain pressure into the container, wherein the reaction product is a carboxylic acid compound, the oxygen source gas is oxygen or air, the catalyst is a copper salt catalyst, the organic solvent is one of acetonitrile, dimethyl sulfoxide and N, N-dimethylformamide and the corresponding carboxylic acid product highest yield after the reaction is 99%. The method has a wide application range, is free of alkali assistants and organic ligands and is easy to separate.
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Paragraph 0133; 0134

(2018/06/16)

Synthesis of CoFeO mixed oxides via an alginate gelation process as efficient heterogeneous catalysts for lignin depolymerization in water
A catalytic oxidative fragmentation of a lignin dimer and polymer extracted from wheat straw was successfully performed under eco-friendly conditions: 10% O2/N2 as the oxidizing agent, water as the solvent (pH ≈ 7), and Co3O4, Fe2O3 and CoFeO mixed oxides as heterogeneous catalysts and at temperatures of T = 150 °C and 200 °C. These catalysts unexpectedly showed tunable selectivity that directly depends on the composition of the selected bimetallic nanoparticles. High selectivity for benzoic acid and alkylbenzene (above 50%) was observed over Co50-Fe50 at 200 °C. Under similar conditions, the conversion of wheat organosolv lignin over Co50-Fe50 at 150 °C for 4 h yielded up to 50 wt% of monomeric species (based on dry lignin) and up to 19% of aromatic molecules with high selectivity to aromatic aldehydes (syringaldehyde and vanillin), up to 60%. An important fraction of water-soluble oligomers, with low molecular weights, was also formed during the catalytic treatment. The oxide nanomaterials were readily separated from the residual lignin during the recyclability test. The yield and the product distribution can be tuned by choosing the oxidation parameters: temperature, reaction time, oxygen partial pressure, solvent and catalyst charges.
Hdidou,Khallouk,Solhy,Manoun,Oukarroum,Barakat
p. 5445 - 5453
(2018/11/20)

Method for degrading lignin
The invention discloses a method for degrading lignin. Water is used as a solvent. The method includes carrying out reaction on the lignin under the effects of double-rhodium catalysts or terpyridine rhodium trichloride catalysts and alkali under the protection of inert gas at the temperatures of 100-120 DEG C for 10-16 hours to degrade the lignin. Compared with existing methods, the method has the advantages that extra hydrogen sources can be omitted, the water is used as the solvent, reaction conditions are mild, the method is easy to implement, high in reaction yield and low in industrial production cost and is green and environmentally friendly, and environmental pollution can be abated.
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Paragraph 0048; 0049; 0050

(2017/10/28)

Promoting Lignin Depolymerization and Restraining the Condensation via an Oxidation-Hydrogenation Strategy
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
p. 3419 - 3429
(2017/06/09)

The selective hydrogenolysis of C-O bonds in lignin model compounds by Pd-Ni bimetallic nanoparticles in ionic liquids
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
p. 11884 - 11889
(2017/09/18)

Self-hydrogen transfer hydrogenolysis of β-O-4 linkages in lignin catalyzed by MIL-100(Fe) supported Pd-Ni BMNPs
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
supporting information
p. 4538 - 4543
(2017/10/13)

Depolymerisation Of Lignin In Biomass
A method of obtaining depolymerized lignin from biomass using a transition metal catalyst and a solvent mixture of organic solvent and water. The invention further relates to a composition obtainable by the method and the production of fuel.
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Paragraph 0067; 0068

(2017/09/07)

Fine Tuning the Redox Potentials of Carbazolic Porous Organic Frameworks for Visible-Light Photoredox Catalytic Degradation of Lignin β-O-4 Models
We report a facile approach to fine tune the redox potentials of π-conjugated porous organic frameworks (POFs) by copolymerizing carbazolic electron donor (D) and electron acceptor (A) based comonomers at different ratios. The resulting carbazolic copolymers (CzCPs) exhibit a wide range of redox potentials that are comparable to common transition-metal complexes and are used in the stepwise photocatalytic degradation of lignin β-O-4 models. With the strongest oxidative capability, CzCP100 (D:A = 0:100) exhibits the highest efficiency for the oxidation of benzylic β-O-4 alcohols, while the highly reductive CzCP33 (D:A = 66:33) gives the highest yield for the reductive cleavage of β-O-4 ketones. CzCPs also exhibit excellent stability and recyclability and represent a class of promising heterogeneous photocatalysts for the production of fine chemicals from sustainable lignocellulosic biomass.
Luo, Jian,Zhang, Xiang,Lu, Jingzhi,Zhang, Jian
p. 5062 - 5070
(2017/08/17)

Acid-Functionalised Magnetic Ionic Liquid [AcMIm]FeCl4 as Catalyst for Oxidative Hydroxylation of Arylboronic Acids and Regioselective Friedel–Crafts Acylation
An acid-functionalised, magnetic, room-temperature ionic liquid, 1-acyl-3-methylimidazolium tetrachloroferrate ([AcMIm]FeCl4), was synthesised and its optical, magnetic, and thermal properties were investigated. The magnetic moment (0.05402 emu in 2 T magnetic fields) showed strong paramagnetic behaviour, and thermogravimetric analysis indicated very good thermal stability with a decomposition temperature higher than 230 °C. Additionally, [AcMIm]FeCl4 efficiently catalysed the oxidative ipso-hydroxylation of arylboronic acids and regioselective Friedel–Crafts acylation without external organic solvent or additives, such as acids, base, and ligands. This functionalised ionic liquid, [AcMIm]FeCl4, was recycled and reused at least six times without significant loss of its catalytic properties and stability.
Saha, Arijit,Payra, Soumen,Dutta, Dipa,Banerjee, Subhash
p. 1129 - 1134
(2017/08/18)

Organocatalytic Chemoselective Primary Alcohol Oxidation and Subsequent Cleavage of Lignin Model Compounds and Lignin
A one-pot two-step degradation of lignin β-O-4 model compounds initiated by preferred oxidation of the primary over the secondary hydroxyl groups with a TEMPO/DAIB system has been developed [TEMPO=2,2,6,6-tetramethylpiperidine-N-oxyl, DAIB=(diacetoxy)iodobenzene]. The oxidised products are then cleaved by proline-catalysed retro-aldol reactions. This degradation methodology produces simple aromatics in good yields from lignin model compounds at room temperature with an extension to organosolv beech-wood lignin (L1) resulting in known cleavage products.
Dabral, Saumya,Hernández, José G.,Kamer, Paul C. J.,Bolm, Carsten
p. 2707 - 2713
(2017/07/13)

Method for synthesizing 2,6-dimethoxyphenol
The invention discloses a method for synthesizing 2,6-dimethoxyphenol. The method includes taking a microreactor as a reaction device and tetrabutylammonium bromide as a catalyst, and enabling pyrogallic acid and dimethyl carbonate to produce the 2,6-dimethoxyphenol by etherification. The method is high in yield and purity, simple in post-treatment and capable of achieving continuous production.
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Paragraph 0011; 0012; 0013; 0014

(2017/08/28)