- 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
-
-
- 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)
-
- Cleavage∕cross-coupling strategy for converting β-O-4 linkage lignin model compounds into high valued benzyl amines via dual C–O bond cleavage
-
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
-
supporting information
(2021/10/29)
-
- Mild selective oxidative cleavage of lignin C-C bonds over a copper catalyst in water
-
The conversion of lignin into aromatics as commodity chemicals and high-quality fuels is a highly desirable goal for biorefineries. However, the presence of robust inter-unit carbon-carbon (C-C) bonds in natural lignin seriously impedes this process. Herein, for the first time, we report the selective cleavage of C-C bonds in β-O-4 and β-1 linkages catalyzed by cheap copper and a base to yield aromatic acids and phenols in excellent yields in water at 30 °C under air without the need for additional complex ligands. Isotope-labeling experiments show that a base-mediated Cβ-H bond cleavage is the rate-determining step for Cα-Cβ bond cleavage. Density functional theory (DFT) calculations suggest that the oxidation of β-O-4 ketone to a key intermediate, i.e., a peroxide, by copper and O2 lowers the Cα-Cβ bond dissociation energy and facilitates its subsequent cleavage. In addition, the catalytic system could be successfully applied to the depolymerization of various authentic lignin feedstocks, affording excellent yields of aromatic compounds and high selectivity of a single monomer. This study offers the potential to economically produce aromatic chemicals from biomass.
- Hu, Yuzhen,Li, Song,Ma, Longlong,Wang, Chenguang,Yan, Long,Zhang, Qi,Zhang, Xinghua,Zhao, Xuelai
-
supporting information
p. 7030 - 7040
(2021/09/28)
-
- Polycarboxylated compounds and compositions containing same
-
Methods of selectively modifying lignin, polycarboxylated products thereof, and methods of deriving aromatic compounds therefrom. The methods comprise electrochemically oxidizing lignin using stable nitroxyl radicals to selectively oxidize primary hydroxyls on β-O-4 phenylpropanoid units to corresponding carboxylic acids while leaving the secondary hydroxyls unchanged. The oxidation results in polycarboxylated lignin in the form of a polymeric β-hydroxy acid. The polymeric β-hydroxy acid has a high loading of carboxylic acid and can be isolated in acid form, deprotonated, and/or converted to a salt. The β-hydroxy acid, anion, or salt can also be subjected to acidolysis to generate various aromatic monomers or oligomers. The initial oxidation of lignin to the polycarboxylated form renders the lignin more susceptible to acidolysis and thereby enhances the yield of aromatic monomers and oligomers obtained through acidolysis.
- -
-
Page/Page column 17-22
(2021/06/09)
-
- A multicentre synergistic polyoxometalate-based metal-organic framework for one-step selective oxidative cleavage of β-: O -4 lignin model compounds
-
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
-
supporting information
p. 248 - 255
(2020/01/13)
-
- Visible-light-induced C-C bond cleavage of lignin model compounds with cyanobenziodoxolone
-
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
-
supporting information
(2020/10/02)
-
- Cleavage of CC and Co bonds in β-O-4 linkage of lignin model compound by cyclopentadienone group 8 and 9 metal complexes
-
Degradation of 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphe-noxy)propane-1,3-diol (1), a model compound for lignin β-O-4 linkage was examined with iron, ruthenium, rhodium and iridium complexes bearing cyclopentadienone ligand. Cyclopentadienone iron complex gave only a small amount of degraded product with reduced molecular weight. Cyclopentadienone ruthenium complex, so called Shvo's catalyst, afforded 3,4-dimethoxybenzaldehyde (a3) in 14.3% yield after CαCβ bond cleavage. On the other hand, cyclopentadienone group-9 metal complexes catalyzed CβO bond cleavage to afford guaiacol (b1) as a main product in up to 74.9% yield.
- Kishino, Masamichi,Kusumoto, Shuhei,Nozaki, Kyoko
-
supporting information
p. 477 - 480
(2020/05/19)
-
- 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
-
supporting information
p. 3489 - 3494
(2020/07/30)
-
- 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)
-
- 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)
-
- 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
-
supporting information
p. 7408 - 7415
(2019/08/15)
-
- Highly Selective Oxidation and Depolymerization of α,γ-Diol-Protected Lignin
-
Lignin oxidation offers a potential sustainable pathway to oxygenated aromatic molecules. However, current methods that use real lignin tend to have low selectivity and a yield that is limited by lignin degradation during its extraction. We developed stoichiometric and catalytic oxidation methods using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidant/catalyst to selectively deprotect the acetal and oxidize the α-OH into a ketone. The oxidized lignin was then depolymerized using a formic acid/sodium formate system to produce aromatic monomers with a 36 mol % (in the case of stoichiometric oxidation) and 31 mol % (in the case of catalytic oxidation) yield (based on the original Klason lignin). The selectivity to a single product reached 80 % (syringyl propane dione, and 10–13 % to guaiacyl propane dione). These high yields of monomers and unprecedented selectivity are attributed to the preservation of the lignin structure by the acetal.
- Lan, Wu,de Bueren, Jean Behaghel,Luterbacher, Jeremy S.
-
supporting information
p. 2649 - 2654
(2019/02/01)
-
- Investigating homogeneous Co/Br-/H2O2 catalysed oxidation of lignin model compounds in acetic acid
-
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
-
p. 384 - 397
(2019/01/28)
-
- 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)
-
- Efficient Oxidation of Benzylic and Aliphatic Alcohols Using a Bioinspired Cross-Bridged Cyclam Manganese Complex with H2O2
-
The cross-bridged cyclam manganese complex Mn(Me2EBC)Cl2 efficiently catalyzes the oxidation of benzylic and aliphatic alcohols at pH 3 in a mixture of acetonitrile and water at room temperature. The environmentally benign and high oxygen content oxidant H2O2 was adopted. Conversions of the alcohols to the corresponding carbonyl compounds reached 98 % with good to excellent selectivity. In addition, several lignin model compounds were also catalytically oxidized under these conditions, with excellent conversion (up to 96 %) and selectivity (up to 99 %).
- Zhang, Zhan,Khrouz, Lhoussain,Yin, Guochuan,Andrioletti, Bruno
-
supporting information
p. 323 - 327
(2018/11/27)
-
- Iridium-catalysed primary alcohol oxidation and hydrogen shuttling for the depolymerisation of lignin
-
Lignin is a potentially abundant renewable resource for the production of aromatic chemicals, however its selective depolymerisation is challenging. Here, we report a new catalytic system for the depolymerisation of lignin to novel, non-phenolic monoaromatic products based on the selective β-O-4 primary alcohol dehydrogenation with a Cp?Ir-bipyridonate catalyst complex under basic conditions. We show that this system is capable of promoting the depolymerisation of model compounds and isolated lignins via a sequence of selective primary alcohol dehydrogenation, retro-aldol (Cα-Cβ) bond cleavage and in situ stabilisation of the aldehyde products by transfer (de)hydrogenation to alcohols and carboxylic acids. This method was found to give good to excellent yields of cleavage products with both etherified and free-phenolic lignin model compounds and could be applied to real lignin to generate a range of novel non-phenolic monomers including diols and di-acids. We additionally show, by using the same catalyst in a convergent, one-pot procedure, that these products can be selectively channelled towards a single di-acid product, giving much simpler product mixtures as a result.
- Lancefield, Christopher S.,Teunissen, Lucas W.,Weckhuysen, Bert M.,Bruijnincx, Pieter C. A.
-
supporting information
p. 3214 - 3221
(2018/07/31)
-
- Method for synthesizing β - O - 4 lignin dimers model compounds (by machine translation)
-
The invention belongs to the field of biological chemical and biological-based material, and in particular relates to a synthetic β - O - 4 lignin dimers model compounds. The phenolic material with the alkali is dissolved in the acetone in magnetic stirring and mixing, [...] ketone material under protection of inert gas in the room temperature to 60 °C reaction 16 - 48 h, filtering the filtrate after reaction is rotary evaporated to obtain crude product, crude after excessive polar organic solvent, washing the collection after dissolving the organic phase, dried and filtered, concentrated in vacuo, re-crystallization, dried under vacuum to get β - O - 4 lignin dimers model compound. The invention synthetic method and the conventional method compared with the universality is relatively strong, mild reaction conditions, the operation is simple, one-step synthesis output is high, and high purity, can reach 98% or more. (by machine translation)
- -
-
Paragraph 0104-0109
(2019/01/08)
-
- Acid promoted C-C bond oxidative cleavage of β-O-4 and β-1 lignin models to esters over a copper catalyst
-
Depolymerisation of lignin to aromatics is a challenging task. We herein report that a Cu(OAc)2/BF3·OEt2 catalyst is effective in simultaneously cleaving C-C bonds in β-1 and β-O-4 ketones, yielding esters and phenols. In-depth studies show that C-H bond activation is the rate determining step for C-C bond cleavage. BF3·OEt2 promotes the reaction via activating the β-C-H bond. This study offers the potential to obtain aromatic esters from lignin.
- Wang,Li,Lu,Li,Zhang,Liu,Luo,Wang
-
supporting information
p. 702 - 706
(2017/08/15)
-
- New protocol of copper-catalyzed oxidative C(CO)[sbnd]C bond cleavage of aryl and aliphatic ketones to organic acids using O2 as the terminal oxidant
-
Catalytic oxidation of C[sbnd]C bond is a key technology to transform petroleum-based as well as sustainable biomass feedstock into more valuable oxygenates. We herein describe a convenient and useful oxidation strategy of converting ketones into carboxylic acids using homogeneous copper catalyst without additives and with O2as the terminal oxidant. A wide range of aryl and aliphatic ketones as well as β–O–4 lignin models were selectively oxidized to acids via C[sbnd]C bond cleavage. Mechanism studies by EPR and in situ NMR elucidate the principles of Cu/O2reactivity that involves C[sbnd]H bond and O2activation via a peroxide species. This provides an important foundation for expanding the scope of useful aerobic oxidation reactions using copper catalysts.
- Liu, Huifang,Wang, Min,Li, Hongji,Luo, Nengchao,Xu, Shutao,Wang, Feng
-
p. 170 - 179
(2017/01/22)
-
- 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)
-
- Lignin Depolymerization with Nitrate-Intercalated Hydrotalcite Catalysts
-
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.
-
p. 1316 - 1328
(2016/02/18)
-
- Photocatalytic Oxidation of Lignin Model Systems by Merging Visible-Light Photoredox and Palladium Catalysis
-
Lignin valorization has long been recognized as a sustainable solution for the renewable production of aromatic compounds. Two-step oxidation/reduction strategies, whereby the first oxidation step is required to "activate" lignin systems for controlled fragmentation reactions, have recently emerged as viable routes toward this goal. Herein we describe a catalytic protocol for oxidation of lignin model systems by combining photoredox and Pd catalysis. The developed dual catalytic protocol allowed the efficient oxidation of lignin model substrates at room temperature to afford the oxidized products in good to excellent yields.
- K?rk?s, Markus D.,Bosque, Irene,Matsuura, Bryan S.,Stephenson, Corey R. J.
-
supporting information
p. 5166 - 5169
(2016/10/14)
-
- Chemoselective oxidant-free dehydrogenation of alcohols in lignin using Cp?Ir catalysts
-
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
-
supporting information
p. 2029 - 2036
(2016/04/19)
-
- Aerobic Oxidation of Olefins and Lignin Model Compounds Using Photogenerated Phthalimide-N-oxyl Radical
-
A metal-free protocol to generate phthalimide-N-oxyl (PINO) radicals from N-hydroxyphthalimide (NHPI) via a photoinduced proton-coupled electron transfer process is reported. Using donor-substituted aromatic ketones, such as 4,4′-bis(diphenylamino)benzophenone (DPA-BP), PINO radicals are efficiently produced and subsequently utilized to functionalize olefins to afford a new class of alkyl hydroperoxides. The DPA-BP/NHPI/O2 photocatalytic system exhibits high efficiency toward the aerobic oxidation of β-O-4 lignin models.
- Luo, Jian,Zhang, Jian
-
p. 9131 - 9137
(2016/10/17)
-
- Hydrogenolysis of a γ-Acetylated Lignin Model Compound with a Ruthenium-Xantphos Catalyst
-
Catalytic hydrogenolysis of a γ-acetylated dimer lignin model compound is effected using a Ru-xantphos catalyst. Mechanistic investigations show mono-aryl degradation products are generated from the β-O-4 substrate as well as a terminal alkene ketone dimer (bis-aryl) that further dimerizes to a tetra-aryl product. Preliminary results using an acetylated kraft lignin as a substrate are also discussed. Graphical Abstract: [Figure not available: see fulltext.]
- Wu, Adam,Lauzon, Jean Michel,James, Brian R.
-
p. 511 - 518
(2015/08/04)
-
- Base-catalysed cleavage of lignin β-O-4 model compounds in dimethyl carbonate
-
A base-catalysed transformation and cleavage of lignin β-O-4 model compounds in dimethyl carbonate is reported. The reaction system consists of readily available bases and inexpensive dimethyl carbonate as a solvent and reagent, affording methoxy benzene or 2-aryloxyvinyl benzene derivatives in good to very good yields. The applicability of the system for the bond cleavage in an organosolv lignin sample was demonstrated.
- Dabral, Saumya,Mottweiler, Jakob,Rinesch, Torsten,Bolm, CarstenU
-
supporting information
p. 4908 - 4912
(2015/11/11)
-
- Iron-catalysed oxidative cleavage of lignin and β-O-4 lignin model compounds with peroxides in DMSO
-
Simple FeCl3-derived iron catalysts are used for the cleavage of β-O-4 linkages in lignin and lignin model compounds. The degradation of the β-O-4 linkages and the resinol structures in both organosolv and kraft lignin was proven by 2D-NMR (HSQC) experiments, and the oxidative depolymerisation of these lignin sources was confirmed by GPC. Key reactive species facilitating this cleavage are methyl radicals generated from H2O2 and DMSO.
- Mottweiler, Jakob,Rinesch, Torsten,Besson, Claire,Buendia, Julien,Bolm, Carsten
-
supporting information
p. 5001 - 5008
(2015/11/16)
-
- Ruthenium-Catalyzed C-C bond cleavage in lignin model substrates
-
Ruthenium-triphos complexes exhibited unprecedented catalytic activity and selectivity in the redox-neutral C-C bond cleavage of the β-O-4 lignin linkage of 1,3-dilignol model compounds. A mechanistic pathway involving a dehydrogenation-initiated retro-aldol reaction for the C-C bond cleavage was proposed in line with experimental data and DFT calculations.
- Vom Stein, Thorsten,Den Hartog, Tim,Buendia, Julien,Stoychev, Spas,Mottweiler, Jakob,Bolm, Carsten,Klankermayer, Jürgen,Leitner, Walter
-
supporting information
p. 5859 - 5863
(2015/05/13)
-
- Selective aerobic benzylic alcohol oxidation of lignin model compounds: Route to aryl ketones
-
A mild and chemoselective oxidation of the α-alcohol in β-O-4'-ethanoaryl and β-O-4'-glycerolaryl ethers has been developed. The benzylic alcohols were selectively dehydrogenated to the corresponding ketones in 60-93-% yield. A one-pot selective route to aryl ethyl ketones was performed. The catalytic system comprises recyclable heterogeneous palladium, mild reaction conditions, green solvents, and oxygen in air as oxidant. Catalytic amounts of a coordinating polyol were found pivotal for an efficient aerobic oxidation. The ligninator: A mild and chemoselective oxidation of the α-alcohol in β-O-4' lignin model compounds is developed. The benzylic alcohols are selectively dehydrogenated to the corresponding ketones in 60-93-% yield. A one-pot selective route to aryl ethyl ketones is performed. The catalytic system comprises recyclable heterogeneous palladium, mild reaction conditions, green solvents, and oxygen in air as oxidant.
- Dawange, Monali,Galkin, Maxim V.,Samec, Joseph S. M.
-
p. 401 - 404
(2015/03/04)
-
- SELECTIVE C-O BOND CLEAVAGE OF OXIDIZED LIGNIN AND LIGNIN-TYPE MATERIALS INTO SIMPLE AROMATIC COMPOUNDS
-
A method to cleave C-C and C-0 bonds in β-Ο-4 linkages in lignin or lignin sub-units is described. The method includes oxidizing at least a portion of secondary benzylic alcohol groups in β-Ο-4 linkages in the lignin or lignin sub-unit to corresponding ketones and then leaving C-0 or C-C bonds in the oxidized lignin or lignin sub-unit by reacting it with an organic carboxylic acid, a salt of an organic carboxylic acids, and/or an ester of an organic carboxylic acids. The method may utilize a metal or metal-containing reagent or proceed without the metal or metal-containing reagent.
- -
-
Page/Page column 26-27; 28
(2015/10/05)
-
- Fe(TAML)Li/(diacetoxyiodo)benzene-mediated oxidation of alcohols: Evidence for mild and selective C-O and C-C oxidative cleavage in lignin model transformations
-
A novel combination of Fe(TAML)Li and (diacetoxyiodo)- benzene for the oxidation of primary and secondary alcohols at 25 °C in acetone is reported. In view of the interesting ability of this system to selectively cleave specific types of C-C bonds of elaborated alcohols, the application of this novel combination to the oxidative cleavage of lignin model molecules was investigated. Considering the numerous supported versions of the oxidant as well as the mild conditions employed, the developed methodology appears to be a promising lignin depolymerization strategy.
- Napoly, Francois,Jean-Gerard, Ludivine,Goux-Henry, Catherine,Draye, Micheline,Andrioletti, Bruno
-
supporting information
p. 781 - 787
(2014/03/21)
-
- SELECTIVE AEROBIC ALCOHOL OXIDATION METHOD FOR CONVERSION OF LIGNIN INTO SIMPLE AROMATIC COMPOUNDS
-
Described is a method to oxidize lignin or lignin sub-units. The method includes oxidation of secondary benzylic alcohol in the lignin or lignin sub-unit to a corresponding ketone in the presence of unprotected primarily aliphatic alcohol in the lignin or lignin sub-unit. The optimal catalyst system consists of HNO3 in combination with another Br?nsted acid, in the absence of a metal-containing catalyst, thereby yielding a selectively oxidized lignin or lignin sub-unit. The method may be carried out in the presence or absence of additional reagents including TEMPO and TEMPO derivatives.
- -
-
Paragraph 0050; 0076; 0077; 0078; 0085; 0086
(2014/09/03)
-
- Chemoselective metal-free aerobic alcohol oxidation in lignin
-
An efficient organocatalytic method for chemoselective aerobic oxidation of secondary benzylic alcohols within lignin model compounds has been identified. Extension to selective oxidation in natural lignins has also been demonstrated. The optimal catalyst system consists of 4-acetamido-TEMPO (5 mol %; TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) in combination with HNO3 and HCl (10 mol % each). Preliminary studies highlight the prospect of combining this method with a subsequent oxidation step to achieve C-C bond cleavage.
- Rahimi, Alireza,Azarpira, Ali,Kim, Hoon,Ralph, John,Stahl, Shannon S.
-
supporting information
p. 6415 - 6418
(2013/06/05)
-
- Chemical conversion of β-O-4 lignin linkage models through Cu-catalyzed aerobic amide bond formation
-
Methods for conversion of the lignin β-O-4 models into amide derivatives and phenols have been developed, which is achieved via chemo-selective oxidation of the secondary benzylic alcohol and subsequent Cu-catalyzed aerobic amide bond formation.
- Zhang, Jian,Liu, Yu,Chiba, Shunsuke,Loh, Teck-Peng
-
supporting information
p. 11439 - 11441
(2013/12/04)
-
- Nature and kinetic analysis of carbon-carbon bond fragmentation reactions of cation radicals derived from SET-oxidation of lignin model compounds
-
Features of the oxidative cleavage reactions of diastereomers of dimeric lignin model compounds, which are models of the major types of structural units found in the lignin backbone, were examined. Cation radicals of these substances were generated by using SET-sensitized photochemical and Ce(IV) and lignin peroxidase promoted oxidative processes, and the nature and kinetics of their C- bond cleavage reactions were determined. The results show that significant differences exist between the rates of cation radical C1-2 bond cleavage reactions of 1,2-diaryl-(β-1) and 1-aryl-2-aryloxy-(β-O-4) propan-1,3-diol structural units found in lignins. Specifically, under all conditions C1-2 bond cleavage reactions of cation radicals of the β-1 models take place more rapidly than those of the β-O-4 counterparts. The results of DFT calculations on cation radicals of the model compounds show that the C1-2 bond dissociation energies of the β-1 lignin model compounds are significantly lower than those of the β-O-4 models, providing clear evidence for the source of the rate differences.
- Cho, Dae Won,Parthasarathi, Ramakrishnan,Pimentel, Adam S.,Maestas, Gabriel D.,Park, Hea Jung,Yoon, Ung Chan,Dunaway-Mariano, Debra,Gnanakaran,Langan, Paul,Mariano, Patrick S.
-
supporting information; experimental part
p. 6549 - 6562
(2010/12/19)
-
- Catalytic C-O bond cleavage of 2-aryloxy-1-arylethanols and its application to the depolymerization of lignin-related polymers
-
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.
-
supporting information; experimental part
p. 12554 - 12555
(2010/12/19)
-
- Photochemistry of lignin model compounds on solid supports
-
The photochemistry of several substituted α-(aryloxy)acetoveratrones that are models for chromophores in lignin has been studied using a combination of laser flash photolysis and product studies in solution and on silica, Na-X zeolite, and cellulose.The lifetimes of the triplet ketones vary substantially with the electron-donating ability of the substituents in the α-aryloxy ring, with values ranging from 30 ns for the 4-methoxy derivative to 5.5 μs for the 4-cyano ketone in acetonitrile.The triplet ketones are considerably longer lived on a silica surface than in solution and do not decay with first-order kinetics; however, they are all shorter lived than triplet acetoveratrone under the same conditions, indicating that β-phenyl quenching and (or) β-cleavage dominate their decay.The same triplets show quite different kinetic behavior in Na-X or cellulose and there is no indication in these systems for the importance of either β-phenyl quenching or β-cleavage in determining the rates of triplet decay.Product studies for α-guaiacoxyacetoveratrone indicate that β-cleavage from the singlet excited state is responsible for product formation; in contrast to solution results, the phenacyl-phenoxyl radical pairs react exclusively by geminate recombination to give rearranged ketones resulting from ortho and para ring coupling of the two radicals.Product formation is very inefficient for this ketone in cellulose, indicating either a low singlet reactivity or efficient geminate recombination of the initial radical pair to regenerate starting material.
- Hurrell, L.,Johnston, L. J.,Mathivanan, N.,Vong, D.
-
p. 1340 - 1348
(2007/10/02)
-
- The Photochemistry of α-Phenoxyacetophenones Investigated by Flash-CIDNP-spectroscopy
-
The photochemistry of 14 different substituted α-phenoxyacetophenones (1) was studied by CIDNP-spectroscopy using XeCl excimer laser (308 nm) and a 250 MHz 1H-NMR spectrometer.To characterize the excited states the electronic absorption and emission spectra as well disappearance quantum yields were investigated also. - Two reaction channels were established: 1) β-cleavage from the singlet state; and 2) the formation of acetophenones via the respective enol forms where the origin of the polarization remains unclear.It is concluded that these are the main reaction channels, since all products formed show polarizations in the CIDNP-spectr a. - In contrast to the current assumptions for the typical acetophenone reaction of (1) leading to the β-cleavage, we are led to interprete the CIDNP-spectra of (1) as a result of a reaction due to the phenoxy part with all characteristics of a photo-Claisen reaction. Keywords: Luminescence / Photochemistry / Radicals / Spectroscopy, CIDNP / Spectroscopy, Nuclear Magnetic Resonance / Spectroscopy, Ultraviolet
- Palm, W.-U.,Dreeskamp, H.,Bouas-Laurent, H.,Castellan, A.
-
-
- Electroorganic Reactions. 38. Mechanism of Electrooxidative Cleavage of Lignin Model Dimers
-
The mechanisms for oxidative cleavage of several phenolic ethers, models for lignins, have been investigated by a detailed comparison of the results of anodic oxidation at nickel anodes in alkaline electrolyte with that of oxidation in acetonitrile in the presence of a triarylamine redox catalyst.The latter reaction is unambiguously initiated by single-electron transfer (SET), and in this case the major product of cleavage is aldehyde (vanillin or syringaldehyde derivatives).At nickel anodes polymerization is predominant although the aldehydes are formed together with larger amounts of the corresponding carboxylic acids.Combinations of 4-hydroxyl, α-keto, β-O-aryl, and β-hydroxymethyl functionality are shown to be crucial for the oxidation at nickel; the carboxylic acid formation probably involves a route with initial hydrogen atom abstraction at the surface.Important chemical conversions precede and accompany oxidation in alkaline media, and these are associated with the propensity for polymerization.
- Pardini, Vera L.,Smith, Carmen Z.,Utley, James H. P.,Vargas, Reinaldo R.,Viertler, Hans
-
p. 7305 - 7313
(2007/10/02)
-