22675-96-3Relevant academic research and scientific papers
One-Pot Transformation of Lignin and Lignin Model Compounds into Benzimidazoles
Guo, Tao,He, Jianghua,Liu, Tianwei,Zhang, Yuetao
, (2022/02/07)
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.
Thio-assisted reductive electrolytic cleavage of lignin β-O-4 models and authentic lignin
Fang, Zhen,Flynn, Michael G.,Jackson, James E.,Hegg, Eric L.
, p. 412 - 421 (2021/01/28)
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.
Cleavage∕cross-coupling strategy for converting β-O-4 linkage lignin model compounds into high valued benzyl amines via dual C–O bond cleavage
Jia, Le,Li, Chao-Jun,Zeng, Huiying
supporting information, (2021/10/29)
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.
Mild selective oxidative cleavage of lignin C-C bonds over a copper catalyst in water
Hu, Yuzhen,Li, Song,Ma, Longlong,Wang, Chenguang,Yan, Long,Zhang, Qi,Zhang, Xinghua,Zhao, Xuelai
supporting information, p. 7030 - 7040 (2021/09/28)
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.
Polycarboxylated compounds and compositions containing same
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Page/Page column 17-22, (2021/06/09)
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.
A multicentre synergistic polyoxometalate-based metal-organic framework for one-step selective oxidative cleavage of β-: O -4 lignin model compounds
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)
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.
Visible-light-induced C-C bond cleavage of lignin model compounds with cyanobenziodoxolone
Zheng, Ming,Huang, Yan,Zhan, Le-Wu,Hou, Jing,Li, Bin-Dong
supporting information, (2020/10/02)
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.
Cleavage of CC and Co bonds in β-O-4 linkage of lignin model compound by cyclopentadienone group 8 and 9 metal complexes
Kishino, Masamichi,Kusumoto, Shuhei,Nozaki, Kyoko
supporting information, p. 477 - 480 (2020/05/19)
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.
Mechanochemical cleavage of lignin models and ligninviaoxidation and a subsequent base-catalyzed strategy
Dushkin, Alexandr V.,Su, Weike,Sun, Chen,Xu, Wenhao,Zheng, Lei
supporting information, p. 3489 - 3494 (2020/07/30)
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.
Organocatalytic Approach to Photochemical Lignin Fragmentation
Yang, Cheng,K?rk?s, Markus D.,Magallanes, Gabriel,Chan, Kimberly,Stephenson, Corey R. J.
supporting information, p. 8082 - 8085 (2020/11/02)
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.
