4013-37-0Relevant articles and documents
Tandem Acid/Pd-Catalyzed Reductive Rearrangement of Glycol Derivatives
Ciszek, Benjamin,Fleischer, Ivana,Kathe, Prasad,Schmidt, Tanno A.
supporting information, p. 3641 - 3646 (2020/03/25)
Herein, we describe the acid/Pd-tandem-catalyzed transformation of glycol derivatives into terminal formic esters. Mechanistic investigations show that the substrate undergoes rearrangement to an aldehyde under [1,2] hydrogen migration and cleavage of an oxygen-based leaving group. The leaving group is trapped as its formic ester, and the aldehyde is reduced and subsequently esterified to a formate. Whereas the rearrangement to the aldehyde is catalyzed by sulfonic acids, the reduction step requires a unique catalyst system comprising a PdII or Pd0 precursor in loadings as low as 0.75 mol % and α,α′-bis(di-tert-butylphosphino)-o-xylene as ligand. The reduction step makes use of formic acid as an easy-to-handle transfer reductant. The substrate scope of the transformation encompasses both aromatic and aliphatic substrates and a variety of leaving groups.
Cleavage of aryl-ether bonds in lignin model compounds using a Co-Zn-beta catalyst
Chang, Hou-Min,Dou, Xiaomeng,Jameel, Hasan,Jiang, Xiao,Li, Wenzhi,Zhu, Chaofeng
, p. 43599 - 43606 (2020/12/25)
Efficient cleavage of aryl-ether linkages is a key strategy for generating aromatic chemicals and fuels from lignin. Currently, a popular method to depolymerize native/technical lignin employs a combination of Lewis acid and hydrogenation metal. However, a clear mechanistic understanding of the process is lacking. Thus, a more thorough understanding of the mechanism of lignin depolymerization in this system is essential. Herein, we propose a detailed mechanistic study conducted with lignin model compounds (LMC) via a synergistic Co-Zn/Off-Al H-beta catalyst that mirrors the hydrogenolysis process of lignin. The results suggest that the main reaction paths for the phenolic dimers exhibiting α-O-4 and β-O-4 ether linkages are the cleavage of aryl-ether linkages. Particularly, the conversion was readily completed using a Co-Zn/Off-Al H-beta catalyst, but 40% of α-O-4 was converted and β-O-4 did not react in the absence of a catalyst under the same conditions. In addition, it was found that the presence of hydroxyl groups on the side chain, commonly found in native lignin, greatly promotes the cleavage of aryl-ether linkages activated by Zn Lewis acid, which was attributed to the adsorption between Zn and the hydroxyl group. Followed by the cobalt catalyzed hydrogenation reaction, the phenolic dimers are degraded into monomers that maintain aromaticity. This journal is
Reductive fractionation of woody biomass into lignin monomers and cellulose by tandem metal triflate and Pd/C catalysis
Huang, Xiaoming,Morales Gonzalez, Olivia M.,Zhu, Jiadong,Korányi, Tamás I.,Boot, Michael D.,Hensen, Emiel J. M.
, p. 175 - 187 (2017/01/24)
A catalytic process for the upgrading of woody biomass into mono-aromatics, hemi-cellulose sugars and a solid cellulose-rich carbohydrate residue is presented. Lignin fragments are extracted from the lignocellulosic matrix by cleavage of ester and ether linkages between lignin and carbohydrates by the catalytic action of homogeneous Lewis acid metal triflates in methanol. The released lignin fragments are converted into lignin monomers by the combined catalytic action of Pd/C and metal triflates in hydrogen. The mechanism of ether bond cleavage is investigated by lignin dimer models (benzyl phenyl ether, guaiacylglycerol-β-guaiacyl ether, 2-phenylethyl phenyl ether and 2-phenoxy-1-phenylethanol). Metal triflates are involved in cleaving not only ester and ether linkages between lignin and the carbohydrates but also β-O-4 ether linkages within the aromatic lignin structure. Metal triflates are more active for β-O-4 ether bond cleavage than Pd/C. On the other hand, Pd/C is required for cleaving α-O-4, 4-O-5 and β-β linkages. Insight into the synergy between Pd/C and metal triflates allowed optimizing the reductive fractionation process. Under optimized conditions, 55 wt% mono-aromatics-mainly alkylmethoxyphenols-can be obtained from the lignin fraction (23.8 wt%) of birch wood in a reaction system comprising birch wood, methanol and small amounts of Pd/C and Al(III)-triflate as catalysts. The promise of scale-up of this process is demonstrated.
Cleavage of the lignin β-O-4 ether bond: Via a dehydroxylation-hydrogenation strategy over a NiMo sulfide catalyst
Zhang, Chaofeng,Lu, Jianmin,Zhang, Xiaochen,Macarthur, Katherine,Heggen, Marc,Li, Hongji,Wang, Feng
supporting information, p. 6545 - 6555 (2018/06/06)
The efficient cleavage of lignin β-O-4 ether bonds to produce aromatics is a challenging and attractive topic. Recently a growing number of studies have revealed that the initial oxidation of CαHOH to CαO can decrease the β-O-4 bond dissociation energy (BDE) from 274.0 kJ mol-1 to 227.8 kJ mol-1, and thus the β-O-4 bond is more readily cleaved in the subsequent transfer hydrogenation, or acidolysis. Here we show that the first reaction step, except in the above-mentioned pre-oxidation methods, can be a Cα-OH bond dehydroxylation to form a radical intermediate on the acid-redox site of a NiMo sulfide catalyst. The formation of a Cα radical greatly decreases the Cβ-OPh BDE from 274.0 kJ mol-1 to 66.9 kJ mol-1 thereby facilitating its cleavage to styrene, phenols and ethers with H2 and an alcohol solvent. This is supported by control experiments using several reaction intermediates as reactants, analysis of product generation and by radical trap with TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) as well as by density functional theory (DFT) calculations. The dehydroxylation-hydrogenation reaction is conducted under non-oxidative conditions, which are beneficial for stabilizing phenol products.
Novel non-hydrolytic templated sol-gel synthesis of mesoporous aluminosilicates and their use as aminolysis catalysts
Skoda, David,Styskalik, Ales,Moravec, Zdenek,Bezdicka, Petr,Babiak, Michal,Klementova, Mariana,Barnes, Craig E.,Pinkas, Jiri
, p. 24273 - 24284 (2016/03/15)
A novel non-hydrolytic sol-gel (NHSG) synthesis of mesoporous aluminosilicate xerogels is presented. The polycondensation between silicon acetate, Si(OAc)4, and tris(dimethylamido)alane, Al(NMe2)3, leads to homogeneous alu
Titania-photocatalyzed transfer hydrogenation reactions with methanol as a hydrogen source: Enhanced catalytic performance by Pd-Pt alloy at ambient temperature
Zhao, Yubao,Pan, Feng,Li, Hui,Xu, Guo Qin,Chen, Wei
, p. 454 - 458 (2014/03/21)
Hydrogenation reactions are of great importance in scientific research and in industry productions. Herein, we designed a novel system to realize photocatalytic transfer hydrogenation by using solar light as the energy input and methanol as the hydrogen source. In this reaction, titania loaded with Pd-Pt bimetallic alloy nanocrystals as a cocatalyst exhibited photocatalytic performance that was remarkably superior to that exhibited by titania with Pd or Pt alone as the cocatalyst. This work has shed light on the rational design of multifunctional catalysts through selecting appropriate bimetallic alloys as efficient cocatalysts. Light up, as if you have a catalyst: Photocatalytic transfer hydrogenation is efficiently realized on Pd-Pt/TiO2 under mild reaction conditions with the use of light irradiation as the energy input and methanol as the hydrogen source at ambient temperature. The Pd-Pt alloy cocatalyst exhibits enhanced catalytic performance relative to that of the monometallic Pd or Pt component. Copyright
Ether-directed ortho-C-H olefination with a palladium(II)/monoprotected amino acid catalyst
Li, Gang,Leow, Dasheng,Wan, Li,Yu, Jin-Quan
supporting information, p. 1245 - 1247 (2013/03/13)
Weak coordination is powerful! A PdII-catalyzed olefination of ortho-C-H bonds of arenes directed by weakly coordinating ethers is developed by using monoprotected amino acid (MPAA) ligands. This finding provides a method for chemically modifying ethers, which are abundant in natural products and drug molecules. HFIP=hexafluoroisopropanol. Copyright
Graphene oxide as an acid catalyst for the room temperature ring opening of epoxides
Dhakshinamoorthy, Amarajothi,Alvaro, Mercedes,Concepcion, Patricia,Fornes, Vicente,Garcia, Hermenegildo
supporting information; experimental part, p. 5443 - 5445 (2012/07/28)
The minute amount of hydrogen sulfate groups introduced into the graphene oxide (GO) obtained by Hummers oxidation of graphite renders this material as a highly efficient, recyclable acid catalyst for the ring opening of epoxides with methanol and other primary alcohols as nucleophile and solvent.
A generalized approach for iron catalyzed chemo- and regioselective formation of anti-Markovnikov acetals from styrene derivatives
Chowdhury, Abhishek Dutta,Lahiri, Goutam Kumar
supporting information; experimental part, p. 3448 - 3450 (2012/05/20)
Fe(BF4)2·6H2O in the presence of pyridine-2,6-dicarboxylic acid and PhI(OAc)2 can efficiently catalyze the formation of chemoselective dialkyl acetals from styrene derivatives with anti-Markovnikov regioselectivity in good to high yields under mild and benign reaction conditions.
"Cation pool" method based on C-C bond dissociation. Effective generation of monocations and dications
Okajima, Masayuki,Suga, Seiji,Itami, Kenichiro,Yoshida, Jun-Ichi
, p. 6930 - 6931 (2007/10/03)
The "cation pools" of alkoxyarylcarbenium ions were effectively generated by the oxidative C-C bond dissociation using low temperature electrolysis. The present method is especially effective for the generation and accumulation of dications, which react with carbon nucleophiles. Copyright
