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Zr oxo cluster bifunctional catalyst: The Zr oxo cluster [Zr₆O₄(OH)₄ (HSCH₂CH₂COO)₁₂]₂ has been developed, and then the molecular catalyst with Lewis acid and Brönsted acid sites were attained by the oxidation of the sulfhydryl group of the Zr oxo cluster with H₂O₂. The resulting bifunctional catalyst showed a superior catalytic activity for alcoholysis of furfural to alkyl levulinates.

Abstract

A novel dodecanuclear Zr oxo cluster [Zr₆O₄(OH)₄ (HSCH₂CH₂COO)₁₂]₂ (ZrO-SH-10) has been constructed under the room temperature, followed by oxidation of the sulfhydryl group with H₂O₂ to achieve a bifunctional catalyst with Lewis acid and Brönsted acid sites. The characterization of catalysts indicated that {Zr₆O₄} cluster core can be stabilized with a shell of carboxylate ligands, and the resulting ZrO-SO₃H was formed as a discrete molecular catalyst, exhibiting superior activity and recyclability for the cascade conversion of furfural to alkyl levulinate by the integration of transfer hydrogenation and alcoholysis in n-butanol. The yield of n-butyl levulinate can achieve as high as 91 % under the optimum conditions. Meanwhile, no leaching of the active species was found, which confirmed the structure of the Zr oxo cluster was air and moisture-stable. On the basis of the studies on the reaction kinetics and isotope tracking, the reaction mechanism was proposed accordingly.

Polymeric ionic liquids for conversion of cellulose into levulinic acid: A high levulinic acid yield of 79.4 % was achieved when used cellulose as substrates and sulphonic acid-functionalized polymeric ionic liquids as catalyst.

Abstract

Sulphonic acid-functionalized polymeric ionic liquids (PILs) were synthesized and applied into catalytic conversion of cellulose into levulinic acid (LA). The structure, thermal stability, and Hammett acidity function (H₀) of PILs were characterized and all were more thermostable than those of small-molecular ionic liquids (IL). At the optimum reaction conditions, the LA yield was maximized to 79.4 % by catalyst [Pim]CH₃SO₃. More importantly, catalyst [Pim]CH₃SO₃ performed well in other biomass conversion, such as cellobiose, starch and rice husk. The product LA can be easily extracted by methyl isobutyl ketone from the reaction mixture. The PILs with high catalytic activity were easily recycled with an LA yield up to 68.9 % even after five cycles. These sufficient PILs will offer new approaches for transforming biomass to platform chemicals.

Nature, Published online: 13 December 2022; doi:10.1038/d41586-022-04372-2

Dual catalysis is one of the most powerful strategies for the development of chemical reactions in organic synthesis. This Perspective aims to introduce the different categories of dual catalytic systems and demonstrate their benefits in constructing new chemical bonds and enhanced stereoselectivity.

Abstract

Dual catalysis is one of the most powerful strategies for the development of chemical reactions in organic synthesis. This strategy can be divided into cooperative catalysis, relay catalysis, and sequential catalysis according to the actual mode of operation and the communication between the catalysts. In recent years, such strategy has been applied in a large number of studies since it has the advantages of: 1) increasing reactivity and enabling challenging transformations; 2) offering a powerful way of controlling the stereoselectivity of asymmetric reactions, which is challenging for traditional catalytic systems; 3) catalyze the stereodivergent synthesis of molecules bearing one or more stereocenters from the same starting materials. This Perspective, which intends to introduce the reader to EurJOC special collection on Dual Catalysis , aims to summarize and introduce the different categories of dual catalysis and demonstrate their benefits in constructing new chemical bonds in a selective manner. Finally, current challenges and new trends in dual catalysis will be also presented.

Simplicity is the ultimate sophistication. β-O-4 linkages are found to undergo selective hydrodeoxygenation forming β-O-4 linkages bearing a methylene group at the C_α position. This process also stabilizes lignin fragments. In addition, carbohydrates in RCF lignin oil are found to be oligo(arabino)xylan alcohols, which are not covalently bonded to lignin.

Abstract

Reductive Catalytic Fractionation (RCF) of lignocellulosic materials produces lignin oil rich in monomer products and high-quality cellulosic pulps. RCF lignin oil also contains lignin oligomers/polymers and hemicellulose-derived carbohydrates. The variety of components makes lignin oil a complex matrix for analytical methods. As a result, the signals are often convoluted and overlapped, making detecting and quantifying key intermediates challenging. Therefore, to investigate the mechanisms underlining lignin stabilization and elucidate the structural features of carbohydrates occurring in the RCF lignin oil, fractionation methods reducing the RCF lignin oil complexity are required. This report examines the solvent fractionation of RCF lignin oil as a facile method for producing lignin oil fractions for advanced characterization. Solvent fractionation uses small volumes of environmentally benign solvents (methanol, acetone, and ethyl acetate) to produce multigram lignin fractions comprising products in different molecular weight ranges. This feature allows the determination of structural heterogeneity across the entire molecular weight distribution of the RCF lignin oil by high-resolution HSQC NMR spectroscopy. This study provides detailed insight into the role of the hydrogenation catalyst (Raney Ni) in stabilizing lignin fragments and defining the structural features of hemicellulose-derived carbohydrates in lignin oil obtained by the H-transfer RCF process.

Nature, Published online: 07 November 2022; doi:10.1038/d41586-022-03442-9