Catalytic conversion of cellulose-based biomass and glycerol to lactic acid

Catalytic transformation of cellulose into value-added chemicals is of great importance for utilization of renewable and abundant biomass. Due to the high oxygen content, cellulose serves as an ideal candidate for the production of oxygenates, in particular lactic acid which is a versatile building block in chemical industry. The efficient conversion of cellulose to lactic acid generally requires selective activation of specific C–O and C–C bonds, and therefore multifunctional catalysts that combine several key reactions including hydrolysis, isomerization and retro-aldol fragmentation are highly desirable. This review article highlights the recently developed catalytic systems and catalysts for the selective transformation of cellulose and cellulose-derived carbohydrates into lactic acid, lactates and/or its esters. Emphases will be put on the reaction mechanism and key factors that exert effects on the catalytic performances. In addition, the catalytic transformation of glycerol, a C_3 compound over-supplied from biodiesel industry, will also be surveyed. Recent advances in the development of new catalysts or strategies are analyzed and discussed to gain insight into the transformation of C_3 compound to lactic acid.     

Catalytic transformations of cellulose and its derived carbohydrates into 5-hydroxymethylfurfural,levulinic acid,and lactic acid

The catalytic transformation of cellulose into key building-block or platform chemicals such as 5-hydoxymethylfurfural(HMF),levulinic acid,and lactic acid under mild conditions,has attracted much attention in recent years,as these conversions can be operated without consumption of hydrogen or oxygen and thus are more economical compared to the hydrogenolysis or oxidation of cellulose.This review article highlights recent advances in the development of novel catalysts or catalytic processes for the conversion of cellulose and its derived carbohydrates into HMF,levulinic acid,and lactic acid or their esters under inert atmosphere.We also analyze efficient catalytic systems for HMF production,in particular Lewis acids combined with ionic liquid or biphasic systems.For the formations of levulinic and lactic acids or their esters,we focus on the reactions in aqueous and alcohol media catalyzed by multifunctional catalysts that combine the functions of hydrolysis,isomerization,and dehydration-rehydration or retro-aldol reactions.The reaction mechanism for each process will also be discussed to gain insights into the activation of C–O and C–C bonds in the absence of hydrogen or oxygen.     

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/crosscoupling strategy for converting 4-O-5 linkage lignin model compounds into high value-a...     

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/crosscoupling strategy for converting 4-O-5 linkage lignin model compounds into high value-a...     

Transformation of bio-derived acids into fuel-like alkanes via ketonic decarboxylation and hydrodeoxygenation: Design of multifunctional catalyst,kinetic and mechanistic aspects

The combination of a low cost source of Biofine's levulinic acid with available way of valeric acid synthesis opens up new opportunities for valeric acid as a promising bio-derived source for synthesis of valuable compounds for transportation sector. The present review illustrates the development of different approaches to one–pot synthesis of fuel-like alkanes from lignocellulose derived carboxylic acids where particular focus is given to valeric acid consecutive decarboxylative coupling(ketonization) and ketone hydrodeoxygenation in a single reactor over one catalyst bed. The key factors that influence the catalytic performance on both ketonization and hydrodeoxygenation steps as well as their cross-influence will be clarified to provide insights for the design of more efficient catalysts for the one-pot transformation. Valeric acid is considered as a potential acid source from viewpoint of cost effectiveness and feasibility of such transformation with reasonable alkane yield. The both reaction mechanisms and kinetics will also be discussed to understand deeply how the selective C–C coupling and following C=O hydrogenation can be achieved.     

Hydrogen-bond-assisted transition-metal-free catalytic transformation of amides to esters

The amide C-N cleavage has drawn a broad interest in synthetic chemistry,biological process and pharmaceutical industry.Transition-metal,luxury ligand or excess base were always vital to the transformation.Here,we developed a transition-metalfree hydrogen-bond-assisted esterification of amides with only catalytic amount of base.The proposed crucial role of hydrogen bonding for assisting esterification was control experiments,density functional theory(DFT)calculations and kinetic studies.Besides broad substrate scopes and excellent functional groups tolerance,this base-catalyzed protocol complements the conventional transition-metal-catalyzed esterification of amides and provides a new pathway to catalytic cleavage of amide C–N bonds for organic synthesis and pharmaceutical industry.     

Transformations of N-arylpropiolamides to indoline-2,3-diones and acids via C≡C triple bond oxidative cleavage and C(sp^2)–H functionalization

A new palladium-catalyzed oxidative conversion of N-arylpropiolamides and H2O to various indoline-2,3-diones and acids through the C≡C triple bond cleavage and C(sp2)–H functionalization is described,which is promoted by a cooperative action of catalytic CuBr2,2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO)and O2.The method provides a practical tool for transformations of alkynes by means of a C–H functionalization strategy,which enables the formation of one C–C bond and multiple C–O bonds in a single reaction with high substrates compatibility and excellent functional group tolerance.     

Synthesis of unnatural amino acids through palladium-catalyzed C(sp~3)-H functionalization

Unnatural a-amino acids have been extensively used in the modern drug discovery and protein engineering studies. They have also found applications in the development of chiral molecular catalysts and the total synthesis of diverse natural products. Accordingly the development of cost-effective approaches for the preparation of unnatural a-amino acids has received increasing attentions. Among all the available methods for this purpose, direct C–H functionalization of simple amino acids represents one of the most attractive approaches because it exhibits good atom-economy and step-efficiency. In particular, selective functionalization of either the primary or secondary C(sp~3)–H bonds in the amino acids has been explored to make versatile C–C, C–N, C–O, C–B and C–F bonds to modify the side chain of amino acids and even peptides. The present review surveys the recent advances of synthesis of chiral unnatural a-amino acids and peptides through palladium-catalyzed functionalization of un-activated C(sp~3)–H bonds.     

Special Topic on Major Research Program: Catalysis Science for Carbon-based Energy Conversion

<正>The major research program,"Catalysis science for carbon-based energy conversion",from the national science foundation of China(NSFC)answers to the main strategic needs of China for the efficien use of carbon-based energy and targets to address the key scientifi issues involved in the catalytic interfaces.The research program aims to improve the catalytic activation of C–H and C–O bonds and the C–C coupling process,     

C–F bond activation under transition-metal-free conditions

The unique properties of fluorine-containing organic compounds make fluorine substitution attractive for the development of pharmaceuticals and various specialty materials, which have inspired the evolution of diverse C–F bond activation techniques.Although many advances have been made in functionalizations of activated C–F bonds utilizing transition metal complexes,there are fewer approaches available for nonactivated C–F bonds due to the difficulty in oxidative addition of transition metals to the inert C–F bonds. In this regard, using Lewis acid to abstract the fluoride and light/radical initiator to generate the radical intermediate have emerged as powerful tools for activating those inert C–F bonds. Meanwhile, these transition-metal-free processes are greener, economical, and for the pharmaceutical industry, without heavy metal residues. This review provides an overview of recent C–F bond activations and functionalizations under transition-metal-free conditions. The key mechanisms involved are demonstrated and discussed in detail. Finally, a brief discussion on the existing limitations of this field and our perspective are presented.     

Direct conversion of corn cob to formic and acetic acids over nano oxide catalysts

Considering energy shortage, large molecules in corn cob and easy separation of solid catalysts, nano oxides are used to transform corn cob into useful chemicals. Because of the microcrystals, nano oxides offer enough accessible sites for cellulose, hemicellulose and monosaccharide from corn cob hydrolysis and oxidant. Chemical conversion of corn cob to organic acids is investigated over nano ceria, alumina, titania and zirconia under various atmospheres. Liquid products are mainly formic and acetic acids. A small amount of other compounds, such as D-xylose,D-glucose, arabinose and xylitol are also detected simultaneously. The yield of organic acids reaches 25%–29% over the nano oxide of ceria,zirconia and alumina with 3 h reaction time under 453 K and 1.2 MPa O2. The unique and fast conversion of corn cob is directly approached over the nano oxides. The results are comparative to those of biofermentation and offer an alternative method in chemically catalytic conversion of corn cob to useful chemicals in a one-pot chemical process.     

纤维素催化转化为高附加值化学品的研究进展

Currently,under huge pressure from energy demands and environmental problems,much attention is being paid to biomass conversion,which will play an important role in meeting the requirements for a sustainable society.As the most abundant biomass on earth, cellulose is usually used as the first research target for biomass conversion.In this review,the recalcitrant structure of cellulose is discussed and non-catalytic hydrolysis by hot-compressed water and catalytic hydrolysis using solid acids are then considered.We also review the catalytic conversion of cellulose into valuable chemicals including hexitols(sorbitol and mannitol),ethylene glycol,and related compounds using various heterogeneous catalysts.     

Insight into the function of base-promoted Cu-containing catalysts for highly efficient hydrogenolysis of cellulose into polyols

The Cu-containing catalysts were synthesized via thermal treatment of the Cu Mg Al hydrotalcite with a fixed metal ratio at various calcination temperatures. The bi-functional solid base catalysts exhibited high activity for the hydrogenolysis of highly concentrated cellulose. The hydrotalcite precursors and the calcined samples were characterized by means of X-ray diffraction(XRD), thermogravimetric analysis(TG),N_2 adsorption–desorption, temperature-programmed reduction of H_2(H_2-TPR), temperature-programmed desorption of CO_2(CO_2-TPD) and dissociative N_2O adsorption. The characterization results indicated that the transformation of structure was caused by the increasing calcination temperature, which could further influence the numbers of the base sites and metal active sites in the CuMgAl catalysts. The hydrogenolysis of cellulose was systematically investigated over different catalytic systems. With the CuMgAl-600 catalyst, complete conversion of cellulose can be accomplished and the highest yield obtained is 81.4%,with total polyols yields obtained are 59.1% for the C2–C3 polyols. In addition, either the in-situ hydroxyl or the hydrated OH-due to the "memory effect" of hydrotalcite as Br?nsted bases, was proved to exhibit promotional effect on the hydrogenolysis of cellulose, which could effectively substitute the effect of ionizing alkali. Furthermore, it is noteworthy that the conversion of cellulose could maintain up to 90.2%with unobvious formation of coke-like precipitates when the cellulose concentration reached a high level of 18%.     

Direct and selective methanation of biomass via oxygenvacancy‐mediated catalysis

正Producing biofuels from renewable biomass resources is considered to be an effective way to reduce carbon emissions and is helpful for establishing sustainable society [1]. Bio‐methane (CH4) is a promising and available clean energy in the future owing to its properties such as high calorific values, low carbon emissions and full miscibility and interchangeability with natural gas or shale gas. Therefore, the production of me‐thane directly from waste biomass resources like straw is highly attractive. However, because of the robustness and vari‐ety of C–C bonds and C–O bonds existing in biomass molecules,it is very difficult to achieve high‐selective methanation of bio‐     

Recent advances in asymmetric synthesis with CO_2

Carbon dioxide(CO_2) is an important and appealing C1 building block in chemical synthesis due to its nontoxicity, abundance,availability and sustainability. Tremendous progress has been achieved in the chemical transformation of CO_2 into high valueadded organic chemicals. However, the asymmetric synthesis with CO_2 to form enantioenriched molecules, especially the catalytic process, has lagged far behind. The enantioselective incorporation of CO_2 into organic compounds is highly desirable,as the corresponding chiral products, such as carboxylic acids and amino acids, are common structural units in a vast array of natural products and biologically active compounds. Herein, we discuss recent progress toward the enantioselective incorporation of CO_2 into organic molecules, which mainly rely on three strategies: 1) kinetic resolution or desymmetrization of epoxides with CO_2 to form chiral cyclic carbonates and polycarbonates; 2) nucleophilic attack of O-or N-nucleophiles to CO_2 in tandem with asymmetric C–O bond formation to prepare chiral cyclic carbonates and carbamates; 3) direct enantioselective nucleophilic attack of organometallic reagents to CO_2 with asymmetric C–C bond formation. Finally, challenges and future outlook in this area are also presented.     

Visible-light-mediated external-reductant-free reductive cross coupling of benzylammonium salts with (hetero)aryl nitriles

Herein we report a novel visible-light-mediated external reductant-free reductive cross coupling for the construction of C sp~2–C sp~3 bonds. A variety of benzylammonium salts underwent selective coupling with(hetero)aryl nitriles to deliver important diarylmethanes under mild reaction conditions. Importantly, photocatalysts can be omitted for many cases, which might involve the electron donor acceptor(EDA) complex. Mechanistic studies indicated benzylic radicals might be involved as the key intermediates. Moreover, the in situ generated NMe_3 via cleavage of C–N bond in ammonium salts acts as the electron donor,thus avoiding the use of external-reductant.     

Catalytic enantioselective synthesis of β-amino alcohols by nitrene insertion

Chiral β-amino alcohols are important building blocks for the synthesis of drugs, natural products, chiral auxiliaries, chiral ligands and chiral organocatalysts. The catalytic asymmetric β-amination of alcohols offers a direct strategy to access this class of molecules. Herein, we report a general intramolecular C(sp~3)–H nitrene insertion method for the synthesis of chiral oxazolidin-2-ones as precursors of chiral β-amino alcohols. Specifically, the ring-closing C(sp~3)–H amination of N-benzoyloxycarbamates with 2 mol% of a chiral ruthenium catalyst provides cyclic carbamates in up to 99% yield and with up to 99% ee.The method is applicable to benzylic, allylic, and propargylic C–H bonds and can even be applied to completely non-activated C(sp~3)–H bonds, although with somewhat reduced yields and stereoselectivities. The obtained cyclic carbamates can subsequently be hydrolyzed to obtain chiral β-amino alcohols. The method is very practical as the catalyst can be easily synthesized on a gram scale and can be recycled after the reaction for further use. The synthetic value of the new method is demonstrated with the asymmetric synthesis of a chiral oxazolidin-2-one as intermediate for the synthesis of the natural product aurantioclavine and chiral β-amino alcohols that are intermediates for the synthesis of chiral amino acids, indane-derived chiral Box-ligands, and the natural products dihydrohamacanthin A and dragmacidin A.     

Electrochemically mediated decarboxylative acylation of N-nitrosoanilines with α-oxocarboxylic acids

An efficient palladium-catalyzed electrooxidation C–H acylation reaction of N-nitrosoanilines with α-oxocarboxylic acids was developed. The anodic oxidation of the Pd(Ⅱ) intermediate was found to be the key to complete the reaction. In this case, the N-nitroso group was observed to be an effective directing group for C–H activation reaction. Moreover, the synthetic transformation of derivatives of natural products(L-menthol, dehydroepiandrosterone, and pregnenolone) was successfully realized. Fi...     

凝结相中功能性碳材料和碳纳米复合物催化转化生物质制备可再生化学品(英文)

The production of chemicals from lignocellulosic biomass provides opportunities to synthesize chemicals with new functionalities and grow a more sustainable chemical industry. However, new challenges emerge as research transitions from petrochemistry to biorenewable chemistry. Compared to petrochemisty, the selective conversion of biomass-derived carbohydrates requires most catalytic reactions to take place at low temperatures ( 300 °C) and in the condensed phase to prevent reactants and products from degrading. The stability of heterogeneous catalysts in liquid water above the normal boiling point represents one of the major challenges to overcome. Herein, we review some of the latest advances in the field with an emphasis on the role of carbon materials and carbon nanohybrids in addressing this challenge.     

Insight into the formation mechanism of levoglucosenone in phosphoric acid-catalyzed fast pyrolysis of cellulose

The catalytic fast pyrolysis of cellulose impregnated with phosphoric acid (H_3PO_4) offers a promising method for the selective production of levoglucosenone (LGO),a valuable anhydrosugar product.However,the fundamental mechanism for selective LGO formation is unclear.Herein,quantum chemistry calculations and catalytic fast pyrolysis experiments were performed to reveal the formation mechanism of LGO in H3_PO_4-catalyzed cellulose pyrolysis.H_3PO_4 significantly decreased the energy barriers of the pyrolytic reactions and altered the competitiveness of the LGO formation pathways,promoting LGO formation.Through different pathways in the non-catalytic and H3P04-catalyzed conditions,LGO is mainly produced from the primary decomposition of glucose units of cellulose and secondary conversion of levoglucosan.The major catalytic formation pathways of LGO comprise similar reactions,with dehydration at the 3-OH+2-H site as the rate-determining step.Importantly,secondary conversion of 1,4;3,6-dianhydro-α-D-glucopyranose is not feasible for LGO formation,in contrast to previous reports.In addition,a high degree of polymerization is beneficial for the selectivity of LGO formation in the catalytic process,because the glycosidic bond is important for the formation of the bicyclic structure (1,5-and1,6-acetal rings).