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The Fischer-Helferich glycosidation reaction is generally the initial step in the conversion of glucose to levulinate in alcohol media. However, the relevant molecular mechanism catalyzed by Al-based catalysts is still not well understood. In this work, the reaction mechanism of the glycosidation from glucose to methyl glycosides catalyzed by Al

The reaction mechanism of the conversion of methyl levulinate (ML) to γ-valerolactone (GVL) catalyzed by Al(OiPr)3 has been probed using DFT calculations.

Shell biorefinery is an emerging concept that upcycles the major components of crustacean shell waste, such as chitin, into value-added chemicals and materials. Producing biomass-derived 5-hydroxymethylfurfural (HMF) is a hot...

Ionic liquids (ILs) had shown a great catalytic effect in the conversion of fructose to 5-hydroxymethylfurfural (HMF), but the dehydration mechanism remains ambiguous. In this work, density functional theory (DFT)...

The catalytic hydrolysis/alcoholysis of biomass carbohydrates into levulinic acid/levulinate esters (alkyl levulinates) as green biofuels and value-added chemicals holds great promise for achieving the goals of sustainable chemistry. Bifunctional catalysts...

Cellulose can be dissolved in ionic liquids (ILs) and it can be recovered by adding anti-solvent such as water or alcohol. Besides, the regenerated cellulose can be used for textiles, degradable membranes, hydrogels/aerogels, etc. But the regenerated mechanism of cellulose remains ambiguous. In this work, a Density Functional Theory (DFT) calculation is reported for the cellulose regeneration from a cellulose/1-n-butyl-3-methylimidazolium acetate (BmimOAc)/water mixture. To investigate the microcosmic effects of the anti-solvents, we analyzed the structures and H-bonds of BmimOAc-nH2O and cellobiose-ILs-nH2O (n = 0–6) clusters. It can be found that when n ≥ 5 in the BmimOAc-nH2O clusters, the solvent-separated ion pairs (SIPs) play a dominant position in the system. With the increasing numbers of water molecules, the cation-anion interaction can be separated by water to reduce the effects of ILs on cellulose dissolution. Furthermore, the BmimOAc-nH2O and cellobiose-ILs (n = 0–6) clusters tend to be a more stable structure with high hydration in an aqueous solution. When the water molecules were added to the system, H-bonds can be formed among H2O, the hydroxyl of cellulose, and the oxygen of OAc. Therefore, the interactions between cellobiose and ILs will be decreased to promote cellulose regeneration. This work would provide some help to understand the mechanism of the cellulose regeneration from the view of theoretical calculation.

The experiments on cellulose dissolution/regeneration have made some achievements to some extent, but the mechanism of cellulose regeneration in ionic liquids (ILs) and anti-solvent mixtures remains elusive. In this work, the cellulose regeneration mechanism in different anti-solvents, and at different temperatures and concentrations, has been studied with molecular dynamics (MD) simulations. The IL considered is 1-ethyl-3-methylimidazolium acetate (EmimOAc). In addition, to investigate the microcosmic effects of ILs and anti-solvents, EmimOAc-nH2O (n = 0–6) clusters have been optimized by Density Functional Theory (DFT) calculations. It can be found that water is beneficial to the regeneration of cellulose due to its strong polarity. The interactions between ILs and cellulose will become strong with the increase in temperature. The H-bonds of cellulose chains would increase with the rising concentrations of anti-solvents. The interaction energies between cellulose and the anions of ILs are stronger than that of cations. Furthermore, the anti-solvents possess a strong affinity for ILs, cation–anion pairs are dissociated to form H-bonds with anti-solvents, and the H-bonds between cellulose and ILs are destroyed to promote cellulose regeneration.

Biomass-derived γ-valerolactone (GVL) is a versatile chemical that can be used in various fields. As an efficient, cheap, and sustainable catalyst, Al(OiPr)

Ionic liquids (ILs) have shown high catalytic activity in the degradation of poly(ethylene terephthalate) (PET), but the effects of the anions and cations, as well as the mechanism, remain ambiguous. Glycolysis is an important recycling method that converts waste PET into monomers through various chemical reactions. To reveal the role of ILs and the molecular mechanism of the glycolysis of PET, density functional theory (DFT) calculations have been carried out for the possible pathways for the generation of bis(hydroxyethyl)terephthalate (BHET) catalyzed by isolated anions/cations and ion pairs at different sites. The pathway with the lowest barrier for the glycolysis of PET is the cleavage of the C–O ester bond, which generates the BHET monomer. The synergistic effects of the cations and anions play a critical role in the glycolysis of PET. The cations mainly attack the carbonyl oxygen of PET to catalyze the reaction, and the anions mainly form strong H-bonds with PET and ethylene glycol (EG). In terms of the mechanism, the H-bonds render the hydroxyl oxygen of EG more electronegative. The cation coordinates the carbonyl oxygen of the ester, and the hydroxyl oxygen of EG attacks the ester group carbon of PET, with proton transfer to the carbonyl oxygen. A four-membered-ring transition state would be formed by PET, EG, and the IL catalyst, which regularly accelerates the degradation of PET. These results provide fundamental help in understanding the roles of ILs and the mechanism of IL-catalyzed PET degradation.

Keggin-type polyoxometalate derived ionic liquids (POM-ILs) have recently been presented as effective solvent systems for biomass delignification. To investigate the mechanism of lignin dissolution in POM-ILs, the system involving POM-IL ([C4C1Im]3[PW12O40]) and guaiacyl glycerol-β-guaiacyl ether (GGE), which contains a β-O-4 bond (the most dominant bond moiety in lignin), was studied using quantum mechanical calculations and molecular dynamics simulations. These studies show that more stable POM-IL structures are formed when [C4C1Im]+ is anchored in the connecting four terminal oxygen region of the [PW12O40]3- surface. The cations in POM-ILs appear to stabilize the geometry by offering strong and positively charged sites, and the POM anion is a good H-bond acceptor. Calculations of POM-IL interacting with GGE show the POM anion interacts strongly with GGE through many H-bonds and π-π interactions which are the main interactions between the POM-IL anion and GGE and are strong enough to force GGE into highly bent conformations. These simulations provide fundamental models of the dissolution mechanism of lignin by POM-IL, which is promoted by strong interactions of the POM-IL anion with lignin.

The catalytic isomerization of glucose to fructose has been deemed a vital step in biorefinery, while the isomerization mechanism in alcoholic media still remains ambiguous. Hereby, density functional theory (DFT) calculations were carried out to investigate the isomerization mechanism of glucose over aluminum-based catalysts in methanol media. Al3+ was apt to coordinate with methanol and cyclic β-d-glucose (CDG) to form various complexes. It was found that [Al(CH3O)2(CH3OH)2]+ was the most stable one in +1 charge complexes based on the DFT calculations and ESI-MS experiments. Furthermore, the four-coordination complex [(η2O4,O6-CDG)Al(CH3O)2]+ was predicted to be the most preferable. Ionic species formed between Al3+ and the solvent can further assemble with glucose to catalyze the isomerization. The isomerization proceeds mainly by three steps, including ring-opening, hydride shift, and ring-closing with the migration of H from the C2–H to the O1–H bond (hydride shift) as the rate-determining step. The ...

The use of 2,5-dimethylfuran (DMF) and acrylic acid (AA) as the reactants to produce aromatics catalyzed by Bronsted acid ionic liquids (ILs) has been achieved successfully under mild conditions. The whole conversion process including Diels–Alder (D–A) cycloaddition, ring-opening/decarboxylation, and dehydration was investigated by density functional theory (DFT) calculations which were also verified by experiments. Two pathways for the activation of DMF were proposed: unprotonated oxygen of the DMF (UPOD) and direct protonated oxygen of the DMF (POD). In the UPOD pathways, two routes (endo and exo), in which the overall rate was limited by the ring-opening step, produce p-xylene or 2,5-dimethylbenzoic acid (DMBA), respectively, whereas in POD pathways, the limiting step of DMBA production was attributed to the D–A cycloaddition. The role of Bronsted acid ILs was mainly reflected in the proton transferability. The present study provides basic aids to understand the mechanism of converting furanics and AA ...

Aerogels derived from corn stalks are promising materials for wide use, due to their biodegradability and biocompatibility. However, preparation of cellulose-rich aerogels directly from corn stalks is a tedious and complicated process. In this study, generation of cellulose-rich aerogels was achieved by a facile approach relying on an ionic liquid and amido-sulfonic acid used as solvents. By this method, cellulose-rich aerogels were directly obtained from corn stalks through a process whereby lignin was separated from the other components of the corn stalks in one step, an approach simplifying the traditional fabrication processes. The composition, morphology and thermal stability of the obtained aerogels were investigated as they were related to the ionic liquid solvent systems used. Furthermore, the dye adsorption mechanism of cellulose-rich aerogels was simulated. In the most favourable case, the obtained aerogel was free of lignin and had the cellulose content as high as 88.1%. In addition, the aerogel possessed a porous three-dimensional structure with a high specific area (201 m2 g−1) and good thermal stability. Owing to its excellent properties, this cellulose-rich porous aerogel is expected to have a potential use in dye adsorption and other fields. This aerogel displayed an absorption capacity of 549 mg g−1 for Congo red and 302 mg g−1 for Coomassie brilliant blue.

Recycling of discarded polyethylene terephthalate (PET) is an important issue for both environmental protection and resource conservation purposes. In this work, a dissolution-degradation strategy has been developed for recycling PET by adding solvents such as aniline, nitrobenzene, 1-methyl-2-pyrrolidinone (NMP), or dimethyl sulfoxide (DMSO) into the traditional PET glycolysis system. The results show that the conversion of PET reaches 100% and the yield of monomer bis(hydroxyalkyl) terephthalate (BHET) reaches 82% during 1 min with zinc acetate as catalyst in DMSO at 463 K. Importantly, this strategy can be applied to a variety of catalysts. The simulation and in situ IR results indicate that the π–π interaction between PET and aromatic solvents plays a key role in PET dissolution, which leads to fast degradation. This promising dissolution-degradation strategy can improve the glycolysis efficiency of PET dramatically and may be applied to the degradation process of other polyesters.

Cellulose/zinc oxide (ZnO) aerogels are traditionally produced using methods harmful to the environment because of the acids and alkalis that are involved in the production process. This study repo...

Ionic liquids (ILs) present superior catalytic performance in the glycolysis of ethylene terephthalate (PET). To investigate the microscopic degradation mechanism of PET, density functional theory (DFT) calculations have been carried out for the interaction between ILs and dimer, which is considered to symbolize PET. We found that hydrogen bonds (H-bonds) play a critical role in the glycolysis process. In this study, 24 kinds of imidazolium-based and tertiary ammonium-based ILs were used to study the effect of different anions and cations on the interaction with PET. Natural bond orbital (NBO) analysis, atoms in molecules (AIM) and reduced density gradient (RDG) approaches were employed to make in-depth study of the nature of the interactions. It is concluded that the interaction of cations with dimer is weaker than that of anions and when the alkyl chain in the cations is replaced by an unsaturated hydrocarbon, the interaction will become stronger. Furthermore, anions play more important roles than cations in the actual interactions with dimer. When the hydrogen of methyl is replaced by hydroxyl or carboxyl, the interaction becomes weak for the amino acid anions and dimer. This work also investigates the interaction between dimer and ion pairs, with the results showing that anions play a key role in forming H-bonds, while cations mainly attack the oxygen of carbonyl and have a π-stacking interaction with dimer. The comprehensive mechanistic study will help researchers in the future to design an efficient ionic liquid catalyst and offer a better understanding of the mechanism of the degradation of PET.

An intriguing p-n conversion of thermoelectric property was observed in a water-ionic liquid ([EMIm][Ac]) binary system with precise control over water content. The highest p-type and n-type Seebeck coefficient were optimized at water-[EMIm][Ac] molar ratio of 2:1 and 4:1, respectively. DFT calculation illustrates that a configuration of solvent separation ion pairs is preferred at the water-[EMIm][Ac] molar ratio of 4:1, leading to the p-n conversion through weakening interaction between anion clusters and gold electrodes. Furthermore, p-n thermocapacitive converters were integrated to enhance the output Seebeck voltages. This work opens up new perspectives for harvesting low grade heat with the use of fluidic materials.

As a new kind of solvent and catalyst, the functionalized ionic liquids (ILs) had been successfully used in the conversion of fructose to high value-added biofuels. In this work, a detailed density functional theory (DFT) calculation had been carried out to investigate the interactions of fructose-ILs system. To study the effect of different anions and cations on the interaction with fructose, 25 different kinds of functionalized imidazolium-based ILs were calculated by using M06-2X-D3/6-311 + G** level. It was found that the interaction energies of fructose-anions were higher than those of the fructose-cations. The interaction will become stronger for the fructose and ILs when the alkyl chain of imidazolium-based cations was replaced with a functional group (COOH, OH or HSO3). However, when the length of the alkyl chain increased, it will result in a decrease in interaction energy due to the steric effect. In the anions (Y–SO3), the greater electronegativity of SO3 will lead to strong interaction with fructose. Also, this work simulates the interaction of fructose and ion pairs, with the results showing that hydrogen bonds (H-bonds) and π-stacking play an important role in the system. The present study provided basic aids to understand the structures and noncovalent interaction of fructose and functionalized ILs as well as the microscopic mechanism of fructose dissolution in the ILs.

Correction for ‘Efficient transformation of CO2 to cyclic carbonates using bifunctional protic ionic liquids under mild conditions’ by Xianglei Meng et al., Green Chem., 2019, 21, 3456–3463, DOI: 10.1039/C9GC01165J.

The high-efficiency synthesis of biofuel γ-valerolactone (GVL) from biomass-derived levulinates is a challenging task. The Meerwein-Ponndorf-Verley (MPV) reduction with its extraordinary chemoselectivity is advantageous for the hydrogenation process, compared to the molecular-hydrogen-based process using noble metal catalysts. Therefore, we used a classical Al-based isopropoxide to catalyze transfer hydrogenation (CHT) of methyl levulinate (ML) to GVL. A high yield of GVL up to 97.6% could be achieved using 2-proponal as the H-donor and solvent under mild conditions (150 °C, 30 min). Besides, three reaction stages were observed in the conversion, including transesterification, hydrogenation and cyclization. LC/MS analysis and the density functional theory (DFT) caculations revealed that Al atom of Al(OiPr)3 as the electron transfer center activated ester carbonyl of the substrate via four-membered transition states before activating the ketone carbonyl, resulting in the occurrence of transesterification prior to the hydrogenation. In addition, 2-propanol as proton transfer carrier assisting the cyclization process was proved to be the lowest-energy pathway. Our work shed light on the role of Al (OiPr)3 in the MPV reduction of ML, providing a comprehensive understanding on the metal alkoxide catalysis mechanism for GVL production.

A series of 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU) based bifunctional protic ionic liquids (DBPILs) were easily prepared by acid–base reactions at room temperature. They were used to catalyze the cycloaddition reaction of CO2 with epoxides under mild conditions. As a metal free catalyst, the best DBPIL showed a 92% yield of products within 6 hours at 30 °C and 1 bar CO2 without any solvents and co-catalysts. It could afford carbonates in good yields with broad epoxide substrate scope and CO2 from simulated flue gas (15% CO2/85% N2). IR spectroscopy and DFT studies were carried out to investigate the mechanism of the cycloaddition reaction. The results showed that the DBPILs could activate both CO2 and epoxides by alkoxy anions and powerful hydrogen-bonding, which was well consistent with experiments.