Prediction of Hydroxymethylfurfural Yield in Glucose Conversion through Investigation of Lewis Acid and Organic Solvent Effects

Designing solvent systems using self-evolving solubility databases and graph neural networks

Designing solvent systems is key to achieving the facile synthesis and separation of desired products from chemical processes, so many machine learning models have been developed to predict solubilities. However, breakthroughs are needed to address deficiencies in the model's predictive accuracy and generalizability; this can be addressed by expanding and integrating experimental and computational solubility databases. To maximize predictive accuracy, these two databases should not be trained separately, and they should not be simply combined without reconciling the discrepancies from different magnitudes of errors and uncertainties. Here, we introduce self-evolving solubility databases and graph neural networks developed through semi-supervised self-training approaches. Solubilities from quantum-mechanical calculations are referred to during semi-supervised learning, but they are not directly added to the experimental database. Dataset augmentation is performed from 11 637 experimental solubilities to >900 000 data points in the integrated database, while correcting for the discrepancies between experiment and computation. Our model was successfully applied to study solvent selection in organic reactions and separation processes. The accuracy (mean absolute error around 0.2 kcal mol-1 for the test set) is quantitatively useful in exploring Linear Free Energy Relationships between reaction rates and solvation free energies for 11 organic reactions. Our model also accurately predicted the partition coefficients of lignin-derived monomers and drug-like molecules. While there is room for expanding solubility predictions to transition states, radicals, charged species, and organometallic complexes, this approach will be attractive to predictive chemistry areas where experimental, computational, and other heterogeneous data should be combined.

Atomic Layer Deposition of the Geometry Separated Lewis and Brønsted Acid Sites for Cascade Glucose Conversion

Solid acid catalysts with bi-acidity are promising as workhouse catalysts in biorefining to produce high-quality chemicals and fuels. Herein, we report a new strategy to develop bi-acidic cascade catalysts by separating both acid sites in geometry via the atomic layer deposition (ALD) of Lewis acidic alumina on Brønsted acidic supports. Visualized by transmission electron microscopy and electron energy loss spectroscopy mapping, the ALD-deposited alumina forms a conformal alumina domain with a thickness of around 3 nm on the outermost surface of mesoporous silica-alumina. Solid state nuclear magnetic resonance investigation shows that the dominant Lewis acid sites distribute on the outermost surface, whereas intrinsic Brønsted acid sites locate inside the nanopores within the silica-rich substrate. In comparison to other bi-acidic solid catalyst counterparts, the special geometric distance of Lewis and Brønsted acid sites minimized the synergetic effect, leading to a cascade reaction environment. For cascade glucose conversion, the designed ALD catalyst showed a highly enhanced catalytic performance.

Photocatalytic conversion of sugars to 5-hydroxymethylfurfural using aluminium(III) and fulvic acid

5-hydroxymethylfurfural (HMF) is a valuable and essential platform chemical for establishing a sustainable, eco-friendly fine-chemical and pharmaceutical industry based on biomass. The cost-effective production of HMF from abundant C6 sugars requires mild reaction temperatures and efficient catalysts from naturally abundant materials. Herein, we report how fulvic acid forms complexes with Al³⁺ ions that exhibit solar absorption and photocatalytic activity for glucose conversion to HMF in one-pot reaction, in good yield (~60%) and at moderate temperatures (80 °C). When using representative components of fulvic acid, catechol and pyrogallol as ligands, 70 and 67% HMF yields are achieved, respectively, at 70 °C. Al³⁺ ions are not recognised as effective photocatalysts; however, complexing them with fulvic acid components as light antennas can create new functionality. This mechanism offers prospects for new green photocatalytic systems to synthesise a range of substances that have not previously been considered.

Catalytic Conversion of Carbohydrates into 5-Hydroxymethylfurfural by Phosphotungstic Acid Encapsulated in MIL-101 (Cr, Sn) Catalyst in Deep Eutectic Solvents

Herein, we report the synthesis of bimetal-organic frameworks (BMOFs) with both Brønsted and Lewis acidities, in which phosphotungstic acid (PTA) was encapsulated in BMOFs. It is efficient in converting starch to 5-hydroxymethyl-furfural (HMF) in deep eutectic solvents (DESs) such as choline chloride and formic acid. The highest yield of HMF (37.94%) was obtained using P_0.5/BMOFs_1.0 to catalyze starch in a mixed solvent system comprising DESs and ethyl acetate (EAC) (v/v; 2:3) at 180 °C and a reaction time of 10 min. Employing a DES as a cocatalyst and solvent reduced the use of organic solvents. The catalyst showed adequate reusability, and the HMF yield only decreased by 2.88% after six cycles of reuse compared with that of the initial catalyst. This study demonstrates the application potential of BMOFs in the conversion of biomass to useful molecules with commercial and/or research value.

Sulfonic acid functionalized β zeolite as efficient bifunctional solid acid catalysts for the synthesis of 5-hydroxymethylfurfural from cellulose

Introduction of the sulfonic acid group into H-β zeolite to prepare β-SO₃H bifunctional catalysts for the efficient synthesis of 5-hydroxymethylfurfural (HMF) from cellulose. Catalysts characterization, such as XRD, ICP-OES, SEM (Mapping), FTIR, XPS, N₂ adsorption-desorption isotherm, NH₃-TPD, Py-FTIR demonstrate the sulfonic acid group was successfully grafted onto the β zeolite. A superior HMF yield (59.4 %) and cellulose conversion (89.4 %) was obtained in the H₂O(NaCl)/THF biphasic system under 200 °C for 3 h with β-SO₃H(3) zeolite as catalyst. More valuable, β-SO₃H(3) zeolite converts other sugars and obtains ideal HMF yield, including fructose (95.5 %), glucose (86.5 %), sucrose (76.8 %), maltose (71.5 %), cellobiose (67.0 %), starch (68.1 %), glucan (64.4 %) and also converts plant material (25.1 % for moso bamboo and 18.7 % for wheat straw) with great HMF yield. β-SO₃H(3) zeolite catalyst keeps an appreciable recyclability after 5 cycles. Moreover, in the presence of β-SO₃H(3) zeolite catalyst, the by-products during the production of HMF from cellulose were detected, and the possible conversion pathway of cellulose to HMF was proposed. The β-SO₃H bifunctional catalyst has excellent potential for the biorefinery of high value platform compound from carbohydrates.

Conversion of Glucose to 5-Hydroxymethylfurfural Using Consortium Catalyst in a Biphasic System and Mechanistic Insights

We found an effective catalytic consortium capable of converting glucose to 5-hydroxymethylfurfural (HMF) in high yields (50%). The reaction consists of a consortium of a Lewis acid (NbCl5) and a Brønsted acid (p-sulfonic acid calix[4]arene (CX4SO3H)), in a microwave-assisted reactor and in a biphasic system. The best result for the conversion of glucose to HMF (yield of 50%) was obtained with CX4SO3H/NbCl5 (5 wt%/7.5 wt%), using water/NaCl and MIBK (1:3), at 150 °C, for 17.5 min. The consortium catalyst recycling was tested, allowing its reuse for up to seven times, while maintaining the HMF yield constant. Additionally, it proposed a catalytic cycle by converting glucose to HMF, highlighting the following two key points: the isomerization of glucose into fructose, in the presence of Lewis acid (NbCl5), and the conversion of fructose into HMF, in the presence of CX4SO3H/NbCl5. A mechanism for the conversion of glucose to HMF was proposed and validated.

Effects of environmental factors on the fleroxacin photodegradation with the identification of reaction pathways

The abuse of fluoroquinolones (FQs) antibiotics leads to bacterial resistance and environmental pollution, so it is of great significance to verify the decomposition mechanism for eliminating antibiotic efficiently and conveniently. The effects of various environmental factors and the fleroxacin (FLE) photodegradation mechanisms were investigated by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS), UV-Vis absorption spectroscopy, fluorescence spectroscopy and quantum chemical calculation. Six possible photodegradation reaction paths on T₁ (excited triplet state) were proposed and simulated. The departure of the piperazine ring and the substitution of F atom at C-6 position by OH group were determined as the main reactions based on the reaction rates and energy barriers of each path. The multi-pathway reactions resulted in the fastest photodegradation rates of FLE at pH 6-7 than other pH conditions. NaN₃ would promote FLE photodegradation by inhibiting the reverse reaction of the separation process of F atom at C-8 and the generation of biphenyl molecules, which was a novel and distinctive phenomenon in this report. ·OH would rapidly combine with the free radicals generated in photolysis processes and made a great contribution to FLE photodegradation. Ca²⁺, Mg²⁺ and Ba²⁺ could stabilize the carboxyl group to impede the photo-competitive process of the decarboxylation reaction, while NO₃^- could generate reactive oxygen species to promote photodegradation.

A Combined DFT, Energy Decomposition, and Data Analysis Approach to Investigate the Relationship Between Noncovalent Interactions and Selectivity in a Flexible DABCOnium/Chiral Anion Catalyst System

Developing strategies to study reactivity and selectivity in flexible catalyst systems has become an important topic of research. Herein, we report a combined experimental and computational study aimed at understanding the mechanistic role of an achiral DABCOnium cofactor in a regio- and enantiodivergent bromocyclization reaction. It was found that electron-deficient aryl substituents enable rigidified transition states via an anion-π interaction with the catalyst, which drives the selectivity of the reaction. In contrast, electron-rich aryl groups on the DABCOnium result in significantly more flexible transition states, where interactions between the catalyst and substrate are more important. An analysis of not only the lowest-energy transition state structures but also an ensemble of low-energy transition state conformers via energy decomposition analysis and machine learning was crucial to revealing the dominant noncovalent interactions responsible for observed changes in selectivity in this flexible system.

Selective Hydrogenolysis of 5-Hydroxymethylfurfural to 2-Hexanol over Au/ZrO2 Catalysts

2-Hexanol (2-HOL) is a versatile biomass-derived platform molecule for synthesis of liquid transportation fuels, lubricants, or detergents. Herein, a one-step preparation of 2-HOL using 5-hydroxymethylfurfural (HMF) as a substrate was reported for the first time. Several Au-based catalysts supported on different metal oxides were prepared to explore the relationship between carrier and catalytic activity. The results showed that the highest 2-HOL yield of 65.8 % was obtained at complete HMF conversion over the 5 %Au/ZrO₂ catalyst. The 5 %Au/ZrO₂ catalyst exhibited excellent durability after five consecutive recycling runs, while confirming its remarkable ring-opening hydrogenolysis on other biomass-derived furanics, furfural, with a total yield of 1-pentanol and 2-pentanol of 67.4 %. The distinguished ring-opening hydrogenolysis performance of the Au/ZrO₂ catalyst originated from a synergistic effect between the interfacial Au-O-Zr oxygen vacancies-induced Lewis acidic sites (activating C-OH/C=O bonds) and metallic Au (activating H₂ ). This work provides a possibility for producing 2-HOL from HMF with high yield, expanding the sustainable application of lignocellulosic biomass.

Exploring the effect of acid modulators on MIL-101 (Cr) metal–organic framework catalysed olefin-aldehyde condensation: a sustainable approach for the selective synthesis of nopol

Acid modulated synthesis of MIL-101(Cr) with tunable textural and surface acidic properties for highly selective synthesis of nopol.

Thermally Induced Silane Dehydrocoupling: Hydrophobic and Oleophilic Filter Paper Preparation for Water Separation and Removal from Organic Solvents

Organic solvents with high purity are essential in various fields such as optical, electronic, pharmaceutical, and chemical areas to prevent low-quality products or undesired side-products. Constructing methods to remove impurities such as water residue in organic solvents has been a significant challenge. Within this article, we report for the first time a new method for the preparation of hydrophobic and oleophilic filter paper (named OCFP), based on thermally induced silane dehydrocoupling between cellulose-based filter paper and octadecylsilane. We comprehensively characterized OCFP using various characterization techniques (FTIR, XPS, XRD, and EDS). OCFP showed super-hydrophobic and oleophilic properties as well as remarkable water separation and removal efficiency (>93%) in various organic solvents with sustained reusability. In addition, the analytical results both before and after filtration of an NMR solvent using OCFP indicated that OCFP has an excellent solvent drying efficiency. This work presents a new strategy for the development of super-hydrophobic cellulose-based filter paper, which has great potential for solvent drying and water separation.

Experimental and theoretical studies on glucose conversion in ethanol solution to 5-ethoxymethylfurfural and ethyl levulinate catalyzed by a Brønsted acid

The fundamental understanding of glucose conversion to 5-ethoxymethylfurfural (EMF) and ethyl levulinate (EL) (value-added chemicals from biomass) in ethanol solution catalyzed by a Brønsted acid is limited at present. Consequently, here, the reaction pathways and mechanism of glucose conversion to EMF and EL catalyzed by a Brønsted acid were studied, using an experimental method and quantum chemical calculations at the B3LYP/6-31G(D) and B2PLYPD3/Def2TZVP level under a polarized continuum model (PCM-SMD). By further verification through GC/MS tests, the mechanism and reaction pathways of glucose conversion in ethanol solution catalyzed by a Brønsted acid were revealed, showing that glucose is catalyzed by proton and ethanol, and ethanol plays a bridging role in the process of proton transfer. There are three main reaction pathways: through glucose and ethyl glucoside (G/EG), through fructose, 5-hydroxymethylfurfural (HMF), levulinic acid (LA), and EL (G/F/H/L/EL), and through fructose, HMF, EMF, and EL (G/F/H/E/EL). The G/F/H/E/EL pathway with an energy barrier of 20.8 kcal mol^-1 is considered as the thermodynamic and kinetics primary way, in which the reaction rate of this is highly related to the proton transfer in the isomerization of glucose to fructose. The intermediate HMF was formed from O5 via a ring-opening reaction and by the dehydration of fructose, and was further converted to the main product of EMF by etherification or by LA through hydrolysis. EMF and LA are both unstable, and can partially be transformed to EL. This study is beneficial for the insights aiding the understanding of the process and products controlling biomass conversion in ethanol solution.

Understanding the Effect of Solvent Environment on the Interaction of Hydronium Ion with Biomass Derived Species: A Molecular Dynamics and Metadynamics Investigation

The addition of aprotic solvents results in higher reactivities and selectivities in many key aqueous phase biomass reactions, including the acid-catalyzed conversion of fructose to 5-hydroxyl methyl furfural (HMF). The addition of certain co-solvents inhibits the formation of humins via preferential solvation of key functional groups and can alter reaction kinetics. An important factor in this context is the relative stability of the hydronium ion (the catalyst) in the vicinity of the biomass moiety as compared to that in bulk, as it could determine its efficacy in the protonation step. Hence, in the present work, molecular dynamics (MD) simulations of HMF (the model product) and fructose (the model reactant) in acidic water and water-DMSO mixtures are performed to analyze their interaction with the hydronium ions. We show that the presence of DMSO favors the interaction of the hydronium ion with fructose, whereas it has a detrimental effect on the interaction of hydronium ion with HMF. Well-tempered metadynamics (WT-MTD) simulations are performed to determine the relative stability of the hydronium ion in the immediate vicinity of fructose and HMF, as compared to that in the bulk solvent phase, as a function of solvent composition. We find that DMSO improves the stabilization of the hydronium ions in the first solvation shell of fructose compared to that in the bulk solvent. On the other hand, hydronium ions become less stable in the immediate vicinity of HMF, as the concentration of DMSO increases.

Conversion of Glucose to 5-Hydroxymethylfurfural, Levulinic Acid, and Formic Acid in 1,3-Dibutyl-2-(2-butoxyphenyl)-4,5-diphenylimidazolium Iodide-Based Ionic Liquid

The separation process between 5-hydroxymethylfurfural (HMF) and trace glucose in glucose conversion is important in the biphasic system (aqueous–organic phase), due to the partial solubility property of HMF in water. In addition, the yield of HMF via the dehydration reaction of glucose in water is low (under 50%) with the use of Brønsted acid as a catalyst. Therefore, this study was conducted to optimize the production and separation of products by using a new hydrophobic ionic liquid (IL), which is more selective than water. The new IL (1,3-dibutyl-2-(2-butoxyphenyl)-4,5-diphenyl imidazolium iodide) [DBDIm]I was used as a solvent and was optimized for the dehydration reaction of glucose to make a more selective separation of HMF, levulinic acid (LA), and formic acid (FA). [DBDIm]I showed high performance as a solvent for glucose conversion at 100 °C for 120 min, with a yield of 82.2% HMF, 14.9% LA, and 2.9% FA in the presence of sulfuric acid as the Brønsted acid catalyst.