Synergy of Lewis and Brønsted acids on catalytic hydrothermal decomposition of carbohydrates and corncob acid hydrolysis residues to 5-hydroxymethylfurfural

Efficient Conversion of Glucose to Hydroxymethylfurfural: One-pot Brønsted Base and Acid Promoted Selective Isomerization and Dehydration

Development of elegant, selective, and efficient strategies for the production of value-added platform chemicals from renewable feedstocks are in high demand to achieve the future needs and sustainable goals. In this context, an efficient acid-promoted synthesis of highly valuable hydroxymethylfurfural (HMF) has been demonstrated from glucose, a major constituent of lignocellulosic biomass. The major challenge in the conversion of glucose to HMF is the selective isomerization of glucose to ketose, which in the present work has been successfully addressed through the amine-mediated rearrangement of glucose to aminofructose under Amadori rearrangement. Importantly, subsequent dehydration step affords HMF and regenerates the amine employed in the first step, which could be readily recovered. In addition, scale-up and successful integration into one-pot synthesis of HMF proves the efficiency and applicability of the present transformation in large scale application. In addition, the method was also successfully extended to other monosaccharides and disaccharides to produce HMF.

Formic acid as a sacrificial agent for byproduct suppression in glucose dehydration to 5-hydroxymethylfurfural using NaY zeolite catalyst

Biomass-derived 5-hydroxymethylfurfural (HMF) holds potential for applications in green materials, but its conventional synthesis is hindered by undesired side reactions. This study presents a catalytic system that effectively suppresses the formation of byproducts, thus enhancing HMF yield. The system demonstrated synergistic effects between Lewis acid NaY zeolite and formic acid sacrificial agent for the production of HMF from glucose. The results indicate that formic acid reacts with reactive intermediates from glucose decomposition, preventing their interactions with other sugar-derived species in the dehydration path to HMF. Such effect originates from the neutral formic acid species rather than the dissociated acidic proton normally observed in Brønsted acid-catalyzed reactions. The NaY/formic acid catalysts in isopropanol/water achieved a 57% HMF yield, a significant improvement over 31% and 27% yields with NaY or formic acid alone, respectively. Moreover, performance of the spent catalysts was easily restored to the original state via a simple NaCl wash.

Efficient synthesis of furfurylamine from biomass via a hybrid strategy in an EaCl:Gly–water medium

The objective of this work was to develop an efficient approach for chemoenzymatically transforming biomass to furfurylamine by bridging chemocatalysis and biocatalysis in a deep eutectic solvent of EaCl:Gly–water. Using hydroxyapatite (HAP) as support, heterogeneous catalyst SO42−/SnO2–HAP was synthesized for transforming lignocellulosic biomass into furfural using organic acid as a co-catalyst. The turnover frequency (TOF) was correlated with the pKa value of the used organic acid. Corncob was transformed by oxalic acid (pKa = 1.25) (0.4 wt%) plus SO42−/SnO2–HAP (2.0 wt%) to produce furfural with a yield of 48.2% and a TOF of 6.33 h-1 in water. In deep eutectic solvent EaCl:Gly–water (1:2, v/v), co-catalysis with SO42−/SnO2–HAP and oxalic acid was utilized to transform corncob, rice straw, reed leaf, and sugarcane bagasse for the production of furfural with the yield of 42.4%–59.3% (based on the xylan content) at 180°C after 10 min. The formed furfural could be efficiently aminated to furfurylamine with E. coli CCZU-XLS160 cells in the presence of NH4Cl (as an amine donor). As a result of the biological amination of furfural derived from corncob, rice straw, reed leaf, and sugarcane bagasse for 24 h, the yields of furfurylamine reached >99%, with a productivity of 0.31–0.43 g furfurylamine per g xylan. In EaCl:Gly–water, an efficient chemoenzymatic catalysis strategy was employed to valorize lignocellulosic biomass into valuable furan chemicals.

Preparation of 5-(Acyloxymethyl)furfurals from Carbohydrates Using Zinc Chloride/Acetic Acid Catalyst System and Their Synthetic Value Addition

5-(Acyloxymethyl)furfurals (AMFs) have received considerable attention as hydrophobic, stable, and halogen-free congeners of 5-(hydroxymethyl)furfural (HMF) for synthesizing biofuels and biochemicals. In this work, AMFs have been prepared directly from carbohydrates in satisfactory yields using the combination of ZnCl₂ as the Lewis acid catalyst and carboxylic acid as the Brønsted acid catalyst. The process was initially optimized for 5-(acetoxymethyl)furfural (AcMF) and then extended to producing other AMFs. The effects of reaction temperature, duration, loading of the substrate, and dosage of ZnCl₂ on AcMF yield were explored. Fructose and glucose provided AcMF in 80% and 60% isolated yield, respectively, under optimized parameters (5 wt % substrate, AcOH, 4 equiv ZnCl₂, 100 °C, 6 h). Finally, AcMF was converted into high-value chemicals, such as 5-(hydroxymethyl)furfural, 2,5-bis(hydroxymethyl)furan, 2,5-diformylfuran, levulinic acid, and 2,5-furandicarboxylic acid in satisfactory yields to demonstrate the synthetic versatility of AMFs as carbohydrate-derived renewable chemical platforms.

Semisynthetic transformation of banana peel to enhance the conversion of sugars to 5-hydroxymethylfurfural

This study aimed to efficiently convert banana peels (BP) into 5-hydroxymethylfurfural (HMF) by using an integrated mechanoenzymatic/catalytic approach. There is no report on HMF production using mechanoenzymatic hydrolysis. Moreover, this method enables saccharification of lignocellulose without bulk solvents or pretreatment. The effects of the reaction volume, milling time, and reactive aging (RAging) on the mechanoenzymatic hydrolysis of BP were studied. The solvent-free enzymatic hydrolysis of BP under RAging conditions was found to provide higher glucose (40.5 wt%) and fructose (17.2 wt%) yields than chemical hydrolysis. Next, the conversion of the resulting monosaccharides into HMF in the presence of the AlCl₃·H₂O/HCl-DMSO/H₂O system resulted in 71.9 mol% yield, which is so far the highest HMF yield obtained from cellulosic food wastes. Under identical reaction conditions, direct conversion of untreated BP to HMF yielded 22.7 mol% HMF, suggesting that mechanoenzymatic hydrolysis greatly promotes the release of sugars from BP to improve HMF yield.

Soluble and reusable polymer-based catalysts with Brønsted and Lewis acidity for the one-pot synthesis of hydroxymethylfurfural from glucose

One-pot synthesis of hydroxymethylfurfural from glucose using polymer-based catalysts with Brønsted and Lewis acidity.

Rapid and efficient microwave-assisted guanidine hydrochloride deep eutectic solvent pretreatment for biological conversion of castor stalk

Microwave-assisted guanidine hydrochloride deep eutectic solvents (DESs) was developed for rapid and efficient pretreatment of castor stalk. The DES synthesized with guanidine hydrochloride and lactic acid showed a better delignification (92.02%) and enzymatic saccharification yield (96.3%) than choline chloride and lactic acid DES resulted. In addition, high-purity (up to 98%) lignin was recovered from the pretreatment liquor. The good recyclability of the guanidine hydrochloride-based DES was also proven with up to 90% cellulose hydrolysis with third-time recycled DES without post purification. The proposed microwave-assisted guanidine hydrochloride/lactic acid DES showed its great potentials as a highly effective and recyclable pretreatment solvent for future biorefinery strategies.

Direct conversion of cellulose to ethyl levulinate catalysed by modified fibrous mesoporous silica nanospheres in a co-solvent system

A KCC-1/Al–SO₃H catalyst with Si/Al = 5 was prepared to directly catalyse the synthesis of ethyl levulinate from cellulose in an ethanol/toluene co-solvent system. A reaction yield of 28.8 mol% was achieved after 6 h at 200 °C.

Structural Characterization and Antioxidant Activity of Milled Wood Lignin from Xylose Residue and Corncob

Xylose residue (XR), after diluted acid treatment of corncob, consists of cellulose and lignin. However, structural changes of XR lignin have not been investigated comprehensively, and this has seriously hindered the efficient utilization of lignin. In this study, corncob milled wood lignin (CC MWL), and xylose residue milled wood lignin (XR MWL) were isolated according to the modified milled wood lignin (MWL) method. The structural features of two lignin fractions were thoroughly investigated via fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and two dimensional nuclear magnetic resonance (2D NMR) spectroscopy techniques. XR MWL with higher yield and lower bound carbohydrate contents presented more phenolic OH contents than CC MWL due to partial cleavage of β-O-4. Furthermore, the molecular weights of XR MWL were increased, possibly because of condensation of the lignin during the xylose production. A study on antioxidant activity showed that XR lignin had better radical scavenging ability than that of 2,6-Di-tert-butyl-4-methyl-phenol (BHT) and CC MWL. The results suggested that the lignin in xylose residue, showing great antioxidant properties, has potential applications in food additives.

Cyclopentyl Methyl Ether (CPME): A Versatile Eco-Friendly Solvent for Applications in Biotechnology and Biorefineries

The quest for sustainable solvents is currently a matter of intense research and development, as solvents significantly contribute heavily to the waste generated by chemical industries. Cyclopentyl methyl ether (CPME) is a promising eco-friendly solvent with valuable properties such as low peroxide formation rate, stability under basic and acidic conditions, and relatively high boiling point. This Review discusses the potential use of CPME for applications in biotechnology (e.g., biotransformations, as solvent or cosolvent), biorefineries, and bioeconomy (e.g., for furan synthesis or as an extractive agent in liquid-liquid separations), as well as for other purposes, such as chromatography or peptide synthesis. Although CPME is currently produced by petrochemical means with a remarkably high atom economy, its biogenic production can be envisaged from substrates such as cyclopentanol or cyclopentanone, which can be derived from furfural or from (bio-based) adipic acid, respectively. The combination of the promising properties of CPME as a (co)solvent with a future (economic) biogenic origin would be advantageous for setting strategies aligned with the sustainable chemistry principles.

Cyclopentyl Methyl Ether: An Elective Ecofriendly Ethereal Solvent in Classical and Modern Organic Chemistry

Solvents represent one of the major contributions to the environmental impact of fine-chemical synthesis. As a result, the use of environmentally friendly solvents in widely employed reactions is a challenge of vast real interest in contemporary organic chemistry. Within this Review, a great variety of examples showing how cyclopentyl methyl ether has been established as particularly useful for this purpose are reported. Indeed, its low toxicity, high boiling point, low melting point, hydrophobicity, chemical stability towards a wide range of conditions, exceptional stability towards the abstraction of hydrogen atoms, relatively low latent heat of vaporization, and the ease with which it can be recovered and recycled enable its successful employment as a solvent in a wide range of synthetic applications, including organometallic chemistry, catalysis, biphasic reactions, oxidations, and radical reactions.

Efficient conversion of glucosamine to levulinic acid in a sulfamic acid-catalyzed hydrothermal reaction

Glucosamine is a monomer of chitosan, which is a biopolymer derived from the exoskeletons of crustaceans. This work investigated the conversion of glucosamine into the platform chemical levulinic acid (LA), in a sulfamic acid-catalyzed hydrothermal reaction. The optimized results of LA production showed that the conditions of 200 °C, 125 g L-1 glucosamine, 0.3 M sulfamic acid, and 15 min produced a 33.76 ± 0.19 mol% LA yield. The same conditions produced only 0.14 mol% 5-HMF yield. These results show that glucosamine is a potential bioresource to produce platform chemicals. Also, in the field of biofuels and chemical synthesis processes, the catalytic system using sulfamic acid is significant.

Influence of a Lewis acid and a Brønsted acid on the conversion of microcrystalline cellulose into 5-hydroxymethylfurfural in a single-phase reaction system of water and 1,2-dimethoxyethane

5-Hydroxymethylfurfural (HMF) is a typical dehydration product of C6 carbohydrates, and it can be converted into a series of chemicals and liquid fuels. In this study, an advanced low-boiling single-phase reaction system consisting of water and 1,2-dimethoxyethane (DMOE) was proposed for the production of HMF from microcrystalline cellulose (MCC). AlCl₃ and H₃PO₄ were selected as the Lewis acidic catalyst and Brønsted acidic catalyst, respectively, and the influence of these two catalysts on the conversion behavior of MCC was studied. The results showed that MCC could be selectively converted into HMF or levulinic acid (LA) by altering the solvent composition. As for the composition of the catalyst, high AlCl₃ content favored the generation of HMF, whereas high H₃PO₄ content could decrease the HMF yield and promote the formation of glucose and fructose. The highest HMF yield of 49.42% was obtained at an AlCl₃–H₃PO₄ ratio of 1 : 0.8. GC-MS analysis suggested that much MCC was transformed into furans and cyclopentenones in the presence of AlCl₃, while anhydrosugars tended to be generated with a high H₃PO₄ proportion in the catalyst. Besides, FTIR analysis of the insoluble humin formed during MCC conversion indicated that AlCl₃ could also facilitate the depolymerization of MCC.

An advanced single-phase reaction system consisting of water–DMOE solvent, AlCl₃ and H₃PO₄ for high-efficiency HMF production from cellulose.