Poly-benzylic ammonium chloride resins as solid catalysts for fructose dehydration

Organocatalytic Dehydration of Fructose-Based Carbohydrates into 5-Hydroxymethylfurfural in the Presence of a Neutral Inner Salt

A series of organic sulfonate inner salts, viz., aprotic imidazolium- and pyridinium-based zwitterions bearing sulfonate groups (-SO₃^-), were synthesized for the catalytic conversion of fructose-based carbohydrates into 5-hydroxymethylfurfural (HMF). The dramatic cooperation of both the cation and anion of inner salts played a crucial role in the HMF formation. The inner salts have excellent solvent compatibility, and 4-(pyridinium)butane sulfonate (PyBS) affords the highest catalytic activity with 88.2 and 95.1% HMF yields at almost full conversion of fructose in low-boiling-point protic solvent isopropanol (i-PrOH) and aprotic solvent dimethyl sulfoxide (DMSO), respectively. The substrate tolerance of aprotic inner salt was also studied through changing the substrate type, demonstrating its excellent specificity for catalytic valorization of fructose-moiety-containing C6 sugars, such as sucrose and inulin. Meanwhile, the neutral inner salt is structurally stable and reusable; after being recycled four times, the catalyst showed no appreciable loss of its catalytic activity. The plausible mechanism has been elucidated based on the dramatic cooperative effect of both the cation and sulfonate anion of inner salts. The noncorrosive, nonvolatile, and generally nonhazardous aprotic inner salt used in this study will benefit many biochemical-related applications.

One-Pot Tandem Transformation of Inulin as Fructose-Rich Platform Towards 5-Hydroxymethylfurfural: Feedstock Advantages, Acid-Site Regulation and Solvent Effects

The valorization of non-grain biomass feedstocks to value-added chemicals, polymers and alternative fuels is a crucial route for the utilization of renewable resources. Inulin belongs to a type of fructans, which is a pivotal platform bridging upstream fructose-rich biomass feedstocks typically represented by Jerusalem artichoke and downstream platform molecules such as alcohols, aldehydes and acids. Fructose can be directly obtained from the inulin hydrolysis and further converted into various platform chemicals, which is a more environmentally economical route than the conventional catalytic upgrading of cellulose. Nevertheless, most perspectives over the last decade have focused on the valorization of cellulose-derived carbohydrates, without much emphasis on the practical importance of one-pot transformation of inulin. In this review, we aim to demonstrate an efficient one-pot tandem transformation system of the inulin as fructose-rich platform towards 5-hydroxymethylfurfural (HMF). Core concerns are placed on elucidating the contributing roles of acid sites and solvents in enhancing the overall catalytic performance. The perspectives presented in this review may contribute to the innovation in the catalytic refining of fructose-rich non-grain biomass and the development of a greener biomass-based energy system.

Solvent Effects Enable Efficient Tandem Conversion of Cellulose and Its Monosaccharides Towards 5-Hydroxymethylfurfural

The biomass-derived platform compound 5-hydroxymethylfurfural (HMF) has been hailed as the "Sleeping Giant" due to its promising applications, and it occupies a critical spot in the biomass upgrading roadmap. HMF is typically produced from cellulose and its monosaccharides via a complex tandem conversion with multiple steps (i. e., cellulose depolymerization, glucose isomerization, fructose dehydration, etc.). Previous investigations have confirmed the irreplaceable contribution of solvents in regulating the tandem conversion of cellulose and its monosaccharides to HMF. However, the potential effects of solvents in contributing to this multi-step tandem process have not yet been clearly elucidated. In this context, this Review aims to provide in-depth insights into the intrinsic interactions between solvent system and substrate conversion (cellulose and its monosaccharides conversion), reaction regulation (reaction activity and selectivity regulation), as well as product acquisition (humins formation inhibition and product purification). It attempts to elucidate specific solvent effects to promote a more efficient tandem conversion of cellulose and its monosaccharides towards HMF. The insights provided in this Review may contribute to a more sustainable HMF production from biomass feedstocks and a further development of greener solvent systems.

Conversion of inulin-rich raw plant biomass to 2,5-furandicarboxylic acid (FDCA): Progress and challenge towards biorenewable plastics

The current commercial plastic manufactures have been produced using petroleum-based resource. However, due to concerns over the resource depletion and the environmental sustainability, bioresource-based manufacturing processes have been developed to cope against these concerns. Bioresource-derived 2,5-furandicarboxylic acid (FDCA) can be utilized as a building block material for plastic manufactures. To date, numerous technologies have been developed for the production of FDCA using various types of bio-based feedstocks such as hydroxymethylfurfural (HMF), 6-C sugars, and polysaccharides. The commercial companies produce FDCA using HMF-based production processes due to their high production efficiency, but the high price of HMF is a problem bottleneck. Our review affords important information on breakthrough approaches for the cost-efficient and sustainable production of FDCA using raw plant feedstocks rich in inulin. These approaches include bioprocessing technology based on the direct use of raw plant feedstocks and biomodification of the target plant sources. For the former, an ionic liquid-based processing system is proposed for efficient pretreatment of raw plant feedstocks. For the latter, the genes encoding the key enzymes; sucrose:sucrose 1-fructoyltransferase (1-SST), fructan:fructan 1-fryuctosyltransferase (1-FFT), fructan 1-exohydrolase (1-FEH), and microbe-derived endoinulinase, are introduced for biomodification conducive to facilitating bioprocess and improving inulin content. These approaches would contribute to cost-efficiently and sustainably producing bio-based FDCA.

LiCl-promoted-dehydration of fructose-based carbohydrates into 5-hydroxymethylfurfural in isopropanol

The carbohydrate-derived 5-hydroxymethylfurfural (HMF) is one of the most versatile intermediate chemicals, and is promising to bridge the growing gap between the supply and demand of energy and chemicals. Developing a low-cost catalytic system will be helpful to the production of HMF in industry. Herein, the commercially available lithium chloride (LiCl) and isopropanol (i-PrOH) are used to construct a cost-effective and low-toxic system, viz., LiCl/i-PrOH, for the preparation of HMF from fructose-based carbohydrates, achieving ∼80% of HMF yield under the optimum conditions. The excellent promotion effect of LiCl on fructose conversion in i-PrOH could be attributed to the synergistic effect of LiCl with i-PrOH through the LiCl-promoted and i-PrOH-aided dehydration process, and the co-operation of LiCl and i-PrOH for stabilizing the as-formed HMF by hydrogen/coordination bonds, giving a low activation energy of 68.68 kJ mol-1 with a pre-exponential factor value of 1.2 × 104 min-1. The LiCl/i-PrOH system is a substrate-tolerant and scalable catalytic system, fructose (scaled up 10 times), sucrose, and inulin also give 73.6%, 30.3%, and 70.3% HMF yield, respectively. Moreover, this system could be reused 8 times without significant loss of activity. The readily available and low-toxic LiCl, the sustainable solvent (i-PrOH), the renewable starting materials, and the mild reaction conditions make this system promising and sustainable for the industrial production of HMF in future.

Preparation of kapa carrageenan-based acidic heterogeneous catalyst for conversion of sugars to high-value added materials

A novel composite based on kappa-Carrageenan (κC) was prepared using N,N-methylene bisacrylamide (MBA) as the crosslinking agent. 5-Hydroxymethylfurfural (5-HMF) was produced by catalytic dehydration of fructose and glucose with MBA grafted κC (κC-g-MBA) as the solid acid catalyst due to sulfonic acid groups in biopolymer skeletons. Various reaction parameters such as optimization of the quantity of the catalyst, temperature, reaction time, and solvent were performed. It was established that for fructose dehydration, the best reaction conditions were the 160 °C as the optimized reaction temperature and 1 h reaction time, respectively. Under these conditions, the HMF yield and fructose conversion were 94.2% and 95.5%, respectively. Furthermore, 160 °C and 2 h were the best reaction temperature and reaction time for glucose dehydration, respectively. Under similar conditions, the HMF yield and glucose conversion are 47% and 93%, respectively. The catalyst was readily prepared from inexpensive materials with considerable reusability and reactivity.

Importance of the synergistic effects between cobalt sulfate and tetrahydrofuran for selective production of 5-hydroxymethylfurfural from carbohydrates

CoSO₄/THF can selectively catalyze conversion of fructose to HMF, which is a cost-effective route for production and separation of HMF.

Base-Assisted Conversion of Protonated d-Fructose to 5-HMF: Searching for Gas-Phase Green Models

A gas-phase investigation of the d-fructose dehydration reaction in the presence of base has been performed by the joint application of mass spectrometric techniques and theoretical calculations. Protonated addition products of d-fructose and base were generated in the gas phase by electrospray ionization using several bases of different proton affinity. The intermediates, products and decomposition channels were investigated by ion trap mass spectrometry. Electronic structure calculations allowed the identification of the ionic intermediates and products of a selected system containing NH₃, helping to rationalize the observed reaction pathways. The obtained results show that the final product, the protonated 5-hydroxymethyl-2-furaldheyde [5-HMF]H⁺, is better formed using selected bases and only if these remain clustered until the end of the dehydration process.

Transformation of corncob into furfural by a bifunctional solid acid catalyst

A transformation route was developed for the conversion of raw corncob into furfural by a Clbearing solid acid catalyst (HSCSO₃H) prepared by the hydrothermal carbonization and sulfonation of sucralose. The catalytic performances of HSCSO₃H in selected solvents were demonstrated and optimized, where a furfural yield of 90.8 mol% (20.9 wt%) was achieved at 448 K in 30 min in γ-valerolactone/water system. Interestingly, significant furfural yields were also obtained from cellulose. The effect of elevated temperature on furfural yield from high initial feedstock loading was also investigated. HSCSO₃H with COOH, phenolicOH, and Cl as binding sites and SO₃H as the catalytic site on its surface presents a bifunctional catalyst, and synergic effects of these functional groups, reaction solvent property and temperature are made responsible for the good catalytic performances. The catalytic strategy proposed in this study demonstrated an effective transformation of corncob into furfural with a high yield.

Highly Selective Deoxydehydration of Tartaric Acid over Supported and Unsupported Rhenium Catalysts with Modified Acidities

The deoxydehydration (DODH) of sugar acids to industrially important carboxylic acids is a very attractive topic. Oxorhenium complexes are the most-often employed DODH catalysts. Because of the acidity of the rhenium catalysts, the DODH products of sugar acids were usually in the form of mixture of free carboxylic acids and esters. Herein, we demonstrate strategies for the selective DODH of sugar acids to free carboxylic acids by tuning the Lewis acidity or the Brønsted acidity of the rhenium-based catalysts. Starting from tartaric acid, up to 97 % yield of free maleic acid was achieved. Based on our strategies, functional polymer immobilized heterogeneous rhenium catalysts were also developed for the selective DODH conversion of sugar acids.

One-Pot Conversion of Carbohydrates into Furan Derivatives via Furfural and 5-Hydroxylmethylfurfural as Intermediates

Recently, there has been growing interest in the transformation of renewable biomass into value-added fuels and chemicals. The catalytic conversion of naturally abundant carbohydrates can generate two-important furan chemicals: 5-hydroxymethylfurfural (HMF) from C6 carbohydrates and furfural from C5 carbohydrates. Both HMF and furfural have received great interest as precursors in the synthesis of commodity chemicals and liquid fuels. In recent years, a trend has emerged to integrate sequential catalytic processes involving multistep reactions for the direct one-pot transformation of carbohydrates into the aimed fuels and chemicals. One-pot reactions have remarkably unique and environmentally friendly benefits, including the fact that isolation and purification of intermediate compounds can be avoided. Herein, the present article aims to review recent advances in the one-pot conversion of carbohydrates into furan derivatives via furfural and HMF as intermediates. Special attention will be paid to the catalytic systems, mechanistic insight, reaction pathways, and catalyst stability. It is expected that this review will guide researchers to develop effective catalytic systems for the one-pot transformation of carbohydrates into furan derivatives.

Selective Conversion of 5-Hydroxymethylfuraldehyde Using Cp*Ir Catalysts in Aqueous Formate Buffer Solution

The highly selective hydrogenation/hydrolytic ring-opening reaction of 5-hydroxymethylfuraldehyde (5-HMF) was catalyzed by homogeneous Cp*Ir(III) half-sandwich complexes to produce 1-hydroxy-2,5-hexanedione (HHD). Adjustment of pH was found to regulate the distribution of products and reaction selectivity, and full conversion of 5-HMF to HHD with 99 % selectivity was achieved at pH 2.5. A mechanistic study revealed that the hydrolysis/ring-opening reaction of 2,5-bis-(hydroxymethyl)furan is the important intermediate reaction step. In addition, an isolated yield of 85 % for HHD was obtained in a 10 g-scale experiment, and the reaction with fructose as the starting material also led to a 98 % GC yield (71.9 % to fructose) of HHD owing to the excellent tolerance of the catalyst under acidic conditions.

Enzyme Mimics: Advances and Applications

Enzyme mimics or artificial enzymes are a class of catalysts that have been actively pursued for decades and have heralded much interest as potentially viable alternatives to natural enzymes. Aside from having catalytic activities similar to their natural counterparts, enzyme mimics have the desired advantages of tunable structures and catalytic efficiencies, excellent tolerance to experimental conditions, lower cost, and purely synthetic routes to their preparation. Although still in the midst of development, impressive advances have already been made. Enzyme mimics have shown immense potential in the catalysis of a wide range of chemical and biological reactions, the development of chemical and biological sensing and anti-biofouling systems, and the production of pharmaceuticals and clean fuels. This Review concerns the development of various types of enzyme mimics, namely polymeric and dendrimeric, supramolecular, nanoparticulate and proteinic enzyme mimics, with an emphasis on their synthesis, catalytic properties and technical applications. It provides an introduction to enzyme mimics and a comprehensive summary of the advances and current standings of their applications, and seeks to inspire researchers to perfect the design and synthesis of enzyme mimics and to tailor their functionality for a much wider range of applications.

One-pot synthesis of sulfonated graphene oxide for efficient conversion of fructose into HMF

Sulfonated graphene oxide prepared through a one-pot method shows excellent catalytic performance for the dehydration of fructose into 5-hydroxymethylfurfural.

Novel Ordered Mesoporous Carbon Based Sulfonic Acid as an Efficient Catalyst in the Selective Dehydration of Fructose into 5-HMF: the Role of Solvent and Surface Chemistry

Novel ionic liquid derived ordered mesoporous carbons functionalized with sulfonic acid groups IOMC-ArSO3H and GIOMC-ArSO3H were prepared, characterized, and examined in the dehydration reaction of fructose into 5-hydroxymethylfurfural (5-HMF) both in aqueous and nonaqueous systems. To study and correlate the surface properties of these carbocatalysts and some other SBA-15 typed solid acids with 5-HMF yield, hydrophilicity index (H-index) were employed in the fructose dehydration. Our study systematically declared that almost a criterion may be expected for application of solid acids in which by increasing H-index value up to 0.8 the HMF yield enhances accordingly. More increase in H-index up to 1.3 did not change the HMF yield profoundly. Although, it has been shown that the catalyst with larger H-index (∼1.3) resulted in higher activity both in aqueous and 2-propanol systems, during the recycling process deactivation occurs because of more water uptake and the catalysts with optimum amount of H-index (∼0.8) is more robust in the dehydration of fructose.

Selective aerobic oxidation of 5-HMF into 2,5-furandicarboxylic acid with Pt catalysts supported on TiO2 - and ZrO2 -based supports

Pt catalysts prepared over different metallic oxide supports were investigated in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in alkaline aqueous solutions with air, to examine the combined effect of the support and base addition. The base (nature and amount) played a significant role in the degradation or oxidation of HMF. Increasing amounts of the weak NaHCO3 base improved significantly the overall catalytic activity of Pt/TiO2 and Pt/ZrO2 by accelerating the oxidation steps, especially for the aldehyde group. This was highlighted by a proposed kinetic model that gave very good concentration-time fittings. Moreover, the promotion of the catalyst with bismuth yielded a PtBi/TiO2 catalytic system with improved activity and stability. Y2 O3  and La2 O3 ZrO2 -supported catalysts exhibited lower activity than Pt/ZrO2 , which suggests no cooperative effect of the weakly basic properties introduced and the homogeneous base. Quantitative oxidation of HMF (0.1 M) and high yields of FDCA (>99 %) were obtained in less than 5 h by using an HMF/Pt molar ratio of 100 and Na2 CO3 as a weak base over PtBi/TiO2 (Bi/Pt=0.22).

Carbonaceous microspheres prepared by hydrothermal carbonization of glucose for direct use in catalytic dehydration of fructose

Carbonaceous material prepared from the hydrothermal carbonization of glucose was used directly without any in situ functionalization or post-modification, and exhibited good catalytic activity for fructose dehydration to 5-hydroxymethylfurfural.

Aerobic oxidation of hydroxymethylfurfural and furfural by using heterogeneous Cox Oy -N@C catalysts

2,5-Furandicarboxylic acid (FDCA) is considered to be a promising replacement for terephthalic acid since they share similar structures and properties. In contrast to FDCA, 2,5-furandicarboxylic acid methyl (FDCAM) has properties that allow it to be easily purified. In this work, we reported an oxidative esterification of 5-hydroxymethylfurfural (HMF) and furfural to prepare corresponding esters over Cox Oy -N@C catalysts using O2 as benign oxidant. High yield and selectivity of FDCAM and methyl 2-furoate were obtained under optimized conditions. Factors which influenced the product distribution were examined thoroughly. The Cox Oy -N@C catalysts were recycled five times and no significant loss of activity was detected. Characterization of the catalysts could explain such phenomena. Using XPS and TGA, we made a thorough investigation of the effects of ligand and pyrolysis temperature on catalyst activity.