Recent Advances in the Catalytic Synthesis of 2,5-Furandicarboxylic Acid and Its Derivatives

Hierarchical Nickel-Cobalt-Based Transition Metal Oxide Catalysts for the Electrochemical Conversion of Biomass into Valuable Chemicals

The upgrading of biomass into sustainable and valuable fine chemicals is an alternative to the use of state-of-the-art petrochemicals. The conversion of 5-hydroxymethylfurfural (HMF) biomass derivative into 2,5-furandicarboxylic acid (FDCA) has been recognized as an economical and green approach to replace the current polyethylene terephthalate based plastic industry. However, this reaction mostly relies on noble-metal-based catalysts for the sluggish aerobic oxidation of alcohol groups. In this work, we report a series of hierarchical Ni-Co-based transition metal oxide catalysts for HMF oxidation by electrocatalysis. Comprehensive material characterization and electrochemical evaluation have been performed. A 90 % FDCA yield, nearly 100 % Faradaic efficiency, and robust stability were achieved for NiCo₂ O₄ nanowires. As non-precious-metal catalysts, Ni-Co-based transition metal oxides may open up new potential materials for highly efficient electrochemical biomass upgrading.

Two furan-2,5-dicarboxylic acid solvates crystallized from dimethylformamide and dimethyl sulfoxide

Furan-2,5-dicarboxylic acid (FDCA) has been ranked among the top 12 bio-based building-block chemicals by the Department of Energy in the US. The molecule was first synthesized in 1876, but large-scale production has only become possible since the development of modern bio- and chemical catalysis techniques. The structures of two FDCA solvates, namely, FDCA dimethylformamide (DMF) disolvate, C₆H₄O₅·2C₃H₇NO, (I), and FDCA dimethyl sulfoxide (DMSO) monosolvate, C₆H₄O₅·C₂H₆OS, (II), are reported. Solvate (I) crystallizes in the orthorhombic Pbcn space group and solvate (II) crystallizes in the monoclinic P-1 space group. In (I), hydrogen bonds form between the carbonyl O atom in DMF and a hydroxy H atom in FDCA. Whilst in (II), the O atom in one DMSO molecule hydrogen bonds with hydroxy H atoms in two FDCA molecules. Combined with intermolecular S...O interactions, FDCA molecules form a two-dimensional network coordinated by DMSO.

Lipase-Catalyzed Synthesis of Furan-Based Oligoesters and their Self-Assembly-Assisted Polymerization

We investigate the synthesis of bio-based hydrophilic and hydrophobic oligoesters, which in turn are derived from easily accessible monomers from natural resources. In addition to the selection of renewable monomers, Novozyme 435, an immobilized lipase B from Candida antarctica was used for the oligomerization of monomers. The reaction conditions for oligomerization using Novozyme 435 were established to obtain a moderate-to-good yield. The average number of repeating units and the molecular weight distribution of hydrophilic and hydrophobic oligoester were identified by using NMR spectroscopy, gel-permeation chromatography, and MS. The oligoester derived from a hydrophilic monomer self-assembled to form a viscous solution, which upon further heating resulted in the formation of a polymer by the intermolecular Diels-Alder reaction. The viscosity of the solution and the assembly of oligoester to form a fibrous structure were investigated by using rheological studies, XRD, and SEM. The molecular weight of the cross-linked polymer was identified by using matrix-assisted laser desorption/ionization-MS. The thermal properties of the bio-based polymers were investigated by using thermogravimetric analysis and differential scanning calorimetry. For the first time, the self-assembly-assisted polymerization of an oligoester is reported using the intermolecular Diels-Alder reaction, which opens a new avenue in the field of polymer science.

Catalytic Transformation of Cellulose and Its Derivatives into Functionalized Organic Acids

Cellulose is a promising renewable and abundant resource for the production of high-value chemicals, in particular, organic oxygenates, because of its high oxygen/carbon ratio. The sustainable production of hydroxycarboxylic acids and dicarboxylic acids, such as gluconic/glucaric acid, lactic acid, 2,5-furandicarboxylic acid, adipic acid, and terephthalic acid, most of which are monomers of key polymers, have attracted much attention in recent years. The synthesis of these organic acids from cellulose generally involves several tandem reaction steps, and thus, multifunctional catalysts that can catalyze the selective activation of specific C-O or C-C bonds hold the key. This review highlights recent advances in the development of efficient catalytic systems and new strategies for the selective conversion of cellulose or its derived carbohydrates into functionalized organic acids. The reaction mechanism is discussed to offer deep insights into the regioselective cleavage of C-O or C-C bonds.

Electrochemical Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid (FDCA) in Acidic Media Enabling Spontaneous FDCA Separation

2,5-Furandicarboxylic acid (FDCA) has become an increasingly desirable platform chemical to replace terephthalic acid in the production of a variety of polymeric materials, including polyethylene terephthalate. FDCA can be produced by the oxidation of 5-hydroxymethylfurfural (HMF), which can be derived from cellulosic biomass. Oxidation of HMF to FDCA is typically performed under basic conditions. Separation of FDCA is most easily accomplished by lowering the pH until FDCA is insoluble and filtering it from solution. In a large-scale process, this would lead to a high operating cost to purchase the required acid and base and to dispose of the resulting salt waste. In this study, electrochemical oxidation of HMF was carried out in acidic media by using a manganese oxide (MnO_x ) anode to remove the need to vary the pH to separate FDCA. The MnO_x anode afforded a FDCA yield of 53.8 % in a pH 1 H₂ SO₄ solution, in which FDCA precipitation occurred spontaneously from the same reaction solution without altering the pH or other aspects of the solution composition. Electrochemical oxidation in acidic media offers a new pathway to convert HMF into maleic acid, which is another desirable biomass-derived platform molecule. The performance of the MnO_x anode was investigated in comparison with that of a Pt anode to identify unique electrocatalytic properties of the MnO_x anode for HMF oxidation.

Ruthenium Supported on High-Surface-Area Zirconia as an Efficient Catalyst for the Base-Free Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

Several ZrO₂ -supported ruthenium catalysts were prepared and utilized in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) under base-free conditions. Full conversion of HMF and almost perfect selectivity towards FDCA (97 %) were achieved after 16 h by using pure O₂ as an oxidant and water as a solvent. The catalytic tests show that the size of the Ru particles is crucial for the catalytic performance and that the utilization of high-surface-area ZrO₂ leads to formation of very small Ru particles. Superior activity was obtained for catalysts based on ZrO₂ that had been synthesized by a surface-casting method and has high surface areas up to 256 m²  g^-1 . In addition to good activity and selectivity, these catalysts show also high stability and constant activity upon recycling, confirming the suitability of Ru/ZrO₂ in the base-free oxidation of HMF.

Cobalt-metalloid alloys for electrochemical oxidation of 5-hydroxymethylfurfural as an alternative anode reaction in lieu of oxygen evolution during water splitting

The electrochemical water splitting commonly involves the cathodic hydrogen and anodic oxygen evolution reactions (OER). The oxygen evolution reaction is more energetically demanding and kinetically sluggish and represents the bottleneck for a commercial competitiveness of electrochemical hydrogen production from water. Moreover, oxygen is essentially a waste product of low commercial value since the primary interest is to convert electrical energy into hydrogen as a storable energy carrier. We report on the anodic oxidation of 5-hydroxymethylfurfural (HMF) to afford the more valuable product 2,5-furandicarboxylic acid (FDCA) as a suitable alternative to the oxygen evolution reaction. Notably, HMF oxidation is thermodynamically more favorable than water oxidation and hence leads to an overall improved energy efficiency for H₂ production. In addition, contrary to the “waste product O₂”, FDCA can be further utilized, e.g., for production of polyethylene 2,5-furandicarboxylate (PEF), a sustainable polymer analog to polyethylene terephthalate (PET) and thus represents a valuable product for the chemical industry with potential large scale use. Various cobalt–metalloid alloys (CoX; X = B, Si, P, Te, As) were investigated as potential catalysts for HMF oxidation. In this series, CoB required 180 mV less overpotential to reach a current density of 55 mA cm⁻² relative to OER with the same electrode. Electrolysis of HMF using a CoB modified nickel foam electrode at 1.45 V vs RHE achieved close to 100% selective conversion of HMF to FDCA at 100% faradaic efficiency.

Combinatorial synthetic pathway fine-tuning and comparative transcriptomics for metabolic engineering of Raoultella ornithinolytica BF60 to efficiently synthesize 2,5-furandicarboxylic acid

The compound 5-hydroxymethylfurfural (HMF) has attracted much attention due to its versatility as an important bio-based platform chemical. Here, we engineered Raoultella ornithinolytica BF60 as a whole-cell biocatalyst for a highly efficient synthesis of 2,5-furandicarboxylic acid (FDCA) from HMF. Specifically, various expression cassettes of key genes, such as hmfH (gene encoding HMF/furfural oxidoreductase [HmfH]) and hmfo (gene encoding HMF oxidase), were designed and constructed for fine-tuning FDCA synthesis from HMF. The FDCA titer reached 108.9 mM with a yield of 73% when 150 mM HMF was used as the substrate. This yield was 16% higher than that without balancing key gene expression in FDCA synthetic pathways. Additionally, to strengthen HmfH expression at the translational level, ribosomal binding site (RBS) sequences, which were computationally designed using the RBS calculator, were assembled into HmfH expression cassettes. The HmfH expression in the presence of these sequences enhanced FDCA titer to 139.6 mM with a yield of 93%. Next, previously unknown candidate genes, such as aldR, dkgA, akR, AdhP1, and AdhP2, which encode enzymes that catalyze the reactions leading to the formation of the undesired product 2,5-bis(hydroxymethyl)furan (HMF alcohol) from HMF, were identified by RNA-sequencing-based transcriptomics. Combinatorial deletion of these five candidate genes led to an 88% reduction in HMF alcohol formation and 12% enhancement in FDCA production (175.6 mM). Finally, FDCA synthesis was further improved by the substrate pulse-feeding strategy, and 221.5 mM FDCA with an 88.6% yield was obtained. The combinatorial synthetic pathway fine-tuning and comparative transcriptomics approach may be useful for improving the biocatalysis efficiency of other industrially useful compounds.

Sustainable Synthesis of Oxalic and Succinic Acid through Aerobic Oxidation of C6 Polyols Under Mild Conditions

The sustainable chemical industry encompasses a shift from the use of fossil carbon to renewable carbon. The synthesis of chemicals from nonedible biomass (cellulosic or oil) represents one of the key steps for "greening" the chemical industry. In this paper, we report the aerobic oxidative cleavage of C6 polyols (5-HMF, glucose, fructose and sucrose) to oxalic acid (OA) and succinic acid (SA) in water under mild conditions using M@CNT and M@NCNT (M=Fe, V; CNT=carbon nanotubes; NCNT=N-doped CNT), which, under suitable conditions, were recoverable and reusable without any loss of efficiency. The influence of the temperature, O₂ pressure (PO2 ), reaction time and stirring rate are discussed and the best reaction conditions are determined for an almost complete conversion of the starting material and a good OA yield of 48 %. SA and formic acid were the only co-products. The former could be further converted into OA by oxidation in the presence of formic acid, resulting in an overall OA yield of >62 %. This process was clean and did not produce organic waste nor gas emissions.

Creating a more robust 5-hydroxymethylfurfural oxidase by combining computational predictions with a novel effective library design

BACKGROUND

HMF oxidase (HMFO) from Methylovorus sp. is a recently characterized flavoprotein oxidase. HMFO is a remarkable enzyme as it is able to oxidize 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA): a catalytic cascade of three oxidation steps. Because HMF can be formed from fructose or other sugars and FDCA is a polymer building block, this enzyme has gained interest as an industrially relevant biocatalyst.

RESULTS

To increase the robustness of HMFO, a requirement for biotechnological applications, we decided to enhance its thermostability using the recently developed FRESCO method: a computational approach to identify thermostabilizing mutations in a protein structure. To make this approach even more effective, we now developed a new and facile gene shuffling approach to rapidly combine stabilizing mutations in a one-pot reaction. This allowed the identification of the optimal combination of seven beneficial mutations. The created thermostable HMFO mutant was further studied as a biocatalyst for the production of FDCA from HMF and was shown to perform significantly better than the original HMFO.

CONCLUSIONS

The described new gene shuffling approach quickly discriminates stable and active multi-site variants. This makes it a very useful addition to FRESCO. The resulting thermostable HMFO variant tolerates the presence of cosolvents and also remained thermotolerant after introduction of additional mutations aimed at improving the catalytic activity. Due to its stability and catalytic efficiency, the final HMFO variant appears to be a promising candidate for industrial scale production of FDCA from HMF.

Selective Hydrodeoxygenation of Alkyl Lactates to Alkyl Propionates with Fe-based Bimetallic Supported Catalysts

Hydrodeoxygenation (HDO) of methyl lactate (ML) to methyl propionate (MP) was performed with various base-metal supported catalysts. A high yield of 77 % MP was obtained with bimetallic Fe-Ni/ZrO₂ in methanol at 220 °C and 50 bar H₂ . A synergistic effect of Ni increased the yield of MP significantly when using Fe-Ni/ZrO₂ instead of Fe/ZrO₂ alone. Moreover, the ZrO₂ support contributed to improve the yield as a phase transition of ZrO₂ from tetragonal to monoclinic occurred after metal doping giving rise to fine dispersion of the Fe and Ni on the ZrO₂ , resulting in a higher catalytic activity of the material. Interestingly, it was observed that Fe-Ni/ZrO₂ also effectively catalyzed methanol reforming to produce H₂ in situ, followed by HDO of ML, yielding 60 % MP at 220 °C with 50 bar N₂ instead of H₂ . Fe-Ni/ZrO₂ also catalyzed HDO of other short-chain alkyl lactates to the corresponding alkyl propionates in high yields around 70 %. No loss of activity of Fe-Ni/ZrO₂ occurred in five consecutive reaction runs demonstrating the high durability of the catalyst system.

M3+O(–Mn4+)2 clusters in doped MnOx catalysts as promoted active sites for the aerobic oxidation of 5-hydroxymethylfurfural

M³⁺O(–Mn⁴⁺)₂ clusters in doped MnO_x catalysts are principal active sites that make oxygen ‘easy come, easy go’.

Improved production of 2,5-furandicarboxylic acid by overexpression of 5-hydroxymethylfurfural oxidase and 5-hydroxymethylfurfural/furfural oxidoreductase in Raoultella ornithinolytica BF60

2,5-Furandicarboxylic acid (FDCA) is a promising bio-based building block and can be produced by biotransformation of 5-hydroxymethylfurfural (HMF). To improve the FDCA production, two genes-one encoding HMF oxidase (HMFO; from Methylovorus sp. strain MP688) and another encoding for HMF/Furfural oxidoreductase (HmfH; from Cupriavidus basilensis HMF14)-were introduced into Raoultella ornithinolytica BF60. The FDCA production in the engineered whole-cell biocatalyst increased from 51.0 to 93.6mM, and the molar conversion ratio of HMF to FDCA increased from 51.0 to 93.6%.

Fabrication of mesoporous POMs/SiO2nanofibers through electrospinning for oxidative conversion of biomass by H2O2and oxygen

The oxidation process for mesoporous H₅PMo₁₀V₂O₄₀/SiO₂nanofiber catalyst.

Efficient conversion of 5-hydroxymethylfurfural to high-value chemicals by chemo- and bio-catalysis

5-hydroxymethylfurfural (HMF) is a very important versatile platform compound derived from renewable biomass.

Toward biomass-derived renewable plastics: Production of 2,5-furandicarboxylic acid from fructose

We report a process for converting fructose, at a high concentration (15 weight %), to 2,5-furandicarboxylic acid (FDCA), a monomer used in the production of polyethylene furanoate, a renewable plastic. In our process, fructose is dehydrated to hydroxymethylfurfural (HMF) at high yields (70%) using a γ-valerolactone (GVL)/H₂O solvent system. HMF is subsequently oxidized to FDCA over a Pt/C catalyst with 93% yield. The advantage of our system is the higher solubility of FDCA in GVL/H₂O, which allows oxidation at high concentrations using a heterogeneous catalyst that eliminates the need for a homogeneous base. In addition, FDCA can be separated from the GVL/H₂O solvent system by crystallization to obtain >99% pure FDCA. Our process eliminates the use of corrosive acids, because FDCA is an effective catalyst for fructose dehydration, leading to improved economic and environmental impact of the process. Our techno-economic model indicates that the overall process is economically competitive with current terephthalic acid processes.

Fe–Zr–O catalyzed base-free aerobic oxidation of 5-HMF to 2,5-FDCA as a bio-based polyester monomer

An environment-friendly and economical route for 5-hydroxymethylfurfural (HMF) aerobic oxidation to 2,5-furandicarboxylic acid (FDCA) in an ionic liquid (IL)-promoted base-free reaction system was reported using Fe–Zr–O as a catalyst.

Biocatalytic Valorization of Furans: Opportunities for Inherently Unstable Substrates

Biogenic furans (furfural and 5-hydroxymethylfurfural) are expected to become relevant building blocks based on their high degree of functionality and versatility. However, the inherent instability of furans poses considerable challenges for their synthetic modifications. Valorization routes of furans typically generate byproducts, impurities, wastes, and a cumbersome downstream processing, compromising their ecological footprint. Biocatalysis may become an alternative, given the high selectivity of enzymes, together with the mild reaction conditions applied. This Review critically discusses the options for enzymes in the upgrading of furans. Based on previous reports, a variety of biocatalytic transformations have been applied to furans, with successful cases both in aqueous and in water-free media. Options comprise the biodetoxification of toxic furans in hydrolysates, selective syntheses based on oxidation-reduction processes, solvent-free esterifications, or carboligations to afford C₁₂ derivatives. Reported strategies show in general promising but still modest productivities (2-30 g_product  L^-1  d^-1 , depending on the example). There are opportunities with high potential and deserving of further development, scale-up, and technoeconomic assessment, to entirely validate them as realistic alternatives.

Carbon Support Surface Effects in the Gold-Catalyzed Oxidation of 5-Hydroxymethylfurfural

Oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid is an important transformation for the production of bio-based polymers. Carbon-supported gold catalysts hold great promise for this transformation. Here we demonstrate that the activity, selectivity, and stability of the carbon-supported gold nanoparticles in the oxidation of 5-hydroxymethylfurfural strongly depend on the surface properties of the carbon support. Gold nanoparticles supported on basic carbon materials with a low density of functional groups demonstrate higher activity in 5-hydroxymethylfurfural oxidation (TOF_Au up to 1195 h^-1), higher selectivity to 2,5-furandicarboxylic acid, and better stability in comparison to gold nanoparticles supported on carbon materials with acidic surface groups. Surface groups of basic carbon supports that are positively charged under the reaction conditions result in a higher adsorption and local concentration of hydroxyl ions, which act as cocatalysts for gold and enhance gold-catalyzed dehydrogenation. Negatively charged surface groups of acidic carbons repel hydroxyls and the intermediate monoacid anions, which leads to lower reaction rates and a high selectivity toward 2,5-hydroxymethylfurancarboxylic acid. Understanding the role of support surface charge and local hydroxyl anion concentration provides a basis for the rational design of the optimal carbon support surface chemistry for highly active, selective, and stable catalysts for the oxidation of 5-hydroxymethylfurfural and related reactions.

A facile and effective method for preparation of 2.5-furandicarboxylic acid via hydrogen peroxide direct oxidation of 5-hydroxymethylfurfural

In this paper, 2,5-furandicarboxylic acid (FDCA) was efficiently prepared by the direct oxidation of 5-hydroxymethylfurfural (5-HMF) using hydrogen peroxide (H2O2) in alkaline conditions without any catalysts. The effects of reaction parameters on the process were systematically investigated and the optimal parameters were obtained as follows: molar ratio of 5-HMF:KOH:H2O2 was 1:4:8, reaction temperature and reaction time were determined as 70°C and 15 minutes, respectively. Under these conditions, the yield of FDCA was 55.6% and the purity of FDCA could reach 99%. Moreover, we have speculated the detailed oxidation mechanism of 5-HMF assisted by hydrogen peroxide in alkaline condition to synthesize FDCA.

Porous Zirconium-Furandicarboxylate Microspheres for Efficient Redox Conversion of Biofuranics

Biofuranic compounds, typically derived from C₅ and C₆ carbohydrates, have been extensively studied as promising alternatives to chemicals based on fossil resources. The present work reports the simple assembly of biobased 2,5-furandicarboxylic acid (FDCA) with different metal ions to prepare a range of metal-FDCA hybrids under hydrothermal conditions. The hybrid materials were demonstrated to have porous structure and acid-base bifunctionality. Zr-FDCA-T, in particular, showed a microspheric structure, high thermostability (ca. 400 °C), average pore diameters of approximately 4.7 nm, large density, moderate strength of Lewis-base/acid centers (ca. 1.4 mmol g^-1 ), and a small number of Brønsted-acid sites. This material afforded almost quantitative yields of biofuranic alcohols from the corresponding aldehydes under mild conditions through catalytic transfer hydrogenation (CTH). Isotopic ¹ H NMR spectroscopy and kinetic studies verified that direct hydride transfer was the dominant pathway and rate-determining step of the CTH. Importantly, the Zr-FDCA-T microspheres could be recycled with no decrease in catalytic performance and little leaching of active sites. Moreover, good yields of C₅ (i.e., furfural) or C₄ products [i.e., maleic acid and 2(5H)-furanone] could be obtained from furfuryl alcohol without oxidation of the furan ring over these metal-FDCA hybrids. The content and ratio of Lewis-acid/base sites were demonstrated to dominantly affect the catalytic performance of these redox reactions.

Heterogeneously-Catalyzed Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid with MnO2

A simple non-precious-metal catalyst system based on costeffective and ubiquitously available MnO₂ , NaHCO₃ , and molecular oxygen was used to convert 5-hydroxymethylfurfural (HMF) to 2,5-difurandicarboxylic acid (FDCA) as a bioplastics precursor in 91 % yield. The MnO₂ catalyst could be recovered by simple filtration and reused several times. The present system was also applicable to the aerobic oxidation of other biomass-derived substrates and the gram-scale oxidation of HMF to FDCA, in which 2.36 g (86 % yield) of the analytically pure FDCA could be isolated.