Feasibility of enhancing production of 5-hydroxymethylfurfural using deep eutectic solvents as reaction media in a high-pressure reactor

Pd-Catalyzed Miyaura Borylation and Telescopic Borylation/Suzuki-Miyaura Cross-Coupling Processes in Deep-Eutectic Solvents

We report an efficient procedure to carry out palladium-catalyzed Miyaura borylation reactions of (hetero)aromatic halides and triflates in choline chloride (ChCl)-based deep eutectic solvents (DESs). The procedure employs bis(pinacolato)diboron as a boron source and a catalyst prepared in situ from readily available Pd2(dba)3 and the phosphine ligand XPhos. Reactions proceed well in different ChCl-based DESs, among which the best results were provided by environmentally friendly and biodegradable mixtures with glycerol and glucose. The reaction tolerates both EDG and EWG substituents on the substrates and can be run on different halides (chloride, bromide, iodide) and pseudohalides (triflate). Furthermore, for several substrates, the catalyst loading can be reduced to 1 mol % Pd (0.5% mol Pd2(dba)3) without compromising the reaction yield. Moreover, we show that the Miyaura borylation protocol in DES can be combined with a subsequent Suzuki-Miyaura cross-coupling reaction in a one-pot procedure, allowing access to various biaryl products and demonstrating its synthetic utility by preparing the precursors of two compounds with reported applications in the photovoltaics sector. Finally, two green metrics (E-factor and EcoScale) of the new one-pot procedure in DES were calculated and compared with literature values to assess the potential advantages in terms of waste reduction, safety, and energy consumption.

Novel Challenges on the Catalytic Synthesis of 5-Hydroxymethylfurfural (HMF) from Real Feedstocks

The depletion of fossil resources makes the transition towards renewable ones more urgent. For this purpose, the synthesis of strategic platform-chemicals, such as 5-hydroxymethylfurfural (HMF), represents a fundamental challenge for the development of a feasible bio-refinery. HMF perfectly deals with this necessity, because it can be obtained from the hexose fraction of biomass. Thanks to its high reactivity, it can be exploited for the synthesis of renewable monomers, solvents, and bio-fuels. Sustainable HMF synthesis requires the use of waste biomasses, rather than model compounds such as monosaccharides or polysaccharides, making its production more economically advantageous from an industrial perspective. However, the production of HMF from real feedstocks generally suffers from scarce selectivity, due to their complex chemical composition and HMF instability. On this basis, different strategies have been adopted to maximize the HMF yield. Under this perspective, the properties of the catalytic system, as well as the choice of a suitable solvent and the addition of an eventual pretreatment of the biomass, represent key aspects of the optimization of HMF synthesis. On this basis, the present review summarizes and critically discusses the most recent and attractive strategies for HMF production from real feedstocks, focusing on the smartest catalytic systems and the overall sustainability of the adopted reaction conditions.

Microwave-assisted deep eutectic solvents/dimethyl sulfoxide system for efficient valorization of sugar bagasse waste into platform chemicals: A biorefinery approach for circular bioeconomy

The exploitation of lignocellulosic biomass (LB) such as sugar bagasse waste in biorefineries is the most cost-effective and favourable sustainable approach to producing essential platform chemicals, materials, and energy environmentally benignly. Herein, a microwave-mediated deep eutectic solvents (DESs)/dimethyl sulfoxide (DMSO) system for efficiently processing LB waste into platform chemicals was proposed thereof. Under optimized appropriate diverse parameters such as solvent varieties, catalyst dosage, DMSO addition, reaction time and temperature, the proposed catalytic system (i.e., microwave mediated DESs/DMSO system) has demonstrated significant yields of 5-hydroxymethylfurfural (5-HMF), furfural (FF) and levulinic acid (LevA) of 31.29 %, 28.38 % and 35.65 %, respectively. These favourable results were obtained at the reaction temperature of 140 °C for 40 min. The anticipated catalytic system's activation energy (Ea) was found to be 29.11 kJ/mol. Hence, a practical, inexpensive and sustainable process with the potential of high-value platform chemicals, explicitly for a sustainable strategy in a circular bioeconomy was proposed.

Whole Cell Biocatalysis of 5-Hydroxymethylfurfural for Sustainable Biorefineries

The implementation of cost-effective and sustainable biorefineries to substitute the petroleum-based economy is dependent on coupling the production of bioenergy with high-value chemicals. For this purpose, the US Department of Energy identified a group of key target compounds to be produced from renewable biomass. Among them, 5-hydroxymethylfurfural (HMF) can be obtained by dehydration of the hexoses present in biomass and is an extremely versatile molecule that can be further converted into a wide range of higher value compounds. HMF derivatives include 2,5-bis(hydroxymethyl)furan (BHMF), 5-hydroxymethyl-furan-2-carboxylic acid (HMFCA), 2,5-diformylfuran (DFF), 5-formyl-2-furancarboxylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA), all presenting valuable applications, in polymers, bioplastics and pharmaceuticals. Biocatalysis conversion of HMF into its derivatives emerges as a green alternative, taking into account the high selectivity of enzymes and the mild reaction conditions used. Considering these factors, this work reviews the use of microorganisms as whole-cell biocatalysts for the production of HMF derivatives. In the last years, a large number of whole-cell biocatalysts have been discovered and developed for HMF conversion into BHMF, FDCA and HMFCA, however there are no reports on microbial production of DFF and FFCA. While the production of BHMF and HMFCA mainly relies on wild type microorganisms, FDCA production, which requires multiple bioconversion steps from HMF, is strongly dependent on genetic engineering strategies. Together, the information gathered supports the possibility for the development of cell factories to produce high-value compounds, envisioning economical viable biorefineries.

Recent catalytic routes for the preparation and the upgrading of biomass derived furfural and 5-hydroxymethylfurfural

Furans represent one of the most important classes of intermediates in the conversion of non-edible lignocellulosic biomass into bio-based chemicals and fuels. At present, bio-furan derivatives are generally obtained from cellulose and hemicellulose fractions of biomass via the acid-catalyzed dehydration of their relative C6-C5 sugars and then converted into a wide range of products. Furfural (FUR) and 5-hydroxymethylfurfural (HMF) are surely the most used furan-based feedstocks since their chemical structure allows the preparation of various high-value-added chemicals. Among several well-established catalytic approaches, hydrogenation and oxygenation processes have been efficiently adopted for upgrading furans; however, harsh reaction conditions are generally required. In this review, we aim to discuss the conversion of biomass derived FUR and HMF through unconventional (transfer hydrogenation, photocatalytic and electrocatalytic) catalytic processes promoted by heterogeneous catalytic systems. The reaction conditions adopted, the chemical nature and the physico-chemical properties of the most employed heterogeneous systems in enhancing the catalytic activity and in driving the selectivity to desired products are presented and compared. At the same time, the latest results in the production of FUR and HMF through novel environmental friendly processes starting from lignocellulose as well as from wastes and by-products obtained in the processing of biomass are also overviewed.

Metabolic engineering of Saccharomyces cerevisiae for the production of top value chemicals from biorefinery carbohydrates

The implementation of biorefineries for a cost-effective and sustainable production of energy and chemicals from renewable carbon sources plays a fundamental role in the transition to a circular economy. The US Department of Energy identified a group of key target compounds that can be produced from biorefinery carbohydrates. In 2010, this list was revised and included organic acids (lactic, succinic, levulinic and 3-hydroxypropionic acids), sugar alcohols (xylitol and sorbitol), furans and derivatives (hydroxymethylfurfural, furfural and furandicarboxylic acid), biohydrocarbons (isoprene), and glycerol and its derivatives. The use of substrates like lignocellulosic biomass that impose harsh culture conditions drives the quest for the selection of suitable robust microorganisms. The yeast Saccharomyces cerevisiae, widely utilized in industrial processes, has been extensively engineered to produce high-value chemicals. For its robustness, ease of handling, genetic toolbox and fitness in an industrial context, S. cerevisiae is an ideal platform for the founding of sustainable bioprocesses. Taking these into account, this review focuses on metabolic engineering strategies that have been applied to S. cerevisiae for converting renewable resources into the previously identified chemical targets. The heterogeneity of each chemical and its manufacturing process leads to inevitable differences between the development stages of each process. Currently, 8 of 11 of these top value chemicals have been already reported to be produced by recombinant S. cerevisiae. While some of them are still in an early proof-of-concept stage, others, like xylitol or lactic acid, are already being produced from lignocellulosic biomass. Furthermore, the constant advances in genome-editing tools, e.g. CRISPR/Cas9, coupled with the application of innovative process concepts such as consolidated bioprocessing, will contribute for the establishment of S. cerevisiae-based biorefineries.

Synthesis of 2,5-furandicarboxylic acid by a TEMPO/laccase system coupled with Pseudomonas putida KT2440

A novel biological approach for the production of FDCA by a TEMPO/laccase system coupled with Pseudomonas putida KT2440 was established.