; Karine De Oliveira Vigier. Catalytic Conversion of Carbohydrates to Furanic Derivatives in the Presence of Choline Chloride

Production of Alkyl Levulinates from Carbohydrate-Derived Chemical Intermediates Using Phosphotungstic Acid Supported on Humin-Derived Activated Carbon (PTA/HAC) as a Recyclable Heterogeneous Acid Catalyst

This work reports a straightforward and high-yielding synthesis of alkyl levulinates (ALs), a class of promising biofuel, renewable solvent, and chemical feedstock of renewable origin. ALs were prepared by the acid-catalyzed esterification of levulinic acid (LA) and by the alcoholysis of carbohydrate-derived chemical platforms, such as furfuryl alcohol (FAL) and α-angelica lactone (α-AGL). Phosphotungstic acid (PTA) was chosen as the solid acid catalyst for the transformation, which was heterogenized on humin-derived activated carbon (HAC) for superior recyclability. Using HAC as catalyst support expands the scope of valorizing humin, a complex furanic resin produced inevitably as a side product (often considered waste) during the acid-catalyzed hydrolysis/dehydration of sugars and polymeric carbohydrates. Under optimized conditions (150 °C, 7 h, 25 wt.% of 20%PTA/HAC-600 catalyst), ethyl levulinate (EL) was obtained in an 85% isolated yield starting from FAL. Using the general synthetic protocol, EL was isolated in 88% and 84% yields from LA and α-AGL, respectively. The 20%PTA/HAC-600 catalyst was successfully recovered from the reaction mixture and recycled for five cycles. A marginal loss in the yield of ALs was observed in consecutive catalytic cycles due to partial leaching of PTA from the HAC support.

Selective Aerobic Oxidation of Alcohols in Low Melting Mixtures and Water and Use for Telescoped One-Pot Hybrid Reactions

An efficient, selective and sustainable protocol was developed for the CuCl₂/TEMPO/TMEDA‐catalyzed aerobic oxidation of activated alcohols to the corresponding carbonyl compounds using water or the environmentally friendly low melting mixture (LMM) d‐fructose‐urea as the reaction medium. Such oxidation reactions proceed under mild (room temperature or 40 °C) and aerobic conditions, with the carbonyl derivatives isolated in up to 98 % yield and within 4 h reaction time when using the above‐mentioned LMM. The potential application of this methodology is demonstrated by setting up useful telescoped, one‐pot two‐step hybrid transformations for the direct conversion of primary alcohols either into secondary alcohols or into valuable nitroalkenes, by combining oxidation processes with nucleophilic additions promoted by highly polarized organometallic compounds (Grignard and organolithium reagents) or with nitroaldol (Henry) reactions, respectively.

Improved Production of 5-Hydroxymethylfurfural in Acidic Deep Eutectic Solvents Using Microwave-Assisted Reactions

Hydroxymethylfurfural (5-HMF) is a key platform chemical, essential for the production of other chemicals, as well as fuels. Despite its importance, the production methods applied so far still lack in sustainability. In this work, acidic deep eutectic solvents (DES), acting both as solvent and catalyst, were studied for the conversion of fructose into 5-HMF using microwave-assisted reactions. These solvents were screened and optimized by varying the hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA). The bio-based solvent γ-valerolactone (GVL) was also applied as additive, leading to a boost in 5-HMF yield. Then, a response surface methodology was applied to further optimize operating conditions, such as reaction time, temperature and wt.% of added GVL. The highest 5-HMF yield attained, after optimization, was 82.4% at 130 °C, in 4 min of reaction time and with the addition of 10 wt.% of GVL. Moreover, a process for 5-HMF recovery and DES reuse was developed through the use of the bio-based solvent 2-methyltetrahydrofuran (2-Me-THF), allowing at least three cycles of 5-HMF production with minimal yield losses, while maintaining the purity of the isolated 5-HMF and the efficacy of the reaction media.

Reaction Mechanism of the Microwave-Assisted Synthesis of 5-Hydroxymethylfurfural from Sucrose in Sugar Beet Molasses

5-hydroxymethylfurfural (HMF) stands out among the chemical products derived from biomass as a building block in the chemical industry. The conventional production of HMF is usually carried out from fructose, glucose, or other monosaccharides as feedstock, but sugar beet molasses, a by-product of the sugar industry containing sucrose (45–55%), is promising. This exploratory study used three aqueous stock solutions and one biphasic system as the sources of sucrose. The dehydration of sucrose to 5-hydroxymethylfurfural was assisted by microwave heating and subcritical water conditions. The maximum yield of HMF was 27.8 mol % for the aqueous solution of synthetic sucrose at 80 min of treatment. Although HMF yield was 7.1 mol % in the aqueous sugar beet molasses solution, it increased 2-fold after clarification (15.1 mol %) and 1.6-fold in the biphasic system (11.4 mol %). These are favorable outcomes since this is an exploratory investigation. The pseudo-first-order model fitted experimental data from the conversion of the sucrose from the stock solutions, and kinetic parameters were estimated and compared. The estimated reaction rate constant showed that inversion of sucrose is faster than fructose dehydration to HMF, but the latter reaction was the rate-determining step only for the biphasic system. The maximum partition coefficient value was four between 40 min and 60 min of reaction, calculated at room temperature. These predictions help investigators to estimate conversions and selectivity when pilot plants need to be simulated.

Catalytic Conversion of Biomass to Furanic Derivatives with Deep Eutectic Solvents

Biomass is the only renewable organic carbon resource in nature, and the transformation of abundant biomass into various chemicals has received immense spotlight. As a novel generation of designer solvents, deep eutectic solvents (DESs) have been widely used in biorefinery due to their excellent properties including low cost, easy preparation, and biodegradability. Although there have been some reports summarizing the performance of DESs for the transformation of biomass into various chemicals, few Reviews illuminate the relationship between the functional structure of DESs and catalytic conversion of biomass. Hence, this Minireview comprehensively summarizes the effects of the types of functional groups in DESs on catalytic conversion of biomass into furanic derivatives, such as carboxylic acid-based hydrogen-bond donors (HBDs), carbohydrate-based HBDs, polyalcohol-based HBDs, amine/amide-based HBDs, spatial structure of HBDs, and various hydrogen-bond acceptors (HBAs). It also further summarizes the effects of adding different additives into the DESs on the synthesis of high value-added chemicals, including water, liquid inorganic acids, Lewis acids, heteropoly acids, and typical solid acids. Moreover, current challenges and prospects for the application of DESs in biomass conversion are provided.

Deep Eutectic Solvents as Catalysts for Upgrading Biomass

Deep eutectic solvents (DESs) have emerged as promising green solvents, due to their versatility and properties such as high biodegradability, inexpensiveness, ease of preparation and negligible vapor pressure. Thus, DESs have been used as sustainable media and green catalysts in many chemical processes. On the other hand, lignocellulosic biomass as an abundant source of renewable carbon has received ample interest for the production of biobased chemicals. In this review, the state of the art of the catalytic use of DESs in upgrading the biomass-related substances towards biofuels and value-added chemicals is presented, and the gap in the knowledge is indicated to direct the future research.

Controlling the Reaction Networks for Efficient Conversion of Glucose into 5-Hydroxymethylfurfural

Biomass-derived hexose constitutes the main component of lignocellulosic biomass for producing value-added chemicals and biofuels. However, the reaction network of hexose is complicated, which makes the highly selective synthesis of one particular product challenging in biorefinery. This Review focuses on the selective production of 5-hydroxymethylfurfural (HMF) from glucose on account of its potential significance as an important platform molecule. The complex reaction network involved in glucose-to-HMF transformations is briefly summarized. Special emphasis is placed on analyzing the complexities of feedstocks, intermediates, (side-) products, catalysts, solvents, and their impacts on the reaction network. The strategies and representative examples for adjusting the reaction pathway toward HMF by developing multifunctional catalysts and promoters, taking advantage of solvent effects and process intensification, and synergizing all measures are comprehensively discussed. An outlook is provided to highlight the challenges and opportunities faced in this promising field. It is expected to provide guidance to design practical catalytic processes for advancing HMF biorefinery.

One-pot selective conversion of lignocellulosic biomass into furfural and co-products using aqueous choline chloride/methyl isobutyl ketone biphasic solvent system

This study investigated simultaneous lignocellulose fractionation and conversion in a one-pot reaction using an aqueous choline chloride/methyl isobutyl ketone (ChCl/MIBK) biphasic solvent system. Under the optimized condition (170 °C, 60 min, 0.6 wt% H₂SO₄, 10.7 wt% solid loading), the biphasic solvent solubilized 96% xylan in raw switchgrass, which was simultaneously converted to furfural with a yield of 84.04%. The biphasic solvent was also able to selectively extract lignin, which had a high purity (93.1%), and uncondensed moieties (i.e., Hibbert's ketone), as well as decreased molecular weight and polydispersity index. The resultant pulp was enriched with cellulose (73.3%), which can be completely hydrolyzed into glucose within 48 h via enzymatic hydrolysis. Aqueous ChCl was successfully recycled and reused for atleast three cycles with similar performance in switchgrass fractionation. This study demonstrated that aqueous ChCl/MIBK biphasic system was an effective solvent system for co-production of furfural, high quality technical lignin and digestible cellulose for further upgrading.

Going Beyond the Limits of the Biorenewable Platform: Sodium Dithionite-Promoted Stabilization of 5-Hydroxymethylfurfural

The lack of thermal and storage stability and occurrence of side reactions during the processing of 5-hydroxymethylfurfural (5-HMF) limits its potential as biorenewable platform molecule. The addition of small amounts of the readily available sodium dithionite has a remarkable effect on promoting the stability of 5-HMF and inhibiting side reactions, thus helping to circumvent such limitations. The addition of sodium dithionite led to improvements in thermal stability (120 °C, 4 h, neat; 100 % vs. 37 %), under distillation (yield: 85 % vs. 52 %), and in a wide range of reactions, including 5-HMF synthesis under biphasic conditions (yield: 98 % vs. 67 %; purity: 92 % vs. 83 %) and 5-HMF transformations, such as Knoevenagel condensation with Meldrum's acid (yield: 96 % vs. 74 %), Cannizaro reaction (yield: quantitative vs. 83 %), and condensation with primary diamines to give pyridinium salts (yield: 88 % vs. 60 %).