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The development of sustainable plastics from abundant renewable feedstocks has been limited by the complexity and efficiency of their production, as well as their lack of competitive material properties. Here we demonstrate the direct transformation of the hemicellulosic fraction of non-edible biomass into a tricyclic diester plastic precursor at 83% yield (95% from commercial xylose) during integrated plant fractionation with glyoxylic acid. Melt polycondensation of the resulting diester with a range of aliphatic diols led to amorphous polyesters (Mn = 30–60 kDa) with high glass transition temperatures (72–100 °C), tough mechanical properties (ultimate tensile strengths of 63–77 MPa, tensile moduli of 2,000–2,500 MPa and elongations at break of 50–80%) and strong gas barriers (oxygen transmission rates (100 µm) of 11–24 cc m−2 day−1 bar−1 and water vapour transmission rates (100 µm) of 25–36 g m−2 day−1) that could be processed by injection moulding, thermoforming, twin-screw extrusion and three-dimensional printing. Although standardized biodegradation studies still need to be performed, the inherently degradable nature of these materials facilitated their chemical recycling via methanolysis at 64 °C, and eventual depolymerization in room-temperature water.

We explore the selective electrocatalytic hydrogenation of lignin monomers to methoxylated chemicals, of particular interest, when powered by renewable electricity. Prior studies, while advancing the field rapidly, have so far lacked the needed selectivity: when hydrogenating lignin-derived methoxylated monomers to methoxylated cyclohexanes, the desired methoxy group (-OCH3) has also been reduced. The ternary PtRhAu electrocatalysts developed herein selectively hydrogenate lignin monomers to methoxylated cyclohexanes.molecules with uses in pharmaceutics. Using X-ray absorption spectroscopy and in situ Raman spectroscopy, we find that Rh and Au modulate the electronic structure of Pt and that this modulating steers intermediate energetics on the electrocatalyst surface to facilitate the hydrogenation of lignin monomers and suppress C-OCH3 bond cleavage. As a result, PtRhAu electrocatalysts achieve a record 58% faradaic efficiency (FE) toward 2-methoxycyclohexanol from the lignin monomer guaiacol at 200 mA cm(-2), representing a 1.9x advance in FE and a 4x increase in partial current density compared to the highest productivity prior reports. We demonstrate an integrated lignin biorefinery where wood-derived lignin monomers are selectively hydrogenated and funneled to methoxylated 2-methoxy-4-propylcyclohexanol using PtRhAu electrocatalysts. This work offers an opportunity for the sustainable electrocatalytic synthesis of methoxylated pharmaceuticals from renewable biomass.

Furan-2,5-dicarboxylic acid (FDCA) is a biomass-derived diacid that can be used to make polymers including polyethylene furandicarboxylate (PEF), a highly attractive substitute for petroleum-derived polyethylene terephthalate (PET). Current FDCA syntheses require edible fructose as the feedstock, entail a difficult oxidation step that generates undesirable aldehyde impurities, and have moderate yields. As an alternative, carbonate-promoted C–H carboxylation enables the synthesis of FDCA from 2-furoic acid and CO2. This route is potentially advantageous because 2-furoic acid is made from furfural, a feedstock produced commercially from inedible lignocellulosic biomass, and it obviates late-stage oxidation. In the carboxylation reaction, salt mixtures composed of alkali furan-2-carboxylate (furoate) and alkali carbonate (M2CO3) are heated under CO2 in the absence of solvent or catalysts to form furan-2,5-dicarboxylate (FDCA2−), which is subsequently protonated to produce FDCA. Previously, high yields were achieved on small-scale reactions using caesium furoate and Cs2CO3. In this work, we investigate the carboxylation reaction using alkali furoate/M2CO3 salts containing cation blends and describe reaction conditions that provide high yields on a preparative scale. We show that the carboxylation proceeds efficiently with K+/Cs+ blends that have a high K+ content (up to 4 : 1 K+ : Cs+). Removing H2O, which is a by-product of the reaction, is important for suppressing decomposition pathways. The accumulation of the FDCA2− product inhibits the reaction. Integrating these lessons, we demonstrate the carboxylation of furoate on a 1 mol scale using a fixed-bed flow reactor with 89% isolated yield of pure FDCA upon protonation.

Molten salts at intermediate temperatures enable efficient carbonate-promoted carboxylation of very weakly acidic C–H bonds, revealing a new way to transform inedible biomass and carbon dioxide into valuable feedstock chemicals. The idea that the greenhouse gas carbon dioxide might be used as a source of feedstock chemicals is attractive but usually impractical — although it reacts readily with carbon-centred nucleophiles, generating the nucleophiles requires a high energy input. But now, inspired by the RuBisCO enzyme which catalyses carbon fixation in plants, Aanindeeta Banerjee et al. demonstrate that molten salts containing alkali metals at intermediate temperatures enable efficient carbonate-promoted carboxylation of very weakly acidic C–H bonds. The potential of this chemistry was illustrated by converting 2-furoic acid (readily made from inedible biomass) into the useful bio-based feedstock furan-2,5-dicarboxylic acid. Using carbon dioxide (CO2) as a feedstock for commodity synthesis is an attractive means of reducing greenhouse gas emissions and a possible stepping-stone towards renewable synthetic fuels1,2. A major impediment to synthesizing compounds from CO2 is the difficulty of forming carbon–carbon (C–C) bonds efficiently: although CO2 reacts readily with carbon-centred nucleophiles, generating these intermediates requires high-energy reagents (such as highly reducing metals or strong organic bases), carbon–heteroatom bonds or relatively acidic carbon–hydrogen (C–H) bonds3,4,5. These requirements negate the environmental benefit of using CO2 as a substrate and limit the chemistry to low-volume targets. Here we show that intermediate-temperature (200 to 350 degrees Celsius) molten salts containing caesium or potassium cations enable carbonate ions (CO32–) to deprotonate very weakly acidic C–H bonds (pKa > 40), generating carbon-centred nucleophiles that react with CO2 to form carboxylates. To illustrate a potential application, we use C–H carboxylation followed by protonation to convert 2-furoic acid into furan-2,5-dicarboxylic acid (FDCA)—a highly desirable bio-based feedstock6 with numerous applications, including the synthesis of polyethylene furandicarboxylate (PEF), which is a potential large-scale substitute for petroleum-derived polyethylene terephthalate (PET)7,8. Since 2-furoic acid can readily be made from lignocellulose9, CO32–-promoted C–H carboxylation thus reveals a way to transform inedible biomass and CO2 into a valuable feedstock chemical. Our results provide a new strategy for using CO2 in the synthesis of multi-carbon compounds.

Lignin is one of the most promising sources of renewable aromatic hydrocarbons. Current methods for its extraction from lignocellulosic biomass-which include the kraft, sulfite, and organosolv processes-result in the rapid formation of carbon-carbon bonds, leading to a condensed lignin that cannot be effectively depolymerized into its constituent monomers. Treatment of lignocellulosic biomass with aldehydes during lignin extraction generates an aldehyde-stabilized lignin that is uncondensed and can be converted into its monomers at near-theoretical yields. Here, we outline an efficient, reproducible, and scalable process for extracting and purifying this aldehyde-stabilized lignin as a solid, which can easily be re-dissolved in an organic solvent. Upon exposure to hydrogenolysis conditions, this material provides near-theoretical yields of aromatic monomers (~40-50% of the Klason lignin for a typical hardwood). Cellulose and hemicellulose are also efficiently fractionated. This protocol requires 6-7 h for the extraction of the stabilized lignin and a basic proficiency in synthetic chemistry.

Problem solved: an air-stable 2-pyridyl borane that can effectively couple to a wide range of aryl and heteroaryl halides and pseudohalides has evaded the synthesis community for decades. The discovery that Cu(DEA)(2) powerfully enables palladium-mediated cross-couplings with air-stable boronates 1 has finally provided a general solution to this problem. DEA=diethanolamine, DMF=N,N'-dimethylformamide, Tf=trifluoromethanesulfonyl.

A wide range of 2-pyridyl and other difficult-to-access heterocyclic N-methyliminodiacetic acid boronates can be readily prepared from the corresponding bromides via a new method involving direct transligation of 2-heterocyclic trialkoxyborate salts with N-methyliminodiacetic acid (MIDA) at elevated temperatures.

The cross-coupling of air-stable 2-pyridyl MIDA boronates with a variety of aryl halides and triflates under conditions A) is highly efficient for the preparation of various functionalized pyridine derivatives bearing aryl substituents at position 2.

Endocarp biomass, which forms much of the inedible portion of nuts and stone fruits, is a promising feedstock for aromatic chemical production due to its high lignin content and because it is a food industry waste. Here, we tested the nut shells and fruit kernels of seven species and report that their aromatic monomer yields can surpass those obtained using wood chips by up to 30% on a dry biomass basis due to their high lignin content. We also observed that acid-catalyzed aldehyde-assisted fractionation (AAF) facilitates lignin valorization when using industrially relevant particle sizes (3–5 mm) with monomers yields that are 80% to 170% higher than those obtained with reductive catalytic fractionation (RCF) for similarly sized particles. This difference was highly correlated with the feedstock surface area, demonstrating the importance of acidic pretreatment for substrates with low accessibility and/or large particles.

Existing lignocellulosic biomass fractionation processes produce lignin with random, interunit C-C bonds that inhibit its depolymerization and constrain its use. Here, we exploit the aldehyde stabilization of lignin to tailor its structure, functionality, and resulting properties, expanding its potential uses. We use bifunctional aldehydes to install specific functionality in lignin and thereby control its physical properties. Rational selection of the aldehyde allows for the formation of acetal-stabilised lignins that are soluble in either polar or non-polar solvents such as water and toluene. Exploiting these novel solubility properties, the effect of solvent on lignin hydrogenolysis is elucidated through the hydrogenolysis of select lignins. Through this study, we notably demonstrate the hydrogenolysis of sodium glyoxylate stabilised lignin in water, opening new avenues for the development of green chemical processes.

Lignin is a promising candidate for the replacement of fossil-based materials, due to its natural abundance and aromatic structure. This same structure poses major challenges to lignin's exploitation for material development. The harsh conditions generally needed for its isolation make it susceptible to uncontrollable side reactions that limit its further upgrading and/or functionalization. Here, by using aldehyde-assisted fractionation (AAF), we have extracted lignin while avoiding condensation reactions and, at the same time, introduced new functional groups on the lignin in a single step. By using a multifunctional aldehyde such as terephthalic aldehyde (TALD), we used acetal functionalization to prevent the dehydration and condensation of lignin's β-O-4 linkage and introduced an aldehyde on the lignin backbone. By tuning the amount of TALD during the extraction process, we were also able to precisely control the degree of chemical functionalization. We then exploited the reactivity of the newly functionalized biopolymer to increase phenolation reactions yields in both acid and basic environment, in order to provide better lignins for incorporation in phenol formaldehyde resins. These TALD-lignins were more reactive than Kraft lignin or mild organosolv lignin extracted in an acid solution of 80% ethanol in water, which could facilitate their use for developing more sustainable resins and materials.

Lignin is one of the most promising sources of renewable aromatic hydrocarbons. Current methods for its extraction from lignocellulosic biomass—which include the kraft, sulfite, and organosolv processes—result in the rapid formation of carbon–carbon bonds, leading to a condensed lignin that cannot be effectively depolymerized into its constituent monomers. Treatment of lignocellulosic biomass with aldehydes during lignin extraction generates an aldehyde-stabilized lignin that is uncondensed and can be converted into its monomers at near-theoretical yields. Here, we outline an efficient, reproducible, and scalable process for extracting and purifying this aldehyde-stabilized lignin as a solid, which can easily be re-dissolved in an organic solvent. Upon exposure to hydrogenolysis conditions, this material provides near-theoretical yields of aromatic monomers (~40–50% of the Klason lignin for a typical hardwood). Cellulose and hemicellulose are also efficiently fractionated. This protocol requires 6–7 h for the extraction of the stabilized lignin and a basic proficiency in synthetic chemistry. This protocol describes procedures for isolating and purifying uncondensed formaldehyde- and propionaldehyde-stabilized lignins from lignocellulosic biomass, and for recovering highly digestible cellulose and stabilized xylose.