Ewoud

A novel and practical strategy is developed to prepare a new CO surrogate (cellulose-CO) derived from naturally abundant cellulose and established an efficient protocol for its application in carbonylative reactions. The cellulose-CO exhibits excellent reactivity with a very mild CO-release conditions, and also shows excellent compatibility and toleration in a variety of carbonylative systems. Notably, the cellulose-CO shows excellent chemical stability which can be stored on the bench exposed to air for at least 12 months, showing great practicability and conveniences. With these properties, this newly designed cellulose-CO can be used as a stable, cheap, green and efficient CO surrogate in CO chemistry.

Abstract

The highly toxic and flammable nature of CO lead to high handling demand for its use and storage, undoubtedly constricting its further academic exploration for carbonylative reactions in laboratory. Although many CO surrogates have been developed and applied in carbonylative reactions instead of CO gas, exploration of more versatile CO surrogates for diverse carbonylations is still highly desirable. Here we report a cellulose-based CO surrogate (cellulose-CO), which prepared from cheap and abundant cellulose through a simple and green process. The very mild and efficient CO release makes this reagent a highly competitive candidate for providing CO in carbonylation. This surrogate is compatible with a wide variety of functional groups in various carbonylative reactions due to the excellent compatibility of cellulose-CO. Moreover, the cellulose-CO exhibits excellent chemical stability which can be stored exposed to air for 12 months, making this CO surrogate a robust and general reagent in CO chemistry.

Nature Synthesis, Published online: 11 January 2024; doi:10.1038/s44160-023-00473-6

The use of a universal chemical programming language (χDL) to encode and execute synthesis procedures for a variety of chemical reactions is reported, including reductive amination, ring formation, esterification, carbon–carbon bond formation and amide coupling. These procedures are validated and repeated in two international laboratories and on three independent robots.

Nature, Published online: 10 January 2024; doi:10.1038/d41586-024-00033-8

The 300-kilogram primate couldn’t adapt when a changing environment forced a dietary shift.

This work demonstrates a 2-step lignin-first fraction strategy using a bifunctional catalyst consisting of Pd supported on ß-zeolite. Furthermore, crucial insights for process optimization are explored: Effect of delignification temperature, comparison of ß-zeolite performance of varying compositional and morphological properties, synergistic effects of bifunctional Pd/ß-zeolite and catalyst stability studies.

Abstract

This work demonstrates an additive and hydrogen-free 2-step lignin-first fractionation in flow-through. First, solvolytic delignification renders lignin liquors with its native chemical structure largely intact; and second, ß-zeolite catalytic depolymerization of these liquors leads to similar monomer yields as the corresponding 1-step fractionation process. Higher delignification temperatures lead to slightly lower ß−O−4 content in the solvated lignin, but does not affect significantly the monomer yield, so a higher temperature was overall preferred as it promotes faster delignification. Deposition of Pd on ß-zeolite resulted in a bifunctional hydrogenation/dehydration catalyst, tested during the catalytic depolymerization of solvated lignin with and without hydrogen addition. Pd/ß-zeolite displays synergistic effects (compared to the Pd/γ-Al₂O₃ and ß-zeolite tested individually and as a mixed bed), resulting in higher monomer yield. This is likely caused by increased acidity and the proximity between the metallic and acid active sites. Furthermore, different ß-zeolite with varying SAR and textural properties were studied to shed light onto the effect of acidity and porosity in the stabilization of lignin monomers. While some of the catalysts showed stable performance, characterization of the spent catalyst reveals Al leaching (causing acidity loss and changes in textural properties), and some degree of coking and Pd sintering.

Continuous flow technology has been applied to various reductive amination processes. The advantages of flow reactors, including temperature control, mass transfer intensification, and residence time distribution, have significantly improved the reaction performance. Furthermore, this technology provided a platform for scientific research, such as kinetic studies. This article summarized the application of continuous flow technology in reductive amination.

Abstract

Reductive amination with hydrogen is a green and atom-efficient method to construct amines from accessible aldehydes and ketones. Flow reactors, with superior mass and heat transfer rate because of higher specific surface area, have emerged as a powerful tool to conduct reductive amination with high efficiency and selectivity. This article discusses the influence of catalysts, solvents, temperatures, additives, and substrate properties on reductive amination. Following this, a summary of research on reductive amination with hydrogen in flow reactors is provided. The investigations were classified based on distinct nitrogen sources, encompassing the use of ammonia, amines, and nitro compounds. Based on the influencing factors and reaction cases, the article analyzes the enhancement effects of temperature control, mass transfer intensification, and residence time distribution in flow reactors on the reductive amination. Finally, the article gives a conclusion by addressing challenges and prospects for further developments in this field.

Synthesis
DOI: 10.1055/s-0042-1751542

Carbonylation reactions have been widely used to construct carbonyl-containing molecules or carbon enhancement reactions, which are mostly catalyzed by noble metals (Pd, Rh, Ru, Ir). In this review, we introduce the copper-catalyzed carbonylation reactions that have been developed in our group. Diverse reactions have been developed using various substrates, including the carbonylation of C–H activated alkanes, the difunctionalization of unsaturated C–C bonds, and the carbonylation of alkyl halides via the radical pathway.1 Introduction2 Cu-Catalyzed Carbonylation of C(sp 3)–H Bonds3 Cu-Catalyzed Carbonylative Difunctionalization of Unsaturated Bonds4 Cu–X (H or B) Mediated Acylation of Unsaturated Bonds with Electrophiles5 Cu–X (H or B) Mediated Carbonylation of Unsaturated Bonds6 Cu-Catalyzed Carbonylation of Alkyl Halides7 Other Types of Copper-Catalyzed Carbonylation Reactions8 Conclusion and Outlook
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Article in Thieme eJournals:
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Science, Volume 383, Issue 6678, Page 77-81, January 2024.

An unprecedented strategy has been proposed, using electrocatalysis to selectively depolymerize lignin into valuable aliphatic compounds in an aqueous solvent system under ambient conditions. Our innovative approach breaks down lignin‘s aromatic structure, yielding sodium levulinate, sodium 4-hydroxyvalerate, sodium formate, and sodium acetate as major products, representing an important milestone into lignin valorization and sustainability.

Abstract

Replacing crude oil as the primary industrial source of carbon-based chemicals has become crucial for both environmental and resource sustainability reasons. In this scenario, wood arises as an excellent candidate, whilst depolymerization approaches have emerged as promising strategies to unlock the lignin potential as a resource in the production of high-value organic chemicals. However, many drawbacks, such as toxic solvents, expensive catalysts, high energy inputs, and poor product selectivity have represented major challenges to this task. Herein, we present an unprecedented approach using electrocatalysis for the simultaneous depolymerization and dearomatization of lignin in aqueous medium under ambient conditions. By employing water/sodium carbonate as a solvent system, we demonstrated a pathway for selectively depolymerizing lignin under reductive electrochemical conditions using carbon as an electrocatalyst. After reductive electrocatalysis, the presence of aromatic compounds was no longer detected via nuclear magnetic resonance (NMR) spectroscopy. Further characterization by NMR, FTIR spectroscopy, and mass spectrometry revealed the major presences of sodium levulinate, sodium 4-hydroxyvalerate, sodium formate, and sodium acetate as products. By achieving a complete dearomatization, valuable aliphatic intermediates with enhanced reactivity were selectively obtained, opening new avenues for further synthesis of many different organic chemicals, and contributing to a more sustainable and circular economy.

Nature Synthesis, Published online: 03 January 2024; doi:10.1038/s44160-023-00464-7

David Ford, Senior Director of Chemistry at Snapdragon Chemistry, talks to Nature Synthesis about using flow chemistry in process development and reaction scale-up.

An integrated “functionalization-defunctionalization” approach efficiently produces bio-based surfactants directly from the hemicellulose and lignin fractions of lignocellulosic biomass. The performance of the resulting sugar and lignin-based surfactants are competitive with existing commercial products, highlighting the potential for using these biomass fractions as surfactants with minimal structural modification.

Abstract

Concerns over the sustainability and end-of-life properties of fossil-derived surfactants have driven interest in bio-based alternatives. Lignocellulosic biomass with its polar functional groups is an obvious feedstock for surfactant production but its use is limited by process complexity and low yield. Here, we present a simple two-step approach to prepare bio-based amphiphiles directly from hemicellulose and lignin at high yields (29 % w/w based on the total raw biomass and >80 % w/w of these two fractions). Acetal functionalization of xylan and lignin with fatty aldehydes during fractionation introduced hydrophobic segments and subsequent defunctionalization by hydrogenolysis of the xylose derivatives or acidic hydrolysis of the lignin derivatives produced amphiphiles. The resulting biodegradable xylose acetals and/or ethers, and lignin-based amphiphilic polymers both largely retained their original natural structures, but exhibited competitive or superior surface activity in water/oil systems compared to common bio-based surfactants.

Science, Volume 382, Issue 6672, Page 815-820, November 2023.

Nature, Published online: 14 November 2023; doi:10.1038/d41586-023-03506-4

Article-processing charges levied by publishers on authors have become an integral — and sometimes unpopular — part of the open-access revolution. Other options are being explored.

This review provides an in-depth analysis of the use of Polyoxometalates (POMs) for catalytic lignin conversion. We examine various strategies including thermal catalysis, electrocatalysis, and tandem processes. The paper also highlights investigations into polyoxometalate-ionic liquids and POM-deep eutectic solvents, as well as solidification or immobilization techniques for POMs. Furthermore, we discuss the future prospects and challenges of POM catalytic lignin conversion.

Abstract

Lignin, an inherently heterogeneous arylpropanoid polymer, presents a unique resource for the sustainable manufacture of aromatic chemicals and fuels. Recently, numerous catalytic strategies for lignin valorization have been explored. Polyoxometalates (POMs), with their distinctive structures enabling control of redox processes in lignin conversion, have been of particular interest. However, a comprehensive assessment of this emerging field of study is currently missing. This paper aims to fill this gap with a detailed review of the use of POMs for catalytic lignin conversion into value-added compounds. This review delves into various catalytic lignin conversion techniques, including thermal catalysis, electrocatalysis, and tandem processes for lignin separation, depolymerization, and upgrading. Moreover, we highlight innovative investigations utilizing polyoxometalate-ionic liquids (POM-ILs), POM-deep eutectic solvents (POM-DESs), and solidification or immobilization techniques for POMs as lignin valorization catalysts. Lastly, we discuss the future prospects and challenges in the domain of POM catalytic lignin conversion.

We describe the optimization and scale-up of two consecutive reaction steps in the synthesis of bio-derived alkoxybutenolide monomers that have been reported as potential replacements for acrylate-based coatings (Sci. Adv., 2020, 6, eabe0026). These monomers are synthesized by (i) oxidation of furfural with photo-generated singlet oxygen followed by (ii) thermal condensation of the desired 5-hydroxyfuranone intermediate product with an alcohol, a step which until now has involved a lengthy batch reaction. The two steps have been successfully telescoped into a single kilogram-scale process without any need to isolate the 5-hydroxyfuranone between the steps. Our process development involved FTIR reaction monitoring, FTIR data analysis via 2D-visualization and two different photo-reactors (i) a semi-continuous photo-reactor based on a modified rotary evaporator where FTIR and 2D-correlation spectroscopy (2D-COS) revealed the loss of the methyl formate co-product and (ii) our fully continuous Taylor Vortex photo-reactor which enhanced the mass transfer and permitted the use of near-stoichiometric equivalents of O2. The use of inline FTIR monitoring and modelling greatly accelerated process optimization in the Vortex reactor. This led to scale up of the photo-oxidation with an 85% yield and a projected productivity of 1.3 kg day-1, with a space time yield of 0.06 mol day-1 mL-1. Higher productivities could be achieved whilst sacrificing yield; e.g. 5 kg day-1 at 65% yield. The second step, the thermal condensation of 5-hydroxyfuranone, was transformed from a 20 h batch reflux reaction to a < 1 minute thermal flow reaction in a reactor only 3 mL in volume operating at 200 oC with projected productivities of >700 g day-1. Proof of concept for telescoping the two steps was established with an overall two-step yield of 67%, producing a process with projected productivity of 1.1 kg day-1 of the methoxybutenolide monomer without any purification of the 5-hydroxyfuranone intermediate.

Single-pot conversion of furfural (FAL) to alkyl levulinates (ALs) without using molecular hydrogen has been studied over ZSM-5-based Ni−W bimetallic catalysts. The catalyst developed in the present study exhibited excellent catalytic performance towards the production of various ALs from FAL using primary and secondary alcohols as source of hydrogen as well as reactant.

Abstract

A single–pot conversion of furfural (FAL) to alkyl levulinates (AL) without using molecular hydrogen has been studied over ZSM-5-based Ni−W bimetallic catalysts. The metal-metal and metal-support interactions in the bi-metallic catalyst are tailored by adopting appropriate synthesis protocol to conceive the superior catalytic performance. Insights on the structural properties and structure-properties relationship of catalyst is described using the data obtained through various characterization techniques like FTIR, XRD, NH₃-TPD, H₂-TPR, TEM, UV-Vis, and X-ray photoelectron spectroscopy. The catalyst synthesis method is observed to influence catalyst properties and catalytic activity strongly. The present study indicates the formation of Ni−W bimetallic interface enhances the catalytic performance towards AL formation. However, the probability of interface formation is mainly governed by synthesis protocol. The study highlights the importance of selecting a suitable synthesis route to achieve desirable catalyst properties for obtaining enhanced catalytic performance. The Ni/W@ZSM-5 catalyst developed in the present study exhibited excellent catalytic performance towards the production of various ALs from FAL using primary and secondary alcohols as source of hydrogen as well as reactant.