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Nature, Published online: 01 August 2023; doi:10.1038/d41586-023-02419-6

The month’s sharpest science shots — selected by Nature’s photo team.

Nature Synthesis, Published online: 31 July 2023; doi:10.1038/s44160-023-00372-w

Developing reaction conditions for radical–radical cross-dehydrogenative amination reactions is challenging. Now a nickel-catalysed asymmetric electrochemical cross-dehydrogenative amination reaction between acylimidazoles and nitrogen nucleophiles is developed to access structurally diverse α-amino carbonyls that can be used to synthesize (+)-γ-secretase inhibitor, (+)-flamprop-methyl and (+)-flamprop-isopropyl.

Polymer networks functionalized with dual-cleavable imine and acetal bonds are developed to enable efficient chemical recycling. These poly(imine-acetal)s facilitate depolymerization into primary building blocks, offering ample design spaces for various polymer types. Furthermore, this innovative approach allows straightforward compound separation, leading to the conservation of chemical resources and promoting closed-loop recycling scheme.

Abstract

Chemical recycling offers a promising solution for the end-of-life treatment of synthetic polymers. However, the efficient recovery of well-defined recycled building blocks continues to be a major challenge, especially for crosslinked thermosets. Here, we developed vanillin-based polymer networks functionalized with dual-cleavable imine and acetal bonds that facilitate chemical recycling to primary building blocks and their convenient separation at the molecular level. A library of crosslinked poly(imine-acetal)s was synthesized by combining the in-bulk synthesized liquid di-vanillin acetal monomer (DVA) with commercially available liquid di- and triamines under solvent-free conditions. These thermosets showed tailor-made thermal and mechanical properties along with outstanding chemical recyclability. Under aqueous acidic conditions, poly(imine-acetal)s selectively and completely disintegrate into small molecules. During the polymer design stage, these compounds were carefully selected to enable facile separation without tedious techniques. As a result, the primary building blocks were isolated in high yields and purity and immediately reused to produce fresh polymers with identical thermomechanical properties. Since our “design for recycling” concept aims at obtaining the primary building blocks rather than monomers after depolymerization, a plethora of possibilities are unlocked to utilize these chemical resources, including closed-loop recycling as portrayed.

To be or not to be burnt: that's the question. Read more about kraft lignin: the potential, the chemistry of how it is formed, and stateof-the-art applications in both fuels and materials. A technoeconomic discussions discloses two important economic incentives to recover lignin from pulp production.

Abstract

Kraft lignin, a by-product from the production of pulp, is currently incinerated in the recovery boiler during the chemical recovery cycle, generating valuable bioenergy and recycling inorganic chemicals to the pulping process operation. Removing lignin from the black liquor or its gasification lowers the recovery boiler load enabling increased pulp production. During the past ten years, lignin separation technologies have emerged and the interest of the research community to valorize this underutilized resource has been invigorated. The aim of this Review is to give (1) a dedicated overview of the kraft process with a focus on the lignin, (2) an overview of applications that are being developed, and (3) a techno-economic and life cycle asseeements of value chains from black liquor to different products. Overall, it is anticipated that this effort will inspire further work for developing and using kraft lignin as a commodity raw material for new applications undeniably promoting pivotal global sustainability concerns.

Nature, Published online: 26 July 2023; doi:10.1038/d41586-023-02409-8

Atomic bomb historian Richard Rhodes talks to Nature about how researchers fare in the film, and what it gets right and wrong.

New synthetic procedures for benzylic functionalization of lignin-derived phenolics are reported. The two developed copper-catalyzed reactions are part of a net two-step synthetic protocol where lignin monomers are first converted into their corresponding benzyl hexafluoroisopropyl ethers and then engaged in allylation and alkynylation reactions. In this way, a number of unsaturated fragments amenable to further monomer upgrading can be installed.

Abstract

Within the field of lignin biorefining, significant research effort has been dedicated to the advancement of catalytic methods for lignocellulose depolymerization. However, another key challenge in lignin valorization is the conversion of the obtained monomers into higher value-added products. To address this challenge, new catalytic methods that can fully embrace the inherent complexity of their target substrates are needed. Here, we describe copper-catalyzed reactions for benzylic functionalization of lignin-derived phenolics via intermediate formation of hexafluoroisopropoxy-masked para-quinone methides (p-QMs). By controlling the rates of copper catalyst turnover and p-QM release, we have developed copper-catalyzed allylation and alkynylation reactions of lignin-derived monomers to install various unsaturated fragments amenable to further synthetic applications.

Nature, Published online: 12 July 2023; doi:10.1038/d41586-023-02289-y

Powerful space telescope reveals star-forming region — image of the week.

The refinement of biomass, particularly lignin, for the production of chemicals as a solution to the energy crisis, has been substantiated as a potentially promising technology. The effective amalgamation of photocatalytic technology with biomass refining has received considerable attention recently. Nonetheless, the current research landscape is heavily concentrated on lignin molecular models, with little attention being paid to the study of actual lignin. This Review highlights recent progress in the photoreforming of actual lignin for the production of energy or chemicals.

Abstract

Photoreforming of lignocellulosic biomass to simultaneously produce gas fuels and value-added chemicals has gradually emerged as a promising strategy to alleviate the fossil fuels crisis. Compared to cellulose and hemicellulose, the exploitation and utilization of lignin via photoreforming are still at the early and more exciting stages. This Review systematically summarizes the latest progress on the photoreforming of lignin-derived model components and “real” lignin, aiming to provide insights for lignin photocatalytic valorization from fundamental to industrial applications. Considering the complexity of lignin physicochemical properties, related analytic methods are also introduced to characterize lignin photocatalytic conversion and product distribution. We finally put forward the challenges and perspective of lignin photoreforming, hoping to provide some guidance to valorize biomass into value-added chemicals and fuels via a mild photoreforming process in the future.

Publication date: 28 July 2023

Source: Tetrahedron Letters, Volume 125

Author(s): Ramteke Prachi, Manjinder Singh Gill

Nature, Published online: 19 June 2023; doi:10.1038/d41586-023-01935-9

Energy released from molecules under strain can promote difficult chemical reactions. A practical method has been developed that uses an overlooked, highly strained compound to rapidly construct complex organic products.

Simpler, cheaper, accurate: Low-field, or benchtop, nuclear magnetic resonance (NMR) spectrometers prove capable of quantitative analysis of pyrolysis oils from a range of lignocellulosic feedstocks. The NMR estimates of total carbonyl content compare favorably with titrations while the acquired spectra allow for the quantification of carbonyl groups such as ketones, aldehydes and quinones. Benchtop NMR spectrometers are cheaper than their superconducting counterparts and require neither cryogens nor deuteriated solvents.

Abstract

Pyrolysis bio-oils, one of the products of lignocellulosic biomass pyrolysis, have the potential to be widely used as fuels. The chemical composition of bio-oils is very complicated as they contain hundreds, if not thousands, of different, mostly oxygen-containing, compounds with a wide distribution of physical properties, chemical structures, and concentrations. Detailed knowledge of bio-oil composition is crucial for optimizing both the pyrolysis processes and for any subsequent upgrading into a more viable fuel resource. Here we report the successful use of low-field, or benchtop, nuclear magnetic resonance (NMR) spectrometers in the analysis of pyrolysis oils. Pyrolysis oils from four different feedstocks were derivatized and analyzed using ¹⁹F NMR techniques. The NMR results compare favorably with titrations for total carbonyl content. In addition, the benchtop NMR spectrometer proves able to reveal key spectral features, thus allowing the quantification of different carbonyl groups, such as aldehydes, ketones and quinones. Benchtop NMR spectrometers are typically compact, cheaper than their superconducting counterparts and do not require cryogens. Their use will make NMR analysis of pyrolysis oils easier and more accessible to a wide range of different potential users.

Nature, Published online: 08 June 2023; doi:10.1038/d41586-023-01846-9

The high cost of ‘reformatting’ prompts a call for journals to change their requirements.

Nature, Published online: 01 June 2023; doi:10.1038/d41586-023-01801-8

First truly single aperiodic tile discovered that can cover an infinite surface without repeating itself.