Ewoud

Guidelines for identifying heavy phenolic lignin depolymerization products via MS/MS were established, and the dissociation principles of typical linkages were determined from HCD analysis. A dozen heavy products were identified, and real-time dynamic structural evolution was monitored. This method provides a simple and universal approach for characterizing lignin conversion systems.

Abstract

The efficient conversion of lignin contributes to reducing human reliance on fossil energy. As a complicated biopolymer, studies on the mechanism of lignin depolymerization is limited by inadequate structural identification of high molecular weight (MW) products like heavy phenolics. Up to now, no individual method can generate both MW and structural information in operando conditions. As a promising approach, tandem mass spectrometry (MS/MS) techniques can provide structural information via the dissociation of target ions. In this study, MS/MS technique was performed both in offline and in-situ mode during lignin depolymerization. The fundamental guidelines based on MS/MS dissociation principles for typical inter-unit linkages like β-O-4, 5-5, β-β, β-5, and β-1 were well established. Based on that, major phenolic dimers are successfully identified, including chemical formula and types of inter-unit linkages. More significantly, real-time monitoring of structural evolution was achieved by applying in-situ MS/MS analysis during lignin depolymerization. The results show the different evolution pathways of isomers with same chemical formula, confirming that structural changes during lignin depolymerization are common and obvious. Overall, this study develops an advanced strategy for the full-view analysis of lignin depolymerization, achieving the static analysis of composition and structure, both monitoring the dynamic evolution of structures.

Science, Volume 386, Issue 6718, Page 144-146, October 2024.

Oxidative cleavage of aromatic C(sp2)−O bond is implemented using water as oxygen source and oxoammonium salt as oxidant, which is efficiently applied into cleavage of lignin model compounds and depolymerization of PPO. The oxoammonium cation activates water to form hydroxy-oxoammonium adduct, which plays the key role in the oxidative cleavage. The recycling of oxoammonium cation is confirmed via electrolysis.

Abstract

Oxidative cleavage of aromatic C(sp²)−O bond is important to the conversion of biomass and plastic wastes into value-added chemicals. Here we put forward the oxidative cleavage of para-C−O bonds in phenolic compounds in use of oxoammonium salts as oxidant and water as the oxygen source. The mechanism is that oxoammonium cation activates water to form hydroxy-oxoammonium adduct and thus realizes the ipso-substitution of 4-alkoxyphenol, which is proved by substituent effect, isotope labelling experiments, and kinetic analysis. Furthermore, this protocol is successfully applied into the depolymerization of both lignin model compounds with α-O-5 and 4-O-5 linkages and polyphenylene oxide (PPO).

Synlett
DOI: 10.1055/a-2413-0458

The radical/palladium relay catalysis for C–H bond carbonylation is an attractive research topic in synthetic chemistry. It can rapidly prepare carbonylated molecules for synthetic or pharmaceutical applications from highly sought-after feedstocks, such as alkylarenes, alkanes, alkenes, or ethers. The main objective of this Synpacts article is to summarize the development of this research area, mainly focusing on radical/palladium relay catalysis for the carbonylation of single and double C–H bonds.1 Introduction2 Radical/Palladium Relay Catalysis for Single C–H Bond Carbonylation Reaction3 Radical/Palladium Relay Catalysis for Double C–H Bond Carbonylation Reaction4 Conclusions
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

This work reports on a new family of eco-friendly optical polymers: aromatic poly(dithioacetal)s, which are characterized by efficient degradability, thermostability, colorless features, and high refractive index properties. We have also demonstrated their closed-loop recycling that allows successful recovery without deterioration of polymer properties.

Abstract

In the quest for eco-friendly optics, high refractive index polymers (HRIPs) with degradability have been one of the desirable optical materials for realizing eco-friendly and efficient lighting technologies. However, it has been challenging for HRIPs to simultaneously realize thermostability, high refractive index (RI), visible transparency, and efficient degradability, all of which are essential for their practical use. In this context, we herein focus on aromatic poly(dithioacetal)s, composed of visible-transparent yet degradable dithioacetal moieties and rigid phenylene sulfide spacers, exhibiting moderately high T _g (> 60 °C), high RI (> 1.7), and colorless film features. In addition, poly(dithioacetal)s can balance (1) high stability under the operating conditions even upon heating and (2) quantitative degradability that can selectively yield cyclic low-molecular-weight products that can be further repolymerized upon further addition of an acid catalyst. These results provide a key concept for high refractive index polymers that allow on-demand degradability and recyclability without compromising their high potential thermal and optical properties.

Synthesis
DOI: 10.1055/s-0043-1775032

This study aims to delineate the synthesis of eugenol derivatives, starting with hydroxyl group protection and then the subsequent oxidation stages. Initially, eugenol underwent conversion into acetyleugenol and benzyleugenol during the protection phase. Subsequently, a kinetic oxidation of acetyleugenol with KMnO4 via GC-MS analysis resulted in the identification of four compounds. The kinetic investigation indicated the primary formation of diolacetyleugenol, succeeded by aldehyde eugenol, which further gets converted into its respective carboxylic acid. Additionally, acetyleugenol and benzyleugenol underwent oxidation with CrO3, yielding the corresponding carboxylic acids.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

Organocatalyzed group transfer polymerization (O-GTP) of muconic esters leads to bio-sourced and degradable polymers analogous to polyacrylates. This O-GTP method proves ultra-fast, converting 100 % of the monomer in one minute in toluene at room temperature. Chemical modification of the internal double bonds offers additional leverage either for modulating polymer properties or for chemical degradation.

Abstract

The quest for polymers that would be at the same time bio-based and degradable after usage, in addition to offering chemical post-modification options, remains a daunting challenge in contemporary polymer science. Despite advances in polymer chemistry, attempts at controlling the chain-growth polymerization of muconate esters remain unexplored. Here we show that dialkyl muconates can be rapidly polymerized by organocatalyzed group transfer polymerization (O-GTP). O-GTP is conducted to completion at room temperature in toluene within a few minutes, using 1-ethoxy-1-(trimethylsiloxy)-1,3-butadiene (ETSB) as initiator and 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)-phosphoranylidenamino]-2 λ ${\lambda }$ 5,4 λ ${\lambda }$ 5 catenadi(phosphazene) (P₄-t-Bu) as catalyst. Chain extension experiments and synthesis of all muconate-type block copolymers can also be achieved. Furthermore, polymuconates are amenable to facile post-polymerization modification reactions. This is showcased through the hydrolysis of the ester side chains leading to well-defined poly(muconic acid), and by epoxidation of the C=C double bonds of the main chain. Last but not least, these internal alkene groups can be selectively cleaved by ozonolysis, demonstrating the upcyclability of polymuconates under oxidative conditions. This work demonstrates that polymuconates constitute a unique platform of bio-based polymers, easily modifiable in addition to being chemically degradable under user friendly experimental conditions.

Nature, Published online: 24 September 2024; doi:10.1038/d41586-024-02693-y

Simone Willis studied part-time alongside multiple paid roles. Here’s how she managed her time, met deadlines and protected her mental health.

Nature, Published online: 20 September 2024; doi:10.1038/d41586-024-03070-5

The concepts were judged by reviewers. They were not told who or what had created them.

Aminolysis of epoxides is a promising way to construct C−N bonds without producing any byproduct. In this article, it was revealed that titania-zirconia supported molybdenum oxide as a solid acid catalyst could accelerate the reaction, and be applied for continuous-flow systems with high efficiency. Furthermore, sequential-flow synthesis of an important API, Rivaroxaban intermediate was achieved utilizing hydrogenation and aminolysis to afford the desired product in 73 %.

Abstract

We report a solid-acid catalyzed aminolysis of epoxides under continuous-flow conditions. A titania-zirconia supported molybdenum oxide catalyst demonstrated exceptional substrate compatibility, enabling the synthesis of β-amino alcohols in excellent yields with high catalyst durability. Characterization of the catalyst revealed the crucial role of the titania-zirconia ratio in optimizing its performance. Furthermore, this method was applied to the efficient, sequential-flow synthesis of a rivaroxaban intermediate (an oral anticoagulant and the first direct factor Xa inhibitor), combining a hydrogenation step with the aminolysis reaction without the need for intermediate isolation.

New lignocellulose biorefinery technologies that enable the conversion of lignin into platform chemicals are essential to reduce our future dependence on fossil resources. In this study, we investigate the Brønsted acid-catalyzed O-demethylation of guaiacol in hot-pressurized water (HPW) as a model reaction for transforming lignin-derived phenolic substrates featuring ortho methoxy groups. We compare the effects of Brønsted mineral acid (HCl) and microporous solid acid (H-BEA zeolite) in water to elucidate the hydrolysis mechanism and the impact of zeolite microporosity on reaction rates. Operando molecular modeling combined with experimental kinetic studies reveals that, regardless of the catalyst type, O-demethylation follows a concerted, one-step O-activated SN2 mechanism. This mechanism involves a strong hydrogen bond between guaiacol and a hydronium ion as an ionic contact pair. Protons confined within the zeolite form more active undercoordinated hydronium ions, which are associated with lower enthalpic requirements and thus accelerate the hydrolysis. The molecular organization of solvent and reactants around the confined catalytic active site plays a crucial role in modulating the association of the reacting species. These proof-of-concept results demonstrate the significant influence of solvent (water) coordination on acid-catalyzed bimolecular reactions, such as hydrolysis, within confined spaces.

The Van-der-Waals distance of a thiol and ene is depicted. After the thiol-ene reaction a thioether bond is formed resulting in a shorter interatomic distance. This shrinkage leads to stress in the polymer which can be reduced by radical-mediated redox-rearrangements catalyzed by thiols. A compact cyclic acetal extent to a longer linear ester. This volumetric expansion is counteracting the shrinkage resulting from the thiol-ene reaction.

Abstract

Polarity-reversal catalysts (PRCs) for hydrogen-atom transfer reactions have been known in radical chemistry for more than 60 years but are rarely described and utilized in the field of photopolymerization up to now. Herein, we present the use of thiols in a unique dual function as thiol-ene click reagents and as polarity-reversal catalyst (PRC) for the radical-mediated redox rearrangements of benzylidene acetals. During the rearrangement reaction, cyclic benzylidene acetals are transformed into benzoate esters leading to a significant volumetric expansion to reduce thermoset shrinkage. We were able to show that this expansion on a molecular level reduces shrinkage and polymerization stress but does not significantly affect the (thermo−)mechanical properties of the cross-linked networks. One of the key advantages of this process lies in its simplicity. No additives like sensitizers or combinations of different initiators (radical and cationic) are needed. Furthermore, the same light source can be used for both the polymerization reaction and expansion through rearrangement. Additionally, the applied photoinitiator enables spatial and temporal control of the polymerization; thus, the developed system can be an excellent platform for additive manufacturing processes.

Photocatalytic conversion of biomass is becoming increasingly important, with the photocatalytic transformation of lignin being both attractive and challenging. This article presents the first use of graphitic carbon nitride for the photocatalytic conversion of a β-5 model compound, revealing depolymerization products.

Abstract

As a globally abundant source of biomass, lignocellulosic biomass has been the centre of attention as a potential resource for green energy generation and value-added chemical production. A key component of lignocellulosic biomass, lignin, which is comprised of aromatic monomers, is a potential feedstock for value added chemical production. The cleavage processes of the linkages between monomers to obtain high value products, however, requires significant investigation as it is a complex, non-facile process. This study focuses on the photocatalytic valorization of a β-5 lignin model compound, a key linkage in the lignin structure. It was found that greater yields of aromatic products were obtained from the photocatalytic conversion of β-5 lignin model compound using carbon nitride (CN) when compared to Evonik P25 titanium dioxide (TiO₂). Products of the β-5 model compound photocatalytic conversion were determined and C−C bond cleavage was observed. It was also determined that the solvent participated in the reactions with the introduction of a cyano group to one of the products. Radical quenching experiments revealed that superoxide radicals participated in the CN photocatalytic conversion. These results reveal for the first time the products and possible mechanism of the photocatalytic transformation of β-5 model compounds using CN photocatalysis.

Nature, Published online: 04 September 2024; doi:10.1038/d41586-024-02580-6

Machine learning has been used to turn a survey of local waste-management practices into a global inventory of plastic emissions. The data show that tackling plastic pollution will require reduced production and consumption.

The new silica-immobilized TEMPO catalysts were developed and applied for continuous-flow aerobic oxidation conditions in this paper. The new TEMPO catalysts have higher durability than the commercially available immobilized TEMPO catalyst, and its turnover frequency (TOF) achieved 15 h⁻¹. Also, the deactivation pathway of our catalyst was investigated, and the nitrosation of the N−O bond was observed after the reaction.

Abstract

2,2,6,6′-Tetramethylpiperidine-N-oxyl (TEMPO) is a highly efficient oxidation catalyst, valued for its environmentally benign nature, particularly in comparison to transition-metal catalysts. Despite their merits, TEMPO-based catalysts are not notably cost-effective. Immobilization of TEMPO onto supports offers a promising strategy to overcome this limitation. In this work, we present the synthesis and application of immobilized TEMPO catalysts 2–5, prepared via a straightforward condensation reaction, for the aerobic oxidation of alcohols. These catalysts demonstrate remarkable activity for alcohol oxidations under continuous-flow conditions, employing nitric acid as the co-catalyst. Notably, catalyst 2 immobilized by COOH silica gel exhibits outstanding performance for the oxidation of benzyl alcohol by oxygen gas, achieving a turnover frequency (TOF) of 15 h⁻¹ and a turnover number (TON) exceeding 300. Catalyst 2 further demonstrates broad substrate scope, effectively oxidizing primary, secondary, and benzylic alcohols. Post-reaction analysis of spent catalyst 2 reveals that deactivation primarily stems from nitrosation of the N−O bond. Interestingly, the amide moiety remains intact despite the harsh acidic reaction conditions.