Aromatic Monomers Research Articles

Ionothermal synthesis of Cs3Bi2Br9 quantum dots-decorated covalent triazine frameworks composite photocatalyst and their application in selective cleavage of C–C bonds in lignin

In order to further improve the yield of aromatic monomers from renewable resources, the selective cleavage of C–C bonds in lignin get more and more attention. In this work, Cs3Bi2Br9 (CBB) and covalent triazine frameworks (CTFs) complexes were firstly prepared by facile melting salt method. Due to CBB quantum dots embedded in CTF frame structure, the conversion rate of the composite photocatalyst for 2-phenoxy-1-phenylethanol (pp-ol) reached 100% under visible-light irradiation in 6 h. In-depth investigations verified that the electronic structure of the photocatalyst could be adjusted by changing calcination temperature. The electronic structure of the photocatalyst affected the type and the tendency of free radical, and then affected the selectivity of C-C bond cleavage. This work provides a simple method to prepare photocatalytic and used for aromatics production from renewable biomass feedstocks.

Depolymerization of Pine Wood Organosolv Lignin in Ethanol Medium over NiCu/SiO2 and NiCuMo/SiO2 Catalysts: Impact of Temperature and Catalyst Composition.

The process of thermocatalytic conversion of pine ethanol lignin in supercritical ethanol was studied over NiCu/SiO2 and NiCuMo/SiO2 catalysts bearing 8.8 and 11.7 wt.% of Mo. The structure and composition of ethanol lignin and the products of its thermocatalytic conversion were characterized via 2D-HSQC NMR spectroscopy, GC-MC. The main aromatic monomers among the liquid products of ethanol lignin conversion were alkyl derivatives of guaiacol (propyl guaiacol, ethyl guaiacol and methyl guaiacol). The total of the monomers yield in this case was 12.1 wt.%. The temperature elevation up to 350 °C led to a slight decrease in the yield (to 11.8 wt.%) and a change in the composition of monomeric compounds. Alkyl derivatives of pyrocatechol, phenol and benzene were observed to form due to deoxygenation processes. The ratio of the yields of these compounds depended on the catalyst, namely, on the content of Mo in the catalyst composition. Thus, the distribution of monomeric compounds used in various industries can be controlled by varying the catalyst composition and the process conditions.

Enantioselective Amination of 4-Substituted Pyrazolones Catalyzed by Oxindole-Containing Thioureas and by a Recyclable Linear-Polymer-Supported Analogue in a Continuous Flow Process.

A highly efficient organocatalytic amination of 4-substituted pyrazolones with azodicarboxylates mediated by a novel quinine-derived thiourea with a 3,3-diaryl-oxindole scaffold is reported. This synthetic method furnished 4-amino-5-pyrazolones in high yields and with excellent enantioselectivities (up to 97:3 er) at room temperature in short reaction times. Moreover, a linear-polymer-supported bifunctional thiourea, synthesized by reacting a bifunctional aromatic monomer (biphenyl) with isatin in superacidic media and further derivatization, was proven to be also an efficient heterogeneous organocatalyst for this α-amination reaction. The practical value of this process was demonstrated by the use of the immobilized catalyst in recycling experiments, maintaining the activity without additional reactivation, and in flow processes, allowing the synthesis of 4-amino-pyrazolone derivatives in a gram scale with high yield and enantioselectivity.

Synthesis, Characterization, and Evaluation of Antioxidant and Physical Properties of New Bifunctional Aromatic Monomers Containing Imine and Heterocyclic Rings in The Main Chain.

New various monomers with di amine functional groups have been synthesized, containing di azomethine or di seven-membered heterocyclic rings in the backbone. A condensation reaction of benzidine with 4-amino benzaldehyde with some drops of glacial acetic acid in ethanol absolute prepared bi-functional amino groups monomer with azomethine core P1(4-[(1E)-[4[4-(E)-(4-aminophenyl)methylidene]amino]phenyl}phenylimino methyl aniline). The next step was the Cycloaddition reaction of P1 with succinic, malic, and phthalic anhydrides used to obtain aromatic heterocyclic monomers with oxazepane and oxazepine rings containing lactone and lactam groups. All the synthesized monomers were characterized spectrally with many techniques (FT.IR,1 H1.NMR, C13-NMR) that were used to investigate the functional groups in the structure of monomers. Monitoring the progress and completion of the reaction was performed using thin-layer chromatography (TLC). Physical characterizations, including detecting the melting point, purity, colour, retardation factor, molecular formula, and molecular weight, the polarized optical microscope (POM) used for Image-based microscopic interpretation of prepared compounds. All the prepared monomers are considered effective antioxidant agents as they give free radicals scavenging over 60%, reaching 80 %; this activity makes them useful in large numbers of industries as they can scavenge the free radicals that the industrial product may be exposed, which increases its shelf life and enhance its effectiveness.

Direct synthesis of N, S co‐doped graphynes via copolymerization strategy for electrocatalytic application

AbstractGraphynes (GYs) are a novel set of carbon allotropes with high potential as future catalytic electrodes for oxygen reduction reactions because of their unique physical and chemical properties. In recent years, a number of heteroatom‐doped graphdiyne (GDYs) based electrocatalysts have been developed. However, the development of GYs has made slow progress due to their limited synthetic strategies. Here, the first case of nitrogen and sulfur co‐doped graphynes (NS‐GYs) synthesized through the copolymerization between hydrogen‐deficient heterocyclic aromatic monomers via the Sonogashira–Hagihara cross‐coupling reaction is reported. The NS‐GYs exhibit abundant porosity after heat treatment with large specific area and high heteroatom content for use as potential electrocatalysts. In addition, NS‐GY‐3‐800 with the best electrocatalytic performance shows excellent power density and stability in Zn‐air batteries.

Autoxidation Catalysis for Carbon-Carbon Bond Cleavage in Lignin.

Selective lignin depolymerization is a key step in lignin valorization to value-added products, and there are multiple catalytic methods to cleave labile aryl-ether bonds in lignin. However, the overall aromatic monomer yield is inherently limited by refractory carbon-carbon linkages, which are abundant in lignin and remain intact during most selective lignin deconstruction processes. In this work, we demonstrate that a Co/Mn/Br-based catalytic autoxidation method promotes carbon-carbon bond cleavage in acetylated lignin oligomers produced from reductive catalytic fractionation. The oxidation products include acetyl vanillic acid and acetyl vanillin, which are ideal substrates for bioconversion. Using an engineered strain of Pseudomonas putida, we demonstrate the conversion of these aromatic monomers to cis,cis-muconic acid. Overall, this study demonstrates that autoxidation enables higher yields of bioavailable aromatic monomers, exceeding the limits set by ether-bond cleavage alone.

A novel solid acid bearing thiophene group: Preparation and catalytic performance in cellulose hydrolysis

Two different aromatic monomers, naphthalene and benzothiophene, were ingeniously selected to prepare a solid acid with thiophene groups, which can selectively convert cellulose into glucose. The content of thiophene groups in the solid acids was regulated by adjusting the proportion of aromatic monomers. The effect of thiophene groups on physico-chemical structures and catalytic activity of solid acids was discussed. The experiment results indicate that the sulfur content in solid acids was up to 19.57 wt%. The introduction of thiophene groups increased –SO3H group density and adsorption capacity by 30.99 % and 64.36 %, respectively. These positive changes result in excellent catalytic activity of solid acids. The cellulose conversion rate and glucose selectivity reached 78.9 % and 97.1 % respectively at 150 °C and 7 h.

The ionic liquids upon perchlorate to promote the C-C/C-O bonds cleavage in alkali lignin under photothermal synergism

Transforming lignin into aromatic monomers is critically attractive to develop green and sustainable energy supplies. However, the usage of the additional catalysts like metal or base/acid is commonly limited by the caused repolymerized and environmental issues. The key step is to mediate electron transfer in lignin to trigger lignin C-C/C-O bonds cleavage without the catalysts mentioned above. Here, we report that the ionic liquids [BMim][ClO4] was found to trigger lignin electron transfer to cleave the C-C/C-O bonds for aromatic monomers without any additional catalyst. The proton transfer from [BMim]+ to [ClO4]− could polarize the anion and decrease its structure stability, upon which the active hydroxyl radical generated and induced lignin C-C/C-O bonds fragmentation via free radical-mediated routes with the assistance of photothermal synergism. About 4.4 wt% yields of aromatic monomers, mainly composed of vanillin and acetosyringone, are afforded in [BMim][ClO4] under UV-light irradiation in the air at 80 °C. This work opens the way to produce value-added aromatic monomers from lignin using an eco-friendly, energy-efficient, and simple route that may contribute to the sustainable utilization of renewable natural resources.

Electrocatalytic valorization of lignocellulose-derived aromatics at industrial-scale current densities

Electrocatalytic hydrogenation of lignocellulosic bio-oil to value-added chemicals offers an attractive avenue to use the increasing intermittent renewable electricity and biomass-derived feedstocks. However, to date the partial current densities to target products of these reactions are lower than those needed for industrial-scale productivity, which limits its prospects. Here we report a flow-cell system equipped with a Rh diffusion electrode to hydrogenate lignocellulose-derived aromatic monomers, such as furans and lignin monomers, to value-added chemicals. We achieve high faradaic efficiencies up to 64% at industrial-scale current densities of 300–500 mA cm−2, representing high productivities to target products. A screening of electrocatalysts indicates that only by highly-electrolyte-permeable Rh diffusion electrodes are we able to unite current density with faradaic efficiency. We apply in-situ infrared reflection–absorption spectroscopy to investigate the electrode-potential-dependent reaction pathways and intermediates, confirming a wide potential window for efficient electrocatalytic hydrogenation of lignocellulose-derived aromatics to target products.

Using Enhanced Sampling Simulations to Study the Conformational Space of Chiral Aromatic Peptoid Monomers.

Peptoids, or N-substituted glycines, are peptide-like materials that form a wide variety of secondary structures owing to their enhanced flexibility and a diverse collection of possible side chains. Compared to that of peptides, peptoids have a substantially more complex conformational landscape. This is mainly due to the ability of the peptoid amide bond to exist in both cis- and trans-conformations. This makes conventional molecular dynamics simulations and even some enhanced sampling approaches unable to sample the complete energy landscapes. In this article, we present an extension to the CGenFF-NTOID peptoid atomistic forcefield by adding parameters for four side chains to the previously available collection. We employ explicit solvent well-tempered metadynamics simulations to optimize our forcefield parameters and parallel bias metadynamics to study the cis-trans isomerism for SN1-phenylethyl (s1pe) and SN1-naphthylethyl (s1ne) peptoid monomers, the free energy minima generated from which are validated with available experimental data. In the absence of experimental data, we supported our atomistic simulations with ab initio calculations. This work represents an important step toward the computational design of peptoid-based materials.

Free radical (Co)Polymerization of aromatic vinyl monomers derived from vanillin

Chemical structure (effect of functional substituents on vinyl bond reactivity) was used as a criterion to evaluate the (co)polymerization behavior of vanillin-derived 3-allyl-5-vinylveratrole, 4-vinylveratrole, and 2-glycidoxy-5-vinylanisole in chain-growth polymerization mechanism. After polymerization, allyl and epoxy functional groups of monomer units remain unaffected as macromolecular side groups and can be utilized in post-polymerization reactions (in particular, cross-linking). Due to the intermolecular chain transfer to polymer, a fraction of branched macromolecules can be formed in free radical polymerization of 3-allyl-5-vinylveratrole. At the same time, the kinetic study shows a similar polymerization rate for all the three investigated biobased aromatic vinyl monomers.Determined in copolymerization with methyl methacrylate Q-e values indicate that 3-allyl-5-vinylveratrole, 4-vinylveratrole and 2-glycidoxy-5-vinylanisole behave like conventional vinyl monomers and can be copolymerized interchangeably. In this manner, macromolecules with controlled amounts of cross-linkable epoxy and allyl groups incorporated into the backbone can be synthesized. Based on the glass transition temperature of the homopolymers thereof (66–93 °C), biobased aromatic vinyl monomers can serve as “rigid” macromolecular fragments and be applied in the formulation of thermoset polymer coatings. Being derived from renewable resources, 3-allyl-5-vinylveratrole, 4-vinylveratrole, and 2-glycidoxy-5-vinylanisole can be considered as a replacement for petroleum-based commodity styrene in the production of various industrial polymeric materials that utilize aromatic monomers.

Selective Cleavage of Methylene Linkage in Kraft Lignin over Commercial Zeolite in Isopropanol.

Lignin is an aromatic polymer that constitutes over 30 wt% of lignocellulosic biomass and is the most important source of renewable aromatics in nature. The global paper industry generates more than 70 million tons of Kraft lignin annually. Depolymerization of Kraft lignin to value-added monomers can significantly enhance the profitability of biorefinery. However, the method is impeded by the severe condensation of Kraft lignin during the pulping process, which forms robust C-C bonds and results in low monomer yields. In this study, we present a stepwise approach for producing valuable aromatic monomers from Kraft lignin through the cleavage of both C-O and C-C bonds. The approach initiated with complete cleavage of C-O bonds between lignin units within Kraft lignin through alcoholysis in isopropanol, resulting in a monomer yield of 8.9 %. Subsequently, the selective cleavage of methylene linkages present in the residual dimers and oligomers was achieved with commercial MCM-41 zeolite in the same pot, proceeding with an additional monomer yield of 4.0 %, thereby increasing the total monomer yield by 45 %. This work provides an avenue for increasing the depolymerization efficiency of Kraft lignin.

High‐Affinity Hybridization of Complementary Aromatic Oligoamide Strands in Water

AbstractWe prepared a series of water‐soluble aromatic oligoamide sequences all composed of a segment prone to form a single helix and a segment prone to dimerize into a double helix. These sequences exclusively assemble as antiparallel duplexes. The modification of the duplex inner rim by varying the nature of the substituents borne by the aromatic monomers allowed us to identify sequences that can hybridize by combining two chemically different strands, with high affinity and complete selectivity in water. X‐ray crystallography confirmed the expected antiparallel configuration of the duplexes whereas NMR spectroscopy and mass spectrometry allowed us to assess precisely the extent of the hybridization. The hybridization kinetics of the aromatic strands was shown to depend on both the nature of the substituents responsible for strand complementarity and the length of the aromatic strand. These results highlight the great potential of aromatic hetero‐duplex as a tool to construct non‐symmetrical dynamic supramolecular assemblies.

High-Affinity Hybridization of Complementary Aromatic Oligoamide Strands in Water.

We prepared a series of water-soluble aromatic oligoamide sequences all composed of a segment prone to form a single helix and a segment prone to dimerize into a double helix. These sequences exclusively assemble as antiparallel duplexes. The modification of the duplex inner rim by varying the nature of the substituents borne by the aromatic monomers allowed us to identify sequences that can hybridize by combining two chemically different strands, with high affinity and complete selectivity in water. X-ray crystallography confirmed the expected antiparallel configuration of the duplexes whereas NMR spectroscopy and mass spectrometry allowed us to assess precisely the extent of the hybridization. The hybridization kinetics of the aromatic strands was shown to depend on both the nature of the substituents responsible for strand complementarity and the length of the aromatic strand. These results highlight the great potential of aromatic hetero-duplex as a tool to construct non-symmetrical dynamic supramolecular assemblies.

The bifunctional active sites on carbon supported Fe-Mo bimetallic catalyst to improve Kraft lignin liquefaction

Carbon-supported Fe-Mo bimetallic catalysts were synthesized for the thermal catalytic ethanolysis of lignin to liquid fuels composed of aromatic monomers. A yield of 40.7 wt % of lignin oil, consisting of 38.8 wt % phenol monomers and 39.3 wt % benzeneacetaldehyde monomers, was obtained in the presence of Fe-Mo-P catalysts (1:0.5) at 290 °C for 4 h in the supercritical ethanol solvent (6.5 MPa). The catalysts exhibited a rich distribution of α-MoC nanoparticles, Fe0 nanoclusters, surface oxygen defects, and active species of Mo6+ and phosphoric acid on the graphitized microporous carbon substrate. The synergistic effects of these active components were crucial for enhancing lignin liquefaction efficiency. The ethanolysis of the lignin model compound revealed that the Fe-Mo bimetallic catalyst can facilitate double cracking of C-C/C-O bonds under supercritical ethanol conditions. In situ Raman and FT-IR characterization were performed to monitor the transformation of the Fe-Mo bimetallic catalyst from the precursor to the carbon material, including the dehydration and carbonization of the organic precursor.

Engineering multiple defect sites on ultrathin graphitic carbon nitride for efficiently photocatalytic conversion of lignin into monomeric aromatics via selective C–C bond scission

Lignin depolymerisation via photocatalytic cleavage of the selective interunit linkage in lignin could be a sustainable approach to produce monomeric aromatic chemicals. However, the insufficient investigation of interunit C–C bond fragmentation has obstructed the rational design of efficient photocatalytic system and further limit the yields of aromatic monomers from lignin depolymerisation. Herein, this work developed the ultrathin g-C3N4 with multiple defective sites by simple self-assembly process and in-situ thermal gas-shocking/etching process to catalyse the cleavage of lignin C–C bonds under visible light irradiation. Compared with the pristine g-C3N4, the developed g-C3N4 photocatalyst exhibited a superior catalytic activity (improved 102 %) and selectivity (∼90 %) in the cleavage of C–C bonds in lignin. This study demonstrated that the defects construction and ultrathin structure can optimise the electronic structures of g-C3N4 for better separation and transfer of photoinduced charges. And the control experiments and DFT calculation indicated that the created defect sites can promote the generation of essential reactive radicals (e.g., the activation of O2) and radical intermediates (C–H activation). The present work provides useful insights for the rational use of defect engineering in designing the efficient photocatalytic system for the conversion of lignin into aromatic monomers via the C–C bond cleavage.

Catalytic hydropyrolysis of biomass using natural zeolite-based catalysts

Natural clinoptilolite (coded as Escott), synthetic BEA, and mixed Escott-BEA zeolites supported nickel and iron catalysts were employed for catalytic hydropyrolysis of eucalyptus globulus leaves. Comparing non-catalytic pyrolysis and catalytic pyrolysis in N2, the use of catalysts along with H2 (30 bar) resulted in improved yields of liquid oil and gas products, with reduced production of biochar/coke. Moreover, the biochar from catalytic hydropyrolysis showed a higher mesopore surface area (97 m2/g) than non-catalytic biochar (74 m2/g). Incorporating a small amount of BEA into Escott weakens the metal-support interaction, enhances H2 adsorption activity and increases the catalyst acidity, leading to an improved aromatic monomers selectivity while preventing excessive cracking of liquid oil. Consequently, Ni-Fe/Escott-BEA catalyst shows the highest content of valuable liquid organic components. Ni-Fe/Escott, with the largest Ni particles and lowest acidity, exhibits higher selectivity to methane and naphthalenes products. In contrast, Ni-Fe/BEA with excessive acid sites exhibited significantly lower content of liquid organic products but higher yields of C2-C5 gas products and deposited carbon, primarily ascribed to its high acidity promoting coupling, cracking and deoxygenation reactions. The deactivation of Brønsted acid sites was more pronounced than Lewis acid sites, underscoring their crucial role in coupling reactions and leading to increased coke deposition.

Low-temperature pretreatment by AlCl3-catalyzed 1,4-butanediol solution for producing ‘ideal’ lignin with super-high content of β-O-4 linkages

High contents of internal β-O-4 linkages in lignin are critical for high-yield production of high-value aromatic monomers by depolymerization. However, it remains great challenge due to lack of suitable protection strategy. In this work, a very effective lignin-first strategy was developed to produce ideal lignin with a super high content of β-O-4 linkages (up to 72 %) from poplar, in which the pretreatment was undertaken at low temperatures of 90–130 °C with the use of AlCl3-catalyzed 1, 4-butanediol solution. 2D-HSQC NMR spectra revealed that lignin β-O-4 linkages were protected from etherification of the OH group by 1, 4-butanediol at the α position of lignin aliphatic chains. Besides, the OH groups at the γ position of lignin was also etherified, leading the formation of a structure of Ph-CH=CHCH2O(CH2)4OH. Interestingly, structure protection facilitated the formation of lignin nanoparticles via self-assembly (<100 nm). In addition, it was observed from pyrolysis results that addition of 1, 4-butanediol remarkably protected the structure of lignin by avoiding condensation, promoting the production of aromatics. The cellulose-rich fraction possessed a high cellulose digestibility of 91.64 % by enzymatic hydrolysis at a cellulase dosage of 15 FPU/g cellulose, approximately 6-fold untreated poplar (15.91 %). This low-temperature lignin-first strategy was of great importance for multi-products biorefining lignocellulose because it leads to the production of both lignin with super high content of β-O-4 linkages for depolymerization and highly digestible cellulose for sugar production.

The roles played by anionic and cationic species in the curing process of aromatic nitrile resins

Understanding the curing mechanism of aromatic nitrile (AN) resins is crucial for improving their curing efficiency. Blending the Bronsted acid-containing aromatic nitrile monomers (ACN) and Bronsted base-containing aromatic nitrile monomers (BCN) is a novel approach that simultaneously lowers the melting point and rapid curing reaction temperature of AN resins. To investigate the impact of anionic and cationic species on the curing behavior of ACN-BCN blends, a series of ACN-BCN blends were designed and synthesized. DSC and TGA results demonstrated a significant improvement in the curing efficiency when ACN and BCN blended, the curing temperature decreased by more than 50 ℃, accompanied by a decrease in melting point. According to the DMA results, the Tg of the cured substance of the system can reach 405 ℃ at the curing temperature of 325 ℃. The curing behaviors of ACN-BCN blends were studied through thermal analysis and spectroscopic analysis, which indicates that cationic species can polarize the cyano rather than attack the cyano groups, promoting their curing reaction. Moreover, it was determined that while cationic species play a polarizing role on the cyano, active anionic species attack the cyano, serving as the rate-determining step in the curing process of ACN-BCN blends.

Tuning the Electrochemical Properties of Poly‐thiophenes with a 2,5‐Dithienil‐N‐subtituted‐pyrrole Bearing an Aniline Moiety for Electrochromic Devices

AbstractConducting polymers find applications as active materials in electrochromic devices thanks to their tunable optoelectronic and electrochemical properties. Such versatility can be further enhanced by copolymerizing various aromatic monomers in order to produce new materials. In this work, we present different copolymers obtained by electropolymerization of an N‐substituted dithienylpyrrole (SNSBA) with either 3,4‐ethylendioxythiophene (EDOT) or bithiophene (BTh). The electrochemical, spectroscopic, and electrical properties were characterized across their different neutral and charged states by means of ex‐situ and in‐situ spectroelectrochemical techniques. The peculiar feature of SNSBA lies in the aniline bearing substituent of the central pyrrole unit that allows polymerization to occur at three different sites, yielding a cross‐linked polymer network. Our findings show that the SNSBA comonomer not only influences the optoelectronic properties of the final materials with respect to their homopolymers, but also induces a lowering of the hysteresis of the insulating/conducting transition (ΔEG&lt;280 mV), likely due to the cross‐linked nature of the polymer layer. These features are promising to develop a new class of copolymers for electrochromic devices with stable, reversible, and fast operation.