Bond Construction Research Articles

Electrocatalytic Upgrading of Plastic and Biomass-Derived Polyols to Formamide under Ambient Conditions.

Electrocatalytic upgrading of wasted plastic and renewable biomass represents a sustainable method to produce chemicals but is limited to carbohydrates, leaving other value-added chemicals, such as organonitrogen compounds, being scarcely explored. Herein, we reported an electrocatalytic oxidation strategy to transform polyethylene terephthalate (PET) plastic-derived ethylene glycol (EG) and biomass-derived polyols into formamide, in the presence of ammonia (NH3) over a tungsten oxide (WO3) catalyst. Taking EG-to-formamide as an example, we achieved a high formamide productivity of 537.7 μmol cm-2 h-1 with FE of 43.2 % at a constant current of 100 mA cm-2 in a flow electrolyzer with 12-h test, representing a more advantageous performance compared with previous reports for formamide electrosynthesis. Mechanistic understanding revealed that the cleavage of the C-C bond in the EG was facilitated by nucleophilic attack of in situ formed nitrogen radicals from NH3, with resultant C-N bond construction and eventually formamide production. Furthermore, this strategy can be extended to transformation of PET bottle and a series of biomass-derived polyols with carbon number from three (glycerol) to six (glucose), producing formamide with high efficiencies. This work demonstrates a sustainable upgrading strategy of plastic and biomass that may have implications to more value-added chemicals production beyond carbohydrates.

Electrocatalytic Upgrading of Plastic and Biomass‐Derived Polyols to Formamide under Ambient Conditions

AbstractElectrocatalytic upgrading of wasted plastic and renewable biomass represents a sustainable method to produce chemicals but is limited to carbohydrates, leaving other value‐added chemicals, such as organonitrogen compounds, being scarcely explored. Herein, we reported an electrocatalytic oxidation strategy to transform polyethylene terephthalate (PET) plastic‐derived ethylene glycol (EG) and biomass‐derived polyols into formamide, in the presence of ammonia (NH3) over a tungsten oxide (WO3) catalyst. Taking EG‐to‐formamide as an example, we achieved a high formamide productivity of 537.7 μmol cm−2 h−1 with FE of 43.2 % at a constant current of 100 mA cm−2 in a flow electrolyzer with 12‐h test, representing a more advantageous performance compared with previous reports for formamide electrosynthesis. Mechanistic understanding revealed that the cleavage of the C−C bond in the EG was facilitated by nucleophilic attack of in situ formed nitrogen radicals from NH3, with resultant C−N bond construction and eventually formamide production. Furthermore, this strategy can be extended to transformation of PET bottle and a series of biomass‐derived polyols with carbon number from three (glycerol) to six (glucose), producing formamide with high efficiencies. This work demonstrates a sustainable upgrading strategy of plastic and biomass that may have implications to more value‐added chemicals production beyond carbohydrates.

Hydrogen bonds-based flexible regulation of acetaminophen adsorption/desorption behavior in aqueous system: Role of the smart thermoresponsive graphene oxide

Adsorption and regeneration techniques are crucial for the treatment of pharmaceuticals in drinking water. However, adsorbents with strong adsorption binding force and simple regeneration have been a challenging issue in the adsorption area that has not been successfully resolved. In this study, a thermos-responsive smart adsorbent, poly (N-isopropylacrylamide) modified graphene oxide (GO-g-PNIPAM) was successfully synthesized using a “graft from” surface-initiated atom-transfer radical polymerization (Si-ATRP) technology. Acetaminophen (Acet) has an excellent efficient adsorption/desorption behavior (107.40/83.9 mg/g) that is potentially flexible controlled by the modified adsorbent only by adjusting the temperature. This exceptional property is primarily caused by the phenomenon that PNIPAM cooperated with GO to undergo hydrophilic transformation in response to temperature changes, allowing for the free construction and deconstruction of hydrogen bonds between PNIPAM and contaminants. More importantly, as external factors (NaCl and urea) are mediated, the development of hydrogen bonds would be further encouraged to further stabilized the efficiency, and the desorption temperature would continue decrease by 2 and 6 °C, respectively, to promote the regeneration process. This outstanding work provides novel perspectives for subsequent smart sensitive materials to flexibly regulate the treatment efficiency of pollutants.

Electrocatalytic Coupling of Nitrate and Formaldehyde for Hexamethylenetetramine Synthesis via C-N Bond Construction and Ring Formation.

Hexamethylenetetramine (HMTA) is extensively used in the defense industry, medicines, food, plastics, rubber, and other applications. Traditional organic synthesis of HMTA relies on ammonia derived from the Haber process at high temperatures and pressures. In contrast, electrochemical methods enable a safe and green one-pot synthesis of HMTA from waste NO3-. However, HMTA synthesis through the electrochemical method is challenging owing to the complex reaction pathways involving C-N bond construction and ring formation. In this study, HMTA was efficiently synthesized over electrochemical oxidation-derived copper (e-OD-Cu), with a yield of 76.8% and a Faradaic efficiency of 74.9% at -0.30 VRHE. The catalytic mechanism and reaction pathway of HMTA synthesis on e-OD-Cu were investigated through a series of in situ characterization methods and density-functional theory calculations. The results demonstrated that the electrocatalytic synthesis of HMTA involved a tandem electrochemical-chemical reaction. Additionally, the results indicated that the presence of Cu vacancies enhanced substrate adsorption and inhibited the further hydrogenation of C═N. Overall, this study provides an electrocatalytic method for HMTA synthesis and an electrochemical strategy for constructing multiple C-N bonds.

Amidation of β‐Keto Sulfonyl Fluorides via C−C Bond Cleavage

AbstractA simple protocol for amide bond construction using β‐keto sulfonyl fluorides (BKSFs) as the acyl surrogates has been achieved. The reaction of BKSFs with a range of amines could be performed in presence of N‐bromosuccinimide (NBS), affording various amides with diverse functionalities. Preliminary mechanistic studies revealed that the dibromo‐substituted sulfonyl fluorides could be the key intermediate in this amidation process.

Mechanistic insight into C−S bond construction using CO2 as a carbon source: Synthesis of benzothiazoles from 2-aminothiophenols in imidazolium acetate

DFT calculations on synthesis of benzothiazoles via cyclization of 2-aminothiophenols with CO2 and triethoxysilane have revealed a novel mechanism that fundamentally differs from previously proposed mechanisms. In this new mechanism, the acetate anion plays a pivotal role in both stages of the reaction: first, in the formation of the formoxysilane intermediate via CO2 reduction, and second, in its subsequent transformation to the product, benzothiazoles. The acetate anion acts as a nucleophile to activate the Si−H bond of triethoxysilane in the CO2 reduction stage and as a base, deprotonating 2-aminothiophenol and generating a HOAc molecule, which then acts as a proton shuttle in the subsequent transformations leading to the final product. Throughout the whole reaction process, it is the acetate anion that plays a substantial role in catalyzing the reaction by activating the Si–H bond of triethoxysilane, contrasting with the previous notion that the imidazolium cation activates CO2 through the formation of a NHC-CO2 adduct. Furthermore, the proposed mechanism offers a rational explanation for the observed inefficiency of imidazolium trifluoromethansulfonate as a catalyst for this reaction. The elucidation of this new mechanism sheds light on the intricate details of the benzothiazole synthesis and may inspire further investigations in this field.

Applications of Baker-venkataraman Rearrangement in the Synthesis of Promising Organic Molecules

Abstract:: In organic synthesis, carbon-carbon bond formation is the fundamental transformation to create the carbon backbone of organic molecules and this key reaction is very popular in the improvement of organic chemistry, which exists at the bottom of the heart of the chemical sciences. The Baker- Venkataraman rearrangement has received great attention in the formation of 1,3-diketones through the regioselective construction of carboncarbon bonds. This rearrangement is an important type of chemical transformation in which the intramolecular migration of the ester acyl group takes place to provide 1,3-diketones in the presence of the base. Generally, 1,3-diketones or ortho-hydroxydibenzoylmethane derivatives undergo cyclization to provide the corresponding flavones in the presence of concentrated sulfuric acid. The Baker-Venkataraman rearrangement is frequently employed in the preparation of flavones and chromones. Besides, anthrapyran and anthracyclin antibiotics, benzopyrans, coumarins, xanthones, etc., are also synthesized with the help of these reactions. This review deals with the brilliant application of the Baker-Venkataraman rearrangement in the synthesis of promising organic compounds.

Visible Light-Induced Copper-Catalyzed Regio- and Stereoselective Difluoroalkylthiocyanation of Alkynes.

The first regio- and stereoselective difluoroalkylthiocyanation of alkynes with BrCF2R and KSCN has been disclosed under visible light-induced copper catalysis. The copper complex photosensitizer formed in situ not only promotes the generation of CF2-alkyl radicals but also facilitates the construction of C-SCN bonds, allowing the reaction to proceed smoothly without any additional photocatalysts or radical initiators. Moreover, the challenging internal alkynes can also be transformed to deliver CF2-derived tetrasubstituted olefins with potential applications in agricultural and medicinal chemistry.

Ambient-Light-Promoted Stereospecific Synthesis of (Z)-Vinyl Thioesters under Solvent- and Catalyst-Free Conditions.

An ambient-light-promoted stereospecific olefinic C(sp2)-S bond construction of thioacids and 1,1-diarylethenes has been demonstrated, affording various (Z)-vinyl thioesters in 51-85% yields under solvent- and catalyst-free conditions. Mechanistic studies indicated that the formation of thioacid-olefin complexes is responsible for generating a carbonyl thiyl radical and dioxygen in the air participates in the reaction and functions as a traceless reagent. Moreover, synthetic applications have been demonstrated by the gram scale synthesis and aggregation-induced emission property of representative compound 3i.

Building Block-Centric Approach to DNA-Encoded Library Design.

DNA-encoded library technology grants access to nearly infinite opportunities to explore the chemical structure space for drug discovery. Successful navigation depends on the design and synthesis of libraries with appropriate physicochemical properties (PCPs) and structural diversity while aligning with practical considerations. To this end, we analyze combinatorial library design constraints including the number of chemistry cycles, bond construction strategies, and building block (BB) class selection in pursuit of ideal library designs. We compare two-cycle library designs (amino acid + carboxylic acid, primary amine + carboxylic acid) in the context of PCPs and chemical space coverage, given different BB selection strategies and constraints. We find that broad availability of amines and acids is essential for enabling the widest exploration of chemical space. Surprisingly, cost is not a driving factor, and virtually, the same chemical space can be explored with "budget" BBs.

Nano-SiO2/polyurethane modified unsaturated polyester resin mortar for thin layer repairing on airport pavement

This paper introduces a novel toughened polymer mortar designed for runway repair, featuring outstanding impact resistance, high strength, and cost-effectiveness. To augment the toughness of unsaturated polyester (UP) polymer mortar, nano-SiO2 and polyurethane (PU) were incorporated. Firstly, the optimal dosages of nano-SiO2 and PU were determined through tensile test and impact test. Then, the modification mechanism of nano-SiO2/PU on UP resin was explored by microscopic image technology. In addition, the compression, flexural, fluidity, flexural bond strength and construction time tests were carried out to determine the optimal formula of nano-SiO2/PU modified UP resin mortar. Finally, the durability, impact resistance, impermeability resistance, skid resistance, and interlayer bond strength of modified UP resin mortar were studied and compared with those of pure UP resin mortar and epoxy (EP) resin mortar. Results show that the optimum proportion by mass for nano-SiO2/polyurethane modified UP resin is, UP resin: PU: dibutyltin dilaurate: nano-SiO2: initiator: accelerator: diluent: plasticizer = 1: 0.1: 0.002: 0.01: 0.01: 0.01:0.15:0.01. Furthermore, the mass proportion of modified UP resin to aggregate is 1: 1.2. In nano-SiO2/PU modification of UP resin, the -NCO groups of PU have been involved in chemical interaction with the -OH group of UP, while nano-SiO2 and UP resin are blended physically only. Compared with pure UP resin mortar, the nano-SiO2/PU modified UP resin mortar exhibited a 44% reduction in shrinkage rate, approximately 20% less corrosion loss, a 32% decrease in freeze-thaw loss, a 37% improvement in impact resistance, and increased shear bonding strength, flexural bonding strength, and tensile bonding strength by 44%, 33%, and 47%, respectively. Although the modified UP resin mortar demonstrated slightly lower performance in terms of dry shrinkage, corrosion resistance, skid resistance, and tensile bond strength compared to EP resin mortar, its freeze-thaw durability, impact resistance, flexural bond strength, and shear bond strength surpassed those of EP resin mortar. All three materials exhibited excellent impermeability. Leveraging the advantages of PU and nano-SiO2, the modified UP resin presents a promising repair material for airport pavement with enhanced toughness, high stability, and reduced cost.

In-Sb Covalent Bonds over Sb2Se3/In2Se3 Heterojunction for Enhanced Photoelectrochemical Water Splitting.

Antimony selenide is a promising P-type photocatalyst, but it has a large number of deep energy level defects, leading to severe carrier recombination. The construction of a heterojunction is a common way to resolve this problem. However, the conventional heterojunction system inevitably introduces interface defects. Herein, we employ in situ synthesis to epitaxially grow In2Se3 nanosheets on Sb2Se3 nanorods and form In-Sb covalent interfacial bonds. This petal-shaped heterostructure reduced interface defects and enhanced the efficiency of carrier separation and transport. In this work, the photocurrent density in the proposed Sb2Se3/In2Se3 photocathode is 0.485 mA cm-2 at 0 VRHE, which is 30 times higher than that of pristine Sb2Se3 and it has prominent long-term stability for 24 h without obvious decay. The results reveal that the synergy of the bidirectional built-in electric field constructed between In2Se3 and Sb2Se3 and the solid In-Sb interfacial bonds together build a high-efficiency transport channel for the photogenerated carriers that display enhanced photoelectrochemical (PEC) water-splitting performance. This work provides efficient guidance for reducing interface defects via the in situ synthesis and construction of interfacial bonds.

Media and Natural Disasters: Organising Storytelling in the Age of Climate Change

Starting on 2 November 2023, some territories in the Region of Tuscany in Italy were hit by exceptionally intense meteorological and calamitous events. The Region of Tuscany’s government was immediately at the forefront of relief, assisting the population, and aiding restoration. On 3 November, a national state of emergency was declared due to flooding. Journalistic communication is an essential aspect of disaster mitigation, preparedness, response and recovery. In terms of protecting people and reducing damage, journalists and the media have an important role to play. This article reports an Italian case study analysing the behaviour of local media in cases of natural disaster. Nine focus groups were conducted with local journalists covering the flood emergency. The results highlight the role of social and institutional mediation, rather than mere dissemination, played by the local press in emergency situations, a central element in the construction of a community bond, precisely in moments of insecurity and disorientation. The narration of a disaster from the inside seems to have allowed the emergence and representation of hitherto unknown social realities in Tuscany. The goal of the news coverage was widened, making it possible to respond better to the diverse interests of the reading public and to satisfy in a short time and exhaustively the information needs of individual communities in difficulty.

Formation and catalytic potential of sheet like nanostructured amino functionalized graphene oxide Schiff's base immobilized by Cu nanoparticles in Click reaction, oxidation of fluorene and in photodegradation of methylene blue

A heterogeneous catalyst, environmentally benign, containing copper immobilized over amino functionalized Schiff's base graphene oxide was prepared. The prepared nanocatalyst was explored in various organic transformations such as in tri-azoles formation, in oxidation and the degradation of methylene blue. Click chemistry was employed in the formation of triazoles for the construction of carbon-heteroatom bonds which have many applications ranging from drug discovery to material science. Our present work focused on graphene-based nanocatalyst (Cu @NH2GO) which provided excellent efficiency and catalytic activity in carrying out organic transformations. The prepared nanocatalyst was characterized and examined by various spectroscopic techniques such as X-ray diffraction (PXRD), thermo gravimetric analysis (TGA), field emission-scanning electron microscopy (FE-SEM), EDX, high-resolution transmission electron microscopy (HR-TEM), Fourier transformer infrared spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS). TEM images showed the light grey sheets of silane functionalized Schiff's base on which Cu nanoparticles were immobilized. The catalyst was also explored for the degradation of methylene blue which provided an effective path for the treatment of wastewater. Methylene Blue is one of the environmentally persistent, carcinogenic and mutagenic cationic dyes. A large volume of methylene blue containing wastewater is discharged into groundwater or surface water. So it becomes necessary to degrade the toxic dye by the use of a prepared nanocatalyst (Cu @NH2GO). Moreover, the catalyst possesses excellent stability and reusability.

Tungsten Oxide Dispersed on Silica as Robust and Readily Available Oxo/Imido Heterometathesis Catalyst.

Continuing our investigation of catalytic oxo/imido heterometathesis as novel water-free method for C=N bond construction, we report here the application of classical transition metal oxides dispersed on silica (MOx/SiO2, M=V, Mo, W) as cheap, robust and readily available alternative to the catalysts prepared via Surface Organometallic Chemistry (SOMC). The oxide materials demonstrated activity in heterometathetical imidation of ketones, WO3/SiO2 being the most efficient. We also describe a new well-defined supported W imido complex (≡SiO)W(=NMes)2(Me2Pyr) (Mes=2,4,6-Me3C6H2, Me2Pyr=2,5-dimethylpyrrolyl) and characterize it with SOMC protocols, which allowed us to identify the position of W on the oxo/imido heterometathesis activity scale (Mo<W<Ta) and showed that W in fact provides an optimal balance between activity and stability. Noteworthy, the performance of WO3/SiO2 was only slightly inferior to that of the SOMC analog enabling the efficient synthesis of a broad range of ketimines hardly accessible by classical methods, in most cases W being a competitive and robust alternative to the most active albeit highly sensitive Ti imido systems. Combined with the availability of the catalyst, this facilitates a more widespread application of heterometathesis methodology in organic synthesis including potential larger scale applications.

Paired electrocatalysis unlocks cross-dehydrogenative coupling of C(sp3)-H bonds using a pentacoordinated cobalt-salen catalyst

Cross-dehydrogenative coupling of C(sp3)-H bonds is an ideal approach for C(sp3)-C(sp3) bond construction. However, conventional approaches mainly rely on a single activation mode by either stoichiometric oxidants or electrochemical oxidation, which would lead to inferior selectivity in the reaction between similar C(sp3)-H bonds. Herein we describe our development of a paired electrocatalysis strategy to access an unconventional selectivity in the cross-dehydrogenative coupling of alcoholic α C(sp3)-H with allylic (or benzylic) C-H bonds, which combines hydrogen evolution reaction catalysis with hydride transfer catalysis. To maximize the synergistic effect of the catalyst combinations, a HER catalyst pentacoordinated Co-salen is disclosed. The catalyst displays a large redox-potential gap (1.98 V) and suitable redox potential. With the optimized catalyst combination, an electrochemical cross-dehydrogenative coupling protocol features unconventional chemoselectivity (C-C vs. C-O coupling), excellent functional group tolerance (84 examples), valuable byproduct (hydrogen), and high regio- and site-selectivity. A plausible reaction mechanism is also proposed to rationalize the experimental observations.

Electromagnetic Mill-Promoted Palladium-Catalyzed Heck-Type Cyclization/Decarboxylative Coupling of (Z)-1-Iodo-1,6-diene with Propiolic Acids.

Electromagnetic mill (EMM)-promoted solid-state cascade Heck-type cyclization/decarboxylative coupling of propiolic acid with (Z)-1-iodo-1,6-diene derivate was demonstrated. The reaction was realized via palladium catalysis, which is solvent-free and involves no additional heating. The collision between ferromagnetic rods could not only be a favor to the mixing between the solid substrates and the catalyst system, but also the thermogenic action could accelerate this transformation. More importantly, this EMM strategy realized multiple bond construction under mechanochemical conditions in one pot.

Bacterial Hydrazine Biosynthetic Pathways Featuring Cupin/Methionyl tRNA Synthetase-like Enzymes.

Nitrogen-Nitrogen (N-N) bond-containing functional groups in natural products and synthetic drugs play significant roles in exerting biological activities. The mechanisms of N-N bond formation in natural organic molecules have garnered increasing attention over the decades. Recent advances have illuminated various enzymatic and nonenzymatic strategies, and our understanding of natural N-N bond construction is rapidly expanding. A group of didomain proteins with zinc-binding cupin/methionyl-tRNA synthetase (MetRS)-like domains, also known as hydrazine synthetases, generates amino acid-based hydrazines, which serve as key biosynthetic precursors of diverse N-N bond-containing functionalities such as hydrazone, diazo, triazene, pyrazole, and pyridazinone groups. In this review, we summarize the current knowledge on hydrazine synthetase mechanisms and the various pathways employing this unique bond-forming machinery.

Unique biomedical application of fluorescence derivatization based on palladium-catalyzed coupling reactions for HPLC analysis of pharmaceuticals and biomolecules.

Palladium-catalyzed coupling reactions are versatile and powerful tools for the construction of carbon-carbon bonds in organic synthesis. Although these reactions have favorable features that proceed selectively in mild reaction conditions using aqueous organic solvents, no attention has been given to their application in the field of biomedical analysis. Therefore, we focused on these reactions and evaluated the scope and limitations of their analytical performance. In this review, we describe the pros and cons and future trends of fluorescence derivatization of pharmaceuticals and biomolecules based on palladium-catalyzed coupling reactions such as Suzuki-Miyaura coupling, Mizoroki-Heck coupling, and Sonogashira coupling reactions for HPLC analysis.

Digital: The Promise of the Unlimited?

At the crossroads of notions of Technical and Human lies the notion of limits. Let us question the vocabulary: here, limits in the plural, boundaries, edges…, to be also nuanced with the meanings of bounded, limited. They seem negative: could limits be flaws, deficiencies, or challenges to overcome? Indeed, the Human appears to be limited by the body in the three dimensions of space and in that of time; therefore, there would be physical and material limits, or weaknesses, on which technology can certainly act concretely. But should we necessarily surpass them and seize upon technologies to achieve this? On the other hand, we have the impression that our mind, being more immaterial, could project itself infinitely and onto everything, including the technologies themselves. Could it be that humans are made of an unlimited spirit that creates technology, housed in a limited body served by it? The digital is omnipresent in our lives, and we must take the time to study the new technical-societal relationship developing with it. Guided by contemporary philosophers and thinkers, we will examine what defines a technique in its specific case: its lineage, technologies, dissemination, and interactions with humans. We will explore 1/how the digital represents a technical lineage, 2/how this technique and its technologies have evolved in contemporary societies, its widespread impact on communication and the construction of social bonds, 3/how humanity has adapted to these transformations by becoming hypermodern, 4/the new relationship between humans and time, and 5/why time becomes the place and moment of the social life to survive the digital regime and hypermodernity. Despite its theoretical content and level of abstraction, this paper speaks to us, inhabitants of a digital world, who continually use digital technologies and always desire more, faster, in an irresistible need for speed and unlimited.