Showing papers on "Ether published in 2019"
TL;DR: A route to the synthesis of hindered ethers is developed, in which electrochemical oxidation is used to liberate high-energy carbocations that are then captured by an alcohol that enables the formation of a range of ethers that would otherwise be difficult to access.
Abstract: Hindered ethers are of high value for various applications; however, they remain an underexplored area of chemical space because they are difficult to synthesize via conventional reactions1,2. Such motifs are highly coveted in medicinal chemistry, because extensive substitution about the ether bond prevents unwanted metabolic processes that can lead to rapid degradation in vivo. Here we report a simple route towards the synthesis of hindered ethers, in which electrochemical oxidation is used to liberate high-energy carbocations from simple carboxylic acids. These reactive carbocation intermediates, which are generated with low electrochemical potentials, capture an alcohol donor under non-acidic conditions; this enables the formation of a range of ethers (more than 80 have been prepared here) that would otherwise be difficult to access. The carbocations can also be intercepted by simple nucleophiles, leading to the formation of hindered alcohols and even alkyl fluorides. This method was evaluated for its ability to circumvent the synthetic bottlenecks encountered in the preparation of 12 chemical scaffolds, leading to higher yields of the required products, in addition to substantial reductions in the number of steps and the amount of labour required to prepare them. The use of molecular probes and the results of kinetic studies support the proposed mechanism and the role of additives under the conditions examined. The reaction manifold that we report here demonstrates the power of electrochemistry to access highly reactive intermediates under mild conditions and, in turn, the substantial improvements in efficiency that can be achieved with these otherwise-inaccessible intermediates.
194 citations
TL;DR: This work demonstrates silyl ether metathesis reaction as a new, robust dynamic covalent chemistries to introduce plasticity, reprocessability, and recyclability to thermosets.
Abstract: Vitrimers are a new class of polymeric materials that simultaneously offer the desired physical properties of thermosets and malleability/reprocessability of thermoplastics. Despite significant progress being made in the field of vitrimers, there exists a critical need for the development of robust dynamic covalent chemistries for the production of strong and thermally stable vitrimers. In this work, we discovered a new silyl ether metathesis reaction and used it for the preparation of vitrimers with exceptional thermal stability. In small-molecule model studies, we observed that silyl ether motifs directly exchange under anhydrous conditions catalyzed by a Bronsted or Lewis acid catalyst. For initial vitrimer demonstration, a commodity polymer, poly(ethylene-co-vinyl alcohol) (PEOH), was silylated with trimethylsilyl (TMS) groups followed by cross-linking with a bis-silyl ether cross-linker. The resulting thermoset showed exceptional thermal stability while maintaining malleability/reprocessability at elevated temperatures. The vitrimer properties such as recyclability and stress relaxation at various temperatures were carefully investigated. The material was reprocessable at 150 °C while also exhibiting good creep resistance at temperatures below its melting transition (Tm). This work demonstrates the silyl ether metathesis reaction as a new, robust dynamic covalent chemistry to introduce plasticity, reprocessability, and recyclability to thermosets.
152 citations
TL;DR: This work reports an economical and environmentally friendly, external hydrogen-free method for the selective cleavage of lignin and lign in model compounds into value-added chemicals.
Abstract: Selective hydrogenolysis of the Caryl–O bonds in lignin is a key strategy for the generation of fuels and chemical feedstocks from biomass. Currently, hydrogenolysis has been mainly conducted using hydrogen, which is flammable and not sustainable or economical. Herein, an external hydrogen-free process for aryl ethers hydrogenolysis in lignin models and dioxasolv lignin over nickel nanoparticles supported on Al2O3, is reported. Kinetic studies reveal that the transfer hydrogenolysis activity of the three model compounds decreased in the following order: benzyl phenyl ether (α-O-4), 2-phenylethyl phenyl ether (β-O-4) and diphenyl ether (4-O-5), which linearly corresponds to their binding energies and the activation energies. The main reaction route for the three model compounds was the cleavage of the ether bonds to produce aromatic alkanes and phenol, and the latter was further reduced to cyclohexanol. Dioxasolv lignin depolymerization results exhibit a significant Caryl–O decrease over the Ni nanoparticles supported on Al2O3 with iso-propanol as the hydrogen source through 2D-HSQC-NMR analysis, which confirmed the transfer hydrogenolysis conclusion in the model study. This work provides an economical and environmentally-friendly method for the selective cleavage of lignin and lignin model compounds into value-added chemicals.
124 citations
TL;DR: In this paper, the authors investigated compression ignition characteristics for different concentrations of diethyl ether in diesel - Calophyllum Inophyllium Methyl Ester blends and found that the brake thermal efficiency was reduced by 5.3% with increase in brake specific fuel consumption.
117 citations
TL;DR: A photochemical method that under visible light irradiation, selectfluor can effectively promote the oxidative cross-coupling between alcohols and heteroarenes without the external photocatalysis, achieving the selective α sp3 C–H arylation of alcohol, even in the presence of ether.
Abstract: Considering the synthetic value of introducing active alcoholic hydroxyl group, developing C-H functionalization of alcohols is of significance. Herein, we present a photochemical method that under visible light irradiation, selectfluor can effectively promote the oxidative cross-coupling between alcohols and heteroarenes without the external photocatalysis, achieving the selective α sp3 C-H arylation of alcohol, even in the presence of ether. The N-F activation of selectfluor under blue LEDs irradiation is evidenced by electron paramagnetic resonance (EPR) study, which is the key process for the oxidative activation of α sp3 C-H alcohols. The observed reactivity may have significant implications for chemical transformations.
111 citations
TL;DR: Application of the total oxidizable precursor (TOP) assay in its proposed enhanced form revealed high levels of PFEAs, the presence of precursors that form perfluoroalkyl carboxylic acids, and the absence of precursor that form P FEAs in surface water impacted by PFAS-containing wastewater discharges.
Abstract: Per- and polyfluoroalkyl substances (PFASs) are widely used anthropogenic chemicals. The PFAS class includes almost 5000 registered compounds, but analytical methods are lacking for most PFASs. The total oxidizable precursor (TOP) assay was developed to indirectly quantify unknown PFASs that are precursors to commonly measured perfluoroalkyl acids. To understand the behavior of recently identified per- and polyfluoroalkyl ether acids (PFEAs), including fluorinated replacements and manufacturing byproducts, we determined the fate of 15 PFEAs in the TOP assay. Ten perfluoroalkyl ether acids and a chlorinated polyfluoroalkyl ether acid (F-53B) were stable in the TOP assay and represent terminal products that are likely as persistent as historically used PFASs. Adding perfluoroalkyl ether acids and F-53B to the target analyte list for the TOP assay is recommended to capture a higher percentage of the total PFAS concentration in environmental samples. In contrast, polyfluoroalkyl ether acids with a -O-CFH- moiety were oxidized, typically to products that could not be identified by liquid chromatography and high-resolution mass spectrometry. Application of the TOP assay in its proposed enhanced form revealed high levels of PFEAs, the presence of precursors that form perfluoroalkyl carboxylic acids, and the absence of precursors that form PFEAs in surface water impacted by PFAS-containing wastewater discharges.
108 citations
TL;DR: In this paper, a mixture of biobased poly(ethylene terephthalate) and isopropyl alcohol fractioned hardwood organosolv lignin was used to obtain a turbostratic carbon phase and a smooth surface.
105 citations
TL;DR: A supramolecular polymeric adhesive prepared from non-viscous, non-polymeric materials by water-participant hydrogen bonds displays strong, reversible adhesion to hydrophilic surfaces, a property that forecasts the application of hydrogen bonding in advanced supramolescular materials.
Abstract: A supramolecular polymeric adhesive was prepared from non-viscous, non-polymeric materials by water-participant hydrogen bonds. Pt-pyridine coordination and water-crown ether hydrogen bonding combine to effect the supramolecular polymerization. The supramolecular polymeric adhesive displays strong, reversible adhesion to hydrophilic surfaces, a property that forecasts the application of hydrogen bonding in advanced supramolecular materials.
85 citations
TL;DR: Sanaee et al. as mentioned in this paper presented a novel high-performance mixed matrix membrane (MMM) with a low amount (< 2wt.%) of filler loading, in which the synthesized copper nanoparticles (Cu) incorporated into a glycerol-modified poly(Pebax 1657, Pe).
81 citations
TL;DR: A novel amphoteric membrane was designed by blending triple tertiary amine-grafted poly(2,6-dimethyl-1,4-phenylene oxide) with sulfonated poly(ether ether ketone) (SPEEK) for vanadium redox flow batteries and exhibits an excellent performance.
Abstract: A novel amphoteric membrane was designed by blending triple tertiary amine-grafted poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-TTA) with sulfonated poly(ether ether ketone) (SPEEK) for vanadium red...
78 citations
TL;DR: Tailor-made star polymers comprised of cross-linked cores containing polymeric pseudo-crown ether cavities and linear poly(ethylene oxide) (PEO) arms are designed via cation template-assisted cyclopolymerization as discussed by the authors.
TL;DR: In this paper, a nanocomposite membrane based on sulfonated poly (ether ether ketone) (SPEEK) and core-shell TiO2 nanoparticles was prepared.
TL;DR: A poly(ether imide) (PEI) membrane that has good chemical and mechanical stabilities was designed and synthesized in this article, which was fabricated by solution casting of chloromethylated PEI (CM-PEI), followed by quaternization and alkalization.
TL;DR: In this paper, a crosslinked single-component polyarylene ether nitrile (CSC-PEN) composites were fabricated and improved dielectric properties of the composite were obtained.
22 Jul 2019
TL;DR: In this article, PBF2-Br was used as an ion exchange membrane (AEM) with flexible alkyl pendent chains terminated with piperidinium cations, achieving a peak power density of 410 mW cm-2 for an alkaline fuel cell using the selected PBF1-OH (OH- form) as AEM.
Abstract: Ether-bond-free polyfluorene (PBF) anion exchange membranes (AEMs) containing flexible alkyl pendent chains terminated with piperidinium cations were prepared via one-pot, superacid-catalyzed polycondensation and a subsequent quaternization reaction. Hydrophilic and hydrophobic microphase segregation was observed in all AEMs. The hydroxide conductivity of PBF2-Br reaches up to 86 mS cm–1 at 80 °C, and 1H NMR showed no measurable degradation after alkaline treatment in aqueous NaOH (1 M) solution for 1200 h at 80 °C. Besides, a peak power density of 410 mW cm–2 was achieved at 60 °C for an alkaline fuel cell using the selected PBF1-OH (OH– form) as AEM.
TL;DR: A non-comprehensive review of the structural motifs and catalytic applications of crown ether-containing transition metal catalysts is reviewed, then the development of catalysts based on "pincer-crown ether" ligands that bridge the primary and secondary coordination spheres are detailed.
TL;DR: In this article, a new cross-linking agent grafted with SO3H groups via side chain spacer by sultone group ring-opening reaction was proposed for vanadium redox flow battery applications.
TL;DR: Wang et al. as discussed by the authors developed a facile and effective strategy to prepare super-hydrophobic/super-oleophilic nanofibrous composite membranes, which perfectly integrated the two processes of electrospinning and fixing hydrophobic TiO2 nanoparticles to the surface of interconnected poly(arylene ether nitrile) (PEN) nanofibrers using EVO-STIK serious glue.
Abstract: Nanofibrous membranes with super-wetting feature exhibit promising application for oil/water emulsion separation, but achieving durability and high separation efficiency in harsh environments remains challenging. Herein, we developed a facile and effective strategy to prepare super-hydrophobic/super-oleophilic nanofibrous composite membranes, which perfectly integrated the two processes of electrospinning and fixing hydrophobic TiO2 nanoparticles to the surface of interconnected poly(arylene ether nitrile) (PEN) nanofibers using EVO-STIK serious glue. As a result, the constructed super-hydrophobic PEN/P–TiO2 nanofibrous composite membranes (WCA = 165 ± 2.4°) exhibited excellent separation efficiency (99.75 ± 0.12%) under gravity drive, with extremely high separation flux of 6853.65 ± 274 L/m2·h for surfactant-free emulsions and 3531.62 ± 231 L/m2·h for surfactant-stabilized emulsions. More importantly, the obtained PEN/P–TiO2 nanofibrous composite membranes showed stable super-hydrophobic feature and oil/water emulsion separation performance in harsh environments such as strongly corrosive solutions, physical damage, and high/low-temperature systems. Therefore, the super-wetting nanofibrous membranes with easy-handling, durable, and efficient oil/water separation performance could find potential application for emulsified oil-water separation system in harsh environments.
TL;DR: The newly developed adsorbent has a potential application for removing cesium out of wastewater and salt lakes and shows good agreement with the Langmuir and the pseudo-second-order models.
TL;DR: This group of molecules is an interesting example that illustrates why older predictive models for the sensitivity values of energetic materials like bond dissociation enthalpy and electrostatic potential sometimes give results that deviate significantly from the experimentally determined values.
Abstract: Decades after the initial discovery of bis(2,4,6-trinitrophenyl) ether derivatives, the first single-crystal X-ray structures for three members of this compound class can finally be shown and the analytical data could be completed. This group of molecules is an interesting example that illustrates why older predictive models for the sensitivity values of energetic materials like bond dissociation enthalpy and electrostatic potential sometimes give results that deviate significantly from the experimentally determined values. By applying newer models like Hirshfeld surface analysis and fingerprint plot analysis that utilize the crystal structure of an energetic material, the experimentally found trend of sensitivities could be understood and the older models could be brought into a proper perspective. In the future, the prediction of structure-property relationships for energetic molecules starting from a crystal structure can be achieved and should be pursued.
TL;DR: In this article, the authors investigated the pyrolysis mechanism of typical ether linkages in biomass including β-1,4-glycosidic bond, α-O-4 bond and methoxyl using cellobiose, benzylphenyl ether and guaiacol as the model compounds.
TL;DR: In this paper, bifunctional Ru/hydroxyapatite has been prepared via ion exchange and subsequent reduction, which could efficiently catalyze the cleavage of various compounds containing aromatic ether bonds without additional bases.
TL;DR: In this article, a functionalized nanocrystal cellulose bearing amino and sulfonic acid groups (Am-sNCC) is prepared through a two-step chemical modification of microcrystal celluloses powders, first by sulfonic acids and then by a 3-trimethoxysilyl propyl ethylenediamine.
TL;DR: In this paper, the effects of Ru and RuO2 on hydrogenolysis of the Cβ-O bonds of lignin model compounds were investigated using X-ray diffraction and H2 Temperature-programmed reduction (TPR).
Abstract: Lignin is a potential renewable feedstock for aromatic compounds. Lignin glues cellulose and hemicellulose together in a rigid structure that protects plants from weather, insects, and disease. This rigidity also poses a barrier to cleavage of lignin into aromatic compounds. Typically, lignin is depolymerized by metal-catalyzed hydrogenolysis of its β-O-4 aryl ether (Cβ-O) bonds; this process requires high H2 pressure. Here, we show that the abundant aliphatic hydroxyl groups (Cα-OH) in lignin structure, can serve as the hydrogen source in Ru-catalyzed hydrogenolysis of the Cβ-O bonds. We pretreated the Ru/C catalyst under reducing and oxidizing conditions to generate various Ru/RuO2 ratios. Then we investigated the effects of Ru and RuO2 on hydrogenolysis of the Cβ-O bonds of lignin model compounds. We used X-ray diffraction (XRD) and H2 Temperature-programmed reduction (TPR) to determine changes of grain size and Ru content of the Ru/C catalysts, respectively. Our results revealed that Ru/C catalyzed hydrogenolysis of β-O-4 aryl ether bonds with internal hydrogen (self-hydrogen) as a hydrogen source. The elimination of external H2 in lignin hydrogenolysis is an efficient approach for lignin conversion to valuable aromatic chemicals.
TL;DR: In this article, a new and efficient magnetic nanocatalyst has been fabricated via covalent grafting of an aza-crown ether Cu(II) complex on silica coated iron oxide support.
TL;DR: Mechanism studies including electron spin resonance, fluorescence quenching experiments, and density functional theory (DFT) calculations proved the aryl migration pathway, which enables access to non-phenolic arylamine products from lignin conversion.
Abstract: Depolymerization of lignin meets the difficulty in cleaving the robust aryl ether bond. Herein, through installing an internal nucleophile in the β-O-4′ linkage, the selective cleavage of aryl ethe...
TL;DR: In this paper, a sidechain-type quaternized aromatic polyelectrolytes named QBz-PEEK-x have been synthesized via one-step benzylation modification of commercial poly(ether ether ketone) (PEEK).
TL;DR: It is shown that light can trigger sequence variations in abiotic information-containing polymers that possess photo-sensitive monomers that possess light-inert p-nitrobenzyl ether substituents.
Abstract: Light-induced alteration of macromolecular information plays a central role in biology and is known to influence health, aging and Darwinian evolution. Here, we report that light can also trigger sequence variations in abiotic information-containing polymers. Sequence-coded poly(phosphodiester)s were synthesized using four phosphoramidite monomers containing either photo-sensitive or photo-inert substituents. These monomers allow different sequence manipulations. For instance, using two light-cleavable monomers containing o-nitrobenzyl ether and o-nitroveratryl ether motifs, photo-erasable digital polymers were prepared. These polymers can be decoded by tandem mass spectrometry but become unreadable after UVA exposure. The opposite behavior, i.e. photo-revealable sequences, was obtained with polymers made of two isobaric monomers containing light-cleavable o-nitrobenzyl ether and light-inert p-nitrobenzyl ether substituents. Furthermore, when the latter two monomers were used in conjunction with a third monomer bearing a light-inert OH group, site-directed photo-mutations were induced in synthetic polymers. This was used herein to change the meaning of binary sequences.
TL;DR: This work uses mass spectrometry based technologies to detect and quantify 137 ether lipids to define a phenotype of healthy humans with exceptional lifespan, and demonstrates that a specific ether lipid signature can be obtained to define the centenarian state.
Abstract: A lipid profile resistant to oxidative damage is an inherent trait associated with animal lifespan. However, there is a lack of lipidomic studies on human longevity. Here we use mass spectrometry based technologies to detect and quantify 137 ether lipids to define a phenotype of healthy humans with exceptional lifespan. Ether lipids were chosen because of their antioxidant properties and ability to modulate oxidative stress. Our results demonstrate that a specific ether lipid signature can be obtained to define the centenarian state. This profile comprises higher level of alkyl forms derived from phosphatidylcholine with shorter number of carbon atoms and double bonds; and decreased content in alkenyl forms from phosphatidylethanolamine with longer chain length and higher double bonds. This compositional pattern suggests that ether lipids from centenarians are more resistant to lipid peroxidation, and that ether lipid signature expresses an optimized feature associated with exceptional human longevity. These results are in keeping with the free radical theory of aging.
TL;DR: Based on the chemical characteristics of sucrose, a synthesized sucrose-citric acid (SC) adhesive was prepared, featuring suitable viscosity and high solid content, which satisfied the China National Standard GB/T 9846-2015.
Abstract: The development of eco-friendly adhesives is a major research direction in the wood-based material industry. Previous research has already demonstrated the mixture of sucrose and citric acid could be utilized as an adhesive for the manufacture of particleboard. Herein, based on the chemical characteristics of sucrose, a synthesized sucrose-citric acid (SC) adhesive was prepared, featuring suitable viscosity and high solid content. The investigation of synthesis conditions on the bond performance showed that the optimal mass proportion between sucrose and citric acid was 25/75, the synthesis temperature was 100 °C, and the synthesis time was 2 h. The wet shear strength of the plywood bonded with SC adhesive, which was synthesized at optimal conditions and satisfied the China National Standard GB/T 9846-2015. The synthesis mechanism was studied by both 13C NMR analysis and HPLC, and the chemical composition manifesting caramelization reaction occurred during the synthesis process. The results of ATR FT-IR indicated the formation of a furan ring, carbonyl, and ether groups in the cured insoluble matter of the SC adhesive, which indicated dehydration condensation as the reaction mechanism between sucrose and citric acid.