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Showing papers on "Ether published in 2014"


Journal ArticleDOI
TL;DR: The experiments suggest that the major product distribution is similar for all model compounds, but a stable phenyl-dihydrobenzofuran species is observed in the acidolysis of two of the γ-carbinol containing model compounds.
Abstract: Acid catalysis has long been used to depolymerize plant cell wall polysaccharides, and the mechanisms by which acid affects carbohydrates have been extensively studied. Lignin depolymerization, however, is not as well understood, primarily due to the heterogeneity and reactivity of lignin. We present an experimental and theoretical study of acid-catalyzed cleavage of two non-phenolic and two phenolic dimers that exhibit the β-O-4 ether linkage, the most common intermonomer bond in lignin. This work demonstrates that the rate of acid-catalyzed β-O-4 cleavage in dimers exhibiting a phenolic hydroxyl group is 2 orders of magnitude faster than in non-phenolic dimers. The experiments suggest that the major product distribution is similar for all model compounds, but a stable phenyl-dihydrobenzofuran species is observed in the acidolysis of two of the γ-carbinol containing model compounds. The presence of a methoxy substituent, commonly found in native lignin, prevents the formation of this intermediate. Reacti...

297 citations


Journal ArticleDOI
TL;DR: This study describes a molecular-defined iron complex, which allows for the hydrogenation of aryl, alkyl, heterocyclic nitriles and dinitriles, and constitutes the first example of an homogeneous catalyst, which permits the selective hydrogenations of industrially important adipodinitrile to 1,6-hexamethylenediamine.
Abstract: The catalytic hydrogenation of carboxylic acid derivatives represents an atom-efficient and clean reduction methodology in organic chemistry. More specifically, the selective hydrogenation of nitriles offers the possibility for a green synthesis of valuable primary amines. So far, this transformation lacks of useful, broadly applicable non-noble metal-based catalyst systems. In the present study, we describe a molecular-defined iron complex, which allows for the hydrogenation of aryl, alkyl, heterocyclic nitriles and dinitriles. By using an iron PNP pincer complex, we achieve very good functional group tolerance. Ester, ether, acetamido as well as amino substituents are not reduced in the presence of nitriles. Moreover, nitriles including an α,β-unsaturated double bond and halogenated derivatives are well tolerated in this reaction. Notably, our complex constitutes the first example of an homogeneous catalyst, which permits the selective hydrogenation of industrially important adipodinitrile to 1,6-hexamethylenediamine.

244 citations


Journal ArticleDOI
TL;DR: Hydrogenation of alkyl and aryl ketones using H2 is catalytically achieved in 18 examples using 5 mol % B(C6F5)3 in an ethereal solvent.
Abstract: Hydrogenation of alkyl and aryl ketones using H2 is catalytically achieved in 18 examples using 5 mol % B(C6F5)3 in an ethereal solvent. In these cases the borane and ether behave as a frustrated Lewis pair to activate H2 and effect the reduction.

218 citations


Journal ArticleDOI
TL;DR: The photoredox-mediated coupling of benzylic ethers with Schiff bases has been accomplished and Mechanistic studies suggest that a reductive quenching pathway of the photocatalyst is operable.
Abstract: The photoredox-mediated coupling of benzylic ethers with Schiff bases has been accomplished. Direct benzylic C–H activation by a combination of a thiol catalyst with an iridium photocatalyst and subsequent radical–radical coupling with secondary aldimines affords a variety of β-amino ether products in good to excellent yields. Mechanistic studies suggest that a reductive quenching pathway of the photocatalyst is operable.

210 citations


Journal ArticleDOI
TL;DR: A method for cobalt-catalyzed, aminoquinoline-directed ortho-functionalization of sp2 C–H bonds with alkenes has been developed and excellent functional group tolerance is observed.

208 citations


Journal ArticleDOI
TL;DR: The dehydroaryloxylation of aryl alkyl ethers using pincer iridium catalysts is reported, which represents a rare fully atom-economical method for ether C-O bond cleavage.
Abstract: The development of efficient catalytic methods to cleave the relatively unreactive C-O bonds of ethers remains an important challenge in catalysis. Building on our group's recent work, we report the dehydroaryloxylation of aryl alkyl ethers using pincer iridium catalysts. This method represents a rare fully atom-economical method for ether C-O bond cleavage.

183 citations


Journal ArticleDOI
TL;DR: A method for direct carbonylation of aminoquinoline benzamides has been developed andBenzoic and acrylic acid derivatives can be carbonylated by carbon monoxide affording imides in good yields.

176 citations


Journal ArticleDOI
TL;DR: In this article, the influence of reaction conditions (temperature, acidity) on the catalytic performance of supported Pt, Pd and Ru catalysts for the aqueous phase hydrodeoxygenation (HDO) of lignin model compounds was systematically investigated.

168 citations


Journal ArticleDOI
TL;DR: In this article, a series of Ni-containing catalysts with activated carbon, SBA-15, SiO2, and γ-Al2O3 supports were investigated for removing OCH3 from anisole.

164 citations


Journal ArticleDOI
TL;DR: A new approach is reported, which combines fast nucleophilic addition of H2S to an aldehyde group and the subsequent intramolecular thiolysis of dinitrophenyl ether, and can be used to develop efficient and effective H 2S probes.

159 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the stability of benzyl trimethylammonium (BTMA)-functionalized polyaromatic membranes and computed the barrier heights of aryl-aryl cleavage.
Abstract: Alkaline stability of benzyl trimethylammonium (BTMA)-functionalized polyaromatic membranes was investigated by computational modeling and experimental methods. The barrier height of hydroxide initiated aryl-ether cleavage in the polymer backbone was computed to be 85.8 kJ/mol, a value lower than the nucleophilic substitution of the α-carbons on the benzylic position of BTMA cationic functional group, computed to be 90.8 kJ/mol. The barrier heights of aryl–aryl cleavage (polymer backbone) are 223.8–246.0 kJ/mol. The computational modeling study suggests that the facile aryl–ether cleavage is not only due to the electron deficiency of the aryl group but also due to the low bond dissociation energy arising from the ether substituent. Ex situ degradation studies using Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR) spectroscopy indicated that 61% of the aryl–ether groups degraded after 2 h of treatment in 0.5 M NaOH at 80 °C. BTMA cationic groups degraded slowly over 48 h under the ...

Journal ArticleDOI
TL;DR: In this article, a mild and robust heterogeneous palladium-catalyzed CO bond cleavage of 2-aryloxy-1-arylethanols using formic acid as reducing agent in air was developed.
Abstract: A mild and robust heterogeneous palladium-catalyzed CO bond cleavage of 2-aryloxy-1-arylethanols using formic acid as reducing agent in air was developed. The cleaved products were isolated in 92–98 % yield; and by slightly varying the reaction conditions, a ketone, an alcohol, or an alkane can be generated in near-quantitative yield. This reaction is applicable to cleaving the b-O-4’-ether bond found in lignin polymers of different origin. The reaction was performed on a lignin polymer model to generate either the monomeric aryl ketone or alkane in a quantitative yield. Moderate depolymerization was achieved with native lignin at similar reaction conditions. Mechanistic studies under kinetic control indicate that an initial palladium-catalyzed dehydrogenation of the alcohol is followed by insertion of palladium to an enol equivalent. A palladium–formato complex reductively cleaves the palladium–enolate complex to generate the ketone.

Journal ArticleDOI
TL;DR: In this paper, a depolymerization of lignin was performed in subcritical water at 265 °C, 65 MPa for reaction times between 1-6 h in a batch reactor and in the presence of formic acid (FA) and Pd/C catalyst.

Journal ArticleDOI
TL;DR: A series of imidazolium-functionalized poly(ether ether ketone)s (PEEK-ImOHs) were successfully synthesized by a two-step chloromethylation-Menshutkin reaction followed by hydroxide exchange as mentioned in this paper.

Journal ArticleDOI
TL;DR: Higher lignin conversion to liquid products and maximum carbon conversion was achieved in this study and the presence of substituted phenols and aromatic ethers in liquid products was shown.

Journal ArticleDOI
TL;DR: In this paper, the production of alkyl levulinates from furfuryl alcohol (FAL) in alcohol media was investigated at moderate temperature in the presence of Bronsted acidic ionic liquids.

Journal ArticleDOI
TL;DR: The thermodynamically leveraged conversion of ethers and alcohols to saturated hydrocarbons is achieved efficiently with low loadings of homogeneous M(OTf)n + heterogeneous Pd tandem catalysts, and the reaction scope extends to efficient conversion of biomass-derived ethers to the corresponding alkanes.
Abstract: The thermodynamically leveraged conversion of ethers and alcohols to saturated hydrocarbons is achieved efficiently with low loadings of homogeneous M(OTf)n + heterogeneous Pd tandem catalysts (M = transition metal; OTf = triflate; n = 4). For example, Hf(OTf)4 mediates rapid endothermic ether ⇌ alcohol and alcohol ⇌ alkene equilibria, while Pd/C catalyzes the subsequent, exothermic alkene hydrogenation. The relative C–O cleavage rates scale as 3° > 2° > 1°. The reaction scope extends to efficient conversion of biomass-derived ethers, such as THF derivatives, to the corresponding alkanes.

Journal ArticleDOI
TL;DR: The benzoyl peroxide-promoted α-phenanthridinylation of ether by isocyanide is developed, proceeding throughDual C-H bond cleavage and dual C-C bond formation, which represents a facile pathway leading to 6-substituted phenanthridine derivatives.

Journal ArticleDOI
TL;DR: Hybrid membranes of sulfonated poly(ether ether ketone) (SPEEK) and mesoporous silica SBA-15 are prepared with various mass ratios for vanadium redox flow battery (VRB) application and investigated in detail as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, the authors explored catalytic pathways for the cleavage of ether bonds in benzyl phenyl ether (BPE) in liquid phase using Ni- and zeolite-based catalysts.

Journal ArticleDOI
TL;DR: In this article, the C-O aryl ether was cleaved by parallel hydrogenolysis and hydrolysis (hydrogenolysis combined with HO* addition) on Ni.

Journal ArticleDOI
TL;DR: In this paper, modified vinyl ether-based superplasticizers were synthesized from maleic anhydride (MA) and 4-hydroxy butyl vinyl ether (HBVE).
Abstract: Common polycarboxylate ether (PCE) superplasticizers that possess polyethylene glycol (PEG) graft chains exhibit high sensibility toward clay impurities contained in concrete aggregates and limestone powder. The presence of clay greatly weakens their dispersing ability. In this study, modified vinyl ether-based PCEs were synthesized from maleic anhydride (MA) and 4-hydroxy butyl vinyl ether (HBVE). We found that successful copolymerization of these two monomers is dependent on incorporation of at least ∼30 wt % of a maleic monoalkyl ester as an auxiliary comonomer. The resulting terpolymers were characterized and tested for their dispersing ability in cement paste in the absence and presence of montmorillonite. The MA–monoalkyl maleate–HBVE terpolymers are little affected by montmorillonite. Sorption measurements and X-ray diffraction analysis suggest that this novel type of PCE interacts with montmorillonite only via surface adsorption, whereas conventional PCEs possessing PEG graft chains incorporate ch...

Journal ArticleDOI
TL;DR: In this paper, a series of heterocyclic poly(aryl ether ketone)s containing 3,5-dimethyl phthalazinone moieties were synthesized via copolymerization of 4-(3,5dimethyl-4-hydroxyphenyl)(2H)-phthalazin-1-one, 4-(4,hydroxymhenyl), 4,4′-difluorobenzophenone.
Abstract: A series of heterocyclic poly(aryl ether ketone)s containing 3,5-dimethyl phthalazinone moieties were synthesized via the copolymerization of 4-(3,5-dimethyl-4-hydroxyphenyl)(2H)-phthalazin-1-one, 4-(4-hydroxyphenyl)(2H)-phthalazin-1-one and 4,4′-difluorobenzophenone. The resulting polymers were brominated with N-bromosuccinimide as the bromination reagent. Brominated poly(phthalazinone ether ketone) (BPPEK) with a degree of substitution in the range of 0.48–0.82 was obtained. Quaternized poly(phthalazinone ether ketone) anion exchange membranes (QBPPEK) were prepared from BPPEK membranes with trimethylamine as the amination reagent. Ion exchange capacity (IEC) values of the QBPPEK membranes were in the range of 0.82–1.53 mmol g−1. Compared with Nafion117 membrane, QBPPEK membranes showed much lower vanadium permeability. Coulombic efficiencies of the vanadium redox flow battery (VRB) with QBPPEK membranes were higher than that with the Nafion117 membrane. The energy efficiency of the VRB increased with an increase in the IEC of the QBPPEK membrane. The energy efficiency of the VRB cell with the QBPPEK membrane having an IEC of 1.53 mmol g−1 was 88%, which was higher than that of the cell with the Nafion117 membrane. During 100 charge–discharge cycles, the QBPPEK anion exchange membrane showed a stable performance.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the physical and chemical phenomena at the origin of the influence of cellulose ethers on flow onset of cement pastes. And they measured the formation of a new interaction network in the system, which found its origin in the bridging of cement grains by adsorbed ether molecules.

Journal ArticleDOI
TL;DR: C-O bond cleavage of allylic alkyl ether was realized in a Pd-catalyzed hydrogen-bond-activated allylicAlkylation using only alcohol solvents and can be easily extended to the asymmetric synthesis of enantiopure products (99% ee).

Journal ArticleDOI
TL;DR: A trityl ion mediated C-H functionalization of ethers with a wide range of nucleophiles at ambient temperature has been developed, displaying high chemoselectivity and good functional group tolerance and highlighting the capacity of the protocol in complex molecule synthesis.
Abstract: A trityl ion mediated C-H functionalization of ethers with a wide range of nucleophiles at ambient temperature has been developed. The reaction displays high chemoselectivity and good functional group tolerance. The protocol also exhibits excellent regio- and diastereoselectivities for the unsymmetric ethers, thus stereoselectively generating highly functionalized disubstituted 2,5-trans tetrahydrofurans (THF), 2,6-trans tetrahydropyrans (THP), 2,6-trans dihydropyrans (DHP), and 1,3-trans isochromans, and highlighting the capacity of the protocol in complex molecule synthesis.

Journal ArticleDOI
TL;DR: Complexes of a new multidentate ligand combining a rigid, strongly donating pincer scaffold with a flexible, weakly donating aza-crown ether moiety are reported, which exhibits tridentate, tetradentate, and pentadentate coordination modes.
Abstract: Complexes of a new multidentate ligand combining a rigid, strongly donating pincer scaffold with a flexible, weakly donating aza-crown ether moiety are reported. The pincer-crown ether ligand exhibits tridentate, tetradentate, and pentadentate coordination modes. The coordination mode can be changed by Lewis base displacement of the chelating ethers, with binding equilibria dramatically altered through lithium and sodium cation–macrocycle interactions. Cation-promoted hydrogen activation was accomplished by an iridium monohydride cation ligated in a pentadentate fashion by the pincer-crown ether ligand. The rate can be controlled on the basis of the choice of cation (with lithium-containing reactions proceeding about 10 times faster than sodium-containing reactions) or on the basis of the concentration of the cation. Up to 250-fold rate enhancements in H/D exchange rates are observed when catalytic amounts of Li+ are added.

Journal ArticleDOI
TL;DR: To develop a metal-organic framework for hydrogen storage, SNU-200 incorporating a 18-crown-6 ether moiety as a specific binding site for selected cations has been synthesized and exhibits characteristic gas-sorption properties depending on the bound cation.
Abstract: To develop a metal–organic framework (MOF) for hydrogen storage, SNU-200 incorporating a 18-crown-6 ether moiety as a specific binding site for selected cations has been synthesized. SNU-200 binds K+, NH4+, and methyl viologen(MV2+) through single-crystal to single-crystal transformations. It exhibits characteristic gas-sorption properties depending on the bound cation. SNU-200 activated with supercritical CO2 shows a higher isosteric heat (Qst) of H2 adsorption (7.70 kJ mol−1) than other zinc-based MOFs. Among the cation inclusions, K+ is the best for enhancing the isosteric heat of the H2 adsorption (9.92 kJ mol−1) as a result of the accessible open metal sites on the K+ ion.

Journal ArticleDOI
TL;DR: In this paper, NiNPs with tailored porosity and integrated Ni NPs (Ni@SiC) were synthesized via microphase separation of polycarbosilane-block-polyethylene followed by its pyrolysis.
Abstract: SiC materials with tailored porosity and integrated Ni NPs (Ni@SiC) were synthesized via microphase separation of polycarbosilane-block-polyethylene followed by its pyrolysis. Changing the length of organic block allowed the synthesis of micro, meso and hierarchical Ni@SiC materials which were characterized by PXRD, TEM, TGA, and nitrogen physisorption. Selective hydrogenolysis of aryl ethers mimicking the most abundant linkages of lignin was achieved in water avoiding the possible hydrogenation of aromatic rings. The sustainable production of fine chemicals and fuels from re- newable resources is a burgeoning and challenging research area. (1) Lignocellulose biomass (cellulose, hemi-cellulose and lignin) is a key resource whose availability is plentiful and its utilisation will allay the fears regarding competition with food supplies. (1, 2) Although cellulose can be depolymerised in many ways, (3) selective cleavage of aryl ether (CArO) and especially diaryl ether substructures of lignin is challenging. (4) Lignin con- stitutes 15-30 % of woody biomass (5) with an energy content of up to 40 % of this biomass (6) and its selective depolymerisa- tion (through hydrogenolysis) is crucial for the generation of fuel and chemicals from renewable resources. Selective cleav- age of the CArO bond of lignin model compounds in organic solvents has been reported by the use of molecular catalysts (V, (7) Ru (8) and Ni (9) complexes) and heterogeneous catalysts

Journal ArticleDOI
TL;DR: A new family of iron catalysts capable of promoting chemoselective α-oxidation of a range of ethers with excellent mass balance and high turnover numbers under 1 atm of O2 with no need for any additives is reported.
Abstract: Selective α-oxidation of ethers under aerobic conditions is a long-pursued transformation; however, a green and efficient catalytic version of this reaction remains challenging. Herein, we report a new family of iron catalysts capable of promoting chemoselective α-oxidation of a range of ethers with excellent mass balance and high turnover numbers under 1 atm of O2 with no need for any additives. Unlike metalloenzymes and related biomimetics, the catalyst produces H2 as the only byproduct. Mechanistic investigations provide evidence for an unexpected two-step reaction pathway, which involves dehydrogenative incorporation of O2 into the ether to give a peroxobisether intermediate followed by cleavage of the peroxy bond to form two ester molecules, releasing stoichiometric H2 gas in each step. The operational simplicity and environmental friendliness of this methodology affords a useful alternative for performing oxidation, while the unique ability of the catalyst in oxygenating a substrate via dehydrogenat...