Showing papers on "Ether published in 2012"

Ni-catalyzed cleavage of aryl ethers in the aqueous phase.

Abstract: A novel Ni/SiO2-catalyzed route for selective cleavage of ether bonds of (lignin-derived) aromatic ethers and hydrogenation of the oxygen-containing intermediates at 120 °C in presence of 6 bar H2 in the aqueous phase is reported. The C–O bonds of α-O-4 and β-O-4 linkages are cleaved by hydrogenolysis on Ni, while the C–O bond of the 4-O-5 linkage is cleaved via parallel hydrogenolysis and hydrolysis. The difference is attributed to the fact that the Caliphatic–OH fragments generated from hydrolysis of α-O-4 and β-O-4 linkages can undergo further hydrogenolysis, while phenol (produced by hydrolysis of the 4-O-5 linkage) is hydrogenated to produce cyclohexanol under conditions investigated. The apparent activation energies, Ea(α-O-4) < Ea(β-O-4) < Ea(4-O-5), vary proportionally with the bond dissociation energies. In the conversion of β-O-4 and 4-O-5 ether bonds, C–O bond cleavage is the rate-determining step, with the reactants competing with hydrogen for active sites, leading to a maximum reaction rate a...

Solvent Effects on the Hydrogenolysis of Diphenyl Ether with Raney Nickel and their Implications for the Conversion of Lignin

Abstract: The conversion of lignin, the most recalcitrant of the biopolymers, is necessary for a carbon-efficient utilization of lignocellulosic materials. In this context, hydrogenolysis of lignin is a process receiving increasing attention. In this report, the solvent effects on the hydrogenolysis of diphenyl ether and lignin with Raney Ni are addressed. The Lewis basicity of the solvent very much affects the catalytic activity, so Raney Ni in nonbasic solvents is an extremely active catalyst for hydrogenolysis and hydrogenation. In basic solvents, however, Raney Ni is a less active, but much more selective catalyst for hydrogenolysis while preserving the aromatic products. With regard to the reactions with lignin, assessing the complexity of the product mixtures by two-dimensional GC×GC-MS revealed solvent effects on the product distribution. Reaction in methylcyclohexane resulted in cyclic alcohols and cyclic alkanes, whereas reaction in 2-propanol led to cyclic alcohols, cyclic ketones, and unsaturated products. The hydrogenolysis of lignin in methanol, however, produced mostly phenols. Overall, these results demonstrate that the solvent plays a key role in directing the selectivity and, thus, it must be taken into consideration in the design of catalytic systems for conversion of lignin by hydrogenolysis of C-O ether bonds.

Degradation of imidazolium- and quaternary ammonium-functionalized poly(fluorenyl ether ketone sulfone) anion exchange membranes

Abstract: Imidazolium and quaternary ammonium-functionalized poly(fluorenyl ether ketone sulfone)s were synthesized successfully with the same degree of cationic functionalization and identical polymer backbones for a comparative study of anion exchange membranes (AEMs) for solid-state alkaline membrane fuel cells (AMFCs). Both anion exchange membranes were synthesized using a new methyl-containing monomer that avoided the use of toxic chloromethylation reagents. The polymer chemical structures were confirmed by 1H NMR and FTIR. The derived AEMs were fully characterized by water uptake, anion conductivity, stability under aqueous basic conditions, and thermal stability. Interestingly, both the cationic groups and the polymer backbone were found to be degraded in 1 M NaOH solution at 60 °C over 48 h as measured by changes of ion exchange capacity and intrinsic viscosity. Imidazolium-functionalized poly(fluorenyl ether ketone sulfone)s had similar aqueous alkaline stability to quaternary ammonium-functionalized mater...

ICAR ATRP with ppm Cu Catalyst in Water

Abstract: Initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) with ppm amount of Cu catalyst was successfully developed in water. For the first time, Cu catalyst concentrations of 100 ppm and lower were used in aqueous media to prepare well-defined macromolecules. Polymers of oligo(ethylene oxide) methyl ether acrylate were synthesized with low dispersity (Mw/Mn = 1.15–1.28) using 20–100 ppm of an active CuBr/tris(pyridin-2-ylmethyl)amine-based catalyst in the presence of excess bromide anions. This technique was used to synthesize a thermoresponsive block copolymer of poly(oligo(ethylene oxide) methyl ether methacrylate)-b-poly(oligo(ethylene oxide) methyl ether acrylate). The methacrylic block had a lower critical solution temperature (LCST = 77 ± 2 °C) below that of the acrylic block. The hydrodynamic diameter of ca. 10 nm at temperatures below the LCST is consistent with free polymer chains in solution, and the diameter of ca. 30 nm above the LCST is consistent with...

Composite membranes based on sulfonated poly(ether ether ketone) and SDBS-adsorbed graphene oxide for direct methanol fuel cells

Abstract: Sodium dodecylbenzene sulfonate (SDBS) adsorbed graphene oxide (GO) has been used as a filler to modify sulfonated poly(ether ether ketone) (SPEEK). The incorporation of SDBS-GO greatly increases the ion-exchange capacity (IEC), water uptake, and proton conductivity, while it reduces the methanol permeability through the SPEEK membranes. With well controlled contents of SDBS-GO, the composite membranes exhibit higher IEC, water uptake, and proton conductivity and lower methanol permeability than Nafion® 112, making them attractive as proton exchange membranes (PEMs). These superior characteristics make the composite membranes with optimized SDBS-GO contents exhibit superior performance in direct methanol fuel cells (DMFCs) compared to the plain SPEEK or Nafion® 112 membranes.

A highly active bifunctional iridium complex with an alcohol/alkoxide-tethered N-heterocyclic carbene for alkylation of amines with alcohols.

Abstract: A series of new iridium(III) complexes containing bidentate N-heterocyclic carbenes (NHC) functionalized with an alcohol or ether group (NHC?OR, R=H, Me) were prepared. The complexes catalyzed the ...

Predicting autoxidation stability of ether- and amide-based electrolyte solvents for Li-air batteries.

Abstract: Finding suitable solvents remains one of the most elusive challenges in rechargeable, nonaqueous Li–air battery technology. Although ether and amides are identified as stable classes of aprotic solvents against nucleophilic attack by superoxide, many of them are prone to autoxidation under oxygen atmosphere. In this work, we use density functional theory calculations coupled with an implicit solvent model to investigate the autoxidative stability of ether- and N,N-dialkylamide-based solvents. The change in the activation free energy for the C–H bond cleavage by O2 is consistent with the extent of peroxide production for each class of solvent. Conversely, the thermodynamic stability alone is not sufficient to account for the observed variation in solvent reactivity toward O2. A detailed understanding of the factors influencing the autoxidative stability provides several strategies for designing molecules with enhanced air/O2 stability, comparable or superior to that of structurally related hydrocarbons. Th...

On the Mechanism of the Initiation Reaction in Grubbs–Hoveyda Complexes

Abstract: Grubbs–Hoveyda-type complexes with variable 4-R (complexes 1: 4-R = NEt2, OiPr, H, F, NO2) and 5-R substituents (complexes 2: 5-R = NEt2, OiPr, Me, F, NO2) at the 2-isopropoxy benzylidene ether ligand and with variable 4-R substituents (complexes 3: 4-R = H, NO2) at the 2-methoxy benzylidene ether ligand were synthesized and the respective Ru(II/III) redox potentials (ranging from ΔE = +0.46 to +1.04 V), and UV–vis spectra recorded. The initiation kinetics of complexes 1–3 with the olefins diethyl diallyl malonate (DEDAM), butyl vinyl ether (BuVE), 1-hexene, styrene, and 3,3-dimethylbut-1-ene were investigated using UV–vis spectroscopy. Electron-withdrawing groups at the benzylidene ether ligands were found to increase the initiation rates, while electron-donating groups lead to slower precatalyst activation; accordingly with DEDAM, the complex 1(NO2) initiates almost 100 times faster than 1(NEt2). The 4-R substituents (para to the benzylidene carbon) were found to have a stronger influence on physical an...

Nitrogen heterocyclic ring dichlorin allyl ether compounds with insecticidal activity

Abstract: The invention discloses a nitrogen heterocyclic ring dichloro-allyl ether compound which is shown in a formula (1) and has the insecticidal activity, and a preparation method thereof, wherein, R, n, A, and B are limited, as shown in an instruction book

Atomic Oxygen on Graphite: Chemical Characterization and Thermal Reduction

Abstract: The chemisorption of O atoms on graphite and the thermal reduction of the oxidized surface were studied by means of high energy resolution photoelectron spectroscopy with synchrotron radiation. The C 1s and O 1s core levels and the valence band spectra were used to identify the different oxidizing surface species and to evaluate the extension of the sp2 conjugation as a function of oxidation time and annealing temperature. We found that epoxy groups are the dominant species only at the low oxidation stage, and ethers and semiquinones form as oxidation proceeds. The evolution of the ether/epoxy ratio with increasing oxygen coverage provides evidence for the occurrence of C–C bond unzipping. Epoxy groups are the functionalities with the lowest thermal stability and start to desorb around 370 K, strongly affecting the desorption temperature of other functional groups. The ratio between ethers and epoxy groups determines the balance between epoxy–epoxy and epoxy–ether reactions, the latter promoting the remov...

Salting-in and salting-out of water-soluble polymers in aqueous salt solutions.

Abstract: To obtain further experimental evidence for the mechanisms of the salting effect produced by the addition of salting-out or sating-in inducing electrolytes to aqueous solutions of water-soluble polymers, systematic studies on the vapor-liquid equilibria and liquid-liquid equilibria of aqueous solutions of several polymers are performed in the presence of a large series of electrolytes. Polymers are polyethylene glycol 400 (PEG400), polyethylene glycol dimethyl ether 250 (PEGDME250), polyethylene glycol dimethyl ether 2000 (PEGDME2000), and polypropylene glycol 400 (PPG400), and the investigated electrolytes are KCl, NH(4)Cl, MgCl(2), (CH(3))(4)NCl, NaCl, NaNO(3), Na(2)CO(3), Na(2)SO(4), and Na(3)Cit (tri-sodium citrate). Aqueous solutions of PPG400 form aqueous two-phase systems with all the investigated salts; however, other investigated polymers form aqueous two-phase systems only with Na(2)CO(3), Na(2)SO(4), and Na(3)Cit. A relation was found between the salting-out or sating-in effects of electrolyte on the polymer aqueous solutions and the slopes of the constant water activity lines of ternary polymer-salt aqueous solutions, so that, in the case of the salting-out effect, the constant water activity lines had a concave slope, but in the case of the salting-in effects, the constant water activity lines had a convex slope. The effect of temperature, anion of electrolyte, cation of electrolyte, and type and molar mass of polymers were studied and the results interpreted in terms of the solute-water and solute-solute interactions. The salting-out effect results from the formation of ion (specially anion)-water hydration complexes, which, in turn, decreases hydration, and hence, the solubility of the polymer and the salting-in effect results from a direct binding of the cations to the ether oxygens of the polymers.

Nickel-mediated hydrogenolysis of C-O bonds of aryl ethers: what is the source of the hydrogen?

Abstract: Mechanistic studies of the hydrogenolysis of aryl ethers by nickel were undertaken with (diphosphine)aryl methyl ethers. A Ni(0) complex containing Ni–arene interactions adjacent to the aryl–O bond was isolated. Heating led to aryl–O bond activation and generation of a nickel aryl methoxide complex. Formal β-H elimination from this species produced a nickel aryl hydride which can undergo reductive elimination in the presence of formaldehyde to generate a carbon monoxide adduct of Ni(0). The reported complexes map out a plausible mechanism of aryl ether hydrogenolysis catalyzed by nickel. Investigations of a previously reported catalytic system using isotopically labeled substrates are consistent with the mechanism proposed in the stoichiometric system, involving β-H elimination from a nickel alkoxide rather than cleavage of the Ni–O bond by H2.

Synthesis of 1‐Octanol and 1,1‐Dioctyl Ether from Biomass‐Derived Platform Chemicals

Abstract: The happy medium: A new catalytic pathway for the synthesis of the linear primary C(8) alcohol products 1-octanol and dioctyl ether from furfural and acetone has been developed using retrosynthetic analysis. This opens a general strategy for the synthesis of medium-chain-length alcohols from carbohydrate feedstock.

Synthesis and Modification of Poly(ether ether ketone) and their Properties: A Review

Abstract: Synthetic aromatic polyarylether ketones are known for their high performance applications. Poly(ether ether ketone) is an important material which is most widely used in such aggressive environments as nuclear plants, oil and geothermal wells, chemical plants, and high-pressure steam valves. Considering the wide range of properties of PEEK polymers, a variety of structurally modified PEEK polymers are also reported. This review covers the detail of different synthetic and modification procedure, the characterization technique applied on PEEK. In brief, morphological and related properties are also described.

What causes the low viscosity of ether-functionalized ionic liquids? Its dependence on the increase of free volume

Abstract: A series of 12 ether-functionalized room temperature ionic liquids (RTILs) and their alkyl counterparts (short of an oxygen atom) were prepared and characterized to investigate the reason for the alkoxy chain effect on decreasing viscosity and how to best apply it. In addition to the ability of the alkoxy chains to decrease viscosity (ηO/η, as low as 0.594) and its activation energy (ΔEη, as low as -4.14 kJ mol−1), they were also found to be able to increase the total free volume (ΔFVO, up to 4.93 mL mol−1), by using density and surface tension. Furthermore, both the obtained ηO/η and ΔEη values for the 12 pairs of RTILs show a strong decreasing dependence on ΔFVO. Accordingly, the reason for the alkoxy chain effect on decreasing viscosity was proposed to be due to the ability of the highly flexible alkoxy chains to increase the total free volume, which offers the convenience of transport for the adjacent molecules. To maximize this effect, the alkoxy groups were supposed to contain a rod-like alkyl tail and a short –CH2– spacer between the ether O atom and the cationic N atom, and be in an environment without hydrogen bond donors. Generally, the ether-functionalized pyrrolidinium and ammonium RTILs possess high conductivity (up to 4.97 mS cm−1 at 25 °C) and wide electrochemical windows (∼5.75 V), indicating their significant promise for electrochemical applications.

Influence of Side-Chain on Structural Order and Photophysical Properties in Thiophene Based Diketopyrrolopyrroles: A Systematic Study

Abstract: In this work, we have synthesized a series of TDPP derivatives with different alkyl groups such as n-hexyl (−C6H13) 3a, 2-ethylhexyl (-(2-C2H5)C6H12) 3b, triethylene glycol mono methyl ether (-(CH2CH2O)3cH3, TEG) 3c, and octadodecyl (-(8-C8H17)C12H22) 3d. N,N dialkylation of thiophene-diketopyrrolopyrrole (TDPP, 1) strongly influences its solubility, solid state packing, and structural order. These materials allow us to explicitly study the influence of alkyl chain on solid state packing and photophysical properties. TDPP moiety containing two different alkyl groups 3e (TEG and 2-ethylhexyl) and 3f (TEG and n-hexyl) were synthesized for the first time. The absorption spectra of all derivatives exhibited a red shift in solid state when compared to their solution spectra. The type of alkyl chains leads to change in the optical band gaps in solid state. The fluorescence study reveals that TDPP derivatives have strong π–π interaction in the solid state and the extent of bathochromic shift is due to combinatio...

Molybdenum(VI) dioxo complexes employing Schiff base ligands with an intramolecular donor for highly selective olefin epoxidation.

Abstract: Reaction of [MoO(2)(η(2)-tBu(2)pz)(2)] with Schiff base ligands HL(X) (X = 1-5) gave molybdenum(VI) dioxo complexes of the type cis-[MoO(2)(L(X))(2)] as yellow to light brown solids in moderate to good yields. All ligands coordinate via its phenolic O atom and the imine N atom in a bidentate manner to the metal center. The third donor atom (R(2) = OMe or NMe(2)) in the side chain in complexes 1-4 is not involved in coordination and remains pendant. This was confirmed by X-ray diffraction analyses of complexes 1 and 3. Complexes 1, 3, and 5 exist as a mixture of two isomers in solution, whereas complexes 2 and 4 with sterically less demanding substituents on the aromatics only show one isomer in solution. All complexes are active catalysts in the epoxidation of various internal and terminal alkenes, and epoxides in moderate to good yields with high selectivities are obtained. In the challenging epoxidation of styrene, complexes 1 and 2 prove to be very active and selective. The selectivity seems to be influenced by the pendant donor arm, as complex 5 without additional donor in the side chain is less selective. Experiments prove that the addition of n-butyl methyl ether as intermolecular donor per se has no influence on the selectivity. The basic conditions induced by the NMe(2) groups in complexes 3 and 4 lead to lower activity.

A material with high electromagnetic radiation shielding effectiveness fabricated using multi-walled carbon nanotubes wrapped with poly(ether sulfone) in a poly(ether ether ketone) matrix

Abstract: An electromagnetic radiation absorber material with high shielding effectiveness as well as good mechanical and thermal properties was produced using multi-walled carbon nanotubes (MWCNTs) wrapped in poly(ether sulfone) (PES) dispersed in a poly(ether ether ketone) (PEEK) matrix fabricated by melt-blending. The electromagnetic, mechanical, and thermal properties of this material were characterized using a vector network analyzer, universal tester, and thermal gravimetric analyzer, respectively. The results indicate that wrapped-MWCNT–PEEK composites show different degrees of improvement in the measured properties compared to pure PEEK. This is attributed to the high conductivity of MWCNTs, the good dispersion of wrapped-MWCNTs in PEEK, and the strong interfacial adhesion between wrapped-MWCNTs and PEEK.

Aryl Ether as a Negishi Coupling Partner: An Approach for Constructing C ? C Bonds under Mild Conditions

Abstract: An etheric Negishi coupling: The first cross-coupling reaction between aryl alkyl ethers and dianion-type zincate reagents to afford biaryl compounds through selective cleavage of the etheric C(sp(2))-O bond was developed. Dianion-type zincates showed excellent reactivity toward the aromatic ethers under mild conditions, with good functional group compatibility (see scheme).

Highly efficient blue electrophosphorescent polymers with fluorinated poly(arylene ether phosphine oxide) as Backbone.

Abstract: In view of the tolerance of F atoms in FIrpic to the nucleophilic aromatic substitution polymerization, an activated fluorinated poly(arylene ether phosphine oxide) backbone is used to construct novel blue electrophosphorescent polymers containing FIrpic as the blue emitter, because they can be synthesized under a milder temperature of 120 °C. Compared with the counterparts prepared at high temperature (165 °C), unexpected bathochromic shift is successfully avoided, and a state-of-art luminous efficiency as high as 19.4 cd A(-1) is achieved. The efficiency is comparable to the corresponding physical blend system, which indicates that the fluorinated poly(arylene ether phosphine oxide) has the potential to be used as the platform for the development of high-performance all-phosphorescent white polymer based on single polymer system.

Sulfur, oxygen, and nitrogen mustards: stability and reactivity.

Abstract: Mustard gas, bis(β-chloroethyl) sulfide (HD), is highly toxic and harmful to humans and the environment. It comprises one class of chemical warfare agents (CWAs) that was used in both World Wars I and II. The three basic analogues or surrogates are: the monochloro derivative, known as the half mustard, 2-chloroethyl ethyl sulfide (CEES); an oxygen analogue, bis(β-chloroethyl) ether (BCEE); and several nitrogen analogues based on the 2,2′-dichlorodiethylamine framework (e.g., HN1, HN2, and HN3). The origin of their toxicity is considered to be from the formation of three-membered heterocyclic ions, a reaction that is especially accelerated in aqueous solution. The reaction of these cyclic ion intermediates with a number of important biological species such as DNA, RNA and proteins causes cell toxicity and is responsible for the deleterious effects of the mustards. While a number of studies have been performed over the last century to determine the chemistry of these compounds, early studies suffered from a lack of more sophisticated NMR and X-ray techniques. It is now well-established that the sulfur and nitrogen mustards are highly reactive in water, while the oxygen analog is much more stable. In this study, we review and summarize results from previous studies, and add results of our own studies of the reactivity of these mustards toward various nonaqueous solvents and nucleophiles. In this manner a more comprehensive evaluation of the stability and reactivity of these related mustard compounds is achieved.