Showing papers on "Ether published in 2000"

Solvophobically Driven π-Stacking of Phenylene Ethynylene Macrocycles and Oligomers

Abstract: Phenylene ethynylene macrocycles and oligomers with three different side-chain linking groups (ester, benzyl ether, and phenyl ether) were synthesized to investigate their tendency to undergo solvent induced π-stacked organization. 1H NMR, UV, and fluorescence spectroscopies were used to probe two types of π-stacked supramolecular organizations: the intramolecular conformational ordering of the oligomers, and the intermolecular aggregation of the macrocycles. One important conclusion is that solvent can play a very dramatic role in modulating the strength of the interactions that drive the association of these π-stacked structures. The other important conclusion is that in a given solvent, the nature of the side chain linking group strongly influences the π-stacking propensities. It was found that macrocycles and oligomers with the ester side chain linking group were prone to adopt π-stacked structures in a range of solvents, whereas the corresponding macrocycles with benzyl ether and phenyl ether side c...

Effect of the property of solid acid upon syngas-to-dimethyl ether conversion on the hybrid catalysts composed of Cu–Zn–Ga and solid acids

Abstract: Syngas-to-dimethyl ether (STD) conversion was examined on various hybrid catalysts. The catalyst composed of a methanol-synthesis catalyst and a silica-rich silica–alumina showed high dimethyl ether (DME) yield (55.5%) with a good selectivity (93.5%). The effects of water on the acid property and on the reaction were examined. At atmospheric pressure, Lewis acid–base pairs were major active sites for methanol dehydration. At higher pressures, however, water formed by methanol dehydration was strongly adsorbed on Lewis acid sites, suppressing the DME formation. The solid-acid catalyst having Bronsted acid sites with moderate acid strength was the best catalyst for the STD process. Modification of the methanol-synthesis catalysts with Pd was effective to enhance the STD activity at low temperatures.

Degradation pathways during the treatment of methyl tert-butyl ether by the uv/h2o2 process

Abstract: The application of the UV/H2O2 process to the degradation of methyl tert-butyl ether (MTBE) in dilute aqueous solution resulted in the generation of tert-butyl formate (TBF), 2-methoxy-2-methyl propionaldehyde (MMP), formaldehyde, acetone, tert-butyl alcohol (TBA), and methyl acetate as primary byproducts. Other intermediates, such as carbonyl compounds (hydroxy-iso-butyraldehyde, hydroxyacetone, pyruvaldehyde) and organic acids (hydroxy-iso-butyric, formic, pyruvic, acetic, oxalic) were also detected and quantified during the irradiation. A good organic carbon balance is obtained throughout the treatment, indicating that almost all of the intermediates have been detected. The TOC pattern shows that eventually all the organic compounds are mineralized. Various analytical techniques, such as GC/MS, GC, IC, HPLC, and TOC analysis, were employed in order to identify and quantify the organic products. The detailed reaction mechanism proposed in this study for the degradation of MTBE by •OH-driven oxidation pr...

Application of the Russig−Laatsch Reaction to Synthesize a Bis[5]helicene Chiral Pocket for Asymmetric Catalysis

Abstract: The enantiomers of a bis[5]helicenediol ligand ([5]HELOL) have been synthesized in appreciable amounts by a procedure in which key steps are the union of p-benzoquinone with an enol ether of 3-acetylphenanthrene and the displacement of phenol and phenol ether functions by alcohols (the Russig−Laatsch reaction). This diol catalyzes the addition of diethylzinc to aldehydes and gives nonracemic alcohols with enantiomeric excesses as high as 81%. The stereoselectivities and yields are much greater than when the catalyzing diol is BINOL. The enantioselectivities are greater also than those of other reactions catalyzed by helicene ligands.

Ion Association and Ion Solvation Effects at the Crystalline−Amorphous Phase Transition in PEO−LiTFSI

Abstract: From band shape analyses of the strong 740 cm-1 Raman mode of the TFSI anion, we deduce that the crystalline state of the P(EO)nLiTFSI system contains a very small amount of ion pairs (≈7%), most probably belonging to the minor amorphous phase, for the n ≥ 6 range. For all-amorphous samples, we found a small amount of ion pairs for n ≥ 8, but a significant amount (≈24%) for n = 6. This increase in ion pair formation coincides with a decrease in the relative solvation of lithium cations by polymeric ether oxygens, as detected from a careful study of the 863 cm-1 polymer-cation “breathing mode”. We therefore propose that the local ionic structure is preserved during the melting of n ≥ 8 compositions, but that there is a changeover from a predominately ether oxygen lithium coordination to a combined ether oxygen and anionic coordination of the lithium cations for more concentrated samples upon melting.

Cytotoxic biflavonoids from Selaginella delicatula.

Abstract: Four new biflavonoidsrobustaflavone 4‘-methyl ether (1), robustaflavone 7,4‘-dimethyl ether (2), 2‘ ‘,3‘ ‘-dihydrorobustaflavone 7,4‘, -dimethyl ether (3), and 2‘ ‘,3‘ ‘-dihydrorobustaflavone 7,4‘, 7‘ ‘-trimethyl ether (4)as well as two known biflavonoids, robustaflavone and amentoflavone, and three caffeoylquinic acids, 3,5-di-O-caffeoylquinic acid, 3,4-di-O-caffeoylquinic acid, and 4,5-di-O-caffeoylquinic acid, were isolated from Selaginella delicatula. The structures of the new compounds were established by spectroscopic analysis and chemical modification. The cytotoxic activity of these compounds on various tumor cell lines was evaluated, and both compounds 1 and 3 significantly suppressed the growth of Raji and Calu-1 tumor cell lines.

Poly(phenylene ether)-polyvinyl thermosetting resin

Abstract: A capped poly(phenylene ether) resin composition is formed from (1) a poly(phenylene ether) compound (PPE) in which at least a portion, preferably substantially all of the hydroxyl groups have been reacted with a compound containing ethylenic unsaturation (carbon-carbon double bonds) which is further reactive with unsaturated monomers (reactively endcapped PPE) and (2) a curable unsaturated monomer composition. The composition optionally contains a polymerization catalyst; a flame-retardant compound; and fibrous reinforcement. The composition can be cured to form a laminate, and clad with copper to form a circuit board.

Oxidative Cracking of Precipitated Hardwood Lignin by Hydrogen Peroxide

Abstract: Precipitated hard-wood lignin (PHL) is a major byproduct in the biomass-to-ethanol process. Oxidative cracking of PHL by hydrogen peroxide in aqueous medium was investigated as a means to produce potentially useful chemicals. The cracking reaction takes place at moderate temperatures (80-160 degrees C), giving mono- and dicarboxylic acids as the main products. The yields of these products are in the range of 30-50% of initial lignin. The reaction mechanism and the product distribution are dependent upon the reaction conditions, especially the pH. The reaction under strong alkaline condition proceeds well even at low reaction temperatures (80-90 degrees C). Under acidic conditions, higher temperatures (130-160 degrees C) are required to attain the same degrees of cracking. The reaction patterns of the oxidative cracking reaction involve the cleavage of lignin ring, aryl ether bond, or other linkages within lignin. By using the findings of this investigation and those of previous work, we have illustrated the reaction pathways for degradation of PHL under alkaline and acidic conditions. Aldehydes and aromatic acids are intermediate products in the oxidative degradation of lignin. However, they were produced only in trace amounts owing to rapid degradation induced by hydrogen peroxide.

Surface Modification of Silicone Elastomer Using Perfluorinated Ether

Abstract: The surface properties of a poly(dimethylsiloxane) elastomer have been modified by reacting an allyl amide functional perfluorinated ether (PFE) to the siloxane network by a hydrosilation reaction. Examination of the surface by contact angle and X-ray photoelectron spectroscopy revealed that the perfluorinated ether migrates to the surface of the polymer, thus reducing its surface energy from 22 to about 8 mJ/m2 without affecting its bulk material properties. The resultant surface however exhibits higher contact angle hysteresis than that seen with the PFE-free elastomer. These results indicate that the higher energy amide functionalities of the perfluorinted ether are available for interfacial interaction, even though they are buried below the PFE layer. This study demonstrates that a high-energy group can be pulled to the free surface of a polymer by the driving forces of the lower energy groups segregating to the surface. The high-energy groups are available for further chemical interactions when the s...

Asymmetric synthesis of alpha-amino acids based on carbon radical addition to glyoxylic oxime ether

Abstract: The first asymmetric synthesis of alpha-amino acids based on diastereoselective carbon radical addition to glyoxylic imine derivatives is reported. The addition of an isopropyl radical, generated from i-PrI, Bu(3)SnH, and Et(3)B in CH(2)Cl(2) at 25 degrees C, to achiral glyoxylic oxime ether 1 proceeded regioselectively at the imino carbon atom of the oxime ether group to give an excellent yield of the C-isopropylated product 2. The competitive reaction using glyoxylic oxime ether 1 and aldoxime ether 4 showed that the reactivity of the glyoxylic oxime ether toward nucleophilic carbon radicals was enhanced by the presence of a neighboring electron-withdrawing substituent. Thus, the alkyl radical addition to glyoxylic oxime ether 1 proceeded smoothly even at -78 degrees C, in contrast to the unactivated aldoxime ether 4. A high degree of stereocontrol in the carbon radical addition to the glyoxylic oxime ether was achieved by using Oppolzer's camphorsultam as a chiral auxiliary. The stannyl radical-mediated reaction of the camphorsultam derivative 6 with an isopropyl radical at -78 degrees C afforded a 96:4 diastereomeric mixture, 7a, of the C-isopropylated product. The reductive removal of the benzyloxy group of the major diastereomer (R)-7a, by treatment with Mo(CO)(6) and the subsequent removal of the sultam auxiliary by standard hydrolysis, afforded the enantiomerically pure D-valine (R)-12 without any loss of stereochemical purity. To evaluate the new methodology, a variety of alkyl radicals were employed in the addition reaction which gave the alkylated products 7 with excellent diastereoselectivity, allowing access to a wide range of enantiomerically pure natural and unnatural alpha-amino acids. Even in the absence of Bu(3)SnH, treatment of 6 with alkyl iodide and Et(3)B at 20 degrees C gave the C-alkylated products 7 with moderate diastereoselectivities. The use of Et(2)Zn as a radical initiator, instead of Et(3)B, was also effective for the radical reaction. The enantioselective isopropyl radical addition to 1 using (R)-(+)-2, 2'-isopropylidenebis(4-phenyl-2-oxazoline) and MgBr(2) gave excellent chemical yield of the valine derivative 2 in 52% ee.

Isomerization Reaction of Olefin Using RuClH(CO)(PPh3)3

Abstract: When methyl 5-(tert-butyldiphenylsilyl)oxy-2-pentenoate was refluxed in toluene in the presence of RuClH(CO)(PPh3)3 (5 mol %), double-bond migration took place to afford methyl 5-(tert-butyldiphenylsilyl)oxy-4-pentenoate in high yield. This means that the double bond conjugated with the ester moiety migrates to a deconjugated position by a ruthenium catalyst. We planned to prepare an enol ether from α,β-unsaturated compounds having an ether moiety in a tether using ruthenium-catalyzed isomerization of the double bond. As a result, silyl or benzyl enol ether was obtained from the α,β-unsaturated ester having alcohol protected by the silyl or benzyl group in a tether in high yield. In this reaction, double bond migration of α,β-unsaturated ketone and α,β-unsaturated amide took place to produce deconjugated compounds. Moreover, the double bond of α,β-unsaturated ester having a triple or double bond in a molecule migrated to produce conjugated enyne and diene. On the other hand, treatment of a bis-metalated c...

Densities and Viscosities of Seven Glycol Ethers from 288.15 K to 343.15 K

Abstract: Densities and viscosities of seven glycol ethers consisting of 1-methoxy-2-propanol, 3-methoxy-1-butanol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, ethylene glycol tert-butyl methyl ether, and diethylene glycol diethyl ether were measured from 288.15 K to 343.15 K at atmospheric pressure. Densities were determined using a vibrating-tube densimeter. Viscosities were measured with an automatic Ubbelohde capillary viscometer. The estimated uncertainties of the measurements were ±0.1% for density and ±0.9% for viscosity. The data were correlated using simple expressions and were also used to develop a model for the viscosity based on the Hildebrand fluidity equation.

Determination of methyl tert-butyl ether in surface water by use of solid-phase microextraction.

Abstract: A new method based on solid-phase microextraction (SPME) has been developed for the determination of methyl tert-butyl ether (MTBE) in surface water at sub-ppb concentrations. The combination of SP...

Synthesis and Metal Ion Complexation Studies of Proton-Ionizable Calix[4]azacrown Ethers in the 1,3-Alternate Conformation

Abstract: A series of novel N-chromogenic calix[4]arene azacrown ethers were synthesized as selective extractants of potassium ion. 1,3-Alternate calix[4]arene azacrown ethers were prepared by reacting 25,27-dipropyloxy-26,28-bis(5-chloro-3-oxapentyloxy) calix[4]arenes with p-toluenesulfonamide in the presence of potassium carbonate. The coupling reaction of calix[4]arene azacrown ether with 2-hydroxy-5-nitrobenzyl bromide in the presence of triethylamine in THF gave the chromogenic calix[4]arene azacrown ether in moderate yield. These compounds show high potassium selectivity over other metal ions as shown by two-phase extraction, bulk liquid membrane, and 1H NMR studies on a ligand−metal complex. It is assumed that the OH of the chromogenic group attached on nitrogen can assist the complexation by encapsulation of the metal.

Synthesis, characterization, and thermal properties of novel arylene sulfone ether polyimides and polyamides

Abstract: A new aromatic sulfone ether diamine was synthesized by nucleophilic aromatic substitution reaction of 5-amino-1-naphthol with bis(4-chlorophenyl) sulfone in the presence of potassium carbonate in a polar aprotic solvent. Polycondensation reactions of the obtained diamine with pyromellitic dianhydride (PMDA), benzophenonetetracarboxylic dianhydride (BTDA), and hexafluoroisopropylidene diphthalic anhydride (6FDA) resulted in preparation of thermally stable poly(sulfone ether imide)s. Poly(sulfone ether amide)s also were prepared by reaction of the diamine with terephthaloyl chloride (TPC) and isophthaloyl chloride (IPC). The prepared monomer and polymers were characterized by conventional methods. Physical and mechanical properties of polymers, including thermal stability, thermal behavior, solution viscosity, solubility behavior, and modulus, also were studied.

Fluorine containing vinyl ethers

Abstract: The present invention describes a novel process for the preparation of perfluorovinyl ethers. The process involves providing a hydrocarbon precursor that may be partially halogenated, fluorinating the precursor to provide a perfluorinated intermediate, and converting the perfluorinated intermediate to the desired perfluorinated ether. Novel perfluorovinyl ethers are also provided.

Rigidified calixarenes bearing four carbamoylmethylphosphineoxide or carbamoylmethylphosphoryl functions at the wide rim

Abstract: Conformationally rigidified tetraCMPO derivatives have been prepared from calix[4]arene bis(crown ether) 4 a in which adjacent oxygens are bridged at the narrow rim by two diethylene glycol links. Acylation of the tetraamine 4 c with the CMPO-active ester 5 b gave the tetraphosphine oxide 6 a, while the tetraphosphinate 6 b and the tetraphosphonate 6 c were obtained by Arbuzov reaction of tetrabromoacetamido derivative 7 with PhP(OEt)2 or P(OEt)3. The extraction ability of these CMPO derivatives was checked for selected lanthanides and actinides and compared with the analogous compounds 1 b, 10 b and 10 d derived from calix[4]arene tetrapentyl ether. All rigidified bis(crown ether) ligands are more effective extractants than their pentyl ether counterparts and require only 1/10 of the concentration (cL=10−4 M) to obtain the same distribution coefficients, while with CMPO itself a 2000-fold concentration is necessary. This could be a consequence of a better preorganisation of the ligating functions owing to the rigidity which on the other hand did not change the observed selectivity for americium (DAm/DEu=9–19) and for light lanthanides over heavy ones. NMR relaxivity titration curves show that the complex of Gd3+ with ligand 6 a is highly oligomerised in anhydrous acetonitrile over a large range of ligand:metal concentration ratios. Nuclear magnetic relaxation dispersion (NMRD) profiles also showed that large oligomers were formed, and their mean tumbling times were deduced from the Solomon-Bloembergen-Morgan equations. The NMR spectra of dia- and paramagnetic lanthanide complexes with 6 a agreed with the presence of two conformers with an elongated calix[4]arene skeleton in which the distances between opposite methylene groups are different. Contrary to what was observed with ligand 2 a, the addition of nitrate ions does not labilize the metal complexes, presumably because of the rigidification effect of the ether bridges. Single-crystal X-ray structures were obtained for the active ester 5 b and for diphenylphosphorylacetic acid 5 a.

Synthesis and Surface Functionalization of Aliphatic Polyether Dendrons

Abstract: The convergent synthesis and surface modification of a novel family of aliphatic polyether dendrons is described. The synthesis utilizes methallyl dichloride as the monomeric building block along with peripheral benzyl ether and ketal protected hydroxy functionalities. The allylic nature of the electrophilic moieties of methallyl dichloride facilitates their nucleophilic displacement by 2 equiv of the appropriate terminal alcohol group. Having served its activating function during the coupling step, the alkene focal point can then be efficiently transformed into a primary alcohol via hydroboration−oxidation leading to a nucleophile that may then be coupled again to additional monomer. Repetition of these coupling and activation steps affords higher generation dendrons. Taking advantage of the versatility of the convergent approach and the rugged nature of the aliphatic ether building blocks, dendrimers with tailored solubility properties and well-defined unsymmetrical surfaces can be obtained.

Regioselective synthesis of rapamycin derivatives

Abstract: This invention provides a regioselective process for preparing a 42-ester or ether of rapamycin, and 31-silyl ether intermediates.

The synthesis and glass-forming properties of phthalocyanine-containing poly(aryl ether) dendrimers.

Abstract: The synthesis, structural characterisation and properties of a number of phthalocyanine-containing dendrimers are described. Peripheral substitution of phthalocyanine (Pc) with four poly(aryl ether) dendritic wedges (1st, 2nd or 3rd generation) produces materials whose properties are dominated both by the columnar self-association of the Pc core and by the glass-forming character of the dendritic substituents. Asymmetric Pcs containing a single poly(aryl ether) dendron display a columnar mesophase, the structure of which can be frozen into an anisotropic glass at room temperature. Placing the dendritic wedges at the axial sites of silicon phthalocyanine prohibits self-association and gives materials from which can be fabricated robust, isotropic solid solutions of Pc with high glass transition temperatures. A single crystal X-ray diffraction analysis of one of these compounds illustrates the ability of the axial dendrons to prevent cofacial aggregation in the solid state.