Showing papers on "Ether published in 2004"

Transferable Potentials for Phase Equilibria. 6. United-Atom Description for Ethers, Glycols, Ketones, and Aldehydes

Abstract: The extension of the transferable potentials for phase equilibria−united atom (TraPPE−UA) force field to the ether, glycol, ketone, and aldehyde functionalities is presented. New parameters for the ether oxygen, the carbonyl carbon (ketones), the carbonyl methine (aldehydes), and a special intramolecular hydrogen-bond term were fitted to the vapor−liquid coexistence curves for selected one-component systems. Coupled−decoupled configurational bias Monte Carlo simulations in the Gibbs or grand canonical ensemble were used to compute the vapor−liquid coexistence curves for the neat systems of dimethyl ether, ethyl methyl ether, diethyl ether, dipropyl ether, diisopropyl ether, methyl tert-butyl ether, 1,2-ethanediol, 2-methoxyethan-1-ol, 1,2-dimethoxyethane, 1,3-propanediol, acetone, 2-pentanone, 2-octanone, acetaldehyde, pentanal, and octanal. Additional simulations were performed for the binary mixtures of diethyl ether + ethanol and acetone + hexane. Excellent agreement with experimental results was found...

Photochemical reaction mechanisms of 2-nitrobenzyl compounds: methyl ethers and caged ATP.

Abstract: The mechanism of methanol photorelease from 2-nitrobenzyl methyl ether (1) and 1-(2-nitrophenyl)ethyl methyl ether (2), and of ATP release from adenosine-5‘-triphosphate-[P3-(1-(2-nitrophenyl)ethyl)] ester (‘caged ATP', 3) was studied in various solvents by laser flash photolysis with UV−vis and IR detection In addition to the well-known primary aci-nitro transients (A, λmax ≈ 400 nm), two further intermediates preceding the release of methanol, namely the corresponding 1,3-dihydrobenz[c]isoxazol-1-ol derivatives (B) and 2-nitrosobenzyl hemiacetals (C), were identified The dependencies of the reaction rates of A−C on pH and buffer concentrations in aqueous solution were studied in detail Substantial revision of previously proposed reaction mechanisms for substrate release from 2-nitrobenzyl protecting groups is required: (a) A novel reaction pathway of the aci-tautomers A prevailing in buffered aqueous solutions, eg, phosphate buffer with pH 7, was found (b) The cyclic intermediates B were identifi

Sulfonated Poly(aryl ether ketone)s Containing the Hexafluoroisopropylidene Diphenyl Moiety Prepared by Direct Copolymerization, as Proton Exchange Membranes for Fuel Cell Application†

Abstract: A series of sulfonated poly(aryl ether ketone) (SPAEK-6F) copolymers were prepared by aromatic nucleophilic polycondensation of hexafluoroisopropylidene diphenol with 5,5‘-carbonylbis(2-fluorobenze...

Solvent Extraction of Sr2+ and Cs+ Based on Room-Temperature Ionic Liquids Containing Monoaza-Substituted Crown Ethers

Abstract: A series of N-alkyl aza-18-crown-6 ethers were synthesized and characterized by NMR spectroscopy and mass spectrometry. These monoaza-substituted crown ethers in ionic liquids were investigated as recyclable extractants for separation of Sr2+ and Cs+ from aqueous solutions. The pH-sensitive complexation capability of these ligands allows for a facile stripping process to be developed so that both macrocyclic ligands and ionic liquids can be reused. The extraction efficiencies and selectivities of these monoaza-substituted crown ethers for Na+, K+, Cs+, and Sr2+ were studied in comparison to those of dicyclohexano-18-crown-6 under the same conditions. The extraction selectivity order for dicyclohexano-18-crown-6 in the ionic liquids investigated here was K+ ≫ Sr2+ > Cs+ > Na+. The extraction selectivity order for N-alkyl aza-18-crown-6, in which the alkyl group is varied systematically from ethyl to n-dodecyl, was Sr2+ ≫ K+ > Cs+ > Na+ in 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide and ...

Low-melting, low-viscous, hydrophobic ionic liquids: 1-alkyl(alkyl ether)-3-methylimidazolium perfluoroalkyltrifluoroborate.

Abstract: A series of twenty two hydrophobic ionic liquids, 1-alkyl(alkyl ether)-3-methylimidazolium ([C(m)mim]+ or [C(m)O(n)mim]+; where Cm is 1-alkyl, Cm = nCmH(2m+1), m = 1-4 and 6; C(m)O(n) is 1-alkyl ether, C2O1 = CH3OCH2, C3O1 = CH3OCH2CH2, and C5O2 = CH3(OCH2CH2)2) perfluoroalkyltrifluoroborate ([RFBF3]-, RF = CF3, C2F5, nC3F7, nC4F9), have been prepared and characterized. Some of the important physicochemical properties of these salts including melting point, glass transition, viscosity, density, ionic conductivity, thermal and electrochemical stability, have been determined and were compared with those of the reported [BF4](-)-based ones. The influence of the structure variation in the imidazolium cation and the perfluoroalkyltrifluoroborate ([RFBF3]-) anion on the above physicochemical properties was discussed. The key features of these new salts are their low melting points (-42 to 35 degrees C) or extremely low glass transition (between -87 and -117 degrees C) without melting, and considerably low viscosities (26-77 cP at 25 degrees C).

Ruthenium-catalyzed functionalization of aryl carbon-oxygen bonds in aromatic ethers with organoboron compounds.

Abstract: The ruthenium-catalyzed reaction of aryl ethers having a carbonyl group at the ortho position to the ether group with organoboronates (R−B(OCH2CMe2CH2O), R = aryl, alkenyl, and alkyl) resulted in site-selective C−C bond formation. Among the transition metal complexes screened, the RuH2(CO)(PPh3)3 complex showed the highest activity. Several aromatic ketones having methoxy or phenoxy groups at the ortho position can also be used in this coupling reaction. A variety of arylboronates containing electron-donating (NMe2, OMe, methyl, and vinyl) and -withdrawing (F and CF3) groups reacted with methoxy ketones to give the corresponding coupling products in high yields.

Hydrogen storage by reversible hydrogenation of pi-conjugated substrates

Abstract: Processes are provided for the storage and release of hydrogen by means of a substantially reversible catalytic hydrogenation of extended pi-conjugated substrates which include large polycyclic aromatic hydrocarbons, polycyclic aromatic hydrocarbons with nitrogen heteroatoms, polycyclic aromatic hydrocarbons with oxygen heteroatoms, polycyclic aromatic hydrocarbons with alkyl, alkoxy, nitrile, ketone, ether or polyether substituents, pi-conjugated molecules comprising 5 membered rings, pi-conjugated molecules comprising six and five membered rings with nitrogen or oxygen hetero atoms, and extended pi-conjugated organic polymers. The hydrogen, contained in the at least partially hydrogenated form of the extended pi-conjugated system, can be facilely released for use by a catalytic dehydrogenation of the latter in the presence of a dehydrogenation catalyst which can be effected by lowering the hydrogen gas pressure, generally to pressures greater than 0.1 bar or raising the temperature to less than 250° C. or less, or by a combination of these two process parameters.

Metal-Ion Sensing Fluorophores with Large Two-Photon Absorption Cross Sections: Aza-Crown Ether Substituted Donor-Acceptor-Donor Distyrylbenzenes

Abstract: Chromophores based on a donor−acceptor−donor structure possessing a large two-photon absorption cross section and one or two mono-aza-15-crown-5 ether moieties, which can bind metal cations, have been synthesized. The influence of Mg2+ binding on their one- and two-photon spectroscopic properties has been investigated. Upon binding, the two-photon action cross sections at 810 nm decrease by a factor of up to 50 at high Mg2+ concentrations and this results in a large contrast in the two-photon excited fluorescence signal between the bound and unbound forms, for excitation in the range of 730 to 860 nm. Experimental and computational results indicate that there is a significant reduction of the electron donating strength of the aza-crown nitrogen atom(s) upon metal ion binding and that this leads to a blue shift in the position as well as a reduction in the strength of the lowest-energy two-photon absorption band. The molecules reported here can serve as models for the design of improved two-photon excitabl...

Solvent extraction of amino acids into a room temperature ionic liquid with dicyclohexano-18-crown-6

Abstract: Amino acids Trp, Gly, Ala, Leu are extracted efficiently from aqueous solution at pH 1.5-4.0 (Lys and Arg at pH 1.5-5.5) into the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) with dicyclohexano-18-crown-6 (CE). The most hydrophilic amino acids such as Gly are extracted as efficiently as the less hydrophilic (92-96%). The influence of pH, amino acid and crown ether concentration, volume ratio of aqueous and organic phases, and presence of some cations on amino acid recovery were studied. The ratio of amino acid to crown ether in the extracted species is 1:1 for cationic Trp, Leu, Ala, and Gly and to 1:2 for dicationic Arg and Lys. This ionic liquid extraction system was used successfully for the recovery of amino acids from pharmaceutical samples and fermentation broth, and was followed by fluorimetric determination.

A new artificial cyclase for polyprenoids: enantioselective total synthesis of (-)-chromazonarol, (+)-8-epi-puupehedione, and (-)-11'-deoxytaondiol methyl ether.

Abstract: This paper describes a new artificial cyclase, optically pure 3-o-fluorobenzyloxy-2-hydroxy-2'-(p-methoxybemzyl)-1,1'-binaphthyl.SnCl4, which is effective for the enantioselective cyclization of 2-(polyprenyl)phenol derivatives to afford polycyclic terpenoids bearing a chroman skeleton such as (-)-chromazonarol, (+)-8-epi-puupehedione, a key synthetic intermediate of (+)-wiedendiol, and (-)-11'-deoxytaondiol methyl ether.

Polycarbonate and process for producing the same

Abstract: A polycarbonate comprising ether diol residues which can be produced from a carbohydrate of the formula: (1) and comprising diol residues of the formula: -O-(CmH2m)-O- (2) (wherein m is an integer of 2 to 12), wherein the ratio of ether diol residues to all the diol residues is in the range of 65 to 98 wt.%, the polycarbonate having a glass transition temperature of 90°C or higher.

Surface Properties and Catalytic Activity of TiO2–ZrO2 Mixed Oxides in Dehydration of Methanol to Dimethyl Ether

Abstract: A series of TiO2–ZrO2 mixed oxides with varying molar ratio of TiO2 to ZrO2 were prepared by the co-precipitation method. The crystalline phases of the oxides were characterized by XRD and their acid–base properties by TPD of NH3 and CO2 and IR of adsorbed pyridine. The catalytic activities were investigated for the vapor phase dehydration of methanol to dimethyl ether (DME) in a fixed-bed reactor under atmospheric pressure. The mixed oxides are highly amorphous in nature. The acid–base properties and CH3OH conversion activity are increasing with TiO2 content and an optimum value is achieved for a molar ratio of Ti/Zr in the vicinity of 1/1. At lower reaction temperature (<300 °C), the selectivity for DME is nearly 100%. A good correlation is observed between dehydration activity and the acid–base properties of the TiO2–ZrO2 catalysts. It is significant to note that TiO2–ZrO2 catalysts show high stability against water during dehydration reaction. Based on our results, a surface mechanism involving both acid–base sites has been proposed for DME formation.

Total synthesis of brevetoxin B

Abstract: Brevetoxin-B (BTX-B), produced by the red tide organism, Gymnodium breve Davis, is the first member of marine polycyclic ethers to be structurally elucidated and one of the most potent neurotoxins. The structural feature is a trans-fused polycyclic ether ring system with 23 stereocenters. Its unique, complex structure and potent biological activity have attracted the attention of synthetic organic chemists. Total synthesis of BTX-B has been accomplished via the coupling of the ABCDEFG and IJK-ring segments, each ether ring of which was stereoselectively and efficiently constructed on the basis of SmI2-induced intramolecular cyclization, 6-endo-cyclization of hydroxy epoxide, ring-closing olefin metathesis, and SmI2-induced intramolecular Reformatsky-type reaction. Several kinds of double reactions at the left and right sides were efficiently used through the synthesis.

Synthesis of Poly(arylene ether ether ketone ketone) Copolymers Containing Pendant Sulfonic Acid Groups Bonded to Naphthalene as Proton Exchange Membrane Materials

Abstract: A new series of wholly aromatic poly(ether ether ketone ketone) containing pendant sulfonic acid groups (SPAEEKK) were conveniently prepared by potassium carbonate mediated nucleophilic polycondensation reactions of inexpensive commercially available monomers 1,3-bis(4-fluorobenzoyl)benzene (BFBB), sodium 6,7-dihydroxy-2-naphthalenesulfonate (DHNS), and 4,4‘-biphenol or hydroquinone in N-methyl-2-pyrrolidone (NMP) at 170 °C. FT-IR and NMR were used to characterize the structures and the sulfonate or sulfonic acid contents (SC) of the polymers. Flexible membrane films were obtained by casting N,N-dimethylacetamide (DMAc) solutions of copolymers. Membrane films in acid form were then obtained by treating the sodium form membrane films in 2 N sulfuric acid at room temperature. Glass-transition temperatures (Tg's) and decomposition temperatures (Td's) of SPAEEKKs in both sodium and acid forms were determined. Water uptake and swelling ratio values increased with SCs and temperatures. The proton conductivities...

Fluorescence Enhancement of the Water- Soluble Poly{1,4-phenylene-[9,9-bis- (4-phenoxybutylsulfonate)]fluorene-2,7-diyl} Copolymer in n-Dodecylpentaoxyethylene Glycol Ether Micelles

Abstract: Interest is increasing in water-soluble conjugated polymers in areas such as chemical/biological sensors1,2 and self-assembly systems.3 In addition, introduction of ink jet printing for fabricating light-emitting diode (LED) displays4 will increase demand for these waterbased systems. Marked changes in fluorescence occur on adding surfactants.1b,2c Both surfactant complexation1b and breakup of polymer aggregates2c have been proposed as explanations. The high fluorescence yields and blue emission of polymers involving 2,7-linked fluorene units make them among the most attractive classes of conjugated polymers for devices5 and good candidates for the above applications. We report the effect of the nonionic n-dodecylpentaoxyethylene glycol ether (C12E5) on properties of the water-soluble poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer (PBS-PFP, Figure 1B). The polymer (Mh n) ∼6500 g mol-1) was synthesized by condensation of 2,7dibromo-9,9-bis(4-sulfonylbutoxyphenyl)fluorene (A) and 1,4-phenylenediboronic acid using Pd(PPh3)4 as catalyst. Details of synthesis and characterization are given in the Supporting Information. Aqueous solutions of PBS-PFP showed a broad absorption around 381 nm and a structured fluorescence (λmax 424, 448, 475 nm (shoulder)). Band shapes are similar to the related copolymer poly[2,7-(9,9-bis(2′ethylhexylfluorene)-alt-1,4-phenylene] (PFP).6 Upon addition of C12E5 (3.3 × 10-8-5.34 × 10-4 M) to PBSPFP (6 mg/L, 9.2 × 10-7 M),7 blue shifts in absorption (11 nm) and emission (13 nm, Figure 2) maxima, and marked increases in absorbance and fluorescence intensity were observed. With a poly(ethylene oxide) of similar size to C12E5 headgroup (PEG 200 e 2.3 × 10-4 M), only a decrease in fluorescence intensity was observed, with no change in band shape, showing the importance of the surfactant. Fluorescence quantum yields (Φf), lifetimes, and shifts in emission maxima are shown as functions of surfactant concentration (Figure 3).7 Although the decay should strictly be treated as biexponential, with the time resolution of our system and the relatively small difference in the lifetimes, it was not possible to obtain a statistically significant separation into two exponentials, and the decay was taken as monoexponential. All these properties change at surfactant concentrations greater than the C12E5 critical micelle concentration (cmc, (5 ( 2) × 10-5 M),8,9c suggesting they result from incorporation of polymer into micelles. PBS-PFP † Universidade de Coimbra. ‡ Universidad de Burgos. § Bergische Universität Wuppertal. * Corresponding authors. E-mail: burrows@ci.uc.pt; mjtapia@ ubu.es. Figure 1. Synthetic scheme and structure of poly{1,4phenylene-[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7diyl}. Volume 37, Number 20 October 5, 2004

Molecular tectonics. Porous hydrogen-bonded networks built from derivatives of pentaerythrityl tetraphenyl ether.

Abstract: The symmetric four-armed geometry of pentaerythrityl tetraphenyl ether (5) makes it a valuable starting point for building complex molecular and supramolecular structures. In particular, it provides a core to which multiple sites of attractive intermolecular interaction can be attached, thereby creating compounds predisposed to form complex networks by association. To facilitate exploitation of the pentaerythrityl tetraphenyl ether core in such ways, we have prepared more than 20 new derivatives by efficient methods. Of special interest are compounds 3 and 4, which incorporate four diaminotriazine groups attached to the meta and para positions of the pentaerythrityl tetraphenyl ether core. Crystallization of compounds 3 and 4 from DMSO/dioxane is directed by hydrogen bonding of the diaminotriazine groups according to well-established motifs, thereby producing three-dimensional networks. In forming these networks, each molecule of compound 3 forms a total of 12 hydrogen bonds with six others, whereas each molecule of compound 4 forms a total of 16 hydrogen bonds with four others. Both networks are highly porous and define significant interconnected channels for the inclusion of guests. In crystals of compounds 3 and 4, the fraction of the volume accessible to guests is 66% and 57%, respectively. In both cases, the pentaerythrityl tetraphenyl ether cores adopt conformations that deviate substantially from tetrahedral geometry. It is noteworthy that the inherent flexibility of the core does not favor the formation of close-packed guest-free structures.

Axial-Selective Prins Cyclizations by Solvolysis of α-Bromo Ethers

Abstract: Prins cyclizations are intramolecular electrophilic additions of oxocarbenium ions. They lead to tetrahydropyrans with a heteroatom at the 4-position, and usually show moderate-to-high selectivity for equatorial substitution. We have found that Prins cyclizations carried out under specific conditions produce tetrahydropyrans with almost exclusive formation of the axial 4-substituent. TMSBr, AcBr, and TMSI all lead to axial-selective Prins cyclizations with α-acetoxy ether substrates in the presence lutidine. The mechanism appears to involve solvolysis of the intermediate α-bromo ether rather than specific or Lewis acid-catalyzed rearrangement. The scope of the reaction, the high yields, and the stereoselectivity make this a valuable new method for tetrahydropyran formation.

Cyclopentane heptan(ENE)OIC acid, 2-heteroarylalkenyl derivatives as therapeutic agents

Abstract: The present invention provides cyclopentane heptanoic acid, 2 heteroaryl alkyl or alkenyl derivatives which may be substituted in the 1-position with hydroxyl, alkyloxy, amino and amido groups, eg 1-OH cyclopentane heptanoic acid, 2 heteroarylalkenyl derivatives In particular, these derivatives are 7-[5-hydroxy-2-(heteroatom-substituted hydroxyhydrocarbyl)-3-hydroxycyclopentyl] heptanoic or heptenoic acids and amine, amide, ether, ester and alchohol derivatives of said acids wherein one or more of said hydroxy groups are replaced with an ether group These compounds are potent ocular hypotensive and are particularly suited for the management of glaucoma Moreover, the compounds of this invention are smooth muscle relaxants with broad application in systemic hypertensive and pulmonary diseases; with additional application in gastrointestinal disease, reproduction, fertility, incontinence, shock, inflammation, immune regulation, disorder of bone metabolism, renal dysfunction, cancer and other hypoproliferative diseases

A cohesion/tension mechanism explains the gating of water channels (aquaporins) in Chara internodes by high

Abstract: Isolated internodes of Chara corallina have been used to study the gating of aquaporins (water chan nels) in the presence of high concentrations of osmo tic solutes of different size (molecular weight). Osmolytes were acetone and three glycol ethers: ethylene glycol monomethyl ether (EGMME), diethy lene glycol monomethyl ether (DEGMME), and triethy lene glycol monoethyl ether (TEGMEE). The 'osmotic efficiency' of osmolytes was quite different. Their reflection coefficients ranged between 0.15 (acetone), 0.59 (EGMME), 0.78 (DEGMME), and 0.80 (TEGMEE). Bulk water permeability (Lp) and diffusive permeabil ities (Ps) of heavy water (HDO), hydrogen peroxide

Rationally functionalized deltahedral zintl ions: synthesis and characterization of [Ge9-ER3]3-, [R3E-Ge9-ER3]2-, and [R3E-Ge9-Ge9-ER3]4- (E=Ge, Sn; R=Me, Ph).

Abstract: Six new derivatized deltahedral Zintl ions have been synthesized by reactions between the known Zintl ions Ge(9) (n-) with the halides R(3)EX and/or the corresponding anions R(3)E(-) for E=Ge or Sn. This rational approach is based on our previous discovery that these derivatization reactions are based on nucleophilic addition to the clusters. All species were structurally characterized as their salts with potassium countercations sequestered in 2,2,2-crypt or [18]crown-6 ether. The tin-containing anions were characterized also in solutions by (119)Sn NMR spectroscopy. The reaction types for such substitutions and the structures of the new anions are discussed.