Showing papers on "Tetrahydrofuran published in 2000"

An Acidity Scale for Phosphorus-Containing Compounds Including Metal Hydrides and Dihydrogen Complexes in THF: Toward the Unification of Acidity Scales

Abstract: More than 70 equilibrium constants K between acids and bases, mainly phosphine derivatives, have been measured in tetrahydrofuran (THF) at 20 °C by 1H and/or 31P NMR. The acids were chosen or newly synthesized in order to cover the wide pKαTHF range of 5−41 versus the anchor compound [HPCy3]BPh4 at 9.7. These pKαTHF values are approximations to absolute, free ion pKaTHF and are obtained by crudely correcting the observed K for 1:1 ion-pairing effects by use of the Fuoss equation. The acid/base compounds include 14 phosphonium/phosphine couples, 17 cationic hydride/neutral hydride couples, 9 neutral polyhydride/anionic hydride couples, 14 dihydrogen/hydride couples, and 4 other nitrogen- and phosphorus-based acids. The effects on pKα of the counterions BAr‘4- and BF4- vs BPh4- and [K(2,2,2-crypt)]+ versus [K(18-crown-6)]+ are found to be minor after correcting for differences in inter-ion distances in the ion-pairs involved. Correlations with ν(M−H) noted here for the first time suggest that destabilizatio...

Structural diversity in solvated lithium aryloxides. Syntheses, characterization, and structures of [Li(OAr)(THF)x]n and [Li(OAr)(py)x]2 complexes where OAr = OC6H5, OC6H4(2-Me), OC6H3(2,6-(Me))2, OC6H4(2-Pr(i)), OC6H3(2,6-Pr(i)))2, OC6h4(2-Bu(t)), OC6H3(2,6-Bu(t)))2.

Abstract: A series of sterically varied aryl alcohols H-OAr [OAr = OC6H5 (OPh), OC6H4(2-Me) (oMP), OC6H3(2,6-(Me))2 (DMP), OC6H4(2-Pr(i)) (oPP), OC6H3(2,6-(Pr(i)))2 (DIP), OC6H4(2-Bu(t)) (oBP), OC6H3(2,6-(Bu(t)))2 (DBP); Me = CH3, Pr(i) = CHMe2, and Bu(t) = CMe3] were reacted with LiN(SiMe3)2 in a Lewis basic solvent [tetrahydrofuran (THF) or pyridine (py)] to generate the appropriate "Li(OAr)(solv)x". In the presence of THF, the OPh derivative was previously identified as the hexagonal prismatic complex [Li(OPh)(THF)]6; however, the structure isolated from the above route proved to be the tetranuclear species [Li(OPh)(THF)]4 (1). The other "Li(OAr)(THF)x" products isolated were characterized by single-crystal X-ray diffraction as [Li(OAr)(THF)]4 [OAr = oMP (2), DMP (3), oPP (4)], [Li(DIP)(THF)]3 (5), [Li(oBP)(THF)2]2, (6), and [Li(DBP)(THF)]2, (7). The tetranuclear species (1-4) consist of symmetric cubes of alternating tetrahedral Li and pyramidal O atoms, with terminal THF solvent molecules bound to each metal center. The trinuclear species 5 consists of a six-membered ring of alternating trigonal planar Li and bridging O atoms, with one THF solvent molecule bound to each metal center. Compound 6 possesses two Li atoms that adopt tetrahedral geometries involving two bridging oBP and two terminal THF ligands. The structure of 7 was identical to the previously reported [Li(DBP)(THF)]2 species, but different unit cell parameters were observed. Compound 7 varies from 6 in that only one solvent molecule is bound to each Li metal center of 7 because of the steric bulk of the DBP ligand. In contrast to the structurally diverse THF adducts, when py was used as the solvent, the appropriate "Li(OAr)(py)x" complexes were isolated as [Li(OAr)(py)2]2 (OAr = OPh (8), oMP (9), DMP (10), oPP (11), DIP (12), oBP (13)) and [Li(DBP)(py)]2 (14). Compounds 8-13 adopt a dinuclear, edge-shared tetrahedral complex. For 14, because of the steric crowding of the DBP ligand, only one py is coordinated, yielding a dinuclear fused trigonal planar arrangement. Two additional structure types were also characterized for the DIP ligand: [Li(DIP)(H-DIP)(py)]2 (12b) and [Li2(DIP)2(py)3] (12c). Multinuclear (6,7Li and 13C) solid-state MAS NMR spectroscopic studies indicate that the bulk powder possesses several Li environments for "transitional ligands" of the THF complexes; however, the py adducts possess only one Li environment, which is consistent with the solid-state structures. Solution NMR studies indicate that "transitional" compounds of the THF precursors display multiple species in solution whereas the py adducts display only one lithium environment.

Cagelike Precursors of High-Molar-Mass Silsesquioxanes Formed by the Hydrolytic Condensation of Trialkoxysilanes

Abstract: High-molar-mass silsesquioxanes (SSQO) based on (3-glycidoxypropyl)trimethoxysilane (GPMS) and (3-methacryloxypropyl)trimethoxysilane (MPMS) were synthesized. The hydrolytic condensation of GPMS was performed using HCOOH (0.1 N) as catalyst, keeping the molar ratio H2O/Si = 3. A first step was performed in tetrahydrofuran (THF) at 50 °C, followed by a second step in diglycidyl ether of bisphenol A (DGEBA), where temperature was increased in steps up to 140 °C. The hydrolytic condensation of MPMS was performed in bulk with HCOOH 98%, at T = 50 or 70 °C, using molar ratios of HCOOH/Si = 3 or 6. Homogeneous solutions were obtained for both silanes. The reaction was followed by size exclusion chromatography (SEC), and final products were characterized by matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF MS), FTIR, and 1H and 29Si NMR. Molar-mass distributions showed the presence of clusters corresponding to products formed in different generations. With the...

Polymer conformations of gas-hydrate kinetic inhibitors: A small-angle neutron scattering study

Abstract: We have used small-angle neutron scattering to characterize the polymer conformations of four nonionic water soluble polymers: poly(ethylene oxide), poly(N-vinyl-2-pyrollidone), poly(N-vinyl-2-caprolactam), and an N-methyl, N-vinylacetamide/N-vinyl-2-caprolactam copolymer. The last three of these are able to kinetically suppress hydrate crystallization, and their inhibitor activity ranges from moderate to very effective. This attribute is of significant commercial importance to the oil and gas industry, but the mechanism of the activity is unknown. The dilute-solution polymer conformation in a hydrate-forming tetrahydrofuran/water fluid shows little difference among the four polymers: the majority of the scattering is that expected for a polymer in a good solvent. Each solution also exhibits some additional low-q scattering which we attribute to aggregates. In the presence of a hydrate-crystal/liquid slurry, the three inhibitor polymers significantly change their conformation. Utilizing results from our p...

Isotope Effects and the Mechanism of Chlorotrimethylsilane-Mediated Addition of Cuprates to Enones

Abstract: Kinetic isotope effects were determined for the chlorotrimethylsilane-mediated reactions of cyclohexenone with lithium dibutylcuprate in tetrahydrofuran and with lithium butyl(tert-butylethynyl)cuprate in ether. For the reaction in tetrahydrofuran, the observation of a significant carbonyl oxygen isotope effect (16k/17k = 1.018−1.019) and small olefinic carbon isotope effects (12k/13k = 1.003−1.008) is consistent with rate-limiting silylation of an intermediate π-complex. Theoretically predicted isotope effects for model reactions support this conclusion. Rate-limiting silylation is also supported by relative reactivity studies of chlorotrimethylsilane versus chlorodimethylphenylsilane. The absence of a significant butyl-group carbon isotope effect on product formation indicates that the cuprate butyl groups are nonequivalent in the intermediate leading to the product-determining step. In diethyl ether the isotope effects revert to values similar to those found previously in reactions of cyclohexenone wit...

Mineralization of 1,4-dioxane in the presence of a structural analog.

Abstract: A mixed culture with the ability to aerobically biodegrade 1,4-dioxane in the presence of tetrahydrofuran (THF) was enriched from a 1,4-dioxane contaminated aquifer. This consortium contained 3–4 morphologically different types of colonies and was grown in mineral salts media. Biodegradation of 1,4- dioxane began when THF concentrations in batch experiments became relatively low. No biodegradation of 1,4-dioxane was observed in the absence of THF and the measured cell yield was similar during degradation of 1,4-dioxane with THF or with THF alone. However, when the consortium was grown in the presence of 14C-1,4-dioxane plus THF, 2.1% of the radiolabeled 1,4-dioxane was present in the particulate fraction. The majority of the 14C (78.1%) was recovered as 14CO2, while 5.8% remained in the liquid fraction. This activity is interesting since the non-growth substrate is mineralized, yet only minimally assimilated into biomass. Using THF as the growth substrate, 1,3-dioxane, methyl t-butyl ether, ethyl t-butyl ether and t-amyl methyl ether.

Synthesis of Poly(p-phenylene)-Based Photoresponsive Conjugated Polymers Having Azobenzene Units in the Main Chain

Abstract: Poly(p-phenylene)-based novel conjugated polymers having photoisomerizable azobenzene units in the main chain were prepared by the palladium-catalyzed Suzuki coupling of 1,3-propanediol diesters of 1,4-phenylenediboronic acids with 4,4‘-diiodoazobenzenes, and the reversible cis−trans isomerizations of azobenzene units were achieved. Despite their stiff structures, the polymers are soluble in common organic solvents such as chloroform, toluene, and tetrahydrofuran if either or both of the monomers possess n-hexyl side chains on the aromatic rings. The resulting polymers possess high molecular weights (Mn > 7 × 103) and are thermally stable (T0 > 350 °C) and fluorescent. The azobenzene units in the conjugated polymer backbone underwent the photochemical cis−trans reversible isomerizations in both tetrahydrofuran and toluene upon irradiation with UV light of appropriate wavelengths at 20 °C. The thermal cis-to-trans isomerization was also readily accomplished in toluene at 80 °C. Moreover, the solid-state ph...

Chlorophyll a self-assembly in polar solvent-water mixtures.

Abstract: The conversion of chlorophyll a (Chl a) monomers into large aggregates in six polar solvents upon addition of water has been studied by means of absorption, fluorescence spectroscopy and fluorescence lifetime measurements for the purpose of elucidating the various environmental factors promoting Chl a self-assembly and determining the type of its organization. Two empirical solvent parameter scales were used for quantitative characterization of the different solvation properties of the solvents and their mixtures with water. The mole fractions of water f1/2 giving rise to the midpoint values of the relative fluorescence quantum yield were determined for each solvent, and then various solvent-water mixture parameters for the f1/2 values were compared. On the basis of their comparison, it is concluded that the hydrogen-bonding ability and the dipole-dipole interactions (function of the dielectric constant) of the solvent-water mixtures are those that promote Chl a self-assembly. The influence of the different nature of the non-aqueous solvents on the Chl aggregation is manifested by both the different water contents required to induce Chl monomer-->aggregate transition and the formation of two types of aggregates at the completion of the transition: species absorbing at 740-760 nm (in methanol, ethanol, acetonitrile, acetone) and at 667-670 nm (in pyridine and tetrahydrofuran). It is concluded that the type of Chl organization depends on the coordination ability and the polarizability (function of the index of refraction) of the organic solvent. The ordering of the solvents with respect to the f1/2 values--methanol < ethanol < acetonitrile < acetone < pyridine < tetrahydrofuran--yielded a typical lyotropic (Hofmeister) series. On the basis of this solvent ordering and the disparate effects of the two groups of solvents on the Chl a aggregate organization, it is pointed out that the mechanism of Chl a self-assembly in aqueous media can be considered a manifestation of the Hofmeister effect, as displayed in the lipid-phase behavior (Koynova et al., Eur. J. Biophys. 25, 261-274, 1997). It relates to the solvent ability to modify the bulk structure and to distribute unevenly between the Chl-water interface and bulk liquid.

Solvent- and counterion-specific swelling behavior of poly(acrylic acid) gels

Abstract: The collapse of alkali metal poly(acrylate) (PAAM) gels was investigated for various water/organic solvent mixture systems: methanol (MeOH), ethanol (EtOH), 2-propanol (2PrOH), t-butanol (tBuOH), dimethyl sulfoxide (DMSO), acetonitrile (AcN), acetone, tetrahydrofuran (THF), and dioxane. In order to ascertain the counterion specificity in the swelling behavior, four kinds of alkali metal counterions were used: Li+, Na+, K+, and Cs+. Remarkable solvent and counterion specificities were observed for every counterion species and every solvent system, respectively. For example, in aqueous EtOH the dielectric constants (Dcr) at which collapse occurred were in the order PAACs < PAALi < PAAK < PAANa. On the other hand, the Dcr at which PAALi gel collapsed increased in the order tBuOH < dioxane < THF < MeOH < 2PrOH < EtOH < acetone < AcN < DMSO, where the Dcr ranged from about 39 to about 67. This was in contrast to our previous observation for a partially quaternized poly(4-vinyl pyridine) (P4VP) gel, which collapsed in a much narrower Dcr region in similar mixed solvents. The present solvent- and counterion-specific collapses are discussed on the basis of solvent properties such as the dielectric constant and Gutmann's donor number and acceptor number of a pure solvent. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2791–2800, 2000

High surface area sol-gel route prepared hydrogenation catalysts

Abstract: This invention concerns novel compositions, useful as hydrogenation catalyst, said compositions comprising metals and metal ions such as ruthenium (Ru) or palladium (Pd) dispersed in and distributed throughout a matrix comprising an inorganic or silicon oxide network. The catalyst may be prepared by the sol-gel method; a solution of at least one catalytic metal compound is added to a solution of at least one metal alkoxide selected from Al, Ti, Nb, Zr, Ta, Si and other inorganic alkoxides, and then gelling the mixture. Promotors such as rhenium (Re), molybdenum (Mo) and tin (Sn) may be added. The catalyst may be used in the reduction of metallic acid or gamma-butyrolactone to tetrahydrofuran (THF) and 1,4-butanediol (BDO).

Photocatalytic degradation of aqueous tetrahydrofuran, 1,4-dioxane, and their mixture with TiO 2

Abstract: Photocatalytic degradation of tetrahydrofuran, 1,4-dioxane, and their mixture in a slurry pho- toreactor was studied. Using both GC/MS and ion chromatography (IC) methods, possible intermediates were detected and the reaction mechanism pathways for both compounds were proposed. Kinetic models were developed and the kinetic parameters were estimated using a statistical method of non-linear parameter es- timation in which all experimental data were utilized. It was shown that tetrahydrofuran was disappeared via direct oxidation as well as hydroxyl radical attack. A modified Langmuir-Hinshelwood described the degrada- tion behavior of tetrahydrofuran and the binary system. 1,4-Dioxane obeyed a simple Langmuir-Hinshelwood kinetic form in the single compound system.

Synthesis of highly isotactic poly(N, N-diethylacrylamide) by anionic polymerization with Grignard reagents and diethylzinc

Abstract: N,N-Dimethylacrylamide (DMA) and N,N-diethylacrylamide (DEA) were polymerized with various Grignard reagents in tetrahydrofuran at -78 °C in the presence of diethylzinc (Et 2 Zn). Highly isotactic poly(DEA) was produced in quantitative yield with tert-butylmagnesium bromide and Et 2 Zn, whereas atactic poly(DEA) was generated in the absence of Et 2 Zn. No stereospecific polymerization of DMA proceeded with Grignard reagent in the presence of Et 2 Zn. The highly isotactic poly-(DEA) obtained was soluble in water and showed the characteristic coil-globule transition phenomenon.

Synthesis and characterization of new cardo polyamides and polyimides containing tert‐butylcyclohexylidene units

Abstract: A new cardo diamine monomer, 1,1-bis[4-(4-aminophenoxy)phenyl]-4-tert-butylcyclohexane containing tert-butylcyclohexylidene units was prepared in three steps from 4-tert-butylcyclohexanone. The monomer was reacted with various aromatic dicarboxylic acids and tetracarboxylic dianhydrides to produce polyamides and polyimides, respectively. All the polymers, characterized by X-ray diffraction, are amorphous. These cardo polymers exhibit good solubility in a variety of solvents. Almost all polymers are soluble in N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridine, and even in tetrahydrofuran (THF) and cyclohexanone. The polymers show glass transition temperatures between 244-310°C. and decomposition temperatures at 10% mass loss ranging from 486-526°C in nitrogen. The tough and flexible polymer films have tensile strength of 77-137 MPa, elongations at breaks of 5-14% and tensile moduli of 2.0-2.6 GPa.

Synthesis and characterization of a novel AlQ3‐containing polymer

Abstract: In this article, the synthesis of a tris(8-hydroxyquinoline)aluminum (AlQ3)-containing poly(arylene ether) (4) is reported. The presence of AlQ3 pendants in polymer 4 is confirmed by NMR, ultraviolet–visible, photoluminescence, and gel permeation chromatography analyses. This is the first report of the attachment of AlQ3 complexes as side chains to a polymer. Polymer 4 has a glass-transition temperature of 217.8 °C and is thermally stable with a 5% weight-loss temperature greater than 500 °C under nitrogen, as determined by differential scanning calorimetry and thermogravimetric analyses, respectively. Polymer 4 is quite soluble in common organic solvents, such as tetrahydrofuran, N,N-dimethylacetamide, and CHCl3. A composite that is 80 wt % polymer 4 and 20 wt % AlQ3 forms a transparent and tough film when cast from its chloroform solution. The application of this AlQ3-containing polymer in light-emitting diodes is under investigation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2887–2892, 2000

Density Functional Theory Study on the Aggregation and Dissociation Behavior of Lithium Chloride in THF and Its Interaction with the Active Centers of the Anionic Polymerization of Methyl Methacrylate and Styrene

Abstract: The structure of LiCl in tetrahydrofuran (THF) solution and its effect on the structure and stability of active sites of the anionic polymerization of methyl methacrylate (MMA) and styrene (St) was studied using the quantum-chemical density functional theory (DFT) approach. In the case of MMA anionic polymerization, it was found that LiCl forms stable mixed aggregates with ester enolates which model the PMMA living chain ends, thus preventing them from self-aggregation. They may even stabilize more reactive zwitterionic structures of these chain ends. The dissociation of solvated LiCl dimers to form Li + (THF)4 cations is slightly endothermic in THF, while scavenging of Li + (THF)4 by LiCl dimers to produce more stable quintuple cations ((THF)3Li-Cl-Li(THF)2-Cl-Li(THF)3) + is even exothermic. Therefore, if the concentration of LiCl exceeds a certain threshold value, Li + (THF)4 cations should effectively be scavenged by LiCl dimers. Thus, increasing LiCl concentration below the threshold concentration should lead to an increase in the concentration of free Li + (THF)4 cations. In the anionic polymerization of styrene in the presence of LiCl this results in the suppression of PSt-Li chain end dissociation due to the common ion effect, slowing down the polymerization. Further addition of LiCl above the threshold concentration should decrease the concentration of free Li + (THF)4 cations, leading to enhanced PSt-Li chain end dissociation, thus increasing the polymerization rate, in agreement with kinetic data reported in the literature.

Solvation of Li+ by Acetone, THF, and Diethyl Ether in the Gas Phase and the Ion−Molecule Association Mechanism

Abstract: Fourier transform ion cyclotron resonance spectrometry has been employed to study the solvation of the Li+ ion with acetone, tetrahydrofuran (THF), and diethyl ether (DEE) in the gas phase. LiILi+ ...

Binary Mutual Diffusion Coefficients of Aqueous Cyclic Ethers at 25 °C. Tetrahydrofuran, 1,3-Dioxolane, 1,4-Dioxane, 1,3-Dioxane, Tetrahydropyran, and Trioxane

Abstract: Taylor dispersion and differential refractometry are used to measure mutual diffusion coefficients (D) for the binary mixtures 1,4-dioxane + water, 1,3-dioxolane + water, and tetrahydrofuran + water at 25 °C. For each of these systems the plot of D against composition shows a pronounced minimum. Activity and viscosity data for aqueous 1,4-dioxane are used to discuss the strong composition dependence of D in terms of changes in the mobilities and thermodynamic driving forces. Diffusion coefficients are also reported for dilute aqueous solutions of 1,3-dioxane, tetrahydropyran, and trioxane. The limiting diffusion coefficients of the infinitely dilute aqueous ethers are discussed in terms of ring size, number and relative location of the oxygens, and the ether partial molar volume. A second or a third oxygen in the five- or six-membered rings reduces the ether partial molar volumes by about 10 cm3·mol-1 and increases the limiting diffusion coefficients by (0.14 to 0.21) × 10-5 cm2·s-1.

A practical route for the preparation of poly(4-hydroxystyrene), a useful photoresist material

Abstract: The synthesis and characterization of poly(4-hydroxystyrene) (PHS) and poly(4-vinylphenol) (PVPh) by the polymer modification route are reported. Polystyrene prepared by free-radical and anionic polymerization was acetylated quantitatively to poly(4-acetylstyrene) (ACPS) with acetyl chloride and anhydrous aluminum trichloride in carbon disulfide. The acetylation worked equally well in a mixture of 1,2-dichloroethane (DCE) and nitrobenzene containing largely DCE. The extent of the acetylation was estimated by 1 H NMR. The oxidation of ACPS was carried out with various oxidizing agents and reaction conditions. The peracetic acid oxidation in chloroform resulted in quantitative oxidation to poly(4-acetoxystyrene) (APS) as estimated by 1 H NMR spectroscopy. The treatment of APS with hydrazine hydrate in dioxane resulted in the formation of PVPh. Deacetylation occurred with equal versatility in a mixture of aqueous sodium hydroxide and tetrahydrofuran. All the polymers were characterized via gel permeation chromatography, IR, UV, 1 H NMR, and 13 C NMR spectroscopic techniques. This is the first report on the synthesis of ACPS, APS, and PHS of reasonably narrow molecular weight distributions or otherwise by the polymer modification route.

Solution Properties of Cellulose Tris(phenyl carbamate). 1. Characterization of the Conformation and Intermolecular Interaction

Abstract: The radius of gyration 〈S2〉1/2, hydrodynamic radius RH, intrinsic viscosity [η], and second virial coefficient A2 for cellulose tris(phenyl carbamate) (CTC) in tetrahydrofuran (THF) at 25 °C were d...

Zeolite-Like Sorption of Volatile Organics in β-[CuL2] (L = {CF3COCHCOC(CH3)2OCH3}-)†

Abstract: The β-form of the title copper(II) acetylacetonate derivative shows zeolite-like behavior, as exemplified by its ability to absorb volatile guests instantly and reversibly over a wide range of guest pressures. Sorption isotherms with methylene chloride, chloroform, carbon tetrachloride, n-pentane, acetone, tetrahydrofuran, and diethyl ether were determined at 30 °C or over a range of temperatures. For all guests tested, sorption occurred even at minimal guest pressure, indicating the presence of porosity of the host sorbent even without included species present. The nature of the isotherms as well as other characteristics suggests a physical mode of sorption on the inner hydrophobic surface of the host pores. With increasing pressure, the isotherms quickly reached plateau values corresponding to a guest/host ratio of 2/3 for compact molecules and to a lower value for n-pentane and diethyl ether. At elevated temperatures and low guest pressure, the porous β-form collapses to the dense, α-form of the comple...

Tetrahydrofuran amino acids—versatile building blocks for unnatural biopolymers: lack of secondary structure in oligomeric carbopeptoids derived from a D-galacto-5-(aminomethyl) tetrahydrofuran-2-carboxylic acid

Abstract: The efficient synthesis of a D-galacto-configured tetrahydrofuran amino acid from a seven-carbon lactone as a monomer for the generation of sequence-defined structured biopolymer mimics is described. Investigations into the characteristics of homooligomeric derivatives of this monomer indicate that they do not adopt well defined secondary structures. The unanticipated formation of a heterooligomeric derivative and investigations into its solution structure are also described.