Showing papers on "Tetrahydrofuran published in 1998"

Cobalt Porphyrin Catalyzed Reduction of CO2. Radiation Chemical, Photochemical, and Electrochemical Studies

Abstract: Several cobalt porphyrins (CoP) have been reduced by radiation chemical, photochemical, and electrochemical methods, in aqueous and organic solvents. In aqueous solutions, the CoIP state is stable at high pH but is shorter lived in neutral and acidic solutions. Stable CoIP is also observed in organic solvents and is unreactive toward CO2. One-electron reduction of CoIP leads to formation of a species that is observed as a transient intermediate by pulse radiolysis in aqueous solutions and as a stable product following reduction by Na in tetrahydrofuran solutions. The spectrum of this species is not the characteristic spectrum of a metalloporphyrin π-radical anion and is ascribed to Co0P. This species binds and reduces CO2. Catalytic formation of CO and HCO2- is confirmed by photochemical experiments in acetonitrile solutions containing triethylamine as a reductive quencher. Catalytic reduction of CO2 is also confirmed by cyclic voltammetry in acetonitrile and butyronitrile solutions and is shown to occur ...

Cobalt-Porphyrin Catalyzed Reduction of CO2: Radiation Chemical, Photochemical, and Electrochemical Studies

Abstract: Several cobalt porphyrins (CoP) have been reduced by radiation chemical, photochemical, and electrochemical methods, in aqueous and organic solvents. In aqueous solutions, the CoIP state is stable at high pH but is shorter lived in neutral and acidic solutions. Stable CoIP is also observed in organic solvents and is unreactive toward CO2. One-electron reduction of CoIP leads to formation of a species that is observed as a transient intermediate by pulse radiolysis in aqueous solutions and as a stable product following reduction by Na in tetrahydrofuran solutions. The spectrum of this species is not the characteristic spectrum of a metalloporphyrin π-radical anion and is ascribed to Co0P. This species binds and reduces CO2. Catalytic formation of CO and HCO2- is confirmed by photochemical experiments in acetonitrile solutions containing triethylamine as a reductive quencher. Catalytic reduction of CO2 is also confirmed by cyclic voltammetry in acetonitrile and butyronitrile solutions and is shown to occur ...

Strategies for the analysis of polar solvents in liquid matrixes.

Abstract: Various approaches to the analysis of polar compounds in different matrixes by solid-phase microextraction (SPME) were studied. The analysis of polar analytes in nonpolar matrixes was performed with custom-made SPME fibers coated with Nafion perfluorinated resin. The sensitivity of this fiber in this type of analysis was better by 1 order of magnitude on average as compared to those of any of the commercially available fibers. The fiber was the most sensitive for the most polar of the compounds studied, i.e., methanol. Determination of methanol, ethanol, and 2-propanol in unleaded gasoline was illustrated. Except for methanol, the fiber did not perform very well in the analysis of alcohols in water. The fiber was capable of extracting water from benzene. SPME analysis of polar compounds in water was studied using aqueous solutions of acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), 2-propanol, 2-methyl-2-propanol, and tetrahydrofuran. Fibers coated with poly(dimethylsiloxane)/divinylbenzene yi...

The aza-payne rearrangement : a synthetically valuable equilibration

Abstract: An aza-Payne rearrangement of N-activated 2-aziridinemethanols, synthesized in an optically active form, with potassium tert-butoxide (ButOK), potassium hydride (KH), or sodium hydride (NaH) at near 0 °C in common aprotic solvents such as tetrahydrofuran (THF), toluene, or a mixed solvent of THF–HMPA followed by quenching at low temperature gives the corresponding epoxy sulfonamides in high yields. The anionic reaction intermediates, generated by treatment of 2-aziridinemethanols with a base, react readily in a one-pot manner with a variety of nucleophiles such as organocopper reagents, thiols, and trimethylsilyl cyanide to yield the optically active corresponding functionalized 1,2-amino alcohols in good yields. Upon exposure of 2,3-epoxy amines to an equimolar mixture of ButOK and BuLi (super base) in a mixed solvent of THF and n-hexane at –78 °C, the equilibrium lies exclusively toward the hydroxyaziridine forming direction.

Preparation and Characterization of Poly(vinyl chloride‐co‐vinyl acetate)‐Based Gel Electrolytes for Li‐Ion Batteries

Abstract: Poly(vinyl chloride) (PVC)-based electrolytes, a class of the most promising polymer electrolytes, are found to suffer from solvent exudation. Two strategies were employed to suppress this shortcoming, one involving the replacement of PVC with poly(vinyl chloride-co-vinyl acetate) (PVCAC) copolymer and the other the direct utilization of solvents for PVC or PVCAC instead of using an auxiliary carrier solvent (e.g., tetrahydrofuran, THF). The thermodynamics of polymer solubility was particularly emphasized in the latter approach. N,N-dimethylformamide (DMF) and N-methyl pyrrolidionone (NMP) are preferred cosolvents of ethylene carbonate (EC) and/or propylene carbonate (PC). The PVCAC-based gel electrolytes prepared were then characterized by ionic conductivity, cyclic voltammetry, and ac impedance data. The results indicate that electrolytes containing NMP/EC mixed solvent exhibit conductivities exceeding 10{sup {minus}3} S/cm whereas the electrolytes containing DMF/EC/PC exhibit conductivities around 10{sup {minus}4} S/cm at room temperature. Moreover, the former category was found to be oxidatively stable up to 4.9 V vs. Li/Li{sup +} and the latter to 4.6 V vs. Li/Li{sup +}. Finally, ac impedance results suggest that the stability of the Li/electrolyte interface needs further improvement, which is a crucial task for most polymer gel electrolytes at present.

Soluble Supports Tailored for Organic Synthesis: Parallel Polymer Synthesis via Sequential Normal/Living Free Radical Processes

Abstract: To expand the availability and solubility range of polymer supports for liquid-phase organic synthesis (LPOS) we have applied a sequence of normal and “living” free radical polymerization to generate a library of block copolymers possessing either block or graft architecture with initiators 1−4 and a diverse set of vinyl monomers 5−9. The structure, molecular weight, and polydispersity (PD) of the individual library members have been determined by size exclusion chromatography (SEC), 1H and 13C NMR, and as a function of the solubility of each polymer in a range of solvents. One copolymer, polyBS-DS (Mn = 17 000, PD = 1.54) derived from 4-tert-butylstyrene (6, BS), 3,4-dimethoxystyrene (7, DS), and initiator 1 has a solubility profile [soluble in toluene, tetrahydrofuran (THF), ether, acetone and methylene chloride (DCM), insoluble in methanol and water] that is different from the present polymer of choice for LPOS, poly(ethylene) glycol (PEG), and has been studied in some detail as a new support in LPOS. ...

(meth)acrylate derivative having lactone structure, polymer, photoresist composition, and formation of pattern

Abstract: PROBLEM TO BE SOLVED: To obtain a new (meth)acrylate derivative useful in e.g. producing resins used as photoresist materials with excellent dry etching resistance, transparency, substrate adhesion, and resolution. SOLUTION: Thie new compound is shown by formula I (R1 and R2 are each H or methyl), e.g. 5-acryloyloxy-2,6-norbornanecarbolactone. The compound of formula I is obtained, for example, by reaction between 5-hydroxy-2,6- norbornanecarbolactone and acryloyl chloride in an inert organic solvent such as tetrahydrofuran in the presence of a base. Furthermore, it is preferable that this compound of formula I is either homopolymerized or copolymerized with another polymerizable compound to prepare e.g. a copolymer of formula II (R1 to R3 and R5 are each H or methyl; R4 is a group decomposable with an acid; R6 is H or a 1-12C hydrocarbon; (x), (y) and (z) are each 0 or 1, x+y+z=1) with a weight-average molecular weight of 2,000-200,000.

Palladium-Catalyzed Regioselective [3 + 2] Cycloaddition of Vinylic Oxiranes with Activated Olefins. A Facile Synthesis of Tetrahydrofuran Derivatives

Abstract: The reaction of certain activated olefins (Michael acceptors) 5 with vinylic oxiranes 1 in the presence of catalytic amounts of Pd(PPh3)4 (5 mol %) in THF at 40 °C gave the corresponding [3 + 2] cycloaddition products 6. In all cases the reactions proceeded in regioselective manner, affording the corresponding polysubstituted tetrahydrofuran derivatives. The nature of electron-withdrawing group in activated olefins affected significantly the reactivity of substrates. Michael acceptors having sterically less bulky electron-withdrawing groups were essential for the cycloaddition reaction, and the presence of two electron-withdrawing groups at the α-position was needed. Accordingly, activated olefins having (CN, CN), (CN, CO2Et), (CN, SO2Ph), (Meldrum's type), and (SO2Ph, SO2Ph) could be used as a Michael acceptor. The present reaction provides a new method for the synthesis of tetrahydrofuran derivatives from vinylic oxiranes and Michael acceptors.

Preparation and X-Ray Crystal Structures of Tetrahydrofuran-Complexed Rare Earth Chlorides — a Structurally Rich Series

Abstract: Anhydrous lanthanoid metal chlorides LnCl3(thf)n (Ln = La, Ce, Nd, Sm, n = 2; Ln = Tb, Ho, n = 2·5; Ln = Dy, Tm, n= 2·7; Ln = Gd, Yb, Lu, n = 3; Ln = Er, n = 3·5) have been prepared in excellent yield by the direct reaction of the lanthanoid metal powders with hexachloroethane in tetrahydrofuran (thf), and (Ln = Eu, n = 0·8; Ln = La, n = 1·7; Ln = Pr, n = 2; Ln = Gd, n = 2·5; Ln = Er, n = 3) in good yield except for EuCl3(thf)0·8 from bulk metal. [YbCl3(thf)2]2 was prepared by prolonged treatment of solid YbCl3(thf)3 with pentane. The X-ray crystal structures of [LnC3(thf)2] (Ln = La, Ce or Pr), [LnCl3(thf)3.5] (Ln = Gd or Er), [YbCl3(thf)3] and [LaCl3(thf)(H2O)] have been determined. For [LaCl3(thf)2], a square antiprismatic single-stranded polymer, ... La(-Cl)3(thf)3La(-Cl)3(thf)2 ..., is the first eight-coordinate LnCl3(thf)n complex. The metal is surrounded by two sets of three bridging chlorines and cis thf oxygens. [LnCl3(thf)2] (Ln = Ce, Pr) have seven-coordinate structures with doubly chloride-bridged linear chains, ... LnCl(µ-Cl)3(thf)2LnCl(µ-Cl)2(thf)2 ... where the lanthanoid atom exists in a pentagonal bipyramidal environment, the pentagonal bipyramidal plane being defined by four chloride atoms and one oxygen atom of the thf ligand, and the axial positions being occupied by a chloride and a thf oxygen atom. [LnCl3(thf)3.5] (Ln = Gd, Er) crystallize as discrete ion pairs, [LnCl2(thf)5]+ [LnCl4(thf)2]¯. The lanthanoid atom in the cation displays pentagonal bipyramidal geometry with two apical chloride atoms and five equatorial thf ligands while the anion has quasi-regular octahedral stereochemistry with trans thf ligands. [LaCl3(thf)(H2O)] displays an eight-coordinate two-dimensional polymeric array with six bridging chlorides per lanthanum atom. Far-infrared spectra have been recorded for a number of products and used as a basis for structural proposals, particularly for products with fractional thf.

Efficient zirconocene-coupling of silicon-substituted diynes to polymers and macrocycles

Abstract: The zirconocene-coupling of diynes with internal silicon substituents, MeC⋮CMe2SiArSiMe2C⋮CMe (1: Ar = 1,4-C6H4; 2: Ar = 1,3-C6H4; 3: Ar = 4,4‘-C6H4C6H4), generates regiospecific polymers containing zirconacyclopentadiene in the main chain (5−7). These organometallic polymers hydrolyze cleanly to butadienediyl polymers of the type [Me2SiArSiMe2CHCMeCMeCH]n (11−13), and polymer 5 reacts with iodine to give the iodine-containing polymer [1,4-Me2SiC6H4SiMe2C(I)CMeCMeC(I)]n (14). The organometallic polymers undergo facile and high-yield degradations to macrocycles under mild conditions (refluxing tetrahydrofuran solution). The size and shape of the resulting macrocycles depend upon the nature of the diyne spacer group. Thus, polymers 5 and 7 containing parallel diyne units convert to the trimeric macrocycles [Me2SiArSiMe2C4Me2ZrCp2]3 (15: Ar = 1,4-C6H4; 24: Ar = 4,4‘-C6H4C6H4), while polymer 6 gives the dimeric macrocycle [1,3-Me2SiC6H4SiMe2C4Me2ZrCp2]2 (18). The dimeric macrocycle [Me2SiC6H4SiMe2C6H4SiM...

Trifunctional Organolithium Initiator Based on 1,3,5-Tris(1-Phenylethenyl)benzene. Synthesis of Functionalized, Three-Armed, Star-Branched Polystyrenes

Abstract: A novel hydrocarbon-soluble, trifunctional organolithium initiator for anionic polymerization has been developed on the basis of the addition of 3 mol of sec-butyllithium with 1,3,5-tris(1-phenylethenyl)benzene. Well-defined, three-armed, star-branched polystyrenes have been synthesized using this initiator in benzene solution with stoichiometric amounts of tetrahydrofuran. The efficiency of the initiation reaction was evaluated by a combination of UV−visible spectroscopy and size-exclusion chromatography analysis. The minimum arm molecular weight for complete initiation was found to be about 5.7 × 10 3 g /mol for this initiator system. The structures of the star-branched polymers were investigated by molecular weight characterization, intrinsic viscosity, and the corresponding values of g‘ (0.80−0.81); these stars were also compared with an analogous symmetrical, three-armed, polystyrene star prepared by the end-linking reaction of 3 mol of poly(styryl)lithium with 1,3,5-tris(1-phenylethenyl)benzene as t...

Stereoselective Synthesis of Quaternary Benzylic Carbons Using C2 Symmetric Imidazolines and Tetrahydrofuran as Electrophile

Abstract: Alkylative ring opening of tetrahydrofuran in the presence of 9-BBN triflate is studied. Dianions derived from C2 symmetric imidazolines induce excellent to modest acyclic diastereoselectivity to f...

Raman Spectroscopic Studies of THF Clathrate Hydrate

Abstract: Raman spectra were collected for tetrahydrofuran (THF) hydrate, a structure II clathrate hydrate (CH) that was prepared from THF and a dilute solution of D2O in H2O (5% D2O) in a 17:1 ratio. The vibrational modes observed include (1) the uncoupled O−D vibrational modes of HDO in H2O between 10 and 170 K and (2) the THF ring breathing mode (predominantly C−C−C−C stretches) between 10 and 170 K. The low-frequency host lattice modes and the THF C−H stretching modes at 10 K are also presented. The spectral line attributed to the C−C−C−C vibrational mode of the enclathrated THF molecules broadened, and a pronounced shoulder developed on the low-frequency side as the temperature decreased. This anomalous behavior is attributed to the inhibition of rapid reorientational motion of the enclathrated THF molecules at T < 100 K. Analysis of the uncoupled O−D vibrations indicates that the frequency increases (and thus the hydrogen bond strength decreases) with increasing temperature. The vibrational frequency of the u...

Preparation and Properties of Hyperbranched Poly(ether ketones) with a Various Number of Phenylene Units

Abstract: New AB2 type monomers, with a various number of phenylene units, were prepared and converted to hyperbranched poly(ether ketones) by polymerization. Four kinds of AB2 type monomers, 4-hydroxy-3‘,5‘-bis(4-fluorobenzoyl)-biphenyl, 1, 4-hydroxy-3‘‘,5‘‘-bis(4-fluorobenzoyl)-p-terphenyl, 2, 4-hydroxy-3‘‘‘,5‘‘‘-bis(4-fluorobenzoyl)-p-quarterphenyl, 3, and 4-hydroxy-3‘‘‘‘,5‘‘‘‘-bis(4-fluorobenzoyl)-p-quinquephenyl, 4, were synthesized in a stepwise manner starting from 3,5-bis(4-fluorobenzoyl)phenol, 5, repeating a series of conversions of the hydroxy group to the triflate, cross-coupling reaction of the triflate with (p-methoxyphenyl)boronic acid, and cleavage of the methyl ether. Four kinds of hyperbranched poly(ether ketones) were prepared by the polymerization of the four AB2 type monomers. Obtained hyperbranched poly(ether ketones) from 1 and 2 were soluble in various organic solvents including N-methyl-2-pyrrolidone, m-cresol, chloroform, and tetrahydrofuran, but those from 3 and 4 were insoluble in organi...

Biocompatible polymeric coating material

Abstract: The invention provides a biocompatible polymeric coating material, wherein the polymeric material is selected from the group consisting of linear, dendrimeric and branched polymers which contain primary, secondary, tertiary or quaternary amine groups with hydrophobic side chains and which polymers are insoluble, or only slightly soluble, in aqueous solution at a pH range between 3 and 11 and soluble in at least one organic solvent selected from the group consisting of alcohols, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, chloroform, dichloromethane, hexanes and mixtures thereof.

Synthesis of Adenophostin Analogues Lacking the Adenine Moiety as Novel Potent IP3 Receptor Ligands: Some Structural Requirements for the Significant Activity of Adenophostin A

Abstract: 1-O-Tetrahydrofuranyl-α-d-glucopyranose derivatives 5−8 were designed and synthesized as novel IP3 receptor ligands. The glycosidation reactions between fluoroglycosyl donor 23 and tetrahydrofuran derivatives 11−14 as glycosyl acceptors selectively gave the corresponding α-glycosides, which were converted into the target compounds 5−8 via the introduction of phosphate groups using the phosphoramidite method. Among these compounds, 1-O-tetrahydrofuranyl-α-d-glucopyranose trisphosphate derivatives 5 and 8 significantly inhibited the binding of [3H] IP3 to IP3 receptor from porcine cerebella, with IC50 values of 25 and 27 nM, respectively, which were comparable to the affinity of IP3 itself.

Spectroscopic Studies on Brooker's Merocyanine

Abstract: The origin of the multiple absorption bands of Brooker's merocyanine, 1-(4-aza-4-methylphenyl)-2-trans-(4-oxyphenyl)ethene, found in the visible region of the spectrum in solvents such as chloroform and tetrahydrofuran, has been explored experimentally using 1H and 13C NMR spectroscopy and theoretically using molecular orbital methods. While NMR analysis rules out the presence of a cis conformer, AM1/COSMO calculations in various solvents strongly suggest that there are a number of stable nonplanar conformations of the merocyanine as well as a dimer which are predicted to absorb at longer and shorter wavelengths, respectively, than the favored planar conformer. Spectroscopic analysis at variable temperature is supportive with the intensity of the longer wavelength absorption initially reducing with decreasing temperature, followed by an increase in the concentration of dimers and possibly aggregates. Further support is provided by synthesis of the corresponding nonplanar merocyanine containing methyl grou...