Showing papers on "Tetrahydrofuran published in 2016"

A comparative study on the impact of different glymes and their derivatives as electrolyte solvents for graphite co-intercalation electrodes in lithium-ion and sodium-ion batteries

Abstract: The abundance of sodium has recently sparked considerable interest in sodium-ion batteries (NIBs). Their similarity to conventional lithium-ion technology is obvious; however, the cell chemistry often significantly deviates. Graphite, although being the standard negative electrode in Li-ion batteries, is largely inactive for Na-ion storage in conventional non-aqueous carbonate-based electrolytes, for example. Very recently, it has been demonstrated that graphite can be activated for Na-ion storage in cells with ether-based electrolytes. The storage mechanism is based on co-intercalation of solvent molecules along with the Na-ions, forming ternary graphite intercalation compounds (t-GICs). This process is highly reversible but yet poorly understood. Here, we provide a comprehensive study on the formation and the stability of t-GICs. A series of ether solvents are being discussed: linear glymes with different chain lengths (mono-, di-, tri-, and tetraglyme), several derivatives with side groups as well as tetrahydrofuran (THF) as a cyclic ether and one crown ether. We show that the redox potentials shift depending on the ether chain length and mixing of ethers might enable tailoring of the redox behaviour. The inferior behaviour of triglyme is likely due to the less ideal ion coordination. Complementary experiments with lithium are made and demonstrate the superior behaviour of sodium. We find that the increase in graphene layer spacing during intercalation only slightly depends on the chain length and is in the range of 250%, and still mechanical stability is preserved. We further show the t-GICs possess chemical stability and demonstrate that the kinetically favoured charge transfer is probably due to the absence of a solid electrolyte interphase.

An AIE active probe for specific sensing of Hg 2+ based on linear conjugated bis-Schiff base

Abstract: A novel aggregation-induced emission (AIE) active linear conjugated bis-Schiff base compound, (E)-N,N′-bis(4-(Z)-2-(4-butoxyphenyl)-1-cyanovinylphenyl)-1,4-benzenebismethaneimine (4) containing α-cyanostilbene unit was designed, synthesized and characterized. The distinct change of color and/or fluorescence emission of 4 + Hg2+ in tetrahydrofuran (THF) and THF/water solution provided a simple and easy discrimination way for Hg2+ by “naked eye” or using a UV lamp. The aggregating patterns of 4 were applied to explain the mechanism of sensing. The as-synthesized sample showed comparatively high selectivity and sensitivity to Hg2+ through fluorescence “turn-on” response with a low detection limit (3.4 × 10−9 M in THF, 2.4 × 10−7 M in THF/water). The results implied that the as-made sample could effectively act as Hg2+ sensor not only in THF and THF/water but in living cells.

Experimental verifications of Mpemba-like behaviors of clathrate hydrates

Abstract: The exact mechanism of the Mpemba effect of water was recently investigated microscopically and explained on the basis of the cooperative relationship between intramolecular polar-covalent bonds (O-H) and intermolecular hydrogen bonds (O:H). We posited that this relationship might exist in clathrate hydrates since they consist of hydrogen-bonded host water frameworks and enclathrated guest molecules. The formation of tetrahydrofuran (THF) hydrate, which is the simplest clathrate hydrate, was investigated by using differential scanning calorimetry and Raman spectroscopy. THF hydrates show the Mpemba effect at lower initial temperatures, but formation times were delayed at higher initial temperatures because the evaporated THF molecules should be liquefied to correspond to the stoichiometric concentration of guest molecules to form sII clathrate hydrates. However, even though the formation time was delayed at higher initial temperatures, the rates of heat emission during THF hydrate formation, measured in a bulk state, roughly increased as the initial temperature increased. Moreover, we observed that the O: H stretching phonons of water in the THF hydrate showed a blue shift, and the O-H stretching mode showed a redshift as temperature decreased. Both the rate of heat emission and the Raman shift of these two bonds imply that a cooperative relationship between the covalent bond and the hydrogen bond exists in THF hydrate as pure water. The formation kinetics of THF hydrate therefore might depend on its initial temperature, thus showing Mpemba-like behavior.

Tuning the Solid State Emission of the Carbazole and Cyano-Substituted Tetraphenylethylene by Co-Crystallization with Solvents.

Abstract: Solid state emissive materials with high quantum yields and tunable emissions are desirable for various applications. A new TPE derivative (1) with two carbazole moieties and two cyano groups is reported, which shows typical aggregation induced emission behavior. Four crystals 1a, 1b, 1c, and 1d are obtained after crystallization from N,N-dimethylformamid (DMF), trichloromethane (CHCl3 ), tetrahydrofuran (THF), and dichloromethane (CH2 Cl2 ), respectively. Crystal structural analyses reveal that (i) molecules of 1 co-crystallize with DMF, CHCl3 , THF, and CH2 Cl2 in 1a, 1b, 1c, and 1d, respectively, and (ii) conformations of 1 are different within 1a, 1b, 1c, and 1d, and compound 1 within crystal 1a adopts the most twisting conformation. Crystalline solids 1a, 1b, 1c, and 1d exhibit high emission quantum yields up to 0.65, but their emission colors are varied from blue to green. In comparison, the amorphous solid of 1 is yellow-emissive with emission maximum at 542 nm. Moreover, the blue- or green-emissive crystalline solids and the yellow-emissive amorphous solid can be inter-converted by the grinding of crystalline solids and exposure of the amorphous solid to vapors of appropriate solvents. It is also demonstrated that microrods of 1a, 1b, and 1d show typical optical waveguiding behavior.

Ruthenium-Catalyzed C-H Bond Activation Approach to Azolyl Aminals and Hemiaminal Ethers, Mechanistic Evaluations, and Isomer Interconversion.

Abstract: C(sp3)–N bond-forming reactions between benzotriazole and 5,6-dimethylbenzotriazole with N-methylpyrrolidinone, tetrahydrofuran, tetrahydropyran, diethyl ether, 1,4-dioxane, and isochroman have been conducted using RuCl3·3H2O/t-BuOOH in 1,2-dichloroethane. In all cases, N1 and N2 alkylation products were obtained, and these are readily separated by chromatography. One of these products, 1-(isochroman-1-yl)-5,6-dimethyl-1H-benzotriazole, was examined by X-ray crystallography. It is the first such compound to be analyzed by this method, and notably, the benzotriazolyl moiety is quasi-axially disposed, consistent with the anomeric effect. This has plausible consequences, not observed previously. In contrast to other hemiaminal ether-forming reactions, which proceed via radicals, this Ru-catalyzed process is not suppressed in the presence of a radical inhibitor. Therefore, an oxoruthenium-species-mediated rapid formation of an oxocarbenium intermediate is believed to occur. In the radical-trapping experiment,...

Association and Dissociation of Grignard Reagents RMgCl and Their Turbo Variant RMgCl⋅LiCl

Abstract: Grignard reagents RMgCl and their so-called turbo variant, the highly reactive RMgCl⋅LiCl, are of exceptional synthetic utility. Nevertheless, it is still not fully understood which species these compounds form in solution and, in particular, in which way LiCl exerts its reactivity-enhancing effect. A combination of electrospray-ionization mass spectrometry, electrical conductivity measurements, NMR spectroscopy (including diffusion-ordered spectroscopy), and quantum chemical calculations is used to analyze solutions of RMgCl (R=Me, Et, Bu, Hex, Oct, Dec, iPr, tBu, Ph) in tetrahydrofuran and other ethereal solvents in the absence and presence of stoichiometric amounts of LiCl. In tetrahydrofuran, RMgCl forms mononuclear species, which are converted into trinuclear anions as a result of the concentration increase experienced during the electrospray process. These trinuclear anions are theoretically predicted to adopt open cubic geometries, which remarkably resemble structural motifs previously found in the solid state. The molecular constituents of RMgCl and RMgCl⋅LiCl are interrelated via Schlenk equilibria and fast intermolecular exchange processes. A small portion of the Grignard reagent also forms anionic ate complexes in solution. The abundance of these more electron-rich and hence supposedly more nucleophilic ate complexes strongly increases upon the addition of LiCl, thus rationalizing its beneficial effect on the reactivity of Grignard reagents.

Mechanism of Slow Crystal Growth of Tetrahydrofuran Clathrate Hydrate

Abstract: Tetrahydrofuran (THF) clathrate hydrate has been frequently used in experimental studies instead of gas hydrates because it forms at a temperature higher than the ice point under ambient pressure. In this paper, we compare the crystal growth rates of THF hydrate and ice using molecular dynamics simulations. It is demonstrated that the crystal growth of THF hydrate is much slower than that of ice. The growth rates of THF hydrate significantly deviate from a standard kinetic model known as the Wilson–Frenkel model, whereas it reproduces the temperature dependence of the growth rate of ice. The slow crystal growth and the deviation from the Wilson–Frenkel model are attributed to the trapping of THF molecules in open small cages at the hydrate surface. We calculate the free energy profile of a THF molecule transferring from the bulk solution phase to the hydrate surface using the umbrella sampling technique. It is shown that a THF molecule trapped in an open small cage needs to cross one or two free energy ba...

Pressure-Dependent Competition among Reaction Pathways from First- and Second-O2 Additions in the Low-Temperature Oxidation of Tetrahydrofuran.

Abstract: We report a combined experimental and quantum chemistry study of the initial reactions in low-temperature oxidation of tetrahydrofuran (THF). Using synchrotron-based time-resolved VUV photoionization mass spectrometry, we probe numerous transient intermediates and products at P = 10–2000 Torr and T = 400–700 K. A key reaction sequence, revealed by our experiments, is the conversion of THF-yl peroxy to hydroperoxy-THF-yl radicals (QOOH), followed by a second O2 addition and subsequent decomposition to dihydrofuranyl hydroperoxide + HO2 or to γ-butyrolactone hydroperoxide + OH. The competition between these two pathways affects the degree of radical chain-branching and is likely of central importance in modeling the autoignition of THF. We interpret our data with the aid of quantum chemical calculations of the THF-yl + O2 and QOOH + O2 potential energy surfaces. On the basis of our results, we propose a simplified THF oxidation mechanism below 700 K, which involves the competition among unimolecular decompo...

Rhodium-Catalyzed Oxy-Aminofluorination of Diazoketones with Tetrahydrofurans and N-Fluorobenzenesulfonimide

Abstract: We have developed a rhodium-catalyzed oxy-aminofluorination method for transformation of diazoketones. The reaction is based on addition of tetrahydrofuran derivatives and N-fluorobenzenesulfonimide (NFSI) to the diazoketone substrate. The reaction can be performed under mild conditions with high regioselectivity. The synthetic scope involves a wide variety of diazoketones and tetrahydrofuran derivatives. The reaction is supposed to proceed via a tetrahydrofuran based onium ylide intermediate, which is formed from rhodium-carbenoid.

Molecular dynamics study on the nucleation of methane + tetrahydrofuran mixed guest hydrate.

Abstract: The nucleation of methane (CH4), tetrahydrofuran (THF), and CH4 + THF hydrates are investigated by microsecond MD simulations. These three systems exhibit distinct structural developments in the aqueous phase quantified by the formation of cage structures of hydrogen bonded water molecules. The development of a cluster of cages in the CH4 system is limited by the scarce CH4 molecules in the solution, while in the THF system it is limited by the short lifetime of cages. In the CH4 + THF mixed guest system, a small cluster of caged CH4 molecules can be rapidly stabilized by abundant neighboring cages of THF molecules. Therefore, the induction time of the CH4 + THF mixed guest system is found to be significantly shorter than that of the pure CH4 and pure THF systems. Furthermore, the structure of cages found in the initially formed cage clusters are often different from the typical 5126n (n = 0, 2, 3, 4) cages observed in clathrate hydrate systems. The cluster of cages may grow or transform into structure I or II clathrate hydrate in the later stages.

Synthesis and Stereospecific Polymerization of a Novel Bulky Styrene Derivative

Abstract: A novel vinylbiphenyl monomer, 2-methoxy-5-phenylstyrene (MOPS), was designed and efficiently synthesized to investigate the stereospecific polymerization of bulky and polar styrenic derivative. Regardless of its large side group and electron-donating o-methoxy substituent, this compound showed a high polymerizability and was readily converted to the corresponding polymers with moderate to high molecular mass through radical, anionic, and coordination polymerizations. The resultant polymers were characterized by a combination of 1H/13C NMR spectrometry, thermal analysis, and wide-angle X-ray diffraction. Radical polymerization initiated by AIBN in toluene at 60 °C produced a syndiotactic-rich (rr = 0.37) polymer as most bulky vinyl monomers, whereas anionic polymerizations induced by n-BuLi yielded only isotactic-rich polymers no matter if polar tetrahydrofuran (−78 °C, mm = 0.54) or apolar toluene (−40 °C, mm = 0.78) was employed as the solvent. The isotactic-rich microstructure obtained by anionic polym...

Ate Complexes in Iron‐Catalyzed Cross‐Coupling Reactions

Abstract: Iron-catalyzed cross-coupling reactions have an outstanding potential for sustainable organic synthesis, but remain mechanistically poorly understood. Here, we use electrospray-ionization (ESI) mass spectrometry to identify the ionic species formed in these reactions and characterize their reactivity. Transmetalation of Fe(acac) (acac = acetylacetonato) with PhMgCl in tetrahydrofuran (THF) produces anionic iron ate complexes, whose nuclearity (1 to 4 Fe centers) and oxidation state (ranging from -I to +III) crucially depend on the presence of additives or ligands. Upon addition of iPrCl, formation of the heteroleptic FeIII complex [PhFe(iPr)]¯ is observed. Gas-phase fragmentation of this complex results in a reductive elimination and the release of the cross-coupling product with high selectivity.

Formation of Clathrate Hydrates of Water-Soluble Guest Molecules

Abstract: Clathrate hydrates of water-soluble guest molecules, such as ethylene oxide (EO) and tetrahydrofuran (THF), have been often investigated in experimental studies instead of gas hydrates because their dissociation temperatures are higher than the ice point under ambient pressure. We examine the formation mechanism of EO and THF hydrates using molecular dynamics simulations. The crystal growth rates are determined by the simulations of the hydrate/solution two-phase coexistence. It is found that the growth rate of EO hydrate is an order of magnitude higher than that of THF hydrate. The growth rates of THF hydrate largely deviate from the Wilson–Frenkel model, while the model well approximates the growth rates of EO hydrate, indicating that trapping of guest molecules on the hydrate surface, which causes the slowing of crystal growth of THF hydrate, is insignificant for EO hydrate. We also perform long-time simulations of aqueous EO and THF solutions to examine nucleation of clathrate hydrate. Spontaneous nuc...

Imidazolium-Based Poly(Ionic Liquid)s Featuring Acetate Counter Anions: Thermally Latent and Recyclable Precursors of Polymer-Supported N-Heterocyclic Carbenes for Organocatalysis

Abstract: Statistical copoly(ionic liquid)s (coPILs), namely, poly(styrene)-co-poly(4-vinylbenzylethylimidazolium acetate) are synthesized by free-radical copolymerization in methanolic solution. These coPILs serve to in situ generate polymer-supported N-heterocyclic carbenes (NHCs), referred to as polyNHCs, due to the noninnocent role of the weakly basic acetate counter-anion interacting with the proton in C2-position of pendant imidazolium rings. Formation of polyNHCs is first evidenced through the quantitative formation of NHC-CS2 units by chemical postmodification of acetate-containing coPILs, in the presence of CS2 as electrophilic reagent (= stoichiometric functionalization of polyNHCs). The same coPILs are also employed as masked precursors of polyNHCs in organocatalyzed reactions, including a one-pot two-step sequential reaction involving benzoin condensation followed by addition of methyl acrylate, cyanosilylation, and transesterification reactions. The catalytic activity can be switched on and off successively upon thermal activation, thanks to the deprotonation/reprotonation equilibrium in C2-position. NHC species are thus in situ released upon heating at 80 °C (deprotonation), while regeneration of the coPIL precursor occurs at room temperature (reprotonation), triggering its precipitation in tetrahydrofuran. This also allows recycling the coPIL precatalyst by simple filtration, and reusing it for further catalytic cycles. The different organocatalyzed reactions tested can thus be performed with excellent yields after several cycles.

Spectral and dynamical properties of a Zr-based MOF

Abstract: We report on the spectra and dynamics of a Zr-naphthalene dicarboxylic acid (Zr-NDC) MOF in different diluted solvent suspensions and in a concentrated tetrahydrofuran (THF) one. In a diluted diethyl ether (DE) suspension, we observed intraparticle excimer formation between neighboring naphthalene organic linkers, leading to a red-shifted broad band in the emission spectrum and to a dynamics composed of three components τ1 = 650 ps, τ2 = 3.7 ns and τ3 = 13.9 ns, assigned to the excimer photoproduction, monomer and excimer lifetimes, respectively. Furthermore, both absorption and emission spectra show a blue shift in more polar solvents characterized by the solvent polarity function f(e,n). We also observed changes in the excimer formation time (490-840 ps) probably due to a variation in the MOF structural fluctuation induced by solvent filling. The global fluorescence quantum yield of these suspensions is around 0.30 ± 0.05. At higher concentrations of the MOF particles, we observed the absorption and emission signals of aggregates having an intercrystal excimer formation in ∼ 5 ps in a THF suspension, ∼ 100 times shorter than that observed in a diluted one. Our results give the spectral and dynamical properties of a Zr-NDC MOF in solvent suspensions, opening the way to further studies of these kinds of MOFs interacting with fluorescent dyes for possible photonic applications.

Phase Equilibrium of the Methane Hydrate System in the Presence of Mixed Promoters (THF + TBAB) and the Effect of Inhibitors (NaCl, Methanol, and Ethylene Glycol)

Abstract: Tetra-n-butyl ammonium bromide (TBAB) and tetrahydrofuran (THF) are being widely used in gas hydrate research for their potential to store natural gas. The mixed promoter system of THF and TBAB has not yet been investigated for the phase stability conditions of methane hydrate. In this work, the phase stability of methane hydrate has been investigated in the presence of a mixed promoter (THF + TBAB) in the absence and presence of various inhibitors, viz., sodium chloride (NaCl), methanol (MeOH), and ethylene glycol (EG), at various concentrations. The phase equilibrium data has been reported in the temperature and pressure ranges of (282.25–289.65) K and (2.25–6.43) MPa, respectively. The heat of dissociation has been determined using the Clausius–Clapeyron equation for various methane hydrate systems. MeOH is observed to be an effective inhibitor as compared to EG and NaCl on the methane hydrate system formed from the mixed promoter system of THF + TBAB. With an increase in the concentration of MeOH, the...

Tandem Olefin Metathesis/Oxidative Cyclization: Synthesis of Tetrahydrofuran Diols from Simple Olefins

Abstract: A tandem olefin metathesis/oxidative cyclization has been developed to synthesize 2,5-disubstituted tetrahydrofuran (THF) diols in a stereocontrolled fashion from simple olefin precursors. The ruthenium metathesis catalyst is converted into an oxidation catalyst in the second step and is thus responsible for both catalytic steps. The stereochemistry of the 1,5-diene intermediate can be controlled through the choice of catalyst and the type of metathesis conducted. This olefin stereochemistry then controls the THF diol stereochemistry through a highly stereospecific oxidative cyclization.