Presence Of Tetrahydrofuran Research Articles

Actinide Redox-Active Ligand Complexes: Reversible Intramolecular Electron-Transfer in U(dpp-BIAN)2/U(dpp-BIAN)2(THF)

Actinide complexes of the redox-active ligand (dpp-BIAN)(2-) (dpp-BIAN = 1,2-bis(2,6-diisopropylphenylimino)acenaphthylene), U(dpp-BIAN)(2) (1), U(dpp-BIAN)(2)(THF) (1-THF), and Th(dpp-BIAN)(2)(THF) (2-THF), have been prepared. Solid-state magnetic and single-crystal X-ray data for complex 1 indicate a ground-state U(IV)-pi*(4) configuration, whereas a (dpp-BIAN)(2-)-to-uranium electron transfer occurs for 1-THF, resulting in a U(III)-pi*(3) ground configuration. The solid-state magnetic data also indicate that interconversion between the two forms of the complex is possible, limited only by the ability of tetrahydrofuran (THF) vapor to penetrate the solid upon cooling of the sample. In contrast to those in the solid state, spectroscopic data acquired in THF indicate only the presence of the U(IV)-pi*(4) form for 1-THF in solution, evidenced by electronic absorption spectra and by measurement of the solution magnetic moment in THF-d(8) using the Evans method. Also reported is the electrochemistry of the complexes collected in CH(2)Cl(2), CF(3)C(6)H(5), and THF. As expected from the solution spectroscopic data, only small differences are observed in half-wave potentials of ligand-based processes in the presence of THF, consistent with the solution U(IV)-pi*(4) configuration of the complexes in all cases. Density functional theory calculations were undertaken for complexes 1 and 1-THF to determine if intrinsic energetic or structural factors underlie the observed charge-transfer process. While the calculated optimized geometries agree well with experimental results, it was not possible to arrive at a convergent solution for 1-THF in the U(III)-pi*(3) configuration. However, perturbations in the orbital energies in 1 versus 1-THF for the U(IV)-pi*(4) configuration do point to a diminished highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap in 1-THF, consistent with the solid-state magnetic data. These results represent the first example of a stable and well-defined, reversible intramolecular electron transfer in an actinide complex with redox-active ligands.

Capture of carbon dioxide from flue or fuel gas mixtures by clathrate crystallization in a silica gel column

A column of silica gel was employed to contact water with flue gas (CO 2/N 2) mixture to assess if CO 2 can be separated by hydrate crystallization. Three different silica gels were used. One with a pore size of 30 nm (particle size 40–75 μm) and two with a pore size of 100 nm and particle sizes of 40–75 and 75–200 μm respectively. The observed trends indicate that larger pores and particle size increase the gas consumption, CO 2 recovery, separation factor and water conversion to hydrate. Thus, the gel (gel #3) with the larger particle size and larger pore size was chosen to carry out experiments with concentrated CO 2 mixtures and for experiments in the presence of tetrahydrofuran (THF), which itself is a hydrate forming substance. Addition of THF reduces the operating pressure in the crystallizer but it also reduces the gas uptake. Gel #3 was also used in experiments with a fuel gas (CO 2/H 2) mixture in order to recover CO 2 and H 2. It was found that the gel column performs as well as a stirred reactor in separating the gas components from both flue gas and fuel gas mixtures. However, the crystallization rate and hydrate yield are considerably enhanced in the former. Finally the need for stirring is eliminated with the gel column which is enormously beneficial economically.

Heavy Alkali Metal Amides: Role of Secondary Interactions in Metal Stabilization

The coordination chemistry of the bis(diphenylmethylsilyl)amine ligand, HN(SiMePh(2))(2), with the heavy alkali metals potassium and rubidium has been investigated to study its effect on the structure of the resulting compounds. The compounds exhibit extensive intra- and intermolecular M-pi interactions, creating 1-D coordination polymers, [K{N(SiMePh(2))(2)}](infinity) (1) and [Rb{N(SiMePh(2))(2)}](infinity) (3). This motif is maintained in the presence of tetrahydrofuran (THF), as seen in [K{N(SiMePh(2))(2)}thf](infinity) (2). In contrast, use of the tridentate PMDTA allows isolation of a monomeric species, K(pmdta)N(SiMePh(2))(2) (4), which exhibits both agostic and M-pi interactions. The incorporation of macrocyclic 18-crown-6, results in the formation of a rare non-metal bound amido species, {[K(18-crown-6)N(SiMePh(2))(2)]}(infinity) (5), stabilized by M-pi interactions from adjacent [N(SiMePh(2))(2)](-) ligands propagating 1-D coordination polymers.

Formation of Intermicellar-Chained and Cylindrical Micellar Networks From an Amphiphilic Rod−Coil Block Copolymer: Poly(n-hexyl isocyanate)-block-poly(2-vinylpyridine)

Morphologies of the poly(n-hexyl isocyanate)-block-poly(2-vinylpyridine) (PHIC-b-P2VP, fP2VP=0.3) amphiphilic rod-coil block copolymer were studied in rod-selective chloroform (CHCl3), both-block-soluble tetrahydrofuran (THF), and CHCl3/THF mixed solvent systems. Spherical, solid micelles with a P2VP core and PHIC shell were formed in CHCl3, whereas a microphase-separated liquid crystalline morphology was prominent in the presence of THF. In the CHCl3/THF mixed solvent system, a unique long-range intermicellar-chained network (v/v=7/3) and a more evolved cylindrical micellar network (v/v=3/7) were remarkably formed, respectively. PHIC-b-P2VP network nanostructures were used as a template for the in situ synthesis of Au nanoparticles (8 nm) selectively within the functional P2VP core domains.

Atomic force microscopy study of fullerene-based colloids

In this study we have investigated the structure, size and shape of fullerene-based colloids ( nC 60, nC 84) by atomic force microscopy. The fullerene colloids have been synthesized by solvent exchange method. It was found that the size of fullerene particles depends on solubility treatment. The composition of prepared fullerene-based colloids was investigated by Fourier transform infrared spectroscopy (FTIR). In the FTIR spectra, the presence of tetrahydrofuran (THF) could be observed. Based on AFM analysis it was observed the transformation of starting polycrystalline fullerene into monocrystalline after long term ultrasonication. It was concluded that solvent molecules transfer their electrons to fullerene molecules on the surface of monocrystal and establish interactions with fullerene electron rich zone.

Tin‐coupled star‐shaped block copolymer of styrene and butadiene (I) synthesis and characterization

AbstractA new kind of star‐shaped block copolymer: tin‐coupled polybutadiene‐b‐ploy(styrene‐butadiene) ((SB‐B)4Sn) was synthesized by two‐stage anionic polymerization technology. A novel multifunctional organo‐lithium was used as initiator, and two different types of copolymers were formed, namely, S‐PB‐PSB and S‐PB‐PSB‐PS, depending on the styrene content in loading solution (St%). In copolymerization, the homo‐polybutadiene block was formed in the first reaction stage, and the residual blocks were formed in the second stage with the presence of tetrahydrofuran (THF). S‐PB‐PSB was synthesized when the St% was lower than 34.9%, otherwise S‐PB‐PSB‐PS was generated. Nuclear magnetic resonance (NMR) results showed that the amount of vinyl based upon the butadiene content within poly(butadiene‐styrene) blocks decreased dramatically as the St% was increased. Dynamic mechanical thermal analyzer (DMTA) spectra showed broadened loss peak as the St% was increased. Transmission electron microscopy (TEM) was employed to characterize the copolymer morphology, and the results showed different phase‐separated morphologies as St% increased. Mechanical property testing results indicated that these two copolymers met the requirements of high performance tire tread. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Analysis of sulfamerazine in pond water and several fishes by high-performance liquid chromatography using molecularly imprinted solid-phase extraction

The synthesis and evaluation of a molecularly imprinted polymer (MIP) used as a selective solid-phase extraction sorbent and coupled to high-performance liquid chromatography (HPLC) for the efficient determination of sulfamerazine (SMR) in pond water and three fishes are reported. The polymer was prepared using SMR as the template molecule, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the crosslinking monomer in the presence of tetrahydrofuran as the solvent. The SMR-imprinted polymers and nonimprinted polymers were characterized by FT-IR and static adsorption experiments. The prepared SMR-imprinted material showed a high adsorption capacity, significant selectivity and good site accessibility. The maximum static adsorption capacities of the SMR-imprinted and nonimprinted materials for SMR were 108.8 and 79.6 mg g(-1), respectively. The relative selectivity factor of this SMR-imprinted material was 1.6. Several parameters influencing the solid-phase extraction process were optimized. Finally, the SMR-imprinted polymers were used as the sorbent in solid-phase extraction to determine SMR in pond water and three fishes with satisfactory recovery. The average recoveries of the MIP-SPE method were 94.0% in ultrapure water and 95.8% in pond water. Relative standard deviations ranging from 0.3% to 5.2% in MIP were acquired. The results for the SMR concentrations in crucian, carp and wuchang fish were 66.0, 127.1 and 51.5 ng g(-1), respectively. The RSDs (n = 5) were 3.51%, 0.53% and 5.08%, respectively. The limit of detection (LOD) for SMR was 1 ng g(-1) and the limit of quantitation (LOQ) was 3.5 ng g(-1).

Study of vapor–hydrate two-phase equilibria

In recent years, the technology of separating gas mixtures by forming hydrate has received increasing recognition, particularly the separation of light-gas mixtures. We performed an experimental and modeling study of systems containing hydrogen, methane, ethane and ethylene, both with and without the thermodynamic promoter tetrahydrofuran (THF) in water. Vapor–hydrate equilibrium data ( P– T– x– y data) were measured for (H 2 + CH 4), (H 2 + N 2 + CH 4) and (CH 4 + C 2H 4) gas mixtures in the absence and presence of THF. A relatively simple algorithm was used to calculate vapor–hydrate two-phase equilibria. The Patel–Teja equation of state, coupled with a van der Waals–Platteeuw-type hydrate model, was applied to calculate the equilibrium flash of vapor–hydrate phases. The parameters in the hydrate model were determined by correlating the experimental data of hydrate formation conditions. In addition, we predicted the composition of gas mixture in the hydrate phase when structure I and structure II hydrates coexisted in a (CH 4 + C 2H 6) gas mixture. The test results indicated that proposed algorithm is adequate for predicting vapor–hydrate equilibria. Accurate predictions of single-stage equilibrium between the vapor and the hydrate phases are important for developing separation technology via hydrate formation.

Medium-Pressure Clathrate Hydrate/Membrane Hybrid Process for Postcombustion Capture of Carbon Dioxide

This study presents a medium-pressure CO2 capture process based on hydrate crystallization in the presence of tetrahydrofuran (THF). THF reduces the incipient equilibrium hydrate formation conditions from a CO2/N2 gas mixture. Relevant thermodynamic data at 0.5, 1.0, and 1.5 mol % THF were obtained and reported. In addition, the kinetics of hydrate formation from the CO2/N2/ THF system as well as the CO2 recovery and separation efficiency were also determined experimentally at 273.75 K. The above data were utilized to develop the block flow diagram of the proposed process. The process involves three hydrate stages coupled with a membrane-based gas separation process. The there hydrate stages operate at 2.5 MPa and 273.75 K. This operating pressure is substantially less than the pressure required in the absence of THF and hence the compression costs are reduced from 75 to 53% of the power produced for a typical 500 MW power plant.

Pervaporation performance and Transport phenomenon of PVA blend membranes for the separation of THF/water azeotropic mixtures

Dense polymer membranes were made by mixing aqueous solutions of hydrophilic polymers poly(vinyl alcohol) (PVA) and polyethyleneimine (PEI) in different ratios for investigating the separation of Tetrahydrofuran (THF)/water azeotropic mixtures by pervaporation (PV). In order to gain a more detailed picture of the molecular transport phenomenon, we have performed sorption gravimetric experiments at 30 °C to compute diffusion, swelling, sorption and permeability coefficients of PVA/PEI membranes in the presence of THF and water. The membranes were found to have good potential for breaking the azeotrope of THF at 6% concentration of water. An increase in PVA content in the blend caused a reduction in the flux and an increase in selectivity. Among the blends tested in the study, the 5:1 PVA/PEI blend membrane showed the highest separation factor of 181.5, exhibited a flux of 1.28 kg/m2h for THF respectively at azeotropic feed composition.

Aggregation and Ionization Equilibria of Bis(pentafluorophenyl)borinic Acid Driven by Hydrogen-Bonding with Tetrahydrofuran

Bis(pentafluophenyl)borinic acid, Ar2BOH (1, Ar = C6F5), in dichloromethane solution is present as an equilibrium mixture of monomeric (1m) and trimeric (1t) forms. Previous studies showed that water affects both the position and the rate of this equilibrium. Here, the behavior of 1 in the presence of tetrahydrofuran (THF), a nucleophile able to behave as a Lewis base and H-bond acceptor only, has been studied, by monitoring with 1H and 19F NMR the course of titrations performed directly into NMR tubes. The addition, at 183 K, of 0.33 equiv of THF caused the instantaneous and quantitative formation of the hydrogen-bonded adduct between the trimer 1t and one molecule of THF. Homo- and heteronuclear 2D NMR correlation experiments led to a solution structure consistent with the C2-optimized geometry obtained by PM3 computations. The H-bonding of the THF molecule causes major deformations of the molecular geometry of the trimer, so that only one molecule of THF can interact with the trimer, in spite of its three OH groups. Intra- and intermolecular exchange processes involving this adduct have been investigated by 2D EXSY experiments, showing flopping of the cycle conformation, rotation of the aromatic rings around their B−C bonds, and exchange of THF among the three OH groups, in addition to the exchange between free 1t and the adduct. When the amount of added THF was higher than 0.33 equiv, an unexpected ionization process occurred, leading to the cation [Ar2B(OH2)2]+ and to deprotonated 1t, i.e., to the anion [Ar6B3O3H2]- of Cs symmetry. On increasing the temperature, progressive partial fragmentation of the trimeric species was observed. Both 11B NMR evidence and PM3 computations indicated that, at variance with what is observed in the interaction with H2O, the interaction between THF and 1m occurs preferentially via an H-bonded adduct, Ar2BO−H···THF, rather than a Lewis acid−base complex, Ar2B(OH)(THF). This confirms the poor Lewis acidity of the boron atom of 1m.

Experimental and modeling study of kinetics for methane hydrate formation with tetrahydrofuran as promoter

The kinetics behavior of methane hydrate formation in the presence of tetrahydrofuran (THF) as promoter was studied. A set of experimental equipment was designed and constructed. A series of kinetics data for the formation of methane hydrate in the presence of THF were measured with the isochoric method. The influences of temperature, pressure and liquid flow rate on the methane consumption rate were studied respectively. Based on the Chen-Guo hydrate formation mechanism, a kinetics model for the formation of methane hydrate in the presence of THF by using the dimensionless Gibbs free energy difference of quasi-chemical reaction of basic hydrate formation, — δG/RT as the driving force was proposed. The model was used to calculate the rate of methane consumption and it was shown that the calculated results were in good agreement with the experimental results.

Study on the kinetics of hydrate formation in a bubble column

Gas hydrate formation experiments were performed using methane in the presence of tetrahydrofuran (THF) in aqueous solution in a transparent bubble column in which a single pipe or a sintered plate was used to produce bubbles. The mole fraction of THF in aqueous solution was fixed at 6%. The hydrate formation kinetic behaviors on the surface of the rising bubble, the mechanical stability of hydrate shell formed on the surface of the bubble, the interactions among the bubbles with hydrate shell were observed and investigated morphologically. The rise velocities of individual bubbles with hydrate shells of different thickness and the consumption rates of methane gas were measured. A kinetic model was developed to correlate the experimentally measured gas consumption rate data. It was found that the hydrate formation rate on the surface of the moving bubble was high, but the formed hydrate shell was not very easy to be broken up. The bubbles with hydrate shells tended to agglomerate rather than merge into bigger bubble. This kind of characteristic of hydrate shell hindered the further formation of hydrate and led to the lower consumption rate of methane. The consumption rate of methane was found to increase with the decrease of temperature or increase of pressure. The increase of gas flux led to a linear increase in consumption rate of methane. It was demonstrated that the developed kinetic model could be used to correlate the consumption rate satisfyingly.

Production of agrochemical from waste polyesters

AbstractIn this study, agrochemical was produced from waste polyesters. Reactions of waste polyesters [poly (ethylene terephthalate) (PET) and poly (butylene terephthalate) (PBT)] powder with ethylene glycol (EG) in the presence of tetrahydrofurane (THF) using 0.003 mol lead acetate as a catalyst were carried out in a batch reactor at 470 K and at atmospheric pressure conditions. Reactions were undertaken with various particle size ranges from 50 to 512.5 μm, and reaction time from 30 to 70 min for reactions of polyesters. Low molecular weight product of polyester was obtained during this process. In the next stage, hydroxylamine hydrochloride (HAHC), cyclohexylamine (CHA), and potasium hydroxide (KOH) solution were introduced to convert low molecular weight product of polyester into terephthalohydroxamic acid (TPHA) by introduction of HCl (Hydrochloric Acid) as per stoichiometric requirement. TPHA can be used as an agrochemical (insecticide) with appreciable efficiency. To increase the polyester conversion rate, external catalyst (0.003 mol lead acetate) was introduced during the reaction. The product was deposited on the surface of unreacted polyester, which was removed from the surface by introducing dimethyl sulfoxide (DMSO). To accelerate the reaction rate, DMSO, CHA, and THF were introduced during the reaction, which has an industrial significance. Depolymerization of polyester was proportional to the reaction time. Depolymerization of polyester was inversely proportional to the particle size of polyester. Analyses of value‐added product (TPHA) and byproducts [EG and BD (1,4‐butanediol)] as well as polyesters were undertaken. A kinetic model is developed, and experimental data simulated with it, which was consistent with the model. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2504–2510, 2006

Hydrate Formation Conditions of Methane + Ethylene + Tetrahydrofuran + Water Systems

Hydrate formation conditions of (CH4 + C2H4) binary gas mixtures in the presence of tetrahydrofuran (THF) in water were measured in a sapphire cell using the “pressure search” method. The experimental temperature ranged from 277.7 K to 288.2 K, and the pressure ranged from 0.16 MPa to 4.08 MPa. The mole fraction of ethylene in the gas mixtures varied from 6.28 % to 100 %. The mole fraction of THF in the aqueous solution ranged from 4 % to 20 %. The experimental results demonstrated that, in contrast with the case of pure water, the hydrate formation pressures increase with the increase of ethylene composition in the gas mixture in the presence of THF in water.

Glycolytic Aminolysis of Poly (Ethylene Terephthalate) Waste at Atmospheric Pressure for Recovery of a Value Added Insecticide

: Reaction of poly (ethylene terephthalate) waste (PETW) powder with ethylene glycol (EG) in the presence of tetrahydrofurane (THF) using 0.003 mol zinc acetate as a catalyst was carried out in a batch reactor at 470 K and at atmospheric pressure. Reactions were undertaken with various particle size ranges from 50–512.5 µm, and reaction time from 30–70 min at 10 min intervals for reaction of PETW. A low molecular weight product of PETW was obtained during this step. In the next stage hydroxylamine hydrochloride (HAHC), cyclohexylamine (CHA), and potasium hydroxide solution were introduced to convert the low molecular weight product of PETW into terephthalohydroxamic acid (TPHA) by introduction of HCl as per stoichiometric requirement. The TPHA is used as insecticide, and it is highly expensive. To increase the PETW conversion rate, an external catalyst (zinc acetate) was introduced during the reaction. The product was deposited on the surface of unreacted PETW that was removed from the surface by introducing dimethyl sulfoxide (DMSO). To accelerate the reaction rate DMSO, CHA, and THF were introduced during the reaction, which had an industrial significance. Depolymerization of PETW was proportional to the reaction time. Depolymerization of PETW was inversely proportional to the particle size of PETW. Analyses of value added products (TPHA and EG) as well as PETW were undertaken. A kinetic model was developed and experimental data simulated with it that were consistent with the model. A thermodynamic study was undertaken as this is required during transfer of laboratory data through a pilot plant for commercialization.

Hydrate Formation Conditions of a Hydrogen + Methane Gas Mixture in Tetrahydrofuran + Water

Hydrate formation conditions of (H2 + CH4) binary gas mixtures in the presence of tetrahydrofuran (THF) in water were measured in a sapphire cell using the “pressure search” method. The experimental temperature ranged from 277.7 K to 288.4 K, and pressure ranged from 0.12 MPa to 8.86 MPa. The hydrogen composition in the gas mixture varied from 0 mol % to 97.85 mol %. The THF content in the aqueous solution was fixed at 6 mol %.

Functionalization of Poly(styryl)lithium with Styrene Oxide

The functionalization of poly(styryl)lithium with styrene oxide as a route to functional polymers was investigated. When the reaction was performed in benzene at room temperature, analysis of the products by SEC and column chromatography indicated the presence of functional polymer (83.5 wt %), along with unfunctionalized polymer (9.0 wt %), dimeric product (5.6 wt %), and trimeric product (0.1 wt %). The structure of the dimeric product was determined to be head-to-head dimer from both 13C NMR analysis and MALDI−TOF MS and was proposed to result from an electron-transfer mechanism. The dimeric product was eliminated when the functionalization was effected in the presence of tetrahydrofuran (>15 mol equiv). Under these conditions >99 wt % functionalized polymer was obtained as determined by column chromatography and MALDI−TOF MS. Addition of PSLi to the epoxide can occur by addition to the least hindered carbon or by addition to the most hindered carbon. Analysis of the regiochemistry of the chain end was performed by both 13C NMR and APT 13C NMR spectroscopy. It was determined that the product obtained in the presence of tetrahydrofuran contained 53 mol % of the product resulting from addition to the least hindered carbon and 47 mol % resulting from addition to the most hindered carbon.

Photolysis of ortho-Azidobenzoic Acid in Aqueous Solutions and Water–Organic Solvent Mixtures

The photolysis of o-azidobenzoic acid and its potassium salt in water, ethanol, tetrahydrofuran (THF), and ethanol–water and THF–water mixtures was studied by IR and UV spectroscopy and thin-layer chromatography. It was found that the photolysis of o-azidobenzoic acid and potassium o-azidobenzoate in aqueous solutions mainly resulted in 2,1-benzisoxazolone, the intramolecular cyclization product. The process of azepine formation in ethanol or an ethanol–water mixture depends on the nucleophilic nature of ethanol; in this case, water is practically of no importance. The presence of THF in an aqueous solution shifted the singlet nitrene–dehydroazepine equilibrium toward dehydroazepine, which reacts with water to give azepines.

The Influence of Hydrogen Bonding on the Propagation Rate Coefficient in Free‐Radical Polymerizations of Hydroxypropyl Methacrylate

AbstractThe propagation rate coefficient kp was determined for hydroxypropyl methacrylate by applying pulsed laser initiated polymerizations and subsequent analysis of the polymer by size‐exclusion chromatography. kp data were derived for polymerizations in bulk and in several solvents: toluene, tetrahydrofuran (THF), benzyl alcohol, and supercritical CO2. With the exception of THF, no solvent influence on kp was observed. For polymerizations in THF kp values 40% below the corresponding bulk data were obtained. In addition, the activation energy of kp for polymerizations in THF is higher than for the other systems. The results are explained by a complexation of the OH group contained in the ester group with THF. As a consequence, H bonds between OH groups and carbonyl O atoms, which occur in the other systems, are not formed in the presence of THF. This explanation is supported by Raman spectra, which show that association of carbonyl groups does not occur for systems containing THF, whereas for all other systems the occurrence of two peaks at 1 703 cm−1 and 1 720 cm−1 is indicative of the vibrations of two different – associated vs. not associated – types of carbonyl groups. Based on the change in activation energy it is suggested that a true kinetic solvent effect occurs. Temperature dependence of kp for HPMA polymerizations in bulk and in solution of THF. The literature data for bulk polymerizations are taken from ref. 22. Open symbols refer to νrep = 10 Hz and filled symbols to νrep = 25 Hz.imageTemperature dependence of kp for HPMA polymerizations in bulk and in solution of THF. The literature data for bulk polymerizations are taken from ref. 22. Open symbols refer to νrep = 10 Hz and filled symbols to νrep = 25 Hz.