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Heptane
Selected AbstractsSphere-to-Rod Transition of Micelles formed by the Semicrystalline Polybutadiene- block -Poly(ethylene oxide) Block Copolymer in a Selective SolventMACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2010Adriana M. Mihut Abstract We present a morphological study of the micellization of an asymmetric semicrystalline block copolymer, poly(butadiene)- block -poly(ethylene oxide), in the selective solvent n -heptane. The molecular weights of the poly(butadiene) (PB) and poly(ethylene oxide) (PEO) blocks are 26 and 3.5,kg,·,mol,1, respectively. In this solvent, micellization into a liquid PEO-core and a corona of PB-chains takes place at room temperature. Through a thermally controlled crystallization of the PEO core at ,30,°C, spherical micelles with a crystalline PEO core and a PB corona are obtained. However, crystallization at much lower temperatures (,196,°C; liquid nitrogen) leads to the transition from spherical to rod-like micelles. With time these rod-like micelles aggregate and form long needles. Concomitantly, the degree of crystallinity of the PEO-cores of the rod-like micelles increases. The transition from a spherical to a rod-like morphology can be explained by a decrease of solvent power of the solvent n -heptane for the PB-corona chains: n -Heptane becomes a poor solvent at very low temperatures leading to a shrinking of the coronar chains. This favors the transition from spheres to a morphology with a smaller mean curvature, that is, to a cylindrical morphology. [source] Acoustical Properties of Binary Mixtures of Heptane with Ethyl Acetate or Butyl AcetateCHINESE JOURNAL OF CHEMISTRY, Issue 3 2010Divya Shukla Abstract Mixed solvents rather than single pure liquids are of utmost practical importance in chemical and industrial processes as they provide an ample opportunity for the continuous adjustment of desired properties of the medium. Therefore, ultrasonic velocity (u) and density (,) were measured for the binary mixtures formed by heptane with ethyl acetate or butyl acetate at temperatures 293, 298 and 303 K over the entire composition range. Deviation in ultrasonic velocity (,u), deviation in isentropic compressibility (,,s), and excess intermolecular free length (LEf) have been evaluated using the ultrasonic velocity data and the computed results were fitted to the Redlich-Kister polynomial equation. The values of ,u, ,,s and LEf were plotted against the molar fraction of heptane. The observed positive and negative values of excess parameters were discussed in terms of molecular interaction between the components of the mixtures. Experimental values of ultrasonic velocity and density were compared with the results obtained by theoretical estimation procedures. The results were discussed in terms of average absolute deviation (AAD). [source] Dual CD system-modified MEEKC method for the determination of clemastine and its impuritiesELECTROPHORESIS, Issue 19 2010Serena Orlandini Abstract A dual system of CDs was used for the first time in MEEKC with the aim of determining clemastine and its three main related impurities in both drug substances and tablets. The addition of methyl-,-cyclodextrin and heptakis(2,6-di- O -methyl)-,-cyclodextrin to the microemulsion pseudo-stationary phase was essential to increase the resolving power of the system to obtain a baseline separation among the compounds. The best microemulsion composition was identified by mixture design and the effects of the factors concentrations of CDs and voltage were investigated by a response surface study applying a Central Composite Design. In both cases, Derringer's desirability function made it possible to find the global optimum, which corresponded to the following combination: microemulsion, 89.8% 10,mM borate buffer pH 9.2, 1.5% n -heptane and 8.7% of SDS/n -butanol in 1:2 ratio; 18,mM methyl-,-cyclodextrin, 38,mM heptakis(2,6-di- O -methyl)-,-cyclodextrin, 17,kV. By applying these conditions, the separation was completed in about 5.5,min. The method was validated following International Conference on Harmonisation guidelines and was applied to a real sample of clemastine tablets. [source] Porous Silicon-Based Optical Microsensors for Volatile Organic Analytes: Effect of Surface Chemistry on Stability and SpecificityADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Anne M. Ruminski Abstract Sensing of the volatile organic compounds (VOCs) isopropyl alcohol (IPA) and heptane in air using sub-millimeter porous silicon-based sensor elements is demonstrated in the concentration range 50,800 ppm. The sensor elements are prepared as one-dimensional photonic crystals (rugate filters) by programmed electrochemical etch of p++ silicon, and analyte sensing is achieved by measurement of the wavelength shift of the photonic resonance. The sensors are studied as a function of surface chemistry: ozone oxidation, thermal oxidation, hydrosilylation (1-dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene. The thermally oxidized and the dichlorodimethylsilane-modified materials show the greatest stability under atmospheric conditions. Optical microsensors are prepared by attachment of the porous Si layer to the distal end of optical fibers. The acetylated porous Si microsensor displays a greater response to heptane than to IPA, whereas the other chemical modifications display a greater response to IPA than to heptane. The thermal oxide sensor displays a strong response to water vapor, while the acetylated material shows a relatively weak response. The results suggest that a combination of optical fiber sensors with different surface chemistries can be used to classify VOC analytes. Application of the miniature sensors to the detection of VOC breakthrough in a full-scale activated carbon respirator cartridge simulator is demonstrated. [source] Rare Earth Element Concentrations in the Natural Water Reference Materials (NRCC) NASS-5, CASS-4 and SLEW-3GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 2 2007Michael G. Lawrence terres rares; yttrium; pré-concentration; ICP-MS; matériaux de référence du NRCC The rare earth element and yttrium concentrations of the NRCC reference materials North Atlantic Surface seawater, NASS-5; Coastal Atlantic Surface Seawater, CASS-4; and the estuarine water, SLEW-3 have been precisely determined by ICP-MS after ca. 1:8 preconcentration following a triple chelation using HDEHP (phosphoric acid 2-ethylhexyl ester -mono and di ester mixture) in heptane, and back extraction in nitric acid. We propose reference values with uncertainties for all naturally occurring lanthanides and yttrium. Les concentrations en terres rares et en yttrium des matériaux de référence suivants (du NRCC): l'eau de surface de l'Atlantique Nord NASS-5, l'eau de surface de l'Atlantique Côtier CASS-4 et l'eau d'estuaire SLEW-3 ont été déterminées précisément par ICP-MS après concentration d'un facteur 1 : 8 environ, suivie d'une triple chélation avec de l'HDEHP (mixture d'acide phosphorique 2-ethylhexyl ester - mono et di ester) dans de l'heptane et une extraction inverse en acide nitrique. Nous proposons des valeurs de référence avec leur incertitude pour toutes les terres rares naturelles et l'yttrium. [source] 6-(Diazomethyl)-1,3-bis(methoxymethyl)uracil, Synthesis and Transformation into Annulated PyrimidinedionesHELVETICA CHIMICA ACTA, Issue 7 2008Fuyi Zhang Abstract 6-(Diazomethyl)-1,3-bis(methoxymethyl)uracil (5) was prepared from the known aldehyde 3 by hydrazone formation and oxidation. Thermolysis of 5 and deprotection gave the pyrazolo[4,3- d]pyrimidine-5,7-diones 7a and 7b. Rh2(OAc)4 catalyzed the transformation of 5 into to a 2,:,1 (Z)/(E) mixture of 1,2-diuracilylethenes 9 (67%). Heating (Z)- 9 in 12n HCl at 95° led to electrocyclisation, oxidation, and deprotection to afford 73% of the pyrimido[5,4- f]quinazolinetetraone 12. The Rh2(OAc)4 -catalyzed reaction of 5 with 3,4-dihydro-2H -pyran and 2,3-dihydrofuran gave endo/exo -mixtures of the 2-oxabicyclo[4.1.0]heptane 13 (78%) and the 2-oxabicyclo[3.1.0]hexane 15 (86%), Their treatment with AlCl3 or Me2AlCl promoted a vinylcyclopropane,cyclopentene rearrangement, leading to the pyrano- and furanocyclopenta[1,2- d]pyrimidinediones 14 (88%) and 16 (51%), respectively. Similarly, the addition product of 5 to 2-methoxypropene was transformed into the 5-methylcyclopenta-pyrimidinedione 18 (55%). The Rh2(OAc)4 -catalyzed reaction of 5 with thiophene gave the exo -configured 2-thiabicyclo[3.1.0]hexane 19 (69%). The analoguous reaction with furan led to 8-oxabicyclo[3.2.1]oct-2-ene 20 (73%), and the reaction with (E)-2-styrylfuran yielded a diastereoisomeric mixture of hepta-1,4,6-trien-3-ones 21 (75%) that was transformed into the (1E,4E,6E)-configured hepta-1,4,6-trien-3-one 21 (60%) at ambient temperature. [source] A high-temperature chemical kinetic model for primary reference fuelsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2007Marcos Chaos A chemical kinetic mechanism has been developed to describe the high-temperature oxidation and pyrolysis of n -heptane, iso -octane, and their mixtures. An approach previously developed by this laboratory was used here to partially reduce the mechanism while maintaining a desired level of detailed reaction information. The relevant mechanism involves 107 species undergoing 723 reactions and has been validated against an extensive set of experimental data gathered from the literature that includes shock tube ignition delay measurements, premixed laminar-burning velocities, variable pressure flow reactor, and jet-stirred reactor species profiles. The modeled experiments treat dynamic systems with pressures up to 15 atm, temperatures above 950 K, and equivalence ratios less than approximately 2.5. Given the stringent and comprehensive set of experimental conditions against which the model is tested, remarkably good agreement is obtained between experimental and model results. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 399,414, 2007 [source] OH concentration time histories in n -alkane oxidationINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2001D. F. Davidson OH radical concentration time histories were measured behind reflected shocks in the oxidation of four n -alkanes: propane, n -butane, n -heptane, and n -decane. Initial reflected shock conditions of these measurements were 1357,1784 K, 2.02,3.80 atm, with fuel concentrations of 300,2000 ppm, and equivalence ratios from 0.8 to 1.2. OH concentrations were measured using narrow-linewidth ring-dye laser absorption of the R1(5) line of the A,X (0,0) transition at 306.5 nm. These concentration time-history measurements were compared to the modeled predictions of eight large n -alkane oxidation mechanisms currently available in the literature and the kinetic implications of these measurements are discussed. These data, in conjunction with recent measurements of n -alkane ignition times and ethylene yields in n -alkane pyrolysis experiments, also performed in this laboratory, provide a unique database of species concentration time histories for n -alkane mechanism validation. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 775,783, 2001 [source] Synthesis of 6-Substituted 7-Bomoazabicyclo[2.2.1]heptanes via Nucleophilic Addition to 3-Bromo-1-azoniatricyclo[2.2.1.0]-heptane BromideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2005Arnaud Gayet Abstract We describe herein an efficient method for the preparation of a functionalised bicyclic framework (6-substituted 7-bromo-aza-bicyclo[2.2.1]heptane) through the selective opening of the aziridium 2 with organocuprates in up to 90% yield. These interesting chiral building blocks were then utilised as novel ligands in the rearrangement of epoxides to afford chiral allylic alcohols. [source] Influence of the matrix porosity on the synthesis and adsorption behavior of dithiocarbamate styrenic resins toward zinc(II) and cadmium(II) ionsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Priscila A. da Costa Abstract The dependence of the adsorption behavior toward Zn2+ and Cd2+ on the synthesis conditions of dithiocarbamate styrenic resins was investigated. We synthesized styrene,divinylbenzene copolymers with different kinds of porous structures by varying the divinylbenzene (DVB)-to-styrene ratio and the dilution degree of the monomers with n -heptane. The porous structure of these materials was characterized. The introduction of the dithiocarbamate moiety on the copolymers followed a synthetic pathway based on the nitration reaction, reduction of the nitro group to the amino one, and finally, the addition of the amino group to CS2. All of the synthesis steps were monitored by Fourier transform infrared spectroscopy. Only the addition reaction to CS2 was greatly influenced by the copolymer porosity. The effect of the dilution degree on the reaction extension was more pronounced than the effect of the DVB content. The more porous materials with higher dithiocarbamate contents adsorbed a higher amount of ions in a faster way, with Zn2+ being preferable over Cd2+ ions. The difference between the Zn2+ and Cd2+ adsorption rates was enhanced with the copolymer porosity, and also enhanced was the difference between the amounts of ions adsorbed by the copolymer; this suggested that the selectivity toward these ions could be controlled by the copolymer porous structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Wettability investigations on the cellulosic surface of alfa fibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008N. Bohli Abstract A wettability study was performed on samples of alfa fibers with the Wilhelmy plate technique. The set of test liquids employed in the measurement of the contact angles was composed of water, heptane, diiodomethane, ,-bromonaphthalene, and formamide. During their first immersion in high-surface-energy test liquids, the alfa fibers showed anisotropic behavior: they had an advancing contact angle of 67 ± 6° in one orientation of immersion and an angle of 112 ± 9.5° in the opposite one. Optical microscopy revealed the existence of fibrils on the alfa-fiber surface. They kept almost the same orientation and were responsible for the interesting hydrophobic/hydrophilic behavior of the fibers. Contact angle measurements and investigations of the hysteresis were also performed. The various results were examined according to the heterogeneities of the fibers. The surface energy of the alfa fibers was determined with three theoretical models: the geometric model, the Good,Van Oss,Chaudhury model, and the Chang model. A comparative study of these models was undertaken. The study of the wetting properties of alfa fibers will provide essential information for optimized composites and so will help us in choosing the right chemical treatment necessary to enhance adhesion in alfa-fiber-based composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Properties and application of poly(methacrylic acid- co -dodecyl methacrylate- cl - N,N -methylene bisacrylamide) hydrogel immobilized Bacillus cereus MTCC 8372 lipase for the synthesis of geranyl acetateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Madan Lal Verma Abstract A range of fatty acid esters is now being produced commercially with immobilized microbial lipases (glycerol ester hydrolases; EC) in nonaqueous solvents. In this study, a synthetic hydrogel was prepared by the copolymerization of methacrylic acid and dodecyl methacrylate in the presence of a crosslinker, N,N -methylene bisacrylamide. A purified alkaline thermotolerant bacterial lipase from Bacilluscereus MTCC 8372 was immobilized on a poly(methacrylic acid- co -dodecyl methacrylate- cl - N,N -methylene bisacrylamide) hydrogel by an adsorption method. The hydrogel showed a 95% binding efficiency for the lipase. The bound lipase was evaluated for its hydrolytic potential toward various p -nitrophenyl acyl esters with various C chain lengths. The bound lipase showed optimal hydrolytic activity toward p -nitrophenyl palmitate at a pH of 8.5 and a temperature of 55°C. The hydrolytic activity of the hydrogel-bound lipase was enhanced by Hg2+, Fe3+, and NH ions at a concentration of 1 mM. The hydrogel-bound lipase was used to synthesize geranyl acetate from geraniol and acetic acid in n -heptane. The optimization of the reaction conditions, such as catalyst loading, effect of substrate concentration, solvent (n -pentane, n -hexane, n -heptane, n -octane, and n -nonane), reaction time, temperature, molecular sieve (3 Å × 1.5 mm) and scale up (at 50-mL level), was studied. The immobilized lipase (25 mg/mL) was used to perform an esterification in n -alkane(s) that resulted in the synthesis of approximately 82.8 mM geranyl acetate at 55°C in n -heptane under continuous shaking (160 rpm) after 15 h when geraniol and acetic acid were used in a ratio of 100 : 100 mM. The addition of a molecular sieve (3 Å × 1.5 mm) to the reaction system at a concentration of 40 mg/mL in reaction volume (2 mL) resulted in an increase in the conversion of reactants into geranyl acetate (90.0 mM). During the repetitive esterification under optimum conditions, the hydrogel-bound lipase produced ester (37.0 mM) after the eighth cycle of reuse. When the reaction volume was scaled up to 50 mL, the ester synthesized was 58.7 mM under optimized conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Properties of poly(AAc- co -HPMA- cl -EGDMA) hydrogel-bound lipase of Pseudomonas aeruginosa MTCC-4713 and its use in synthesis of methyl acrylateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Shamsher Singh Kanwar Abstract Microbial lipases (E.C. 3.1.1.3) are preferred biocatalysts for the synthesis of esters in organic solvents. Various extracellular thermoalkaliphilic lipases have been reported from Pseudomonas sp. In the present study, a purified alkaline thermoalkalophilic extracellular lipase of Pseudomonas aeruginosa MTCC-4713 was efficiently immobilized onto a synthetic poly(AAc- co -HPMA- cl -EGDMA) hydrogel by adsorption and the bound lipase was evaluated for its hydrolytic potential towards various p -nitrophenyl acyl esters varying in their C-chain lengths. The bound lipase showed optimal hydrolytic activity towards p -nitrophenyl palmitate (p -NPP) at pH 8.5 and temperature 45°C. The hydrolytic activity of the hydrogel-bound lipase was markedly enhanced by the presence of Hg2+, Fe3+, and NH salt ions in that order. The hydrogel-immobilized lipase (25 mg) was used to perform esterification in various n -alkane(s) that resulted in , 84.9 mM of methyl acrylate at 45°C in n -heptane under shaking (120 rpm) after 6 h, when methanol and acrylic acid were used in a ratio of 100 mM:100 mM, respectively. Addition of a molecular sieve (3Å × 1.5 mm) to the reaction system at a concentration of 100 mg/reaction vol (1 mL) resulted in a moderate enhancement in conversion of reactants into methyl acrylate (85.6 mM). During the repetitive esterification under optimum conditions, the hydrogel-bound lipase produced 71.3 mM of ester after 10th cycle of reuse. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 183,191, 2007 [source] Preparation of highly branched polyethylene using (,-diimine) nickel complex covalently supported on modified SiO2JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Hongliu Jiang Abstract Bis(4-(4-amine-3,5-diisopropylbenzyl)-2,6-diisopropylphenylimino) acenaphthene NiBr2 (Catalyst I) was synthesized. The complex covalently supported on Et3Al-treated silica (SC) and used for ethylene polymerization was produced with cocatalyst of common inexpensive alkylaluminum compounds. Polyethylenes (PEs) with branching numbers of 12.94 (1000C) to 116.02 (1000C) were prepared in heptane. The polymerization conditions, such as the cocatalyst, Al/Ni ratio, and temperature, had significant effects on catalytic activity and properties of polyethylenes. Confirmed by high-temperature 13C NMR, the polyethylenes synthesized contain significant amounts of not only methyl but also ethyl, propyl, butyl, pentyl, and other long branches (longer than six carbons). The branching degree of polyethylenes increased with temperature, while their molecular weight and melting point decreased correspondingly, resulting in linear semicrystalline to totally amorphous polymers. The formation of the branches could be illustrated by the chain walking mechanism, which controlled their specific spacing and conformational arrangements with one another. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 103: 1483,1489, 2007 [source] Approach to estimation of absorption of aliphatic hydrocarbons diffusing from interior materials in an automobile cabin by inhalation toxicokinetic analysis in ratsJOURNAL OF APPLIED TOXICOLOGY, Issue 1 2010Toshiaki Yoshida Abstract The interior air of an automobile cabin has been demonstrated in our previous studies to be contaminated by high concentrations of a large variety of aliphatic hydrocarbons diffusing from the interior materials. In the present study, the amounts of seven selected aliphatic hydrocarbons absorbed by the car driver were estimated by evaluating their inhalation toxicokinetics in rats. Measured amounts of the substances were injected into a closed chamber system in which a rat had been placed, and the concentration changes in the chamber were examined. The toxicokinetics of the substances were evaluated based on concentration,time courses using a nonlinear compartment model. Their absorption amounts in humans at the levels of actual concentrations in the cabins without ventilation were extrapolated from the results found with the rats. The absorption amounts estimated for a driver during a 2,h drive were as follows: 6,µg/60,kg of human body weight for methylcyclopentane (interior concentration 23,µg/m3 as median value in previous study), 5,µg for 2-methylpentane (36,µg/m3), 13,µg for n- hexane (65,µg/m3), 51,µg for n- heptane (150,µg/m3), 26,µg for 2,4-dimethylheptane (97,µg/m3), 17,µg for n- nonane (25,µg/m3) and 49,µg for n- decane (68,µg/m3). An inverse relationship was found between the exposure and absorption among the substances (e.g. between n-decane and 2,4-dimethylheptane). These findings suggest that not only the exposure concentrations but also the absorption amounts should be taken into account to evaluate the health effects of exposure to low concentrations of volatile compounds as environmental contaminants. Copyright © 2009 John Wiley & Sons, Ltd. [source] Kinetic and dynamic study of liquid,liquid extraction of copper in a HFMC: Experimentation, modeling, and simulationAICHE JOURNAL, Issue 6 2010M. Younas Abstract In this work, we present the dispersion-free liquid,liquid extraction of copper from aqueous streams in a hollow fiber membrane contactor (HFMC). Copper has been transferred from aqueous solutions to heptane using LIX 84-I (2-hydroxy-5-nonylacetephenone oxime) as extracting agent. In a first step, batch experiments have been performed to identify the extraction kinetics and to measure the partition coefficient of copper aqueous-organic phase system. Then, the continuous recycled-base extraction process has been performed in a HFMC Liqui-Cel® module. The module has been modeled from resistance in series concept to gain the exit concentrations, which are used to develop a dynamic model to calculate the exit concentration of copper from the output of storage tanks. The model has been validated with experimental data at various operating conditions. The integrated process model algorithm was scripted in MATLAB® 7.4 R (a). Simulations have been made for a range of different operating parameters to determine the optimum criterion conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Radiosynthesis of 2- exo -(2,-[18F]Fluoro-3,-(4-fluorophenyl)-pyridin-5,-yl)-7-azabicyclo[2.2.1]heptane ([18F]F2PhEP), a potent epibatidine-based radioligand for nicotinic acetylcholine receptor PET imagingJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 6 2006Gaëlle Roger Abstract 2- exo -(2,-Fluoro-3,-(4-fluorophenyl)-pyridin-5,-yl)-7-azabicyclo[2.2.1]heptane (F2PhEP), a novel, epibatidine-based, ,4,2-selective nicotinic acetylcholine receptor antagonist of low toxicity, as well as the corresponding N- Boc-protected chloro- and bromo derivatives as precursors for labelling with fluorine-18 were synthesized from 7- tert -butoxycarbonyl-7-azabicyclo[2.2.1]hept-2-ene in 13, 19 and 8% overall yield, respectively. [18F]F2PhEP was prepared in 8,9% overall yield (non-decay-corrected) using 1 mg of the bromo derivative in the following two-step radiochemical process: (1) no-carrier-added nucleophilic heteroaromatic ortho- radiofluorination with the activated K[18F]F-Kryptofix®222 complex in DMSO using microwave activation at 250 W for 90 s, followed by (2) quantitative TFA-induced removal of the N -Boc protective group. Radiochemically pure (>95%) [18F]F2PhEP (1.48,1.66 GBq, 74,148 GBq/µmol) was obtained after semi-preparative HPLC (Symmetry® C18, eluent aqueous 0.05 M NaH2PO4 CH3CN: 78/22 (v:v)) in 75,80 min starting from an 18.5 GBq aliquot of a cyclotron-produced [18F]fluoride production batch. Copyright © 2006 John Wiley & Sons, Ltd. [source] An ionic liquid proposed as solvent in aromatic hydrocarbon separation by liquid extractionAICHE JOURNAL, Issue 2 2010Ana B. Pereiro Abstract Liquid,liquid extraction is the most common method for extraction of aromatics from their mixtures with aliphatic hydrocarbons. An ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide [BMpyr][NTf2] was tested as solvent for this separation. The liquid,liquid equilibria (LLE) of the ternary mixtures heptane + benzene, or toluene, or ethylbenzene + [BMpyr][NTf2] were carried out at 298.15 K. The solvent ability of the IL was evaluated in terms of solute distribution ratio and selectivity. The results were compared with those previously reported for the extraction of aromatics from its mixtures with heptane by using ILs. The conventional process using sulfolane as solvent was discussed. The experimental LLE data were correlated by non-random two liquid equation. A proposal of extraction process with this IL as solvent is simulated by conventional software and the results are shown. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Performance study of heptane reforming in the dense ceramic membrane reactorsAICHE JOURNAL, Issue 1 2008Wenliang Zhu Abstract Heptane reforming was investigated in three dense ceramic membrane reactors, where the membranes were modified differently with reforming catalyst. Each reactor displayed distinctive catalytic behavior. The reactor with a bare membrane showed low catalytic activity and low oxygen permeation flux (JO2), but gave stable performance. The left two membranes reactors modified with catalyst both displayed shift processes at the preliminary stage of membrane reaction, not only in JO2 but also in the selectivity of all products. Moreover, the membrane reactor with more catalyst gave higher performance in the case of JO2 and CO selectivity. The observed shift phenomena are due to the activation of catalyst on the membrane surface, and the different amounts of catalyst produce different impaction on the membrane reactions. On the basis of the results in three membrane reactors, a reaction pathway of hydrocarbon reforming in dense ceramic membrane reactor is proposed. Being some different from combustion and reforming mechanism (CRR), hydrocarbon reforming in dense ceramic membrane reactor has its own characteristics. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Environmental damage and occlusal contact area wear of composite restorativesJOURNAL OF ORAL REHABILITATION, Issue 1 2002A. U. J. Yap The chemical environment is one aspect of the oral environment, which could have an appreciable influence on the in-vivo degradation of composite resins. The resin matrix can be softened and fillers constituents can be leached out when composites are exposed to certain chemicals/food-simulating liquids (FSLs). A reciprocal compression sliding wear device was used to study the effects of the chemical environment on occlusal contact area (OCA) wear of four composite restoratives (Silux Plus, Z100, Ariston pHc and Surefil). The effects of FSL on hardness was also investigated and correlated to wear. Thirty-six hardness/wear specimens of each material were made and stored in artificial saliva at 37 °C for 24 h. The specimens were then divided into six groups of six specimens and stored in the following FSL for 1 week at 37 °C: distilled water (W), 0·02 N citric acid (C), 0·02 N lactic acid (L), heptane (H) and 75,25% ethanol,water solution (E). Conditioning in artificial saliva (S) was used as control. After conditioning, the specimens were wear tested at 20 MPa contact stress against SS304 counter-bodies in the respective FSL/artificial saliva up to 20 000 cycles. Wear depth (lm, n=6) was measured using profilometry. Change in hardness (,KHN, Knoop hardness number) was determined by microhardness testing pre- and post-conditioning. Results of statistical analyses (ANOVA/Scheffe's at significance level 0·05) of wear data were as follows: Silux , S, W > L, H, E and C, L > H; Z100 , S, W > all other mediums and E > H; Ariston , all other mediums > H; Surefil , W, C > S, L, H, E (> indicates significantly more wear). With the exception of Surefil, the greatest wear was observed with conditioning and wear testing in water. This ranged from 93·18 ± 21·96 lm for Z100 to 31·43 ± 2·80 lm for Surefil. For all materials, conditioning in heptane resulted in the least wear. This ranged from 8·9 ± 2·2 ,m for Ariston to 16·5 ± 5·9 lm for Silux. The effects of the different FSL on OCA wear were material dependent. No correlation was observed between ,KHN and wear. [source] Non-aqueous reverse micelles media for the SNAr reaction between 1-fluoro-2,4-dinitrobenzene and piperidine,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2006N. Mariano Correa Abstract The kinetics of the nucleophilic aromatic substitution (SNAr) reaction between 1-fluoro-2,4- dinitrobenzene (FDNB) and piperidine (PIP) in ethylene glycol (EG)/ sodium bis (2-ethyl-1-hexyl) sulfosuccinate (AOT)/n -heptane and dimethylformamide (DMF)/AOT/n -heptane non-aqueous reverse micelle systems is reported. EG and DMF were used as models for hydrogen bond donor (HBD) and non-hydrogen bond donor (non-HBD) polar solvents, respectively. The reaction was found not to be base catalyzed in these media. A mechanism to rationalize the kinetic results is proposed in which both reactants may be distributed between the two environments. The distribution constants of FDNB between the organic and each micellar pseudophases were determined by an independent fluorescence method. These results were used to evaluate the amine distribution constant and the intrinsic second-order rate coefficient of the SNAr reaction in the interface. The reaction was also studied in the pure solvents EG and DMF for comparison. The results in EG/AOT/n -heptane at Ws,=,2 give similar kinetic profiles than in water/AOT/n -hexane at W,=,10. With these HBD solvents, the interface saturation by the substrate is reached at around the same value of [AOT] and the intrinsic second-order rate coefficient in the interface, k,b, has comparable values. On the other hand, when DMF is used as a polar non-HBD solvent, the intrinsic second-order rate constant increases by a factor of about 200 as compared to the values obtained using HBD solvents as a polar core. It is concluded that higher catalytic power is obtained when non-HBD solvents are used as polar solvent in the micelle interior. Copyright © 2006 John Wiley & Sons, Ltd. [source] Fluorescence and photoisomerization studies of p -nitrophenyl-substituted ethenylindolesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2006Anil K. Singh Abstract The synthesis, electronic absorption, fluorescence (,f, ,ex, ,f, ,f) and photoisomerization (,t,c, photostationary state composition) properties of 3-(4-nitrophenylethenyl- E)-NH-indole (1), 3-(4-nitrophenylethenyl- E)- N -ethylindole (2) and 3-(4-nitrophenyl ethenyl- E)- N -benzenesulfonylindole (3) in organic solvents of varying polarity are reported. The absorption maximum of these compounds undergoes a moderate red shift with increasing solvent polarity. However, the fluorescence maximum becomes highly red shifted with increasing solvent polarity. Whereas 1 and 2 show broad fluorescence bands, 3 exhibits dual fluorescence. Further, 1 and 2 fluoresce much more efficiently than 3. Correlation of the Stokes shift with solvent polarity parameters such as ,f and ET(30) and excited-state dipole moment indicate a highly polar excited state for 1,3. Time-resolved fluorescence studies show that the fluorescence decays are single- and multi-exponential type, depending on the solvent polarity. Further, 1 and 2 do not show photoisomerization on irradiation. However, 3 is photoactive and shows efficient photoisomerization in non-polar heptane. The sensitivity (,) of the photoreaction is determined in various solvent in terms of the Hammett plot, which showed that the excited states involved are electron deficient in nature and consequently stabilized more by an electron sufficient polar solvent and electron donating substituent. These results led us to suggest the existence of three types of excited states, namely the locally excited state, the intramolecular charge-transfer excited state and the conformationally relaxed intramolecular charge-transfer excited state in the photoprocesses of these compounds. Copyright © 2005 John Wiley & Sons, Ltd. [source] Synthesis of silicon nitride based ceramic nanoparticles by the pyrolysis of silazane block copolymer micellesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2006Kozo Matsumoto Abstract Diblock copolymer poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane)- block- polystyrene (polyVSA- b -polySt) and triblock copolymer poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane)- block- polystyrene- block -poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane) (polyVSA- b -polySt- b -polyVSA), consisting of silazane and nonsilazane segments, were prepared by the living anionic polymerization of 1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane and styrene. PolyVSA- b -polySt formed micelles having a poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane) (polyVSA) core in N,N -dimethylformamide, whereas polyVSA- b -polySt and polyVSA- b -polySt- b -polyVSA formed micelles having a polyVSA shell in n -heptane. The micelles with a polyVSA core were core-crosslinked by UV irradiation in the presence of diethoxyacetophenone as a photosensitizer, and the micelles with a polyVSA shell were shell-crosslinked by UV irradiation in the presence of diethoxyacetophenone and 1,6-hexanedithiol. These crosslinked micelles were pyrolyzed at 600 °C in N2 to give spherical ceramic particles. The pyrolysis process was examined by thermogravimetry and thermogravimetry/mass spectrometry. The morphologies of the particles were analyzed by atomic force microscopy and transmission electron microscopy. The chemical composition of the pyrolysis products was analyzed by X-ray fluorescence spectroscopy and Raman scattering spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4696,4707, 2006 [source] Comprehensive 2-D chromatography of random and block methacrylate copolymersJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10 2010Monique van Hulst Abstract A comprehensive 2-D separation method was developed for the characterization of methacrylate copolymers. In both dimensions conditions were employed that give a critical separation for the homopolymer of one of the monomers in the copolymer, and exclusion behaviour for the other. The 2-D separation was realized by using a normal-phase column in one dimension and a reversed phase column in the other, and by precisely tuning the compositions of the two mobile phases employed. In the normal-phase dimension mixtures of THF and n -hexane or n -heptane were used as mobile phase, and in the reversed-phase dimension mixtures of ACN and THF. Moreover, stationary phase particles had to be selected for both columns that gave an exclusion window appropriate for the molecular size of the sample polymers to be characterized. The 2-D critical chromatography principle was tested with a polystyrene (PS)-polymethylmethacrylate (PMMA) block copolymer and with block and random polybutylmethacrylate (PBMA)-PMMA copolymers. Ideally, the retention time for a copolymer in both dimensions of this system would depend on the size of only one of the blocks, or on the contribution of only one of the monomers to the size of a random copolymer. However, it was found that the elution of the PS-PMMA block copolymer depended on the size of both blocks, even when the corresponding homopolymer of one of the monomers showed critical elution behaviour. Therefore, the method could not be calibrated for block sizes by using homopolymer standards alone. Still, it was shown that the method can be used to determine differences between samples (PS-PMMA and PBMA-PMMA) with respect to total molecular size or block sizes separately, or to average size and chemical composition for random copolymers. Block and random PBMA-PMMA copolymers showed a distinctly different pattern in the 2-D plots obtained with 2-D critical chromatography. This difference was shown to be related to the different procedures followed in the polymerization process, and the different molecular distributions resulting from these. [source] Behaviour of polynuclear aryl sulphonatesLUBRICATION SCIENCE, Issue 3 2005A. K. Singh A series of hexadecyl polynuclear aromatic, decalin, and tetralin sulphonates have been synthesised. The critical micelle concentration (CMC) and surface and interfacial tension values at various concentrations above and below the CMC in both aqueous and non-aqueous media have been determined. The micellar size and shape, the average number of monomers constituting these micelles, and the thermodynamic properties have also been estimated. These studies show that the CMC value in both aqueous and heptane media decreases with an increase in the number of aromatic rings in the sulphonates. The size and shape of the micelles do not change appreciably in heptane, although the number of monomers constituting the micelles changes with a change of structure of the aromatic moiety. The thermodynamic parameters do not seem to affect the surface activity and solubilising properties even though the free energy, enthalpy, and entropy decrease with an increase in the size of the aromatic moiety. The surface and interfacial tension values are the lowest with aqueous and non-aqueous solutions of hexadecyl naphthalene sulphonate, but these values increase with an increase in the number of aromatic rings in the sulphonates. The sizes of the micelles of hexadecyl naphthalene sulphonate in aqueous solutions and the number of monomer molecules constituting the micelles are greater than for the other aromatic sulphonates. Although the sizes of micelles of hexadecyl benzanthracene sulphonate and hexadecyl pentacene sulphonate are comparable, the numbers of molecules constituting these micelles are the smallest. The solubilisation of alkanes in aqueous solutions of sodium naphthalene sulphonate containing electrolyte and isobutanol is the highest, but it falls off rapidly for all the other sulphonates. This shows the extreme sensitivity of solubilisation to the structure of the sulphonates. The detergency increases with an increase in the size of the aromatic moiety. The structure thus has a profound influence on the surface and micellar properties of these sulphonates. These studies are important from the point of view of the use of synthetic sulphonates as additives / surfactants in place of petroleum sulphonates. [source] Effect of Solvents on Living Polymerization of Propylene with [t -BuNSiMe2Flu]TiMe2 -MMAO Catalyst SystemMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 3 2004Kei Nishii Abstract Summary: Batchwise polymerization of propylene was conducted at 0,°C in heptane using [tert -BuNSiMe2Flu]TiMe2 (1) combined with dried methylaluminoxane (MAO) and dried modified methylaluminoxane (MMAO), which were prepared from the toluene solutions of MAO and MMAO by removing the solvent and the free trialkylaluminium. The dried MMAO system quantitatively gave the polymer with higher molecular weight and narrower molecular weight distribution (MWD), ca. 1.3, compared with the dried MAO system. In addition, the polymerization with dried MMAO in toluene, chlorobenzene (CB) and ortho -dichlorobenzene (o -DCB), as solvent, also produced polymers quantitatively with MWD of ca. 1.1,1.3. The number-average molecular weight () of the polymers, obtained with these systems, increased linearly against the polymer yield, while the narrow MWD was retained and the number of polymer chains was almost constant. The results of post-polymerization in heptane and o -DCB proved that the living polymerization proceeded irrespective of the solvent used. The semi-batch polymerizations under an atmospheric pressure of propylene indicated that the propagation rate was more than 10 times higher in o -DCB than in heptane. The 13C NMR analysis of the polymers indicated that the syndiotacticity also depended on the polarity of the solvent and increased in the following order: CB,,,o -DCB,<,toluene,<,heptane. A plausible scheme for the interaction between active species and solvents. [source] A Novel N -Succinylchitosan- graft -Polyacrylamide/Attapulgite Composite Hydrogel Prepared through Inverse Suspension PolymerizationMACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2007Ping Li Abstract A novel N -succinylchitosan- graft -polyacrylamide/attapulgite composite hydrogel was prepared by using N -succinylchitosan, acrylamide and attapulgite through inverse suspension polymerization. The result from FTIR spectra showed that OH of attapulgite, OH and NHCO of N -succinylchitosan participated in graft polymerization with acrylamide. The introduced attapulgite could enhance thermal stability of the hydrogel. Scanning electron microscopy observation indicates that the composite hydrogel has a microporous surface. The volume ratio of heptane to water, weight ratio of acrylamide to N -succinylchitosan and attapulgite content have great influence on swelling ability of the composite hydrogel. The composite hydrogel shows higher swelling rate and pH-sensitivity compared to that of without attapulgite. [source] Sphere-to-Rod Transition of Micelles formed by the Semicrystalline Polybutadiene- block -Poly(ethylene oxide) Block Copolymer in a Selective SolventMACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2010Adriana M. Mihut Abstract We present a morphological study of the micellization of an asymmetric semicrystalline block copolymer, poly(butadiene)- block -poly(ethylene oxide), in the selective solvent n -heptane. The molecular weights of the poly(butadiene) (PB) and poly(ethylene oxide) (PEO) blocks are 26 and 3.5,kg,·,mol,1, respectively. In this solvent, micellization into a liquid PEO-core and a corona of PB-chains takes place at room temperature. Through a thermally controlled crystallization of the PEO core at ,30,°C, spherical micelles with a crystalline PEO core and a PB corona are obtained. However, crystallization at much lower temperatures (,196,°C; liquid nitrogen) leads to the transition from spherical to rod-like micelles. With time these rod-like micelles aggregate and form long needles. Concomitantly, the degree of crystallinity of the PEO-cores of the rod-like micelles increases. The transition from a spherical to a rod-like morphology can be explained by a decrease of solvent power of the solvent n -heptane for the PB-corona chains: n -Heptane becomes a poor solvent at very low temperatures leading to a shrinking of the coronar chains. This favors the transition from spheres to a morphology with a smaller mean curvature, that is, to a cylindrical morphology. [source] A Novel Synthetic Procedure for Stereoblock Poly(propylene) with a Living Polymerization System,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2004Kei Nishii Abstract Summary: Propylene polymerization was conducted at 0,°C in heptane or chlorobenzene (CB) by an ansa -fluorenylamidodimethyltitanium complex combined with dried, modified methylaluminoxane that had been treated by dilution with heptane and successively repeatedly vacuum dried to remove any free trialkylaluminiums. The post-polymerizations testified that the living polymerization proceeded irrespective of the solvent used. The heptane system gave the syndiotactic poly(propylene)s (PPs), whereas the CB system gave almost atactic PPs. After the first polymerization in heptane had been completed, the same amounts of propylene and CB were added for the second polymerization. This procedure gave the syndiotactic-atactic stereoblock PP with narrow molecular-weight distributions. Structure of the ansa -fluorenylamidodimethyltitanium complex and its application to the synthesis of syndiotactic-atactic stereoblock poly(propylene)s reported here. [source] Non-empirical calculations of NMR indirect carbon-carbon coupling constants.MAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2003Bridged bicycloalkanes, Part 5: Abstract All possible J(C,C) of the bicarbocyclic frameworks together with J(C,H) and J(H,H) at bridgeheads in the series of six bridged bicycloalkanes, bicyclo[1.1.0]butane, bicyclo[2.1.0]pentane, bicyclo[3.1.0]hexane, bicyclo[2.2.0]hexane, bicyclo[3.2.0]heptane and bicyclo[3.3.0]octane, were calculated at the SOPPA level with correlation consistent Dunning sets cc-pVTZ-Cs augmented with inner core s-functions and locally dense Sauer sets aug-cc-pVTZ-J augmented with tight s-functions and rationalized in terms of the multipath coupling mechanism and hybridization effects explaining many interesting structural trends. Copyright © 2003 John Wiley & Sons, Ltd. 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