Close-coupling time-dependent quantum dynamics study of the H+HCl reaction

The paper presents a theoretical study of the dynamics of the H + HCl system on the potential energy surface (PES) of Bian and Werner (Bian, W.; Werner, H. -J., J. Chem. Phys. 2000, 112, 220). A time-dependent wave packet approach was employed to calculate state-to-state reaction probabilities for the exchanged and abstraction channels. The most recent PES for the system has been used in the calculations. Reaction probabilities have also been calculated for several values of the total angular momentum J > 0. Those have then been used to estimate cross sections and rate constants for both channels. The calculated cross sections can be compared with the results of previous quasiclassical trajectory calculations and reaction dynamics experimental on the abstraction channel. In addition, the calculated rate constants are in the reasonably good agreement with experimental measurement.

Combined single-pass conversion of methane via oxidative coupling and dehydroaromatization

A new reaction mode, i.e., the combined single-pass conversion of methane via oxidative coupling (OCM) over mixed metal oxide (SLC) catalysts and dehydroaromatization (MDA) over Mo/HZSM-5 catalysts, is reported. With the assistance of an OCM reaction over SLC catalysts in the top layer of the reactor, the deactivation resistance of Mo/HZSM-5 catalysts is remarkably enhanced. Under the selected reaction conditions, the CH(4) conversion decreased from similar to18 to similar to1% and the aromatics yield decreased from 12.8 to 0.1%, respectively, after running the reaction for 960 min on both 6Mo/HZSM-5 and SLC-6Mo/HZSM-5 catalyst system without O(2) in the feed. On the other hand, for the SLC-6Mo/HZSM-5 catalyst system with O(2) in the feed, the deactivation was improved greatly, and after 960 min onstream the CH(4) conversion and aromatics yield were still as high as 12.0 and 8.0%, respectively. The promotion effect mainly appears to be associated with in situ formation of CO(2) in the OCM layer, which reacts with coke via the reverse Boudouard reaction.

Combination of CH4 oxidative coupling reaction with C2H6 oxidative dehydrogenation by CO2 to C2H4

A new process has been suggested for converting natural gas to ethylene by combining oxidative coupling of methane with ethane dehydrogenation to provide an efficient method for the utilization of thermicity and CO2. From their thermodynamics, it is clear that the exothermicity from CH4 oxidative coupling reaction (DeltaH(800degreesC) = -174.3 kJ mol(-1)) can support C2H6 dehydrogenation by CO2 (DeltaH(800degreesC) = + 180.2 kJ mol(-1)). Meanwhile, the two reactions can be conducted under the same reaction conditions, such as the reaction temperature and reaction pressure as well as space velocity. In addition, the CO2 yielded from CH4 oxidative coupling reaction can be directly used for C2H6 dehydrogenation. Two kinds of catalyst are developed for this combined process with an achievement, from which C2H4 content in tail gas can reach attractively 16.4%, which can be used directly to produce ethylbenzene by the alkylation of benzene. (C) 2002 Elsevier Science Ltd. All rights reserved.

Coupling of seagrass (Cymodocea nodosa) patch dynamics to subaqueous dune migratio

The coupling between patch dynamics - described by the patch growth (horizontal and vertical), patch mortality, and life-history of Cymodocea nodosa (Ucria) Aschers., and the disturbance caused by the migration of subaqueous dunes over the plants was examined in a shallow NW Mediterranean bay (Alfacs Bay) where this species maintains a patchy cover. C. nodosa shoots survived substantial burial rates (up to 2.4 mm/day) by growing vertically at rates proportional to, albeit four-fold slower than, burial rates. Patch death was caused by erosion as large subaqueous dunes migrated pass the plant patch. Patch growth was fastest over the progressing slope of the dunes ( similar to 2.5 m year super(-1)) and flowering was also stimulated by sand accretion. The time interval between the passage of consecutive dunes, which sets the time window available for patch development, ranged between 2 and 6 years. This time interval allowed C. nodosa to recolonize bare substrata, with patch formation occurring about half a year after the disturbance, and also allowed established shoots to complete their life-cycle and produce seeds and thus enable subsequent recolonization. The time windows available for patch development also set an upper limit to patch size of about 26 m. Significant cross correlations between dune topography and patch dynamics and plant flowering frequency provide evidence that the spatial heterogeneity in the vegetation is closely associated with the disturbance imposed by the migration of sand dunes. The migration of subaqueous dunes maintains C. nodosa in a continuous state of colonization involving spatially asynchronous patch growth and subsequent mortality, which is ultimately responsible for the characteristic patchy landscape of this Bay. 

Palladium within ionic liquid functionalized mesoporous silica SBA-15 and its catalytic application in room-temperature Suzuki coupling reaction

Initially, pore walls of mesoporous silica SBA-15 with template were modified with chlorotrimethylsilane. Then imidazolium salts were similarly incorporated covalently in the inner pore walls of mesoporous silica SBA-15 albeit without the template. Finally, palladium salts were introduced into the pore channels of the previously processed mesoporous silica via electrostatic interaction. The resulting palladium catalysts demonstrated exceptional activity for the room-temperature Suzuki Coupling reaction in aqueous-organic mixed solvents and good recycling ability for at least 4-6 times.

Immobilization of dipyridyl complex to magnetic nanoparticle via click chemistry as a recyclable catalyst for Suzuki cross-coupling reactions

A magnetic nanoparticle (MNP)-supported di(2-pyridyl)methanol palladium dichloride complex was prepared via click chemistry. The MNP-supported catalyst was evaluated in Suzuki coupling reaction in term of activity and recyclability in DMF. It was found to be highly efficient for Suzuki coupling reaction using aryl bromides as substrates and could be easily separated by an external magnet and reused in five consecutive runs without obvious loss of activity.

Synergistic extraction of rare earths using acid-base coupling extractants of calix[4]arene carboxyl derivative and primary amine N1923

Synergistic effect in the extraction of rare earth (RE) metals by the acid-base coupling (ABC) extractants of calix[4]arene carboxyl derivative Bu-t[4]CH2COOH (H(4)A) and primary amine N1923 (RNH2) has been investigated. The extraction of RE was enhanced by the addition of sodium cations into the aqueous phase not only in the extraction system of Bu-t[4]CH2COOH alone but also in the mixture of Bu-t[4]CH2COOH and N1923. The separation factors (SFs) indicating the extraction selectivity of adjacent RE elements became higher in the mixture system.

Structural stability and magnetic coupling in CaCu3Co4O12 from first principles

The structural, electronic and magnetic properties of CaCu3Co4O12 were studied by use of the full-potential linearized augmented plane wave method. The calculated results indicate that CaCu3Co4O12 is stable both thermodynamically and mechanically. Both GGA (generalized gradient approximation) and GGA + U methods predict that CaCu3Co4O12 is metallic. The ferromagnetic configuration is only slightly more stable in energy compared with the non-magnetic configuration (3.7 meV), suggesting that they are competitive for being the ground state. Co is in the low spin state (S = 1/2).

Carbon dioxide/propylene oxide coupling reaction catalyzed by chromium salen complexes

A series of chromium/Schiff base complexes N,N'-bis(salicylidene)-1,2-phenylenediamino chromium(III) X were prepared and employed for the alternating copolymerization of carbon dioxide with racemic propylene oxide in the presence of (4-dimethylamino)pyridine. The effect of the complex structure and reaction conditions on the catalytic activity, the poly(propylene carbonate)/cyclic carbonate (PPC/PC) selectivity, and the polymer head-to-tail linkages was examined. The experiments indicated that N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-phenylenediamino chromium(III) (NO3) exhibited the highest PPC/PC selectivity as well as polymer head-to-tail linkages and N,N'-bis(3,5-dichlorosalicylidene)-1,2-phenylenediimino chromiu(III) (NO3) possessed the highest catalytic activity among these chromium/Schiff base complexes. The structure of the produced copolymer was characterized by the IR, H-1 NMR, and C-13 NMR measurements.

Carbon dioxide pressure induced heterogeneous and homogeneous Heck and Sonogashira coupling reactions using fluorinated palladium complex catalysts

The Heck reaction of iodobenzene and methyl acrylate was investigated with CO2-philic Pd complex catalysts having fluorous ponytails and the organic base triethylamine (Et3N) in the presence of CO2 under solventless conditions at 80 degrees C. The catalysts are not soluble in the organic phase in the absence Of CO2 and the reaction occurs in a solid-liquid biphasic system. When the organic liquid mixture is pressurized by CO2, CO2 is dissolved into the organic phase and this promotes the dissolution of the I'd complex catalysts. As a result, the Heck reaction occurs homogeneously in the organic phase, which enhances the rate of reaction. This positive effect Of CO2 pressurization competes with the negative effect that the reacting species are diluted by an increasing amount of CO2 molecules dissolved. Thus, the maximum conversion appears at a CO2 pressure of around 4 MPa under the present reaction conditions. The catalysts are separated in the solid granules by depressurization and are recyclable without loss of activity after washing with n-hexane and/or water.

Magnetic Coupling between Copper(II) Ions Mediated by Hydrogen-Bonded (Neutral) Water Molecules

A new hydrogen-bonded dinuclear copper(II) coordination compound has been synthesized from the Schiff-base ligand 6-(pyridine-2-ylhydrazonomethyl)phenol (Hphp). The molecular structure of [Cu-2(php)(2)(H2O2)(2)(ClO4)](ClO4)- (H2O) (1), determined by single-crystal X-ray diffraction, reveals the presence of two copper(II) centers held together by means of two strong hydrogen bonds, with O center dot O contacts of only 2.60-2.68 angstrom. Temperature-dependent magnetic susceptibility measurements down to 3 K show that the two metal ions are antiferromagnetically coupled (J = -19.8(2) cm(-1)). This exchange is most likely through two hydrogen-bonding pathways, where a coordinated water on the first Cu, donates a H bond to the O atoms of the coordinated php at the other Cu. This strong O center dot H (water) bonding interaction has been clearly evidenced by theoretical calculations. In the relatively few related cases from the literature, this exchange path, mediated by a (neutral) coordinated water molecule, was not recognized.

Guanidine/Pd(OAc)(2)-catalyzed room temperature Suzuki cross-coupling reaction in aqueous media under aerobic conditions

A highly efficient Pd(OAc)(2)/guanidine aqueous system for the room temperature Suzuki cross-coupling reaction has been developed. The new water-soluble and air-stable catalyst Pd(OAc)(2)(.)(1f)(2) from Pd(OAc)(2) and 1,1,3,3-tetramethyl-2-n-butylguanidine (1f) was synthesized and characterized by X-ray crystallography. In the presence of Pd(OAc)(2)(.)(1f)(2), coupling of arylboronic acids with a wide range of aryl halides, including aryl iodides, aryl bromides, even activated aryl chlorides, was carried out smoothly in aqueous solvent to afford the cross-coupling products in good to excellent yields and high turnover numbers (TONs) (TONs up to 850 000 for the reaction of 1-iodo-4-nitrobenzene and phenylboronic acid). Furthermore, this mild protocol could tolerate a broad range of functional groups.

Monooxychlorophosphine as a novel and efficient ligand for palladium-catalyzed suzuki-miyaura cross-coupling of aryl chlorides

A new sterically hindered monooxychlorophosphine was synthesized and the complex generated in situ from its reaction with Pd-2(dba)(3) promoted the Suzuki-Miyaura reactions of arylboronic acids with aryl chlorides in good yields.

One-pot synthesis of polyimides via Ni-catalyzed coupling of bis(chlorophthalimide)s

A one-pot synthesis method for the preparation of polyimides containing biphenyl units was developed via nickel-catalyzed coupling reaction of bis(chlorophthalimide)s which were prepared from chloroplithalic anhydrides and diamines in xylene. The resulting polyimides had inherent viscosities of above 0.60dL g(-1). In the meantime, the copolymerizations from a mixture of three isomeric bis(chlorophthalimide)s gave the polymers with inherent viscosities of 0.36-0.55 gdL(-1). The solubility and film formability of the copolymers were better than those of homopolymers from bis(4-chlorophthalimide). The 10% weight loss of these polyimides was between 470 and 531 degrees C.

An infrared study on Langmuir-Blodgett films of octadecylammonium octadecanoate: FWHM and the vibrational coupling

The monolayer of the mixture of octadecanoic acid and octadecylamine with molar ratio 1: 1 has been investigated at the air-water interface. It was found that the monolayer shows a rather stable state at the surface pressure of 30 mN/m and this monolayer can be transferred onto a CaF2 plate by Langmuir-Blodgett (LB) technique. The infrared spectra of LB films indicated that octadecyl ammonium octadecanoate is formed by an intermolecular proton exchange between adjacent carboxylic and aminic groups (COO- and NH3+). In three-layer LB film, the CH2 scissoring mode of the long hydrocarbon chains of octadecyl ammonium octadecanoate shows a broad band feature at about 1468 cm(-1) while this vibrational mode of three-layer LB film of the mixture (1: 1) of deuterated stearic acid and octadecylamine (octadecylammonium octadecanoate-d35, C18H37NH3+C17D35COO-) only shows a narrow band. The broad feature of the CH2 scissoring mode in octadecylammonium octadecanoate probably originates from the coupling between the chain of stearic acid and that of octadecylamine while this kind of coupling could be completely removed in octadecylammonium octadecanoate-d35.