- An investigation of hydrogen bonding between HCl and vinylacetylene: A molecule with two different ?-acceptor sites
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The ground state rotational spectrum of a hydrogen-bonded dimer formed by vinylacetylene and hydrogen chloride has been detected by the pulsed-nozzle, Fourier-transform microwave technique.Vinylacetylene has been chosen as a prototype acceptor molecule containing two different ?-acceptor sites.Rotational constants A0, B0, C0, centrifugal distortion constants ΔJ, ΔJK, δJ, δJK, and three components χaa, χbb - χcc, and χab of the Cl nuclear quadrupole coupling tensor have been determined for each of the three isotopomers CH2CHCCH...HCl, CH2CHCCH...HCl, and CH2CHCCH...D35Cl.These spectroscopic constants have been interpreted in terms of a dimer in which the HCl subunit forms a hydrogen to the CC triple bond in a T-shape configuration, but is displaced from the center of the triple bond by d = 0.04 Angstroem towards the inner C atom, and makes an angle φ = 34 deg with the vinylacetylene plane.The experimental angular geometry is in excellent agreement with that predicted by the Buckingham-Fowler electrostatic model which gives φ = 27 deg.
- Kisiel, Z.,Fowler, P. W.,Legon, A. C.,Devanne, D.,Dixneuf, P.
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- The i.r., Raman and microwave spectra of 1-butene-3-yne (vinylacetylene) and 1-butene-3-yne-4d
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The i.r. spectra of 1-butene-3-yne and 1-butene-3-yne-4d in the vapour phase and as crystalline solids at 90 K were recorded in the region 5000-100 cm-1.Raman spectra, including semiquantitative polarization data, of the neat liquid and of the solid were obtained at 90 K.Microwave spectra of the compounds were recorded in the region 8-40 GHz at ambient temperature.Rotational transitions of the vibrational ground state and of the two lowest vibrational excited states ν13(a') and ν18(a'') were measured.The fundamental frequencies of both compounds were assigned in excellent agreement with the results of normal coordinate calculations.Rotational fine structure was observed for several bands and interpreted as the Q-sub-branches of the perpendicular bands (in the symmetrical top approximation).For six bands the Q-sub-branches were assigned to the proper K-values.The Coriolis coupling constant ξa13,18 was derived from the i.r. and from the microwave spectra.
- Torneng, E.,Nielsen, C. J.,Klaeboe, P.,Hopf, H.,Priebe, H.
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- Reaction Mechanism of the Homogeneous Thermal Decomposition of Acetylene
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A modeling study is reported in which experiments on the rate of and product distribution from C2H2 pyrolysis from 625 to 3400 K are described with a single mechanism.The essential primary mechanism at low temperatures proves to consist of an H-atom, vinyl radical chain H + C2H2 -> C2H3, C2H3 + C2H2 -> C4H4+ H producing vinyl acetylene at early times.At high temperatures this is replaced by the ethynyl chain H + C2H2 -> C2H + H2, C2H + C2H2 + H producing diacetylene.By considering a variety of studies simulteneusly it was possible to assign rate constant expressions to the key elementary reactions.While all of the basic observations on the primary decomposition are accounted for by final mechanism, uncertainties still remain in the rates of secondary reactions and in the magnitudes of the fallof corrections required for the unimolecular reactions involved.
- Tanzawa, T.,Gardiner, W. C.
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- Nitrogen-Modified Activated Carbon Supported Cu(II)Cu(I)/NAC Catalysts for Gas–Solid Acetylene Dimerization
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Improving dispersibility and stability of Cu(II)Cu(I)/activated carbon (AC) is a crucial aspect for enhancing its catalytic performance in the process of gas–solid acetylene dimerization. The Cu(II)Cu(I)/NAC-500 catalyst using nitrogen-modified AC (NAC) as a support, delivered excellent catalytic performance and stability vs undoped Cu(II)Cu(I)/AC at 100?°C and 120?h?1 of C2H2 gas hourly space velocity. Under the optimal conditions, the Cu(II)Cu(I)/NAC-500 catalyst exhibited a stable catalytic performance during a 10?h test with 65% C2H2 conversion; and the selectivity to monovinylacetylene (MVA) reached 86%. The existence of nitrogen species can increase the interaction between copper and the support, and increase dispersion of the copper species on the support, which were benefit for the catalytic performance. Graphic Abstract: [Figure not available: see fulltext.]
- Li, Congcong,Xie, Jianwei,Zhang, Jinli,Dai, Bin
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- A novel risedronic acid-modified Nieuwland catalyst for acetylene dimerization
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Nieuwland catalyst (NC) was modified with different phosphonic acids (Px) and evaluated for their acetylene dimerization activity in monovinyl acetylene (MVA) production. Nearly 49.2% of acetylene conversion and 80.3% of MVA selectivity were obtained in 5 mol% risedronic acid (P2)-modified NC under an acetylene-gas space velocity of 105 h?1 at 80 °C, which was 17.8% higher than the yield of the control NC. The characterization results of NC and P2–NC indicated that the addition of P2 effectively enhanced the stability of the Cu ions and inhibited oxidation of the active component Cu+, improving their catalytic activity and long-term stability.
- Zhang, Qixia,Li, Congcong,Luo, Juan,Xie, Jianwei,Zhang, Jinli,Dai, Bin
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- Hydrazinylbenzenesulfonic Acid-Modified Nieuwland Catalyst for Acetylene Dimerization Reaction
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Abstract: A novel Nieuwland catalytic system, containing 5?mol% of 4-hydrazinylbenzenesulfonic acid (S8), was developed and exhibited an excellent catalytic performance and good stability in the acetylene dimerization reaction. The acetylene conversion reached 57.1%, while the selectivity of monovinylacetylene (MVA) was 75.1%. The yield of MVA was maintained at 42.9% under an acetylene gas hourly space velocity (GHSV) of 80?h?1 at 80?°C, which was increased by 18.8% over the control Nieuwland catalytic system. The addition of S8 increased the dissolution of CuCl in water, inhibited the polymer formation, and hindered the Cu+ loss during the reaction process, thus improving the activity and the long-term stability of the modified Nieuwland catalyst. Graphic Abstract: [Figure not available: see fulltext.]
- Zhang, Qixia,Li, Congcong,Luo, Juan,Xie, Jianwei,Zhang, Jinli,Dai, Bin
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- Kinetics of copper(I)-catalyzed dimerization and hydration of acetylene in water
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The kinetics of the dimerization and hydration of acetylene in water with a copper(I) catalyst, a so-called Nieuwland catalyst, were investigated. The stationary state kinetics for both reactions could be described assuming that the rate-controlling step is a second-order reaction of an activated catalyst, [H-Cl-Cu-C2H], formed in the reaction mixture, with acetylene or water. The activation energies and activation entropies were 12.4 kcal·mol-1 and -33.3 cal·mol-1·K -1 for the acetylene dimerization, and 17.5 kcal·mol -1 and -34.2 cal·mol-1·K-1 for the acetylene hydration, respectively. The large negative values of activation entropy for these reactions may be accounted for by the role of water as a kind of cocatalyst.
- Tokita, Yuichi,Okamoto, Akio,Nishiwaki, Kenichiro,Kobayashi, Mineto,Nakamura, Eiichi
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- Gas-solid acetylene dimerization over copper-based catalysts
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Acetylene dimerization is an important step in an acetylene-based process for chloroprene production, and the traditional catalyst for this transformation is the Nieuwland catalyst in a bubble column reactor. However, the drawbacks of this catalyst are the use of high concentration of a copper reagent, low acetylene conversion and monovinylacetylene (MVA) selectivity, and the difficulty to generate or reuse the catalytic system. Therefore, in this study, we first reported a gas-solid acetylene dimerization reaction by applying copper-supported catalysts, which were prepared via an impregnation technique using CuCl as the precursor. The catalytic activity was examined and discussed in detail by modification of the impregnation solvent, Cu loading amount, reaction temperature, and the acetylene gas hourly space velocity. Under optimal conditions, the catalyst exhibited a maximum acetylene conversion of 48.3% and a monovinylacetylene selectivity of 87.4%. The catalysts were characterized by TGA, XRD, H2-TPR, TEM, BET, XPS and ICP-AES. Not only the preparation, isolation and recycling of the supported catalyst were easy in the gas-solid reaction, but also the supported catalyst overcame the shortcomings of the liquid phase catalyst. The loss of the Cu active species is concluded to be the main factor causing the decrease in the catalytic activity.
- Li, Congcong,Luo, Juan,Zhang, Qixia,Xie, Jianwei,Zhang, Jinli,Dai, Bin
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- HETEROGENIZED CATALYST FOR ACETYLENE DIMERIZATION
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A catalyst and a process for using the catalyst are presented. The catalyst is a heterogeneous catalyst and includes active metal halides bonded to functional groups. The functional groups are bonded to a polymeric backbone to form the structure supporting the catalyst. The catalyst is useful for the dimerization of acetylene to convert the acetylene to a larger hydrocarbon, and in particular to dimerize acetylene to vinylacetylene.
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Paragraph 0034-0037; 0039
(2018/04/12)
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- Formation of fulvene in the reaction of C2H with 1,3-butadiene
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Abstract Products formed in the reaction of C2H radicals with 1,3-butadiene at 4 Torr and 298 K are probed using photoionization time-of-flight mass spectrometry. The reaction takes place in a slow-flow reactor, and products are ionized by tunable vacuum-ultraviolet light from the Advanced Light Source. The principal reaction channel involves addition of the radical to one of the unsaturated sites of 1,3-butadiene, followed by H-loss to give isomers of C6H6. The photoionization spectrum of the C6H6 product indicates that fulvene is formed with a branching fraction of (57 ± 30)%. At least one more isomer is formed, which is likely to be one or more of 3,4-dimethylenecyclobut-1-ene, 3-methylene-1-penten-4-yne or 3-methyl-1,2-pentadien-4-yne. An experimental photoionization spectrum of 3,4-dimethylenecyclobut-1-ene and simulated photoionization spectra of 3-methylene-1-penten-4-yne and 3-methyl-1,2-pentadien-4-yne are used to fit the measured data and obtain maximum branching fractions of 74%, 24% and 31%, respectively, for these isomers. An upper limit of 45% is placed on the branching fraction for the sum of benzene and 1,3-hexadien-5-yne. The reactive potential energy surface is also investigated computationally. Minima and first-order saddle-points on several possible reaction pathways to fulvene + H and 3,4-dimethylenecyclobut-1-ene + H products are calculated.
- Lockyear, Jessica F.,Fournier, Martin,Sims, Ian R.,Guillemin, Jean-Claude,Taatjes, Craig A.,Osborn, David L.,Leone, Stephen R.
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p. 232 - 245
(2015/04/14)
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- Kinetics of the reactions of hydroxyl radicals with diacetylene and vinylacetylene
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Highly unsaturated hydrocarbons like diacetylene (C4H2) or vinylacetylene (C4H4) are important intermediates in combustion that can have impact on soot formation. One of their major loss channels is reaction with hydroxyl radicals (OH). We studied the reactions C4H2 + OH → products (1) and C4H4 + OH → products (2) in a quasi-static reactor with helium as bath gas. The hydroxyl radicals were produced by laser flash-photolysis of nitric acid at a wavelength of 248 nm and detected by laser-induced fluorescence with excitation at 282 nm. The rate coefficients were obtained from the intensity-time profiles under pseudo-first order conditions with respect to OH. We found a virtually temperature-independent rate coefficient for reaction (1): k1 = (1.0 ± 0.3) × 10-11 cm3 s-1 (T = 290-670 K, P = 2.7-30.5 bar) and a weakly negative temperature-dependent rate coefficient for reaction (2): k2(T) = (6.4 ± 1.9) × 10-12 exp (486 K/T) cm3 s-1 (T = 295-740 K, P = 1.7-19.2 bar). For neither of the two reactions pressure dependence was observed. From comparisons with analogous reaction systems, we conclude that the dominating reaction pathway is OH addition, where in the case of C4H4 the double bond is preferred over the triple bond.
- Sommerer, J?rg,Olzmann, Matthias
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p. 495 - 505
(2015/04/14)
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- Strontium chloride modified Nieuwland catalyst in the dimerization of acetylene to monovinylacetylene
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SrCl2 was used as a co-catalyst of CuCl in Nieuwland catalyst and CuCl as the main catalyst, NH4Cl as the solubilizer, water as the solvent and a certain amount of hydrochloric acid, thereby forming Sr-Cu bimetallic cooperative catalysis reaction systems for C2H2 dimerization. Under the optimum condition, the acetylene conversion is 13 % and monovinylacetylene selectivity can reach to 94 %.
- Lu, Jun-Long,Xie, Jian-Wei,Liu, Hai-Yue,Liu, Ping,Liu, Zhi-Yong,Dai, Bin
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p. 8211 - 8214
(2015/02/02)
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- Reaction rate and isomer-specific product branching ratios of C 2H + C4H8: 1-butene, cis -2-butene, trans -2-butene, and isobutene at 79 K
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The reactions of C2H radicals with C4H8 isomers 1-butene, cis-2-butene, trans-2-butene, and isobutene are studied by laser photolysis-vacuum ultraviolet mass spectrometry in a Laval nozzle expansion at 79 K. Bimolecular-reaction rate constants are obtained by measuring the formation rate of the reaction product species as a function of the reactant density under pseudo-first-order conditions. The rate constants are (1.9 ± 0.5) × 10-10, (1.7 ± 0.5) × 10 -10, (2.1 ± 0.7) × 10-10, and (1.8 ± 0.9) × 10-10 cm3 s-1 for the reaction of C2H with 1-butene, cis-2-butene, trans-2-butene, and isobutene, respectively. Bimolecular rate constants for 1-butene and isobutene compare well to values measured previously at 103 K using C2H chemiluminescence. Photoionization spectra of the reaction products are measured and fitted to ionization spectra of the contributing isomers. In conjunction with absolute-ionization cross sections, these fits provide isomer-resolved product branching fractions. The reaction between C2H and 1-butene yields (65 ± 10)% C4H4 in the form of vinylacetylene and (35 ± 10)% C5H6 in the form of 4-penten-1-yne. The cis-2-butene and trans-2-butene reactions yield solely 3-penten-1-yne, and no discrimination is made between cis- and trans-3-penten-1-yne. Last, the isobutene reaction yields (26 ± 15)% 3-penten-1-yne, (35 ± 15)% 2-methyl-1-buten-3-yne, and (39 ± 15)% 4-methyl-3-penten-1-yne. The branching fractions reported for the C2H and butene reactions indicate that these reactions preferentially proceed via CH3 or C2H3 elimination rather than H-atom elimination. Within the experimental uncertainties, no evidence is found for the formation of cyclic species.
- Bouwman, Jordy,Fournier, Martin,Sims, Ian R.,Leone, Stephen R.,Wilson, Kevin R.
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p. 5093 - 5105
(2013/07/25)
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- Bimolecular rate constant and product branching ratio measurements for the reaction of C2H with ethene and propene at 79 K
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The reactions of the ethynyl radical (C2H) with ethene (C 2H4) and propene (C3H6) are studied under low temperature conditions (79 K) in a pulsed Laval nozzle apparatus. Ethynyl radicals are formed by 193 nm photolysis of acetylene (C 2H2) and the reactions are studied in nitrogen as a carrier gas. Reaction products are sampled and subsequently photoionized by the tunable vacuum ultraviolet radiation of the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. The product ions are detected mass selectively and time-resolved by a quadrupole mass spectrometer. Bimolecular rate coefficients are determined under pseudo-first-order conditions, yielding values in good agreement with previous measurements. Photoionization spectra are measured by scanning the ALS photon energy while detecting the ionized reaction products. Analysis of the photoionization spectra yields-for the first time-low temperature isomer resolved product branching ratios. The reaction between C2H and ethene is found to proceed by H-loss and yields 100% vinylacetylene. The reaction between C2H and propene results in (85 ± 10)% C4H4 (m/z = 52) via CH3-loss and (15 ± 10)% C5H6 (m/z = 66) by H-loss. The C 4H4 channel is found to consist of 100% vinylacetylene. For the C5H6 channel, analysis of the photoionization spectrum reveals that (62 ± 16)% is in the form of 4-penten-1-yne, (27 ± 8)% is in the form of cis-and trans-3-penten-1-yne and (11 ± 10)% is in the form of 2-methyl-1-buten-3-yne.
- Bouwman, Jordy,Goulay, Fabien,Leone, Stephen R.,Wilson, Kevin R.
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experimental part
p. 3907 - 3917
(2012/07/02)
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- The first syntheses of (±)-SDEF 678 metabolite and (±)-speciosins A-C
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The epoxyquinone natural products SDEF 678 metabolite, speciosin A, speciosin B and speciosin C have been prepared for the first time via a short synthetic route based around the palladium-catalysed coupling of a halogen-substituted 1,4-benzoquinone monoketal, a Diels-Alder/retro-Diels-Alder sequence and a diastereoselective epoxidation process. The quinone monoketal 13, which was obtained via oxidation of 3-iodophenol, has been converted over six steps into the epoxyquinone natural products SDEF 678metabolite (2) and speciosin A (4), which were subsequently converted into speciosin C (3) and speciosin B (5), respectively.
- Hookins, Daniel R.,Burns, Alan R.,Taylor, Richard J. K.
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supporting information; experimental part
p. 451 - 454
(2011/03/21)
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- UV laser photodeposition of nanomagnetic soot from gaseous benzene and acetonitrile-benzene mixture
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Megawatt KrF laser gas-phase photolysis of benzene and acetonitrile-benzene mixture was studied by using mass spectroscopy-gas-chromatography and Fourier transform infrared spectroscopy for analyses of volatile products, and by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, electron microscopy and magnetization measurements for analyses of solid products deposited from the gas-phase. The results are consistent with carbonization of benzene and decomposition of non-absorbing acetonitrile in carbonizing benzene through collisions with excited benzene and/or its fragments. The solid products from benzene and acetonitrile-benzene mixture have large surface area and are characterized as nanomagnetic amorphous carbonaceous soot containing unsaturated C centers prone to oxidation. The nanosoot from acetonitrile-benzene mixture incorporates CN groups, confirms reactions of benzene fragments with CN radical and has a potential for modification by reactions at the CN bonds.
- Pola, Josef,Ouchi, Akihiko,Mary?ko,Vorlí?ek,?ubrt, Jan,Bakardjieva,Bastl, Zdeněk
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experimental part
p. 188 - 194
(2012/02/02)
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- Syntheses and pyrolyses of furan analogues of α-Oxo- o -quinodimethanes. Formation of methylenecyclobutenone and 1-buten-3-yne via a vinylcarbene-cyclopropene rearrangement
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Flash vacuum pyrolyses (FVP) of benzoic 2-methyl-3-furoic anhydride (12) and benzoic 3-methyl-2-furoic anhydride (13) at 550 °C and ca. 10 -2 Torr both give methylenecyclobutenone (16) and 1-buten-3-yne (17) as the main products. A mechanism involving generation of furan analogues of α-oxo-o-quinodimethane, 10 and 11, from FVP of 12 and 13, respectively, followed by elimination of a CO molecule to give the respective carbenes 34 and 36 is proposed. Carbenes 34 and 36 are interconvertible via a cyclopropene intermediate 35. A ring contraction from 36 will give 16, whereas a ring-opening of 34 followed by elimination of a CO molecule then leads to 17. The proposed mechanism is supported by substituent- and deuterium-labeling study on FVP of the derivatives of 12.
- Tseng, Pen-Wen,Kung, Chen-Yu,Chen, Hsing-Yin,Chou, Chin-Hsing
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experimental part
p. 8440 - 8446
(2011/12/04)
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- Cyclic versus linear isomers produced by reaction of the methylidyne radical (CH) with small unsaturated hydrocarbons
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The reactions of the methylidyne radical (CH) with ethylene, acetylene, allene, and methylacety- lene are studied at room temperature using tunable vacuum ultraviolet (VUV) photoionization and time- resolved mass spectrometry. The CH radicals are prepared by 248 nm multiphoton photolysisof CHBr 3 at 298 K and react with the selected hydrocarbon i n a helium gas flow. Analysis of photoionization efficiency versus VUV photon wavelength permits isomer-specific detection of the reaction products and allows estimation of the reaction product branching ratios. The reactions proceed by either CH insertion or addition followed by H atom elimination from the intermediate adduct. In the CH + C 2 H 4 reaction the C 3 H 5 intermediate decays byH atom loss to yield 70(±8)percent allene, 30(±8)percent methylacetylene, and less than 10percent cyclopropene, in agreement with previous RRKM results. In the CH + acetylene reaction, detection of mai nly the cyclic C 3 H 2 isomer is contrary to a previous RRKM calculations that predicted linear triplet propargylene to be 90percent of the total H-atom coproducts. High-level CBS-APNO quantum calculations and RRKM calculations for the CH + C 2 H 2 reaction presented in this manuscript predict a higher contribution of the cyclic C 3 H 2 (27.0percent) versus triplet propargylene (63.5percent) than earlier predictions. Extensive calculations onthe C 3 H 3 and C 3 H 2 D system combined with experimental isotope ratios for the CD + C 2 H2 reaction indicate that H-atom-assisted isomerization in the present experiments is responsible for the remaining discrepancy between the new RRKM calculations and the experimental results. Cyclic isomers are also found to represent 30(±6)percent of the detected products in the case of CH + methylacetylene, together with 33(±6)percent 1,2,3- butatriene and 37(±6)percent vinylacetylene. The CH + allene reaction gives 23(±5)percent 1,2,3-butatriene and 77(±5)percent vinylacetylene, whereas cyclic isomers are produced below the detection limit in this reaction. The reaction exit channels deduced by comparing the product distributions for the aforementioned reactions are discussed in detail.
- Goulay, Fabien,Trevitt, Adam J.,Meloni, Giovanni,Selby, Talitha M.,Osborn, David L.,et al.
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experimental part
p. 993 - 1005
(2009/06/28)
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- Gas phase surface-catalyzed HCl addition to vinylacetylene: motion along a catalytic surface. Experiment and theory
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Gaseous mixtures of HCl and vinylacetylene were permitted to react in Pyrex IR cells (NaCl windows). Gaseous 4-chloro-1,2-butadiene and 2-chloro-1,3-butadiene (chloroprene) were the major products. Kinetic data (FTIR) generated a rate expression in concert with surface catalysis. Computational studies involving surface associated water provide a view that accounts for the experimentally determined orders and a bifurcated pathway producing both products. The results are in accord with wall-adsorbed reactant(s) as well as previously reported computational studies on the reactants.
- Mascavage, Linda M.,Zhang-Plasket, Fan,Sonnet, Philip E.,Dalton, David R.
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p. 9357 - 9367
(2008/12/23)
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- Deuteration and dimerization of acetylene with a nieuwland catalyst in deuterium oxide
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Efficient deuteration and dimerization of acetylene have been readily attained in deuterium oxide with a Nieuwland catalyst which is practically used for dimerization of acetylene. Copyright
- Tachiyama, Takashi,Yoshida, Makoto,Aoyagi, Tatsuhiro,Fukuzumi, Shunichi
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- Detailed chemical kinetic modeling of pyrolysis of ethylene, acetylene, and propylene at 1073-1373 K with a plug-flow reactor model
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This study examines the predictive capability of our recently proposed reaction mechanism (Norinaga and Deutschmann, Ind Eng Chem Res 2007, 46, 3547) for hydrocarbon pyrolysis at varying temperature. The conventional flow reactor experiments were conducted at 8 kPa, over the temperature range 1073-1373 K, using ethylene, acetylene, and propylene as reactants to validate the mechanism. More than 40 compounds were identified and quantitatively analyzed by on- and off-line gas chromatography. The chemical reaction schemes consisting of 227 species and 827 reactions were coupled with a plug-flow reactor model that incorporated the experimentally measured axial temperature profile of the reactor. Comparisons between the computations and the experiments are presented for more than 30 products including hydrogen and hydrocarbons ranging from methane to coronene as a function of temperature. The model can predict the compositions of major products (mole fractions larger than 10-2) in the pyrolysis of three hydrocarbons with satisfactory accuracies over the whole temperature range considered. Mole fraction profiles of minor compounds including polycyclic aromatic hydrocarbons (PAHs) up to three ring systems, such as phenanthrene, anthracene, and phenylnaphthalene, are also fairly modeled. At temperatures lower than 1273 K, larger PAHs were underpredicted and the deviation became larger with decreasing temperature and increasing molecular mass of PAHs, while better agreements were found at temperatures higher than 1323 K.
- Norinaga, Koyo,Janardhanan, Vinod M.,Deutschmann, Olaf
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p. 199 - 208
(2008/09/18)
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- Production of Propylene and Ethylene from Butane and Ethane
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The present invention relates to a process for producing propylene and ethylene from a light hydrocarbon stream comprising essentially ethane and butane. The process involves a non-catalytic cracking of ethane and normal-butane followed by a metathesis of ethylene and 2-butene to increase the propylene yield. Optionally the by-produced iso-butane is dehydrogenated and subsequently the produced iso-butene is converted to other valuable products like di-isobutylene, alkylate for gasoline blending, tertiary-butyl-ethers, polyisobutylene, methyl-metacrylate or isoprene.
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Page/Page column 6-7
(2008/06/13)
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- Experimental and computational study of the ultraviolet photolysis of vinylacetylene. Part II
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The ultraviolet photochemistry of vinylacetylene (C4H 4) was studied under temperature and pressure conditions similar to Titan's atmosphere by exciting the molecule in a constrained expansion that opens into the ion source region of a time-of-flight mass spectrometer. The primary dissociation products detected by vacuum-ultraviolet ionization were found to be C4H3 and C4H2, in a ratio of 3-10: 1. Subsequent reaction of the C4H3 radicals with the parent C4H4 produced two major secondary products: C8H6 and C6H4. The former was spectroscopically identified as phenylacetylene, confirming that photochemical reactions of C4H4 can produce aromatic molecules. The primary dissociation reaction was also studied computationally. The results were consistent with the experimental findings for C 4H2 and C4H3. However, the major product is C2H2, which is undetected by 118 nm photoionization in the present experiment but should account for roughly two-thirds of the products. Simulations were also performed to confirm that the present experiment accurately represents the 220 nm photochemistry of vinylacetylene at the temperature and pressure of Titan's atmosphere, with a product yield of C2H2: C4H2: C 4H3 of 66: 7: 27. Accounting for the wavelength dependent solar flux on Titan, the estimated absorption cross section of vinylacetylene in the ultraviolet, and the slightly wavelength dependent product distribution, the overall product yield predicted by the simulations for ultraviolet photolysis of vinylacetylene on Titan is C2H2: C 4H2: C4H3 = 65: 8: 27. Finally, a simulation was performed under conditions of a shock tube experiment to examine the differences between thermal and photochemical dissociation. The product yield of this simulation was C2H2: C4H 2: C4H3 = 61: 1: 38. the Owner Societies 2006.
- Stearns, Jaime A.,Zwier, Timothy S.,Kraka, Elfriede,Cremer, Dieter
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p. 5317 - 5327
(2008/02/11)
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- VINYL CHLORIDE MONOMER COMPOSITION
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A vinyl chloride monomer composition characterized in that the vinyl chloride monomer contains a chlorinated saturated hydrocarbon in a concentration of 45-200 ppm by mass. The vinyl chloride monomer composition has excellent polymerizability in polyvinyl chloride production. Furthermore, the composition is stably prevented from undergoing polymerization during storage and can be stably stored over long.
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Page/Page column 6
(2010/11/23)
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- Oligomerization and cyclization reactions of acetylene
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Acetylene was pyrolyzed in a flow system at pressures between 104 and 403 Torr and temperatures between 854 and 971 K. Products were analyzed by gas chromatography with flame ionization and mass spectrometric detection. In some experiments the reactor was
- Xu, Xuejun,Pacey, Philip D.
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p. 326 - 333
(2007/10/03)
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- On-line analysis of gas-phase composition in the combustion chamber and particle emission characteristics during combustion of wood and waste in a small batch reactor
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The emission of participate matter and gaseous compounds during combustion of wood and refuse-derived fuel in a small batch reactor is investigated by laser mass-spectrometric on-line measurement techniques for gas-phase analysis and simultaneous registration of physical aerosol properties (number size distribution). The gas-phase composition is addressed by a laser-based mass spectrometric method, namely, vacuum-UV single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). Particle-size distributions are measured with a scanning mobility particle sizer. Furthermore, a photoelectric aerosol sensor is applied for detection of particle-bound polycyclic aromatic hydrocarbons. The different phases of wood combustion are distinguishable by both the chemical profiles of gas-phase components (e.g., polycyclic aromatic hydrocarbons, PAH) and the particle-size distribution. Furthermore, short disturbances of the combustion process due to air supply shortages are investigated regarding their effect on particle-size distribution and gas-phase composition, respectively. It is shown that the combustion conditions strongly influence the particle-size distribution as well as on the emission of particle-bound polycyclic aromatic hydrocarbons.
- Ferge,Maguhn,Hafner,Muehlberger,Davidovic,Warnecke,Zimmermann
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p. 1393 - 1402
(2007/10/03)
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- Oxidation, ignition and combustion of toluene: Experimental and detailed chemical kinetic modeling
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The oxidation of toluene was studied in a jet-stirred reactor at 1 atm. New experimental results were obtained over the high temperature range 1000-1375 K, and variable equivalence ratio (0.5 ≤ φ ≤ 1.5). Concentration profiles of reactants, stable intermediates and final products were measured by probe sampling followed by online and off-line GC analyses. These experiments were modeled using a detailed kinetic reaction mechanism (120 species and 920 reactions, most of them reversible). This kinetic scheme was also used to simulate the ignition of toluene-oxygen-argon mixtures and the burning velocities of toluene-air mixtures. The presently proposed mechanism has already been validated by simulating the oxidation of benzene at 0.46 to 10 atm under stirred-reactor conditions, the ignition of benzene-oxygen-argon mixtures and the combustion of benzene in flames. Sensitivity analyses and reaction path analyses, based on species rates of reaction, were used to interpret the results. The routes involved in toluene oxidation have been delineated: toluene oxidation proceeds via the formation of benzyl, by H-atom abstraction, and the formation of benzene, by H-atom displacement yielding methyl and benzene; benzyl oxidation yields benzaldehyde, that further reacts yielding phenyl whereas benzyl thermal decomposition yields acetylene and cyclopentadienyl; further reactions of cyclopentadienyl yield vinylacetylene.
- Dagaut,Pengloan,Ristori
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p. 1846 - 1854
(2007/10/03)
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- Preparation of preparing substituted indanones
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a process for the preparation of indanones of the formula II from, indanones of the formula I or of indanones of the formula IIa from indanones of the formula Ia comprises reacting an indanone of the formula I or Ia with a coupling component.
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- An induction period in the pyrolysis of acetylene
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Acetylene was pyrolysed in a flow system between 854 and 970 K, at pressures between 27 and 127 Torr and at residence times between 8 and 1520 ms. Both vinylacetylene and benzene were observed to be primary products, but secondary processes removed vinylacetylene and formed benzene. The orders for the steady-state rates of formation of vinylacetylene and benzene were measured to be 1.8 ± 0.1 and 2.4 ± 0.1, respectively. The corresponding rate constants were found to be, ln(kVA/L mol-1 s-1) = -(165 ± 11) kJ mol-1/RT + (22.7 ± 1.5) and ln(kB/L1.4 mol-1.4 s-1) = -(100 ± 9) kJ mol-1/RT + (15.6 ± 1.1). Induction periods were observed for the first time at these conditions, providing evidence that a free radical process dominates. The order of the initiation reaction was shown to be two. The temperature dependence of the product of the rate constants for the bimolecular, initiation reaction and the termination reaction was determined to be, ln(kikt/L2 mol-2 s-2) = -(261 ± 7) kJ mol-1/RT + (53.1 ± 1.0).
- Xu,Pacey
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p. 2836 - 2844
(2007/10/03)
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- 1,2-Pentadiene decomposition
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1,2-Pentadiene was decomposed in single pulse shock tube experiments. There appear to be a large number of parallel decomposition and isomerization channels. It was shown that the resonance energy of the 1,3-butadiene-2-yl radical is smaller than that of allyl radical by an amount equal to the π bond conjugation energy of butadiene.
- Herzler, Juergen,Manion, Jeffrey A.,Tsang, Wing
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p. 755 - 767
(2007/10/03)
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- A structure-reactivity correlation with three slopes in the elimination kinetics of 2-substituted ethyl N,N-dimethyl-carbamates in the gas phase
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The elimination kinetics of 17 2-substituted ethyl N,N-dimethylcarbamates in the gas phase were determined in the temperature range of 269.5-420.2°C and the pressure range of 24-186 Torr. The reactions in a static system and in the presence of a free radical inhibitor are homogeneous and unimolecular and follow a first-order rate law. The kinetics and thermodynamic parameters are described. The use of several structure-reactivity relationship methods meaningless results, except for Taft σ* values. Three good slopes are originated at σ*(CH3) = 0.00. Slope a: the 2-substituted alkyl groups gave a good straight line when log (k/kCH3) vs σ* values (ρ* = - 1.94 ± 0.30, r = 0.977 at 360°C) were plotted. Slope b: Polar2 substituents gave an approximate straight line with ρ* = - 0.12 ± 0.02, r = 0.936 at 360°C. Slope c:the correlation of multiple bonded and electron-withdrawing substituents interposed by a methylene group at the 2-position of ethyl N,N-dimethylcarbamate was found to give a very good straight line wirh ρ* = 0.49 ± 0.02, r = 0.991 at 360°C. Mechanisms are suggested on the basis of these relationships. The point position of the substituents phenyl (C6H5) and isopropenyl [CH2=C(CH3)] at the 2-position was found to fall far above the three slopes of the lines. These results are interpreted in terms of neighboring group participation of these substituents in the elimination process of the carbamates. However, the acidity of the benzylic and allylic Cβ-H bond for a six-membered cyclic transition state may not be ignored. Copyright
- Chuchani, Gabriel,Nunnez, Oswaldo,Marcano, Norka,Napolitano, Suvighey,Rodriguez, Henry,Dominguez, Marianella,Ascanio, Judany,Rotinov, Alexandra,Dominguez, Rosa M.,Herize, Armando
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p. 146 - 158
(2007/10/03)
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- ArF and KrF lasers-induced gas-phase photolysis of selenophene and telluropllene: Extrusion of Te and Se and intramolecular 1,3-H shift competing with β-C-C cleavage in C4H4 residue
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ArF (193 nm) and KrF (248 nm) laser-induced photolysis of gaseous selenophene and tellurophene (C4H4M, M = Se and Te) has been examined. It is shown that, unlike thiophene and furan, selenophene and tellurophene cleave both M-C bonds and yield the elemental heteroatom (Se, Te), 1-buten-3- yne, and ethyne. The proposed mechanism involves an intermediate ·HC=CH- CH=CH· diradical that decomposes via two competitive pathways, namely, 1,3-H shift to 1-buten-3-yne and/β-cleavage to two molecules of ethyne. It is shown that the relative importance of the channels depends both on the energy of the photon and on the heteroatom. Specifically, the 1,3-H shift/β- cleavage ratios are 2.3 (193 nm, M = Se), 3.6 (248 nm, M = Se), 1.4 (193 nm, M = Te), and 10.5 (248 nm, M = Te). The inertness of the Te residuum and the high preference for the 1,3-H shift in KrF laser photolysis of tellurophene suggest that this photolysis can serve as a source of the C4H4 diradical for mechanistic studies.
- Pola, Josef,Ouchi, Akihiko
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p. 2759 - 2762
(2007/10/03)
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- Laser Irradiation of Monomeric Acetylene and the T-Shaped Acetylene Dimer in Xenon and Argon Matrices
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Irradiation of acetylene (4) in an argon matrix with an ArF laser (λ = 193 nm) yields the ethynyl radical C2H (5) and C2 (6). If the same wavelength is used to irradiate 4 in a xenon matrix, only the infrared signal of the compound Xe-C2 (7) can be detected. The same band is found on irradiation at λ = 248 nm (KrF laser) in a xenon matrix, despite the fact that acetylene (4) does not absorb light of this wavelength. Irradiation of the T-shaped acetylene dimer 9 in an argon or xenon matrix at λ = 193 nm yields butadiyne (11) and vinylacetylene (12). However, irradiation with a KrF laser (λ = 248 nm) in a xenon matrix additionally yields cyclobutadiene (13). The dependence of the mechanisms of the fragmentation and dimerization of acetylene (4) on the matrix material is discussed.
- Maier, Günther,Lautz, Christian
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p. 769 - 776
(2007/10/03)
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- Radical pathways in the thermal decomposition of pyridine and diazines: A laser pyrolysis and semi-empirical study
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The mechanisms of thermal decomposition of pyridine and the three isomeric diazines have been investigated by IR laser pyrolysis in conjunction with stable end-product analysis by FTIR, NMR and GC-MS, and radical detection by EPR spectroscopy. Calculations at semi-empirical and ab initio levels have provided confirmation of potential reaction pathways. For pyridine, reaction is initiated by formation of pyridyl radicals, as indicated by extensive isotope exchange with added deuterium. Experiments with bromopyridines show that open chain radicals arising from ring opening of 2-pyridyl and 3-pyridyl radicals each lead to stable gaseous products, while 4-pyridyl radicals produce solid deposits, and may be the principal agents in soot formation. The evidence suggests that 1,2-diazine decomposes via a molecular route leading to stoichiometric production of HCN and C2H2, while 1,3- and 1,4-diazine follow a pattern of H loss and ring radical opening analogous to that of pyridine.
- Hore, Nathan R.,Russell, Douglas K.
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p. 269 - 275
(2007/10/03)
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- Decomposition of 2-methylfuran. Experimental and modeling study
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The thermal reactions of 2-methylfuran were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1100-1400 K and with overall densities of approx. 3 × 10-5 mol/cm3. A large number of products resulting from unimolecular cleavage of the ring and consecutive free radical reactions were obtained under shock heating. The unimolecular decomposition is initiated by two parallel channels: (1) 1,2-hydrogen atom migration from C(5) to C(4) and (2) a methyl group migration from C(2) to C(3) in the ring. Each channel is followed by two parallel modes of ring cleavage. In the first channel, breaking the O - C(2) and the C(4) - C(5) bonds in the ring yields CO and different isomers of C4H6, whereas breaking of the O - C(2) and the C(3) - C(4) bonds yields CH2CO and two isomers C3H4. In the second channel, breaking the O - C(5), and C(2) - C(3) bonds in the ring yields again CO and isomers of C4H6, whereas in the second mode O - C(5), C(2) - C(3), and C(3) - C(4) are broken to yield CO, C2H2, and C2H4. The four C4H6 isomers in decreasing order of abundance were 1,3-butadiene, 1-butyne, 1,2-butadiene, and 2-butyne. The major decomposition product is carbon monoxide. The rate constant for its overall formation is estimated to be kCO = 1015.88 exp(-78.3 × 103/RT) s-1, where R is expressed in units of cal/(K mol). Other products that were found in the postshock samples in decreasing order of abundance were C4H4, C2H2, CH4, p-C3H4, C2H6, C2H4, a-C3H4, C6H6, C4H4O, C3H6, and C4H2. The total decomposition of 2-methylfuran in terms of a first order rate constant is given by ktotal = 1014.78 exp(-71.8 × 103/RT) s-1. This rate and the production rate of carbon monoxide are slightly higher than the ones found in the decomposition of furan. An oxygen-carbon mass balance among the decomposition products was obtained. A reaction scheme composed of 36 species and some 100 elementary reactions accounts for the product distribution over the temperature range covered in this study. First order Arrhenius rate parameters for the formation of the various reaction products are given, a reaction scheme is suggested, and results of computer simulation and sensitivity analysis are shown. Differences and similarities in the reactions of furan and 2-methylfuran are discussed.
- Lifshitz,Tamburu,Shashua
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p. 1018 - 1029
(2007/10/03)
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- 5(sulfo-/carbamoylmethyl)cyclohexenone oxime ethers
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5-(Sulfo-/carbamoylmethyl)cyclohexenone oxime ethers I STR1 where R1 =C1 -C6 -alkyl; R2 =H, C1 -C6 -alkyl, C1 -C3 -alkoxy-C1 -C3 -alkyl, C3 -C6 -cycloalkyl; R3 =C1 -C4 -alkylsulfonyl or C1 -C4 -alkylcarbonyl; Alk=a C2 -C4 -alkylene, C3 -C4 -alkenylene, C3 -C4 -alkynylene or C2 -C3 -alkyleneoxy chain, it being possible for each chain if desired to carry a C1 -C3 -alkyl group; X1, X2 and X3 =H, halogen, C1 -C4 -haloalkyl, and their salts and esters are described.
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-
- Crossed-beam reaction of carbon atoms with hydrocarbon molecules. II. Chemical dynamics of n-C4H3 formation from reaction of C(3Pj) with methylacetylene, CH3CCH (X1A1)
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The reaction between ground-state carbon atoms, C(3Pj), and methylacetylene, CH3CCH (X1A1), was studied at average collision energies of 20.4 and 33.2 kJ mol-1 using the crossed molecular beams technique. Product angular distributions and time-of-flight spectra of C4H3 at m/e=51 were recorded. Forward-convolution fitting of the data yields weakly polarized center-of-mass angular flux distributions isotropic at lower, but forward scattered with respect to the carbon beam at a higher collision energy. The translational energy flux distributions peak at 30-60 kJ mol-1 and show an average fractional translational energy release of 22%-30%. The maximum energy release as well as the angular distributions are consistent with the formation of the n-C4H3 radical in its electronic ground state. Reaction dynamics inferred from these distributions indicate that the carbon atom attacks the π-orbitals of the methylacetylene molecule via a loose, reactant like transition state located at the centrifugal barrier. The initially formed triplet 1-methylpropendiylidene complex rotates in a plane almost perpendicular to the total angular momentum vector around the BC-axes and undergoes [2,3]-hydrogen migration to triplet 1-methylpropargylene. Within 1-2 ps, the complex decomposes via C-H bond cleavage to n-C4H3 and atomic hydrogen. The exit transition state is found to be tight and located at least 30-60 kJ mol-1 above the products. The explicit identification of the n-C4H3 radical under single collision conditions represents a further example of a carbon-hydrogen exchange in reactions of ground state carbon atoms with unsaturated hydrocarbons. This channel opens a versatile pathway to synthesize extremely reactive hydrocarbon radicals relevant to combustion processes as well as interstellar chemistry.
- Kaiser,Stranges,Lee,Suits
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p. 8721 - 8733
(2007/10/03)
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- The racemization of allene, a two-Step reaction
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For four vinyl- and phenyl-substituted allenes racemization enthalpies have been determined, which are 2-6 kcal · mol-1 below the estimate derived from the parent system by correction for the additional radical stabilization of the intermediate allyldiradical 2(I), indicating the growing importance of the carbene type structure 2(II) for the intermediate. - The racemization of 1,3-dimethylallene 1b at temperatures >300°C in the presence of NO allows the trapping of an intermediate, which is considered to be the orthogonal allyl diradical 2b. From the trapping kinetics (307-388°C), the reversible bimolecular addition of NO at low temperatures (225-285°C) and the strength of the C-NO bond an enthalpy well for the singlet diradical of 2.7 kcal · mol-1 and a singlet-triplet splitting of 5.6 kcal · mol-1 is derived with the triplet being the groundstate. - The postulated intermediate diradical 2 can be stabilized electronically by phenyl and vinyl groups or by strain when incorporated in an eight-membered ring. Thermolyses of the optically active 1,2,5-cyclooctatriene 18 in the presence of oxygen allows to determine the enthalpy well of the corresponding diradical 25 to be 13.1 kcal · mol-1. VCH Verlagsgesellschaft mbH, 1996.
- Roth, Wolfgang R.,Bastigkeit, Thorsten
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p. 2171 - 2183
(2007/10/03)
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- Shock tube and modeling study of 1,3-butadiene pyrolysis
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1,3-Butadiene (1,3-C4H6) was heated behind reflected shock waves over the temperature range of 1200-1700 K and the total density range of 1.3 × 10-5-2.9 × 10-5 mol/cm3. Reaction products were analyzed by gas-chromatography. The concentration change of 1,3-butadiene was followed by UV kinetic absorption spectroscopy at 230 nm and by quadrupole mass spectrometry. The major products were C2H2, C2H4, C4H4, and CH4. The yield of CH4 for a 0.5% 1,3-C4H6 in Ar mixture was more than 10% of the initial 1,3-C4H6 concentration above 1500 K. In order to interpret the formation of CH4 successfully, it was necessary to include the isomerization of 1,3-C4H6 to 1,2-butadiene (1,2-C4H6) and to include subsequent decomposition of the 1,2-C4H6 to C3H3 and CH3. The present data and other shock tube data reported over a wide pressure range were qualitatively modeled with a 89 reaction mechanism, which included the isomerizations of 1,3-C4H6 to 1,2-C4H6 and 2-butyne (2-C4H6).
- Hidaka, Yoshiaki,Higashihara, Tetsuo,Ninomiya, Natsuhiko,Masaoka, Hiromitsu,Nakamura, Takuji,Kawano, Hiroyuki
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p. 137 - 151
(2007/10/03)
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- Small rings, 91: Fragmentation of cyclobutane in a bromine-doped and undoped xenon matrix
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Irradiation (λ = 254 nm) of cyclobutane in a bromine-doped xenon matrix leads to ring opening in spite of the fact that cyclobutane does not absorb in this region. The main products are ethene and 1-butene. The same reaction, but less effectively, occurs upon irradiation with a laser (KrF laser, λ = 248 nm) in the absence of the halogen. The difference in the mechanisms of the two fragmentations is discussed. VCH Verlagsgesellschaft mbH, 1996.
- Maier, Guenther,Senger, Stefan
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- Direct identification of photofragment structures formed in the 193 nm photodissociation of thiophene
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An experimental scheme which involves vacuum ultraviolet photoionization mass spectrometric sampling of laser photodissociation products in a pulsed supersonic molecular beam has been used to identify the isomeric structures of the 193 nm photofragments from thiophene. The primary products observed are vinylacetylene (H2C=CH-C≡CH), acetylene (C2H2), and thioketene (H2C=C=S). Using the 2 + 1 resonance-enhanced multiphoton (REMPI) scheme, we find that S atoms are produced predominantly (≥96%) in 3PJ states with a fine structure distribution of 3P2:3P1:3P0 = 0.82 ± 0.03:0.15 ± 0.03:0.03 ± 0.03. These experimental results indicate that the major dissociation channels are CH2=CH-C≡CH + S(3P) and CH=CH + CH2=C=S. Ab initio multiconfiguration self-consistent-field calculations have been made to rationalize these experimental observations.
- Hsu,Liao,Ma,Ng
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p. 1760 - 1767
(2007/10/02)
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- Thermal Isomerization and Decomposition of 1,2-Butadiene in Shock Waves
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1,2-Butadiene diluted with Ar was heated behind reflected shock waves over the temperature and the total density ranges of 1100 - 1600 K and 1.36*10-5 - 1.75*10-5 mol/cm3.The major products were 1,3-butadiene, 1-butyne, 2-butyne, vinylacetylene, diacetylene, allene, propyne, C2H6, C2H4, C2H2, CH4, and benzene, which were analyzed by gas-chromatography.The UV kinetic absorption spectroscopy at 230 nm showed that 1,2-butadiene rapidly isomerizes to 1,3-butadiene from the initial stage of the reaction above 1200 K.In order to interpret the formation of 1,3-butadiene, 1-butyne, and 2-butyne, it was necessary to include the parallel isomerizations of 1,2-butadiene to these isomers.The present data were successfully modeled with a 82 reaction mechanism.From the modeling, rate constant expressions were derived for the isomerization 1,2-butadiene = 1,3-butadiene to be k3 = 2.5*1013 exp(-63 kcal/RT) s-1 and for the decomposition 1,2-butadiene = C3H3 + CH3 to be k6 = 2.0*1015 exp(-75 kcal/RT) s-1, where the activation energies, 63 kcal/mol and 75 kcal/mol, were assumed.These rate constants are only applicable under the present experimental conditions, 1100 - 1600 K and 1.23 - 2.30 atm.
- Hidaka, Yoshiaki,Higashihara, Tetsuo,Ninomiya, Natsuhiko,Oki, Takashi,Kawano, Hiroyuki
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p. 331 - 342
(2007/10/02)
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- STUDY OF THE BEHAVIOR OF DIALKYL(3-CHLORO-2-BUTENYL)(3-p-CHLOROPHENYLPROPARGYL)AMMONIUM SALTS IN AQUEOUS ALKALINE MEDIUM. SYNTHESIS OF 2,2-DIALKYL-6-CHLORO-4-METHYL-BENZISOINDOLINIUM CHLORIDE SALTS
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Dialkyl-(3-chloro-2-butenyl)(3-p-chlorophenylpropargyl) ammonium salts undergo dehydrochlorination solution with the formation of condensed analogs of isoindolinium salts.
- Chukhadzhyan, E. O.,Atomyan, A. V.,Gevorkyan, N. T.,Chukhadzhyan, El. O.,Kinoyan, F. S.,Babayan, A. T.
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- Thermal Decomposition of 1-Butyne in Shock Waves
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1-Butyne diluted with Ar was heated behind reflected shock waves over the temperature range of 1100 - 1600 K and the total density range of 1.36*10-5 - 1.75*10-5 mol/cm3.Reaction products were analyzed by gas-chromatography.The progress of the reaction was followed by IR laser kinetic absorption spectroscopy.The products were CH4, C2H2, C2H4, C2H6, allene, propyne, C4H2, vinylacetylene, 1,2-butadiene, 1,3-butadiene, and benzene.The present data were successfully modeled with a 80 reaction mechanism. 1-Butyne was found to isomerize to 1,2-butadiene.The initial decomposition was dominated by 1-butyne -> C3H3 + CH3 under these conditions.Rate constant expressions were derived for the decomposition to be k7 = 3.0*1015 exp(-75800 cal/RT) s-1 and for the isomerization to be k4 = 2.5*1013 exp(-65000 cal/RT) s-1.The activation energy 75.8 kcal/mol was cited from literature value and the activation energy 65 kcal/mol was assumed.These rate constant expressions are applicable under the present experimental conditions, 1100 - 1600 K and 1.23 - 2.30 atm.
- Hidaka, Yoshiaki,Higashihara, Tetsuo,Oki, Takashi,Kawano, Hiroyuki
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p. 321 - 330
(2007/10/02)
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- Comparison of Reductive Dechlorination of Hexachloro-1,3-butadiene in Rhine Sediment and Model Systems with Hydroxocobalamin
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Transformations of hexachloro-1,3-butadiene were studied in columns packed with Rhine River sediment and in batch incubations containing titanium(III) citrate and hydroxocobalamin. Columns were operated under various redox conditions. Transformation was observed in a methanogenic column at influent concentrations of 4 and 400 nmol/L but not in columns where oxygen or nitrate were fed as terminal electron acceptors. Hexachloro-1,3-butadiene was reductively dechlorinated to (E,E)-1,2,3,4-tetrachlorobutadiene (> 90 percent) and traces of a trichloro-1,3-butadiene isomer ( 5 percent). (E)-1,1,2,3,4-Pentachloro-1,3-butadiene was detected as intermediary product. Reductive dechlorination in the column was ascribed to the activity of anaerobic microorganisms. In the batch experiments with titanium(III) citrate and hydroxocobalamin, hexachloro-1,3-butadiene (5 and 500 μmol/L) was transformed to an isomer of pentachloro-1,3-butadiene and two compounds with molar masses of 154 and 52, tentatively identified as trichloro-1-buten-3-yn, and 1-buten-3-yn respectively.
- Bosma, Tom N. P.,Cottaar, Francis H. M.,Posthumus, Maarten A.,Teunis, Cees J.,Veldhuizen, Albertus van,et al.
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p. 1124 - 1128
(2007/10/03)
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- Flash Vacuum Pyrolysis of Stabilised Phosphorus Ylides. Part 1. Preparation of Aliphatic and Therminal Alkynes
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Thermal extrusion of Ph3PO from β-oxoalkylidenetriphenylphosphoranes 4 to give the alkynes 5, which under conventional pyrolysis conditions is restricted to cases in which R1 is an electron withdrawing group, has been successfully achieved for R1=H or alkyl by using FVP.The method allows convenient construction of multigram quantities of the alkynes 5 from alkyl halides 1 and allows convenient construction of multigram quantities of the alkynes 5 from alkyl halides 1 and acid chlorides 3 in three steps with good overall yields.Under the conditions used the ylides with R2 = cyclobutyl also undergo less of ethene to provide convenient access to the vinylalkynes 6.
- Aitken, R. Alan,Atherton, J. Ian
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p. 1281 - 1284
(2007/10/02)
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- DIMETHYLCADMIUM, DIMETHYLTELLURIUM, AND DIETHYLMERCURY DISSOCIATION IN AN ELECTRICAL DISCHARGE
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The volatile dissociation products composition of dimethylcadmium, diethyltellurium, and diethylmercury and their binary mixtures have been determined in an electric discharge in a hydrogen stream at room temperature, and compared with the thermal dissociation products composition of the same materials in similar dynamic gas conditions at 200 to 400 deg C.It has been shown that estimating the acetylene concentration allows control over the contamination level in the deposited residue due to carbon.
- Faerman, V. I.,Varakina, E. V.
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p. 116 - 120
(2007/10/02)
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- La photochimie du cis-penta-1,3-diene, en phase gazeuse a 184,9 et 147,0 nm
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We have studied the 184,9 and 147.0 nm photochemistry of gaseous cis-1,3-pentadiene: the main products observed at 184.9 nm are trans-1,3-pentadiene and 1,3-cyclopentadiene.The formation of radicals also occurs as shown through the use of DI as a radical scavenger.Cyclopentadiene is the likely product of successive eliminations of two hydrogen atoms from the photoexcited molecule after rearrangement of the pentadienyl radical to the cyclopentenyl structure: Φ0(cyclo-C5H6) ca.0.25.Elimination of a methyl radical (Φ0 ca. 0.50) also occurs, with formation of CH2=CHCH=CH* and, in a lower yield, CH2=C=CHCH2*.However, it is not possible to identify properly the mechanism of the formation of the latter radical.It may be the result of the isomerization of either the first photoexcited molecule or the excited 1,3-butadienyl radicals.A small amount of 1,4-pentadiene formation is also observed (Φ0 ca 0.035 +/- 0.015).At 147.0 nm, the same characteristics are observed, together with higher fragmentation due to the higher energy content of the photoexcited molecules.It appears that the photofragmentation at both wavelengths is more in line with that of acyclic alkenes than with that of 1,3-butadiene, which tends to undergo isomerization of the photoexcited molecules to the 1,2-butadiene structure. Key words: 1,3-pentadiene, far UV, vacuum UV, photolysis, monomolecular, fragmentation, stabilization.
- Collin, Guy J.,Deslauriers, Helene,Mare, George R. De
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p. 1245 - 1251
(2007/10/02)
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- Kinetics of Pyrolysis of Furan
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The kinetics of pyrolysis of furan vapour diluted in argon have been studied behind reflected shock waves in a shock tube both by time-resolved infrared CO2 laser absorption spectrometry and by single pulse shock techniques of product analysis over the temperature range 1100-1700 K, at pressures of ca. 20 atm and at uniform residence times of ca. 300 μs.The rate of overall disappearance of furan, as measured by absorption spectrometry, was found to be first order in furan concentration, with a rate constant of koverall = 1015.3+/-0.3 exp-1/RT>s-1 in agreement with a previous determination by Lifshitz et al. (A.Lifshitz, M.Bidani and S.Bidani, J.Phys.Chem., 1986, 90, 5373).Principal products were carbon monoxide, C3H4 (propyne and allene) and acetylene.Ketene was identified in the products by FTIR spectroscopy.A detailed chemical reaction model for the pyrolysis was developed and shown to give good predictions of the concentration profiles of furan and the major products.Modelling and thermochemical considerations led to the postulate that the initiation of pyrolysis takes place by C-O bond scission to a biradical which can undergo decomposition, via parallel reaction paths, to the observed products.
- Organ, Phillip P.,Mackie, John C.
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p. 815 - 823
(2007/10/02)
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- Convenient Procedures for t-Butylacetylene and Vinylacetylene
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Treatment of the dichlorides t-C4H9CH2CHCl2 and E-ClCH2CH=CHCH2Cl with a suspension of powdered potassium hydroxide in high-boiling petroleum at elevated temperatures in the presence of Aliquat-336 and pinacol gives t-butylacetylene and vinylacetylene in high yields.Vinylacetylene is also obtainable by treating E-ClCH2CH=CHCH2Cl with a concentrated aqueous solution of KOH in the presence of Aliquat-336.
- Verkruijsse, H.D.,Brandsma, L.
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p. 3355 - 3358
(2007/10/02)
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- Shock Tube Pyrolysis of Pyridine
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The kinetics of pyridine dilute in argon have been studied in a single-pulse shock tube, using cappilary column GC together with GC/MS and FTIR spectroscopy for product determination, over the temperature range of 1300-1800 K and total pressures of 7-11 atm.At the lower end of the studied temperatures, cyanoacetylene was found to be the principal nitrogen-containing product.At elevated temperature hydrogen cyanide predominated.Other major products were acetylene and hydrogen.Thermochemical estimates of the isomeric cyclic pyridyls produced in the pyrolysis indicate that the ortho isomer is unique in being able to undergo facile cleavage to an open-chain cyano radical from which cyanoacetylene is produced.Several sources of HCN were identified in the system.The m- and p-pyridyls may eliminate HCN in a molecular process.An important source of HCN at high temperatures is the addition of H-atoms to cyano compounds, especially cyanoacetylene, but also acetonitrile and acrylonitrile which are produced in the pyrolysis.The pyrolysis is a chain process initiated principally by C-H bond fission to form o-pyridyl.A 58-step reaction model is presented and shown to substantially fit the observed profiles of the major product species.From this model we derive a value for the rate constant of the principal initiation reaction, C5H5N --> o-C5H4N + H (1), of k1=1015.9+/-0.4exp(-98 +/- 3 kcal mol-1/RT)s-1 between 1300 and 1800 K and at a total pressure of about 10 atm.
- Mackie, John C.,Colket III, Meredith B.,Nelson, Peter F.
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p. 4099 - 4106
(2007/10/02)
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