- Asymmetric Counteranion Directed Catalytic Heck/Tsuji-Trost Annulation of Aryl Iodides and 1,3-Dienes
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A chiral anion-mediated asymmetric Heck/Tsuji-Trost reaction of aryl iodides and 1,3-dienes is presented. Chiral indoline derivatives could be afforded with remarkably higher yields and enantioselectivities than our previous chiral ligand-based method. Silver carbonate is employed as both base and halide scavenger to ensure fast and recyclable exchange of the catalytic amount of chiral anions. Fast salt metathesis, as well as the acceleration effect of the chiral anion, could both benefit the stereocontrol of the reaction.
- Xu, Jia-Cheng,Yin, Yi-Zhuo,Han, Zhi-Yong
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supporting information
p. 3834 - 3838
(2021/05/26)
-
- CATALYTIC HYDROCARBON DEHYDROGENATION
-
A catalyst for dehydrogenation of hydrocarbons includes a support including zirconium oxide and Linde type L zeolite (L-zeolite). A concentration of the zirconium oxide in the catalyst is in a range of from 0.1 weight percent (wt. %) to 20 wt. %. The catalyst includes from 5 wt. % to 15 wt. % of an alkali metal or alkaline earth metal. The catalyst includes from 0.1 wt. % to 10 wt. % of tin. The catalyst includes from 0.1 wt. % to 8 wt. % of a platinum group metal. The alkali metal or alkaline earth metal, tin, and platinum group metal are disposed on the support.
- -
-
Paragraph 0056; 0122; 0123
(2021/03/13)
-
- Palladium-Catalyzed Chemoselective Protodecarboxylation of Polyenoic Acids
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Conditions for the first palladium-catalyzed chemoselective protodecarboxylation of polyenoic acids to give the desired polyenes in good yields are presented. The reactions proceed under mild conditions using either a Pd(0) or Pd(II) catalyst and tolerate a variety of aryl and aliphatic substitutions. Unique aspects of the reaction include the requirement of phosphines, water, and a polyene adjacent to the carboxylic acid.
- Al-Huniti, Mohammed H.,Perez, Mark A.,Garr, Matthew K.,Croatt, Mitchell P.
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supporting information
p. 7375 - 7379
(2019/01/03)
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- Ring Opening of Biomass-Derived Cyclic Ethers to Dienes over Silica/Alumina
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We show that cyclic ethers, such 2-methyltetrahydrofuran (2-MTHF), can undergo dehydration to produce pentadienes over SiO2/Al2O3. The catalyst exhibited reversible deactivation due to coke deposition, with the yield to pentadienes decreasing from 68% to 52% at 623 K over 58 h time on stream. A reaction network for 2-MTHF dehydration was proposed on the basis of the results of space time studies. Pentadienes can be produced directly by a concerted hydride shift and dehydration of carbenium intermediates or indirectly through dehydration of pentanal and pentenol. Reaction kinetics studies were performed at temperatures ranging from 573 to 653 K and 2-MTHF partial pressures from 0.21 to 2.51 kPa. The apparent activation energy barrier for 2-MTHF conversion to pentadienes and the reaction rate order for ring opening were determined to be 74 kJ mol-1 and 0.24, respectively, indicating strong interaction between 2-MTHF and the SiO2/Al2O3 surface. Other solid acids such as γ-Al2O3, H-ZSM-5, and Al-Sn-Beta were found to be active for 2-MTHF dehydration to pentadienes. The rate of ring opening decreased in the order 2,5-dimethyltetrahydrofuran > 2-MTHF > tetrahydropyran > tetrahydrofuran. Over SiO2/Al2O3, the dehydration of 2,5-dimethyltetrahydrofuran resulted in 75% yield to hexadiene isomers. (Figure Presented).
- Kumbhalkar, Mrunmayi D.,Buchanan, J. Scott,Huber, George W.,Dumesic, James A.
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p. 5248 - 5256
(2017/08/17)
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- Production of renewable 1,3-pentadiene from xylitol via formic acid-mediated deoxydehydration and palladium-catalyzed deoxygenation reactions
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A two-step synthetic approach for the production of renewable 1,3-pentadiene was reported: xylitol deoxydehydration (DODH) by formic acid to 2,4-pentadien-1-ol, 1-formate (2E), followed by deoxygenation to 1,3-pentadiene over Pd/C. The overall carbon yield of 1,3-pentadiene reached 51.8% under the optimized conditions.
- Sun, Ruiyan,Zheng, Mingyuan,Li, Xinsheng,Pang, Jifeng,Wang, Aiqin,Wang, Xiaodong,Zhang, Tao
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supporting information
p. 638 - 642
(2017/02/26)
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- High yields of piperylene in the transfer dehydrogenation of pentane catalyzed by pincer-ligated iridium complexes
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Conjugated dienes are desirable reagents for several important applications. We report that sterically uncrowded PCP-pincer iridium complexes, including precursors of (iPr4PCP)Ir and (Me2tBu2PCP)Ir, catalyze the transfer d
- Kumar, Akshai,Hackenberg, Jason D.,Zhuo, Gao,Steffens, Andrew M.,Mironov, Oleg,Saxton, Robert J.,Goldman, Alan S.
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p. 368 - 375
(2016/12/16)
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- New cofactor supports α,β-unsaturated acid decarboxylation via 1,3-dipolar cycloaddition
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The bacterial ubiD and ubiX or the homologous fungal fdc1 and pad1 genes have been implicated in the non-oxidative reversible decarboxylation of aromatic substrates, and play a pivotal role in bacterial ubiquinone (also known as coenzyme Q) biosynthesis or microbial biodegradation of aromatic compounds, respectively. Despite biochemical studies on individual gene products, the composition and cofactor requirement of the enzyme responsible for in vivo decarboxylase activity remained unclear. Here we show that Fdc1 is solely responsible for the reversible decarboxylase activity, and that it requires a new type of cofactor: a prenylated flavin synthesized by the associated UbiX/Pad1. Atomic resolution crystal structures reveal that two distinct isomers of the oxidized cofactor can be observed, an isoalloxazine N5-iminium adduct and a N5 secondary ketimine species with markedly altered ring structure, both having azomethine ylide character. Substrate binding positions the dipolarophile enoic acid group directly above the azomethine ylide group. The structure of a covalent inhibitor-cofactor adduct suggests that 1,3-dipolar cycloaddition chemistry supports reversible decarboxylation in these enzymes. Although 1,3-dipolar cycloaddition is commonly used in organic chemistry, we propose that this presents the first example, to our knowledge, of an enzymatic 1,3-dipolar cycloaddition reaction. Our model for Fdc1/UbiD catalysis offers new routes in alkene hydrocarbon production or aryl (de)carboxylation.
- Payne, Karl A. P.,White, Mark D.,Fisher, Karl,Khara, Basile,Bailey, Samuel S.,Parker, David,Rattray, Nicholas J.W.,Trivedi, Drupad K.,Goodacre, Royston,Beveridge, Rebecca,Barran, Perdita,Rigby, Stephen E. J.,Scrutton, Nigel S.,Hay, Sam,Leys, David
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supporting information
p. 497 - 501
(2015/07/02)
-
- CATALYTIC DEHYDRATION OF ALCOHOLS AND ETHERS OVER A TERNARY MIXED OXIDE
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A ternary V—Ti—P mixed oxide is shown to catalytically dehydrate 2-methyl-tetrahydrofuran in high conversion to give piperylene, in good yield. Volatile products collected from this reaction contain piperylene in concentrations as high as 80 percent by weight. Dehydration of glycerol to acrolein in high conversion and moderate selectivity is also demonstrated. The catalyst is also shown to dehydrate other alcohols and ether substrates. The catalyst is resistant to deactivation and maintains activity between runs.
- -
-
Paragraph 0029; 0046
(2013/03/28)
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- Z-selective metathesis homocoupling of 1,3-dienes by molybdenum and tungsten monoaryloxide pyrrolide (MAP) complexes
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Molybdenum or tungsten monoaryloxide pyrrolide (MAP) complexes that contain OHIPT as the aryloxide (hexaisopropylterphenoxide) are effective catalysts for homocoupling of simple (E)-1,3-dienes to give (E,Z,E)-trienes in high yield and with high Z selectivities. A vinylalkylidene MAP species was shown to have the expected syn structure in an X-ray study. MAP catalysts that contain OHMT (hexamethylterphenoxide) are relatively inefficient.
- Townsend, Erik M.,Schrock, Richard R.,Hoveyda, Amir H.
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supporting information; experimental part
p. 11334 - 11337
(2012/09/05)
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- Ni(0)-catalyzed 1,4-selective diboration of conjugated dienes
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Figure Presented. A catalytic stereoselective 1,4-diboration of conjugated dienes with B2(pin)2 was accomplished with Ni(cod) 2 and PCy3 as the catalyst. This reaction broadens the substrate scope of current methods for catalytic diene diboration by including internal and sterically hindered dienes, and it proceeds efficiently at low catalyst loadings. The intermediate allylboronate was oxidized to the stereodefined allylic 1,4-diol.
- Ely, Robert J.,Morken, James P.
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supporting information; experimental part
p. 4348 - 4351
(2010/11/19)
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- Multiphoton infrared initiated thermal reactions of esters: Pseudopericyclic eight-centered cis-elimination
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Multiphoton infrared absorption from a focused, pulsed CO2 laser was used to initiate gas-phase thermal reactions of cis- and trans-3-penten-2-yl acetate. By varying the helium buffer gas pressure, it was possible to deduce the product distribution from the initial unimolecular reactions, separate from secondary reactions in a thermal cascade. Thus, trans-3-penten-2-yl acetate gives 54 ± 5% of β-elimination to give trans-1,3-pentadiene, 40 ± 3% of [3,3]-sigmatropic rearrangement to give cis-3-penten-2-yl acetate and 6 ± 4% of cis-1,3-pentadiene. Similar irradiation of cis-3-penten-2-yl acetate gives 45 ± 1% of β-elimination to give cis-1,3-pentadiene, 32 ± 2% of [3,3]-sigmatropic rearrangement to give trans-3-penten-2-yl acetate and 23 ± 2% of trans-1,3-pentadiene. The latter process is an eight-centered δ-elimination, which is argued to be a pseudopericyclic reaction. Although β-eliminations have been suggested to be pericyclic, B3LYP/ 6-31G(d,p), MP2 and MP4 calculations suggest that both β- and δ-eliminations, as well as [3,3]-sigmatropic rearrangements of esters are primarily pseudopericyclic in character, as judged by both geometrical, energetic and transition state aromaticity (NICS) criteria. Small distortions from the ideal pseudopericyclic geometries are argued to reflect small pericyclic contributions. It is further argued that when both pericyclic and pseudopericyclic orbital topologies are allowed and geometrically feasible, the calculated transition state may be the result of proportional mixing of the two states; this offers an explanation of the range of pseudopericyclic and pericyclic characters found in related reactions.
- Ji, Hua,Li, Li,Xu, Xiaolian,Ham, Sihyun,Hammad, Loubna A.,Birney, David M.
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supporting information; experimental part
p. 528 - 537
(2009/06/28)
-
- Propylene and isoprene production
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A process for producing propylene and isoprene from a feed stream comprising 1-butene and isobutene is disclosed. The feed stream is reacted in a catalytic distillation reactor containing an olefin isomerization catalyst to produce an overhead stream comprising 2-butene and isobutene and a bottoms stream comprising 2-butene. The overhead stream is reacted in the presence of a metathesis catalyst to produce propylene and isoamylenes. Isoprene is produced by dehydrogenation of isoamylenes.
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Page/Page column 3-4
(2009/03/07)
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- Diastereoselective construction of functionalized homoallylic alcohols by Ni-catalyzed diboron-promoted coupling of dienes and aldehydes
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The nickel-catalyzed reaction of carbonyls and dienes was accomplished in a regio- and stereoselective fashion employing a stoichiometric amount of bis(pinacolato)diboron. This reductive coupling furnishes an allyl boronic ester as the reaction product, a compound which was readily converted to the derived allylic alcohol by oxidative workup. Copyright
- Hee, Yeon Cho,Morken, James P.
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body text
p. 16140 - 16141
(2009/05/08)
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- Moving bed process for producing propylene, recycling a fraction of used catalyst
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The invention concerns a process for producing propylene from a steam cracking and/or catalytic cracking light olefinic cut, said process comprising a moving bed catalytic cracking step with a catalyst regeneration loop. The process recycles a portion of the used catalyst to the inlet of the moving bed reactor. The conversion is high using the process of the invention, with a good yield and good propylene selectivity.
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Page/Page column 5-6
(2008/06/13)
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- A general one-pot synthesis of vinyl-thiiranes and conjugated dienes
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The first general synthesis of vinyl-thiiranes 7 and an effiecient preparation of conjugated dienes 8 and 9 is presented. Methodology described for the preparation of these compounds is based on the corresponding readily available thiophosphates 1 and selenophosphates 2.
- Maciagiewicz,Dybowski,Skowronska
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p. 515 - 523
(2007/10/03)
-
- Investigation of bicyclic thioketones as triggers for liquid crystal optical switches
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The axially chiral bicyclic thioketones 11 and 15 were prepared and investigated for suitability as chiroptical triggers in a liquid crystal optical switch. Irradiation of partially resolved 15 with unpolarized light leads to its conversion to the racemic form (photoracemization). However, irradiation of racemic thioketones 11 and 15 with circularly polarized light does not lead to detectable photoresolution. The lack of photoresolution was traced to inefficiency in intramolecular, throughbond triplet energy transfer. These thioketones are not suitable for use as phototriggers.
- Bradford, Rochelle Fisher,Schuster, Gary B.
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p. 1075 - 1080
(2007/10/03)
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- Equilibrium constants for dehydration of water adducts of aromatic carbon-carbon double bonds
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Equilibrium constants (Kde) are reported for the dehydration of hydrates of benzene, naphthalene, phenanthrene, and anthracene. Free energies of formation of the hydrates (ΔG°f(aq)) are derived by combining free energies of formation of the parent (dihydroaromatic) hydrocarbon with estimates of the increment in free energy (ΔGOH) accompanying replacement of a hydrogen atom of the hydrocarbon by a hydroxyl group. Combining these in turn with free energies of formation of H2O and of the aromatic hydrocarbon products furnishes the desired equilibrium constants, The method depends on the availability of thermodynamic data (i) for the hydrocarbons from which the hydrates are derived by hydroxyl substitution and (ii) for a sufficient range of alcohols to assess the structural dependence of ΔGOH. The data comprise chiefly heats of formation and standard entropies in the gas phase and free energies of transfer from the gas phase to aqueous solution (the latter being derived from vapor pressures and solubilities). They also include experimental measurements of equilibrium constants for dehydration of alcohols, especially cyclic, allylic, and benzylic alcohols. In general ΔGOH depends on whether the alcohol is (a) primary, secondary, or tertiary; (b) allylic or benzylic; and (c) open chain or cyclic. Differences in geminal interactions of the hydroxyl group of the alcohol with α-alkyl and vinyl or phenyl groups account for variations in ΔGOH of 5 kcal mol-1. Weaker variations which arise from β-vinyl/OH or β-phenyl/OH interactions present in the aromatic hydrates but not in experimentally studied analogues are estimated as 1.0 kcal mol-1. Equilibrium constants for dehydration may be expressed as their negative logs (pKde). Reactions yielding the following aliphatic, aromatic, and antiaromatic unsaturated products then have pKde values: +4.8, ethene; +15.0, ethyne; +22.1, cyclopropene; +28.4 cyclobutadiene; -22.2, benzene; -14.6, naphthalene; -9.2, phenanthrene; -7.4, anthracene. Large positive values are associated with formation of strained or antiaromatic double bonds and large negative values with aromatic double bonds. Trends in pKde parallel those of heats of hydrogenation. The results illustrate the usefulness of a substituent treatment for extending the range of currently available free energies of formation. In addition to hydroxyl substituent effects, ΔGOH, values of ΔGπ for substitution of a π-bond in a hydrocarbon are reported.
- Dey, Joykrishna,O'Donoghue, AnnMarie C.,More O'Ferrall, Rory A.
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p. 8561 - 8574
(2007/10/03)
-
- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
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Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
-
- Fine particle and gaseous emission rates from residential wood combustion
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Residential wood combustion emissions were analyzed to determine emission rates and to develop chemical emissions profiles that represent the appliances and woods typically used in wood-burning-communities. Over 350 elements, inorganic compounds, and organic compounds were quantified. A range of 4-9 g/kg dry fuel of particulate matter(a dilution stack sampler equipped with a 2.5-μm particle selective cyclone. Emissions were diluted 20-70 times, cooled to ambient temperature, and allowed 80 s for condensation prior to collection. Wood type, wood moisture, burn rate, and fuel load were varied for different experiments. Fine particle and se mivolatile organic compounds were collected on filter/PUF/XAD/PUF cartridges. Inorganic samples and mass were collected on Teflon and quartz filters. Volatile organic carbon compounds were trapped with Tenax (C8- C20), canister (C2-C12), and 2,4-dinitrophenylhydrazine impregnated cartridges (carbonyl compounds). Analysis of particle and semivolatile organic species was conducted by gas chromatography/mass spectrometry. Teflon filters were analyzed for mass by gravimetry, trace elements were analyzed by X-ray fluorescence and ammonium was analyzed by automated colorimetry. Quartz filters were analyzed for organic and elemental carbon by thermal/optical reflectance, and forts were analyzed by ion chromatography. Select quartz filters were analyzed by accelerator mass spectrometry for carbon-12 and carbon-14 abundance. Canister and Tenax samples were analyzed by gas chromatography with a flame ionization detector, and carbonyl compounds were analyzed by high-performance liquid chromatography. Residential wood combustion emissions were analyzed to determine emission rates and to develop chemical emissions profiles that represent the appliances and woods typically used in wood-burning communities. Over 350 elements, inorganic compounds, and organic compounds were quantified. A range of 4-9 g/kg dry fuel of particulate matter (a dilution stack sampler equipped with a 2.5-μm particle selective cyclone. Emissions were diluted 20-70 times, cooled to ambient temperature, and allowed 80 s for condensation prior to collection. Wood type, wood moisture, burn rate, and fuel load were varied for different experiments. Fine particle and semivolatile organic compounds were collected on filter/PUF/XAD/PUF cartridges. Inorganic samples and mass were collected on Teflon and quartz filters. Volatile organic carbon compounds were trapped with Tenax (C8-C20), canister (C2-C12), and 2,4-dinitrophenylhydrazine impregnated cartridges (carbonyl compounds). Analysis of particle and semivolatile organic species was conducted by gas chromatography/mass spectrometry. Teflon filters were analyzed for mass by gravimetry, trace elements were analyzed by X-ray fluorescence, and ammonium was analyzed by automated colorimetry. Quartz filters were analyzed for organic and elemental carbon by thermal/optical reflectance, and ions were analyzed by ion chromatography. Select quartz filters were analyzed by accelerator mass spectrometry for carbon-12 and carbon-14 abundance. Canister and Tenax samples were analyzed by gas chromatography with a flame ionization detector, and carbonyl compounds were analyzed by high-performance liquid chromatography.
- Mcdonald, Jacob D.,Zielinska, Barbara,Fujita, Eric M.,Sagebiel, John C.,Chow, Judith C.,Watson, John G.
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p. 2080 - 2091
(2007/10/03)
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- Gas-phase kinetic and mechanistic studies of some interconverting alkylcyclopropene pairs: Involvement of dialkylvinylidene intermediates and their quantitative behaviour
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The pyrolyses of two isomeric pairs of alkylcyclopropenes, namely 1,3-dimethyl- (15) and 1-ethyl-cyclopropene (16), and 1,3,3-trimethyl- (5) and 1-isopropyl-cyclopropene (17), have been studied in the gas phase. Complete product analyses at various conversions up to 95% were obtained for the decomposition of each compound at five temperatures over a 40°C range. The time-evolution data showed that the isomerisation reactions 15?16 and 5?17 were occurring. Kinetic modelling of each system allowed the determination of rate constants for these and all other decomposition processes. Tests confirmed that all reactions were unimolecular and homogeneous. Arrhenius parameters are reported for overall reactions and individual product pathways. Further kinetic analysis allowed us to extract the propensities (at 500 K) for 1,3-C-H insertion of the dialkylvinylidene intermediates involved in the rearrangements as follows: kprim:ksec: ktert = 1:16.5:46.4. Additional experiments with 13C-labelled cyclopropenes yielded alkyl group migration aptitudes for the dialkylvinylidenes (from the pattern of 13C in the alkyne products) as follows: Me:Et:iPr=1:3.1:1.5. Explanations for these trends are given. Another important finding is that of the dramatic rate enhancements for 1,3-diene product formation from the 1-alkylcyclopropenes; this can be explained by either hyperconjugative stabilisation of the vinylcarbene intermediates involved in this pathway, or their differing propensities to 1,2 H-shift. The observed large variations in product distribution amongst these four cyclopropenes is interpreted in terms of these specific effects on individual pathways.
- Graf Von Der Schulenburg, Wilhelm,Hopf, Henning,Walsh, Robin
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p. 1963 - 1979
(2007/10/03)
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- A general one-pot synthesis of vinyl-thiiranes and conjugated dienes
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The first general synthesis of vinyl-thiiranes 5 and an efficient preparation of conjugated dienes 6 and 7 based on thio, and selenophosphates is described.
- Maciagiewicz,Dybowski,Skowronska
-
p. 3791 - 3794
(2007/10/03)
-
- Catalytic transformations of vinylthiiranes by tungsten carbonyl complexes. A new route to 3,6-dihydro-1,2-dithiins
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W(CO)5(NCMe) (1) has been found to transform vinylthiirane and a series of methyl-substituted vinylthiiranes into a series of 3,6-dihydro-1,2-dithiin compounds. Two equivalents of the vinylthiirane are required, and 1 equiv of a butadiene is formed by the transfer of its sulfur atom to the second vinythiirane, which is then transformed into the dihydrodithiin. The formation of 3,6-dihydro-1,2-dithiin (9) proceeds at 15 turnovers/h at 25°C using vinylthiirane (4) and 1 as the catalyst. The catalyst is long-lived (up to 2000 turnovers have been obtained without loss of activity) and relatively insensitive to air. Methyl substitutents on the vinyl group increase the rate of reaction while methyl substituents on the thiirane ring slow it considerably. The introduction of phosphine ligands to the catalyst also leads to significant increases in the rate of reaction. The dithiin complex W(CO)5(SSCH2CH=CHCH2) (13) was isolated from the catalytic reactions and was structurally characterized. The dihydrodithiin is coordinated to the tungsten atom through one of its two sulfur atoms. Compound 13 was shown to be a species in the catalytic cycle. A mechanism involving a vinylthiirane intermediate that undergoes spontaneous ring opening, followed by addition of a second vinylthiirane to the terminal carbon of the chain, elimination of 1 equiv of butadiene, and formation of a sulfur-sulfur bond leading to 13 is proposed. The vinylthiirane intermediate is regenerated by ligand substitution which releases the dihydrodithiin product. Compound 9 readily polymerizes when its pure form is exposed to visible light. If the polymerization is interrupted at an early stage, 1,2,7,8-tetrathiacyclododeca-4,10-diene (14), a dimer of 9, can be isolated. Compound 14 was obtained in 5.6% yield and was structurally characterized crystallographically.
- Adams, Richard D.,Perrin, Joseph L.
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p. 3984 - 3991
(2007/10/03)
-
- (E)- And (Z)-1-(Phenylsulfonyl)-4-(trimethylsilyl)-2-butenes: Synthetic Equivalents for the 1-(1,3-Butadienyl) Anion and the 1,1-(1,3-Butadienyl) Dianion
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(E)- and (Z)-1-(phenylsulfonyl)-4-(trimethylsilyl)-2-butenes (7 and 8) are converted by n-BuLi to (E)- and (Z)-1-lithio-1-(phenylsulfonyl)-4-(trimethylsilyl)-2-butenes (15 and 16) with retention of initial stereochemistries. Reactions of 15 and 16 with electrophiles (protio and deuterio acids, primary, secondary, and benzyl halides, chloroformates, chlorothioformates, acid chlorides, epoxides, trialkylsilyl chlorides, and triethylgermanyl chloride) in THF or THF/HMPA give the corresponding (E)- and (Z)-1-(phenylsulfonyl)-1-substituted-4-(trimethylsilyl)-2-butenes (32) with stereochemical retention. That β,γ-unsaturated silyl sulfones 32 are formed instead of their α,β-unsaturated (conjugated) isomers are attributed to stabilizing multiple anionic and cationic hyperconjugation and to steric effects as in 29-31. Of importance in synthesis is that 32 are eliminated by TBAF at -20 to 0°C, thermally, or by column chromatography to (E)- (100 to > 93%) rather than (Z)-1-substituted-1,3-butadienes (38). Further, 32 undergo conversions by n-BuLi and various alkylating agents to (unconjugated) 1-(phenylsulfonyl)-1,1-disubstituted-4-(trimethylsilyl)-2-butenes (46) with retention of stereochemistry. Eliminations of 46 by fluoride ion, acid catalysis, or heat yield 1,1-disubstituted-1,3-butadienes (53). Silyl sulfones 7 and 8 are thus synthetic equivalents for the (E)-1-(1,3-butadienyl) anion (44) and the 1,1-(1,3-butadienyl) dianion (57). Silyl sulfones 7 and 8 also undergo efficient stereospecific intramolecular conversions by n-BuLi and α,ω-dihalides to 1,1-cycloalka-1-(phenylsulfonyl)-4-(trimethysilyl)-2-butenes (62 and 71) that are eliminated by fluoride ion, heat, or adsorption chromatography to 1,1-cycloalka-1,3-butadienes (72).
- Meagher, Timothy P.,Yet, Larry,Hsiao, Chi-Nung,Shechter, Harold
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p. 4181 - 4192
(2007/10/03)
-
- Homolytic Bond Dissociation Enthalpies of the C-H Bonds Adjacent to Radical Centers
-
Homolytic bond dissociation enthalpies (BDEs) at 0 and 298 K of the C-H bonds adjacent to various radical centers have been obtained from ab initio CBS-4 (complete basis set) model calculations and experimental data available in the literature. The BDEs of the G-H bonds adjacent to the radical centers derived from 11 saturated hydrocarbons were found to be 33.5 ±3 kcal/mol at 298 K. The BDEs of the C-H bonds adjacent to nine allylic and benzylic radical centers were found to be 48 ±3 kcal/mol at 298 K, but the benzylic C-H BDE of the PhCH2CH2 radical was found to be only 29.7 and 30.5 kcal/mol at 0 and 298 K, respectively. The BDEs of the vinylic C-H bonds adjacent to four vinylic radical centers were found to be 35.5 ±3.5 kcal/mol at 298 K. The BDEs of the vinylic C-H bonds adjacent to three allylic radical centers were found to be 56.5 ±3 kcal/ mol at 298 K. These results suggest that the radical centers weaken the adjacent C-H bond strengths by about 50-70 kcal/mol. The calculated BDEs agree within ±2 kcal/mol with most of the available experimental results. Isomerization enthalpies of butenes and pentenes have been obtained. Substituent effects on BDEs have also been examined.
- Zhang, Xian-Man
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p. 1872 - 1877
(2007/10/03)
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- Hydroformylation process for producing 1,6-hexanedials
-
This invention relates to a hydroformylation process for producing a 1,6-hexanedial which comprises reacting a butadiene with hydrogen and carbon monoxide in the presence of a catalytic amount of rhodium complexed with certain poly-phosphite ligands to achieve high conversions of the butadiene to the 1,6-hexanedial.
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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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- Photochemistry of Polyhaloarenes. 8. The Photodechlorination of Pentachlorobenzene
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Measurements of the intersystem crossing yield of pentachlorobenzene triplet, the quenching of photodechlorination of pentachlorobenzene with fumaronitrile, the dependence of the fluorescence lifetime, and the quantum yield of photodechlorination of pentachlorobenzene upon substrate concentration and the dependence of relative product concentration upon light intensity provide evidence for three pathways to product: direct fission of singlet and triplet and fragmentation of triplet excimer.
- Freeman, Peter K.,Ramnath, N.,Richardson, Alan D.
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p. 3643 - 3646
(2007/10/02)
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- Decomposition of 4,4-Dimethylpent-1-ene in the Presence of Oxygen between 400 and 500 deg C: Oxidation Chemistry of Allyl Radicals
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The decomposition of 4,4-dimethylpent-1-ene (DMP) in the presence of O2 has been used as a source of allyl radicals over the temperature range 400-500 deg C.The reaction has been studied in both KCl-coated (peroxy species destroyed at the surface) and aged boric-acid-coated vessels (peroxy species preserved), and the basic mechanism shown to be: (1) (2).Previous studies have shown that 99percent of the t-butyl radicals undergo reaction (2), so that the system is an excellent source of allyl and HO2 radicals.A full product analysis has carried out over a wide range of mixture composition and associated mechanistic aspects discussed.It is shown that allyl radicals are unreactive towards both DMP and O2 and that they react mainly in radical-radical processes. (3) (8) (18).Values of k8/k18 = 0.37, 0.38 and 0.42 are obtained at 400, 440 and 480 deg C, respectively.From a reasonably reliable estimate of and , values of k8 = (3.3 +/- 0.9) * 1E9 and k18 = (7.4 +/- 2.4) * 1E9 dm3 mol-1 s-1 are obtained at 480 deg C.No previous estimates of these rate constants are available in the literature.Values of k4 have been determined and when combined with independent data at higher temperatures give log(A4/s-1) = 14.19 +/- 0.25 and E4 = 255.5 +/- 5.3 kJ mol-1 over the range 400-1025 deg C.DMP -> (CH3)2C=CH2 + CH3CH=CH2 (4).A value of K11 = (2.5 +/- 1) * 1E2 dm3 mol-1 s-1 has been obtained at 480 deg C and shown to be consistent with the reaction's high endothermicity. (11)
- Lodhi, Zulfiqar H.,Walker, Raymond W.
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p. 681 - 689
(2007/10/02)
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- STANNYLDIENES, NEW TOOLS FOR ORGANIC SYNTHESIS. PREPARATION AND REACTIVITY.
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Tributylstannyl-1,3-dienes could be considered synthetic equivalents of conjugated dienic anions.The preparation of differently substituted 2- and 3-trialkylstannyl-1,3-dienes is reported starting from propargyltrimethylsilane.The position of the stannyl moiety on the dienic skeleton can be controlled by hydrostannylation of (trimethylsilyl)propargyl alcohols or stannyl cupration of (trimetylsilyl)propargyl ketones.The so obtained stannyldienes are submitted to Diels Alder reaction and the corresponding cycloadducts functionalized through the C-Sn bond.Stannyldienes are also suitable for a regiocontrolled transfer of the dienic structure by : a) tin-lithium exchange and further reaction with aldehydes to give conjugated dienic alcohols; b)coupling with acyl chlorides in the presence of palladium catalysts to give conjugated dienic ketones; c) AlCl3 promoted reaction with acyl chlorides to give allenic ketones.
- Nativi, Cristina,Taddei, Maurizio,Mann, Andre
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p. 1131 - 1144
(2007/10/02)
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- Non-perfect Synchronisation of β-Scission with Product Stabilisation in Radical Ring-opening Reactions
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Reduction of cyclobut-2-enylmethyl bromide with tri-n-butyltin hydride gave 3-methylcyclobutene together with trans- and cis-penta-1,3-diene and penta-1,4-diene.The diene products are formed by β-scission of the intermediate cyclobut-2-enylmethyl radicals to give pentadienyl radicals which accept hydrogen at the terminal and central carbon atoms.The rate constants and activation energies of β-scission in the series of radicals cyclobutylmethyl, 3-methylenecyclobutylmethyl, cyclobut-2-enylmethyl were shown to change little with the large increase in product radical stabilisation.This was accounted for in terms of the principle of non-perfect synchronisation, i.e. bond scission occours before the development of resonance delocalisation.Semi-empirical MNDO calculations for the same series of radicals were in full agreement with this interpretation.
- Walton, John C.
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p. 173 - 178
(2007/10/02)
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- LA PHOTOCHIMIE DE L'ISOPRENE GAZEUX DANS LA REGION DE L'ULTRAVIOLET TRES LOINTAIN
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Yields of various products have been measured in the photolysis of isopropene at 184.9, 213.8, and 228.8 nm and at pressures between 1 and 400 Torr.At each wavelength, the major process is the rupture of a C-CH3 bond, which leads to the formation of methyl and CH2=C=CHCH2.The quantum yield for this process is 0.83 +/- 0.08 at 213.8 nm.The lifetime of the intermediate involved in this process is 20 ns at 184.9 nm.Similar quantities of ethylene and C3H4 (φ >/= 0.050) and propene and acetylene (φ >/= 0.023) are measured.All the measured yields decrease with an increase in the pressure.In addition to these fragmentation processes, isomerization reactions are also observed, particularly at 228.8 nm.They lead to the formation of 1,3- and 1,4-pentadiene as well as 3-methyl-1,2-butadiene.The Stern-Volmer plot for each isomer different and each plot shows a strong negative curvature, indicating the coplexity of the reaction process.The lifetime of each intermediate is 2 ns or less.
- Deslauriers, Helene,Dufour, Sylvain,Collin, Guy J.
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p. 1513 - 1519
(2007/10/02)
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- EFFETS PAROIS DANS LA REACTION THERMIQUE DU PROPENE, SEUL OU EN PRESENCE D'HYDROGENE MOLECULAIRE, VERS 800 K.
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PbO-coated or stainless-steel reactor walls significantly accelerate the formation of most of products of the thermal reaction of propene, at 792 K, but they have no effect on allene, methylcyclopentane and 1,4-pentadiene productions.In presence of hydrogen, the accellerating effect of the walls is much lessened; for some products, it turns into an inhibiting effect whereas allene, methylcyclopentane and 1,4-pentadiene productions are still unaffected.These phenomena are interpreted in terms of heterogeneous chain propagations, initiated and terminated by the allyl free radicals of the gas phase.
- Beral, J. M.,Richard, C.,Martin, R.
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- LOCATION AND DESCRIPTION OF ACTIVE SITES FOR Cis-1,3-PENTADIENE ISOMERIZATION AND HYDROGENATION ON MoS2/γAl2O3 CATALYSTS
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Low temperature isomerization and hydrogenation of cis-1,3-pentadiene have been performed on a conventional sulfided 13.8 wtpercent MoO3/γAl2O3 catalyst.This molecule was used to probe the reactivity of the edge planes of the MoS2 active phase in various sulfur unsaturation states obtained by hydrogen reduction of the sulfided catalyst at different temperatures.Both the activity and product distribution show a strong dependence upon the sulfur unsaturation of the (1010) edge plane.The hydrogenation reaction has been found to need three coordinatively unsaturated Mo ions whereas the isomerization can occur on two and four coordinatively unsaturated Mo ions.As sulfur ions or vacancies are bridged in the (1010) plane a description of the sites needs to consider an "elementary ensemble" containing a pair of Mo ions.
- Kasztelan, S.,Jalowiecki, L.,Wambeke, A.,Grimblot, J.,Bonnelle, J. P.
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p. 1003 - 1008
(2007/10/02)
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- Process for preparing 1,4-dihydroxy, 5,8-dihydronaphthalene and related compounds
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1,4-dihydroxy, 5,8-dihydronaphthalene and related compounds are provided from benzoquinone, and 1,3-butadiene which may be substituted with halogen, acyl, and alkyl, in a one step reaction in the presence of a ferric salt catalyst.
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- High-Pressure Photochemistry of Alkenes. 4. The 184.9-nm Photolysis of Cyclopentene
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A systematic study of the 184.9-nm photolysis of cyclopenetene was made in the presence of added propane between 1 Torr and 6 atm.The main products are isomers at pressures higher than 100 Torr.Among them, linear 1,3- and 1,4-pentadienes as well as cyclic vinylcyclopropane and methylenecyclobutane are observed with tiny amounts of isoprene and 1-pentyne.It appears that methylenecyclobutane is the only primary product involving the Rydberg excited state.At a lower pressure, fragmentation products are also observed.They are mainly cyclopentadiene, ethylene, vinyl and allyl radicals, allene, acetylene, and propylene.Hydrogen atoms are also formed with relatively high quantum yields.Acetylene and propylene are probably formed from the same precursor.The formation of ethylene and allene is probably linked to the fragmentation of electronically excited methylenecyclobutane, and its lifetime has been estimated to be ca. 10 ps.
- Makulski, Wlodzimierz,Collin, Guy J.
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p. 708 - 713
(2007/10/02)
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- Facile chloropalladation of vinylcyclopropanes. Isolation of ring-opened 1,2,5-η3-σ,π chelates as kinetic precursors to 1-3-η3-π-allyl final products
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Reactions of vinylcyclopropane (1a), isopropenylcyclopropane (1c), and α-cyclopropyl-4-fluorostyrene (1d) (all are vinylcyclopropanes) with PdCl2(PhCN)2 in low polarity aprotic media (e.g., CDCl3) leads to rapid cyclopropane chloropalladation with formation of 1,2,5-η3-σ,π chelates. In one case (1a) the precursor to chloropalladation - a π complex that may involve Pd(II)-cyclopropane interaction also - is observed by 1H and 13C NMR. The 1,2,5-η3-σ,π complexes rearrange in solution over periods of hours to days to 1-3-η3-π-allyls. In the case of the 1,2,5-η3-σ,π complex from 1a, namely, 6, allyl formation is accompanied by rearrangement (hydrogen shift). Compound 6 rearranges to a π-allyl also in the solid state, but in this case the hydrogen shift path is not followed. Dynamic NMR experiments conducted on 6 lead to the conclusion that very fast chloropalladation/dechloropalladation occurs in solution, in such a way that the carbon alternately getting and losing chlorine dynamically inverts its configuration. This observation leads to a better understanding of earlier published results for chrysanthemate ester isomerizations catalyzed by PdCl2(PhCN)2. In the course of the present work, the molecular structures of the following two compounds were determined by X-ray diffraction: bis(μ-chloro)bis(1,2,5-η 3-2-methyl-3-chloro-1-penten-5-yl)di-palladium(II) (5) and (acetylacetonato)(1-3-η 3-2-methyl-5-chloro-1-penten-3-yl)palladium(II) (9). Crystal data for compound 5: space group P1 (no. 2); a = 5.487 (3) A?, b = 11.959 (2) A?, c = 6.902 (2) A?; α = 89.06 (2)°, β = 107.2 (3)°, γ = 106.3 (3)°; V = 414.1 (5) A?3; Z = 2. The refinement for 5 was based on 1263 reflections with I > 3σ(I) with a final R = 3.4% and Rw = 5.2%. Crystal data for compound 9: space group P21/c (no. 14); a = 4.529 (2) A?, b = 17.026 (3) A?, c = 16.580 (3) A?; β = 92.49 (3)°; V = 1277 (1) A?3; Z = 4. The refinement for 9 was based on 1740 reflections with I > 3σ(I) with final R = 3.4% and Rw = 4.4%.
- Parra-Hake, Miguel,Rettig, Michael F.,Williams, Jimmie L.,Wing, Richard M.
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p. 1032 - 1040
(2008/10/08)
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- MODELLING OF GASPHASE AROMATIZATION IN THE PYROLYSIS OF HYDROCARBONS (PART II).
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The kinetics of the thermal decomposition of n-hexane and some hydrocarbon mixtures was studied experimentally in respect to the homogeneous formation of aromatics. Some 60 reaction products were identified, among them a number of precursor substances. An attempt has been made to extend our previous reaction model for the mathematical simulation of n-hexane gas phase pyrolysis by addition of detailed pathways for the formation of benzene and toluene.
- Stabel,Ederer,Ebert
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p. 1001 - 1005
(2007/10/02)
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- Infrared Multiphoton Isomerization Reactions of Alkenes and Dienes
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The infrared multiphoton laser-induced unimolecular isomerization reactions of several simple alkenes, conjugated alkenes, and pentadienes have been investigated.Excitation of (E)-2-butene, pentene, and hexene results in contrathermodynamic E -> Z isomerization and fragmentation, the isomerization/fragmentation ratio decreasing with increasing chain length and increasing laser fluence.These results are in qualitative agreement with RRKM calculations for average reactant energies of 75-85 kcal/mol.In addition to products of C-C homolysis observed with all three alkenes, 1-butene and 1,3-butadiene are formed from (E)-2-butene. (E)-Crotononitrile undergoes laser-induced isomerization without fragmentation, resulting in quantitative conversion to the Z isomer.In contrast, (E)-methyl crotonate undergoes both isomerization and fragmentation, while (E)-ethyl crotonate undergoes essentially quantitative elimination of ethylene.Irradiation of (E)- or (Z)-1,3-pentadiene at low laser fluences results exclusively in E Z isomerization resulting in steady-state isomer ratios which depend upon the relative magnitude of the single photon cross sections of the two isomers.At higher fluences, both isomers are converted to cyclopentadiene and trace amounts of 1,4-pentadiene.Irradiation of 1,4-pentadiene results in efficient isomerization to (E)- and (Z)-1,3-pentadiene which reacts further to yield cyclopentadiene.The factors which govern these and related infrared multiphoton reactions are discussed.
- Lewis, Frederick D.,Teng, Peter,Weitz, Eric
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p. 2818 - 2826
(2007/10/02)
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- SILVER ION PERTURBATION OF OLEFIN PHOTOCHEMISTRY
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Ag(I) catalysis and inhibition of alkene E/Z photoisomerisation, and its effect on tetramethylethylene photochemistry are reported.
- Morrison, Harry,Koviak, Carol
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p. 2711 - 2714
(2007/10/02)
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- On the Pyrolysis of Unsubstituted Cyclanes - Selectivity of the Formation of Reaction Products, Kinetic Parameters, Mechanistic Interpretations
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The thermal decomposition of cyclopentane (1), cyclohexane (2), cycloheptane (3), cyclooctane (4), cyclodecane (5), and cyclododecane (6) was studied in a laboratory-scale metallic tubular reactor at 650 to 850 deg C in the presence of steam.The kinetic parameters for the overall reactions were determined and the gaseous as well as the liquid reaction products were analyzed and identified by gas chromatography or by the coupling of gas chromatography and mass spectrometry, respectively.It could be shown that from all cyclanes the isomeric α-olefines are formed, if the conversion of the starting cyclanes is small.This supports the view that the cyclane - α-olefin isomerization is an important initial reaction in pyrolysis of 1 up to 6.The results also demonstrate that the main pathway of degradation is a radical chain mechanism via cyclanyl radicals with β(C-C) bond scission and 1.4 or 1.5-H-isomerization of alkenyl radicals as the most important reaction steps.
- Zimmermann, G.,Zychlinski, W.,Bach, G.,Rennecke, D.
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- Isomerisation des radicaux insatures. III. Radicaux α,α,β-, α,β,γ- et α,α,γ-trimethallyles
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α,α,β-, α,β,γ-, and α,α,γ-trimethallyl radicals have been generated in the 147.0-nm gas phase photolysis of 2,3,3-trimethyl-1-butene, 3,4-dimethyl-2-pentene, and 2,4-dimethyl-2-pentene, respectively.Under these conditions, the majority of allyl radicals have an internal energy sufficient for further decomposition: they give rise to the formation of various 1,3-dienes and small amounts of either 1,2- or 2,3-dienes.An internal sigmatropic 1,2-hydrogen atom transfer process is part of the proposed mechanism to explain such products.Moreover, the fragmentation of the trimethyl substituted allyl radicals involves the split of one β(C-C) bond, then one β(C-H), and, to a lesser extent, one central C-CH3 bond.
- Deslauriers, Helene,Collin, Guy J.
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p. 3168 - 3173
(2007/10/02)
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- L'isomerisation de radicaux insatures. II. Les radicaux α-ethallyles et α,γ-dimethallyles formes dans la photolyse de l'hexene-3 et du methyl-4-pentene-2 a 147,0 et 184,9 nm
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The photolysis of cis-3-hexene and 4-methyl-cis-2-pentene has been studied at 147.0 and 184.9 nm.The fragmentation pattern of the photoexcited molecule is normal: it requires, mainly , the split of a C-C bond located in the β position relative to the double bond (ca. 80percent).Some α(C-C), β(C-H), and α(C-H) primary splits complete this mechanism.The formation of α-ethallyl and α,γ-dimethallyl radicals is improtant in 3-hexene and 4-methyl-2-pentene, respectively.An isomerization process, involving these two radicals, is necessary to explaine the formation of part of the 1,3-pentadiene in the 3-hexene system and of all the 1,3-butadiene in the 4-methyl-2-pentene system.This process involves a 1,4-hydrogen atom transfer.
- Collin, Guy J.,Deslauriers, Helene
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p. 944 - 950
(2007/10/02)
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- Process for producing conjugated diolefins
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A process for producing a conjugated diolefin, which comprises oxidatively dehydrogenating a monoolefin having at least 4 carbon atoms in the vapor phase with molecular oxygen to form the corresponding conjugated diolefin, said reaction being carried out in the presence of a catalyst having the general composition formula wherein X represents Zr or Al, Y represents at least one element selected from the group consisting of metal elements of Group Ia of the periodic table, metal elements of Group II of the periodic table, Tl and P, Z represents at least one element selected from the group consisting of In, Ag, Ti, Nb, Ta, Co, La, Ce, Nd and Mn, a, b, c, d, e, f, g, h and i are respectively the atomic numbers of Mo, Bi, Cr, Ni, X, Fe, Y, Z and O, and when a=12, b=0.05-20, c=0.05-20, d=0.1-30, e=0.01-20, f=0.01-20, g=0.001-20, h=0-20, and i is the atomic number of oxygen satisfying the atomic valences of the other elements.
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