- CATALYTIC HYDROCARBON DEHYDROGENATION
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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)
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- Phosphonate-Modified UiO-66 Br?nsted Acid Catalyst and Its Use in Dehydra-Decyclization of 2-Methyltetrahydrofuran to Pentadienes
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Phosphorus-modified all-silica zeolites exhibit activity and selectivity in certain Br?nsted acid catalyzed reactions for biomass conversion. In an effort to achieve similar performance with catalysts having well-defined sites, we report the incorporation of Br?nsted acidity to metal–organic frameworks with the UiO-66 topology, achieved by attaching phosphonic acid to the 1,4-benzenedicarboxylate ligand and using it to form UiO-66-PO3H2 by post-synthesis modification. Characterization reveals that UiO-66-PO3H2 retains stability similar to UiO-66, and exhibits weak Br?nsted acidity, as demonstrated by titrations, alcohol dehydration, and dehydra-decyclization of 2-methyltetrahydrofuran (2-MTHF). For the later reaction, the reported catalyst exhibits site-time yields and selectivity approaching that of phosphoric acid on all-silica zeolites. Using solid-state NMR and deprotonation energy calculations, the chemical environments of P and the corresponding acidities are determined.
- Caratzoulas, Stavros,Chen, Tso-Hsuan,Dauenhauer, Paul,Dorneles de Mello, Matheus,Han, Songi-I,Jain, Sheetal K.,Kumar, Gaurav,Li, Xinyu,Scott, Susannah L.,Tabassum, Tarnuma,Tsapatsis, Michael,Vlachos, Dionisios G.
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supporting information
p. 13260 - 13266
(2020/06/08)
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- Dehydra-decyclization of 2-methyltetrahydrofuran to pentadienes on boron-containing zeolites
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1,3-Pentadiene (piperylene) is an important monomer in the manufacturing of adhesives, plastics, and resins. It can be derived from biomass by the tandem ring-opening and dehydration (dehydra-decyclization) of 2-methyltetrahydrofuran (2-MTHF), but competing reaction pathways and the formation of another isomer (1,4-pentadiene) have limited piperylene yields to MFI > BEA at a given temperature (523 K), indicating the non-identical nature of active sites in these weak solid acids. The diene distribution remained far from equilibrium and was tuned towards the desirable conjugated diene (1,3-pentadiene) by facile isomerization of 1,4-pentadiene. This tuning capability was facilitated by high bed residence times, as well as the smaller micropore sizes among the zeolite frameworks considered. The suppression of competing pathways, and promotion of 1,4-pentadiene isomerization events lead to a hitherto unreported ~86percent 1,3-pentadiene yield and an overall ~89percent combined linear C5 dienes' yield at near quantitative (~98percent) 2-MTHF conversion on the borosilicate B-MWW, without a significant reduction in diene selectivities for at least 80 hours time-on-stream under low space velocity (0.85 g reactant per g cat. per h) and high temperature (658 K) conditions. Finally, starting with iso-conversion levels (ca. 21-26percent) and using total turnover numbers (TONs) accrued over the entire catalyst lifetime as the stability criterion, borosilicates were demonstrated to be significantly more stable than aluminosilicates under reaction conditions (~3-6× higher TONs).
- Dauenhauer, Paul J.,Kumar, Gaurav,Liu, Dongxia,Ren, Limin,Tsapatsis, Michael,Xu, Dandan
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supporting information
p. 4147 - 4160
(2020/07/14)
-
- Efficient Generation and Synthetic Applications of Alkyl-Substituted Siloxycarbenes: Suppression of Norrish-Type Fragmentations of Alkanoylsilanes by Triplet Energy Transfer
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Acylsilanes have been known to undergo isomerization to siloxycarbenes under photoirradiation and the thus generated carbenes can be utilized for various synthetic reactions. But this carbene formation is not necessarily efficient with some alkanoylsilanes because Norrish-type fragmentations compete, which limit the synthetic utility of alkanoylsilanes as carbene precursors. In this study, generation of siloxycarbenes from alkanoylsilanes by visible-light-induced energy transfer was examined by using an Ir complex, [Ir{dF(CF3)ppy}2(dtbpy)]PF6, and was successfully applied to the C?C coupling reactions with boronic esters or aldehydes. This methodology efficiently suppressed undesired Norrish-type reactions and broadened synthetic utility of alkanoylsilanes.
- Abe, Manabu,Hagiwara, Chihiro,Ishida, Kento,Kusama, Hiroyuki,Yamazaki, Hokuto
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p. 1249 - 1253
(2020/02/04)
-
- One-pot Synthesis of 1,3-Butadiene and 1,6-Hexanediol Derivatives from Cyclopentadiene (CPD) via Tandem Olefin Metathesis Reactions
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A novel tandem reaction of cyclopentadiene leading to high value linear chemicals via ruthenium catalyzed ring opening cross metathesis (ROCM), followed by cross metathesis (CM) is reported. The ROCM of cyclopentadiene (CPD) with ethylene using commercially available 2nd gen. Grubbs metathesis catalysts (1-G2) gives 1,3-butadiene (BD) and 1,4-pentadiene (2) (and 1,4-cyclohexadiene (3)) with reasonable yields (up to 24 % (BD) and 67 % (2+3) at 73 % CPD conversion) at 1–5 mol % catalyst loading in toluene solution (5 V% CPD, 10 bar, RT) in an equilibrium reaction. The ROCM of CPD with cis-butene diol diacetate (4) using 1.00 - 0.05 mol % of 3rd gen. Grubbs (1-G3) or 2nd gen. Hoveyda-Grubbs (1-HG2) catalysts loading gives hexa-2,4-diene-1,6-diyl diacetate (5), which is a precursor of 1,6-hexanediol (an intermediate in polyurethane, polyester and polyol synthesis) and hepta-2,5-diene-1,7-diyl diacetate (6) in good yield (up to 68 % or TON: 1180). Thus, convenient and selective synthetic procedures are revealed by ROCM of CPD with ethylene and 4 leading to BD and 1,6-hexanediol precursor, respectively, as key components of commercial intermediates of high-performance materials.
- Turczel, Gábor,Kovács, Ervin,Csizmadia, Eszter,Nagy, Tibor,Tóth, Imre,Tuba, Robert
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p. 4884 - 4891
(2018/09/25)
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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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- Enzymatic Oxidative Tandem Decarboxylation of Dioic Acids to Terminal Dienes
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The biocatalytic oxidative tandem decarboxylation of C7–C18dicarboxylic acids to terminal C5–C16dienes was catalyzed by the P450 monooxygenase OleT with conversions up to 29 % for 1,11-dodecadiene (0.49 g L–1). The sequential nature of the cascade was proven by the fact that decarboxylation of intermediate C6–C11ω-alkenoic acids and heptanedioic acid exclusively gave nonconjugated 1,4-pentadiene; scale-up allowed the isolation of 1,15-hexadecadiene and 1,11-dodecadiene; the system represents a short and green route to terminal dienes from renewable dicarboxylic acids.
- Dennig, Alexander,Kurakin, Sara,Kuhn, Miriam,Dordic, Andela,Hall, Mélanie,Faber, Kurt
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supporting information
p. 3473 - 3477
(2016/07/29)
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- Study of the Formation of the First Aromatic Rings in the Pyrolysis of Cyclopentene
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The thermal decomposition of cyclopentene was studied in a jet-stirred reactor operated at constant pressure and temperature to provide new experimental information about the formation of the first aromatic rings from cyclic C5 species. Experim
- Herbinet, Olivier,Rodriguez, Anne,Husson, Benoit,Battin-Leclerc, Frédérique,Wang, Zhandong,Cheng, Zhanjun,Qi, Fei
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p. 668 - 682
(2016/02/23)
-
- Stereo- and chemoselective character of supported CEO2 catalysts for continuous-flow three-phase alkyne hydrogenation
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TiO2-, Al2O3-, and ZrO2- supported CeO2 catalysts with different Ce loadings were prepared by wet impregnation of the carriers with an acidified solution of cerium ammonium nitrate. The calcined catalysts were characterized by bulk and surface-sensitive techniques, which included microcalorimetry, and evaluated in the three-phase hydrogenation of alkynes under continuous-flow conditions at variable temperature (293-413 K) and pressure (1-90 bar). A number of acetylenic compounds, which contain terminal or internal triple bonds, conjugated unsaturations, and additional functionalities, were systematically assessed. The results revealed the full stereo- and chemoselective character of the ceria catalysts, which outperform the well-known Lindlar catalyst, and open promising perspectives for the revolutionary use of a cost-effective oxide for the production of olefinic compounds in the vitamin and fine chemical industries.
- Vile, Gianvito,Wrabetz, Sabine,Floryan, Leonard,Schuster, Manfred Erwin,Girgsdies, Frank,Teschner, Detre,Perez-Ramirez, Javier
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p. 1928 - 1934
(2014/08/05)
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- RENEWABLE ACRYLIC ACID PRODUCTION AND PRODUCTS MADE THEREFROM
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Processes and methods for making biobased acrylic acid products including acrylic acid, acrylic acid oligomers, acrylic acid esters, acrylic acid polymers and articles from renewable carbon resources are described herein.
- -
-
Paragraph 00140; 00141; 00142; 00143
(2014/01/08)
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- PROCESS FOR THE PRODUCTION OF ALKENES AND/OR AROMATIC COMPOUNDS
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Processes for the production of alkenes are provided. The processes make use of methane as a low cost starting material.
- -
-
Paragraph 0050-0052
(2013/07/05)
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- 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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- Palladium-catalyzed cross-coupling reactions of potassium alkenyltrifluoroborates with organic halides in aqueous media
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Potassium vinyl and alkenyltrifluoroborates are cross-coupled with aryl and heteroaryl bromides using 1 mol % Pd loading of 4-hydroxyacetophenone oxime derived palladacycle or Pd(OAc)2 as precatalysts, K 2CO3 as base, and TBAB as additive and water reflux under conventional or microwave heating to afford styrenes, stilbenoids, and alkenylbenzenes. These borates can be cross-coupled diastereoselectively with allyl and benzyl chlorides using KOH as base in acetone-water (3:2) at 50°C and 0.1 mol % Pd loading, giving the corresponding 1,4-dienes and allylarenes, respectively. These simple phosphine-free reaction conditions allow the palladium recycling from the aqueous phase during up to five runs by extractive separation of the products, which contain 58-105 ppm of Pd.
- Alacid, Emilio,Najera, Carmen
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supporting information; experimental part
p. 2321 - 2327
(2009/07/18)
-
- New synthesis and thermal studies of palladacycloalkanes and their precursors
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A series of new palladacycloalkanes of formula cis-[PdL2(CH2)n] (9. n = 6, L = PPh3; 10. n = 6, L2 = dppe; 11. n = 8, L = PPh3; 12. n = 8, L2 = dppe) have been prepared by two routes. In the first route, the precursor bis(1-alkenyl) complexes cis-[PdL2((CH2)nCH{double bond, long}CH2)2] (1. n = 2, L = PPh3, 2. n = 2, L2 = dppe, 3. n = 3, L = PPh3, 4. n = 3, L2 = dppe) were allowed to react with Grubb's 2nd generation catalyst to give the palladacycloalkenes, cis-[PdL2(CH2)nCH{double bond, long}CH(CH2)n] (5. n = 2, L = PPh3, 6. n = 2, L2 = dppe, 7. n = 3, L = PPh3, 8. n = 3, L2 = dppe), which were then hydrogenated to the palladacycloalkanes, 9-12. In the second route, the di-Grignard reagents BrMg(CH2)nMgBr (n = 6, 8) were reacted with the palladium complex [PdCl2(COD)] followed by immediate ligand displacement to form the respective palladacycloalkanes 10 and 12. The complexes obtained were characterized by a range of spectroscopic and analytical techniques. Thermal decomposition studies were carried out on the palladacycloalkanes 9-12 and the main organic products shown to be 1-alkenes and 2-alkenes.
- Mahamo, Tebello,Zheng, Feng,Sivaramakrishna, Akella,Moss, John R.,Smith, Gregory
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p. 103 - 108
(2008/03/30)
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- Process for waste plastic recycling
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A process for recycling or decomposing waste plastic where such wasteplastic is decomposed in a diluent such as hot oil through actions involvingfree radical precursor, such as polyvinyl chloride or polyurethane, is achievedat low temperature. The thermal decomposition (or pyrolysis) reaction is forabout 1 hour at 375° C., and useable products, such as distillate, coke, and oilare recovered. Additionally the diluent may be recycled within the process.
- -
-
Page/Page column 6
(2010/02/10)
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- 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)
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- DEHYDROCYCLIZATION AND POSITIONAL ISOMERIZATION OF PIPERYLENE. NEW METHOD FOR PRODUCING 1,4-PENTADIENE
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A study haas been made of the conversion of piperylene on oxide catalysts based on group II metaloxides containing Fe2O3.It has been found that, on these catalysts at 630 deg C, piperylene forms cyclopentene, cyclopentadiene, 1,4-pentadiene, cracking products and products of hydrogen transfer (n-pentenes).The highest yield of C5 cyclic hydrocarbons is achieved by Fe2O3-MgO (11percent).Cyclizing activity is also exhibited by indyvidual oxides, and here the yield of cyclic hydrocarbons increases with increasing basicity of the oxide, while the 1,4-pentadiene yield increases in reverse order.The highest 1,4-pentadiene yield is observed on BeO and its compounds with magnesium oxide.The highest yields and selectivity (6 and 77percent respectively) were obtained on a catalyst containing 80percent BeO and 20percent MgO at a temperature of 575 deg C with a volume feed rate of piperylene of 1.0 hr-1 and a steam dilution molar ratio of 1:10.The yield obtained amounts to two thirds of the thermodynamically possible yield.
- Gitis, K. M.,Isagulyants, G. V.
-
-
- Pyrolysis of 1,7-Octadiene and the Kinetic and Thermodynamic Stability of Allyl and 4-Pentenyl Radicals
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Dilute mixtures of 1,7-octadiene in argon have been decomposed in single-pulse shock tube experiments.The main reaction is the breaking of the carbon-carbon allylic bond leading to the formation of allyl and 4-pentenyl radicals.A minor pathway involving a retroene reaction yielded propene and 1,5-pentadiene.Most of the 4-pentenyl radical decomposes to form another allyl and ethylene.Contributions from a cyclization process resulting in the formation of cyclopentene have also been observed.Allyl radical decomposition rate constants have been measured.The following rate expressions have been determined: k(1,7-octadiene -> allyl + 4-pentenyl) = 1.2 +/- 0.8 * 1016 exp(-35700 +/- 400/T)s-1, k(1,7-octadiene -> propene + 1,4-pentadiene) = (3 +/- 1.5) * 1012 exp(-27900 +/- 250/T)s-1, k(4-pentyl -> cyclopentene + H)/k(4-pentenyl -> allyl + ethylene) = 6.9 +/- 4) * 10-3 exp(2118 +/- 500/T), and k(allyl -> allene + H) = 40 +/- 10 s-1 at 1080 K.When compared with lower temperature literature data on hydrogen addition to allene to form allyl, the present results are consistent with a resonance energy of 51 +/- 4 kJ/mol for the allyl radical, a step-size down for collisional deactivation in argon of 500 cm-1, and lead to the high-pressure rate expression k(allyl -> allene + H) = 1.5 * 1011T0.84 exp(-30053/T) s-1 and k(H + allene -> allyl) = 1.2 * 108T0.69 exp(-1513/T) L mol-1 s-1 over the temperature range 350-1200 K.The uncertainty for the decomposition reaction is estimated to be a factor of 1.3 at 1100 K, but may increase to 1 order of magnitude at the lower temperatures.For the addition reaction, the estimated uncertainties are a factor of 1.5 at 350 K increasing to a factor of 2.5 at 1100 K.The disproportionation to combination ratio for allyl radical under high-temperature conditions is considerably less than 0.005.
- Tsang, Wing,Walker, James A.
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p. 8378 - 8384
(2007/10/02)
-
- 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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- 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)
-
- Kinetics of Primary Processes in the Pyrolysis of Cyclopentanes and Cyclohexanes
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Studies of the thermal unimolecular decomposition of cyclopentane, cylohexane, vinylcyclopentane, and vinylcyclohexane have been carried out at temperatures in the range 900-1223 K using the technique of very low-pressure pyrolysis (VLPP).The results show that ring-opening isomerization to open-chain alkenes is the major primary process.Under the experimental conditions the alkenes undergo further decomposition via C-C bond fission and/or retro-ene processes.Application of RRKM theory shows that the VLPP data (falloff regime) are consistent with the following high-pressure rate expressions (at =1100 K) for reactant decay: log(k/s-1)=(16.8+/-0.3)-(355+/-8)/θ for cyclopentane, log(k/s-1)=(16.9+/-0.3)-(361+/-8)/θ for cyclohexane, log(k/s-1)=(16.0+/-0.3)-(304+/-8)/θ for vinylcyclopentane, and log(k/s-1)=(16.0+/-0.3)-(309+/-8)/θ for vinylcyclohexane, where θ=2.303RT kJ/mol.The A factors were based on known values for C-C bond fission in alkanes and alkenes.Comparison of the activation energies for the unsubstituted cycloalkanes with those for the vinyl-substituted cycloalkanes reveals that the effect of the vinyl substituent is close to the established value for the allyl resonance energy.This evidence supports the assumption of a biradical mechanism for the ring opening of medium-sized cycloalkanes.Decomposition of pent-1-ene (the open-chain isomer of cyclopentane) under VLPP conditions yields unimolecular rate constants for overall decay that are consistent with the high-pressure rate expressions log(k/s-1)=(12.5+/-0.4)-(238+/-10)/θ for retro-ene reaction and log(k/s-1)=(16.0+/-0.3)-(296+/-10)/θ for C-C fission.The A factors were assigned from estimates consistent with the results of a recent shock-tube study of the decomposition in the high-pressure regime.The Arrhenius parameters are consistent with previous data on the decomposition of monoolefins via C-C fission and retro-ene pathways.
- Brown, Trevor C.,King, Keith D.,Nguyen, Tam T.
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p. 419 - 424
(2007/10/02)
-
- 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)
-
- Infrared Multiple-Photon Decomposition of Cyclopentene
-
The infrared multiple-photon decomposition of cyclopentene yields cyclopentadiene as the major hydrocarbon product (>95percent).The other products are 1,4-pentadiene and cis- and trans-1,3-pentadiene, along with trace amounts of fragmentation products.The 1,3-pentadienes have not been previously reported in cyclopentene pyrolysis.Typical conversions obtained by focussing the laser beam into the sample ranged from less than 1percent to as much as 20percent per 1E3 pulses with estimated beam waist fluences of approximately 150 J/cm2, indicating that cyclopentene excitation is strongly bottlenecked.No products were detected with collimated beams of 1 J/cm-2 and after 1.7E4 pulses.Reaction product yields increase with increasing wavelength in the fundamental absorption band centered at 1048 cm-1.Excitation originating in the Q branch of this transition results in very small yields.Total C5 yields increase rapidly with increasing fluence at 1029 and 1033 cm-1.A simple model of dissociation in which the focused beam geometry is a circular hyperboloid of revolution predicts fluence-yield behavior that is consistent with experimental observations.Conversion of cyclopentene decreases with increasing cyclopentene pressure between 0.01 and about 0.5 torr, and thereafter increases rapidly with increasing pressure.On the other hand, addition of N2, up to about 200 torr, causes total C5 yields to decrease monotonically over the entire pressure range.A limited number of experiments were done with 1-methylcyclopentene.At the same wavelength (1019 cm-1), pressure, fluence, and weak field absorbance, dehydrogenation of 1-methylcyclopentene gives yields that are as much as 20 times greater than yields from cyclopentene.
- Shoemaker, James O.,Carr, Robert W.
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p. 605 - 612
(2007/10/02)
-
- Reactions of Methylenecyclopropanes, VII. Nickel(0)-catalysed Cycloadditions of Methylenecyclopropanes with Alkyl Acrylates
-
Cycloaddition reactions of methylenecyclopropane (1) and of the ring-methylated methylenecyclopropanes 5, 9, and 12 with alkyl acrylates are performed at nickel(0) catalysts, such as bis(1,5-cyclooctadiene)nickel under mild conditions (0 - 50 deg C).Depending on the degree of methylation of the three-membered ring, 1 and 5 give only alkyl 3-methylenecyclopentanecarboxylates (4 and 6), whereas 9 leads to a mixture of the methylenecyclopentane derivative 10 and the alkyl spirohexanecarboxylate 11, and 12 react to form only the spirohexane derivative 13.With 12 isomerisation to 2,3,3-trimethyl-1,4-pentadiene (15) also takes place.In the case of 9 the ratio of methylenecyclopentane to spirohexanecarboxylate can be influenced by the size of alkyl groups. - In the Ni0-catalysed reactions of 1 with substituted acrylates (methyl crotonate or diethyl maleate) codimerisation to 16 and 17 competes with cyclodimerisation to 2 and 3.
- Binger, Paul,Brinkmann, Axel,Wedemann,Petra
-
p. 2920 - 2930
(2007/10/02)
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- THE 185-NM PHOTOCHEMISTRY OF 2,3-DIAZABICYCLOHEPTENE AND OF ITS DENITROGENATION PRODUCTS BICYCLOPENTANE AND CYCLOPENTENE
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The 185-nm denitrogenation of 2,3-diazabicycloheptene (1) afforded bicyclo pentane (2) and cyclopentene (3) presumably via a "hot" cyclopentane-1,3-diyl diradical (8); 1,4-pentadiene (4) and methylenecyclobutane (5) were secondary products of the 185-nm photolysis of (2) and (3).
- Adam, Waldemar,Oppenlaender, Thomas
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p. 5391 - 5394
(2007/10/02)
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- Hydrogen bonding of O-H and C-H hydrogen donors to Cl-. Results from mass spectrometric measurements of the ion-molecule equilibria RH+Cl-=RHCl-
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Equilibrium constants K1 for reaction RH+Cl-=RHCl- in the gas phase were measured with a high pressure mass spectrometer under chemical ionization conditions.Data for some 40 compounds RH are presented.It is found that the binding free energies (-ΔGo1=RT lnK1)for RH=oxygen acids increase with the gas phase acidity of RH.The strongest bonds are formed with strong acids like HCO2H, CH3CO2H, and phenol.Water and alkyl alcohols give much weaker interactions.A simple relationship between gas phase acidity and binding free energy does not occur for RH=carbon acids.Carbon acids like cyclopentadiene, whose high gas phase acidity is largely due to charge delocalization by conjugation in the completed anion, do not give Cl- adducts with stability commensurate with the acidity.A relationship between gas phase acidity and binding energy is found for carbon acids with carbonyl groups and for the substituted toluenes.Molecular orbital calculations with the STO-3G basis set provide insights to the bonding occurring in RHCl-.For all cases investigated, hydrogen bonding to Cl- provides the most stable structure.Generally the hydrogen bond occurs through the hydrogen which has the highest net positive charge.The hydrogen bond strength is found approximately proportional to this positive charge.Another proportionality is found between the charge transferred from Cl- to RH, on formation of RHCl-, and the strength of the hydrogen bond.
- French, M. A.,Ikuta, S.,Kebarle, P.
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p. 1907 - 1918
(2007/10/02)
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- Infrared Multiphoton Photochemistry of Vinylcyclopropane. Variation of Yield and Branching Ratio with Experimental Parameters
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The infrared photochemistry of vinylcyclopropane has been comprehensively investigated.Irradiation of vinylcyclopropane at relatively low pressures with the partially focused output of a CO2 laser leads to a mixture of the C5 products cyclopentene, cyclopentadiene, 1,4-pentadiene, and cis- and trans-1,3-pentadiene.The composition of the product mixture as well as the total product yields are a sensitive function of experimental parameters.The effects of bath gas pressure, laser power, laser intensity, laser frequency, and number of pulses have been systematically examined.A simple physical picture of the multiphoton activation and resulting decomposition is developed.RRKM theory is employed to calculate energy-dependent unimolecular reaction rates.The model is quite successful in rationalizing these data, providing good evidence for the qualitative validity of a rate equation description of infrared multiphoton dissociation.
- Farneth, William E.,Thomsen, Marcus W.,Schultz, Nancy L.,Davies, Mark A.
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p. 4001 - 4006
(2007/10/02)
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- Dissociation of Propylene Excited by the Impact of Low-Energy Electrons in the Gas Phase
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Dissociation of gaseous propylene excited by the impact of low-energy electrons was investigated by using tritium β-rays in the presence of applied electric fields.The yields of C1-C6 hydrocarbon products are reported depending on the applied potential.To achieve a material balance for the free-radical processes, we performed the experiments at a temperature of 195 K.Decomposition of propylene excited by the electrons having energy below the ionization potential involves mainly either C-H (yielding H + C3H5) or C-C (yielding C2H3 + CH3) bond rupture.The contribution of the latter increases with increasing eletron energy.The experimental results agree quite well with RRKM calculations concerning vibrationally excited propylene molecules in the ground state.In radiolysis in the absence of electric fields the excited molecules appear to have energies higher than, or close to, the ionization threshold.
- Makulski, Wodzimierz,GawYowski Janusz,Niedzielski, Jan
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p. 2950 - 2955
(2007/10/02)
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- Quantum yield of solution photolysis of bicyclohexan-3-one and derivatives
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The quantum yield for photolysis of 0.25 M solutions of bicyclohexan-3-one, 1,5-dimethylbicyclohexan-3-one, and tricyclodecan-8-one in pentane or cyclohexane with 313 nm light are 0.44, 0.52, and 0.32, respectively.
- Kopecky, Kari R.,Gomez, Rodrigo Rico
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p. 1607 - 1609
(2007/10/02)
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- The 9-Decalyl and Related Cations. VI Solvolysis of Pent-4-enyl p-Nitrobenzenesulfonate in 1,1,1,3,3,3-Hexafluoropropan-2-ol and of 3-(Cyclohex-1'-enyl)propyl p-Nitrobenzenosulfonate in 2,2,2-Trifluoroethanol and 1,1,1,3,3,3-Hexafluoropropan-2-ol
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Kinetic and product studies have established that pent-4-enyl p-nitrobenzenesulfonate undergoes insignificant solvolysis (1.5percent) by the ?-route in 1,1,1,3,3,3-hexafluoropropan-2-ol. ?-Participation to give the perhydroinden-3a-yl (8-hydrindyl)cation during the solvolysis of 3-(cyclohex-1'-enyl)propyl p-nitrobenzenesulfonate, a substituted pent-4-enyl derivative, in fluorinated alcohols is, however, significant.In buffered 2,2,2-trifluoroethanol, it occurs to the extent of 30percent; in buffered and unbuffered 1,1,1,3,3,3-hexafluoropropan-2-ol, the values are 96 and 98percent, respectively.
- Ferber, Peter H.,Gream, George E.
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p. 1051 - 1061
(2007/10/02)
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- Photoassisted Isomerisation of Olefins by Platinum Complexes
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Photoassisted isomerisation of carbon-carbon double bonds has been affected for the first time in the presence of platinum complexes; pent-2-ene, hex-2-ene, and 1,2-dichloroethene can be cis-trans interconverted with high efficiency.
- Courtot, Pierre,Pichon, Roger,Salauen, Jean-Yves
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p. 542 - 543
(2007/10/02)
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- Chemistry of Dienyl Anions. II. Crystalline Bis(dienyl)magnesium. Selective Dienylation and Structure in Solution and in the Solid State
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Seven different crystalline bis(dienyl)magnesium TMEDA complexes of open chain or cyclic structure were prepared by metal exchange reaction of corresponding potassium dienides.They are fluxional in solution due to the rapid 1,3-rearrangement.Terminally ?-bonded trans or (E) structure exists primarily in the open chain complexes while centrally ?-bonded cis structure in cyclic dienylmagnesium TMEDA complexes.The former gave 1,3-dienes exclusively but the latter gave 1,4-dienes upon hydrolysis.Molecular structure of bis(2,4-dimethyl-2,4-pentadienyl)magnesium determined by X-ray crystallography showed that it has terminally ?-bonded structure.Addition of dienylmagnesium compounds to acetone followed by hydrolysis gave 1,4-diene derivatives regioselectively but that to diisopropyl ketone gave 1,3-diene derivatives selectively.Unsaturated alcihols with an elongated carbon chain were synthesized by thermal cracking of cyclic ether complexes. 1,3,7-Trienes can be obtained selectively by reaction of appropriate allyl halides in the presence of CuCl catalyst and regiosective dienylation occured by using TiCl2(η5-C5H5)2 as catalyst.
- Yasuda, Hajime,Yamauchi, Michihide,Nakamura, Akira,Sei, Tsuyoshi,Kai, Yasushi,et al.
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p. 1089 - 1100
(2007/10/02)
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