- AlPO4/TiO2 Catalysts. Part 2. - Structure, Texture and Catalytic Activity of Systems Precipitated with Ammonia or Ethene Oxide
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Two series of AlPO4/TiO2 (APTi) catalysts containing different weight compositions have been prepared by the precipitation of AlPO4 (Al/P = 1) on commercial TiO2 (> 99.9 percent Anatase, Aldrich) using ammonia (APTi-A series) or ethene oxide (APTi-E series) as the precipitation agents.Physicochemical characterization of these catalysts was carried our by nitrogen adsorption, TG, X. r. d.., i. r. spectroscopy and surface acid measurements.The surface area, pore volume, crystal structure and surface-acid character were found to be dependent on the precipitation agent, chemical composition and calcination temperature.Changes in surface-acid character were determined by application of a dynamic method that consists in determining both the AlPO4/TiO2's catalytic activity and selectivity in cyclohexene skeletal isomerization using the Bassett-Habgood kinetic model for first-order processes.X-ray diffraction studies show that the incorporated AlPO4 inhibits the polymorphic anatase-rutile transformation in the calcination process of the APTi-A system.Also, APTi-A systems are less affected by thermal treatment than APTi-E ones.It was found that both the apparent rate constant and the selectivity are dependent on the calcination temperature although the most important influence is that of catalyst composition i. e. the AlPO4/TiO2 weight ratio.Thus, a decrease in catalytic activity is observed when TiO2 content increases.Selectivity studies carried out by the OPE curves and the Wheeler criterion show that isomerization products, 1- and 3-methylcyclopentene, are competitive stable primary reaction products coming from cyclohexene across a parallel reaction network.
- Campelo, Juan M.,Garcia, Angel,Luna, Diego,Marinas, Jose M.,Moreno, Maria S.
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- Alkylation of Allylic Derivatives. 10. Relative Rates of Reactions of Allylic Carboxylates with Lithium Dimethylcuprate
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Relative rates of reaction of 19 allylic esters with LiCuMe2 in ether have been determined by a competitive reaction technique.The reactivity range for the series is >3*105.The relationship between structure and reactivity is compatible with a rate-limiting SN2' oxidative addition to give a ?-allyl copper(III) complex.
- Goering, Harlan L.,Kantner, Steven S.,Seitz, Earl P.
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- Tris(aryl)aminium hexachloroantimonates: Convenient one-electron oxidants for chemical electron transfer with bicyclic azoalkanes and bicyclo[2.1.0]pentanes
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Treatment of the parent and bridgehead-substituted 2,3-diazabicyclo[2.2.1]hept-2-enes (1a-d) and their bicyclo[2.1.0]pentanes (2a-d) with catalytic amounts (2-10 mol%) of tris(aryl)aminium hexachloroantimonates afforded the corresponding cyclopentenes (3a-d). A reversal in the regioselectivity of the 1,2 migration was observed for the unsymmetrical derivatives of bicyclo[2.1.0]pentane, namely 2b (methyl substitution) versus 2c (phenyl substitution). This surprising fact is rationalized in terms of delocalization of the positive charge into the aromatic ring for the 1,3-diyl radical cation, as corroborated by AM1 calculations.
- Adam, Waldemar,Sahin, Coskun
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- HYDROSTANNATION DU BICYCLOHEXENE-2: SYNTHESE ET IDENTIFICATION DES METHYL-4 ET METHYL-5 TRIMETHYLSTANNYL-3 CYCLOPENTENES DIASTEREOISOMERES
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4-Methyl- and 5-methyl-3-trimethylstannylcyclopentenes were obtained from bicyclohex-2-ene through hydrostannation.The four isomers were identified by chemical and physicochemical methods such as 90 MHz 1H FT NMR spectroscopy which gives some conformational information in the series of 5-methyl-3-trimethylstannylcyclopentenes.
- Dumartin, Gilles,Quintard, Jean-Paul,Pereyre, Michel
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- Photochemical and ESR spectral evidence for a stereoselective rearrangement of radical cations derived from azoalkanes and bicyclopentanes
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Studies of the photosensitized electron transfer (PET) reactions of anti/syn-5-methylbicyclo[2.1.0]pentane (1a,b) and syn/anti-7-methyl-2,3-diazabicyclo[2.2.1]hept-2-ene (2a,b) have revealed a remarkable stereochemical memory effect. Thus, 1a and 2a furnished only 1-methylcyclopentene (3a) as the rearrangement product, while their isomers 1b and 2b afforded predominantly 3-methylcyclopentene (3b). The pathway responsible for the stereoselective olefin formation can be assigned to a radical cation rearrangement. This was established on the basis of direct ESR evidence showing that the 1,3-diyl radical cations 1a,b?+ detected initially at 80-90 K following the radiolytic oxidation of 1a,b in CF3CCl3 rearranged stereoselectively into the olefin radical cations 3a,b?+ at 105 K. The ESR results further establish that, in the puckered conformations of 1a,b?+, the pseudo-axial substituent on the methylene bridge is in almost perfect coplanar alignment with the radical cation 2p orbital lobes, thus facilitating its stereoselective migration. Also, in agreement with PET results, matrix ESR studies demonstrated that, on radiolytic oxidation of the azoalkanes 2a,b, the olefin radical cations 3a,b?+ were formed with high selectivity, although no precursor radical cations were detected in this case.
- Adam, Waldemar,Walter, Herbert,Chen, Guo-Fei,Williams, Ffrancon
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- Regioselective rearrangement of bridgehead-methyl-substituted radical cations derived from bicyclo[2.1.0]pentanes and 2,3-diazabicyclo[2.2.1]hept-2-enes through photoinduced electron transfer and radiolytic oxidation. Product distribution and matrix ESR studies
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Cyclopentane-1,3-diyl radical cations were generated from the 1-methyl- and 1,4-dimethyl substituted bicyclo-[2.1.0]pentanes 1b,c through photoinduced electron transfer (PET) and radiolytic oxidation. The unsymmetrical bridgehead-substituted bicyclopentane 1b rearranged spontaneously and exclusively to the 3-methylcyclopentene 3b under PET conditions. ESR studies showed similarly that 3b-+ was the only final oxidation product of 1b; the initial radical cation 1b-+ was not detected because it rearranges rapidly and stereoselectively by a 1,2-hydrogen shift to 3b-+, even at 80 K, and no trace of the more stable 1-methylcyclopentene radical cation 3a-+ was observed. This contra--thermodynamic regioselectivity is rationalized in terms of essential localization of positive charge at the tertiary center as the reaction proceeds in the 1,3-diyl radical cation 1b-+. The symmetrical dimethyl derivative 1c rearranged much more reluctantly than 1b despite its lower oxidation potential, and this is attributed to the greater persistence of radical cation 1c-+ through its reluctance to undergo a 1,2-H shift. This was confirmed by direct ESR observation, which also showed that the rearrangement of 1c-+ is much slower than that of the parent cyclopentane- 1,3-diyl radical cation 1-+. This difference is attributed to a larger effect of methyl stabilization on the reactant than on the product, leading to a decrease in exothermicity and an increase in the activation energy for the rearrangement of 1c-+ relative to that of 1-+. The 1-methyl and 1,4-dimethyl substituted 2,3-diazabicyclo [2.2.1]hept-2-enes 2b,c on PET reaction also yielded evidence for the intermediacy of 1,3-diyl radical cations; however, the product distributions suggest that denitrogenation can also be accompanied by concomitant 1,2-H shifts at the stage of the intermediate diazenyl radical cations, albeit with lower efficiency. ESR studies on the oxidation of 2c failed to detect the very stable 1c-+ species on the pathway to the 1,3-dimethylcyclopentene radical cation 3C-+, indicating that denitrogenation of 2C-+ results in a rapid rearrangement to 3c-+ even under matrix-isolation conditions at 77 K. Consequently, the oxidation of these azoalkanes generates highly reactive transients, presumably diazenyl radical cations, which readily denitrogenate and undergo 1,2-H shifts in either a consecutive or concerted manner to form olefin radical cations.
- Adam,Sahin,Sendelbach,Walter,Chen,Williams
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- Nickel Hydride Complexes Supported by a Pyrrole-Derived Phosphine Ligand
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The synthesis of two nickel hydride complexes bearing the pyrrole-derived phosphine ligand CyPNH (2-(dicyclohexylphosphino)methyl-1H-pyrrole) was developed, namely, (κP-CyPNH)(κP,κN-CyPN)NiH and the acid-stable trans-(κP-CyPNH)2Ni(OAc)H·HOAc. (κP-CyPNH)(κP,κN-CyPN)NiH stoichiometrically reduces benzaldehyde and acetophenone in a metal-ligand cooperative manner and catalytically dimerizes ethylene and cycloisomerizes 1,5-cyclooctadiene and 1,5-hexadiene. trans-(κP-CyPNH)2Ni(OAc)H·HOAc, available from the protonation of (κP-CyPNH)(κP,κN-CyPN)NiH with acetic acid, catalyzes the cycloisomerization of 1,5-cyclooctadiene more effectively and produces the less thermodynamically favored cycloisomers of 1,5-cyclooctadiene.
- Collett, Joel D.,Guan, Hairong,Krause, Jeanette A.
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p. 345 - 353
(2022/02/16)
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- PROCESS FOR THE PREPARATION OF 1-METHYL-1-ALKOXYCYCLOPENTANES
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Process for the preparation of cyclopentane derivatives of the formula I in which R is a C1- to C10-alkyl group, which comprises reacting cyclohexanol or cyclohexene or mixtures of both compounds to give 1-methyl-1-cyclopentene (1st stage) and subsequently adding a C1- to C10-alkanol onto the double bond of the 1-methyl-1-cyclopentene (2nd stage).
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- PROCESS FOR THE PREPARATION OF 1-METHYLCYCLOPENTANE DERIVATIVES
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Process for the preparation of 1-methylcyclopentene by thermal reaction of cyclohexanol or cyclohexene or mixtures of both compounds to give 1-methylcyclopentene, wherein the resulting by-products 3-methylcyclopentene and 4-methylcyclopentene (double-bond isomers of 1-methylcyclopentene) are returned to the reaction.
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Page/Page column 5
(2012/05/04)
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- The diagnostic substrate bicyclohexane reveals a radical mechanism for bacterial cytochrome P450 in whole cells
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(Figure Presented) On home ground: The reaction mechanisms of bacterial alkane-oxidizing cytochrome P450s were determined in their native environment using a novel diagnostic substrate probe, bicyclohexane, in whole cells and cell-free extracts (see picture). Purified P450cam also oxidizes bicyclohexane. Clear evidence for a substrate-based radical with a lifetime of 75-250 ps was obtained.
- Austin, Rachel N.,Deng, Dayi,Jiang, Yongying,Luddy, Kate,Van Beilen, Jan B.,Ortiz De Montellano, Paul R.,Groves, John T.
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p. 8192 - 8194
(2008/02/08)
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- High selectivity of MCM-22 for cyclopentanol formation in liquid-phase cyclopentene hydration
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Highly effective formation of cyclopentanol through the liquid-phase hydration of cyclopentene has been attempted on various zeolites catalysts. MCM-22 zeolite was the most selective catalyst, which actively converted cyclopentene to cyclopentanol with a selectivity up to 99%. The effects on the hydration of catalyst preparation method, reaction atmosphere and temperature have been investigated for the MCM-22 catalysts. On the basis of the effect of reaction atmosphere, the mechanism of liquid-phase cyclopentene hydration was proposed. The thermodynamic equilibrium between cyclopentene and cyclopentanol was suggested to control greatly the cyclopentene conversion. The cyclopentene conversion was increased to 10% by increasing the water/cyclopentene ratio. Poisoning using organic amines with different molecular sizes revealed that the hydration occurred mainly in the 10-membered ring channels of MWW structure, which had an elliptic aperture smaller than that of MFI structure, exhibiting a significant shape selectivity by suppressing the etherification cyclopentanol.
- Nuntasri, Duangamol,Wu, Peng,Tatsumi, Takashi
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p. 272 - 280
(2007/10/03)
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- Highly selective formation of cyclopentanol through liquid-phase cyclopentene hydration over MCM-22 catalysts
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MCM-22 catalyst exhibits an extremely high shape selectivity not observed on other zeolites of MFI, MOR and BEA structures, in that it effectively catalyzes the liquid-phase hydration of cyclopentene at a conversion up to 10% and a cyclopentanol selectivi
- Nuntasri, Duangamol,Wu, Peng,Tatsumi, Takashi
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p. 224 - 225
(2007/10/03)
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- Al-MCM-41: Its acidity and activity in cyclohexene conversion
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Investigation of cyclohexene conversion over Al-MCM-41 has shown that the concentrations of Bronsted and Lewis acid sites increase with the Al content of the materials. The conversion follows mainly two mechanisms: cyclohexene skeletal isomerisation (CSI) and hydrogen transfer (HT). The products with 6 carbon atoms in a molecule prevail in all cases. Some amounts of products with 1 to 8 carbon atoms are also formed as a result of cracking or alkylation. All these reactions can occur at the acidic centres of the catalysts. The process of conversion, proceeding over the Bronsted acid sites, results in the formation of coke deposits in addition to volatile products. The amount of coke decreases with increasing reaction temperature and decreasing Al content of the material. The deposits cause a decrease in the effective concentrations of both the Bronsted and Lewis acid sites. Thermodesorption of pyridine has shown that (i) the concentrations of the Bronsted and Lewis acid sites before and after the conversion processes differ only slightly and (ii) the acidic strength of the Bronsted sites is almost independent of their concentration and the Si/Al ratio.
- Rozwadowski,Datka,Lezanska,Wloch,Erdmann,Kornatowski
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p. 5082 - 5086
(2007/10/03)
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- Kinetics and modeling of the thermal reaction of propene at 800 K. Part III. Propene in the presence of small amounts of oxygen
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The thermal reaction of propene was studied around 800 K in the presence of less than 20% O. Initially, the production of H2, CH4, C2H4, C2H6, allene, C3H8, 1,3-butadiene, butenes, 3- and 4-methylcyclopentene, a mixture of 1,4- and 1,5-hexadienes, methylcyclopentane, 4-methylpent-1-ene, and hex-1-ene, was observed along with H2O2, CO, and small quantities of ethanal and CO2. O increases the initial production of H and of most hydrocarbons and, particularly, that of C6 dienes and of cyclenes. A kinetic scheme is proposed in which chains are primarily initiated by a bimolecular step which competes with the second-order initiation of propene pyrolysis. Modeling of the reaction based on the proposed scheme accounts well for the concentration-time profiles.
- Barbe,Baronnet,Martin,Perrin
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p. 503 - 522
(2007/10/03)
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- Selective ring opening cross metathesis of cyclopropenone ketal: A one step synthesis of protected divinyl ketones
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Grubbs ruthenium complex efficiently catalyses ring opening cross metathesis of cyclopropenone ketal and terminal olefins to afford 1,4-divinyl ketone ketals in good yields.
- Michaut, Mathieu,Parrain, Jean-Luc,Santelli, Maurice
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p. 2567 - 2568
(2007/10/03)
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- Catalytic properties of ZrO2-SiO2: Effects of sulfation in the cyclohexene isomerization reaction
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Catalytic properties of ZrO2-SiO2 (14% molar) for cyclohexene conversion (skeletal isomerization and hydrogen transfer) have been studied. Textural and morphological properties were correlated to explain catalytic behavior. XRD, DTA-TGA, N2 adsorption, DRIFT, and acidity measurements by pyridine and dimethylpyridine chemisorption were used to characterize samples. The effect of the sulfation process upon surface structure as well on catalytic activity/selectivity has also been studied. It has been shown that catalytic activities are increased on sulfated samples, but at the same time products of the hydrogen transfer reaction seem to be increased too, lowering the selectivity of the reaction; isomerization always predominates. Sulfation transforms this compound to a relatively selective isomerization catalyst exhibiting greater catalytic activity.
- Navio,Colon,Macias,Campelo,Romero,Marinas
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p. 605 - 613
(2007/10/03)
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- AlPO4-Al2O3 Catalysts with Low Alumina Content. Part IV. -Effect of Fluoride Ion Addition on Texture, Surface Acidity and Catalytic Performance in Cyclohexene and Cumene Conversions
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Fluoride-modified (2.5 wt.percent F(1-)) AlPO4-Al2O3 (APAl-A; 5-25 wt.percent Al2O3) catalysts have been prepared and compared for their catalic activity/selectivity in cyclohexene conversion and cumene cracking.The characterization of catalysts modified with F(1-) was performed using X-ray diffraction (XRD), 27Al and 31P NMR and diffuse reflectance FTIR (DRIFT) spectrooscopies and N2 adsorption methods, and by the measurement of the surface acid character by chemisorption of pyridine (PY) and 2,6-dimethylpyridine (DMPY).Fluoride addition shifted the transition of AlPO4 from an amorphous to a crystalline (α-cristobalite) phase at a lower temperature.Fluoride-treated APAl-A catalysts contained both tetrahedral and octahedral aluminium (their ratio varied with anion type) while phosphorus always remained in P(OAl)4 environments.Moreover, two types of Al surface hydroxy groups at 3786 and 3738 cm-1, and only one type of P surface hydroxy group at 3670 cm-1, are found in the DRIFT spectra of the APAl-A catalysts.The DRIFT measurements also revealed that fluoride ion substitutes hydroxy groups on tetrahedrally coordinated Al and P centres in the surface.The PY and DMPY adsorption (pulse chemisorption and DRIFT spectroscopy) indicates that the addition of fluoride ion appreciably modifies the surface acidity of the AlPO4-Al2O3 catalyst by increasing the number and strength of Broensted acid sites.Furthermore, the addition of fluoride increases remarkably the activity for both processes and, for cyclohexene conversion, in contract to pure AlPO4-Al2O3 catalysts, where skeletal isomerization is the only catalysed reaction, bimolecular hydrogen transfer also takes place.The hydrogen transfer/skeletal isomerization ratio decreases as the Al2O3 loading increases although with all APAl-A-FM (fluoride-modified) catalysts the skeletal isomerization always predominates.The catalytic activities were correlated with both the acidity and the acid strength of the catalyst.Fluoride addition transformed a low activity cracking/dehydrogenation catalyst to one selective for cracking and exhibiting much greater catalytic activity.
- Campelo, J. M.,Garcia, A.,Luna, D.,Marinas, J. M.,Romero, A. A.,et al.
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p. 2265 - 2276
(2007/10/02)
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- Bimolecular Hydrogen Transfer over Zeolites and SAPOs having the Faujasite Structure
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Silica-rich Y zeolites prepared by primary or secondary synthesis and samples of SAPO-37 have been synthesized and characterized.These materials are then evaluated as catalysts for the transformation of cyclohexene.From product distribution at low conversion the relative rates of isomerization and bimolecular hydrogen tranfer are measured and discussed in terms of active site density.
- Dwyer, John,Karim, Khalid,Ojo, Adeola F.
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p. 783 - 786
(2007/10/02)
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- THE ROLE OF THE 1,2-HYDRIDE SHIFT IN THE ISOMERIZATION PROCESSES OF CYCLOALKYL CARBOCATIONS
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The role of successive 1,2-hydride shifts in the isomerization processes of cycloalkylcarbonium ions was demonstrated for the case of the alkylation of isomeric methylcyclopentanols or methylcyclopentenes in the presence of sulfuric acid and the isomerization of cyclohexene at acidic aluminum oxide.
- Voronenkov, V. V.,Dzyuba, I. B.,Kryukov, S. I.,Zhdankin, V. V.
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p. 2236 - 2238
(2007/10/02)
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- Formation de coke, desactivation et regeneration des zeolithes. IV - Transfert d'hydrogene et formation de coke au cours de la transformation du cyclohexene sur une zeolithe USHY. Influence de la temperature de reaction
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On a ultrastabilized protonic Y zeolite (USHY) cyclohexene undergoes various reactions: isomerization into methylcyclopentenes, hydrogen transfer, cracking and formation of carbonaceous deposits ("coke").The transfer of hydrogen which comes either from cyclohexene (with formulation of benzene) or from heavy carbonaceous compounds causes the saturation of cyclohexene and of methylcyclopentenes.While the total transformation rate increases when the temperature increases, the rate of coke formation decreases slightly.This abnormal effect can be due to a modification in the composition of heavy carbonaceous compounds held back in the zeolite pores.The relative significance of various reactions depends very much on the temperature: at 120 deg C "coke" formation is faster than isomerization and much faster than hydrogen transfer, the hydrogen implicated coming from heavy carbonaceous compounds only.From 200 deg C upwards, isomerization and hydrogen transfer become the main reactions.Even if the production of benzene increases significantly with the temperature, hydrogen always comes mainly from the heavy carbonaceous compounds and is transfered faster to methylcyclopentenes than to cyclohexene.Light compounds resulting from the cracking of methylcyclopentenes appear above 350 deg C.The formation of all the products can be explained by mechanisms in which carbenium ion intermediates intervene.
- Magnoux, Patrick,Gallet, Alain,Guisnet, Michel
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p. 810 - 814
(2007/10/02)
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- THE EFFECT OF TITANIUM AND SODIUM IN ALUMINA ON ITS ACIDIC AND CATALYTIC PROPERTIES
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Acidic and catalytic properties of alumina containing amall amounts of Ti(IV) and Na(I) (up to 1 wt.percent of both) were examined.It has been proved that the amount of acid sites with the strength H0 /= 3.3 and the initial reaction rates of cyclohexene isomerisation depend linearly on calculated total electronegativity of the corresponding mixture of oxides.
- Kiratova, Kveta,Rocek, Josef
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- On 1.2-Shift Reactions and C-H-Insertions of Acyclic Alkylidene Carbenes
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Two series of acyclic terminal vinyl bromides (1...4 and 5...7) were tested in the reaction with potassium tert-butoxide as precursors of alkylidene carbenes.As expected 1 up to 4 only give 1-alkynes whereas the 2-methylated vinyl bromides 5, 6 and 7 yield 1-methylated cyclopentenes predominantly besides 2-alkynes.The formation of cyclopentenes indicates a reaction route via alkylidene carbenes and 1,5-C-H-insertion reactions, that of 2-alkynes is convincing evidence for 1,2-alkyl shift reactions in 2-methyl substituted alkylidene carbenes.The selectivity of 1,5-C-H-insertion depends on the degree of alkyl substitution of the C-5-atom.At 240 deg C the selectivity is 1deg:2deg:3deg ca. 1:54:240.
- Ondruschka, Bernd,Remmler, Matthias,Zimmermann, Gerhard,Krueger, Christian
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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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- Copper(II) Triflate, a New Reagent for Mild Dehydration of Alcohols: Synthetic Usefulness and Mechanistic Insight
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The effectiveness of copper(II) triflate (copper(II) trifluoromethanesulfonate) as a new dehydrating reagent for a variety of alcohols has been demonstrated.Based on several control experiments, a possible mechanism is suggested.
- Laali, Khosrow,Gerzina, Robert J.,Flajnik, Christine M.,Geric, Cynthia M.,Dombroski, Ann Marie
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p. 607 - 611
(2007/10/02)
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- KINETICS AND MECHANISM OF SOME VINYL RADICAL CYCLISATIONS
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The vinyl radicals 2a, 2b, and 11 each undergo fast exo ring closure to give 5a, 5b, and 12, the first two of which readily rearrange to ring-expanded radicals.
- Beckwith, Athelstan L.J.,O'Shea, Dennis M.
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p. 4525 - 4528
(2007/10/02)
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- Protium-deuterium exchange of cyclic and acyclic alkanens in dilute acid medium at elevated temperatures
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A modification of the high temperature - dilute acid (HTDA) method for deuterium labelling of aromatic compounds has been applied to the H-D exchange of a number of cyclic and acyclic alkenes.Cyclopentene, cyclohexene, cyclododecene, and tetramethylethylene have been completely exchanged in excellent yield. 1-Methylcyclopentene and 1-methylcyclohexene have also been perdeuterated and cycloheptene and cyclooctene partially labelled but require spinning band distillation or preparative glpc for separation from rearrangement products.A variety of C5-C8 acyclic alkeneshave also been treated under HTDA conditions.
- Werstiuk, Nick Henry,Timmins, George
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p. 530 - 533
(2007/10/02)
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- Electrophilic Cleavage of Cyclopropanes. Acetolysis of Bicyclic and Tricyclic Cyclopropanes
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The acetolysis of a series of bicycloalkanes and propellanes has been studied.The effect of ring strain, caused by changing ring size or introducing a trans-ring fusion, on the rate and products of the reaction has been examined.No correlation was found between rates of acetolysis and strain energy relief, but with the exception of propellane, there is a rough correlation with ionization potentials.The degree of polarization of the C-C bonds in the presence of a proton correlates very well with reactivity and is a controlling factor for the acetolysis rates.The importance of the energies of unoccupied orbitals with the appropriate symmetry in controlling electron polarization is shown by the large difference in rate of reaction between - and propellanes.
- Wiberg, Kenneth B.,Kass, Steven R.,Meijere, Armin de,Bishop, K. C.
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p. 1003 - 1007
(2007/10/02)
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- Skeletal isomerization of cyclohexene on Al2O3 and AlPO4--Al2O3 catalysts
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Cyclohexene skeletal isomerization, in a microcatalytic pulse reactor, was investigated using Al2O3 and AlPO4-Al2O3 as catalysts.Apparent rate constants and apparent activation energies were calculated according to the kinetic model of Bassett-Habgood.Selectivity studies cuncluded that 1-MCP and 3-MCP were competitive products with a first-order kinetics.The rate constants as well as the selectivity at 1-MCP increase with an increase in the number and strength of stronger acid sites, measured by means of the irreversible adsorption of aniline in cyclohexane, at 298 K, using a spectrophotometric method.The parallel reaction pathway, proposed for AlPO4 catalysts, agrees with both the observed rates and selectivities using Al2O3 and AlPO4-Al2O3 catalysts.
- Campelo, J. M.,Garcia, A.,Gutierrez, J. M.,Luna, D.,Marinas, J. M.
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p. 1455 - 1458
(2007/10/02)
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- First Direct Synthesis of Optically Active 3-Methylcyclopentene
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(-)-(S)- and (+)-(R)-3-methylcyclopentene (1) has been prepared in a stereochemically unambiguous synthesis.The (S)-configuration for (-)-1 was confirmed by correlation with (-)-(S)-1-methylindane.
- Sliwka, Hans-Richard,Hansen, Hans-Juergen
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p. 434 - 440
(2007/10/02)
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- Reactions of Cyclanyl Radicals in the Gas Phase. II. Cyclohexyl Radicals from Mixtures of Azomethane and Cyclohexane
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Cyclohexane-azomethane mixtures in argon as diluent were converted by temperatures between 400 and 480 deg C in a stirred flow system.All products were analytically determined in a comprehesive way.In this way not only isomeric C6H11-radicals, which were already known from former investigations, but also hitherto unknown C6H11-radicals, especially the 3-methylcyclopentyl radical, could be detected as a recombination product with methyl radicals or as the corresponding olefinic compounds.From the results the stationary concentrations of important radical species were estimated and mechanistic consequences discussed.
- Ondruschka, B.,Zimmermann, G.,Anders, G.
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p. 853 - 862
(2007/10/02)
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- Skeletal isomerization of cyclohexene on AlPO4 catalysts
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The skeletal isomerization of cyclohexene, in a microcatalyc pulse reactor, was investigated by using aluminium orthophosphates (Al/P=1) as catalysts.An attempt has been made to correlate the isomerization activity the acid properties of the solids, measured by means of the irreversible adsorption of different organic bases in cyclohexane, at 298 K, using a spectrophotometric method. Apparent rate constants were calculated in terms of the kinetic model of Bassett and Habgood.Selectivity studies led to the conclusion that 1-MCP and 3-MCP were competitive products.Correlation between the kinetic selectivity factor, ?, and the number of strong acid sites has been sought. A possible parallel reaction pathway is proposed, which agrees with both the observed rates and selectivities.
- Campelo, J. M.,Garcia, A.,Gutierrez, J. M.,Luna, D.,Marinas, J. M.
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p. 2567 - 2571
(2007/10/02)
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- Characterization of Alumina - A Versatile Catalyst
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Different samples of alumina were prepared by impregnating pure alumina with potassium and fluoride ions and their heats of adsorption by adsorption of pyridine were determined by pulse flow technique in gas chromatograph in the temperature range 180-250 deg C.The heats of adsorption decreased with addition of potassium and increased with addition of fluoride ions.Pure alumina had considerable total acidity; however, the Broensted acidity was negligible.Rate of dehydration of cyclohexanol was faster initially and decreased with increasing contact time.Cyclohexene, an intermediate, registered a maximum at an intermediate contact time and then began to fall, while 1- and 3-methylcyclopentenes kept on increasing; the concentration of 1-methylcyclopentene was always higher than that of 3-methylcyclopentene.The dehydration of cyclohexanol followed a first order kinetics.The mechanism of transformation of cyclohexanol over alumina has been explained in terms of both Broensted and Lewis acid sites.
- Krishnasamy, V.,Ratnasamy, P.
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p. 839 - 842
(2007/10/02)
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- THE EFFECT OF PARTIAL EXCHANGE OF SULPHONATED MACROPOROUS STYRENE-DIVINYLBENZENE COPOLYMERS FOR DIFFERENT IONS ON THEIR CATALYTIC ACTIVITY
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The catalytic activity of sulphonated macroporous styrene-divinylbenzene copolymers, the exchange capacity of which was neutralized from 30, 50 and 80percent by Fe(III) ions and from 30percent by Na ions and that of Wofatit Y-37 ion exchanger neutralized from 10percent of its total exchange capacity by several transition metal ions and by sodium has been studied in isomerization of cyclohexene and dehydration of 1-propanol in the gas phase at 130 deg C.It was demonstrated that in both reactions transition metal ions exhibit additional effect to the expected neutralization of the polymer acid groups.In the case of cyclohexene isomerization, this effect depends on the degree of crosslinking of polymer mass of the catalyst.Such dependence has not been, however, observed in dehydration of 1-propanol.The type of transition metal ions did not exhibit any significant effect on the catalytic activity of the polymer catalysts studied.
- Kmostak, Svatomir,Setinek, Karel
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p. 2354 - 2363
(2007/10/02)
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- Nickel-catalyzed Asymmetric Alkylation of Some Chiral and Achiral Allylic Alcohols
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(-)(R)-1,2-bis(Diphenylphosphino)-1-phenylethane(II) chloride was found to catalyze the asymmetric alkylation of some chiral and achiral allylic alcohols with Grignard reagents, leading to the formation of optically active olefins.Enantiomer discrimination of the substrate takes place in the alkylation of chiral allylic alcohols.
- Consiglio, Giambattista,Morandini,Franco,Piccolo, Oreste
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p. 987 - 989
(2007/10/02)
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