Formation Of Cyclohexene Research Articles

Intact molecular ion formation of cyclohexane and 2,3-dimethyl-1,3-butadiene by excitation with a short, intense femtosecond laser pulse

Cyclohexane and 2,3-dimethyl-1,3-butadiene (DMBD) were ionized and fragmented by 0.8 μm femtosecond pulses with a typical intensity of 4 × 10 13 W cm −2, which were resonant with the cation absorption of cyclohexane and DMBD. Their intact molecular ions were dominant at a pulse duration of 15 fs, whereas the molecules were heavily fragmented by excitation at 205–210 fs. Possible reasons for the formation of intact molecular ions by a short pulse are discussed in terms of the vibrational periods of excited precursor states.

Characterization and catalytic study of Pt [sbnd]Ge/Al 2O 3 catalysts prepared by organometallic grafting

Ge was added to 1% Pt/Al 2O 3 catalyst by controlled surface reaction of Ge( n-C 4H 9) 4 in amounts corresponding nominally to 1/12, 1/8, 1/2, 1, or 2 monolayers. These Pt Ge/Al 2O 3 catalysts were characterized by FTIR of CO, TEM, H 2 chemisorption, and EXAFS as well as tested in catalytic reactions, that is, transformation of hexane, benzene and cyclohexene in the presence of excess hydrogen. Loading of Ge in amounts of 1/12–1/2 monolayers resulted in catalysts with “bimetallic surface.” Loading of 1/12 monolayer of Ge resulted in randomly deposited Ge atoms on the surface of Pt. It hardly affected the catalytic behavior as compared with the Ge-free parent catalyst; 1/8 monolayer of Ge was still located on Pt as single atoms (as shown by EXAFS), but Ge selectively poisoned high coordination sites, active in benzene hydrogenation. This reaction was completely suppressed here, whereas this catalyst was most active in cyclohexene transformation. Pt with 1/8 and 1/2 monolayers of Ge transformed hexane with high selectivity into saturated C 6 products and formed hardly any benzene. The formation of cyclohexane from hexane was also observed, not typical for monofunctional Pt catalysts. Adding 1–2 monolayers of Ge caused a new type of interaction between Pt and Ge containing sites that adsorbed CO but did not adsorb hydrogen. A solid solution of Pt Ge may have arisen here, creating “bulk bimetallic catalysts” with somewhat more surface Pt atoms not interacting with Ge. These catalysts behaved similarly in hydrocarbon transformations as the original parent catalyst. The possible reaction mechanism of hexane transformation is discussed in detail, in terms of thermodynamic limitations of benzene formation and possible surface species.

Reactions of Sterically Congested 1,6‐ and 1,7‐Bis(diazo)alkanes with Elemental Sulfur and Selenium: Formation of Cyclohexene, 1,2‐Dithiocane, 1,2‐Diselenocane, and 1,2,3‐Triselenecane Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Reactions of sterically congested 1,6‐ and 1,7‐bis(diazo)alkanes with elemental sulfur and selenium: Formation of cyclohexene, 1,2‐dithiocane, 1,2‐diselenocane, and 1,2,3‐triselenecane derivatives

AbstractThe reaction of 3,8‐bis(diazo)‐2,2,4,4,7,7,9,9‐octamethyldecane (5) with elemental selenium in 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) at 130°C yielded 1,2‐di‐tert‐butyl‐3,3,6,6‐tetramethylcyclohexene (1) (64%) and trans‐3,8‐di‐tert‐butyl‐4,4,7,7‐tetramethyl‐1,2‐diselenocane (8) (13%), while that of 5 with elemental sulfur in DBU gave trans‐3, 8‐di‐tert‐butyl‐4,4,7,7‐tetramethyl‐1,2‐dithiocane (9) (77%). The reaction of 3,9‐bis(diazo)‐2,2,4,4,8,8,10,10‐octamethylundecane (6) with elemental selenium in DBU at 80°C gave a cyclic triselenide, cis‐4,10‐di‐tert‐butyl‐5,5,9,9‐tetramethyl‐1,2,3‐triselenecane (11), in 15% yield as the only identifiable product. The structures of 9 and 11 were confirmed by X‐ray crystallography. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:351–356, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10046

Influence of the Dispersion of Metallic Particles on the Reaction of Triphenylarsine with Alumina-Supported Nickel

The hydrogenolysis of triphenylarsine with alumina-supported nickel catalysts with various particle sizes was studied at temperatures ranging from 303 to 443 K under 12 bar of hydrogen. The reaction initially takes place selectively on the surface of the nickel particles and leads to the successive hydrogenolysis of –As–Ph bonds with benzene and cyclohexane formation. At 303 K, the reaction stops when the Ni particles are completely covered with grafted– As–Ph fragments. The quantity of fixed arsenic increases with the dispersion of the metal particles. It is proposed that more As–Ph fragments (per metallic atom) are grafted onto edge atoms than onto face atoms of the Ni particles. When the reaction is performed at higher temperature, the As atoms migrate inside the nickel particles easily and form an intermetallic compound. At 373 K, the Ni5As2 phase, very poorly crystallized, is obtained. At 443 K, the reaction leads to a well-crystallized phase NiAs. The dispersion of the catalyst has no influence on the nature of the formed intermetallic species. However, the formation rate of these species increases with the dispersion of the catalysts.

Modeling and Simulation of Four Catalytic Reactors in Series for Naphtha Reforming

In this work the modeling and simulation of catalytic naphtha reforming process is presented. The process model uses an extended version of the kinetic model reported by Krane et al. (Krane, H. G.; Groh, A. B.; Shulman, B. D.; Sinfeit, J. H. Proceedings of the Fifth World Petroleum Congress, 1959; pp 39−51). The new kinetic model utilizes lumped representation of the reactions that take place. These groups range from one to eleven carbon atoms for paraffins (P1−P11), and from six to eleven atoms of carbon for naphthenes (N6−N11) and aromatics (A6−A11). Other reactions that this kinetic model considers are the cyclohexane formation via methylcyclopentane isomerization (MCP ↔ N6) and paraffins isomerization (nPi ↔ iPi). The process model is used to predict temperature and reformate composition profiles in a commercial reforming unit consisting of a series of four catalytic reactors. The agreement between predicted and commercially reported results is very good.

Cyclohexene Formation by Partial Gas-Phase Hydrogenation of Benzene in a Microchannel Reactor Containing Ru-Zn as Catalyst

Cyclohexene Formation by Partial Gas-Phase Hydrogenation of Benzene in a Microchannel Reactor Containing Ru-Zn as Catalyst

Adsorption and thermally induced reactions of halocyclohexanes on a Cu 3Pt(1 1 1) surface

The chemistry of iodocyclohexane, bromocyclohexane and chlorocyclohexane on a Cu 3Pt(1 1 1) surface has been investigated by temperature-programmed desorption (TPD), Auger electron spectroscopy (AES) and near-edge X-ray absorption fine structure (NEXAFS) measurements. Overall, the three halocyclohexanes undergo similar transformations on a Cu 3Pt(1 1 1) surface. C–I, C–Br and C–Cl bonds break between the corresponding temperatures on Cu(1 1 1) and Pt(1 1 1), leaving cyclohexyl species on the surface. The dehydrogenation reaction leading to the formation of benzene takes place at a very low coverage of cyclohexyl. As the surface concentration of halocyclohexane is increased, the dehydrogenation and hydrogenation of cyclohexyl leading to the formation of cyclohexane and cyclohexene dominates surface processes. The ratio of cyclohexene to cyclohexane produced during thermal annealing depends on the halogen involved. The lower C–X dissociation temperature for C–I, as compared to C–Cl and C–Br seems to favor cyclohexane formation. Molecular desorption of halocyclohexanes from monolayer and multilayer becomes significant at a higher dose. No surface carbon was found after thermal desorption under any coverage.

Kinetic Modeling of Naphtha Catalytic Reforming Reactions

In this work a kinetic model for the naphtha catalytic reforming process is presented. The model utilizes lumped mathematical representation of the reactions that take place, which are written in terms of isomers of the same nature. These groups range from 1 to 11 atoms of carbon for paraffins, and from 6 to 11 carbon atoms for naphthenes and aromatics. The cyclohexane formation via methylcyclopentane isomerization and paraffins isomerization reactions were considered in the model. Additionally, an Arrhenius-type variation was added to the model in order to include the effect of pressure and temperature on the rate constants. The kinetic parameters values were estimated using experimental information obtained in a fixed-bed pilot plant. The pilot reactor was loaded with different amounts of catalyst in order to simulate a series of three reforming reactors. The reformate composition calculated with the proposed model agrees very well with experimental information.

Direct formation of cyclohexene via the gas phase catalytic dehydrohalogenation of cyclohexyl halides

The gas phase dehalogenation of cyclohexyl chloride and cyclohexyl bromide (where 423 K≤ T≤523 K) promoted using silica and zeolite supported nickel catalysts in the presence of hydrogen is presented as a viable one step route for the production of cyclohexene. Cyclohexene is generated via the internal elimination of the corresponding hydrogen halide where the process is 100% selective at T≤473 K. At higher temperatures, cyclohexane and benzene were isolated in the product mixture as a result of the combination of catalytic hydrogenolysis, hydrogenation and dehydrogenation steps. Cyclohexene yield was subject to a short term reversible decline with time-on-stream due to a surface poisoning by the hydrogen halide that was produced but the presence of hydrogen served to displace the inorganic halide and extend the productive lifetime of the catalyst. Bromine removal from cyclohexyl bromide was found to be more facile while the use of a higher loaded (15.2% (w/w) as opposed to 1.5% (w/w)) nickel silica is shown to result in appreciably higher dehydrohalogenation rates. Both Na/Y and Ni–Na/Y zeolites promoted cyclohexene formation but exhibited an irreversible deactivation which is attributed to pore blockage by occluded coke. With a view to optimising catalyst efficiency, the effect on cyclohexene yield of varying such process parameters as reaction time and temperature and reactant(s) partial pressures were studied and the catalytic data are compared with thermodynamic predictions.

The cyclohexanol dehydrogenation on Rh [sbnd]Cu/Al 2O 3 catalysts: 2. Chemisorption and reaction

Rh Cu supported on alumina were selected for the dehydrogenation of cyclohexanol. Highly dispersed Rh Cu supported on alumina were obtained and characterized after reduction. The metallic surface area was determined by frontal H 2 chemisorption and by N 2O decomposition followed by TPR. The TPR method for surface oxide reduction after exposing the catalyst to N 2O decomposition for the determination of the active phase is in good agreement with the frontal H 2 chemisorption method on rhodium, copper and bimetallic catalysts. The temperature and time exposition are important parameters for a complete oxidation of the monolayer, in particular for lower concentration of copper. An exposition time of 20 h is needed to complete a monolayer oxidation. Metallic copper is oxidized to Cu 1+ and Cu 2+ although not all Cu 2+ is reduced to Cu 1+ without oxidation of a sublayer. For the bimetallic catalysts Rh Cu a complete monolayer was attained. The TOF values were calculated based on the total active sites which give correct interpretation of the activity. The activity decreases when copper is added to rhodium which was attributed to an ensemble effect. For lower contents the selectivity of ketone was enhanced, which could be explained by simultaneous geometric and electronic effects. The selectivity on the monometallic catalysts prevails toward cyclohexene formation, indicating strong influence of the acidic sites. However, for the bimetallic catalysts it changed drastically toward dehydrogenation. The second metal affects the surface sites enhancing the metallic or bimetallic formation for dehydrogenation. This phenomena explains the electronic effect on bimetallic Rh Cu systems.

Gas Phase Atomic Hydrogen-Induced Hydrogenation of Cyclohexene on the Ni(100) Surface

Gas phase hydrogen atoms add to adsorbed cyclohexene at 100 K on the Ni(100) surface, resulting in cyclohexane formation during subsequent TPR (temperature-programmed reaction) experiments. No C−C bond activation is observed after exposure to gas phase atomic hydrogen. Vibrational and isotope studies indicate that a cyclohexyl intermediate is formed by the addition of gas phase atomic hydrogen to adsorbed cyclohexene. This adsorbed cyclohexyl is hydrogenated primarily by surface hydrogen to form cyclohexane during subsequent heating. Cyclohexane yields increase with increasing atomic hydrogen exposure, and yields in the 90% range have been observed with large atomic hydrogen exposures. In the presence of only coadsorbed hydrogen, no significant hydrogen addition to adsorbed cyclohexene is observed, and cyclohexene desorption dominates during subsequent TPR experiments. Vibrational spectroscopy indicates that π-bonded cyclohexene with the CC bond parallel to the surface is the dominant surface species in the presence of coadsorbed surface hydrogen. In contrast, di-σ-bonded cyclohexene is the dominant species in the absence of coadsorbed hydrogen. In the absence of coadsorbed hydrogen, dehydrogenation of the adsorbed cyclohexene results in benzene formation with increasing temperature. Adsorbed benzene formed by dehydrogenation has been identified after heating to 390 K in the absence of hydrogen using vibrational spectroscopy.

Selective Hydrogenation of Benzene to Cyclohexene on Ru/γ-Al2O3

Hydrogenation of benzene to cyclohexene has been studied over Ru/Al2O3catalysts in the presence of water. Attention has been paid to the influence of reaction conditions, ruthenium precursors, and catalyst pretreatment. The reaction was carried out under kinetic control and under strong mass transfer limitation. In the presence of water the formation of cyclohexene cannot be simply ascribed to physical effects. Mass transfer limitations are, however, important to obtain high selectivities at high conversion. A pretreatment of the catalyst under hydrogen, in the absence of benzene, increases the selectivity to cyclohexene. No effect has been observed when the pretreatment is carried out under nitrogen. Catalysts prepared from RuCl3are more selective with respect to samples prepared from chlorine-free precursors.

ChemInform Abstract: Formation of Cyclohexanes in the Palladium‐Catalyzed Reaction of . epsilon.‐Unsaturated Cyano Esters and Congeners.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Thermodynamic Properties and Ideal-Gas Enthalpies of Formation for Cyclohexene, Phthalan (2,5-Dihydrobenzo-3,4-furan), Isoxazole, Octylamine, Dioctylamine, Trioctylamine, Phenyl Isocyanate, and 1,4,5,6-Tetrahydropyrimidine

The results of a study aimed at improvement of the group-contribution methodology for estimation of thermodynamic properties of organic substances are reported. Specific weaknesses where particular group-contribution terms were unknown, or estimated because of lack of experimental data, are addressed by experimental studies of enthalpies of combustion in the condensed phase, vapor-pressure measurements, and differential scanning calorimetric (dsc) heat-capacity measurements. Ideal-gas enthalpies of formation of cyclohexene, phthalan (2,5-dihydrobenzo-3,4-furan), isoxazole, octylamine, dioctylamine, trioctylamine, phenyl isocyanate, and 1,4,5,6-tetrahydropyrimidine are reported. Two-phase (liquid + vapor) heat capacities were determined for phthalan, isoxazole, the three octylamines, and phenyl isocyanate. Liquid-phase densities along the saturation line were measured for phthalan and isoxazole in the temperature range 298 K to 425 K. The critical temperature and critical density of octylamine were determi...

Formation of cyclohexanes in the palladium catalyzed reaction of ɛ-unsaturated cyano esters and congeners

A previously described palladium-catalyzed cyclization leading to cyclopentane derivatives has been extended to the formation of cyclohexanes by disfavoring the competing Heck reaction. The nature of the nucleophile plays a prominent part in this generalization.

Inverted potential-energy surfaces in the radical-cation Cope rearrangements of hexa-1,5-diene and semibullvalene

Comparison of the radical-cation transformations of hexa-1,5-diene and semibullvalene with the degenerate rearrangements of these neutral compounds reveals that the equilibrium structure of the radical cation in each case corresponds to a symmetrical transition-state structure for the neutral molecule. Thus, the cyclohexane-1,4-diyl radical cation is formed initially by the one-electron oxidation of hexa-1,5-diene, spectroscopic proof of its delocalized chair structure being obtained by matrix-isolation studies. Similarly, it is found that the ionization of semibullvalene generates the bicyclo[3.3.0]octa-2,6-diene-4,8-diyl radical cation as a delocalized mesovalent species corresponding to the case of strong interaction between two allylic groups held in a boat conformation. Spectroscopic studies reveal that the singly occupied molecular orbitals of these diyl and diallyl radical cations are non-bonding and correspond to the respective HOMOs of the neutral transition states. Inversion of the potential-energy surface for the radical cation comes about because the difference between the ionization potentials of the neutral molecule and its transition state exceeds the activation enthalpy for the degenerate rearrangement of the neutral molecule, the low ionization potential of the transition state being attributable to the non-bonding character of its HOMO. The radical-cation rearrangements are therefore termed ‘half-Cope’ reactions since the degeneracy of the reaction coordinate is lifted in going from the neutral molecule to its radical cation. A secondary rearrangement of the cyclohexane-1,4-diyl radical cation to the cyclohexene radical cation by hydrogen transfer is accessible on account of the potential-energy minimum for the intermediate diyl radical cation. In contrast, the lack of cyclohexene formation as a side product of the neutral Cope reaction suggests that in this case there is no intermediate species with a significant potential-energy well along the reaction surface to allow this competitive path to occur.

Rate enhancement and multiplicity in a partially wetted and filled pellet: Experimental study

AbstractPhase transition during an exothermic multiphase reaction was studied experimentally using a single catalytic pellet reactor. Cyclohexene hydrogenation (to cyclohexane) and disproportionation (to benzene and cyclohexane) on Pd/Al2O3 comprised the test reaction system. The steady‐state behavior of the pellet exposed on part of its surface by a flowing liquid rivulet containing the liquid reactant (cyclohexene) and the other part by a flowing gas containing the gaseous reactant (hydrogen) was examined. Measurements included the pellet weight (liquid holdup), degree of external wetting, center and surf ace temperature and overall reaction rates. Two regimes observed are: a low‐rate regime for all hydrogen gas‐phase concentrations in which the partially wetted pellet is filled mostly with liquid and nearly isothermal; a high‐rate regime for hydrogen concentrations exceeding a critical value in which the pellet is filled only partially with liquid and the pellet temperature rise is considerable. Benzene formation was observed in this state. The difference in overall cyclohexane formation rates between the two states was as high as a factor of 20 for the same bulk conditions. Over the range where multiple states were observed, the steady state of the pellet depended on whether the pellet was pref tiled with the reactive gas mixture or with liquid cyclohexene. The range over which the high‐rate state was sustained was the largest for the most active catalyst and declined as the catalyst slowly deactivated. Data features are interpreted using the theoretical foundations of the half‐wetted catalytic slab model (Harold and Watson, 1993).

Structures and properties of anthranilato- and N-phenylanthranilato-rhodium(I) complexes containing triphenylphosphine ligands

The structures of two triphenylphosphine rhodium(I) complexes with anthranilic and N-phenylanthranilic acid, which are active in hdyrogenation of some alkenes, dienes, aromatic and heteroaromatic compounds, are described, together with some of their catalytic properties. A monomeric aminocarboxylate analogue of Wilkinson's catalyst is postulated for the anthranilate complex ( 1) and a dimeric structure with carboxylate bridges and two cis-triphenylphosphine molecules coordinated to each rhodium atom is proposed for N-phenylanthranilate ( 2). On treatment with hydrogen both complexes give cis-dihydrides, but variable temperature 1H and 31P NMR studies of the product derived from 1 reveal that a temperature-dependent equilibrium involving dissociation of PPh 3 occurs. Complexes 1 and 2 are stable under hydrogenation conditions and enable slow hydrogenation of 1-alkenes and cyclohexadienes. For cyclohexadienes some selectivity to cyclohexene formation is observed, especially in DMF. Although the activities of 1 and 2 towards the hydrogenation of arenes and heteroaromatics are generally very low, pyridine can be hydrogenated to piperidine to a substantial degree.

Carbocycle formation via intramolecular insertion of alkynes into titanium-carbon bonds

Treatment of alkyl titanocene chloride complexes with the Lewis acids EtAlCl 2 or Me 2AlCl resulted in intramolecular insertion of a tethered alkyne into the TiC bond. Regioselective alkyne insertion produced exocyclic trisubstituted alkene products resulting from four-, five-, and six-membered ring formation. In the case of cyclohexane formation, the alkyne was found to insert with syn stereoselectivity.