1638-26-2

In this paper we describe the utility of an acid-catalyzed isomerization reaction, specifically, ring-contraction of methylcyclohexane to an isomeric mixture of alkylcyclopentanes as a tool for characterizing the acidic properties of a wide range of platinum-loaded solid acids. Methylcyclohexane isomerization is particularly useful as a solid acidity probe reaction since it is a simple molecule containing one six-membered ring and a single methyl group substituent. As a solid acidity probe molecule methylcyclohexane has a number of advantages over cyclohexane. Ring-contraction of cyclohexane produces a single product, methlycyclopentane. Methylcyclohexane ring-contraction, in contrast, yields a richer and thus more informative product mixture including ethylcyclopentane, and five isomeric dimethylcyclopentanes. For the first time it will be shown that variations in the three primary descriptors of solid acids, acid site density, acid site strength, and shape selectivity, within a wide range of amorphous and crystalline solid acids can be simultaneously ranked using a single component probe reaction, namely, methylcyclohexane ring-contraction.

Mechanistic aspects of Ziegler-Natta olefin insertion, which include catalyst/cocatalyst interactions, chain propagation, and chain termination, have been examined for systems which model the Cp2Ti(Cl)R/RAlCl2 and Cp2Ti(Cl)R/MgX2 catalyst complexes.The reaction of (2-butyl-6-hepten-1-yl)titanocene chloride with (2-propyl-6-hepten-1-yl)aluminum dichloride:diethyl etherate produced 78percent cyclization of the titanocene ligand, while less than 2percent of the ligand originating on aluminum cyclized.In a complementary experiment, the reaction of (2-propyl-6-hepten-1-yl)titanocene chloride and (2-butyl-6-hepten-1-yl)aluminum dichloride:diethyl etherate again produced only intramolecular insertion of the titanium ligand (58percent).Based on these results, equilibretion of ligands through transmetallation between titanium and aluminum did not occur under these reaction conditions, and selective insertion into the titanium-carbon bond was confirmed for this process.Similarly, ligand cyclization with Cp2Ti(Cl)R/MgX2 also occurred through insertion into the titanium-carbon bond.The product distribution generated by the MgX2 was highly solvent dependent.Cyclization in CH2Cl2 was very efficient, while reaction in toluene generated numerous products.Included in the toluene reaction mixture were compounds that resulted from ligand transposition/chain transfer of the titanium ligand. Keywords: Titanium; Aluminium; Magnesium; Olefin insertion; Ziegler-Natta catalysts; Chain transfer

The skeletal isomerization of cycloalkanes with the number of carbons greater than six, cycloheptane, cyclooctane, cyclodecane, and cyclododecane, was performed over sulfated zirconia in liquid phase at 50°C. A main product of methylcyclohexane was formed from cycloheptane via a protonated cyclopropane intermediate, protonated [4.1.0]bicycloheptane, together with small amounts of trans-1,2-dimethylcyclopentane, as- and trans-1,3- dimethylcyclopentanes, 1,1-dimethylcyclopentane, and ethylcyclopentane. A major product from cyclooctane was ethylcyclohexane via a protonated cyclobutane intermediate, protonated [4.2.0]bicyclooctane, followed by cis-1,3- dimethylcyclohexane in addition to small amounts of trans-1,2-, -1,3-, -1,4-dimethylcyclohexanes, 1,1-dimethylcyclohexane, and methylcycloheptane. The detailed reaction-paths for cycloheptane and cyclooctane were shown after additional examinations in reactions of methylcyclohexane, ethylcyclopentane, ethylcyclohexane, and 1,2-dimethylcyclohexane. Cyclodecane was dehydrogenated into cis- or trans-decaline with the evolution of a dihydrogen. Cyclododecane was converted into lots of products, more than 30 species.

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Hydrogenolysis of hydrocarbons with quaternary C atoms (neopentane, neohexane, 2,2,3-trimethylbutane, 2,2- and 3,3-dimethylpentanes and 2,2,3,3-tetramethylbutane) has been studied over Pt and Ni black catalysts.The reactivities of different types of C-C bond have been determined.The probability of C-C bond rupture where one of the carbon atoms is quaternary is inversely proportional to the bond dissociation energy.On Pt, two essential types of hydrogenolysis can be distinguished.One reaction is responsible for the breaking of internal C-C bonds attached to the quaternary carbon atom and the other for demethylation.With larger molecules, the former reaction is preferred and the surface intermediate should be 1,4-diadsorbed, while that for the latter reaction is 1,3-diadsorbed.Nickel, as previously suggested, causes terminal C-C rupture, although with branched hydrocarbon reactants internal C-C bond rupture is also possible, presumably via 1,4-adsorption.

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Conversion of m-cresol was studied on a Pt/HBeta catalyst at 225-350°C and ambient hydrogen pressure. At 250°C, the reaction proceeds through two major reaction pathways: (1) direct deoxygenation to toluene (DDO path); (2) hydrogenation of m-cresol to methylcyclohexanone and methylcyclohexanol on Pt, followed by fast dehydration on Br?nsted acid sites (BAS) to methylcyclohexene, which is either hydrogenated to methylcyclohexane on Pt or ring-contracted to dimethylcyclopentanes and ethylcyclopentane on BAS (HYD path). The initial hydrogenation is the rate-determining step of the HYD path as its rate is significantly lower than those of subsequent steps. The apparent activation energy of the DDO path is 49.7 kJ mol-1 but the activation energy is negative for the HYD path. Therefore, higher temperatures lead to the DDO path becoming the dominant path to toluene, whereas the HYD path, followed by fast equilibration to toluene, is less dominant, owing to the inhibition of the initial hydrogenation of m-cresol.

PURPOSE: A process for ring opening is provided to obtain improved conversion ratio and selectivity in comparison with the case of using hydrogen as a reducing agent. CONSTITUTION: A cyclic hydrocarbon and a reducing agent are provided as supplying materials. The supplying materials are transferred into a reactor (5) and reacted under the presence of a catalyst. A product is separated from the effusion of reaction zone. The catalyst is a heterogeneous catalyst having both acid site and metallic component. The product is obtained by evaporating and heating a mixture containing 100 parts by weight of porous molecular sieve and 0.01-20 parts by weight of water soluble metallic salt. The cyclic hydrocarbon is a naphthene group cyclic hydrocarbon which is pentagonal or hexagonal compound, or an alkyl derivative thereof selected from cyclopentane and cyclohexane. The alkyl derivative is methyl, ethyl, profile, butyl, isopropyl or an isobutyl derivative.

Abstract Different catalytic reactions of methylcyclohexane MCH are performed depending on the nature of the catalytic active site (s) and experimental conditions. Ring contraction RC catalytic processes, producing dimethylcyclopenanes DMCP's of high octane numbers as compared to MCH are catalysed by acidic function of zeolites systems such as HY. Better activity, selectivity and stability concerning these RC reactions were obtained using Pt/HY catalyst. At higher reaction temperature, dehydrogenation of MCH to toluene and hydrocracking reactions are catalyzed by Pt. Comparable catalytic behavior is obtained using a bifunctional (metal-acid) MoO2-x(OH)y/TiO2 (MoTi) system. Different metallic character strength is observed following the suppression of the Br?nsted acid MoOH function(s) to MoO2-x(OA)y/TiO2 (A = Na, K, Rb) by the addition of small amount of alkali metal A. Rubidium addition seems to be the most performant in the dehydrogenation of MCH to toluene. The metallic functions in MoTi and modified AMoTi are not efficient for RO in MCP. In-situ characterization of the different oxidation states of Mo at different experimental conditions were conducted using in-situ XPS-UPS techniques.

The present paper is the second part of a systematic study of the influence of W and Ir loading on the activity of Ir/WO3/ZrO2-SiO2 catalysts for the ring-opening reaction of naphthenic molecules using methylcyclohexane (MCH) as a model compound. A series of Si-stabilized tungstated zirconias, WOx/ZrO2-SiO2, containing up to 3.5 atom W/nm2, was prepared. Ir-based catalysts containing up to 1.2 wt% were obtained by impregnation of these solids. Characterization of the metal dispersion and catalyst acidity was described in a previous article. The objective of the present study was to determine the best metal/acid balance for optimal performance of Ir/WOx/ZrO2-SiO2 catalysts in the ring-opening reaction of MCH. Monofunctional (acid WOx/ZrO2-SiO2 or metal Ir/ZrO2-SiO2) and bifunctional (Ir/WO3/ZrO2-SiO2) catalysts were examined. Based on the analysis of the yields and products distributions, a reaction network was proposed, and kinetic data (e.g., activation energies, initial rates) were calculated. Correlations between characterization results obtained earlier (e.g., acidity, dispersion) and catalytic performance are also reported. The monofunctional acid catalysts WOx/ZrO2-SiO2 showed a low selectivity for ring opening. The ring-contraction activity developed for W surface density above a threshold value of 1 atom W/nm2. This was attributed to the appearance and the development of a relatively strong Broensted acidity monitored by infrared measurements. MCH ring contraction and C5 naphthene ring opening occur according to a classic acid mechanism. For low conversions, the monofunctional metal catalysts Ir/ZrO2-SiO2 exhibited significant selectivity for ring opening that decreased with increasing conversion. Because of the lack of ring-contraction products, the observed activity was attributed to the direct ring opening of the MCH. Ring opening and cracking occur according to a dicarbene mechanism. The study of MCH conversion on Ir/WOx/ZrO2-SiO2 catalysts indicated that MCH ring contraction to alkylcyclopentanes occurs before ring opening. The best yields for ring opening were obtained with the 1.2% Ir/WOx/ZrO2 (1.5 atom of W/nm2). Further increases in W surface density led to a decrease in the indirect ring-opening yield, attributed to a decrease in Ir dispersion. For bifunctional metal/acid catalysts, analysis of the mechanism is less straightforward. The activation energy for C6 ring contraction and indirect C6 ring opening is a function of the metal/acid ratio. For high ratios, indirect ring opening occurs essentially over metallic sites. A decrease in the metal/acid ratio enhances the contribution of acid mechanism.

Removing impurities from a heptane stream by contacting the heptane stream with an acidic catalyst, wherein the contacting reduces a concentration of one or more close boiling impurities, one or more olefins, or both. The impurities are isomerized via contact with the acidic catalyst into species that possess lower octane levels or that do not possess boiling points as near to the boiling point of n-heptane, which promotes separation of the impurities via distillation. Close boiling impurities may include such compounds as cis-1,2-dimethylcyclopentane and methylcyclohexane or may be compounds having boiling points at a standard pressure of 760 Torr in the range of about 96.5 to about 100.5 degrees Celsius including such compounds as cis-1,2-dimethylcyclopentane and methylcyclohexane. The concentration of cis-1,2-dimethylcyclopentane and methylcyclohexane may be reduced by at least about 25 and 10 percent by weight, respectively. The concentration of olefins, as measured by the Bromine Index, may be reduced by at least about 25 percent by weight.

Dependent on n different products are obtained from bicycloalkanes by hydrogenation on Pt and Pd/C catalysts: from n = 5 onward only methylcycloalkanes of the same ring size; with n = 4 additionally 2-7 percent of cycloheptane is formed; with n = 3 ring enlargement increases to 5-20 percent and with n = 2 cyclopentane is the only product.Mainly butane is formed from bicyclobutane and no intermediate could be detected.Explanations are attempted.The expected products are produced on hydrogenation of methyl-substituted derivatives and spiroalkanes.

Deuterium tracer studies with a combined gas-liquid chromatography and mass spectrometry analysis of products and using 2,2,4,4-tetramethylpentane (TMP) as a model reactant establish clearly that the selective cyclisation (SCM) of five-carbon chain alkanes on Ir, Rh, Pd and Pt is by the heterogeneous counterpart of reductive elimination of alkyls in organometallic chemistry.A comparison of cyclisation of TMP, 3,3-dimethylpentane and n-pentane on films of the same series of metals and an extended study of cyclisation of 3,3-dimethylpentane and of n-pentane on a series of Pt-Cu alloy films with variation of hydrogen partial pressure show that more than one mechanism of non-selective cyclisation (NSCM) takes place.The isotopic studies show clearly that a monoadsorbed intermediate is sufficient for bond-shift rearrangement of TMP to 2,2,5-trimethylhexane on Ir, Rh, Pd or Pt.An important major conclusion to be derived from the present work is that one surface metal atom comprises the active centre of the catalytic site for a variety of reactions in addition to simple hydrogenation-dehydrogenation.

The reactions of tert-butyllithium (t-BuLi) with primary α-iodo-ω-haloalkanes and α,ω-dibromoalkanes have been investigated in experiments conducted at -23 deg C in n-pentane-diethyl ether (3:2 by volume) solution.It has been found that production of an α-lithio-ω-haloalkane (1) by metal-halogen interchange at one end of a 1,3-, 1,4-, or 1,5-dihalide results in intramolecular coupling to give cycloalkanes in high yield.As the chain length of the dihalide is increased beyond five carbon atoms the production of an α,ω-dilithio species by interchange at bothends of the dihalide ceases to be excluded by cyclization of 1 and a precipitous drop in the yield of cycloalkane was found to occur in reactions of 1,6-diiodoalkanes with t-BuLi.Metal-halogen interchange was the exclusive process observed in reactions of α,ω-dihalides with t-BuLi provided at least one halogen of the substrate was an iodine.By contrast, similar treatment of α,ω-dibromoalkane provided only minor amounts of product attributable to metal-halogen interchange.Under conditions that provide an essentially quantitative yield of carboxylic product from reductive cyclization of 1 generated from 1,5-diiodo-3,3-dimethylpentane, the corresponding 1,5-dibromide was converted to a mixture composed of cycloalkane, products from Wurtz-type coupling with t-BuLi, and quantities of parent alkane from formal reduction of the dihalide.The mechanism of the metal-halogen interchange was further probed by using 6-halo-1-hexene substrates.Observation of cyclized product from the reaction of t-BuLi with 6-bromo- and 6-iodo-1-hexene demonstrated that the interchange between t-BuLi and primary alkyl bromides and iodides occurs predominantly via single-electron-tranfer (SET) process.Incorporation of alkyl radical-halide ion adducts with halogen dependent lifetimes as intermediates following SET from alkyllithium to alkyl halide serves to explain the disparate behavior of alkyl bromides and iodides when treated with t-BuLi.A unifield SET-mediated mechanism for metal-halogen interchange and Wurtz coupling is presented.

The ionic hydromethylation of olefins with the (CH3)4Si-HCl-AlCl3 system was realized for the first time.A method was developed on the basis of this system for the production of high yields of difficultly obtainable saturated hydrocarbons with a quaternary carbon atom (including bicyclic compounds with an angular methyl group) from acyclic, monocyclic, and bicyclic olefins.

C6-and C5-cyclization of heptane isomers (and also, olefin formation as a related process) over Pt-black have been studied in pulse and circulation systems.Hydrogendeficient conditions favour aromatization, via presumably terminal olefins.C5-Cyclization in the presence of more hydrogen is accompanied by internal olefin formation.Relative reactivities of all heptane isomers have been measured; this shows that cyclization is easier between terminal methyl groups.Optimum hydrogen pressures for both types of cyclization have been determined (and compared with hydrogenolysis, too).Earlier mechanism suggestion for aromatization and cyclopentane formation have been confirmed; the distinction between two types of bond shift mechanisms producing aromatics (from substituted pentanes) and saturated isomers, respectively, has recieved additional support facilitating the identification of these two reactions with mechanisms proposed in the literature.

Carbocyclic three-, four- and five-membered rings are formed in good to excellent yield (87-100percent) upon treatment of the appropriate α,ο-diiodide with t-butyllithium in pentane-ether solution at -23 deg C.The corresponding dibromides do not undergo clean cyclization.

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Hydrocarbons with a quaternary carbon atom have been obtained by alkyl group transfer from group 4 tetra-alkyl derivatives to tertiary carbenium ions in the presence of Lewis acids.