2532-58-3Relevant articles and documents
Catalytic activity of Mo oxide before and after alkali metal addition for methylcyclohexane and methylcyclopentane compounds
Al-Kandari,Mohamed,Al-Kharafi,Katrib
, p. 189 - 193 (2015/07/27)
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.
Methylcyclohexane ring-contraction: A sensitive solid acidity and shape selectivity probe reaction
Mcvicker, Gary B.,Feeley, Owen C.,Ziemiak, John J.,Vaughan, David E. W.,Strohmaier, Karl C.,Kliewer, Wayne R.,Leta, Daniel P.
, p. 2222 - 2226 (2007/10/03)
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.
Isomerization of cycloheptane, cyclooctane, and cyclodecane catalyzed by sulfated zirconia - Comparison with open-chain alkanes
Satoh, Daishi,Matsuhashi, Hiromi,Nakamura, Hideo,Arata, Kazushi
, p. 4343 - 4349 (2007/10/03)
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.
Stereoselectivity of cyclization of substituted 5-hexen-1-yllithiums: Regiospecific and highly stereoselective insertion of an unactivated alkene into a C-Li bond
Bailey, William F.,Khanolkar, Atmaram D.,Gavaskar, Kaustubh,Ovaska, Timo V.,Rossi, Kyllikki,Thiel, Yvonne,Wiberg, Kenneth B.
, p. 5720 - 5727 (2007/10/02)
Substituted 5-hexen-1-yllithiums, 6-10, which were prepared in solutions n-C5H12-Et2O (3:2 by vol) by low-temperature lithium-iodine exchange between t-BuLi and the appropriate iodide, undergo clean, 5-exo-trig cyclization upon warming to give substituted (cyclopentyl)methyllithiums, 11-14, in good yield and with a high degree of stereocontrol. In each case, the major product is the same isomer as that observed in studies of the isomerization of analogously substituted 5-hexen-1-yl radicals, but the organolithium cyclizations are invariably much more stereoselective than radical-mediated processes. Lewis base additives such as THF, TMEDA, and PMDTA serve to increase the rate of cyclization of the substituted 5-hexen-1-yllithiums, but such additives do not reduce the high stereoselectivity of the process. The observed regioselectivities and stereoselectivities of the intramolecular addition of a C-Li bond to an unactivated alkene suggest that the closure of the anion proceeds via a transition state that resembles a chair cyclohexane in which substituents preferentially occupy pseudoequatorial positions. Ab initio molecular orbital calculations at the 3-21G level, which support this transition-state structure (chair-like geometry with a C(1)-C(5) distance of 2.18 ?), suggest that the ground-state structure of 5-hexen-1-yllithium is essentially that of a cyclohexane chair [C(1)-C(5) distance of 3.35 ?] in which the lithium atom is coordinated with the C(5)-C(6) π-bond (Li-C(5) distance of 2.41 ? and Li-C(6) distance of 2.38 ?). The stabilizing interaction of the lithium atom with the π-system of the remote alkene moiety appears to be an important component of the cyclization since it serves to establish a chair-like geometry prior to the activation step leading to (cyclopentylmethyl)lithium. Calculation of the difference in energy between an axially substituted transition state and one bearing an equatorial substituent gave product ratios that were in very good agreement with experimental observations. The activated complex was also modeled via molecular mechanics calculations with modified MM2 parameters, and the results of these analyses were found to be in good accord with both the ab initio results and the experimentally observed selectivities. The preference of a substituent for the pseudoequatorial position in the chair-like transition state is, to a reasonable approximation, given by the conformational energy of the substituent in the cyclohexane system, and the stereoselectivity of cyclizations of substituted 5-hexen-1-yllithiums may be anticipated by recourse to such values.
Reactions of Methyl-Substituted Hex-5-enyl and Pent-4-enyl Radicals
Beckwith, Athelstan L. J.,Easton, Christopher J.,Lawrence, Tony,Serelis, Algirdas K.
, p. 545 - 556 (2007/10/02)
Relative and absolute kinetic data have been determined for ring closure of methyl-substituted hex-5-enyl radicals: 2-methyl-(10a), 3-methyl-(4a), 4-methyl-(5a), 2,2-dimethyl-(10c), 3,3-dimethyl-(4c) and 4,4-dimethyl-hex-5-enyl (5c) radicals, generated by interaction of tributylstannane with the corresponding bromides (1a)-(3a) and (1c)-(3c).Each radical undergoes regiospecific or highly regioselective 1,5-cyclization more rapidly than does the unsubstituted radical (4d).The rate enhancements, which arise mainly from lowering of the activation energy, can be rationalized in terms of the gem-dimethyl effect. 1,5-Ring closures of monosubstituted species are stereoselective: 2-methyl- and 4-methyl-hex-5-enyl radicals (10a) and (5a) give mainly trans products, whereas 3-methylhex-4-enyl radical gives mainly the cis.This behaviour reflects the effect of the substituent on the stabilities of cyclic transition complexes in chair-like conformations.Ring closure of 2,2-dimethylpent-4-enyl radical or of 3,3-dimethylpent-4-enyl radical (19) could not be detected.
CYCLIZATION OF C7-ALKANES OVER Pt BLACK CATALYST
Zimmer, H.,Paal, Z.,Tetenyi, P.
, p. 513 - 532 (2007/10/02)
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.
Stereoselectivity of Ring Closure of Substituted Hex-5-enyl Radicals
Beckwith, Athelstan L. J.,Lawrence, Tony,Serelis, Algirdas K.
, p. 484 - 485 (2007/10/02)
1,5-Ring closure of 1- or 3-substituted hex-5-enyl radicals affords mainly cis-disubstituted cyclic products, whereas 2- or 4-substituted species give mainly trans-products; the significance of this stereoselectivity is demonstrated in the formation of the norbornane system from acyclic precursors.
