Showing papers on "Cyclohexene published in 1994"

A More General Approach to Distinguishing "Homogeneous" from "Heterogeneous" Catalysis: Discovery of Polyoxoanion- and Bu4N+-Stabilized, Isolable and Redissolvable, High-Reactivity Ir.apprx.190-450 Nanocluster Catalysts

Abstract: A more general approach to distinguishing between so-called homogeneous vs heterogeneous catalysts has been developed and intrinsically tested in answering the question {open_quotes}what is the true catalyst in the active hydrogenation system which evolves from cyclohexene, hydrogen, and the discrete, polyoxoanion-supported Ir(I) catalyst precursor (Bu{sub 4}N){sub 5}Na{sub 3}[(1,5-COD)Ir{sm_bullet}P{sub 2}W{sub 15}Nb{sub 3}O{sub 62}]?{close_quotes}. The approach developed and utilized consists of four categories of experiments: (I) catalyst isolation and characterization studies, with an emphasis on TEM; (II) initial kinetic studies, emphasizing whether or not the isolated catalyst can account for the observed kinetics, especially any induction period seen, and whether or not the reaction exhibits a {plus_minus}10% reproducible rate; (III) quantitative phenomenological catalyst poisoning and recovery experiments; (IV) additional kinetic and mechanistic studies and chemical tests, all interpreted with strict adherence to the principle that the correct description of the catalyst (i.e., the correct mechanism) will explain all of the data. The present approach has identified a previously unknown type of hybrid homogeneous-heterogeneous, Ir{sub {approximately}190-450}{sm_bullet}polyoxoanion/Bu{sub 4}N{sup +} catalyst of average composition [Ir(0){sub {approximately}300}(P{sub 4}W{sub 30}Nb{sub 6}O{sub 123}{sup 16{minus}}){sub {approximately}33}](Bu{sub 4}N){sub {approximately}300}Na{sub {approximately}233}.

C-H Bond Activation by Metal Oxo Species: Oxidation of Cyclohexane by Chromyl Chloride

Abstract: Chromyl chloride (CrO 2 Cl 2 ) reacts with cyclohexane solvent at 75 o C to give a dark precipitate along with chlorocyclohexane and a small amount of cyclohexene (in 10.0 and ca. 0.3% yields based on chromium). Hydrolysis of the precipitate, or treatment with a coordinating organic solvent such as acetonitrile, yields cyclohexanone (8.0%) and chlorocyclohexanone (2.5%). Spectroscopic studies of the precipitate indicate that the ketone products are present intact as σ-only ligands. Iodometric titrations of the complex show the average chromium oxidation state to be 3.41. The observed organic products account for only 26% of the chromium oxidizing equivalents used in the reaction; the remainder are most likely consumed in the formation of ring-opened products such as adipic acid

Alkene epoxidation catalysed by iron(III) and manganese(III) tetraarylporphyrins coordinatively bound to polymer and silica supports

Abstract: Four tetraaryl metalloporphyrin catalysts [FeIII, Ar = phenyl and pentafluorophenyl; FeIII and MnIII, Ar = 2,6-dichlorophenyl (FeIIITDCPP and MnIIITDCPP)] have been coordinatively bonded to poly(4-vinylpyridine), and imidazole modified polystyrene (PS-Im) and silica (Si-Im). Evidence is presented that suggests that the iron(III) porphyrins are predominantly bis-ligated to the polymer supports whereas with MnIIITDCPP mono-ligation is preferred. On Si-Im all the complexes are mono-ligated. A fifth metalloporphyrin, the ionic manganese(III) 5,10,15,20-tetra(N-methyl-4-pyridyl)porphyrin (MnIIIT4MPyP); which binds strongly to unmodified silica, does not ligate to Si-lm.Leaching experiments show that FeIIITDCPP is most strongly anchored to the supports. The resulting materials have been used as catalysts for the oxidation of cyclohexene and cyclooctene by iodosylbenzene. The oxidant accountabilities are good and product distributions from reactions under nitrogen are very comparable to those from analogous homogeneous oxidations. However, the rates of the former are markedly lower. Oxidations of cyclohexene, but not of cyclooctene, in air are biphasic. The first phase, where epoxidation predominates, is attributable to an FeIIITDCPP-catalysed oxidation by PhIO and the second, which leads to allylic oxidation, to radical autoxidation.The best catalysts for large turnover epoxidations are FeIIITDCPP and MnIIITDCPP on Si–lm. The causes of the lower yields with catalysts on the more flexible polymer supports are discussed.A limited study with H2O2 as the oxidant reveals that MnIIITDCPP on Si–Im, in contrast to the ionic MnIIIT4MPyP on silica, catalyses the epoxidation of cyclooctene.

4.8 Novel Catalysis of Cesium Salt of Heteropoly Acid and its Characterization by Solid-state NMR

Abstract: Acid-catalyzed reactions by acidic cesium salts of 12-tungstophosphoric acid (H3PW12O40) have been studied in relation to the acidities and microstructure of the particles. Liquid-phase alkylation of 1,3,5-trimethylbenzene with cyclohexene, decomposition of cyclohexylacetate and gas-phase skeletal isomerization of n-butane were performed over heteropoly compounds and other typical solid acids such as zeolites, Nafion-H, SO42-/ZrO2, etc. It was found that Cs2.5H0.5PW12O40 showed very high activities for these reactions and the excellent selectivity for the skeletal isomerization. XRD, TEM and N2 adsorption revealed that Cs2.5H0.5PW12O40 consists of ultrafine primary particles (∼8 nm) and therefore has a high surface area. High resolution solid-state NMR demonstrated that the chemical shift of 31P (central atom of the polyanion) is determined by the number of proton which is directly attached to the polyanion and all protons are distributed randomly through the whole bulk of the particles. Owing to this, Cs2.5H0.5PW12O40 possesses a high surface protonic acidity, which is a reason for its high activity. The quantity of acid sites of Cs2.5H0.5PW12O40 was less than those of zeolites and SO42−/ZrO2 and the acid strength was lower than that of SO42−/ZrO2. It is presumed, therefore, that the acid-base bifunctional action together with the high surface acidity brought about the high activity of Cs2.5H0.5PW12O40.

In situ fiber-optic Raman spectroscopy of organic chemistry in a supercritical water reactor

Abstract: In situ measurements were made of several organic chemical reactions in supercritical water using fiber-optic probes, near-infrared excitation and CCD array detection. The reactions studied include the conversion of cyclohexene to cyclohexane and benzene in the presence of a platinum catalyst, conversion of cyclohexanol to cyclohexene in the presence of a cobalt catalyst and the homopolymerization of styrene. Transition to the supercritical state was marked by a sudden decrease in the background and the appearance of intense Raman bands for dissolved organic compounds. The results indicate that this method of study is both sensitive and rapid enough to permit kinetic measurements, even when reactions are completed in less than 2 min.

Adipic Acid Synthesis via Oxidation of Cyclohexene over Zeolite occulded Manganese Diimine Complexes

Abstract: Adipic acid is produced in high yield by oxidation of cyclohexene with H 2 0 2 , on manganese diimine catalysts ( cis -Manganese bis-2,2′-Bipyridyl complexes in faujasite type zeolites, cis -[Mn(bpy) 2 ] 2 +-NaX and Nay). This catalytic system allows to reach turn-over numbers of 760. The synthesis of cis -[Mn(bpy) 2 ] 2 +-NaFAU proceeds through ion exchange, followed by dehydration and melting the ligand on the dehydrated metal-loaded zeolite. In the last step the temperature and the metal to ligand stoichiometry needs to be carefully controlled. In the described reaction, alkene epoxidation competes with the allylic oxidation and, to a minor extent, with hydration of the double bond. The reaction is faster with (H)Na-Y zeolite, due to the higher Bronsted acid-strength that permits a faster acid-catalysed opening of the epoxide.

Evidence for a (π-allyl)palladium intermediate in the quinone-based palladium-catalysed allylic acetoxylation

Abstract: The mechanism of the quinone-based palladium-catalysed allylic acetoxylation of cyclohexene is studied using 1,2-dideuteriocyclohexene (55–70% D) as substrate; the distribution of the deuterium label in the product, determined by 1H NMR spectroscopy, is that expected for a (π-allyl)palladium intermediate.

Photochemical epoxidation of cyclohexene sensitized by tetraphenylporphyrinatoantimony(V) in the presence of water acting both as an electron and an oxygen donor

Abstract: Visible light irradiation of a reaction mixture involving tetraphenylporphyrinatoantimony(V)(SbVTPP){[SbVTPP(OMe)Br]Br 1 or [SbVTPP(OH)2]OH 2}, methylviologen (MV2+), hydroxide ion and cyclohexene 6 in acetonitrile–water (95:5) under degassed conditions induced formation of MV˙+(one-electron reduced product of MV2+), and oxidation of cyclohexene (with cyclohexene oxide 7 and cyclohex-2-enol 8 as major products and cyclohexane-1, 2-diol 9 in small amounts in the case of 1, and cyclohexene oxide 7 as the sole product in the case of 2). One third of the obtained diol was cis isomer. The oxygen atom of the water molecule in the reaction system was confirmed as being incorporated in the oxidized products of cyclohexene by an experiment using H218O. The overall quantum yield of the photochemical epoxidation was in the order of 10–3, while that of MV˙+ production were in the order of 10–1. Hydroxide ion was shown to have both a negative effect on radical anion formation by reductive quenching of the excited triplet state of SbVTPP, and also a positive effect by acting as an oxygen source itself for the epoxidation. A key intermediate for the epoxidation was presumed to be an antimony(VI) oxo-type porphyrin complex generated by an electron transfer to MV2+ from a singly and doubly deprotonated excited triplet SbVTPP. The different product distributions obtained for 1 and 2 are discussed in relation to the geometrical structures of the presumed key intermediate oxo-complexes.

Process for the production of cyclohexyladipates and adipic acid.

Abstract: Cyclohexyladipates are formed in a staged reactor, e.g. a reactive distillation column. A mixture containing a major amount of benzene and a minor amount of cyclohexene is fed to the lower portion of the reaction zone and adipic acid is fed to the upper portion of the reaction zone, cyclohexyladipates are formed and removed from the lower portion of the reaction zone and benzene is removed from the upper portion of the reaction zone. The reaction zone also contains an acid catalyst.

Photochemical Oxygenation of Cyclohexene through Reductive Quenching of Excited Tetraphenylporphyrinatoantimony(V) by Triphenylphosphine

Abstract: The mechanism of photochemical oxidation of cyclohexene was studied. Tetraphenylporphyrinatoantimony(V), triphenylphosphine, and methylviologen were involved in the multistep process.

Transfer of alkoxycarbonyl from alkyl imidazolium-2-carboxylates to benzyl alcohol, a cyclohexanone enamine and diethylamine

Abstract: Alkylimidazole-2-carboxylates may be alkylated with methyl triflate to give the corresponding N-methylimidazolium salts. These salts react with benzyl alcohol in the presence of 1,4-diazabicyclo[2.2.2]octane, with 1-(pyrrolidin-1-yl)cyclohexene and with diethylamine to give benzyl alkyl carbonates, an enamino ester and a urethane respectively; in one case a tetrahedral intermediate is observed. The corresponding phenyl ester was consumed without attack by benzyl alcohol at the carbonyl group. A 2-cyanoimidazolium salt underwent similar ill-defined consumption whereas a 2-dimethylaminocarbonyl derivative remained unchanged. 2-Methylsulfonylimidazolium salts suffered attack by benzyl alcohol at the ring C-2.

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

Abstract: Phase 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).

The discovery and structure-activity relationships of 1,2,3,6-tetrahydro-4-phenyl-1-[(arylcyclohexenyl)alkyl]pyridines. Dopamine autoreceptor agonists and potential antipsychotic agents.

Abstract: A novel dopamine (DA) autoreceptor agonist, 1,2,3,6-tetrahydro-4-phenyl-1- [(3-phenyl-3-cyclohexen-1-yl)methyl]pyridine (14), was identified. The structure-activity relationships surrounding this compound were studied by synthesis of analogues and evaluation of their dopaminergic activity. The cyclohexene substitution pattern was varied along with the length of the chain connecting the 1,2,3,6-tetrahydro-4-phenylpyridine to the cyclohexene. Compound 14, having the 1,3-substitution pattern and a single methylene chain, was the most potent. The 1,2,3,6-tetrahydro-4-phenylpyridine could be replaced by other aryl-cyclic amines with a slight loss in activity. The phenyl group on the cyclohexene ring could be para substituted; electron-donating groups were better tolerated than electron-withdrawing groups. Finally, the enantiomers of 14 were resolved via the 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate salts. Although both isomers were partial DA agonists, the (+)-enantiomer had higher intrinsic activity than the (-)-enantiomer. Syntheses were developed that allowed rapid preparation of analogues. An X-ray crystal structure determination of an intermediate identified the (+)-isomer of 14 as having R configuration. This compound, designated CI-1007 (PD 143188), was found to have antipsychotic-like activity in behavioral tests; in particular, it was orally active in the conditioned avoidance test in squirrel monkeys with an ED50 of 0.6 mg/kg. The overall profile suggests that (R)-(+)-14 may be a clinically useful antipsychotic agent.

Preparation and properties of ruthenium supported catalysts

Abstract: Two types of impregnation solvents were suggested for preparation of the ruthenium supported catalysts. Charcoal, silica, alumina and titania supports were used. Special attention was paid to reduction and activation conditions of nonreduced and passivated forms, respectively. Hydrogenation of 1-heptene, cyclohexene, benzene and acetophenone in the liquid phase were studied using the prepared catalysts.

FT-IR characterization of carbenium ions, intermediates in hydrocarbon reactions on H-ZSM-5 zeolites

Abstract: A series of N-alkylacetonitrilium ions were characterized by IR spectroscopy on an activated H-ZSM-5 sample pretreated by CD3CN with various adsorbed olefins. Two kinds ofν(C≡N) band were evidenced according to whether the carbenium ion is secondary (2387 cm−1) or tertiary (2376 cm−1). The method is able to detect the isomerization intermediates of cyclohexene into methyl-cyclopentene.