Showing papers on "Cyclohexanone published in 1994"

Hydrogenation of phenol to cyclohexanone over palladium and alkali-doped palladium catalysts

Abstract: Palladium catalysts supported on Al2O3 and MgO were prepared and used in the gas-phase hydrogenation of phenol to cyclohexanone. In all range of conditions investigated, selectivity to cyclohexanone was higher on Pd/MgO than on Pd/Al2O3. On Pd/Al2O3 the reaction rates were found to be of first order with respect to the phenol partial pressure and second order with respect to the hydrogen pressure. On Pd/MgO, instead, the order of reaction with respect to phenol was −1 and the order with respect to hydrogen was about 1. Addition of alkali or alkaline earth metals (Ca, K, Cs) to Pd/Al2O3 increased the activity and the selectivity to cyclohexanone without modifying the orders of reaction. On the basis of the results of this study, a reaction mechanism involving adsorption of phenol on the sites of the support at the interface of the palladium metal particles is proposed. The higher selectivity to cyclohexanone found on Pd/MgO compared to Pd/Al2O3, is explained by two different forms of adsorbed phenol.

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

Photodecomposition of several compounds commonly used as sunscreen agents

Abstract: The photolysis reactions of three compounds commonly used as a sunscreen agents, Parsol 1789 (1-[4-(1,1-dimethylethyl)phenyl]-3-(4-methoxyphenyl)-1,3- propanedione), Oxybenzone ((2-hydroxy-4-methoxyphenyl)phenyl-methanone) and Padimate O (2-ethylhexyl-4-(dimethylamino)benzoate), were investigated to provide a chemical background to aid in the understanding of the photosensitization of the sunscreen agents. Photolysis was carried out in cyclohexane for 70–140 h using a mercury vapor lamp (450W) without excluding oxygen. Irradation of Parsol 1789 in cyclohexane yielded tert -butylbenzene, p - tert -butylbenzoic acid and p -methoxybenzoic acid; products obtained from the combination of the sunscreen with the solvent included the cyclohexyl esters of p -methoxybenzoic acid, p - tert -butylbenzoic acid and methanoic acid; products obtained from the solvent included cyclohexanol, cyclohexanone and dicyclohexyl ether. Irradiation of Oxybenzone in the cyclohexane for 100 h produced no detectable products by either gas or liquid chromatographic analysis. Oxybenzone was recovered unchanged and no products were observed from the photoinitiated reaction of oxygen with the solvent. Irradiation of Padimate O in cyclohexane yielded the ethylhexyl esters of p -aminobenzoic acid, p -monomethylaminobenzoic acid and p -dimethylamino ( o/m )-methylbenzoic acid, as well as products from the photoinitiated reaction of oxygen with the solvent.

Thermodynamic and NMR Study of the Interactions of Cyclodextrins with Cyclohexane Derivatives

Abstract: Equilibrium constants and standard molar enthalpies of reaction have been determined by titration calorimetry for a series of cyclohexane derivatives (cis-1,2-cyclohexanediol, cis,cis-1,3,5-cyclohexanetriol, trans-1,2-cyclohexanediol, cyclohexanol, cyclohexanone, 2-methylcyclohexanone, 2,5-piperazinedione, and δ-valerolactam) with α-cyclodextrin and β-cyclodextrin. For the reactions involving cyclohexanol, standard molar heat-capacity changes were also determined from calorimetric measurements performed at several temperatures. The equilibrium constants for the reactions of these substances with β-cyclodextrin are in all cases larger than those for the corresponding reactions with α-cyclodextrin

µ-Oxo-bridged diiron(III) complexes and H2O2: monooxygenase- and catalase-like activities

Abstract: The µ-oxo-bridged diiron(III) complex [Fe2O(bipy)4(OH2)2][ClO4]41(bipy = 2,2′-bipyridine) was found to exhibit monooxygenase-like activity, using H2O2 as the oxidant. The system oxidizes alkanes to alcohols and ketones quite efficiently (46 mmol of cyclohexanol + cyclohexanone per rnmol complex in 10 min). In the case of adamantane, selectivity for the tertiary hydrogen was indicated by a high normalized C3:C2 ratio of 9:1. The same reaction yields and rates were obtained whether argon or dioxygen was bubbled through the solution. Dimethyl sulfide was transformed into dimethyl sulfoxide and dimethylsulfone and benzene into phenol. These results exclude O2 as a key reactant in this system and suggest that high-valent oxoiron intermediates and hydroxyl radicals are the active species. The potential of this system is strongly limited by the instability of the catalyst and by its strong catalase-like activity. Complex 1 is actually a very efficient catalyst for hydrogen peroxide dismutation, thus transforming 50% of the excess of H2O2 into O2 in 10 min.

Liquid-phase oxidation of cyclohexane over CoAPO-5: Synergism effect of coreactant and solvent effect

Abstract: Cyclohexanone was employed as a coreactant in the liquid-phase oxidation of cyclohexane using glacial acetic acid as a solvent and CoAPO-5 as a catalyst at 105-135°C and 10 kg/cm2. Addition of cyclohexanone increases the rate of cyclohexane oxidation and selectivity to adipic acid. When the cyclohexanone concentration increases, the rate will increase at 115°C but decrease at 135°C, while the cyclohexanone concentration has no obvious effect on the rate at 125°C. The apparent activation energy for cyclohexane oxidation in the cooxidation system is lower than that of cyclohexane oxidation in the system without the addition of cyclohexanone. An increase of catalyst loading in the cooxidation system, though, increases the rate of cyclohexane oxidation but decreases the yield of adipic acid. Use of carboxylic acid, except formic acid, as the solvent is necessary for the oxidation of cyclohexane. Of acetic acid, propionic acid, butyric acid and n-pentanic acid, the use of propionic acid results in the highest reaction rate when the temperature is below 135°C, while these four carboxylic acids give almost the same conversion after 2 h at 135°C.

Selective decomposition of cyclohexyl hydroperoxide to cyclohexanone catalyzed by chromium aluminophosphate-5

Abstract: Chromium substituted aluminophosphate-5 is an active and recyclable catalyst for the selective decomposition of secondary alkyl hydroperoxides to the corresponding ketones. This has practical utility in the conversion of cyclohexane to cyclohexanone. Tert-alkyl hydroperoxides give primarily the corresponding alcohols and dioxygen.

Selectivity dependence on the alloying element of carbon supported Pt-alloy catalysts in the hydrogenation of phenol†

Abstract: Single step vapour phase hydrogenation of phenol over Pt-M/C (M = Cr, V and Zr) alloy catalysts was investigated at atmospheric pressure and 200°C. The alloying element shows a significant effect on the product selectivities. While Pt-Cr/C and Pt-V/C catalysts are highly selective for hydrogenation of phenol to cyclohexanone, the Pt-Zr/C catalysts are predominantly selective to cyclohexanol.

Catalytic oxidation of cyclohexane into cyclohexanol and cyclohexanone over a TiO2/TS-1 system by dioxygen under UV irradiation

Abstract: Cyclohexanol and cyclohexanone are obtained with high selectivity by direct oxidation with molecular oxygen catalysed by a TiO2/TS-1 system under UV irradiation and mild conditions.

Manganese(II) based oxidation of alkanes: generation of a high valent binuclear catalyst in situ

Abstract: The efficiently Mn2+-catalysed oxidation of saturated hydrocarbons by alkylhydroperoxides or iodosylbenzene in the presence of 2,2′-bipyridine in acetonitrile follows the following pathway: Mn2++ bipy →[Mn(bipy)3]2+→[Mn2O2(bipy)4]3+, the latter being identified as the catalytic species; it affords cyclohexanol and cyclohexanone in equal amounts and the remarkable robustness of the active complex, under oxidative conditions, is noted.

Preparation and characterization of silica-supported copper catalysts for the dehydrogenation of cyclohexanol to cyclohexanone

Abstract: Copper dispersed on an alkali-doped silica support, when properly prepared using a precipitation method, was found to be better than CuMgO and CuZnO as regards conversion, selectivity, and especially resistance against sintering for the dehydrogenation of cyclohexanol to cyclohexanone. The optimum precipitation conditions were a precipitation temperature of 90°C, a precipitation time of 4 h and the final pH of the solution higher than 9. The high solution pH was intended to neutralize acidic sites of the support, which were responsible for the formation of side products. The lowest copper loading was desirable to achieve the highest conversion, but the copper loading should be kept above 12% to suppress effectively the formation of side products on the alkali-treated silica surface. Temperature-programmed reduction. X-ray diffraction, transmission electron microscopy and reaction tests revealed that catalysts prepared under the above conditions had highly dispersed metallic copper particles stabilized on a neutralized silica surface.

Oxidation of Cyclohexane in Supercritical Carbon Dioxide Medium

Abstract: Cyclohexane oxidation has been studied in supercritical carbon dioxide medium for homogenizing the initial reaction mixture to produce cyclohexanone and cyclohexanol as the chief reaction products. The kinetic experiments have been performed at three temperatures 410, 423, and 433 K and two pressures 170 and 205 bar. The results have been interpreted in the light of transition state theory and cage effects. Conversions obtained are low compared to the liquid phase oxidation because of dilute concentrations of the reactants. Cyclohexanone is more selectively formed and favored by both pressure and temperature. A 20% increase in pressure results in (1) reduction of the induction period by 50%, (2) a change in activation energy from 13.0 kcal/mol at 170 bar to 22.6 kcal/mol at 205 bar, (3) an increase in the preexponential factor by 5 orders of magnitude, and (4) an increase in the first-order rate constant at 433 K by about 70%. The variation in the observed activation volume from 36 cm[sup 3]/mol at 410 K and 170 bar to [minus]775 cm[sup 3]/mol at 433 K and 205 bar suggests that the reaction in supercritical CO[sub 2] medium can be greatly manipulated.

Synthesis, transformations and biological activity of chloro enamines and ynamines derived from chloroalkenyl- and alkynyl-N-substituted purine and pyrimidine bases of nucleic acids

Abstract: Reactions of nucleic acid bases and related heterocycles 1–5, 18 and 22 with tetra-, tri- and dichloroethylenes 6–9 in hexamethylphosphoric triamide gave the corresponding N-trichloro-, -dichloro- and -chloro- enamines 11–17, 19, 20, 23 and 24 in high regioselectivity (N9 for purines and N1 for pyrimidines). Bases 1, 5, 18, 22 and trichloroethylene 7 gave the respective E-dichloro enamines 15, 16, 20 and 24. Compounds 16 and 20 were identical with the products obtained by addition of bases 1 and 18 to dichloroacetylene. Thymine 18 and compound 7 gave N1,N3-bisdichloro enamine 21 as the major product. The latter exists at room temperature as a mixture of rotamers 28 and 29(ΔG‡≅ 18 kcal mol–1). The reaction of adenine 1 with (Z)-1,2- or 1,1-dichloroethylene 8 or 9 furnished Z-chloro enamine 17 whereas thymine 18 and tetrachloroethylene 6 in dimethyl sulfoxide afforded a reduction product 20. Benzoylation of N9-(trichlorovinyl)adenine 11 gave N6,N6-dibenzoyl derivative 26. The reaction of N1-(dichlorovinyl)cytosine 24 with N,N-dimethylformamide dimethyl acetal afforded amidine 25. Interaction of (E)-N9-(dichlorovinyl)adenine 16 with sodium methoxide gave exclusively E-enamine 27. Trichloro enamines 11–14, 19, 23 and 26 were transformed to ynamines 30–35. Hydrogenation of compounds 30 and 35 furnished N9-ethyladenine 36 and N1-ethylthymine 37. Alkylation of ynamine 30 with acetone 38 gave only carbinol 41 whereas cyclohexanone 39 gave both compound 42 and cyclic ketal 43. The reaction of ynamines 30 and 35 with ketone 40 afforded only ketals 44 and 45. The reaction of compound 30 with N,N-dimethylformamide dimethyl acetal led to N-dimethylaminomethylene derivative 46. Ynamine 30 is a substrate for adenosine deaminase.

Selective hydrogenation of phenol to cyclohexanone catalyzed by a silica-supported chitosan-palladium complex

Abstract: Silica-supported chitosan-palladium complex is shown to be very active and selective in the hydrogenation of phenol to cyclohexanone at different reaction conditions 100% selectivity for cyclohexanone is evident in all the cases The best yield of cyclohexanone was 946 %

Synthesis, Characterization and Catalytic Performance of Nitro-substituted Fe-phthalocyanines on Zeolite Y

Abstract: Nitro substituted iron-phthalocyanines on Y zeolite are synthesized via a ligand exchange reaction starting from a mixture of solids containing ferrocene, 4-nitro-1,2-dicyanobenzene and dry Y zeolite. The nature and loading of the catalyst is verified by Vis-NIR and solid state 13 C-NMR. Purification by soxhlet extraction demonstrates that the nitro-substituted phthalocyanines are not located in the supercages but are adsorbed at the outer surface of Y zeolite crystals. On the contrary, unsubstituted phthalocyanines are encapsulated in the supercages. Nitro-substitution improves considerably the activity of the complexes, as shown by the catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone at 298 K and 0.1 MPa with tertiary butyl hydroperoxide as oxygen donor.

Oxidation of cyclohexanone and cyclohexane to adipic acid by iron-phthalocyanine on zeolite Y

Abstract: Iron-phthalocyanine on zeolite Y has been used for the catalysis of cyclohexanone and cyclohexane into adipic acid, by an environnement-friendly one-pot reaction. Heating and fine-tuning of the solvant allowed high conversion and good selectivity for adipic acid.

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.

Adipic acid prepn. by oxidising cyclohexane with oxygen

Abstract: Prepn. of adipic acid (I) involves single-stage oxidn. of cyclohexane (II) with oxygen in presence of acetic acid and a cobalt salt catalyst (III). All of the (III) used is recovered by: (i) cooling the mixt. from the oxidn. reactor and isolating the pptd. (I) by filtration; (ii) separating the obtd. filtrate into a non-polar phase (A) rich in (II) and a polar phase (B) contg. acetic acid, (III), (I), cyclohexanone, cyclohexanol, cyclohexyl ester and other by-products, the whole of phase (A) and part of phase (B) being recycled (opt. after isolation of (I) in (B)) to the start of the process; and (iii) isolating (III) from the non-recycled part (B') of (B). the novelty is that either: (a) (B') is mixed with 1-10 times its vol. of an inert solvent (IV) for the organic components of (B) (excluding (III)) of b.pt. \-130 deg C under normal pressure, the HOAc in the obtd. mixt. is distilled. off and the (III) which crystallises out is recovered by filtration; or (b) 20-95% of the HOAc in (B') is distilled. off, the ester in the distn. residue is hydrolysed, the organic components of the obtd. aq. phase (excluding (III)) are extd. with a water-immiscible extractant (V) and (III) is recovered from or as the aq. soln..

Synthesis of 3-aryl-1,4-benzoxathianes: application to the preparation of a sweet compound

Abstract: Attempts to prepare 3-phenyl-1,4-benzoxathiane by acid-catalysed ring-closure of 2-(2-hydroxyphenylthio)-2-phenylethanol gave instead 2-phenyl-1,4- benzoxathiane, via a rearrangement probably involving an episulfonium ion. The first synthesis of 3-aryl-1,4-benzoxathianes was obtained by N-bromosuccinimide-promoted oxidative rearrangement of 1,3-oxathiolanes derived from cyclohexanone. The application of this route to the synthesis of 3-(3-hydroxy-4-methoxyphenyl)-1,4-benzoxathiane, a compound ca. 2000 times as sweet as sucrose, is reported.

Redox Molecular Sieves: Recylable Catalysts for Liquid Phase Oxidations

Abstract: Redox molecular sieves have been synthesized by isomorphous substitution in the framework of silicalite-1 and ALPO-5. CrAPO-5 and CrS-1 were shown to be effective catalysts for the decomposition of secondary alkyl hydroperoxides to the corresponding ketones. In the decomposition of cyclohexyl hydroperoxide the highest selectivity to cyclohexanone (86%) was observed with CrAPO-5. CrAPO-5 was also shown to be an effective catalyst for the oxidation of secondary alcohols to the corresponding ketones, alkylbenzenes to acetophenones and cyclohexane to cyclohexanone using tert-butyl hydroperoxide (TBHP) or O 2 , as the terminal oxidant. Evidence is presented in support of the reaction taking place inside the cavity of the molecular sieve.

Vapor-liquid and liquid-liquid equilibria of water, 2-methoxyethanol and cyclohexanone : experiment and correlation

Abstract: Vapor-liquid equilibria and liquid-liquid equilibria of a ternary mixture consisting of water, 2-methoxyethanol and cyclohexanone and in addition of all binary subsystems were studied experimentally at several temperatures. A ternary corrective term in the expression for the Gibbs free energy based on the NRTL model improves simultaneous representation of binary and ternary phase equilibria.