Dehydration Of Cyclohexanol Research Articles

Acidity and acid catalysis of polyatom-substituted H n PW11M1O40 (M=V, Nb, Ta, and W) Keggin heteropolyacid catalysts

Acidity of polyatom-substituted HnPW11M1O40 (M=V, Nb, Ta, and W) Keggin heteropolyacids (HPAs) was measured by NH3-TPD experiments. Acidity decreased in the order of H3PW11W1O40>H4PW11V1O40>H4PW11Nb1O40 >H4PW11Ta 1O40. Vapor-phase dehydration of cyclohexanol was conducted as a model reaction to correlate the acidity with the acid catalysis of HPA catalysts. Yield for cyclohexene (a product by acid catalysis) increased with increasing acidity of HnPW11M1O40 (M=V, Nb, Ta, and W) HPA catalysts. The acidity of HnPW11M1O40 (M=V, Nb, Ta, and W) HPA catalysts could be utilized as a probe of acid catalysis for dehydration of cyclohexanol.

Synthesis, crystal structure, and catalytic properties of a one-dimensional nickel(II) polymer

The title complex [Ni2(C10H9N3)2(C14H8O5)2]n, which has an inversion center, midway between two Ni(II) atoms forms a one-dimensional polymer bridged by 4,4′-oxydibenzoate ligands with a Ni…Ni separation of 14.4705(11) A. The Ni(II) atom is six-coordinated by two N atoms of a bis(2-pyridyl)amine ligand and four O atoms from two 4,4′-oxydibenzoate ligands, to form a distorted octahedron coordination geometry and then are linked via N-H…O and C-H…O hydrogen bonding into a polymeric ribbon structure. The activity and selectivity profiles of the polymer indicate that the optimization temperature and time span are 175°C and 30–40 min for the dehydration of cyclohexanol, respectively.

Influence of the surface acidity of ZSM-5 support on the catalytic activity of Rh/ZSM-5 for hydrodearomatization of toluene

Rh/ZSM-5 catalysts with varied SiO 2/Al 2O 3 ratio (24–900) were prepared and characterized by powder X-ray diffraction, N 2 adsorption–desorption, temperature-programmed desorption of NH 3 and cyclohexanol dehydration model reaction. The hydrodearomatization of toluene was studied at different reaction temperature, reduction temperature, hydrogen partial pressures and in the presence of dibenzothiophene (sulfur compound) in a continuous-down-flow catalytic fixed bed reactor. The hydrodearomatization activity and the sulfur tolerance were observed to be strongly dependent on the acidity of the zeolites particularly upon the proximity between metallic and Brønsted acid sites and the concentration of the Brønsted acid sites.

Synthesis, crystal structure and catalytic activity of a Waugh type polyoxometalate H12[MnMo9O32(KO)6

A Waugh type polyoxometalate H12[MnMo9O32(KO)6] has been synthesized and characterized by single crystal X-ray diffraction, IR, XRD and TG. The compound was crystallized in the trigonal system, space group R3 with a = 15.5380(6) nm, b = 15.5380(6) nm, c = 12.3777(5) nm, α = 90°, β = 90°, γ = 120°, V = 2587.98(18) nm3, Z = 3, R1 = 0.0134, θR2 = 0.0308. The catalytic activity of the title compound for the dehydration of cyclohexanol was determined. The conversion of C6H11OH reached 69.56% and the selectivity of C6H10 was 96% when the amount of catalyst, temperature range and reaction time were 6.59%, 170°C–180°C, 30 min, respectively.

The synthesis of o-cyclohexylphenol in supercritical carbon dioxide: towards a continuous two-step reaction

The use of supercritical carbon dioxide, scCO2, as an environmentally friendly reaction medium for the continuous synthesis of the fine chemical o-cyclohexylphenol has been investigated. The alkylation of phenol was carried out using a solid acid catalyst, γ-Al2O3, using both cyclohexene and cyclohexanol as alkylating agents. Though cheaper, cyclohexanol gave poorer results because of the water formed in the reaction inhibiting the catalyst performance. The possibility of performing the reaction as a two-step process was then investigated. The dehydration of cyclohexanol over the same catalyst was found to be quantitative. Clearly, the water by-product must be eliminated before the alkylation step and, although this was found to be difficult to achieve on a small scale, the process looks promising as a two-step reaction.

Solvent free isomerisation of longifolene with nano-crystalline sulphated zirconia

Nano-crystalline sulphated zirconia catalyst was synthesised using sol–gel technique in acidic, basic and neutral medium. The samples were characterised by X-ray diffraction, DRIFT spectroscopy, nitrogen adsorption–desorption and TG analysis. Bronsted acidity was measured by cyclohexanol dehydration model reaction. The samples were studied for single step, solvent free isomerisation of longifolene to iso-longifolene in a liquid phase batch reactor. The catalyst yielded >90% conversion and ∼100% selectivity for iso-longifolene.

Cerium Containing Al- and Zr-Pillared Clays: Promoting Effect of Cerium (III) Ions on Structural and Catalytic Properties

Ce3+ containing Al- and Zr-pillared clays were prepared by co-hydrolysis and co-intercalation methods, respectively. The materials were characterized by XRD, IR and near IR techniques. The expansion in the clay lattice as a result of pillaring was confirmed from X-ray diffraction study. The basal spacing for the pillared clay materials was observed typically in the range of 18–23 A. The IR and near IR studies were employed to show the presence of acidic and non-acidic hydroxyl groups in the pillared clays. The IR peak at 3630 cm−1 corresponding to the structural hydroxyl groups was more intense in pillared clays than in the parent clay. This peak is retained even after calcination at 500∘C. Various overtone and combination bands were observed in the NIR range of 1200–2500 nm for the pillared clay materials. Pillaring with Al- and Zr-inorganic polycations enhanced the catalytic activity of the parent clays for dehydration of cyclohexanol. The presence of Ce3+ ions in the pillared clays was found to influence catalytic activity and stability of the Bronsted acidic sites. The stabilizing effect of cerium ion in the pillared clays is attributed to the competitive site occupancy and prevention of octahedral migration of the catalytically active protons.

Amorphous titanium hydrogenphosphate?an inorganic sorbent and a catalyst

Amorphous titanium hydrogenphosphate, originally prepared to act as an inorganic sorbent superior for K+ and other alkaline metal ions of certain size, proved to be also an active catalyst in alcohol dehydration. Its activity was tested in cyclohexanol, methanol, and pentanol conversions. The reactions were selective and thus cyclohexene was practically the only product of cyclohexanol dehydration, methanol gave dimethyl ether (DME) as the main product and pentanol yielded pentene isomers, the mutual ratios of which depended on temperature and contact times. Characteristically, the studied catalysts acquired their high activity only after a period of work at temperatures higher than 275 °C, the temperature of an endothermic transition observed in DTA. After the catalyst had been activated, it retained its activity even while working at lower temperatures, but lost it upon staying at room temperature for longer times. Most probably, these changes are related to the increase in the interlayer distance and the insertion of water and alcohol, making thus the inner acidic sites available for the reaction.

Amorphous titanium hydrogenphosphate—an inorganic sorbent and a catalyst

Amorphous titanium hydrogenphosphate, originally prepared to act as an inorganic sorbent superior for K+ and other alkaline metal ions of certain size, proved to be also an active catalyst in alcohol dehydration. Its activity was tested in cyclohexanol, methanol, and pentanol conversions. The reactions were selective and thus cyclohexene was practically the only product of cyclohexanol dehydration, methanol gave dimethyl ether (DME) as the main product and pentanol yielded pentene isomers, the mutual ratios of which depended on temperature and contact times. Characteristically, the studied catalysts acquired their high activity only after a period of work at temperatures higher than 275°C, the temperature of an endothermic transition observed in DTA. After the catalyst had been activated, it retained its activity even while working at lower temperatures, but lost it upon staying at room temperature for longer times. Most probably, these changes are related to the increase in the interlayer distance and the insertion of water and alcohol, making thus the inner acidic sites available for the reaction.

Acylation of toluene using rare earth cation exchanged zeolite β as solid acid catalyst

Abstract The catalytic activity of rare earth cations exchanged zeolite β was studied for the acylation of toluene with acetic anhydride as an acylating agent and nitrobenzene, o -dichlorobenzene and dichloroethane as the solvent in liquid phase in the temperature range of 368–408 K. The rare earth cation exchanged zeolites were observed to have the catalytic activity in the following order: La-β>H-β=Ce-β>Dy-β>Eu-β>Sm-β>Gd-β>Nd-β>Pr-β with more than 95% selectivity towards the p- isomer. Among the solvents studied, nitrobenzene is the most favored for toluene acylation reaction. The correlation of catalytic activities of the different catalysts with the cyclohexanol dehydration as well as DRIFT spectroscopy showed that the toluene acylation is a Bronsted acid catalyzed reaction.

Isomerisation of α-pinene using modified montmorillonite clays

Abstract Liquid phase catalytic isomerisation of α-pinene with natural Indian Montmorillonite modified by sulphuric acid treatment and cation exchange was studied. More than 96% α-pinene conversion is observed for acid treated clays with camphene selectivity ranging from 39 to 49%. For acid treated clays prepared by treating with low normality acid (1–4N), limonene is the main product whereas clay samples prepared with high normality (5–9N) acid, α-terpinene is a main product among monocyclic terpenes. Ce 3+ , Fe 3+ , La 3+ , Ag + , exchanged clays showed higher than 90% conversion for α-pinene with 39–49% selectivity for camphene. However, Li + , Ca 2+ , Mg 2+ exchanged clay showed poor conversion (4–12%) for α-pinene. Observed conversions and selectivities have been explained in terms of surface acidity, structural and textural features of the modified clays determined by using X-ray diffraction and N 2 adsorption at 77 K. Correlation of α-pinene conversion with cyclohexanol dehydration showed that α-pinene conversion is a Bronsted acid catalyzed reaction.

Liquid Phase Friedel‐Crafts Alkylation over Mixed Metal Oxide Catalyst

AbstractLiquid phase Friedel‐Crafts alkylation of benzene with benzyl chloride was carried out over various ferrites viz. CuFe2O4, NiFe2O4, CoFe2O4, ZnFe2O4, and MgFe2O4. Among the various ferrites ZnFe2O4 showed the highest activity. These ferrites were prepared by co‐precipitation technique. The effect of variation of catalyst, speed of agitation and reaction temperature has been studied. Benzylation of other substrates such as toluene, anisole and chlorobenzene was also studied. The catalyst ZnFe2O4 was found to be reusable. The acid base properties of the catalyst were studied by cyclohexanol dehydration reaction and the data was correlated with activity.

Metal oxide-modified ZnO/SiO 2 catalysts for cyclo-dehydrogenation of ethylenediamine with propyleneglycol to 2-methylpyrazine

Metal oxide-modified ZnO /SiO2 catalysts were studied for the cyclo-dehydrogenation of ethylenediamine with propyleneglycol to 2-methylpyrazine at 633 K. The ZnO/SiO2 catalyst showed fairly good ethylenediamine conversion and quantitative propyleneglycol conversion with about 60 mol% of 2-methylpyrazine selectivity, which is due to the existence of large amount of unconverted intermediate, 2-methylpiperazine. Metal oxide (CuO, NiO, Co3O4)-modified ZnO/SiO2 catalysts were prepared to facilitate the dehydrogenation of 2-methylpiperazine to 2-methylpyrazine. About 82 mol% of 2-methylpyrazine selectivity was achieved on CuO and Co3O4 modified ZnO/SiO2 catalysts, with significant increases of pyrazine selectivity. The catalytic properties of the metal oxidemodified ZnO/SiO2 catalysts, pretreated with hydrogen gas as in the cyclo-dehydrogenation, were compared using the well-known probe reaction, the dehydrogenation/ dehydration of cyclohexanol to cyclohexanone or phenol/cyclohexene. The selectivities of pyrazine in the cyclo-dehydrogenation on the metal oxide-modified ZnO/SiO2 catalysts were correlated with the phenol selectivities of the probe reaction. It is proposed that the metallic site of catalyst is responsible for the formation of pyrazine from ethylenediamine dimerization. The improved 2-methylpyrazine yield on CuO/ZnO/SiO2 catalyst was explained by the proper adjustment of catalytic properties, which could be differentiated by the phenol selectivity in the cyclohexanol probe reaction. Thus, the large enhancement of 2-methylpiperazine dehydrogenation to 2-methylpyrazine and the suppression of excess pyrazine formation are supposed to occur on the metallic Cu formed in situ during the reaction during the cyclo-dehydrogenation of ethylenediamine with propyleneglycol.

Influence of acid–base properties of catalysts in the gas-phase dehydration–dehydrogenation of cyclohexanol on amorphous AlPO 4 and several inorganic solids

A series of metal phosphates (Al, Fe, Ni, Ca and Mn) and stoichiometric (Al/Fe=Al/Ca=1) mixed systems: FeAl(PO 4) 2 and Ca 3Al 3(PO 4) 5, were prepared by an ammonia gelation method. Their amorphous character was determined through several physical methods: nitrogen adsorption, DRIFT and XRD patterns. Gas-phase competitive dehydration/dehydrogenation reaction of cyclohexanol was carried out as a probe reaction and cyclohexene was usually the main reaction product, but different amounts of 1- and 3-methylcyclopentenes as well as cyclohexanone were always obtained. These results were compared to those obtained with 17 commercial inorganic solids (several metal oxides, sulfates and phosphates). A main unexpected conclusion was that cyclohexanol dehydration is obtained not only in acid sites but also in basic sites.

Influence of Synthesis Conditions and Cerium Incorporation on the Properties of Zr-Pillared Clays

Zr-pillared clays were prepared from ZrOCl2 pillaring solutions by adopting different preparative conditions. Ce3+ ions are introduced to Zr-pillared clays by co-intercalation method. The resulting samples were characterized by XRD, TGA, N2 sorption and UV-VIS-Diffuse reflectance spectroscopy techniques. Basal spacings in the range of 18–21 A were observed depending upon the preparative condition. TG analysis shows three weight loss regions corresponding to removal of various types of water molecules. All pillared clays show Type-I sorption isotherm typical of microporous materials. Pillaring under refluxing condition is found to have beneficial effect on the surface area and pore volume of the Zr-pillared clay. The chemical environment and location of Ce3+ ions is studied by UV-VIS-DRS. The Ce3+ ions are found to be present in the micropores of the Zr-pillared clays. However heat treatment at higher temperature may result in peripheral interaction between Ce3+ ions and Zr-pillars. Catalytic activity of these pillared clays was evaluated for cyclohexanol dehydration which correlates well with the Bronsted acidity of these materials. The Zr-Pillared clay containing Ce3+ ions show good catalytic activity and stability with reaction time which has been ascribed to the stabilazition of the Bronsted acidic centers.

Acid-Catalyzed Reactions in Carbon Dioxide-Enriched High-Temperature Liquid Water

We report, for the first time, the acceleration of acid-catalyzed reactions in high-temperature liquid water by the addition of carbon dioxide to the reaction medium. The reactions examined are the dehydration of cyclohexanol to form cyclohexene and the alkylation of p-cresol with tert-butyl alcohol to form 2-tert-butyl-4-methylphenol. In some cases, the mean product yield more than doubled when carbon dioxide was added to the aqueous medium. The basis of this rate enhancement is reaction between carbon dioxide and water to yield carbonic acid, which subsequently dissociates to increase the hydronium ion concentration above that of water alone. We also use the thermodynamics of the CO2−H2O system to estimate the pH of carbon dioxide-enriched high-temperature water. This analysis demonstrates that it is possible to lower the pH of high-temperature water by several units through the addition of carbon dioxide to the reaction medium. These results demonstrate the feasibility of using CO2−H2O mixtures as an e...

Cerium Containing MCM-41-Type Mesoporous Materials and their Acidic and Redox Catalytic Properties

The syntheses of cerium containing MCM-41 mesoporous molecular sieves (Ce–MCM-41) were carried out using different hydrothermal methods. However, the Ce–MCM-41 samples were mainly prepared by refluxing the gel mixture at atmospheric pressure under stirring (∼600 rpm). For comparison, the syntheses were also carried out in autoclave under autogeneous pressure both in static and in stirring conditions. Powder X-ray diffraction (XRD), N2 adsorption, diffuse reflectance UV–visible (UV–vis) spectroscopy, IR spectroscopy, solid state magic-angle spinning nuclear magnetic resonance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry (EDX), transmission electron microscopy and thermogravimetric analyses of the samples reveal that well-ordered MCM-41-type mesoporous materials were prepared and Ce is incorporated presumably into the framework position and/or into the walls of silica matrix of MCM-41 structure. The EDX analyses of the samples confirm the presence of Ce in the Ce–MCM-41 samples. Typical XRD patterns of MCM-41-type hexagonal structures and high BET surface areas (983–1414 m2 g−1) with isotherms of type IV of these materials indicate the presence of hexagonal mesopores in the samples. The presence of a strong absorption band centered at ca. 300 nm and the absence of any absorption band at ca. 400 nm in the diffuse reflectance UV–vis spectra indicate the presence of tetra-coordinated cerium in the silica network of Ce–MCM-41 samples. The Ce–MCM-41 samples are active as catalysts for vapor-phase dehydration of cyclohexanol to cyclohexene and hydroxylation of 1-naphthol with aqueous H2O2 and tert-butyl hydroperoxide.

Kinetics and Mechanism of Cyclohexanol Dehydration in High-Temperature Water

We examined cyclohexanol dehydration in pure water at temperatures of 250, 275, 300, 350, and 380 °C with water densities ranging from 0.08 to 0.81 g/cm3. Under these conditions, cyclohexanol dehydrates readily in the absence of added catalysts to form cyclohexene as the major product. The most abundant minor products are 1- and 3-methyl cyclopentenes. The reaction rate and product distribution at 380 °C show a remarkable sensitivity to the water density. At low densities, the reaction is slow, and cyclohexene is the only product. At high densities, the reaction is nearly complete, and methyl cyclopentenes appear along with cyclohexene. The experimental results implied a reaction mechanism that comprises two pathways: (1) reversible cyclohexanol dehydration to form cyclohexene through an E2 mechanism, and (2) subsequent cyclohexene protonation to form the cyclohexyl cation, which rapidly rearranges to form methyl cyclopentyl cations, which then lose a proton to form methyl cyclopentenes. A kinetics model...

The mechanism of gas-phase dehydration of cyclohexanol and the methylcyclohexanols catalysed by zirconium phosphate and zirconium phosphite

By means of deuterium labelling experiments, the mechanism of the gas-phase dehydration of cyclohexanol over a solid zirconium phosphate catalyst has been shown to involve a carbocation with a long lifetime. Product distribution studies have been used to show that the corresponding dehydrations of the 4-methylcyclohexanols also proceed through a carbocation mechanism, but have shown that the 2-methylcyclohexanols react partly by a carbocation mechanism and partly by a synchronous mechanism. Reactions catalysed by zirconium phosphite are slower, but give qualitatively similar products. Our results, and those of earlier workers, may be explained by consideration of the stereochemistry of the substrate absorbed on the catalyst surface; variations from the carbocation reaction result from orientations of the substrate adopted to relieve steric compression at the catalyst surface.

Dehydration and dehydrogenation of cyclohexanol over AlPO4-5 based molecular sieves

The role of incorporated divalent metal (Mn, Mg, Co and Zn) incorporated into the framework of AlPO4-5 in conversion of cyclohexanol has been examined. The influence of these metals to cyclohexene and cyclohexanone selectivities was correlated to the acidity and basicity properties of these molecular sieves. Possible mechanism for the dehydration and dehydrogenation for cyclohexanol was proposed.