Isomerization of α-pinene over dealuminated ferrierite-type zeolites

Isomerization of α-pinene was performed on a series of dealuminated ferrierite (FER)-type zeolites in liquid phase at 363 K using a batch reactor. The course of zeolite dealumination was followed in detail using ²⁹Si, ²⁷Al, ¹H MAS NMR, XRD, FTIR, and sorption of nitrogen. The ammonium form of FER was dealuminated with aqueous solutions of HCl. While retaining the crystallinity of the zeolite particles, the treatments removed up to 53% of the tetrahedrally coordinated aluminum atoms from the FER framework. According to ²⁹Si MAS NMR studies, the framework aluminum atoms located at the 10-membered rings in the main channels of FER (T_B sites) were depleted preferentially from their positions. Even relatively mild dealumination of FER led to an active catalyst containing both Brønsted and Lewis centers, yielding up to 97% conversion of α-pinene at 363 K, in contrast to the 72% observed for the parent hydrogen form. Such catalytic behavior was discussed in terms of the conversion of a reactant inside micropores of the zeolite catalyst, on Brønsted acid centers with enhanced strength located probably in the vicinity of Lewis sites. The selectivity toward camphene and limonene changed smoothly with the dealumination level; thus, a higher selectivity toward limonene was observed at the expense of camphene formation with increasing the n_Si/n_Al ratio of the catalysts. The selectivity toward camphene and limonene was close to 85% for all of the materials studied. The initial rates of α-pinene transformations over FER-type materials exceeded those observed for other catalytic systems, heteropoly acid/SiO₂ and H₂SO₄/ZrO₂. This study demonstrates the successful application of a medium-pore zeolite for the catalytic transformation of α-pinene in liquid phase.     

Isomerization of Alpha-pinene Over Acid Treated Natural Zeolite

In this study, isomerization of α-pinene was studied over several acid-treated natural zeolite catalysts rich in clinoptilolite. Zeolite samples were contacted with HCl at different concentrations at 30°C or at 60°C for 3 and 24 hours and tested in isomerization reaction of alpha-pinene. The catalysts prepared were characterized by XRD, nitrogen adsorption, and acidity studies. Acidity strength and the distribution of Lewis and Brönsted acid sites of the catalysts were determined, and their catalytic activities in α-pinene isomerization and selectivities to main reaction products, camphene and limonene, were investigated. Acid treatment improved the selectivity of catalyst samples to camphene, decreasing the selectivity to limonene, probably forcing limonene to secondary reactions at high conversions.

The kinetics of α-pinene consumption was described by first-order kinetics. Two kinetic models were tested for the reaction mechanism and one model was found to give a good correlation between the theoretical and experimental data. In the models, the key intermediate was the pinylcarbonium ion, which was formed irreversibly from α-pinene.

Number and distribution of Lewis and Brönsted acid sites affect the formation of bicyclic and monocyclic products.     

Isomerization of α-pinene,limonene, α-terpinene,and terpinolene on sulfated zirconia

Transformations of α-pinene, limonene, terpinolene, and α-terpinene were studied in liquid phase on sulfated zirconia having 15% H₂SO₄, with the aim of identifing the pathway of α-pinene isomerization. The principal products obtained in α-pinene isomerization were camphene, tricyclene, limonene, and terpinolene; the concentration maxima observed at 120°C and 180 min were 53, 6.1, 7.7, and 3.0%, respectively. The principal products formed in the limonene transformation after a 20-min reaction time were terpinolene, α-terpinene, and γ-terpinene; then the concentration of these products decreased. The terpinolene reaction yielded principally m-cymenene, whereas the α-terpinene transformation produced p-cymene. Studies of the initial rates of transformation of terpenes indicate a very high rate for α-pinene, intermediate for limonene and α-terpinene, and very low for terpinolene. The scheme proposed to interpret the results of the α-pinene isomerization reaction on sulfated zirconia is in agreement with reaction schemes proposed by A. Allahverdiev, S. Irandoust, and D. Y. Murzin (Isomerization of α-Pinene over Clinoptilolite.     

Variability in water sorption and in particle thickness of standard smectites

Variability in sorbed water content was studied on several standard smectites, as dependent on the relative humidity (RH=0.5, 0.95 and 1.0), on temperature (constant 30 °C and variable room temperature) and on sorption time (t_s=1, 12 and 32 days). The particle thickness, δ was estimated, assuming a given number of molecular layers of sorbed water at the given RH. δ decreased with the increase in the factors mentioned above.The thickest particles in dry state were found in hectorite and in synthetic mica/smectite (SHCa-1 and Syn-1, δ=22 and 20 unit layers [u.l.], respectively), the thinnest ones-in Ca-smectite (SAz-1) and in nontronite (SWa-1, δ=5–6 u.l.) and the intermediate both in Na-smectite (SWy-1) and in Ca-smectite (STx-1), δ=12 and 8 u.l., respectively.On prolonged storage at RH=1.0, t_s=32 days, the smectite particles disintegrated gradually into separate crystallites, δ=3–5 u.l., thus close to the thickness measured by XRD. An exception was hectorite, SHCa-1, with δ=6–8 u.l. possibly due to “gluing” by calcium carbonate present.The decrease in δ (delamination) observed on increasing RH was partly reversible. The hysteresis between water sorption on its increasing (WS) and water retention on its lowering to RH=0.5 (WR) was especially pronounced in SHCa-1, SWy-1 and Syn-1 of initially thick particles. This was due either to a different number of the sorbed water layers, higher in WR, or to incomplete collapse in WR.     

Isomerization of α-pinene to camphene

The catalytic isomerization reaction of α-pinene to camphene over a clinoptilolite catalyst was investigated in a batch reactor open to the atmosphere between 130 and 155°C. The catalyst was selective to the isomerization of α-pinene to camphene. The effects of several variables, such as reaction temperature, amount of catalyst, stirring speed and catalyst particle size, on the conversion of α-pinene and selectivity to camphene were determined. The reaction fits a first-order parallel reaction with rate constants of k ₁ = 3.020·10^?2 e ^?33381.6/RT for the production of camphene and of k ₂ = 1.576·10^?2 e ^?31096.53/RT for the production of limonene.     

ZrO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> Mixed Oxides Xerogel and Aerogel as Solid Acid Catalysts for Solvent Free Isomerization of α-Pinene and Dehydration of 4-Methyl-2-Pentanol

Abstract  

Sulfated and non-sulfated ZrO₂–SiO₂ mixed oxide xerogel and aerogel samples having varied Zr/Si molar ratio were evaluated as solid acid catalysts for the isomerization of α-pinene and dehydration of 4-methyl-2-pentanol. Sulfation resulted into enhancement in the catalytic activity of both xerogel and aerogel samples towards the studied reactions. For example, sulfated catalysts showed 86–98% conversion of α-pinene and 8–35% conversion of 4-methyl-2-pentanol. The selectivity data for camphene and limonene indicated the requirement of moderate acidity. The correlation with cyclohexanol dehydration showed that isomerization of α-pinene is a Br?nsted acid catalyzed reaction. The relationship of 4-methyl-2-pentanol conversion with acid site density and sulfur per unit area was found to be linear.     

Brønsted and Lewis acid catalysis with ion- exchanged clays

An acid-treated montmorillonite clay has been ion-exchanged with Al³⁺, Fe³⁺, Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺ and Na⁺. The catalytic activities of these materials have been measured in the Brønsted acid catalysed rearrangement of α-pinene to camphene, and the Lewis acid catalysed rearrangement of camphene hydrochloride to isobornyl chloride, following thermal activation at temperatures from 75 to 350°C. The surface acidities of the ion-exchanged clays have been measured using a microcalorimetric method involving ammonia adsorption, and through the infrared spectra of adsorbed pyridine. The results show that maximum Brønsted acidity is generated on thermal activation at approximately 150°C and maximum Lewis acidity at 250- -300°C. A good correlation has been found between the surface acidities and the catalytic activities of the ion- exchanged clays in both reactions. A significant result is the relatively low surface Lewis acid strength of Al³⁺- exchanged clays, for which a possible explanation is proposed.     

Evaluation of Fe- and Cr-containing clinoptilolite catalysts for the production of camphene from α-pinene

The catalytic properties of the Cr³⁺- and Fe³⁺-loaded clinoptilolites were screened in the liquid-phase isomerization of α-pinene and the major products were found to be camphene and limonene. Selectivity to camphene was superior for the 0.7Fe-CL catalyst than those observed for the Raw-CL and 0.4Cr-CL catalyst. Over raw clinoptilolite, the proportion of limonene and other isomers reached ～65% while it was ～15% with 0.7Fe-CL and ～56% with 0.4Cr-CL. The results also show that the selectivity to camphene increases with increasing reaction time reaching up to about ～72% at 428 K over 0.7Fe-CL catalyst.     

Investigation of the phase composition and stability of the α-SiAlONs by the Rietveld method

Different compositions of Y- and Nd-α-SiAlONs were sintered at 1825 °C and analysed by the XRD method. The Rietveld technique was used for characterisation of the diffraction pattern and the x value of α-SiAlON, which has a composition of R_x^+vSi_12−(m+n)Al_m+nO_nN_16−n (R=Y, Nd). It was shown that the method yields reliable data for the content of the rare earth cations in the α-SiAlON phase, even in mixtures of α-SiAlONs with β- or α-Si₃N₄, but cannot be used for the determination of the Al and/or O contents of the α-SiAlONs. On the basis of these data, the stability regions of Y- and Nd-α-SiAlONs were established. Furthermore, it was found that the solubility area of the α-SiAlONs depends on the size of the additives. It was also shown that the solubility area of the Y-α-SiAlON is extended to lower X values than those suggested in the literature.     

Trail Pheromone of Myrmicine Ant Pristomyrmex pungens

The myrmicine ant Pristomyrmex pungens marks recruitment trails with poison gland secretions. The effective trail pheromone compound is 6-n-pentyl-2-pyrone. Poison gland components were identified by means of gas chromatographic coupled mass spectrometry. The biological activity was examined in trail-following experiments as well as in gas chromatographic coupled electroantennograms. In addition to 6-n-pentyl-2-pyrone, a number of monoterpenes were found in the poison gland secretion, i.e., α-pinene, camphene, β-pinene, myrcene, α-phellandrene, α-terpinene, and limonene. The terpenoid compounds increased the trail-following response only slightly when offered together with 6-n-pentyl-2-pyrone. In contrast to the latter component, synthetic monoterpenes elicited no orientation behavior in trail-following bioassays.     

Enantiomeric Composition of Monoterpene Hydrocarbons in Some Conifers and Receptor Neuron Discrimination of α-Pinene and Limonene Enantiomers in the Pine Weevil, Hylobius abietis

The enantiomeric composition of seven monoterpene hydrocarbons in headspace volatiles of spruce sawdust and seedlings (Picea abies), pine seedlings (Pinus sylvestris), and branches of juniper (Juniperus communis) was determined by gas chromatographic separation on a -Cyclodextrin column. For the six monoterpenes, -pinene, camphene, -pinene, sabinene, limonene, and -phellandrene, both enantiomers were present, whereas for 3-carene only the (+)-configuration was found. The amount of each enantiomer varied considerably both in relation to total amount of all of them, and for the six pairs also in relation to the opposite enantiomer. One olfactory receptor neuron in the pine weevil (Hylobius abietis) showed a strong response to -pinene when stimulated with all four headspace materials via a GC equipped with a DB-WAX column. The same neuron was subsequently tested with repeated stimulations via the GC effluent containing the (+)- or (–)-enantiomer. A marked better response to (+)- than to (–)--pinene was elicited. Another olfactory receptor neuron that responded strongly to limonene when stimulated with the spruce volatiles was tested for enantiomers of limonene. This neuron responded more strongly to (–)- than to (+)-limonene, when stimulated alternately with each of the limonene enantiomers. Discrimination between enantiomers by plant olfactory receptor neurons suggests that the enantiomeric ratios of volatile compounds may be important in host location by the pine weevil.     

Synthesis and characterization of the first poly(imidazolyl)borate organotin(IV) complex exhibiting a polymeric chain structure

The reaction between SnR_nX_4−n (R=Me, Ph or cy; n=2 or 3) acceptors and sodium tetrakis(imidazol-1-yl)borate, Na[B(im)₄], yields {[B(im)₄]R_nSnCl_4−n−1} compounds. The X-ray crystal structure of [μ-(im)₂B(im)₂SnMe₃] is the first example of a polymeric derivative containing the [B(im)₄]⁻ ligand coordinated in bridging fashion.     

Partition coefficient calculation of selected terpenes and low molecular weight solvents between tall oil fatty acid and air and polydimethyl siloxane oil and air

Headspace gas chromatography-mass spectrometry (GC-MS) has been applied to the analysis of the temperature-dependent tall oil fatty acid (TOFA)/air partition coefficient (k ₁) and the polydimethyl siloxane oil/air partition coefficient (k ₂) of selected terpenes and low molecular weight solvents. As expected, both the TOFA and the silicone oil are effective trapping media for the nonpolar terpenes, but they are also efficient traps for acetone, methanol, n-propanol, and n-butanol. However, several species of low and moderate molecular weight (less than 150 amu) aldehydes, ketones, and organic acids that might adversely affect its trapping capacity were detected in the TOFA. This article will report the empirically gathered data and the subsequent calculation of the partition coefficients for the terpenes: α- and β-pinene, limonene, and α-terpineol and the solvents: acetone, methanol, n-propanol, and n-butanol between 50 and 130°C.     

Analysis of cosolvent effect on supercritical carbon dioxide extraction for α-pinene and 1,8-cineole

The solubilities of α-pinene and 1,8-cineole in supercritical carbon dioxide with and without cosolvent were measured by using a circulation type apparatus coupled with an on-line Fourier transform infrared (FT-IR) spectroscope at 323 K and 8.0 MPa. The cosolvents interested in this work were ethanol, water, acetone and hexane. The solubilities were measured under vapor–liquid two phases. The effects of cosolvents on the solubilities and selectivities of α-pinene and 1,8-cineole in supercritical CO₂ were investigated. The selectivities at feed concentration of cosolvent of 0.056 mol L⁻¹ were increased 1.23 times by ethanol and decreased 0.82 times by hexane. Peng–Robinson equation of state with a quadratic mixing rule was used for correlations of the solubilities for α-pinene and 1,8-cineole in supercritical CO₂ with and without cosolvent. The correlated results reproduce the experimental data of cosolvent effects on the solubilities and selectivities of α-pinene and 1,8-cineole in supercritical CO₂.     

Chlorophyll adsorption by alumina-pillared acid-activated clays

Clays, acid-activated to an optimum level, have been pillared with alumina to give semi-crystalline expanded materials with surface acidities, pore volumes and average pore diameters generally higher than those of the corresponding pillared materials derived from a clay matrix not previously acid-activated. The chlorophyll adsorption capacity of the pillared acid-activated materials is significantly greater than that of pillared, nonactivated clays. The procedures used in the preparation of these pillared acid-activated clays (i.e., temperature of pillaring, method of drying and calcination temperature) have a significant influence on chlorophyll adsorption capacity because they influence both the physical and the chemical properties of the final pillared material. This variation provides a useful means of relating the various properties of the pillared materials to the chlorophyll adsorption capacity. As a result, a correlation has been demonstrated between adsorption capacity and a combination of pore volume and number of strong acid sites (of strength pK_a < −1.5) present in the pillared material. Optimal adsorbents were obtained from freeze-dried samples prepared by exchange at 20°C and calcination in air at 500°C.     

Refractory Clays of the Southern Berlinskoe Deposit Studied for Technological Application

Clays sampled from three core sites of the southern area of the Berlinskoe deposit (Chelyabinsk District, Russia) are analyzed for potential technological application. The clays containing 30.9 – 35.73% Al₂O₃ have a refractoriness of 1670 – 1690°C. The clays can be used as a binder for fabricating chamotte refractories (sample 1) and as a material component for building structures (samples 2 and 3).     

Comparative electrochemical study of myoglobin loaded in different polyelectrolyte layer-by-layer films assembled by spin-coating

Different types of {polycation/polyanion}_n layer-by-layer (LBL) films were assembled on the surface of pyrolytic graphite (PG) electrodes by spin-coating, and then immersed in myoglobin (Mb) solutions at pH 5.0 to load Mb into the films. Compared with the traditional solution-dipping method in LBL assembly, the spin-coating approach was much more time saving but did not show substantial difference in Mb loading. The Mb-loaded LBL films demonstrated nearly reversible cyclic voltammetric (CV) responses for Mb Fe(III)/Fe(II) redox couple, and the surface concentration of electroactive Mb in the films (Γ*, mol cm⁻²) could be used to compare the loading behaviors of Mb in different films. Among the six polyelectrolyte LBL films, {HECE/PSS}_n films assembled with quaternized hydroxyethyl cellulose ethoxylate (HECE) and poly(styrenesulfonate) (PSS) demonstrated the largest Γ* value for loaded Mb and the best performance in electrocatalysis toward hydrogen peroxide. CV, UV–vis spectroscopy and electrochemical impedance spectroscopy (EIS) were used to characterize the films and explore the reason why {HECE/PSS}_n-Mb films showed better electrochemical response than the other Mb-loaded LBL films. The better understanding of the interactions involved in Mb loading may help us to find novel and more suitable protein-loaded LBL film systems in the future.     

Ultrasonic wave aided selective epoxidation of mixed styrene and α-pinene with air over nanosized Co3O4

Catalytic selective epoxidation of mixed biolefins with air over nanosized Co₃O₄ catalyst under mild ultrasonic conditions has been first reported. When the styrene/α-pinene molar ratio was 1:5, the highest conversions were, respectively, reached 81.8 mol% for styrene and 76.1 mol% for α-pinene, with the epoxidation selectivity of 84.1% (styrene oxide) and 94.6% (α-pinene oxide), notably higher than those of the conventional reactions under magnetic stirring. An intermolecular electron-transfer phenomenon between conjugated styrene and electron-rich α-pinene was revealed by UV–vis spectra, which was considerably important for the enhancement of reactivities of both olefinic molecules observed experimentally.     

Palladium-Catalysed Oxidation of Bicycle Monoterpenes by Hydrogen Peroxide in Acetonitrile Solutions: A Metal Reoxidant-Free and Environmentally Benign Oxidative Process

Currently, the oxidative transformations of natural olefins are complicated for competitive reactions such as isomerization, skeletal rearrangements and nucleophilic addition. These concurrent reactions are promoted by metal reoxidant, normally a Lewis acid, and by protic solvent. In this article, the oxidation of terpenes, namely camphene, β-pinene, α-pinene and 3-carene were performed in PdCl₂/H₂O₂/CH₃CN system. This metal reoxidant-free system showed highly efficient, especially on camphene and β-pinene oxidation, which resulted in the selective conversion of these substrates into epoxy-derivates and allylic oxidation products, respectively. Additionally, the effects of the principal reactional parameters such as the peroxide/catalyst and substrate/catalyst molar ratio were also investigated.     

High activity, templated mesoporous SO4/ZrO2/HMS catalysts with controlled acid site density for α-pinene isomerisation

Highly active mesoporous SO₄/ZrO₂/HMS (hexagonal mesoroporous silica) solid acid catalysts with tuneable sulphated zirconia (SZ) content have been prepared for the liquid phase isomerisation of α-pinene. The mesoporous HMS framework is preserved during the grafting process as evidenced by the X-ray diffraction (XRD) and porosimetry with all SO₄/ZrO₂/HMS materials possessing average pore-diameters 20 Å. XRD confirms the presence of a stabilized tetragonal phase of nanoparticulate ZrO₂, with no evidence for zirconia phase separation or the formation of discrete crystallites, consistent with a uniform and highly dispersed SZ coating. The activity towards α-pinene isomerisation scales linearly with Zr loading, while the specific activities are an order of magnitude greater than attainable by conventional methodologies (1 versus 0.08 mol h⁻¹ g Zr⁻¹).