Isomerization Of Α-pinene Oxide Research Articles

Isomerization of α-pinene oxide over cerium and tin catalysts: Selective synthesis of trans-carveol and trans-sobrerol

A remarkable effect of the solvent nature on the acid catalyzed transformation of α-pinene oxide allowed direction of the reaction to either trans-carveol or trans-sobrerol. Each of these highly valuable compounds was obtained in nearly 70% yield using an appropriate polar solvent, whose basicity affected strongly the product distribution. In acetone, a weakly basic solvent, the reaction over heterogeneous sol–gel Sn/SiO 2 or Ce/SiO 2 catalysts gave mainly trans-sobrerol. No leaching of active components occurs under the reaction conditions and the catalysts can be recovered and reused. On the other hand, in more basic solvent, i.e., dimethylacetamide, the reaction was essentially directed to trans-carveol. Due to the leaching problems with Sn/SiO 2 and Ce/SiO 2 materials, the synthesis of trans-carveol was performed under homogeneous conditions using CeCl 3 or SnCl 2 as catalysts with a catalyst turnover number up to ca. 1200. The method represents one of the few examples of the synthesis of isomers from α-pinene oxide, other than campholenic aldehyde, with a sufficient for practical usage selectivity.

Insight into the properties of Fe oxide present in high concentrations on mesoporous silica

Oxide catalysts containing highly dispersed Fe phases supported on a mesoporous, high surface area silica, with iron in a wide range of concentration (4 < Fe 2O 3 mass% < 17), are presented. A suite of techniques was employed to determine the structural, morphologic, surface, electronic, acidic, and red-ox properties of the samples. Although the samples have great variation of the iron loading, they maintained good Fe-dispersion and low metal aggregation, even those with the highest concentrations of iron. By increasing the Fe-loading, the DR–UV–vis spectra showed that the band centered at 360 nm (low nuclearity 2 d-Fe oxo entities) became more intense, while the band at 500 nm (typical of 3 d-Fe 2O 3 nanoparticles) remained of low intensity and quite constant. Formation of significant amount of isolated Fe 3+ centers (band at ca. 230 nm) were also identified, in agreement with EPR evidences. The titrated amount of surface acid sites increased with the Fe loading, because of the increased amount of FeO x species, acting as Lewis acid sites. The test reaction of isomerization of α-pinene oxide revealed the prominent presence of Lewis acid sites on all the samples with main formation of the α-campholenic aldehyde product. The selectivity to α-campholenic aldehyde was around 53% for all the catalysts, independent of the Fe-loading. However, productivity to α-campholenic aldehyde increased with Fe-concentration, because of the increase of reaction rates as higher the Fe content was. Active acid Fe-sites could be associated with isolated Fe centers and in particular with low nuclearity 2 d-Fe oxo entities.

A new, Fe based, heterogeneous Lewis acid: Selective isomerization of α-pinene oxide

Heterogeneous Fe supported catalysts prepared by grafting Fe(III) acetylacetonate under basic conditions onto pure silica and a series of modified silicas with variable amount of zirconia were prepared. Their characterization showed the presence of Fe3+ species, with complete surface dispersion of the iron-phase and without any Fe3O4 presence. These materials exhibit not only excellent activity in the liquid phase isomerization of α-pinene oxide but also good selectivity towards campholenic aldehyde, thus showing their Lewis acid nature.

One-pot synthesis of naturanol from α-pinene oxide on bifunctional Pt-Sn/SiO2 heterogeneous catalysts

Abstract Bifunctional Pt-Sn/SiO2 catalysts with different Sn/Pt ratios have been prepared by co-impregnation, reduced in H2 and tested by means of the one-pot synthesis of α-campholenic alcohol (naturanol) from α-pinene oxide. All results are reported in two sections. In Part I, here presented, characterization of catalysts in terms of microstructure chemical and surface properties by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and acid properties investigated by FT-IR of adsorbed pyridine are included. In the reduced Pt-Sn/SiO2 catalysts, oxidized and/or metallic species, having different microstructural and acid characteristics, strongly dependent on the Sn/Pt ratio have been identified. For Sn/Pt ratios A clear relationship between the intensity of FT-IR bands and the activity in α-pinene oxide isomerization was observed indicating that Lewis acid sites, associated with ionic tin species, present on the surface of bifunctional Pt-Sn/SiO2 catalysts, are active centres favouring the isomerization reaction. Sn addition also increases the selectivity to naturanol, in the subsequent consecutive hydrogenation of campholenic aldehyde intermediate. However, at high loading, the bifunctional effect is less significant because the excess of oxidized tin strongly decreases the catalytic activity. Our results indicate that the Sn/Pt ratio is the key factor in Pt-Sn/SiO2 bifunctional catalysts and influences both activity and selectivity in the one-pot synthesis of naturanol from α-pinene oxide.

One-pot synthesis of naturanol from α-pinene oxide on bifunctional heterogeneous catalysts

Bifunctional Pt–Sn/SiO 2 catalysts have been tested in the one-pot synthesis of α-campholenic alcohol (naturanol, NAT) from α-pinene oxide. The process involve the sequential isomerization of the substrate into α-campholenic aldehyde and its subsequent hydrogenation to naturanol. Optimizing the formulation of the Pt–Sn/SiO 2 catalyst, a maximum naturanol yield of about 60% was obtained. Bifunctional Pt–Sn/SiO 2 catalysts described in the Part I, prepared by co-impregnation varying the Pt and Sn loading and the Sn/Pt ratio, have been tested in the one-pot synthesis of α-campholenic alcohol (naturanol) from α-pinene oxide. The process involves the sequential isomerization of the substrate into α-campholenic aldehyde and the subsequent hydrogenation of this intermediate to naturanol. In this Part II, a kinetic investigation of the catalytic process is reported. First, the isomerization and hydrogenation steps were studied separately. Results obtained indicate that the role of tin in the Pt–Sn/SiO 2 catalysts formulation is crucial, affecting strongly the activity and/or selectivity in both steps. In the isomerization step, the catalytic activity increases linearly with tin loading whereas the selectivity to campholenic aldehyde remains essentially unchanged. In the second step, high tin loadings increase the selectivity to naturanol but a careful control on the Sn/Pt ratio is necessary to obtain a satisfactory hydrogenation rate, because for Sn/Pt > 1 the catalytic activity falls out dramatically. The overall transformation of α-pinene oxide into naturanol was then investigated. It was found that the isomerization of α-pinene oxide to campholenic aldehyde is the step limiting the naturanol yield. Moreover, kinetic tests have shown that the ratio between the isomerization and hydrogenation rate is the other critical factor in order to synthesize naturanol in high yield. Optimizing the formulation of the Pt–Sn/SiO 2 catalysts, a maximum naturanol yield of about 60% was obtained.

Catalytic isomerisation of α-pinene oxide to campholenic aldehyde using silica-supported zinc triflate catalysts

Three silica-supported zinc triflate (Zn(CF 3 SO 3 ) 2 ) catalysts have been studied in a batch reactor for performing isomerisation reaction of α-pinene oxide to campholenic aldehyde. Reaction order was evaluated from the obtained experimental data by using an integral method of data analysis. Reaction rate constants were obtained at different temperatures and activation energies using each catalyst determined. Different catalyst loadings and supports were tested in this study: 0.05 mmol/g Zn-triflate/K60 (Catalyst 1), 0.01 mmol/g Zn-triflate/K100 (Catalyst 2) and 0.05 mmol/g Zn-triflate/HMS 24 (Catalyst 3). Various methods for determining heat of reaction were used in order to calculate thermodynamic parameters. Heat of α-pinene oxide to campholenic aldehyde isomerisation reaction was estimated as −73.2 kJ/mol.

Catalytic isomerisation of α-pinene oxide to campholenic aldehyde using silica-supported zinc triflate catalysts

The performance of silica-supported zinc triflate (Zn(CF 3 SO 3 ) 2 ) catalyst immobilised on the surface of the spinning disc reactor (SDR) has been studied for the isomerisation reaction of α-pinene oxide to campholenic aldehyde. Process selectivity and conversion were assessed to determine the viability of SDR for performing catalytic reactions under a range of SDR operating conditions. Different catalyst loadings and supports were tested in this study: 0.05 mmol/g Zn-triflate/K60 (Catalyst 1), 0.01 mmol/g Zn-triflate/K100 (Catalyst 2) and 0.05 mmol/g Zn-triflate/HMS 24 (Catalyst 3). The latter catalyst was found to give the best performance in the SDR, with observed selectivity of 75% towards campholenic aldehyde and α-pinene oxide conversion of 85% at a disc temperature of 45 °C, disc speed of 1500 rpm and reactant feed flow rate of 6 cm 3 /s. Empirical models relating conversion and selectivity to disc speed and feed flow rate were developed for each catalyst using multiple linear regression analysis of experimental data collected in the study. A comparison with corresponding batch reactions indicates that the high shear rates in the thin SDR film flowing over the immobilised catalyst may give rise to intense mixing characteristics which overcome any mass transfer limitations within the immobilised matrix which would otherwise restrict the reaction rate. The short and controllable disc residence time in the SDR (of the order of seconds) promotes the desired reaction and minimises unwanted side reactions for enhanced process selectivity. These process advantages demonstrate the potential of the SDR to provide a “greener” approach to catalytic reactions.

Isomerization of α-pinene oxide to campholenic aldehyde over Lewis acids supported on silica and titania nanoparticles

Lewis acids (FeCl 3, ZnCl 2, H 3BO 3) supported on SiO 2 and TiO 2 nanoparticles have been tested in the selective isomerization of α-pinene oxide to campholenic aldehyde. The spherical nanoparticle supports with a narrow particles size distribution have been synthesized by the sol–gel method. The morphological and microstructural characterization of the supports and catalysts was carried out by XRD, SEM–EDX and BET surface area measurements. Acid properties were investigated by DTA and FT-IR after adsorption of triethylamine and pyridine as probe molecules. SiO 2 and TiO 2 nanoparticles used as supports have shown negligible acidity and consequently low activity in the isomerization of α-pinene oxide. After Lewis acid promoters addition, the activity was markedly enhanced with a high selectivity to campholenic aldehyde. Lewis acids supported on titania have been found more actives than analogous supported silica catalysts due to the higher surface area of the TiO 2 support. The selectivity instead was found to be independent on the support used. Among the investigated samples, Zn-doped catalysts resulted the most selective. On the basis of FT-IR of adsorbed pyridine, the selectivity to campholenic aldehyde on these catalysts has been correlated to the strength of the Lewis acid sites. Optimising the preparation of the catalysts and reaction conditions, a maximum yield to campholenic aldehyde of 74% was obtained.

Isomerisation of α-pinene oxide over silica supported heteropoly acid H 3PW 12O 40

Silica-supported heteropoly acid H 3PW 12O 40 (PW) has been found to be a very efficient and environmentally benign solid acid catalyst for the liquid-phase isomerisation of α-pinene oxide ( 1). The reaction has been performed in cyclohexane solutions at 15–40 °C to give campholenic aldehyde ( 2) and trans-carveol ( 3) as the main products in up to 98% total yield, with 70% selectivity to more valuable product 2. Both 2 and 3 are expensive ingredients in the fragrance industry. No PW leaching has been observed during the reaction. The catalyst is easily separable from the reaction mixture and reusable without loss of its activity and selectivity.

Isomerisation of α-pinene oxide over B 2O 3/SiO 2 and Al-MSU catalysts

The isomerisation of α-pinene oxide to campholenic aldehyde was investigated over a number of solid acids—B 2O 3/SiO 2, ZnCl 2/MCM-41, Al-MCM-41, HY zeolites and Al-MSU-S FAU. Irrespective of the loading, the selectivity to campholenic aldehyde over B 2O 3/SiO 2 was ∼69% at 25 °C. The initial rate for the isomerisation of α-pinene oxide was a maximum at 15 wt.% B 2O 3 loading. Both Lewis and Brønsted acid sites were present in B 2O 3/SiO 2 samples although at higher loadings of B 2O 3, Brønsted acidity predominated. Under anhydrous conditions, no crystalline phases of boron oxide were detected up to a B 2O 3 loading of 20 wt.%, but upon exposure to ambient environment, boric acid was formed. The Lewis acid, ZnCl 2/MCM-41, was not very active but highly selective (85%) for campholenic aldehyde. Al-MCM-41 and HY zeolites showed high conversion but the selectivity was dependent on the Al content, varying from 49 to 66%. By incorporating both microporosity and mesoporosity in mesostructured Al-MSU-S FAU (Si/Al 70), good activity and selectivity to campholenic aldehyde, 86%, was observed.

Sol–gel synthesis, characterization and catalytic properties of Fe–Ti mixed oxides

Fe 2O 3-TiO 2 solid acid catalysts have been prepared by a sol–gel route, characterized and tested in the isomerization of α-pinene oxide. The textural, morphological and microstructural characterization of the catalysts was carried out by BET surface area measurements, X-ray diffraction (XRD) and scanning electron microscopy with elemental X-ray analysis (SEM-EDX). Characterization data have shown that, on the pure TiO 2 catalyst , titania is mainly in the anatase phase. On the contrary the rutile phase and/or Fe 2TiO 5, amorphous iron–titanium mixed oxides and hematite were found on the Fe-promoted TiO 2 catalysts, depending on the Fe content. Temperature programmed desorption (TPD), microcalorimetry and FT-IR spectroscopy of adsorbed probe basic molecules (ammonia or pyridine) have shown that addition of iron to titania favours formation of new acid sites having a stronger Lewis character. Fe 2O 3-TiO 2 catalysts show a higher activity compared to pure titania in the isomerization of α-pinene oxide to campholenic aldehyde. The products distribution was also influenced by the composition of the catalysts. A correlation between the selectivity to campholenic aldehyde and the amount of Lewis acid sites on the catalysts was found. Based on the characterization and catalytic results, Fe–Ti–O mixed structures were proposed to be the active sites for the selective isomerization of α-pinene oxide to campholenic aldehyde.

A study of some molecularly imprinted polymers as protic catalysts for the isomerisation of α-pinene oxide to trans-carveol

A range of acidic Molecularly Imprinted Polymers (MIPs) were synthesised using the imprint molecule trans-carvyl amine as a transition state analogue for the selective isomerisation of α-pinene oxide to trans-carveol. The amine functionality of the imprint molecule was used to selectively position a sulfonic acid group in the MIP binding pocket utilising 4-styrene sulfonic acid as the functional monomer. Co-polymerisation with varying ratios of styrene and divinylbenzene afforded a range of MIPs which were tested for their ability to effect selective formation of trans-carveol from α-pinene oxide. Although successful imprinting was demonstrated in binding studies, it was shown that solvent effects were dominant in effecting selective formation of trans-carveol. Using DMF as solvent, up to 70% of the products from acid catalysed isomerisation of α-pinene oxide with the polystyrene MIPs were obtained via the necessary para menthyl tertiary carbocation, and industrially important trans-carveol was obtained in 45% yield.

Rearrangement of α-pinene oxide using a surface catalysed spinning disc reactor (SDR)

Isomerisation of α-pinene oxide to campholenic aldehyde was performed by immobilising zinc triflate based catalysts on the surface of a spinning disc reactor (SDR). Two types of catalyst have been studied and the influence of operating parameters such as rotational speed, feed flow rate and reaction temperature on conversion and selectivity towards campholenic aldehyde has been investigated in considerable detail. The findings of the study suggest that immobilising the catalyst on the reactor surface and performing the reaction in continuous mode has potential for achieving benefits of Green Chemical Technology (GCT).

Isomerisation of α-Pinene Oxide on Sulfated Oxides

The acid properties of sulfated alumina, titania and zirconia have been characterised, and these solids compared in the isomerisation of α-pinene oxide in the liquid phase at 273 K. This comparison shows that the formation of campholenic aldehyde requires a mild Lewis acid. Only sulfated alumina is a good catalyst giving yields reaching 76% at full conversion in less than 1 h, though with a relatively high catalyst:reactant ratio. The conditions of preparation of this solid show a significant influence on the acid properties and therefore on the catalytic properties of the resulting solid. The best results are obtained with sulfated alumina prepared with a ratio of hydrolysis of 1 and an activation temperature of about 923 K.

A Method for the Facile Synthesis of Campholene Derivatives

Campholene derivatives obtained by the crossed aldol condensation of Campholene aldehyde (2) with ketones, are quite useful for the synthesis of perfumes. (2) was prepared by the isomerization of α-Pinene oxide (1) in the presence of a solid acid catalyst.The synthesis of 5-(2, 2, 3-trimethyl-3-cyclopenten-1-yl)-3-penten-2-one (3) was conducted by a one-pot procedure in a flask containing (1), acetone, solvent, solid acid catalyst and solid base catalyst.A method for the facile synthesis of (3) was developed using KF/H-Y330 as a solid acid catalyst and Sr(OH)2·8H2O as a solid base catalyst. Other ketones (2-butanone, 3-pentanone, cyclopentanone) could also be used for synthesizing various campholene derivatives with these catalysts.

Isomerization of α-Pinene Oxide with Chromic Acid Adsorbed on Silica Gel or Alumina

Isomerization of α-Pinene Oxide with Chromic Acid Adsorbed on Silica Gel or Alumina

Isomerization of α-Pinene Oxide in Dimethyl Sulfoxide

Isomerization of α-Pinene Oxide in Dimethyl Sulfoxide