Isomerization Of Α-pinene Oxide Research Articles

Preparation, acid modification and catalytic activity of kaolinite nanotubes in α-pinene oxide isomerization.

In this work kaolinite nanotubes (KNT) were obtained from commercial kaolin AKF-78 (Uzbekistan) by starting material sequential intercalation by DMSO and methanol, followed by treatment with a cetyltrimethylammonium chloride solution. Acid functionalization of KNT for catalytic applications was successfully performed for the first time using a two-step treatment with piranha solution (H2SO4-H2O2), which resulted in the removal of organic impurities as synthetic artifacts and an increase in specific surface area by 3.9 times (up to 159 m2 g-1), pore volume by 1.5 times (0.23 cm3 g-1) and acidity by 4.1 times (49 μmol g-1). The values of the porous structure parameters and concentration of acid sites in processed kaolinite nanotubes practically corresponded to those for natural halloysite nanotubes (HNT) modified in the same way. Both types of materials demonstrated catalytic activity in the model reaction of α-pinene oxide isomerization in various solvents, including green ones, with selectivity to trans-carveol up to 55-57% and campholenic aldehyde of 50-51%, depending on the medium used. A satisfactory correlation between solvent polarity and selectivity was also observed. To the best of our knowledge, this is the first example of using modified kaolinite nanotubes per se as a catalyst. Overall, treatment of KNT with piranha solution provides not only catalytic activity but also the opportunity for further functionalization and application of these nanomaterials.

A novel route for isomerization of α-pinene oxide at room temperature under irradiation of light-emitting diodes

Present investigation demonstrates the potential use of HY-zeolite for photochemical applications in the selective isomerization of α-pinene oxide to carveol. In this study, ultraviolet lamp and LED (390 nm) light sources were employed under atmospheric conditions. The results revealed that light penetration through protonated zeolite cavity promotes the hydrogen radical formation, facilitating the isomerization reaction in the presence of dimethylacetamide solvent to achieve up to 60% and 40% conversion of α-pinene oxide to selective carveol (71%) under light irradiation. Here, using in situ spectroscopic studies (EPR and fluorescence), to confirm the hydrogen radical generation after light irradiation on the reaction mixture. Besides, the mechanistic pathway is proposed based on the experimental evidence of the formation of radicals, which is validated by the Density Functional Theory (DFT). By comparing electrical energy consumption for the same reaction using different reaction setups, it is understood that the energy requirement is nearly the same in the case of a reaction performed using a thermal reactor. The power consumption in reactions conducted using thermal, UV lamp and LED-based reactors was 1.6 kW/h, 1.5 kW/h, and 0.00144 kW/h, respectively. It is clear that the energy consumption in thermal and UV lamp-based reactors is higher than that of LED-based reactors, which was 1111 and 1041 times more than LED reactors respectively. Notably, the catalyst was found to be recyclable at least five consecutive runs, and the successful protocol was demonstrated up to 50 g scale.

Selective isomerization of α-pinene oxide totrans-carveol by task-specific ionic liquids: mechanistic insightsviaphysicochemical studies

A waste-free chemical process involving comparatively greener solvents with recyclability is one of the desired goals of sustainable development.

Hierarchical Beta Zeolites As Catalysts in α-Pinene Oxide Isomerization

Hierarchical Beta Zeolites As Catalysts in α-Pinene Oxide Isomerization

Selective isomerization of α-pinene oxide to campholenic aldehyde by ionic liquid-supported indenyl-molybdenum(II)-bipyridine complexes

Campholenic aldehyde (CPA), an important flavor and fragrance intermediate, can be obtained by the Lewis acid-catalyzed isomerization of α-pinene oxide (PinOx), although achieving high yields (>90%) is a difficult challenge due to the high reactivity of the epoxide. In the present work, indenyl-molybdenum(II)-bipyridine complexes [IndMo(bipyR)(CO)2](BF4) (bipyR = 2,2′-bipyridine (R = H) or 4,4′-disubstituted-2,2′-bipyridine) have been combined with various ionic liquid solvents to develop an efficient process for the selective conversion of PinOx to CPA under mild (35 °C) conditions. Excellent CPA yields (95%) were repeatedly obtained within 1 min reaction time for the easily recyclable catalytic system comprising [IndMo(4,4′-dinonyl-2,2′-bipyridine)(CO)2](BF4) and choline bis(trifluoromethylsulfonyl)imide.

Chemoselective isomerization of α-Pinene oxide to trans-Carveol by robust and mild Brønsted acidic zirconium phosphate catalyst

The current study focuses on the synthesis of an inexpensive, efficient, and cost-effective zirconium phosphate (ZrP) and its application in the one-step catalytic valorization of biomass-derived α-Pinene oxide (APO) into trans-Carveol (TC), which is used in the fragrance industry to produce essence oil. Amorphous zirconium phosphate (ZrP) with different P/Zr molar ratios (0.6–2.4) were synthesized using a simple (refluxing) method by controlling the concentration of dopant. The presence of phosphate groups was confirmed by FTIR and XPS analysis. The phosphate functionality provides the Brønsted acidic nature, and the acidity of the catalyst (ZrP3) is 0.9 mmol/g as measured by NH3-TPD analysis. Under optimized reaction conditions, the synthesized Brønsted acid catalyst (ZrP3) was used to valorize APO, resulting in complete conversion with 76% selectivity towards TC. The catalyst was recovered, activated, and reused numerous times with slight loss of activity or selectivity.

Solvent Influence on Selectivity in α-Pinene Oxide Isomerization Using MoO3-Modified Zeolite BETA

Natural source turpentine is an available source of α-pinene oxide. This compound’s value is especially given by the possibility of producing important compounds campholenic aldehyde and trans-carveol. In this work, we would like to present the usage of MoO3-modified zeolite BETA in α-pinene oxide isomerization concerning campholenic aldehyde and trans-carveol formation using a wide range of solvents. Catalyst calcination temperature also influenced the reaction course (selectivity to desired compounds and reaction rate). MoO3-zeolite BETA was prepared by the wet impregnation method and characterized by different techniques. The use of polar aprotic solvents had the most positive effect on the reaction course. Solvent basicity and polarity considerably influenced the reaction rate and selectivity to particular products. The combination of high basicity and the high polarity was the most suitable for the studied reaction from the reaction rate point of view. Selectivity to campholenic aldehyde and trans-carveol was the most influenced by solvent basicity. Higher solvent basicity caused the preferential formation of trans–carveol, influence on selectivity to campholenic aldehyde formation was the opposite. The described catalyst may be used for α-pinene oxide rearrangement to both desired products dependently on the used solvent. Molybdenum offers an exciting alternative for previously described modifications of zeolites for this reaction.

Isomerization of α-pinene oxide to campholenic aldehyde in the presence of Al-SiO2 and magnetic Al-SiO2/Fe3O4 catalysts

In the present work, we demonstrated synthesis of Al-SiO2 and magnetically recoverable Al-SiO2/Fe3O4 systems via grafting of triethylaluminum on SiO2 and SiO2-coated magnetic Fe3O4 nanoparticles, respectively. These materials were characterized by various techniques including elemental and N2-adsorption/desorption analyses, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR) using CO and pyridine as probe molecules. Amount of grafted Al on the support was found to affect the textural, acid–base properties and catalytic behavior in the isomerization of α-pinene oxide (PO) to campholenic aldehyde (CA). Maximal activity and selectivity towards CA was observed in the presence of sample with 12 wt% of alumina. It was demonstrated that 12%Al-SiO2/Fe3O4 can be used as catalyst for at least four successive cycles without loss of activity.

Engineering a Highly Defective Stable UiO-66 with Tunable Lewis- Brønsted Acidity: The Role of the Hemilabile Linker.

The stability of metal–organic frameworks (MOFs) typically decreases with an increasing number of defects, limiting the number of defects that can be created and limiting catalytic and other applications. Herein, we use a hemilabile (Hl) linker to create up to a maximum of six defects per cluster in UiO-66. We synthesized hemilabile UiO-66 (Hl-UiO-66) using benzene dicarboxylate (BDC) as linker and 4-sulfonatobenzoate (PSBA) as the hemilabile linker. The PSBA acts not only as a modulator to create defects but also as a coligand that enhances the stability of the resulting defective framework. Furthermore, upon a postsynthetic treatment in H2SO4, the average number of defects increases to the optimum of six missing BDC linkers per cluster (three per formula unit), leaving the Zr-nodes on average sixfold coordinated. Remarkably, the thermal stability of the materials further increases upon this treatment. Periodic density functional theory calculations confirm that the hemilabile ligands strengthen this highly defective structure by several stabilizing interactions. Finally, the catalytic activity of the obtained materials is evaluated in the acid-catalyzed isomerization of α-pinene oxide. This reaction is particularly sensitive to the Brønsted or Lewis acid sites in the catalyst. In comparison to the pristine UiO-66, which mainly possesses Brønsted acid sites, the Hl-UiO-66 and the postsynthetically treated Hl-UiO-66 structures exhibited a higher Lewis acidity and an enhanced activity and selectivity. This is further explored by CD3CN spectroscopic sorption experiments. We have shown that by tuning the number of defects in UiO-66 using PSBA as the hemilabile linker, one can achieve highly defective and stable MOFs and easily control the Brønsted to Lewis acid ratio in the materials and thus their catalytic activity and selectivity.

Nanoweb Surface-Mounted Metal-Organic Framework Films with Tunable Amounts of Acid Sites as Tailored Catalysts.

Metal-organic frameworks (MOFs) are a promising class of materials for many applications, due to their high chemical tunability and superb porosity. By growing MOFs as (thin-)films, additional properties and potential applications become available. Here, copper (II) 1,3,5-benzenetricarboxylate (Cu-BTC) metal-organic framework (MOF) thin-films are reported, which were synthesized by spin-coating, resulting in "nanowebs", that is, fiber-like structures. These surface-mounted MOFs (SURMOFs) were studied by using photoinduced force microscopy (PiFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The optimal concentration of precursors (10 mm) was determined that resulted in chemically homogeneous, pure nanowebs. Furthermore, the morphology and (un)coordinated Cu sites in the web were tuned by varying the rotation speed of the spin-coating process. X-ray diffraction (XRD) analysis showed that rotation speeds ≥2000 rpm (with precursors in a water/ethanol solution) generate the catena-triaqua-μ-(1,3,5-benzenetricarboxylate)-copper(II), or Cu(BTC)(H2 O)3 coordination polymer. X-ray photoelectron spectroscopy (XPS) highlighted the strong decrease in number of (defective) Cu+ sites, as the nanowebs mainly consist of coordinated Cu2+ Lewis acid sites (LAS) and organic linker-linker, for example, hydrogen-bonding, interactions. Finally, the Lewis-acidic character of the Cu sites is illustrated by testing the films as catalysts in the isomerization of α-pinene oxide. The higher number of LAS (≥3000 rpm), result in higher campholenic aldehyde selectivity reaching up to 87.7 %. Furthermore, the strength of a combined micro- and spectroscopic approach in understanding the nature of MOF thin-films in a spatially resolved manner is highlighted.

Black yet green: Sulfonic acid functionalized carbon as an efficent catalyst for highly selective isomerization of α-pinene oxide to trans-carveol

In this study, an inexpensive, high yielding, and environmentally benign bifunctional acid-base catalyst is prepared using a simple low-temperature hydrothermal carbonization method from a fishery bio-waste, chitosan as a carbon source and sulfuric acid, as _SO3H source. The successful formation of _SO3H group grafted carbon was confirmed by various physiochemical characterization methods such as powder XRD, FTIR, RAMAN, FESEM, EDAX, HRTEM, and XPS. Under the optimized reaction conditions, the bio-derived sulfonated hydrothermal carbon catalyst showed excellent performance for the isomerization of α-pinene oxide to trans-carveol (85% yield) at 160 °C in 1.5 h. The product selectivity was influenced mainly by the type of solvent used for the isomerization. No leaching of the sulfonated groups was observed even after five cycles without any significant loss in conversion and selectivity.

Efficient Isomerization of α-Pinene Oxide to Campholenic Aldehyde Promoted by a Mixed-Ring Analogue of Molybdenocene

The MoIV complex [(η5-indenyl)(η5-cyclopentadienyl)Mo(MeCN)2](BF4)2 (1) has been used to promote two acid-catalyzed epoxide ring-opening reactions under ambient conditions. The alcoholysis of styre...

Solvent-induced selectivity in α-pinene oxide isomerization catalyzed by Fe-modified zeolite beta

α-Pinene oxide rearrangement to important product—trans-carveol and campholenic aldehyde in the presence of zeolite beta modified by various amount of iron (0.625–20 wt%) was studied. The amount of iron influenced initial reaction rate and time for 50% conversion. The initial reaction rate decreased with decreasing amount of iron therefore with decreasing acidity. On the other side, the highest conversion achieved after 180 min was in the case of material modified by 5 wt% of iron. The selectivity was only slightly influenced by the iron amount, but very important was the influence of used solvent on product distribution. Large variety of solvents was used in this reaction (toluene, acetonitrile, 1,4-dioxane, acetone, N,N-dimethylformamide, N,N- dimethylacetamide, dimethyl sulfoxide). Using strongly basic polar solvents (e.g., dimethyl sulfoxide) the main product in the reaction mixture was trans-carveol and using low-basic solvents (e.g. toluene) it was campholenic aldehyde. It was shown that the product distribution may be induced by used solvent.

Heteropoly acid catalysts in upgrading of biorenewables: Synthesis of para-menthenic fragrance compounds from α-pinene oxide

Abstract The isomerization of α-pinene oxide in the presence of Cs2.5H0.5PW12O40 (CsPW) heteropolysalt as solid acid catalyst is reported. The reactions were performed in various solvents, which allowed to obtain trans-carveol, trans-sobrerol and pinol in 60–80% yield each, which exceed the yields reported so far. The CsPW catalyst could be recovered and reused without loss of its activity and selectivity.

Facile synthesis of magnetic macroporous polymer/MOF composites as separable catalysts

Design and synthesis of magnetic macroporous metal–organic frameworks (MOFs) have been of significant interest, in order to improve the catalytic efficiency and reusability. In this work, we prepared magnetic macroporous MOF composites based on as-prepared magnetic macroporous polyacrylamides (MMPam). Different MOFs with or without unsaturated coordinative metal sites, including HKUST-1, MOF-2, UiO-66, and Fe-MIL-101(-NH2) were grown on and within the MMPam matrices. The composites showed hierarchical porosity with both micro- and macropores, which facilitated substrate diffusion to increase the conversion for isomerization of α-pinene oxide from 62% in the case of pure HKUST-1 microparticles to 90% in the case of HKUST-1@MMPam. The magnetic property also endowed the composites with easy recovery and reasonable reusability.

Isomerization of α-pinene oxide over ZSM-5 based micro-mesoporous materials

Few types of ZSM-5 based micro-mesoporous materials obtained via a dual template method, steam-assisted conversion and dual-functional templating were evaluated in α-pinene oxide isomerization. Complete conversion and the highest selectivity towards trans-carveol (ca. 40–43%) were achieved over X-ray amorphous micro-mesoporous aluminosilicates as well as mesoporous molecular sieves AlSi-SBA-15. In addition, X-ray amorphous samples containing the secondary building units of ZSM-5 zeolite demonstrated the highest rate of α-pinene oxide isomerization. The yield of the most desired product trans-carveol to a large extent depends on the accessibility of acid sites to the reagents molecules and acidity of the catalysts (strength and concentration of Brønsted and Lewis acid sites).

Catalytic isomerization of α-pinene oxide in the presence of acid-modified clays

Isomerization of α-pinene oxide was studied at 20–50 °C in the presence of commercial montmorillonites K-10 and K-30, acid-treated illite clay as well as synthetic aluminosilicate AS-36 using cyclohexane as a solvent. The catalysts were characterized by XRD, XRF, FTIR, MAS NMR, thermal analysis and N2 low-temperature sorption methods The main reaction products at 99.9% conversion of the substrate are campholenic and iso-campholenic aldehydes, the largest amount of which (68.1 wt.%) is formed on illite clay treated by 10% HCl. The iso-campholenic/campholenic aldehydes ratio decreases from 0.7 to 0.25 with an increase of acidity of the catalyst from 47 to 153 μmol/g. The content of products with p-menthane structure (trans-carveol, trans-sorberol, p-cymene, pinol) reaches a maximum (33.0 wt.%) in the presence of medium-acid (104.0 μmol/g) K-10 clay. The amount of campholenic aldehyde in reaction mixture increases from 34.3 to 48.2 wt.%, and content of iso-campholenic aldehyde decreases from 33.7 to 17.7 wt.% with increasing the drying (calcination) temperature of illite clay from 50 to 600 °C respectively. The scheme for the formation of reaction products on clays was proposed.

α-Pinene oxide isomerization: role of zeolite structure and acidity in the selective synthesis of campholenic aldehyde

The highest campholenic aldehyde yield (83%) achieved over MCM-22 is a result which rivals the best ones published so far.

Highly selective synthesis of campholenic aldehyde over Ti-MWW catalysts by α-pinene oxide isomerization

Campholenic aldehyde is a highly valuable fine chemical that can be obtained by multistep synthesis from monoterpene α-pinene isolated from turpentine oil.

Bifunctional carbohydrate biopolymers entrapped lipase as catalyst for the two consecutive conversions of α-pinene to oxy-derivatives

Bifunctional catalysts designed as carbohydrate biopolymers entrapping lipase have been investigated for the biotransformation of a natural compound (α-pinene) to oxy-derivatives. Lipases assisted the epoxidation of α-pinene using H2O2 as oxidation reagent and ethyl acetate as both acetate-supplier and solvent affording α-pinene oxide as the main product. Further, the biopolymer promoted the isomerization of α-pinene oxide to campholenic aldehyde and trans-carenol. In this case, the biopolymers played double roles of the support and also active part of the bifunctional catalyst. Screening of enzymes and their entrapping in a biopolymeric matrix (e.g. Ca-alginate and κ-carrageenan) indicated the lipase extracted from Aspergillus niger as the most efficient. In addition, the presence of biopolymers enhanced the catalytic activity of the immobilized lipase (i.e. 13.39×103, 19.76×103and 26.46×103 for the free lipase, lipase-carrageenan and lipase-alginate, respectively). The catalysts stability and reusability were confirmed in eight consecutively reaction runs.