Isomerization Of 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.

Recent Advances and Challenges in the Valorization of α‐Pinene toward Value‐Added Chemicals

AbstractThe transformation of abundantly available bioresources into specialty chemicals, particularly as consumer products, remains an important pursuit in chemical research. In this sense, the valorization of bio‐oil strategies that utilize stable and easy‐to‐handle chemical entity not only creates application‐oriented products but also helps in avoiding the usage of toxic and hazardous chemical sources. Recently, the valorization of α‐pinene (readily/naturally available terpenic compounds) has been explored to prepare a wide range of processes to access perfumery products and remains fast‐growing research for industrial and societal applications. Considering the valorization of α‐pinene, challenges for the synthetic and selective preparation of perfumery chemicals are centered around the design of the catalyst and the setting up of the precise reaction conditions. Extensive research is employed using diverse catalytic approaches to utilize α‐pinene to prepare important perfumery intermediates. In this review, the state‐of‐the‐art, recent advances and challenges in the utilization of α‐pinene are reviewed, emphasizing two main products, i.e., α‐campholenic aldehyde and carveol via α‐pinene oxide isomerization, and discussed the pertinent role of various homogeneous and heterogeneous catalytic systems.

Transformation of Styrene Oxide on Bi-Functional Ni, Co and Cu Catalysts Supported on Zirconia-Alumina: Effect of Depositing Zirconia on Alumina

2-phenyl ethanol (2-PEA) and 2-phenylacetaldehyde (PAA) are important perfumery chemicals which are prepared by hydrogenation and isomerization of styrene oxide (SO) respectively. Activities of Ni, Co and Cu supported on a set of zirconia-alumina supports with varying ZrO2:Al2O3 molar ratio are compared for these reactions. Zirconia was deposited on γ-alumina by deposition-precipitation. All catalysts were characterized by XRD, NH3-TPD, H2-TPR, N2 physisorption, XPS and Raman spectroscopy. Increasing the zirconia content significantly influenced catalyst characteristics. These are correlated with reactivity: i) surface concentration of Ni, Co and Cu (XPS) decreased, which affected conversion of styrene oxide and selectivity to 2-PEA ii) 1 1 1 plane of Cu (XRD) was suppressed which enhanced selectivity of styrene by-product relative to 2-PEA iii) acidity (NH3-TPD) decreased, which adversely affected yield of PAA. Product space time yields (STY) of 2-PEA and PAA correlated well with surface concentration of active metals (XPS) and acidity (NH3-TPD) respectively. Various by-products were identified. Styrene appeared to form by deoxygenation of SO. TPR and Raman spectroscopy indicated strong interaction of Co and Ni with alumina while Cu showed strong interaction with zirconia. This reflected in their XRD crystallite size. Cu has different electronic properties than Co and Ni, which reflected in differences in their behavior. This study directly compares the performance of these transition metals in continuous flow studies and correlates catalyst characteristics with reactivity.

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.

Catalytic conversion of biomass-derived compounds to high added value products using an acid treated natural mordenite

Herein, the mordenite catalyst TECHΝOSA-H2 that originates from volcanic soils in Greek islands is utilized for the synthesis of ethers and acetals from renewable raw materials. Di-furfuryl ether and furfuryl ethyl ether are used in perfumery and fuels, respectively, and are usually produced by employing either homogeneous catalysts or heterogeneous catalysts which however may lead to undesirable polymer products. Using TECHNOSA H2 we achieved yields in di-furfuryl ether and furfuryl ethyl ether 30% and 60%, respectively, in 3 h and 150 °C. We also report the synthesis of citral propylene glycol acetal and citral diethyl acetal, two important compounds in perfumery industry whose industrial synthesis often requires homogeneous catalysts while with TECHNOSA-H2 50% yields are achieved in 20 min and mild temperatures. The nature of the active sites of TECHNOSA-H2 was inspected by its application to relevant test reactions revealing that Brønsted acidity dominates in this catalyst. To that end, the one-step isomerization of a-pinene oxide to campholenic aldehyde and the one-step cyclization of citronellal to isopulegol in 10min were achieved. Finally, the shape selectivity of the catalyst was examined, proving TECHNOSA-H2 to be selective between the (E)- and (Z)- isomers of Citral. Based on our findings, TECHNOSA-H2 applications vary and include acetalization, isomerization and etherification reactions, as well as reactions where shape selectivity between reactants is desired.

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.

Rapid Allylic 1,6 H-Atom Transfer in an Unsaturated Criegee Intermediate.

A novel allylic 1,6 hydrogen-atom-transfer mechanism is established through infrared activation of the 2-butenal oxide Criegee intermediate, resulting in very rapid unimolecular decay to hydroxyl (OH) radical products. A new precursor, Z/E-1,3-diiodobut-1-ene, is synthesized and photolyzed in the presence of oxygen to generate a new four-carbon Criegee intermediate with extended conjugation across the vinyl and carbonyl oxide groups that facilitates rapid allylic 1,6 H-atom transfer. A low-energy reaction pathway involving isomerization of 2-butenal oxide from a lower-energy (tZZ) conformer to a higher-energy (cZZ) conformer followed by 1,6 hydrogen transfer via a seven-membered ring transition state is predicted theoretically and shown experimentally to yield OH products. The low-lying (tZZ) conformer of 2-butenal oxide is identified based on computed anharmonic frequencies and intensities of its conformers. Experimental IR action spectra recorded in the fundamental CH stretch region with OH product detection by UV laser-induced fluorescence reveal a distinctive IR transition of the low-lying (tZZ) conformer at 2996 cm-1 that results in rapid unimolecular decay to OH products. Statistical RRKM calculations involving a combination of conformational isomerization and unimolecular decay via 1,6 H-transfer yield an effective decay rate keff(E) on the order of 108 s-1 at ca. 3000 cm-1 in good accord with the experiment. Unimolecular decay proceeds with significant enhancement due to quantum mechanical tunneling. A rapid thermal decay rate of ca. 106 s-1 is predicted by master-equation modeling of 2-butenal oxide at 298 K, 1 bar. This novel unimolecular decay pathway is expected to increase the nonphotolytic production of OH radicals upon alkene ozonolysis in the troposphere.

Influence of the Support on Propene Oxidation over Gold Catalysts

The epoxidation of propene without forming a substantial amount of byproducts is one of the holy grails of catalysis. Supported Cu, Ag and Au catalysts are studied for this reaction and the activity of the supported metals is generally well understood. On the contrary, limited information is available on the influence of the support on the epoxide selectivity. The reaction of propene with equal amounts of hydrogen and oxygen was tested over gold nanoparticles deposited onto CeO2, TiO2, WO3, γ-Al2O3, SiO2, TiO2-SiO2 and titanosilicate-1. Several metal oxide supports caused further conversion of the synthesized propene oxide. Strongly acidic supports, such as WO3 and titanosilicate-1, catalyzed the isomerization of propene oxide towards propanal and acetone. Key factors for achieving high PO selectivity are having inert or neutralized surface sites, a low specific surface and/or a low density of surface -OH groups. This work provides insights and practical guidelines to which metal oxide support properties lead to which products in the reaction of propene in the presence of oxygen and hydrogen over supported gold catalysts.

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.

Electrogenerated BF3 From Tetrafluoroborate-Based Ionic Liquids: Theoretical And Experimental Studies Towards Selective Styrene Oxide Isomerization

The anodic oxidation of tetrafluoroborate anion yields the Lewis acid BF3. If this reaction is carried out in an imidazolium ionic liquid, a quite stable system containing BF3 is obtained, whose reactivity is similar to the one of BF3·Et2O, but less harmful. The two reagents’ stabilities were compared by computational analysis, strongly suggesting a higher stability for BF3/BMIm-BF4 system. The effect of substituents on the imidazolium ring and of the electrochemical configuration on BF3 reactivity were studied in a model reaction, styrene oxide isomerization. The experimental conditions were defined for the selective formation of phenylacetaldehyde or of 2-benzyl-4-phenyl-1,3-dioxolane. Moreover, the formation of N-heterocyclic carbene-BF3 adduct was confirmed when carrying out the electrolysis in an undivided cell. Electrogenerated BF3/BMIm-BF4 system demonstrated to be a valid alternative to commercial BF3·Et2O.

Selective Catalytic Isomerization of β‐Pinene Oxide to Perillyl Alcohol Enhanced by Protic Tetraimidazolium Nitrate

A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of β‐pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT‐IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss.

High‐Level Production of Phenylacetaldehyde using Fusion‐Tagged Styrene Oxide Isomerase

AbstractAn order‐of‐magnitude improvement in the production of phenylacetaldehyde to 3.37 M (405 g L−1) from the enzymatic isomerisation of styrene oxide was achieved. A small ubiquitin‐related modifier (SUMO) tag increases the productivity of the whole‐cell biocatalytic system by enhancing the expression of active membrane‐bound styrene oxide isomerase (SOI) while retaining enzyme catalytic efficiency and broad natural substrate scope. The isomerisation was performed by using Escherichia coli expressing SUMO‐tagged SOI in an organic‐aqueous biphasic system to yield 96% of phenylacetaldehyde.magnified image

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.

Identification of potential technologies for 1,4‐Butanediol production using prospecting methodology

Abstract1,4‐Butanediol (1,4‐BDO) is a four‐carbon diol used for industrial applications such as organic solvents, and the production of adhesives, fibers and polyurethanes. 1,4‐BDO currently is produced through several petrochemical routes: hydrogenation of maleic anhydride, isomerization of propylene oxide, acetoxylation of butadiene, and the reaction between formaldehyde and acetylene. The current trends in 1,4‐BDO production involve the utilization of renewable sources such as biomass. In this context, the present study aimed to identify promising technologies of 1,4‐BDO production through prospecting methodology based on the analyses of patents and scientific article, describing the most relevant aspects of those emerging technologies. An increasing amount of 1,4‐BDO production focused on biotechnological routes has been reported, with the US heavily involved in the development of new technologies. This study tracked three promising technologies which have potential for application in a biorefinery context because those processes involve (i) production of 1,4‐BDO from sugars, classified herein as the biotechnological route; (ii) production of intermediates from sugar fermentation followed by catalytic conversion into 1,4‐BDO, classified herein as the hybrid route, and (iii) furan/furfural conversion into 1,4‐BDO. © 2020 Society of Chemical Industry

Catalytic degradation of ethylene oxide over Ag/α-Al2O3

Ethylene oxide (EO) degradation over Ag/α-Al2O3 catalysts involves bifunctional pathways, whereby α-Al2O3 surfaces catalyze hydration, isomerization, dimerization, and oxidation while Ag surfaces facilitate combustion and isomerization of ethylene oxide. EO degradation reactions run over Ag/α-Al2O3, α-Al2O3, and intrapellet mixtures thereof with co-feeds of O2 and oxygenate products show that Ag surfaces are more reactive than α-Al2O3 and that oxygenate products generated over α-Al2O3 combust over Ag much more (>30x) readily than EO. These observations suggest that additives which mitigate surface hydration of α-Al2O3 and combustion activity of Ag will most effectively mitigate EO degradation.

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.

The application of TS-1 materials with different titanium contents as catalysts for the autoxidation of α-pinene

Titanium-silicalite TS-1 catalysts with different titanium contents were synthesized by the hydrothermal method and characterized by means of the FTIR, UV–Vis, XRD, XRF, and SEM techniques. The studies showed that in the tested reaction system the process of isomerization of α-pinene over these TS-1 catalysts did not occur; however, the self-oxidation of α-pinene did proceed. The main directions of autoxidation of α-pinene were the double-bond oxidation and the oxidations at allylic positions 2 and 10. This work presents the explanation of the mechanism of the α-pinene self-oxidation process. In addition, isomerization and hydration products of α-pinene oxide were formed. It was found that the optimal condition for the production of the oxide is to perform the autoxidation process at the temperature of 80 °C for the TS-1 20:1 catalyst (content 1 wt%), and at the reaction time of 24 h. Under these conditions, the selectivity of α-pinene oxide was 30.25 mol%, and the conversion of α-pinene reached 41.81 mol%. In addition to the production of α-pinene oxide, verbenol, verbenone, and campholenic aldehyde can also be obtained, which are products that can find valuable applications in the cosmetics industry, in medicine, and in the production of various polymers.

Direct Gas-Phase Oxidation of Propylene to Acetone in the Presence of H2 and O2 over Au/TS-1 Catalyst.

A novel process for the preparation of acetone is reported by gas-phase oxidation of propylene in the presence of H2 and O2 with Au supported TS-1 catalyst (Au/TS-1). By elevating the reaction temperature to 280°C, Au/TS-1 catalyzes 11.6% propylene generating acetone with 70.6% selectivity, and 8.2% acetone in onepass yield. Acetone is originated from propylene oxide isomerization, which is mainly attributed to the surface of the Lewis base and high reaction temperature. Furthermore, small Au nanoparticle size promotes the reaction.