Isomerization Of Epoxides Research Articles

Preparing kaolinite nanotubes and their catalytic activation by acid treatment

Aluminosilicate nanotubes (ANT) with a length of 600–1000 nm and a diameter of 15–25 nm were obtained by successive intercalation of kaolin with dimethyl sulfoxide and methanol followed by treatment with a cetyltrimethylammonium chloride solution. It is shown for the first time that the treatment of ANT with a mixture of H2SO4 –H2O2 leads to removing organic impurities from them and appearing catalytic activity in the α-pinene epoxide isomerization, the products of whicn are campholenic (41.4 %) and iso-campholenic (22.7 %) aldehydes in cyclohexane and trans-carveol (up to 56.0 %) in dimethyl sulfoxide.

A Synergistic Bimetallic Ti/Co-Catalyzed Isomerization of Epoxides to Allylic Alcohols Enabled by Two-State Reactivity.

Isomerization of epoxides into versatile allylic alcohols is an atom-economical synthetic method to afford vicinal bifunctional groups. Comprehensive density functional theory (DFT) calculations were carried out to elucidate the complex mechanism of a bimetallic Ti/Co-catalyzed selective isomerization of epoxides to allyl alcohols by examining several possible pathways. Our results suggest a possible mechanism involving (1) radical-type epoxide ring opening catalyzed by Cp2Ti(III)Cl leading to a Ti(IV)-bound β-alkyl radical, (2) hydrogen-atom transfer (HAT) catalyzed by the Co(II) catalyst to form the Ti(IV)-enolate and Co(III)-H intermediate, (3) protonation to give the alcohols, and (4) proton abstraction to form the Co(I) species followed by electron transfer to regenerate the active Co(II) and Ti(III) species. Moreover, bimetallic catalysis and two-state reactivity enable the key rate-determining HAT step. Furthermore, a subtle balance between dispersion-driven bimetallic processes and entropy-driven monometallic processes determines the most favorable pathway, among which the monometallic process is energetically more favorable in all steps except the vital hydrogen-atom transfer step. Our study should provide an in-depth mechanistic understanding of bimetallic catalysis.

Dendritic ZSM-5 zeolites as highly active catalysts for the valorization of monoterpene epoxides.

Dendritic ZSM-5 zeolites were investigated in the isomerization of monoterpene epoxides, including limonene-1,2-epoxide (LE), α-pinene epoxide, and β-pinene epoxide, which yields high-value compounds used in fragrances, cosmetics, and pharmaceuticals. The fresh catalysts were thoroughly characterized using XRD, Ar physisorption, pyridine-FTIR, TEM, FTIR/DTBPyr, and 27Al MAS NMR. In comparison with conventional and hierarchical ZSM-5 materials, the dendritic zeolite with a crystallization time of 4 days (d-ZSM-5/4d) was the most active material, with a turnover frequency value of 4.4 min-1 for LE isomerization. Likewise, remarkable yields of dihydrocarvone (DHC, 63%, 70 °C, 2 h), campholenic aldehyde (72.4%, 70 °C, 5 min), and myrtanal (47.7%, 50 °C, 5 min) were obtained with this material that exhibited the largest mesopore/external surface area (360 m2 g-1), showing also the narrowest mesopore size distribution. A direct relationship was observed between the TOF values and the concentration of external Brønsted acid sites, showing the presence of strong steric/diffusional limitations that are greatly overcome with the dendritic zeolites. The lower reactivity of trans-LE compared to cis-LE was attributed to the larger steric hindrance of the oxygen atom. Exploration of the solvent influence revealed that the reaction rate of LE was favored by non-polar solvents, while highly selective DHC formation occurred in the solvents of medium polarity. The d-ZSM-5/4d sample was shown to be robust because catalytic activity could be completely recovered by air calcination.

Study on synthesis of mesoporous ZSM-5 zeolite using carboxymethyl cellulose mesopore directing agent for re-arrangement of epoxide

This current work presents a study on using carboxylmethyl cellulose (CMC) as mesopore directing agent for synthesis of mesoporous ZSM-5 zeolite. The results showed that CMC, a cellulose derivative can be used as potential mesopore directing agent for synthesis of mesopore zeolite material. The obtained ZSM-5 zeolite was characterized by XRD, SEM methods and was used as catalyst for the isomerization of epoxide to synthesize aldehyde. The synthesized ZSM-5 catalyst exhibited a high catalytic activity and selectivity in the reaction. The highest conversion of about 98,2% was obtained when the isomerization of styrene carried out at suitable reaction conditions.

Selective Catalytic Epoxidation-Hydration of α-Pinene with Hydrogen Peroxide to Sobrerol by Durable Ammonium Phosphotungstate Immobilized on Imidazolized Activated Carbon.

It is presented that the activated carbon was carboxylated with hydrogen peroxide and then acylated with 2-methylimidazole to prepare the porous carbon support with a surface imidazolated modification. Through the adsorption of phosphotungstic acid on the fundamental site of an imidazolyl group and then adjusting the acid strength with the ammonia molecule, a catalytic carbon material immobilized with ammonium phosphotungstate (AC-COIMO-NH4PW) was obtained, which was used to catalyze a one-pot reaction of convenient α-pinene and hydrogen peroxide to sobrerol. The bifunctional active site originated from the dual property of ammonium phosphotungstate, as the oxidant and acid presenting a cooperatively catalytic performance, which effectively catalyzes the tandem epoxidation-isomerization-hydration of α-pinene to sobrerol, in which the solvent effect of catalysis simultaneously exists. The sobrerol selectivity was significantly improved after the acid strength weakening by ammonia. Monomolecular chemical bonding and anchoring of ammonium phosphotungstate at the basic site prevented the loss of the active catalytic species, and the recovered catalyst showed excellent catalytic stability in reuse. Using acetonitrile as the solvent at 40 °C for 4 h, the conversion of α-pinene could reach 90.6%, and the selectivity of sobrerol was 40.5%. The results of five cycles show that the catalyst presents excellent stability due to the tight immobilization of ammonium phosphotungstate bonding on the imidazolized activated carbon, based on which a catalytic-cycle mechanism is proposed for the tandem reaction.

Styrene Oxide Isomerase-Catalyzed Meinwald Rearrangement in Cascade Biotransformations: Synthesis of Chiral and/or Natural Chemicals.

Styrene oxide isomerase (SOI) catalyzes the Meinwald rearrangement of aryl epoxides to carbonyl compounds via a 1,2-trans-shift in a stereospecific manner. A number of cascade biotransformations with SOI-catalyzed epoxide isomerization as a key step have been developed to convert readily available substrates into valuable chiral chemicals. Cascade conversion of terminal or internal alkenes into chiral acids, alcohols or amines was achieved, which involved SOI-catalyzed enantio-retentive isomerization of terminal epoxides via 1,2-H shift, or internal epoxides via 1,2-methyl shift. SOI-involved cascades were also developed to convert racemic epoxides into chiral acids or amines via dynamic kinetic resolution. Additionally, combining SOI-catalyzed isomerization with enantioselective C-C bond forming enzymes enabled the synthesis of chiral amino acids or amino alcohols from racemic epoxides. Finally, integration of SOI-involved cascades with biosynthesis pathways allowed for the direct utilization of renewable substrates for the sustainable synthesis of high-value natural chemicals such as alcohols, acids, and esters.

Evaluation of the Isomerization of α-Pinene Epoxide to Campholenic Aldehyde Using a Catalyst Obtained from Orange Peels (Citrus sinensis)

Orange peels (Citrus sinensis) are an abundant lignocellulosic residue that can be used as a carbon source to obtain solids with catalytic potential in the transformation of terpenes and their oxides into value-added products. This research seeks to evaluate the isomerization of α-pinene epoxide to campholenic aldehyde using a catalyst obtained from orange peels. The material OAC-Zn was obtained by activation of orange peel with ZnSO4.7H2O followed by thermal treatment at 500 °C; an additional solid was obtained from orange peel by pyrolysis at 500 °C (OC-500). XRD revealed the presence of ZnO and ZnS in OAC-Zn; TGA analysis indicated thermal stability in OAC-Zn and OC-500 materials; SEM images showed porous surfaces of different morphology, and the presence of microporosity in OC-500 and mesoporosity in the OAC-Zn that was confirmed by physical nitrogen adsorption. The elements C, O, Zn and S was identified in OAC-Zn by EDX analysis. The results of TPD-NH3 showed that the solids contained medium and weak acidity. Campholenic aldehyde was synthesized with a 96 % selectivity over a mesoporous carbonaceous material obtained from orange peels using ZnSO4.7H2O as activating agent

Mechanistic insights into amide formation from aryl epoxides and amines catalyzed by ruthenium pincer complexes: a DFT study.

The synthesis of amides is of great significance in academia and industrial fields. Herein, density functional theory (DFT) studies were employed to investigate the mechanism of the formation of amides via aryl epoxides and amines catalyzed by ruthenium pincer complexes. The entire reaction mainly comprises three processes: isomerization of epoxides to aldehydes, aldimine condensation, and amide formation. Calculated results showed that bipyridine-based Ru-PNN A1 (PNN = 2-(di-tert-butylphosphinomethyl)bipyridine) pincer complexes could be potential highly catalytic species for the synthesis of amides and that the rate-determining step is the amine-assisted hydrogen elimination with a free energy barrier of 28.0 kcal mol-1. This study might not only provide new insights into the future of the formation of amides by transition-metal complexes but also facilitate the theoretical guidance needed to design novel transition-metal catalysts.

Solid-catalyzed synthesis of isomers–free terpinen–4–ol

Terpinen–4–ol is a natural product with wide application in the fragrance and agrochemical industry, currently extracted from tea tree oil or synthesized from either base–promoted rearrangement of 1,4–cineol or acid–catalyzed hydration of limonene. However, these synthetic processes, based on aggressive, unrecoverable homogeneous reagents, are non–selective and give significant amounts of isomers, which severely complicate and make more expensive the purification of the active substance. Here we show the isomers–free synthesis of terpinen–4–ol, exclusively over solid catalysts such as alumina, nanotitania and Pd/C, in >60% yield, by selective epoxidation, isomerization of terpinolene epoxide and allyl alcohol hydrogenation. The synthesis can be performed either in batch or in flow mode for the isomerization of terpinolene epoxide. The use of bare nanotitania as a selective epoxide isomerization catalyst, here demonstrated, opens new ways for the synthesis of quaternary alcohols.

Enzyme-Catalyzed Meinwald Rearrangement with an Unusual Regioselective and Stereospecific 1,2-Methyl Shift.

The Meinwald rearrangement is a synthetically useful reaction but often lacks regioselectivity and stereocontrol. A significant challenge in the Meinwald rearrangement of internal epoxides is the non-regioselective migration of different substituents to give a mixture of products. Herein, an enzyme-catalyzed regioselective and stereospecific 1,2-methyl shift in the Meinwald rearrangement of internal epoxides is reported. Styrene oxide isomerase (SOI) catalyzed the unique isomerization of internal epoxides through 1,2-methyl shift without 1,2-hydride shift to give the corresponding aldehydes and a cyclic ketone as the sole product. SOI-catalyzed isomerization showed high stereospecificity, fully retaining the stereoconfiguration. The synthetic utility of this enzymatic Meinwald rearrangement was demonstrated by its incorporation into three new types of enantioselective cascades, to convert trans-β-methyl styrenes into the corresponding R-configured alcohols, acids, or amines in high ee and yield.

Enzyme‐Catalyzed Meinwald Rearrangement with an Unusual Regioselective and Stereospecific 1,2‐Methyl Shift

AbstractThe Meinwald rearrangement is a synthetically useful reaction but often lacks regioselectivity and stereocontrol. A significant challenge in the Meinwald rearrangement of internal epoxides is the non‐regioselective migration of different substituents to give a mixture of products. Herein, an enzyme‐catalyzed regioselective and stereospecific 1,2‐methyl shift in the Meinwald rearrangement of internal epoxides is reported. Styrene oxide isomerase (SOI) catalyzed the unique isomerization of internal epoxides through 1,2‐methyl shift without 1,2‐hydride shift to give the corresponding aldehydes and a cyclic ketone as the sole product. SOI‐catalyzed isomerization showed high stereospecificity, fully retaining the stereoconfiguration. The synthetic utility of this enzymatic Meinwald rearrangement was demonstrated by its incorporation into three new types of enantioselective cascades, to convert trans‐β‐methyl styrenes into the corresponding R‐configured alcohols, acids, or amines in high ee and yield.

Effect of reaction conditions and kinetics of the isomerization of β-pinene epoxide to myrtanal in the presence of Fe/MCM-41 and Fe/SBA-15

Effect of reaction conditions and kinetics of the isomerization of β-pinene epoxide to myrtanal in the presence of Fe/MCM-41 and Fe/SBA-15

Thermodynamics of the Isomerization of Monoterpene Epoxides.

In this contribution, the thermodynamic analysis of α- and β-pinene epoxide isomerization over Fe and Cu supported on MCM-41 is presented using computational chemistry and group contribution methods (GCMs). Some physical–chemical data (Tc, Pc, vc, Zc, ω, Tb, Tfus) and thermodynamic (S°298.15, Cp,298.15°, Cv,298.15°, ΔHf,298.15°, ΔGf,298.15°, ΔHvb°, ΔHfus, CpL) properties obtained by different GCMs are reported for several monoterpenes and monoterpenoids, which significantly contribute to the knowledge of the properties of these compounds. Density functional theory (DFT), PBE-D3/6-311G(d,p), was employed for determining the Gibbs free energy and the heat of reaction associated with the transformation of monoterpene epoxides into aldehydes, ketones, and related oxygenated compounds in the presence of different solvents and at several temperatures. The calculations were compared with available data reported and the experimental results of the catalytic reactions. The transformation of α- and β-pinene epoxides into aldehydes appears to be more spontaneous and favorable than their transformations into alcohols in a wide range of temperatures. These results are in agreement with the experiments over Fe/MCM-41 and Cu/MCM-41, where α-pinene epoxide isomerization yields campholenic aldehyde (50–80% selectivity) as the main product. The 1.7Fe/MCM-41 material was more active in all solvents than 1.3Cu/MCM-41 for both α- and β-pinene epoxide isomerization. However, perillyl alcohol (20–70% selectivity) was the most favored for the isomerization reaction, except when ethyl acetate was the solvent. Enthalpy and Gibbs free energy of the studied reactions estimated by both GCMs and DFT calculations did not show large differences for most of the reactions at evaluated temperatures.

Selective synthesis of high-added value chemicals from α-pinene epoxide and limonene epoxide isomerization over mesostructured catalysts: Effect of the metal loading and solvent

Isomerization of α-pinene epoxide was performed over several Fe or Cu supported on MCM-41 and SBA-15 catalysts. The effect of the metal loading and polarity of the solvent on substrate conversion and selectivity was analyzed. It was found that materials containing Fe are more active but less selective to campholenic aldehyde and trans-carveol than materials with Cu, difference that was related with the size of the metal oxide particles and strength/type of the acid sites. An increasing of the solvent polarity decreases formation of campholenic aldehyde, the most desirable compound from α-pinene epoxide. Also, it was showed that trans-carveol is an intermediate in the production of p-cymene. Selectivity to campholenic aldehyde up to 82% can be achieved over Cu/MCM-41 as heterogeneous catalyst at soft reaction conditions (70 °C, 2.5 h, 25 mg, 750 rpm, toluene as solvent). From limonene epoxide isomerization over Fe/SBA-15, dihydrocarvone and limonene-1,2-diol production depended on the type of solvent. An increasing of polarity of the solvent, appears to increase selectivity to dihydrocarvone while limonene-1,2-diol is favored with solvents of lower polarity (mainly cyclohexane and hexane). Reuse of Fe materials were also tested for both monoterpene epoxides showing that Fe supported on MCM-41 and SBA-15 can be used several times (up to 5 times) without any loss of catalytic activity for the synthesis of campholenic aldehyde from α-pinene epoxide and dihydrocarvone (and limonene-1,2-diol) from limonene epoxide.

Selective Synthesis of Perillyl Alcohol from β-Pinene Epoxide over Ti and Mo Supported Catalysts

Isomerization of β-pinene epoxide to perillyl alcohol using several materials based on titanium and molybdenum is reported. The metals were incorporated on SBA-15, MCM-41 and SiO2 supports by incipient wetness impregnation and characterized by XRD, atomic absorption, BET, Raman spectroscopy, diffuse reflectance UV–Vis spectroscopy, TPD-NH3 and 29Si NMR. After metal incorporation, crystallinity and surface area of both MCM-41 and SBA-15 decreased. UV–Vis and Raman also revealed the presence of MoO3 species and no presence of TiO2. In addition, Ti materials showed less amount of acid sites than catalysts containing Mo. Synthesis of perillyl alcohol from β-pinene epoxide was affected by the content of acid sites; Mo/SBA-15 catalyst was more active than Mo/MCM-41 and Mo/SiO2 supported materials. Over Mo/SBA-15 a complete β-pinene epoxide conversion and perillyl alcohol selectivity of 63% were obtained at 1 h of reaction, results that are similar to the best activity reported up to now; Mo/SBA-15 can be recycled at least six times without any appreciable loss of conversion nor selectivity. Finally, a reaction pathway is proposed based on experimental information, explaining the exclusive formation of perillyl alcohol from β-pinene epoxide.

Proton-accelerated Lewis acid catalysis for stereo- and regioselective isomerization of epoxides to allylic alcohols.

The isomerization of epoxides to allylic alcohols was developed via proton-accelerated Lewis acid catalysis. The addition of tBuOH as a proton source is the key to the efficient catalytic cycle. Trisubstituted epoxides, including enantioenriched derivatives, were selectively converted to secondary-allylic alcohols without loss of enantiopurity.

Isomerization of Epoxides into Allylic Alcohols Catalyzed by Supported Au Nanoparticles on TiO2: A Mechanistic Insight.

Based on primary and β-secondary isotope effects, it is established that the isomerization of epoxides into allylic alcohols catalyzed by supported Au nanoparticles proceeds via an unsymmetrical concerted transition state in which there is partial positive charge developing on the C-O carbon atom progressing C-H abstraction. A carbocationic intermediate can be formed only in cases of sufficient stabilization of the positive charge by appropriate substituents.

Catalytic Isomerization of α-Pinene Epoxide Over a Natural Zeolite

Isomerization of α-pinene epoxide was carried out over a Colombian natural zeolite as potential geocatalyst with heulandite, chabazite and clipnotilolite as main crystallographic phases; the heulandite was identified as the active phase. Over synthetic zeolites, isomerization of α-pinene epoxide depended on Si/Al ratio, unit cell and the kind of structure. The best solvent was toluene and not isomerization activity was observed in presence of solvents with carboxyl groups. Complete α-pinene epoxide conversion and 45% selectivity to campholenic aldehyde were obtained at 70 °C, with fencholenic aldehyde, carveol, and p-cymene as main by-products. Decrease of activity of natural zeolite was associated with loss of acid sites. A reaction mechanism based on experimental and computational data was proposed including adsorption of α-pinene epoxide on Fe or Al sites of the natural zeolite; a reaction rate constant of 4.02 × 10–4 mol g−1 min−1 was estimated from a pseudo homogeneous kinetic model.

Corrigendum: Isomerization of Epoxides

Corrigendum: Isomerization of Epoxides

Reaction Mechanism of the Isomerization of Monoterpene Epoxides with Fe3+ as Active Catalytic Specie: A Computational Approach.

The reaction mechanism of the isomerization of α and β-pinene epoxides with Fe species as catalysts was studied with density functional theory (DFT) calculations and an experimental methodology. β-pinene epoxide can be isomerized into myrtanal and myrtenol in four steps, while in the case of perillyl alcohol, two additional steps are necessary. On the other hand, high selectivity to myrtanal obtained experimentally can be explained by the number of steps and the kind of the hydrogen transference that is easier for this compound in comparison with myrtenol and perillyl alcohol. A thermodynamic analysis showed that transformation into myrtenol, myrtanal, and perillyl alcohol is spontaneous but transformation into myrtanal is the most favorable. In the case of α-pinene epoxide rearrangement, a mechanistic study was carried out toward the optimization of the possible intermediates. Synthesis of campholenic aldehyde and carveol from α-pinene epoxide was carried out through three steps after the coordination of oxygen to iron, showing that in contrast to carveol formation, campholenic aldehyde synthesis is spontaneous. Analysis of ∇2ρ, the total energy density (H = V + G), and the |V|/G ratio evaluated at the bond critical point of the Fe-O bond showed for both epoxides that such interaction is closed shell instead of covalent. Apparently, α-pinene epoxide can be isomerized faster that β-pinene epoxide with Fe3+, which is in agreement with previous experimental results. This is the first report where a reaction mechanism of isomerization of monoterpenes epoxides is studied based on very detailed experimental and computational methodologies.