Epoxidation Of Monoterpenes Research Articles

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.

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.

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.

Easy Epoxidation of Monoterpenes from Common Starting Materials

Epoxidation of monoterpenes, α-pinene, β-pinene, limonene, α-terpinene, and (R)-carvone was carried out by the in situ production of a peroxyacid rather than direct addition of such an expensive and difficult to handle chemical. Previous reports showed use of metal catalysts with high yields, while methodologies without catalysts at high temperature showed yields lower than 30%. The authors report a methodology that produces peroxyacetic acid in situ yielding up to 75% pure epoxide at room temperature avoiding the use of catalysts. The products were analyzed by gas chromatography mass spectrometry (GC-MS), and structures were characterized by 1H and 13C nuclear magnetic resonance (NMR).

Kinetics of the Aqueous Phase Reactions of Atmospherically Relevant Monoterpene Epoxides.

Laboratory and field measurements have demonstrated that an isoprene-derived epoxide intermediate (IEPOX) is the origin of a wide range of chemical species found in ambient secondary organic aerosol (SOA). In order to explore the potential relevance of a similar mechanism for the formation of monoterpene-derived SOA, nuclear magnetic resonance techniques were used to study kinetics and reaction products of the aqueous-phase reactions of several monoterpene epoxides: β-pinene oxide, limonene oxide, and limonene dioxide. The present results, combined with a previous study of α-pinene oxide, indicate that all of these epoxides will react more quickly than IEPOX with aqueous atmospheric particles, even under low-acidity conditions. As for α-pinene oxide, the observed products can be mainly rationalized with a hydrolysis mechanism, and no long-lived organosulfate or nitrate species nor species that retain the β-pinene bicyclic carbon backbone are observed. As bicyclic ring-retaining organosulfate and nitrate species have been previously observed in monoterpene-derived SOA, it appears that monoterpene-derived epoxides may not be as versatile as IEPOX in producing a range of SOA species, and other mechanisms are needed to rationalize organosulfate and nitrate formation.

A Computational Examination of the Uncatalyzed Meinwald Rearrangement of Monoterpene Epoxides

Epoxides are relatively reactive compounds and may undergo decomposition or rearrangement reactions at elevated temperatures, and gas chromatographic analysis of essential oils may cause thermal decomposition or rearrangement of epoxide components at gas chromatographic temperatures. Density functional theory (DFT) calculations were carried out using the B3LYP functional at the 6-31 1++G**//6-3 IG* level of theory on the Meinwald rearrangements of α- pinene oxide (two different mechanisms leading to transpinocamphone and a-campholenal), cis-limonene oxide (leading to trans-dihydrocarvone), tran s- limonene oxide (leading to cisdihydrocarvone), 6,7-epoxymyrcene (leading to 2-methyl-6-methylene-7-octen-3-one), and 1,2-epoxy-2,5-dimethyl-3-viny4- hexene (two mechanisms leading to 5-methyl-3-vinyl-4-hexenal and 8-methyl-5,7-nonadien-2-one). Free energies of activation for the uncatalyzed Meinwald rearrangement of common monoterpene epoxides are relatively large, being of the order of 70 kcal/mol, and are, therefore, not predicted to be important reactions at gas chromatographic temperatures.

Optimization of the lipase mediated epoxidation of monoterpenes using the design of experiments—Taguchi method

This work deals with the optimization of the Candida antartica lipase B (CALB) mediated epoxidation of monoterpenes by using the design of experiments (DoE) working with the Taguchi Method. Epoxides are essential organic intermediates that find various industrial applications making the epoxidation one of the most investigated processes in chemical industry. As many as 8 parameters such as the reaction medium, carboxylic acid type, carboxylic acid concentration, temperature, monoterpene type, monoterpene concentration, hydrogen peroxide concentration and amount of lipase were optimized using as less as 18 runs in triplicates (54 runs). As a result, the hydrogen peroxide concentration used was found to be the most influential parameter of this process while the type of monoterpene was least influential. Scaling up of the reaction conditions according to the findings of the optimization achieved full conversion in less than 6h. In addition, a purification process for the epoxides was developed leading to an isolated yield of ca. 72.3%, 88.8% and 62.5% for α-pinene, 3-carene and limonene, respectively.

Synthesis of the fragrance terpene epoxides and selective monocyclization promoted by camphor and oxone®

AbstractA high level of regio‐selectivity in the epoxidation of monoterpenes with camphor and oxone® at pH 7 has been observed. This methodology when applied to acyclic terpenes such as citronellyl acetate, geranyl acetate yielded mainly chiral 6(S),7‐epoxides. Similarly, farnesyl acetate yielded 10(S),11‐epoxide. Alternatively, unsaturated monocyclic terpene alcohol such as (‐)‐α‐terpineol, 6‐methyl‐hept‐5‐en‐2‐ol, when treated with camphor and oxone® at pH ~4‐5 led to one‐pot oxidative‐cyclization to yield (‐)‐trans‐2‐(S)‐hydroxy‐1,8‐cineole and (+)‐2,2,6‐trimethyl‐tetrahydropyran‐3‐ol respectively. In addition, the epoxides, trans‐2‐hydroxyl‐cineole and its acetate synthesized herein have good perfumery value with woody and sweet aromas. Copyright © 2016 John Wiley & Sons, Ltd.

A one pot reaction cascade of in situ hydrogen peroxide production and lipase mediated in situ production of peracids for the epoxidation of monoterpenes

In this work, the epoxidation of monoterpenes in the presence of Candida antartica lipase B (CALB) by the in situ generation of peroxy acid was combined with the industrial anthraquinone (AQ) process of hydrogen peroxide production. The reaction cascade consists of two major steps: reduction of an AQ to its corresponding anthrahydroquinone (AHQ) followed by the reverse auto-oxidation step of AHQ to AQ yielding equimolar amounts of hydrogen peroxide. Temperatures for each of the steps, ratio of substrate to catalyst, possible inhibition of lipases by the AQ and reaction medium (a mixture of hydrophobic and hydrophilic solvents) to be used were investigated. By using this reaction cascade, the addition of large amounts of hydrogen peroxide was avoided and conversions to epoxides of up to 83 (±9)% for limonene, 76 (±8)% for α-pinene and 82 (±8)% for 3-carene were achieved within 16h.

ChemInform Abstract: Selective Epoxidation of Monoterpenes with Methyltrioxorhenium and H2O2.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A novel and efficient catalytic epoxidation of monoterpenes by homogeneous and heterogeneous methyltrioxorhenium in ionic liquids

A convenient and efficient synthesis of monoterpene epoxides by application of methyltrioxorhenium and heterogeneous poly(4-vinylpyridine)/methyltrioxorhenium and microencapsulated polystyrene/methyltrioxorhenium catalytic systems in ionic liquids is described here. It was found that even highly sensitive terpenic epoxides were obtained in excellent yields. Environmentally friendly, easily available and low cost (UHP) urea hydrogen peroxide adduct was used as the primary oxidant. Catalysts were stable systems for at least four recycling oxidations. Experimental results showed that the reactions performed in ionic liquids were more selective and efficient than the ones performed in molecular solvents.

Selective Epoxidation of Monoterpenes with H2O2 and Polymer‐Supported Methylrheniumtrioxide Systems.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Selective epoxidation of monoterpenes with H 2O 2 and polymer-supported methylrheniumtrioxide systems

A convenient and efficient synthesis of monoterpene epoxides by application of heterogeneous poly(4-vinylpyridine)/methyl rhenium trioxide (PVP/MTO) and polystyrene/methyl rhenium trioxide (PS/MTO) systems is described. Even highly sensitive terpenic epoxides were obtained in excellent yield. Environment friendly, easily available, and low cost H 2O 2 was used as oxidant. Catalysts were stable systems for at least five recycling experiments.

Oxidation of α-hydroxy containing monoterpenes using titanium silicate catalysts: comments on regioselectivity and the role of acidity

The regioselective epoxidation of monoterpenes in the liquid phase has been studied using the titanosilicates TS-1 and TiAlβ. A range of oxidants (hydrogen peroxide, tert-butyl hydroperoxide and urea–hydrogen peroxide complex) have been studied in detail. The allylic alcohols linalool and geraniol have been studied alongside the non-allylic alcohol citronellol and the diene dihydromyrcene to help determine the role of the hydroxy group in these reactions. Dihydromyrcene is selectively epoxidised at the more electron rich double bond regardless of the catalyst–oxidant–solvent system used. Geraniol can undergo allylic assisted epoxidation with TS-1–acetone–hydrogen peroxide and TiAlβ–acetonitrile–urea–hydrogen peroxide. With TiAlβ–hydrogen peroxide–methanol, the reaction shows an induction period in the conversion of geraniol which is considered to be characteristic of the autocatalytic removal of titanium from the catalyst framework. Reactions with citronellol show this titanium removal is entirely due to the presence of the allylic alcohol moiety. Finally, epoxidation of linalool and the subsequent in situ conversion of the epoxide to the furano- and pyrano-oxides were studied. The ratio of furano- and pyrano-oxides formed was considered to be due, in part, to the pore geometry and the Bronsted acidity of the catalyst.

Selective epoxidation of monoterpenes with methyltrioxorhenium and H 2O 2

In the presence of pyridine as a co-catalyst, CH 3ReO 3 catalyses the epoxidation of terpenes such as α-pinene with H 2O 2 with minimal rearrangement of the epoxide. Pyridine is also critical to suppress isomerisation of the olefin substrate (in case of nerol, geraniol). The reaction can be directed towards selective single or double epoxidation, or in one step towards the rearranged product ( e.g. from linalool to the ring-closure product linalool oxide).

Selective Oxidation of Monoterpenes with Hydrogen Peroxide Catalyzed by Peroxotungstophosphate (PCWP)

Catalytic epoxidation of monoterpenes with aqueous hydrogen peroxide catalyzed by peroxotungstophosphate (PCWP) under biphase conditions using chloroform as the solvent was examined. A variety of terpenes was oxidized to the corresponding monoepoxides or diepoxides in good yields under mild conditions. For example, limonene (1) was converted into limonene oxide (1a) in which the cyclohexene double bond was selectively epoxidized in almost quantitative yield. The oxidation of γ-terpinene (2) with 2.2 equiv of 35% H2O2 took place with high stereoselectivity to give cis-diepoxide 2c. In terpenes bearing electron-withdrawing groups such as neryl acetate (3), geranyl acetate (4), citral (5), and geranyl nitrile (6), the double bonds remote from the substituents were epoxidized in preference to the others. The epoxidation of linalool (9) by the present catalyst−oxidant system produced the cyclic products, hydroxy furan 9a and hydroxy pyran 9b, rather than epoxide. tert-Butyl alcohol was successfully employed as the solvent by treating a hydrogen peroxide solution of tert-butyl alcohol with MgSO4 prior to use. The regioselectivities in the epoxidation of monoterpenes can be favorably explained from the electron densities of the double bonds which were estimated using the CAChe system.

Hydrogenolysis of bicyclic monoterpene epoxides in the presence of raney nickel and determination of the structures of α- and β-3,4-epoxy caranes

Bicyclic monoterpene epoxides, α-pinene oxide, 2,3-epoxybornane, α- and β-3,4-epoxycaranes were hydrogenated under high hydrogen pressure in the presence of Raney nickel catalyst. The products obtained were analysed by VPC and were identified by comparison with authentic samples. The effect of anions, OH −, Cl −, Br −, and I − for the hydrogenolysis was also examined. The results are summarized in the Tables. From the results, the structures of these bicyclic monoterpene epoxides, α-pinene oxide, 2,3-epoxybornane, α- and β-3,4-epoxycaranes were confirmed to be V, XII, XIX and XXI, respectively.