Epoxidation Of Olefins Research Articles

Biphasic gas–liquid millifluidic system for carbon dioxide plasma chemistry: Application to controlled selective epoxidation

The integration of nonthermal CO2 plasma for olefin epoxidation within a biphasic gas–liquid millifluidic system is presented. In this innovative approach, CO2 is efficiently reduced to CO and O atoms, facilitating the epoxidation of olefins. Analysis of the system’s effluent shows that epoxide production efficiency and yields, optimized to 90 %, significantly surpass those of traditional plasma methods, attributed to the enhanced gas–liquid mass transfer within the millifluidic environment. Moreover, O atoms generated from CO2 decomposition was observed to travel up to 30 mm in the post-plasma discharge area, enhancing the gas–liquid flow system’s efficiency. By capturing O atoms in the epoxidation reaction with olefins, the reverse reaction with CO is minimized, which in turn, markedly increases CO yield under the same conditions without olefins. These findings demonstrate that olefin epoxidation can be activated through CO2 plasma discharge in a controlled, selective, and catalyst-free manner under gentle conditions. This synergy between nonthermal plasma and millifluidic technologies paves the way for overcoming current limitations in plasma chemistry with industrial relevance.

Development of a Purely Isolable (Dimorpholino)triazine-Based Reagent for the Epoxidation of Alkenes

AbstractA triazine-based reagent, 2-hydroperoxy-4,6-dimorpholino-1,3,5-triazine (Triazox-II), was developed for alkene epoxidation. This reagent can be prepared from inexpensive starting materials (cyanuric chloride and morpholine) on a 15 mmol scale in two steps with 54% overall yield and isolated as a pure, bench-stable solid with low sensitivity to impact and friction. Triazox-II exhibited higher solubility in chlorinated solvents than the previously reported reagent Triazox. Epoxidation using Triazox-II was conducted in various solvents, with a preference for CH2Cl2 at 0.5 M concentration, resulting in epoxides in 83–94% yield. The reaction was conducted under mild conditions owing to the low acidity of the reaction coproduct.

New mixed ligand oxido-vanadium(V) complexes with O,O-donor and diimine ligands: Synthesis, crystal structure and catalytic activity in eco-friendly oxidation of olefins and phenol

The facile synthesis and structural characterization of a set of three new oxidovanadium(V) complexes of general formula [VO2(L)(diimine)], where L is ethyl-maltol(emal) (1), deferiprone(def) (2) or, maltol(mal) (3), and diimine is 5,6-dimethyl-1,10-phenanthroline(5,6-DMP) are described. The neutral complexes 1–3 have been comprehensively characterized by employing various analytical and spectroscopic techniques including single crystal X-ray diffraction analysis. The coordination geometry around the V(V) in each of the complexes was indicated by XRD-analysis to be distorted octahedral with equatorial plane being occupied by the deprotonated O,O-donor ligands. The complexes 1–3 could be successfully implemented in organic oxidations viz., hydroxylation of phenol (PH) and olefin epoxidation under environmentally clean organic-solvent-free conditions with aqueous H2O2 as oxidant. Phenol was selectively converted into dihydroxybenzene (DHB) products, catechol (CT) and hydroquinone (HQ) (HQ/CT=1.3:1) with aqueous H2O2 as oxidant at room temperature, with a TON value of 266. Moreover, the catalysts showed impressive activity in epoxidation of styrene and a range of cyclic olefins such as cyclohexene, cyclooctene, and norbornene in absence of organic solvent, to provide high conversion (up to 100 %) with excellent epoxide selectivity and good TON values. The catalysts are stable and afford recyclability for multiple cycles of epoxidation with virtually unaltered catalytic activity.

Thermostabilization and molecular dynamics simulation of NaStyA for highly enantioselective (R)-epoxidation of styrene analogues

Chiral epoxides are one of the most versatile building blocks in organic synthesis, but the asymmetric epoxidation of unfunctionalized terminal olefins remains a challenge. NaStyA is a styrene monooxygenase from Nocardia altamirensis that functions as an enantioselective epoxygenase for terminal olefins. To improve its robustness, we investigated over 50 mutants designed via evolutionary- and energy-based approaches, and successfully identified 18 beneficial mutations, which then led to a combinatorial mutant of TM18 with drastically enhanced thermostability and solvent tolerance while retaining excellent activity and enantioselectivity. Its turnover frequency and half-life at 50 °C were increased to 5- and 148-fold of the parental. In the epoxidation of terminal olefins, TM18 achieved high product yields of over 4-fold of the parental, and excellent enantiomeric excess of 99 % to >99 % ee. The analysis of trajectory data from molecular dynamics simulations further validated that the mutations in TM18 increased its local rigidity, as inferred by RMSF and PCA analyses and through novel salt bridges formation. Furthermore, TM18 displayed reduced residue cross-correlation motions. The combined effects of these mutations result in an overall improvement in the structural and dynamic thermostability of TM18.

Enhanced Photobiocatalytic Cascades at Pickering Droplet Interfaces.

Developing new methods to engineer photobiocatalytic reactions is of utmost significance for artificial photosynthesis, but it remains a grand challenge due to the intrinsic incompatibility of biocatalysts with photocatalysts. In this work, photocatalysts and enzymes were spatially colocalized at Pickering droplet interfaces, where the reaction microenvironment and the spatial distance between two distinct catalysts were exquisitely regulated to achieve unprecedented photobiocatalytic cascade reactions. As proof of the concept, ultrathin graphitic carbon nitride nanosheets loaded with Au nanoparticles were precisely positioned in the outer interfacial layer of Pickering oil droplets to produce H2O2 under light irradiation, while enzymes were exactly placed in the inner interfacial layer to catalyze the subsequent biocatalytic oxidation reactions using in situ formed H2O2 as an oxidant. In the alkene epoxidation and thioether oxidation, our interfacial photobiocatalytic cascades showed a 2.0-5.8-fold higher overall reaction efficiency than the photobiocatalytic cascades in the bulk water phase. It was demonstrated that spatial localization of the photocatalyst and the enzyme at Pickering oil droplet interfaces not only provided their respective preferable reaction environments and intimate proximity for rapid H2O2 transport but also protected the enzyme from oxidative inactivation caused by the photogenerated species. These remarkable interfacial effects contributed to the significantly enhanced photobiocatalytic cascading efficiency. Our work presents an innovative photobiocatalytic reaction system with manifold benefits, providing a cutting-edge platform for solar-driven chemical transformations via photobiocatalysis.

Aliphatic Olefin Epoxidation with Hydrogen Peroxide Catalyzed by an Integrated Mn/TS-1/N System

AbstractPropylene liquid-phase epoxidation with 50–75% H2O2 is an important process for the industrial production of propylene oxide (PO). To realize a propylene epoxidation process that proceeds with low hydrogen peroxide concentration, we developed an integrated Mn/TS-1/N catalytic system via in-situ reaction of Mn/TS-1 with an N-donor ligand, affording the PO product in excellent yield with only 30 wt% H2O2. Other long-chain aliphatic epoxides were also readily synthesized by this catalytic epoxidation system. Moreover, in addition to the standard micro-pressure reactor, a continuous-flow microreactor was developed that executed the hydrogen peroxide propylene oxide (HPPO) process with excellent efficiency for 1300 hours. This innovative Mn/TS-1/N catalyzed epoxidation represents a promising direction for advancing HPPO industrial processes, offering improved efficiency while minimizing the reliance on high concentrations of H2O2.

Heterogeneously Catalyzed Partial Oxidation of Styrene on a Silver Surface

AbstractThe epoxidation of olefins on Ag/O systems is a significant industrial‐scale process within heterogeneous catalysis. However, the details of the surface reaction remain controversial, and it has been highly challenging to reconcile the findings from cataltyic studies under reaction conditions with the highly detailed static studies under carefully controlled ultra‐high vacuum (UHV) conditions. In this study, we combine molecular beam surface scattering and ion imaging techniques to explore the partial oxidation of styrene. This experimental approach enhances the sensitivity to the extent that we can directly observe the partial oxidation product, styrene oxide, under UHV conditions. We note that partial oxidation exclusively occurs at high oxygen coverages, which we attribute to the reaction of styrene with electrophilic oxygen formed specifically at elevated coverages.

The Juliá-Colonna Reaction: A Phase-Transfer Catalyzed Enantioselective Olefin Epoxidation

Juliá and Colonna were one of the firsts chemists reporting examples of enantioselective organocatalyzed reactions, namely the Phase-Transfer Catalysis (PTC) olefin epoxidation. Although some reviews exist on the Juliá-Colonna reaction, none is devoted specifically to it. After an introduction reporting the main publications gathered in three tables, this review is organized into a) olefin epoxidation; b) other enantioselective catalysts; c) Juliá-Colonna papers; d, e) papers citing the "Juliá-Colonna" epoxidation with special stress on those by Stanley M. Roberts. This review summarizes the papers by these authors and reports the most relevant improvements.

Unveiling Non-Covalent Interactions in Novel Cooperative Photoredox Systems for Efficient Alkene Oxidation in Water.

A new cooperative photoredox catalytic system, [RuII(trpy)(bpy)(H2O)][3,3'-Co(8,9,12-Cl3-1,2-C2B9H8)2]2, 5, has been synthesized and fully characterized for the first time. In this system, the photoredox catalyst [3,3'-Co(8,9,12-Cl3-1,2-C2B9H8)2]-[Cl6-1]-, a metallacarborane, and the oxidation catalyst [RuII(trpy)(bpy)(H2O)]2+, 2 are linked by non-covalent interactions. This compound, along with the one previously synthesized by us, [RuII(trpy)(bpy)(H2O)][(3,3'-Co(1,2-C2B9H11)2]2, 4, are the only examples of cooperative molecular photocatalysts in which the catalyst and photosensitizer are not linked by covalent bonds. Both cooperative systems have proven to be efficient photocatalysts for the oxidation of alkenes in water through Proton Coupled Electron Transfer processes (PCETs). Using 0.05 mol% of catalyst 4, total conversion values were achieved after 15 min with moderate selectivity for the corresponding epoxides, which decreases with reaction time, along with the TON values. However, with 0.005 mol% of catalyst, the conversion values are lower, but the selectivity and TON values are higher. This occurs simultaneously with an increase in the amount of the corresponding diol for most of the substrates studied. Photocatalyst 4 acts as a photocatalyst in both the epoxidation of alkenes and their hydroxylation in aqueous medium. The hybrid system 5 shows generally higher conversion values at low loads compared to those obtained with 4 for most of the substrates studied. However, the selectivity values for the corresponding epoxides are lower even after 15 min of reaction. This is likely due to the enhanced oxidizing capacity of CoIV in catalyst 5, resulting from the presence of more electron-withdrawing substituents on the metallacarborane platform.

Identification of an Epoxide Metabolite of Amitriptyline In Vitro and In Vivo.

Amitriptyline (ATL), a tricyclic antidepressant, has been reported to cause various adverse effects, particularly hepatotoxicity. The mechanisms of ATL-induced hepatotoxicity remain unknown. The study was performed to identify the olefin epoxidation metabolite of ATL and determine the possible toxicity mechanism. Two glutathione (GSH) conjugates (M1 and M2) and two N-acetylcysteine (NAC) conjugates (M3 and M4) were detected in rat liver microsomal incubations supplemented with GSH and NAC, respectively. Moreover, M1/M2 and M3/M4 were respectively found in ATL-treated rat primary hepatocytes and in bile and urine of rats given ATL. Recombinant P450 enzyme incubations demonstrated that CYP3A4 was the primary enzyme involved in the olefin epoxidation of ATL. Treatment of hepatocytes with ATL resulted in significant cell death. Inhibition of CYP3A attenuated the susceptibility to the observed cytotoxicity of ATL. The metabolic activation of ATL most likely participates in the cytotoxicity of ATL.

Concise Synthesis of (-)-isoaltholactone and (±)-5-epi-OBn-Goniotriol

Concise route for the synthesis of (-)-isoaltholactone and (±)-5-epi-OBn-Goniotriol were described. Key features for the (-)-isoaltholactone synthesis involved; a) diastereoselective and enantioselective aldol reaction between chiral pyrrolidine substituted γ-benzyloxy vinylogous urethane enolate and cinnamaldehyde afforded highly stereoselective syn δ-lactone, b) allylic 1,3-strain controlled epoxidation of styryl alkene following the stereospecific opening of the epoxide assisted by a proximal benzyloxy group completed the synthesis. Reaction of simple pyrrolidine substituted γ-benzyloxy vinylogous urethane enolate and cinnamaldehyde gave anti δ-lactone. Epoxidation and epoxide opening of the styryl alkene substrate of anti δ-lactone derivative was also investigated, which led to the synthesis of (±)-5-epi-OBn-Goniotriol.

Investigating the Mukaiyama-type epoxidation reaction of alkenes with Cr(III) salophen catalysts: A confrontation between experiments and DFT calculations

This study aimed at the complete elucidation of the mechanism of the Mukaiyama-type alkene epoxidation reaction using the [(salophen)CrIIICl] precatalyst, by combining spectroscopic (UV–visible and EPR) studies, catalytic reactivity and quantum chemical modeling. These studies performed in parallel allowed us to propose a detailed reaction scheme, in which two consecutive active species incorporating both {salophen(CrV = O)} moieties were formed in situ, resulting in two distinct catalytic regimes.

Effects of silanol defects and Ti site location within Ti-MWW on alkene epoxidation with aqueous hydrogen peroxide

Catalytic reaction kinetics and thermodynamics within zeolites respond to the physical properties of the framework through noncovalent interactions with solvents. Here, we demonstrate that rates of alkene epoxidations depend sensitively upon the topological location of Ti atoms and the density of silanol ((SiOH)x) defects in hydrothermally synthesized Ti-MWW catalysts. Turnover rates for 1-hexene epoxidation do not change systematically with (SiOH)x density unlike previous reports for other zeolite framework. Site-averaged turnover rates on Ti-MWW catalysts with the greatest portion of Ti sites located in sinusoidal channels exceed those on materials with most Ti in supercages by a factor of 40-fold. These differences appear to reflect free energy contributions and compensation between activation enthalpies and entropies, induced by the structural organization of solvent molecules that responds differently to the topological locations of active sites and the presence of defects.

Molecular Basis for Chemoselectivity Control in Oxidations of Internal Aryl-Alkenes Catalyzed by Laboratory Evolved P450s.

P450 enzymes naturally perform selective hydroxylations and epoxidations of unfunctionalized hydrocarbon substrates, among other reactions. The adaptation of P450 enzymes to a particular oxidative reaction involving alkenes is of great interest for the design of new synthetically useful biocatalysts. However, the mechanism that these enzymes utilize to precisely modulate the chemoselectivity and distinguishing between competing alkene double bond epoxidations and allylic C-H hydroxylations is sometimes not clear, which hampers the rational design of specific biocatalysts. In a previous work, a P450 from Labrenzia aggregata (P450LA1) was engineered in the laboratory using directed evolution to catalyze the direct oxidation of trans-β-methylstyrene to phenylacetone. The final variant, KS, was able to overcome the intrinsic preference for alkene epoxidation to directly generate a ketone product via the formation of a highly reactive carbocation intermediate. Here, additional library screening along this evolutionary lineage permitted to serendipitously detect a mutation that overcomes epoxidation and carbonyl formation by exhibiting a large selectivity of 94 % towards allylic C-H hydroxylation. A multiscalar computational methodology was applied to reveal the molecular basis towards this hydroxylation preference. Enzyme modelling suggests that introduction of a bulky substitution dramatically changes the accessible conformations of the substrate in the active site, thus modifying the enzymatic selectivity towards terminal hydroxylation and avoiding the competing epoxidation pathway, which is sterically hindered.

Facile encapsulation of a cobalt complex inside the micropores of ZIF-8 through the bottle around the ship method: A novel heterogeneous catalyst for epoxidation of alkenes

A novel and stable heterogeneous catalyst for alkene epoxidation reaction, named as CoDMG@ZIF-8, has been synthesized by facile encapsulation of Co(III) complex i.e. [Co(DMGH)(DMGH2)Cl2] (abbreviated as CoDMG, DMGH2 denotes for dimethylglyoxime and DMGH denotes for dimethylglyoxime mono anion) inside the ZIF-8 micropores via a solvothermal process. Based on the results of fourier transform-infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) technique and field emission scanning electron microscopy (FE-SEM), it was observed that the catalyst has maintained the structure, crystallinity and morphology of the parent ZIF-8 as well. Furthermore, CHN, DRS (diffuse reflectance spectra), energy dispersive X-ray (EDX), induced coupled plasma (ICP-OES), thermal gravimetric (TGA) and nitrogen adsorption-desorption (BET method) analyses have confirmed the encapsulation of the CoDMG complex. The epoxidation reaction was performed using tert‑butyl hydroperoxide (TBHP) in CH3CN solvent in the presence of catalyst. By optimizing the reaction parameters, a total conversion of 96 % with 82 % selectivity towards the epoxide product, was achieved. It was found that both CoDMG complex and ZIF-8 exhibited lower efficiency individually, while the encapsulation of this complex inside the ZIF-8 micropores has resulted to superior activity. Finally, the epoxidation of various alkenes such as cyclohexene, 2-norbornene, α-pinene, styrene and 1-hexene under the optimized reaction condition, have been studied and the catalytic mechanism was also proposed.

In Situ Observation of Solvent-Mediated Cyclic Intermediates during the Alkene Epoxidation/Hydration over a Ti-Beta/H2O2 System.

Solvent effects in catalytic reactions have received widespread attention as they can promote reaction rates and product selectivities by orders of magnitude. It is well accepted that the stable five-membered cyclic intermediates formed between the solvent molecules and Ti species are crucial to the alkene epoxidation in a heterogeneous Ti(IV)-H2O2 system. However, the direct spectroscopic evidence of these intermediates is still missing and the corresponding reaction pathway for the alkene epoxidation remains unclear. By combining in situ 13C MAS NMR, two-dimensional (2D) 1H-13C heteronuclear correlation (HETCOR) NMR spectroscopy and theoretical calculations, the five-membered ring structures, where the protic solvents (ROH), and aprotic solvent (acetone), coordinate and stabilize the active Ti species, are identified for the first time over Ti-Beta/H2O2 system. Moreover, the role of these cyclic intermediates in the alkene epoxidation/hydration conversion is clarified. These results provide new insights into the solvent effect in liquid-phase epoxidation/hydration reactions over Ti(IV)-H2O2 system.

In Situ Observation of Solvent‐Mediated Cyclic Intermediates during the Alkene Epoxidation/Hydration over a Ti‐Beta/H2O2 System

AbstractSolvent effects in catalytic reactions have received widespread attention as they can promote reaction rates and product selectivities by orders of magnitude. It is well accepted that the stable five‐membered cyclic intermediates formed between the solvent molecules and Ti species are crucial to the alkene epoxidation in a heterogeneous Ti(IV)−H2O2 system. However, the direct spectroscopic evidence of these intermediates is still missing and the corresponding reaction pathway for the alkene epoxidation remains unclear. By combining in situ 13C MAS NMR, two‐dimensional (2D) 1H−13C heteronuclear correlation (HETCOR) NMR spectroscopy and theoretical calculations, the five‐membered ring structures, where the protic solvents (ROH), and aprotic solvent (acetone), coordinate and stabilize the active Ti species, are identified for the first time over Ti‐Beta/H2O2 system. Moreover, the role of these cyclic intermediates in the alkene epoxidation/hydration conversion is clarified. These results provide new insights into the solvent effect in liquid‐phase epoxidation/hydration reactions over Ti(IV)−H2O2 system.

Molybdenum Catalysts Supported on Porous Aromatic Frameworks in Epoxidation of Olefins

Molybdenum Catalysts Supported on Porous Aromatic Frameworks in Epoxidation of Olefins

Inclusion complexes of cucurbit[n]urils (n = 7, 8) with η5‐cyclopentadienyl methyl tricarbonyl molybdenum(II) and their use in epoxidation catalysis

There are very few known examples of supramolecular compounds comprising molybdenum species hosted inside the portals/cavities of cucurbit[n]urils (CBn). In this work, CB7 and CB8 macrocycles have been studied as hosts for the carbonyl complex [CpMo(CO)3Me] (1) (Cp = η5‐C5H5). Compounds were isolated in the solid state and characterized as genuine 1:1 inclusion complexes (1@CBn) by elemental and thermogravimetric analyses, powder X‐ray diffraction, scanning electron microscopy, 13C{1H} cross‐polarization magic‐angle spinning NMR, FT‐IR, Raman, and diffuse reflectance UV–Vis spectroscopies. The host–guest structures can act as supramolecular precatalysts for olefin epoxidation. Based on the model reaction of cis‐cyclooctene with hydroperoxide oxidants (tert‐butylhydroperoxide or hydrogen peroxide), the structural features of 1@CBn as well as the operating conditions influence the catalytic process. The metal species in 1@CBn undergo oxidative decarbonylation in situ, giving oxidized metal species that are catalytically active for olefin epoxidation. The type of oxidant and solvent influences the catalytic activity and stability. 1@CB8 was more stable than 1@CB7 with regard to catalyst recycling and reuse. Based on the substrate scope investigation, for relatively large olefins, such as the fatty acid methyl ester methyl oleate, the size of the macrocyclic host may be a determining factor for catalytic activity.

A tale of two topological isomers: Uptuning [FeIV(O)(Me4cyclam)]2+ for olefin epoxidation

TMC-anti and TMC-syn, the two topological isomers of [FeIV(O)(TMC)(CH3CN)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, or Me4cyclam), differ in the orientations of their FeIV=O units relative to the four methyl groups of the TMC ligand framework. The FeIV=O unit of TMC-anti points away from the four methyl groups, while that of TMC-syn is surrounded by the methyl groups, resulting in differences in their oxidative reactivities. TMC-syn reacts with HAT (hydrogen atom transfer) substrates at 1.3- to 3-fold faster rates than TMC-anti, but the reactivity difference increases dramatically in oxygen-atom transfer reactions. R2S substrates are oxidized into R2S=O products at rates 2-to-3 orders of magnitude faster by TMC-syn than TMC-anti. Even more remarkably, TMC-syn epoxidizes all the olefin substrates in this study, while TMC-anti reacts only with cis-cyclooctene but at a 100-fold slower rate. Comprehensive quantum chemical calculations have uncovered the key factors governing such reactivity differences found between these two topological isomers.