Catalytic Epoxidation Research Articles

Recent advances in catalytic and non-catalytic epoxidation of terpenes: a pathway to bio-based polymers from waste biomass.

Epoxides derived from waste biomass are a promising avenue for the production of bio-based polymers, including polyamides, polyesters, polyurethanes, and polycarbonates. This review article explores recent efforts to develop both catalytic and non-catalytic processes for the epoxidation of terpene, employing a variety of oxidizing agents and techniques for process intensification. Experimental investigations into the epoxidation of limonene have shown that these methods can be extended to other terpenes. To optimize the epoxidation of bio-based terpene, there is a need to develop continuous processes that address limitations in mass and heat transfer. This review discusses flow chemistry and innovative reactor designs as part of a multi-scale approach aimed at industrial transformation. These methods facilitate continuous processing, improve mixing, and either eliminate or reduce the need for solvents by enhancing heat transfer capabilities. Overall, the objective of this review is to contribute to the development of commercially viable processes for producing bio-based epoxides from waste biomass.

Visible-light-induced aerobic epoxidation with vitamin B2-based photocatalyst.

Herein we described the catalytic epoxidation of α,β-enone, with peroxide in situ generated, via a predominant single electron transfer and a minor energy transfer pathway. We use inexpensive natural vitamin B2 (riboflavin, RF) or its simple ester (riboflavin tetraacetate, RFT) as the photocatalysts, commonly used 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) as both the electron source and organic base, and ambient air as the terminal oxidant, under visible-light irradiation and room temperature.

Catalytic Epoxidation of Oleic Acid and Subsequent Ring-Opening by In Situ Hydrolysis for Production Dihydroxystearic Acid

Catalytic Epoxidation of Oleic Acid and Subsequent Ring-Opening by In Situ Hydrolysis for Production Dihydroxystearic Acid

Hydrothermal Modification of TS-1 Zeolites with Organic Amines and Salts to Construct Highly Selective Catalysts for Cyclopentene Epoxidation

Developing efficient heterogeneous catalysts for cyclic olefins epoxidation is highly attractive for meeting the growing need for various cyclic epoxides. Herein, hierarchical TS-1 zeolite with relatively abundant mesopores and less amount of surface hydroxyl groups was obtained by hydrothermal modification of an as-synthesized TS-1 zeolite with a mixed solution of ammonia, tetrapropylammonium bromide (TPABr) and KCl. The post-modified TS-1 zeolite exhibited much higher catalytic activity (52% conversion) and epoxide selectivity (98%) for the epoxidation of cyclopentene than the conventional TS-1 zeolites. The excellent catalytic activity of the hierarchical TS-1 could be mainly assigned to the enhancement of the mass transport ability and the accessibility of the active Ti species, while the improvement of epoxidation selectivity may be mainly related to the introduction of a certain amount of K+ that can effectively modulate the coordination environment of Ti species as well as the polarity of the zeolite. This work demonstrated that a highly active and selective catalyst for the H2O2-mediated cyclopentene epoxidation could be obtained by concurrently generating mesopore and extinguishing the unfavorable defective hydroxyl groups through the simple hydrothermal treatment of the conventional TS-1 zeolite with a mixed base/salt solution.

Manifesting Direction-Specific Complexation in [HFIP-H·H2O2]-: Exclusive Formation of a High-Lying Conformation.

Size-selective, negative ion photoelectron spectroscopy in conjunction with quantum chemical calculations is employed to investigate the geometric and electronic structures of a protype system in catalytic olefin epoxidation research, that is, deprotonated hexafluoroisopropanol ([HFIP-H]-) complexed with hydrogen peroxide (H2O2). Spectral assignments and molecular electrostatic surface analyses unveil a surprising prevalent existence of a high-lying isomer with asymmetric dual hydrogen-bonding configuration that is preferably formed driven by influential direction-specific electrostatic interactions upon H2O2 approaching [HFIP-H]- anion. Subsequent inspections of molecular orbitals, charge, and spin density distributions indicate the occurrence of partial charge transfer from [HFIP-H]- to H2O2 upon hydrogen-bonding interactions. Accompanied with electron detachment, a proton transfer occurs to form the neutral complex of [HFIP·HOO•] structure. This work conspicuously illustrates the importance of directionality encoded in intermolecular interactions involving asymmetric and complex molecules, while the produced hydroperoxyl radical HOO• offers a possible new pathway in olefin epoxidation chemistry.

Charge transformation of framework titanium (Ⅳ) into titanium (Ⅲ) in vanadium-titanium doped MFI zeolite for enhanced alkene epoxidation

Simultaneous insertion of double heteroatom in the MFI framework generally gives rise to synergistic catalysis effect, however the specific origins for synergistic catalysis is still nebulous. In this study, vanadium-titanium doped MFI zeolite was synthesized via one-pot hydrothermal synthesis with the addition of (NH4)2CO3 and applied as heterogeneous catalyst for the synergistic catalysis of 1-hexene and cyclohexene epoxidation. Simultaneous incorporation of vanadium and titanium induced the partial charge transformation of titanium (Ⅳ) into titanium (Ⅲ), which was verified by EPR and XPS characterizations. UV-Raman and UV–Vis spectra disclosed that partial charge transformation mainly occurred for framework titanium (Ⅳ). In addition, simultaneous insertion of vanadium and titanium gave rise to more Lewis acid sites as well as larger external surface area for VTS(0.15) zeolite in comparison to VS(0.15) and TS(0.15) zeolite. The prepared VTS(0.15) zeolite presented a TOF value of 118.8 h−1 for 1-hexene epoxidation, which is 7.8 folds and 1.3 folds of VS(0.15) and TS(0.15) respectively. Partial charge transformation of framework titanium (Ⅳ) into titanium (Ⅲ), robust Lewis acid sites as large external surface area may induce the synergistic catalysis effect for VTS(0.15) zeolite in the epoxidation reactions. Moreover, the obtained VTS(0.15) zeolite particles showed good reusability for more than five cycles.

Metal-ligand cooperation in the catalytic oxidation of (R)-carvone by Ga(NO3)3/H2O2

In this work, the catalytic epoxidation of (R)-carvone by the Ga(NO3)3/H2O2 system was studied alongside the metal-ligand cooperation by exploring 17 different ligands. It was observed that the acidic ligands such as acetic acid mostly favor the epoxidation of the endocyclic double bond of (R)-carvone (22% yield, 1 h), while nitrogen heterocycles direct the epoxidation to the exocyclic double bond, especially the ones that are unsubstituted or have electron-donating groups, such as pyrazine (28% yield, 5 h), 4-dimethylaminopyridine (28% yield, 8 h), and 1-methyimidazole (43% yield, 8 h). Pyrazinecaboxylic acid favored the epoxidation of the exocyclic double bond (25%, 3 h). EPR analysis of both Ga(NO3)3/H2O2 and Ga(NO3)3/PCA/H2O2 systems indicates the presence of hydroxyl radicals in the reaction medium, although these do not determine the epoxidation rate that is likely regulated by the interaction of Ga-peroxo complexes with (R)-carvone. This study contributes to widening the application of the cooperating ligand concept in molecular catalysis toward further development of more selective and efficient epoxidation reactions catalyzed by non-transition metal centers.

Active epoxidation bipyridine-oxodiperoxotungstate catalysts

Herein, we report the preparation of four compounds obtained by the reaction of H3PW12O40/H3PO4/H2O2 with 2,2’-bpy (a-22) or 4,4’-bpy (a-44) and H3PW12O40/H2O2 with 2,2’-bpy (b-22) or 4,4’-bpy (b-44) for the catalytic epoxidation of cyclooctene with H2O2 under monophasic conditions. The anions of the four compounds are composed of oxodiperoxotungstate WO(O2)2 moieties and their overall anionic structures are less condensed than the pristine [PW12O40]3− polyoxometalate (PW12) precursor (Raman and IR spectroscopies). The peroxo anions and bipyridine interact in a way differing from one bpy isomer to the other. Isomer 4,4’-bpy interacts electrostatically with the peroxo species and 2,2’-bpy in a coordinative mode. Compounds synthesized with isomer 2,2’-bpy (a-22 and b-22) are more epoxidation-active than those containing 4,4’-bpy (a-44 and b-44). Compounds a-22 and b-22 share the same structure (PXRD), but a-22 exhibits substantially better catalytic activity. This superior catalytic efficiency is associated to the presence of phosphatooxoperoxotungstates PWn (n = 1; 2; 3; 4) species with high n value (namely PW4 > PW3 >> PW2) (31P NMR and Raman spectroscopies). The PWn species are produced before reaction with bipyridine as a result of the degradation of PW12 with H2O2 which, under the employed conditions, is complete after 30 min. In the aqueous solution, the PWn species are present in different concentrations and coexist in a fast-dynamic equilibrium. Under the operated catalytic conditions, our materials outperform the homogeneous benchmark catalyst of Venturello ((C6H13)4N+)3[PW4O24]3−) which shows poor activity. The most active a-22 and b-22 catalysts are partially dissolved in the liquid medium, but they precipitate as the epoxide builds in the reaction medium, allowing for potential catalyst separation and reuse. It is revealed that H2O2 is required not only to generate epoxidation activity, but to preserve the structure of the catalyst, since without it, the structural damaged appears irreversible.

Catalytic aerobic epoxidation of bio-renewable alkenes using organic carbonates as green solvents

Epoxides are important products in industry and organic synthesis. However, for large-scale applications, the methodologies are outdated due to the use of toxic reactants/solvents under non-safe conditions. In this work, we present a safer process for the epoxidation of alkenes which is aligned with green chemistry principles. A series of bio-renewable substrates was selectively epoxidized under mild conditions using environmentally friendly molecular oxygen as a final oxidant, isobutyraldehyde as a sacrificial reagent and a robust solid material based on a non-noble metal (cobalt) as a heterogeneous catalyst. Several organic carbonates, which are considered as sustainable solvents in modern ranks and are very scarcely exploited in epoxidation, have been studied as a reaction medium for this reaction. Dimethyl carbonate was proved to be an excellent green alternative to replace undesirable industrial solvents allowing to combine both high catalyst performance and high process sustainability.

Styrene epoxidation catalyzed by polyoxometalate/quaternary ammonium phase transfer catalysts: The effect of cation size and catalyst deactivation mechanism

Catalytic epoxidation of alkenes is an important type of organic reaction in chemical industry, and the deep insight into catalyst deactivation will help to develop new epoxidation process. In this work, series of quaternary ammoniums bearing different cationic sizes, i.e. MTOA+ (methyltrioctylammonium, [(C8H17)3CH3N]+), HTMA+(hexadecyltrimethylammonium, [(C16H33)(CH3)3N]+) and DMDOA+ (dimethyldioctadecylammonium, [(C18H37)2(CH3)2N]+) were incorporated with polyoxometalate (POM) anions to prepare phase transfer catalysts (PTCs), which were used in the styrene epoxidations. Among them, (MTOA)3PW4O24 exhibits the best catalytic performance judged from the highest styrene conversion rate (52%) and styrene oxide selectivity (93%), during which the styrene epoxidation conditions were optimized. Meanwhile, the deactivation mechanism of this kind of PTCs was proposed firstly, i.e. in the case of low H2O2 content, the oxidant can only be used in the styrene epoxidation, in which the catalyst can transform into stable Keggin-type POM. But when the content of H2O2 is higher, the excess H2O2 can re-activate the Keggin-type POM into active (PW4O24)3− anions, which can trigger the ring-opening polymerization of styrene oxide. Consequently, the catalyst is deactivated by adhered poly(styrene oxide) irreversibly, which was determined by NMR spectra. In this situation, the active moiety {PO4[WO(O2)2]4}3− in phase-transfer catalytic system can break into some unidentified species with low W/P ratio with the presence of epoxides. This work will be beneficial for the design of new PTCs in alkene epoxidation in fine chemical industry.

GTM-3, an Extra-Large Pore Enantioselective Chiral Zeolitic Catalyst.

The development of chiral zeolitic catalysts possessing extra-large pores and endowed with the capability of enantioselectively processing bulky products represents one of the greatest challenges in chemistry. Here, we report the discovery of GTM-3, an enantio-enriched extra-large pore chiral zeolite material with -ITV framework structure, obtained using a simple enantiopure organic cation derived from the chiral pool, N,N-ethyl-methyl-pseudoephedrinium, as the chiral-inductor agent. We demonstrate the enantio-enrichment of GTM-3 in one of the two enantiomorphic polymorphs using the two enantiomers of the organic cation. Interestingly, we prove the ability of this zeolitic material to perform enantioselective catalytic operations with very large substrates, here exemplified by the catalytic epoxide aperture of the bulky trans-stilbene oxide with alcohols, yielding unprecedented product enantiomeric excesses up to 30%. Our discovery opens the way for the use of accessible chiral zeolitic materials for the catalytic asymmetric synthesis of chiral pharmaceutical compounds.

Silver Cyanide Powder‐Catalyzed Selective Epoxidation of Cyclohexene and Styrene with its Surface Activation by H2O2(aq) and Assisted by CH3CN as a Non‐Innocent Solvent

AbstractWe undertake silver cyanide (AgCN) powder for its catalytic epoxidation of cyclohexene or styrene in CH3CN with variable substrate‐to‐solvent volume ratios using H2O2(aq) at 60 °C. The reaction mixtures can facilely separate into organic and aqueous layers. Cyclohexene oxide can be produced in the organic layer with 100 % selectivity from the substrate cyclohexene, while styrene oxide was identified with 80 % selectivity against benzaldehyde in styrene oxidation. After reactions, we can recycle the AgCN particles with comparable bulk property clarified via XRD, XPS, XAS, FT‐IR, and 13C‐SS NMR spectroscopy. Using H218O2 as the oxidant, both epoxide products and acetamide are highly enriched with 18O‐atom, indicating that the π bond‐activation is essential for forming the cyclohexene/styrene oxides in the organic and acetamide in the aqueous layers. The oxidation of cyclohexene/styrene catalyzed by AgCN powder through surface activation by H2O2(aq) and assisted by the non‐innocent CH3CN‐originated acetamide can achieve highly selective π‐bond activation with high reactivity.

Site-Selective Catalytic Epoxidation of Alkene with Tunable, Atomic Precision by Molecularly Imprinted Artificial Epoxidases.

Distinction of chemical functionality by their local chemical environment is a skill mastered by enzymes, evident from the selective synthesis, cleavage, and transformation of peptides, nucleic acids, and polysaccharides that abound with the same type of functional groups. In contrast, synthetic catalysts are generally better at differentiating functional groups based on their electronic and steric properties. Here we report artificial epoxidases prepared through molecular imprinting of surface-core doubly cross-linked micelles, followed by efficient functionalization of the imprinted site in the micellar core via photoaffinity labeling. The size and shape of the active sites are tuned by the modularly synthesized templates, with the oxygen-delivering peroxy acid group positioned accurately. These catalysts are used in epoxidation of alkene in water with hydrogen peroxide under mild conditions, without any additional additives. Most importantly, atomic precision is achieved in the catalysis and enables alkenes to be distinguished that differ in the position of the carbon-carbon double bond by a single carbon.

Automated search for optimal surface phases (ASOPs) in grand canonical ensemble powered by machine learning.

The surface of a material often undergoes dramatic structure evolution under a chemical environment, which, in turn, helps determine the different properties of the material. Here, we develop a general-purpose method for the automated search of optimal surface phases (ASOPs) in the grand canonical ensemble, which is facilitated by the stochastic surface walking (SSW) global optimization based on global neural network (G-NN) potential. The ASOP simulation starts by enumerating a series of composition grids, then utilizes SSW-NN to explore the configuration and composition spaces of surface phases, and relies on the Monte Carlo scheme to focus on energetically favorable compositions. The method is applied to silver surface oxide formation under the catalytic ethene epoxidation conditions. The known phases of surface oxides on Ag(111) are reproduced, and new phases on Ag(100) are revealed, which exhibit novel structure features that could be critical for understanding ethene epoxidation. Our results demonstrate that the ASOP method provides an automated and efficient way for probing complex surface structures that are beneficial for designing new functional materials under working conditions.

Synthesis, characterization, DFT calculations, and catalytic epoxidation of two oxovanadium(IV) Schiff base complexes

The present paper reports the synthesis, characterization, and DFT calculations of two oxovanadium (IV) Schiff base complexes symbolized as VOL1 and VOL2, which prepared by the reaction of bivalent tridentate Schiff base ligands (E)-2-((5-chloro-2-hydroxybenzylidene)amino)acetic acid and (E)-2-((2-hydoxy-5-nitrobenzylidene)amino)acetic acid and VO(acac)2 as vanadium source. The Schiff base ligands and its oxovanadium (IV) complexes were characterized by the elemental analysis (C, H, N), FTIR, 1H NMR and 13C NMR, DFT calculations were performed to derive some of their molecular properties. Schiff base ligands coordinated to vanadium center via nitrogen from the azomethine group and one oxygen from the hydroxyl attached to the benzene ring and one oxygen from hydroxyl of carboxyl group. The catalytic activity of the two complexes were tested against cyclooctene and found that both complexes were highly effective and selective in optimized conditions when used as cyclooctene epoxidation catalysts with the conversion percentage of 91.85% (with VOL1) and 87.40% (with VOL2) at 78 °C within a period of ten hours. To understand the structural properties of the two complexes, the two complexes were well optimized at B3LYP/6-31G(d,p) level of theory, structural parameters such as electron affinity, global electrophilicity, global hardness, electronegativity, ionization potential, and electron chemical potential based on HOMO and LUMO energy values were calculated.

The Fabrication of PMo11Fe Cluster Supporting on SBA-15 and Catalytic Epoxidation of Cyclooctene with H2O2 as Oxidant

The Fabrication of PMo11Fe Cluster Supporting on SBA-15 and Catalytic Epoxidation of Cyclooctene with H2O2 as Oxidant

Epoxidation catalysts prepared by encapsulation of molybdenum hexacarbonyl in UiO-66(Zr/Hf)-type metal-organic frameworks

The confinement and catalytic behavior of Mo(CO)6 species inside UiO-66 (zirconium and hafnium) metal-organic frameworks (MOFs) have been investigated by means of multitechnique characterization and catalytic olefin epoxidation. Mo(CO)6 was encapsulated in nanocrystalline MOFs by solvothermal and vapor phase impregnation methods (STI and VPI, respectively), resulting in Mo loadings of 2.0–8.8 wt% (STI) or 15 wt% (VPI). Powder X-ray diffraction, SEM-EDS, N2 adsorption, FT-IR and 13C{1H} CP MAS NMR collectively confirmed immobilization within the pore spaces of the hosts, which maintained their bulk crystallinity and crystal morphologies. CO resonances in the 13C{1H} CP MAS NMR spectra were assigned to hexacarbonyl guest molecules located in the larger pore spaces, such as the octahedral cavities (for STI and VPI samples), and in more restricted environments such as the tetrahedral cavities (for the VPI sample). FT-IR spectra displayed the characteristic pattern of νCO stretching modes for an octahedral symmetry molecule slightly perturbed by interaction of one of the carbonyl groups with the MOF support. The spectra evidenced the formation of a weak hydrogen bonding interaction of the type μ3-OH···OCMo(CO)5 involving the μ3-OH groups that are exclusively present in the tetrahedral cavities of the UiO-66 structure. The Mo(CO)6 loaded MOFs are active and reusable pre-catalysts for cis-cyclooctene epoxidation, exhibiting excellent epoxide selectivity (up to quantitative epoxide yield within 1 h reaction) and tert-butyl hydroperoxide efficiency. Catalyst recycling and retention of structural integrity were demonstrated for UiO-66(Hf) loaded with 8.8 wt% Mo by the STI method. The UiO-66(Hf) host may be a better catalyst support than its Zr counterpart due its smaller crystallite size (≈100 nm) and higher defectivity. The substrate scope was broadened for Mo(8.8-STI)/Hf-MOF which promoted the epoxidation of biobased olefins (methyl oleate and dl-limonene) and oxidative dehydrogenation of cyclooctanol to cyclooctanone.

Stereoselective synthesis of trisubstituted epoxides via cobalt catalysis

Catalytic epoxide synthesis by transition-metal catalysis offers an atom- and step-economical route from readily available aldehydes and diazocarbonyl compounds.

Synthesis of nanoscale CuO via precursor method and its application in the catalytic epoxidation of styrene.

Nanoscale CuO with diameters in the range of 7–8 nm has been synthesized via a two-step precipitation–calcination method using copper(ii) isonicotinate tetrahydrate as the precursor. The first step involves the room temperature stirring of an alkaline ethanolic solution of the precursor which gives a non-crystalline CuO species, while the second step involves the calcination of the product of the first step at 180 °C to form nanocrystalline CuO which has been characterized by PXRD, TEM, SEM, H2-TPR and Raman spectroscopy, etc. The CuO material has shown excellent catalytic activity in the oxidation of styrene using TBHP as the oxidizing agent leading to complete styrene conversion with more than 95% styrene oxide selectivity at the end of 6 h. The oxide catalyst can be reused for at least 6 successive runs without significant loss in activity.

Epoxidation of soybean oil by insitu formation of peracid in the presence of zeolites

The catalytic epoxidation of soybean oil with hydrogen peroxide as oxidant has been accomplished using HZSM-5-, HYand Hß- zeolite catalysts. The prepared catalysts are characterized by XRD, FTIR, and BET surface area. The catalytic epoxidation of soybean oil is studied as a function of time. The results show that all three catalysts exhibit higher conversion and selectivity of epoxidized soybean oil. Optimized protocol provides 85 %, 83 % and 70.55 %, conversion, selectivity and yield, respectively with HZSM-5 catalyst. The reaction occurs inside the pores of the zeolite framework via insitu formation of performic acid which further catalyzed by acid sites.