A green epoxidation system with poly(4‐vinylpyridine) microsphere‐supported molybdenum catalyst

The immobilization of molybdenum (Mo) compounds on poly(4‐vinylpyridine) (P4VP) microspheres for catalytic epoxidation was reported. P4VP‐supported Mo compounds were highly efficient and selective for the epoxidation of cis‐cyclooctene using hydrogen peroxide (H₂O₂) as oxygen source. When ethanol was used as solvents, outstanding catalytic activity and selectivity were observed for Mo‐containing catalysts in the epoxidation of cis‐cyclooctene. A completely green epoxidation system based on H₂O₂ and cleaner solvent has been achieved, and the heterogenized Mo catalyst can be recovered for five times without loss of its activity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 558–562, 2010     

Remarkable enhancement of aerobic epoxidation reactivity for olefins catalyzed by μ-oxo-bisiron(III) porphyrins under ambient conditions

With μ-oxo dimeric iron(III) porphyrins [(Fe^IIITPP)₂O] as catalyst, isobutylaldehyde as co-reductant, and dioxygen as oxidant, an efficient model system for epoxidation of olefins has been developed. Compared with mono-metalloporphyrins as catalyst, a remarkable enhancement of reactivity was obtained for the present olefin epoxidation system, in which the turnover number (TON) of the catalyst has doubled from about 700 million to 1400 million. Moreover, a plausible mechanism involving both binuclear and mononuclear intermediate has been proposed.     

Stereochemical studies of tricyclo[6.2.1.O.1·6]undecanes—II : Stereochemistry of isolongifolene epoxide

The stereochemistry of epoxidation and hydroboration of isolongifolene has been elucidated by comparison with the chemistry of the C₂-desmethyl epoxides and their transformation products. The main factors controlling the stereochemistry of epoxidation of isolongifolene are the bicycloheptyl moiety and the C-2β methyl substituent.     

Catalytic Performance of Amorphous Ti/SiO2 in the Gas-Phase Epoxidation of Propylene with H2O2

The epoxidation of propylene with dilute H₂O₂ aqueous solution over titanium silicalite-1 (TS-1) zeolite catalyst is a green chemical reaction for propylene oxide (PO) production. Carrying out the reaction in gas-phase can get rid of problems caused by using methanol solvent. This paper reports an attempt of using non-zeolite catalyst for the gas-phase epoxidation. Amorphous Ti/SiO₂, obtained by grafting amorphous SiO₂ with TCl₄ in ethanol solvent in a chemical liquid-phase deposition (CLD) process, has been used as the catalyst. Results show that the CLD Ti/SiO₂ with appropriate Si/Ti molar ratio is an active catalyst for gas-phase epoxidation, achieving 9.8 % propylene conversion and 66.9 % PO selectivity with 40.3 % H₂O₂ utilization, which indicates that this amorphous Ti/SiO₂ catalyst deserves extensive studies in the future.     

State of titanium in Ti-containing silica and silicalite catalysts in relation to their oxidation activity

The nature of active titanium species for epoxidation of olefins with H₂O₂ and t-butyl hydroperoxide has been investigated for titanium silicalite (TS-1), titania silica (TiO₂/SiO₂) prepared by a sol-gel method, and titanium oxide supported on silica by a CVD method (TiO₂/SiO₂-CVD). IR and XANES analyses suggested that Ti in TiO₂/SiO₂ and TiO₂/SiO₂-CVD has a tetrahedral configuration bonded to SiO₂ and that in TS-1 has a configuration composed of >Ti=O or related to it. Their configurations are closely related to their reactivities for epoxidation of olefins in which the former works with t-butyl hydroperoxide and the latter with H₂O₂.     

Two hydrogen-bond-cross-linked molybdenum (VI) network polymers: synthesis, crystal structures and cyclooctene epoxidation with H2O2

Two molybdenum (VI) hydrogen-bonded network polymers [MoO₂F₄]·(4,4′-H₂bpd)(H₂O)₂ (1) and [MoO₂Cl₃(H₂O)]·(4,4′-H₂bpd)Cl (2) (bpd = bipiperidine) have been synthesized and examined as catalysts for epoxidation of cyclooctene. Complexes of the Mo compounds containing the bpd ligand are prepared and characterized by infrared spectroscopy, thermogravimetric and elemental analyses. They have been structurally characterized by single crystal X-ray diffraction analysis. The structures of both the complexes are shown to be comprised of molybdenum and two protonated N-ligand cations that have resulted in a cross-linked hydrogen-bonded network structure. These complexes are applicable as catalysts for the cis-cyclooctene epoxidation reactions with hydrogen peroxide as a source of oxygen and NaHCO₃ as a cocatalyst. It has been observed that the formation of the oxidant peroxymonocarbonate ion, HCO₄ ⁻ by hydrogen peroxide and bicarbonate enhances the epoxidation reaction. Both the complexes have exhibited a good activity and a very high selectivity for the formation of cyclooctene oxide. An erratum to this article can be found at     

A route to magnetically separable nanocatalysts: Combined experimental and theoretical investigation of alkyl substituent role in ligand backbone towards epoxidation ability

We have prepared two chiral Schiff base ligands, H₂L¹ and H₂L², and one achiral Schiff base ligand, H₂L³, by treating 2,6‐diformyl‐4‐methylphenol separately with (R )‐1,2‐diaminopropane, (R )‐1,2‐diaminocyclohexane and 1,1′‐dimethylethylenediamine, in ethanolic medium, respectively. The complexes MnL¹ClO₄ ( 1 ), MnL²ClO₄ ( 2 ), MnL³ClO₄ ( 3 ), FeL¹ClO₄ ( 4 ), FeL²ClO₄ ( 5 ) and FeL³ClO₄ ( 6 ) have been obtained by reacting the ligands H₂L¹, H₂L² and H₂L³ with manganese(III) perchlorate or iron(III) perchlorate in methanol. Circular dichroism studies suggest that ligands H₂L¹ and H₂L² and their corresponding complexes have asymmetric character. Complexes 1 – 6 have been used as homogeneous catalysts for epoxidation of alkenes. Manganese systems have been found to be much better than iron counterparts for alkene epoxidation, with 3 as the best catalyst among manganese systems and 6 as the best among iron systems. The order of their experimental catalytic efficiency has also been rationalized by theoretical calculations. We have observed higher enantiomeric excess product with catalysts 1 and 4 , so they were attached to surface‐modified magnetic nanoparticles to obtain two new magnetically separable nanocatalysts, Fe₃O₄@dopa@MnL¹ and Fe₃O₄@dopa@FeL⁴. They have been characterized and their alkene epoxidation ability has been investigated. These catalysts can be easily recovered by magnetic separation and recycled several times without significant loss of catalytic activity. Hence our study focuses on the synthesis of a magnetically recoverable asymmetric nanocatalyst that finds applications in epoxidation of alkenes and at the same time can be recycled and reused.     

Density functional study of ethylene oxidation on an Ag(111) surface

The mechanism of ethylene epoxidation on Ag surfaces has been investigated using the density functional method and Ag _n clusters (n = 3 to 10) modeling the Ag(111) surface. The adsorption energy of O₂ to the Ag clusters was strongly dependent on the HOMO level of the cluster, and the clusters with higher HOMO levels afforded larger O₂ adsorption energies. The energetics was investigated for both the molecular and atomic oxygen epoxidation mechanisms. For the atomic oxygen mechanism, epoxidation was found to proceed without an activation energy, whereas a small amount of activation energy (about 5 kcal/mol) was calculated for the molecular oxygen mechanism. Received: 2 July 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999     

Epoxidation of Soybean Oil in the Course of Cooxidation with Hydrogen Peroxide in the Presence of Propanoic Acid and Chlorinated KU-2 × 8 Cation Exchanger

Pattern of soybean oil epoxidation catalyzed by chlorinated KU-2 × 8 cation exchanger in the presence of H₂O₂ and propanoic acid was studied. The epoxidation rate and the selectivity of formation and yield of the epoxidation product were studied as influenced by the concentration of H₂O₂, C₂H₅COOH, and the catalyst. Some kinetic and activation parameters of soybean oil epoxidation were determined.     

Synthetic, spectral and catalytic activity studies of ruthenium bipyridine and terpyridine complexes: Implications in the mechanism of the ruthenium(pyridine-2,6-bisoxazoline)(pyridine-2,6-dicarboxylate)-catalyzed asymmetric epoxidation of olefins utilizing H2O2

Various Ru(L₁)(L₂) (1) complexes (L₁ = 2,2′-bipyridines, 2,2′:6′,2″-terpyridines, 6-(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl-2,2′-bipyridinyl or 2,2′-bipyridinyl-6-carboxylate; L₂ = pyridine-2,6-dicarboxylate, pyridine-2-carboxylate or 2,2′-bipyridinyl-6-carboxylate) have been synthesized (or in situ generated) and tested on epoxidation of olefins utilizing 30% aqueous H₂O₂. The complexes containing pyridine-2,6-dicarboxylate show extraordinarily high catalytic activity. Based on the stereoselective performance of chiral ruthenium complexes containing non-racemic 2,2′-bipyridines including 6-[(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl]-[2,2′]bipyridinyl new insights on the reaction intermediates and reaction pathway of the ruthenium-catalyzed enantioselective epoxidation are proposed. In addition, a simplified protocol for epoxidation of olefins using urea hydrogen peroxide complex as oxidizing agent has been developed.     

Gas-phase propene epoxidation over coinage metal catalysts

Propene oxide (PO) is a very important bulk chemical and is produced on a scale of about 7.5 million tons per year. In industry, PO is produced via multiple reaction steps in the liquid phase, using hazardous chlorine or costly organic hydroperoxides as oxidants. Accordingly, development of a simple and green process to produce PO has been desired. This paper presents an overview of one-step propene epoxidation in the gas phase over coinage metal catalysts with a mixture of O₂ and H₂ or with molecular O₂ alone as oxidant. Silver (Ag) and gold (Au) catalysts can catalyze propene epoxidation with a mixture of O₂ and H₂, with high selectivity, whereas copper (Cu) catalysts cannot. In this reaction Au catalysts are much more active than Ag catalysts. All the coinage metals can catalyze propene epoxidation by molecular O₂, but with selectivity usually below 60%. The valence states of Cu species and the sizes of Ag particles and Au particles are of crucial importance in PO synthesis.     

UV‐Assisted Removal of Inactive Peroxide Species for Sustained Epoxidation of Cyclooctene on Anatase TiO2

Epoxidation of olefins with H₂O₂ is one of the most important reactions in organic synthesis. We found that anatase TiO₂ can be a good catalyst for the epoxidation of cyclooctene with H₂O₂ at room temperature. However, the catalyst deactivated quickly in the presence of excess amount of H₂O₂ because of the formation of inactive side‐on Ti‐η²‐peroxide species on the surface of TiO₂, the presence of which was confirmed by isotope‐labelled resonance UV Raman spectroscopy and kinetics studies. Interestingly, the epoxidation reaction could be dramatically accelerated under irradiation of UV light with λ≥350 nm. This phenomenon is attributed to the photo‐assisted removal of the inactive peroxide species, through which the active sites on the surface of anatase TiO₂ are regenerated and the catalytic epoxidation of cyclooctene with H₂O₂ is resumed. This finding provides an alternative for sustained epoxidation reactions on TiO₂ at room temperature. Moreover, it also has significant implications on the deactivation pathway and possible solutions in Ti‐based heterogeneous catalysis or photocatalysis.     

Oxidative transformations of cembrane diterpenoids III. Epoxycembrenes

Summary 1. It has been established that the epoxidation of cembrene with perbenzoic and peracetic acids takes place stereospecifically at each of the trisubstituted double bonds with the formation of 4S,5R-, 7S,8S-, and 11S,12S-monoepoxycembrenes, the structures and absolute configurations of which have been established by spectral methods.2. Epoxidation of cembrene at the C₁₁–C₁₂ double bonds under the conditions used takes place preferentially as compared with epoxidation at the C₇–C₈ double bond.Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Academy of Sciences of the USSR. Novosibirsk State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 525–531, July–August, 1977.     

Synthesis of enantiopure 2-amino-1-phenyl and 2-amino-2-phenyl ethanols using enantioselective enzymatic epoxidation and regio- and diastereoselective chemical aminolysis

Several enantiopure 1,2-amino alcohols have been prepared by combining a stereoselective enzymatic epoxidation of styrenes with regio- and stereoselective chemical reactions. An interesting reactivity has been noted concerning the reaction of epoxides and NH₃ under microwave activation.     

Characterization and catalytic performance of methyl-grafted Ti-HMS catalysts prepared by the CVD method

Methyl-grafted Ti-HMS catalysts were prepared by the chemical vapor deposition (CVD) method using TiCl₄ as titanium source and various organic silanes as silylating agents. The catalysts were characterized by XRD, N₂-adsorption-desorption, FTIR, ²⁹Si NMR, TGA, DR UV-vis, and evaluated by the epoxidation of propylene using cumene hydroperoxide (CHP) as oxidant. The results reveal that the silylated Ti-HMS catalysts are more active than the unsilylated Ti-HMS catalyst, and the methyl-grafted Ti-HMS catalyst silylated with hexamethyldisilazane (HMDSZ) exhibits better epoxidation performance than the analogues silylated with trimethylchlorosilane (TMCS) or dimethyldichorosilane (DMDCS). It is proposed that not only the form of T-O-SiMe_n (n = 2 or 3) but also the breakage of Ti-O-T (Si-O-Si or Si-O-Ti) are observed in silylation using Cl-containing silylating agents (TMCS or DMDCS), which decrease the hydrophobicity of Ti-HMS catalysts and destroy the tetracoordinated titanium species that responsible for the epoxidation performance. This phenomenon has not been observed in silylation with HMDSZ.     

Liquid-phase epoxidation of cyclooctene with O2 over CoOx/SiO2 catalyst prepared by sol–gel method

A series of CoO_x/SiO₂ catalysts has been prepared by the sol–gel method and characterized with XRD, N₂ adsorption/desorption, diffuse reflectance UV–vis spectroscopy, Raman spectroscopy as well as TPR techniques. This type of material is highly active and selective for the epoxidation of cyclooctene with atmospheric molecular oxygen. Although all the catalysts attained at different pH values are amorphous, their catalytic activities are remarkably different because the pH values influence not only the coordination state of Co species but also the textural structures of the prepared catalysts, in which CoO_x/SiO₂ obtained at pH below 5 is highly active and selective for the epoxidation of cyclooctene with atmospheric O₂. The prepared CoO_x/SiO₂ catalysts are highly stable and can be recycled at least four times without significant loss of activity and selectivity.     

Supramolecular Assembly Based on Octamolybdate and Triazole Derivative: Crystal Structure and Catalytic Application in Olefin Epoxidation

A novel polyoxometalate-based compound, [H(atrz)]₄[(atrz)₂(Mo₈O₂₆)]·2H₂O (1) (atrz = 3-amino-1,2,4-triazole), has been synthesized by traditional hydrothermal method, and characterized by means of elemental analysis, FT-IR spectroscopy, Powder X-ray diffraction and single-crystal X-ray. The compound 1 contains a 2D supramolecualr layer which is constructed from [(atrz)₂(γ-Mo₈O₂₆)]^4? units via intermolecular hydrogen-bonding interactions. Furthermore, the adjacent 2D layers are packed together through the aromatic π?π stacking interactions and exhibits a 3D supramolecular structure. The catalytic properties of 1 were investigated in olefin epoxidation with tert-butylhydroperoxide (t-BuOOH) as the oxidant. It was found that compound 1 could serve as active and stable heterogeneous catalyst for the epoxidation of cyclooctene and 1-octence. Besides, introducing copper ions into compound 1 could further improve the catalytic activity for olefin epoxidation.     

Kinetics of epoxidation of 2-methyl-2-pentene

The kinetics of epoxidation of 2-methyl-2-pentene with cumene hydroperoxide catalyzed by MoO₂ (acac)₂ has been studied in the temperature range of 35–65°C. The observed kinetic behavior is consistent with the formation of a hydroperoxide-catalyst complex and a simple competitive inhibition step, involving the formation of an inactive epoxide-catalyst complex. The reaction parameters have been calculated.     

An efficient organic solvent-free methyltrioxorhenium-catalyzed epoxidation of alkenes with hydrogen peroxide

Methyltrioxorhenium/3-methylpyrazole has proved to be an efficient catalytic system for epoxidation of alkenes with aqueous 35% H₂O₂ in excellent yields under organic solvent-free conditions. The yields of epoxides by the organic solvent-free epoxidation are comparable to those using CH₂Cl₂ as the organic solvent. The epoxidations of simple alkenes under organic solvent-free conditions are slower than those in CH₂Cl₂, while the epoxidations of alkenols such as citronellol are faster than those in CH₂Cl₂.     

Oxidation of alkenes catalysed by molybdenum(VI)–oxodiperoxo complex anchored on the surface of magnetic nanoparticles under solvent‐free conditions

A new epoxidation catalyst has been prepared by grafting a molybdenum(VI)–oxodiperoxo complex containing an oxazine ligand, [MoO(O₂)₂(phox)], on chloro‐functionalized Fe₃O₄ nanoparticles. The synthesized heterogeneous catalyst (MoO(O₂)₂(phox)/Fe₃O₄ was characterized using powder X‐ray diffraction, scanning and transmission electron microscopies, vibrating sample magnetometry, energy‐dispersive X‐ray analysis, Fourier transform infrared spectroscopy and inductively coupled plasma atomic emission spectroscopy. The immobilized complex gave high product yields and high selectivity for epoxide compared to the corresponding homogeneous one in the epoxidation of various olefins in the presence of tert ‐butyl hydroperoxide at 95°C without any co‐solvent. Also, the heterogeneous catalyst can be recycled without a noticeable change in activity and selectivity.