A simple and versatile method for alkene epoxidation using aqueous hydrogen peroxide and manganese salophen catalysts

We describe a simple and versatile method for the catalytic epoxidation of a broad range of olefins (e.g., ketones, esters, and alkyl halides) with aqueous H₂O₂ using manganese salophen catalysts. Low catalyst loading, short reaction times, and a simple reaction setup (e.g., no pH buffer is required) are salient features of the system, which unites the benefits of H₂O₂ as an oxidant with the versatility and modularity of salen-based catalysts.     

Convenient method for epoxidation of alkenes using aqueous hydrogen peroxide

[reaction: see text] The complex [Ru(tpy)(pydic)] (1a) is an active catalyst for epoxidation of alkenes by aqueous 30% hydrogen peroxide in tertiary alcohols. The protocol is simple to operate and gives the corresponding epoxides in good to excellent yields. Chiral enantiopure [Ru(tpy)(pydic)] complexes have been synthesized and successfully applied in this procedure.     

A catalytic, environmentally benign method for the epoxidation of unsaturated terpenes with hydrogen peroxide

Various unsaturated terpenes were selectively oxidised to the corresponding epoxides in good yields using phosphate buffered hydrogen peroxide and catalytic amounts of tungstate under halide free conditions. The selectivity of the reaction to epoxides was significantly increased with respect to the ionic strength of the aqueous phase of the system.     

Kinetics of propylene epoxidation with hydrogen peroxide

The kinetics of propylene oxidation to propylene oxide in the presence of a titanium-containing zeolite in an isopropyl alcohol medium is reported. The influence of the concentrations of the starting substances and reaction products and temperature on the rate of the process is considered. A mathematical model has been derived from the experimental data obtained. The rate constants, adsorption equilibrium constants, and activation energies of the reactions have been calculated.     

Catalytic epoxidation of polyisobutylene-co-isoprene with hydrogen peroxide

Polyisobutylene-co-isoprene (PIBI) can be epoxidized with hydrogen peroxide in the presence of methyltrioctylammonium tetrakis (diperoxotungsto) phosphate(3-) as the catalyst in a biphasic system. The effects of the reaction time and temperature, the ratio of the organic phase to the aqueous phase, the concentration of the catalyst and polymer and stirring intensity, respectively, are studied on the conversion of double bonds to oxirane groups. ¹H-NMR analysis confirms the absence of ring opening side reactions in this epoxidation reaction system. The kinetics of the reaction are discussed. The rate constants are measured at four temperatures and the activation energy for the reaction is determined as 54.2kJ/mol. The optimum reaction temperature is about 60°C.     

A new efficient iron catalyst for olefin epoxidation with hydrogen peroxide

A new aminopyridine ligand derived from bipiperidine (the product of full reduction of bipyridine, bipy) coordinates to iron(II) in a cis-α fashion, yielding a new selective catalyst for olefin epoxidation with H(2)O(2) under limiting substrate conditions.     

Kinetics of allyl chloride epoxidation with hydrogen peroxide

The kinetics of allyl chloride oxidation to epichlorohydrin in the presence of titanium-containing zeolite was studied. The influence of the concentrations of the initial substances, reaction products, and temperature on the rate of the process was considered. The mathematical model of the process was constructed on the basis of the experimental data obtained. The rate constants, adsorption equilibrium constants, and activation energies of the reactions were calculated.     

A chiral iron-sexipyridine complex as a catalyst for alkene epoxidation with hydrogen peroxide

A chiral iron-sexipyridine complex-hydrogen peroxide mixture is a highly efficient catalytic system for styrene epoxidation with excellent reactivity (3 min, 95% yield) and chemoselectivity (98%).     

An improved methyltrioxorhenium-catalyzed epoxidation of alkenes with hydrogen peroxide

Methyltrioxorhenium (MTO)-catalyzed epoxidation of alkenes with H(2)O(2) has been significantly improved by using 3-methylpyrazole as an additive. A system consisting of 35% H(2)O(2) and MTO-3-methylpyrazole in CH(2)Cl(2) catalyzes the epoxidation of various alkenes in excellent yields. The catalytic activity of MTO-3-methylpyrazole surpasses MTO-pyrazole and MTO-pyridine catalysts. Quantitative yields of epoxides from cyclic and internal alkenes were obtained with only 0.05-0.1 mol% of MTO in the presence of 10 mol% of 3-methylpyrazole.     

Aldehyde-catalyzed epoxidation of unactivated alkenes with aqueous hydrogen peroxide

The organocatalytic epoxidation of unactivated alkenes using aqueous hydrogen peroxide provides various indispensable products and intermediates in a sustainable manner. While formyl functionalities typically undergo irreversible oxidations when activating an oxidant, an atropisomeric two-axis aldehyde capable of catalytic turnover was identified for high-yielding epoxidations of cyclic and acyclic alkenes. The relative configuration of the stereogenic axes of the catalyst and the resulting proximity of the aldehyde and backbone residues resulted in high catalytic efficiencies. Mechanistic studies support a non-radical alkene oxidation by an aldehyde-derived dioxirane intermediate generated from hydrogen peroxide through the Payne and Criegee intermediates.

An atropisomeric two-axis aldehyde is capable of catalysing the organocatalytic epoxidation of unactivated alkenes using hydrogen peroxide as the oxidant.     

Efficiency of phase-transfer catalysis in cyclopentene epoxidation with hydrogen peroxide

The effect of the structure and amount of the phase-transfer catalyst (quaternary ammonium salts) and the solvent effect on cyclopentene oxidation with an aqueous hydrogen peroxide solution in the liquid-liquid two-phase system was studied. The phase-transfer catalyst and solvent ensuring high reaction rate and high selectivity with respect to target products were chosen.     

A simple, iron-catalyzed, pyridine-assisted hydrogen peroxide epoxidation system

A simple and inexpensive system comprised of H(2)O(2)-pyridine-FeCl(3)·6H(2)O for the catalysis of olefin epoxidation was established. Intriguingly, the reactivity of this system greatly depends on the amounts of pyridine. Various substrates, including aromatic and aliphatic olefins, were epoxidized by this simple system in moderate to excellent yields.     

Indirect catalytic epoxidation with hydrogen peroxide electrogenerated in ionic liquids

Hydrogen peroxide was generated in room temperature ionic liquids by electrolysis, which was then used for the epoxidation of lipophilic alkenes under a carbon dioxide-saturated environment and in the presence of catalytic amount of manganese salt. ¹³C NMR showed that the active peroxymonocarbonate (HCO₄⁻) was generated from the mixture of H₂O₂, CO₂, and water in the ionic liquids. Most lipophilic alkenes were selectively epoxidized within 4-5 h. The ionic liquids can be recovered and reused without any deterioration in the performance.     

Cyclopentadienyl-silsesquioxane titanium complexes: highly active catalysts for epoxidation of alkenes with aqueous hydrogen peroxide

Titanium complexes bearing an unprecedented tridentate cyclopentadienyl-silsesquioxanate ligand provide a new class of efficient and selective catalysts for epoxidation of olefins with aqueous hydrogen peroxide under homogeneous conditions.     

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.     

Asymmetric organocatalytic epoxidation of alpha,beta-unsaturated aldehydes with hydrogen peroxide

The first asymmetric organocatalytic epoxidation of alpha,beta-unsaturated aldehydes is presented. A chiral bisaryl-silyl-protected pyrrolidine acts as a very selective epoxidation organocatalyst using simple oxidation agents, such as hydrogen peroxide and tert-butyl hydroperoxide. The asymmetric epoxidation reactions proceed under environmental friendly reaction condition in, for example, water mixtures of alcohols, and the scope of the reaction is demonstrated by the formation of optically active alpha,beta-epoxy aldehydes in high yields and enantioselectivities >94% ee. Furthermore, the direct synthesis of the sex pheromone from an acaric mite by asymmetric epoxidation of citral is presented.     

A versatile method for the preparation of allenic alcohols

A convenient three step procedure to a variety of allenic alcohols is described, which relies on a highly unusual partitioning between two reaction pathways depending on the mode of addition of a reagent.