Elena F. Kozhevnikova

Heteropoly acid catalysts for the synthesis of fragrance compounds from biorenewables: isomerization of limonene oxide

The liquid-phase isomerization of limonene oxide was studied in the presence of heteropoly acid catalysts in aprotic solvents in homogeneous and heterogeneous systems. Among the catalysts were bulk and silica-supported tungstophosphoric acid H3PW12O40 and its acidic Cs salt Cs0.5H0.5PW12O40 (CsPW). The reaction gave dihydrocarvone, a valuable fragrance intermediate, as the main product with turnover numbers of up to 8000. The nature of the solvent had a strong effect on reaction rate and selectivity. CsPW (0.1 mol%) was found to be a highly efficient and truly heterogeneous catalyst for this reaction, providing 82% yield of dihydrocarvone in 1,4-dioxane as a solvent under ambient conditions. This simple catalytic method represents economically attractive route to industrially important compounds starting from bio-renewable substrates easily available from essential oils.

'Particle size - activity relationship for CoFe2O4 nanoparticle CO oxidation catalysts'

The inverse spinel CoFe2O4 is prepared as nanoparticles with a range of controlled sizes. Synthesis is performed using solvothermal and coprecipitation chemistry, and a two capping group coprecipitation procedure using oxalic acid and ethylenediamine or triethanolamine is shown to afford sub-10 nm, controlled size nanoparticles. A pronounced particle size–activity relationship is observed for CO oxidation catalysis for the studied range of particle sizes. In addition, these unsupported nanoparticle catalysts readily undergo activation during catalysis and exhibit both structural and performance stability under the test reaction conditions.

Heteropoly Acid Catalysts for the Synthesis of Fragrance Compounds from Biorenewables: Cycloaddition of Crotonaldehyde to Limonene, α‐Pinene, and β‐Pinene

The interaction of widespread monoterpenes limonene, α‐pinene, and β‐pinene with crotonaldehyde using silica‐supported tungstophosphoric heteropoly acid H3PW12O40 and its acidic cesium salt Cs2.5H0.5PW12O40 as solid acid catalysts in dichloroethane solutions results in cycloaddition, which gives the same fragrant oxabicyclo[3.3.1]nonene product in a high yield. The product is likely to be formed through an α‐terpenyl carbenium ion intermediate, which is generated from monoterpene protonation and undergoes nucleophilic attack by crotonaldehyde. Both H3PW12O40 and Cs0.5H0.5PW12O40 are efficient and truly heterogeneous cycloaddition catalysts.

Polyisobutylene oligomer-bound polyoxometalates as efficient and recyclable catalysts for biphasic oxidations with hydrogen peroxide

Polyisobutylene (PIB) oligomer-bound amines render Keggin polyoxometalates (POM) heptane soluble, making them efficient and recyclable catalysts for environmentally benign biphasic oxidations with hydrogen peroxide. This is illustrated using both oxidative desulfurization and alkene epoxidation reactions that can be efficiently carried out in a heptane–water two-phase system occurring through facile phase transfer of POM by the amine terminated PIB oligomer.

Heteropoly Acid Catalysts for the Synthesis of Fragrance Compounds from Biorenewables: The Alkoxylation of Monoterpenes

The cesium salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40, is an active and environmentally friendly solid‐acid catalyst for the liquid‐phase alkoxylation of widespread monoterpenes, such as camphene, limonene, α‐pinene, and β‐pinene. These reactions provide isobornyl or α‐terpenyl ethers, useful as fragrances, in good to excellent yields. The reactions are equilibrium‐controlled and occur with high catalyst turnover numbers (TONs) up to 1500–4200 without catalyst leaching. Heteropoly acid H3PW12O40 also efficiently catalyzes the alkoxylation of these monoterpenes under homogeneous conditions with TONs up to 1500–11 300.

Heteropoly acid as a novel efficient catalyst for Fries rearrangement

Heteropoly acid H3PW12O40 is a very efficient and environmentally benign catalyst for the Fries rearrangement of phenyl acetate in homogeneous or heterogeneous liquid-phase systems at 100-150 degrees C.

Alkylaminophosphazenes as Efficient and Tuneable Phase-Transfer Agents for Polyoxometalate-Catalysed Biphasic Oxidation with Hydrogen Peroxide

Alkylaminophosphazenes (RPN) are efficient and tuneable phase‐transfer agents for environmentally benign biphasic oxidation with hydrogen peroxide catalysed by polyoxometalates (POMs). Substituent groups on the phosphazene ring can be varied to modify the phase‐transfer efficiency of RPN for use in water–organic two‐phase systems. Active phosphazene–polyoxometalate aggregates that self‐assemble in situ from RPN and Keggin POMs, such as PMo12O403− and PW12O403−, were found to be efficient and recyclable catalysts for the oxidation of benzothiophenes and the epoxidation of alkenes with hydrogen peroxide. Lipophilic phosphazene cations present in these aggregates render the POM soluble in organic media. Catalyst activity in the biphasic oxidation with H2O2 varies with the RPN substituent alkylamino groups with respect to the solvent system used. The activity decreases in the series of POMs: PMo12O403−>PW12O403−≫SiW12O404− irrespective of the solvent system used.

Highly Active and Recyclable Metal Oxide Catalysts for the Prins Condensation of Biorenewable Feedstocks

Metal oxides such as Nb2O5, Cr2O3, and especially a ZnIICrIII mixed oxide are demonstrated to be highly active and recyclable heterogeneous catalysts for Prins condensation, which provides a clean, high‐yielding route for the synthesis of nopol through the condensation of biorenewable β‐pinene with paraformaldehyde. ZnCr mixed oxide with an optimum Zn/Cr atomic ratio of 1:6 gave 100 % nopol selectivity at 97 % β‐pinene conversion, with the catalyst easily recovered and recycled. The acid properties of Nb2O5 and ZnCr mixed oxide were characterized by the diffuse reflectance IR Fourier transform spectroscopy of adsorbed pyridine and ammonia adsorption microcalorimetry. An appropriate combination of acid–base properties of ZnCr mixed oxide is believed to be responsible for its efficiency.

Heteropoly acid catalysts for the synthesis of fragrance compounds from bio-renewables: acetylation of nopol and terpenic alcohols

The cesium salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40, is an active and environmentally friendly heterogeneous catalyst for the liquid-phase acetylation of nopol and several biomass-derived terpenic alcohols (i.e., α-terpineol, nerol, geraniol, linalool, menthol, isoborneol, perillyl alcohol, carveol, isopulegol, carvacrol and nerolidol) with acetic anhydride. The resulting flavor and fragrance acetic esters, which are widely used in perfumery, household and food products, are obtained in good to excellent yields. The reactions occur at room temperature with low catalyst loadings without substantial catalyst leaching and can be performed with stoichiometric amounts of an acetylating agent in solvent free systems.

Multifunctional catalysis by Pd-polyoxometalate: one-step conversion of acetone to methyl isobutyl ketone

Pd metal supported on Cs2.5H0.5PW12O40 is an efficient bifunctional catalyst for the one-step conversion of acetone to methyl isobutyl ketone in gas and liquid phase.