5 research outputs found
Heteropoly acids as catalysts for Fries reaction
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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
Coupling of monoterpenic alkenes and alcohols with benzaldehyde catalyzed by silica-supported tungstophosphoric heteropoly acid.
The reactions of biomass-based substrates, i.e., limonene, -pinene, -pinene, terpinolene, -terpineol,nerol and linalool, with benzaldehyde in the presence of tungstophosphoric heteropoly acid H3PW12O40(HPW) supported on silica give an oxabicyclo[3.3.1]nonene compound with fragrance characteristics ingood to excellent yields. The reactions apparently involve the formation of -terpenyl carbenium ion bythe protonation of alkene or dehydration of alcohol followed by the nucleophilic attack of benzaldehyde.The subsequent oxonium-ene cyclization of the resulting oxocarbenium ion gives the oxabicyclic product.The process is an environmentally benign and heterogeneous and can be performed under mild conditionswith low catalyst amounts and no significant leaching of active components
Heteropoly acid catalysis for the isomerization of biomass-derived limonene oxide and kinetic separation of the trans-isomer in green solvents.
Terpenes are an abundant class of natural products, which is important for flavor and fragrance industry. Many acid catalyzed reactions used for upgrading terpenes still involve mineral acids as homogeneous catalysts and/or toxic solvents. Heteropoly acids represent a well-established eco-friendly alternative to conventional acid catalysts. As these reactions are usually performed in the liquid phase, solvents play a critical role for the process sustainability. In the present work, we developed a catalytic route to valuable fragrance ingredients, dihydrocarvone and carvenone, from limonene oxide by its isomerization using silica-supported tungstophosphoric acid as a heterogeneous catalyst and dialkylcarbonates as green solvents. The reaction pathway can be switched between dihydrocarvone and carvenone (obtained in 90% yield each) simply by changing the reaction temperature. In addition, we developed an efficient method for kinetic separation of trans-limonene oxide from commercial cis/trans-limonene oxide mixture and stereoselective synthesis of trans-dihydrocarvone
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., a-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