Navegando por Autor "Cotta, Rafaela Ferreira"

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Coupling of monoterpenic alkenes and alcohols with benzaldehyde catalyzed by silica-supported tungstophosphoric heteropoly acid.
(2017) Cotta, Rafaela Ferreira; Rocha, Kelly Alessandra da Silva; Kozhevnikova, Elena Fedorovna; Kozhevnikov, Ivan V.; Gusevskaya, Elena Vitalievna
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.
Coupling of phenylacetaldehyde and styrene oxide with biorenewable alkenes in eco-friendly solvents.
(2021) Cotta, Rafaela Ferreira; Martins, Rafael Araújo; Rocha, Kelly Alessandra da Silva; Kozhevnikova, Elena Fedorovna; Kozhevnikov, Ivan V.; Gusevskaya, Elena Vitalievna
Acidic cesium salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40 (CsPW), is an excellent solid acid catalyst for the reaction of phenylacetaldehyde with biorenewable monoterpenic alkenes: limonene, α-terpineol, α-pinene and β-pinene. Simultaneously with a conventional oxonium-ene cyclization to give an oxabicyclo[3.3.1] nonene compound, phenylacetaldehyde undergoes Friedel-Crafts alkylation by the monoterpenes resulting in a new product with an unusual fused tetracyclic structure, obtained in ca. 80 % yield. A combined yield for both products was up to 95 %. Styrene oxide can be also used as a starting material for these reactions to give the same products in up to 85 % combined yield. A novel one-pot tandem process thus developed involves the isomeri- zation of styrene oxide into phenylacetaldehyde and cycloaddition of the latter to the monoterpene, with both steps being catalyzed by CsPW. The reactions were performed in green solvents diethylcarbonate or anisole, which have high sustainability ranks in modern solvent selection guides, comparable to those of ethanol and water.
Heteropoly acid catalysis for the isomerization of biomass-derived limonene oxide and kinetic separation of the trans-isomer in green solvents.
(2019) Cotta, Rafaela Ferreira; Martins, Rafael; Pereira, Matheus Mello; Rocha, Kelly Alessandra da Silva; Kozhevnikova, Elena Fedorovna; Kozhevnikov, Ivan V.; Gusevskaya, Elena Vitalievna
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 in upgrading of biorenewables : cycloaddition of aldehydes to monoterpenes in green solvents.
(2017) Cotta, Rafaela Ferreira; Rocha, Kelly Alessandra da Silva; Kozhevnikova, Elena Fedorovna; Kozhevnikov, Ivan V.; Gusevskaya, Elena Vitalievna
Acidic Cs salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40 (CsPW), is excellent solid acid catalyst for liquid-phase cycloaddition reactions of biomass-based and easily available from essential oils monoterpenic compounds, such as limonene, α-terpineol, α-pinene, β-pinene and nerol, with aldehydes, including benzaldehyde, crotonaldehyde as well as biomass-derived cuminaldehyde and trans-cinnamaldehyde. The reactions give oxabicyclo[3.3.1]nonene compounds potentially useful for the fragrance and pharmaceutical industries in good to excellent yields. The process is environmentally benign and can be performed in biomass-derived solvent 2-methyltetrahydrofuran and eco-friendly “green” organic solvents such as dimethylcarbonate and diethylcarbonate under mild conditions at low catalyst loadings without leaching problems. The solid CsPW catalyst can be easily separated from the reaction media and low-boiling solvents can be removed by distillation. Silica-supported H3PW12O40 also demonstrated good performance in these reactions.