DEQUI - Departamento de Química
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Navegando DEQUI - Departamento de Química por Assunto "Acid catalysis"
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Item 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 VitalievnaThe 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.Item 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 VitalievnaAcidic 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.Item Heteropoly acid catalysts in the valorization of the essential oils : acetoxylation of b-caryophyllene.(2010) Rocha, Kelly Alessandra da Silva; Rodrigues, Nathália V. S.; Kozhevnikov, Ivan V.; Gusevskaya, Elena VitalievnaH3PW12O40 (PW), the strongest heteropoly acid in the Keggin series, is an active and environmentally friendly catalyst for the liquid-phase conversion of b-caryophyllene (1) to b-caryolanyl acetate (2) in homogeneous and heterogeneous systems. An efficient and clean method for the synthesis of 2, providing amixture containing two stereoisomeric b-caryolanyl acetates 2a and 2b, 2a/2b = 80/20 mol/ mol, with 100% GC yield, has been developed using PW as a homogeneous catalyst under mild reaction conditions. The reaction occurs at 25 8C with a catalyst turnover number of 2000. The catalyst can be recovered without neutralization and reused without loss of activity and selectivity.Item Isomerization of styrene oxide to phenylacetaldehyde over supported phosphotungstic heteropoly acid.(2010) Costa, Vinícius Vieira; Rocha, Kelly Alessandra da Silva; Kozhevnikov, Ivan V.; Gusevskaya, Elena VitalievnaSilica-supported H3PW12O40 (PW), the strongest heteropoly acid in the Keggin series, is an efficient, environmentally friendly heterogeneous catalyst for the liquid-phase isomerization of styrene oxide into phenylacetaldehyde, an industrially important intermediate for fine chemical synthesis. The reaction occurs in cyclohexane as a solvent under mild conditions at 25–70 ◦C with low catalyst loadings and without PW leaching in solution. At 60 ◦C, the yield of phenylacetaldehyde reaches 92% at 97% styrene oxide conversion, with a catalyst turnover number of 19 600. The catalyst can be recovered and reused.Item Phosphotungstic heteropoly acid as efficient heterogeneous catalyst for solvent-free isomerization of a-pinene and longifolene.(2009) Rocha, Kelly Alessandra da Silva; Robles Azocar, Patrícia Alejandra; Kozhevnikov, Ivan V.; Gusevskaya, Elena VitalievnaSilica-supported H3PW12O40 (PW), the strongest heteropoly acid in the Keggin series, is an efficient, environmentally friendly heterogeneous catalyst for the liquid-phase isomerization of a-pinene and longifolene into their more valuable isomers – camphene and isolongifolene, respectively, which are intermediates in the synthesis of expensive fragrances. The reactions occur under solvent-free conditions in the temperature range of 80–100 8C, with low catalyst loadings (0.15–5 wt%) and high turnover numbers (up to 6000 per proton). The catalyst can be easily recovered and reused. No PW leaching is observed in the reaction system.