resumo
The preparation and characterization (FT-IR, FT-Raman, B-11 MAS NMR, diffuse reflectance, elemental analysis) of a novel boron peroxotungstate (BTBA)(4)H[BW4O24] (BTBA = benzyltributylammonium) is reported, along with its use in the homogeneous oxidation of cis-cyclooctene, geraniol, linalool and (-)-carveol with H2O2 as oxidant and acetonitrile as solvent. High catalytic activity was registered for all the substrates studied under homogeneous conditions, namely 99% of conversion of geraniol after 2 h, 93% for linalool after 5 h, 74% for cis-cyclooctene after 6 h, and 100% for (-)-carveol after 2 h of reaction. Some oxidation studies were carried out with the Venturello complex, [PW4O24](3-), in the same conditions. Furthermore, the boron peroxotungstate (BW4) was immobilized using two different strategies: (a) BW4 anchored into a functionalized silica (aptesSiO(2)) giving BW4@aptesSiO(2) and (b) BW4 encapsulated on a metal organic framework, commonly referred as MIL-101, giving BW4@MIL-101. The catalytic activity of both heterogeneous materials was investigated for geraniol oxidation and the results were compared with those obtained with BW4 under homogeneous conditions. The encapsulated boron peroxotungstate (BW4@MIL-101) gave rise to the best results, reaching complete conversion of geraniol after 3 h of reaction and 78% selectivity for 2,3-epoxygeraniol. Additionally, this heterogeneous catalyst could be reused without appreciable loss of catalytic activity, affording similar 2,3-epoxygeraniol selectivity. The heterogeneous catalysts' stability was also investigated after the oxidation reactions by different characterization techniques. (C) 2012 Elsevier B. V. All rights reserved.
palavras-chave
HYDROGEN-PEROXIDE; SELECTIVE OXIDATION; ALLYLIC ALCOHOLS; DINUCLEAR PEROXOTUNGSTATE; MODIFIED SILICA; EPOXIDATION; MONOTERPENES; TUNGSTEN; OLEFINS; H2O2
categoria
Chemistry; Engineering
autores
Santos, ICMS; Balula, SS; Simoes, MMQ; Cunha-Silva, L; Neves, MGPMS; de Castro, B; Cavaleiro, AMV; Cavaleiro, JAS
nossos autores
Ana Maria Vieira Silva Viana Cavaleiro
Professor Catedrático
Isabel Cristina Maia da Silva Santos Vieira
Investigador Júnioragradecimentos
Special thanks are due to Professor Joao Rocha for his help with 11B MAS NMR and to Dr. Rosario Domingues for the MALDI-MS spectra. Thanks are due to Fundacao para a Ciencia e a Tecnologia (FCT, Portugal) and FEDER for funding QOPNA through the Project PEst-C/QUI/UI0062/2011, for REQUIMTE financial support through the project PEst-C/EQB/LA0006/2011, and for CICECO financial support, and the R&D project PTDC/CTM/100357/2008.