Microwave-assisted molybdenum-catalysed epoxidation of olefins

resumo

The performance of CpMo(CO)(3)CH(3) as a catalyst precursor in the epoxidation of cis-cyclooctene and R-(+)-limonene with tert-butylhydroperoxide (TBHP), at 55 degrees C, was investigated for the first time using microwave (MW)-assisted heating, and the results were compared with those obtained using conventional heating with a thermostated oil bath (OB). The reactions were carried out under monophasic (no co-solvent, or with 1,2-dichloroethane, toluene, hexane) or biphasic liquid-liquid (using the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF(4)]) conditions. The heating methods did not affect product selectivity: 100% to cyclooctene oxide, and 93% to limonene oxide (66-72% diastereomeric excess, trans-1,2-(+)-limonene oxide) at 80% limonene conversion. However, the initial reaction rates strongly depend on the applied heating method. The favourable MW effect is essentially due to the faster heating up of the reaction mixture increasing the overall epoxidation rate in the early stage of the heating process, which is supported experimentally by a comparison of (i) the measured temperature vs time curves, (ii) the kinetic data for the MW method with that for the OB method where the reagents and reactor walls are pre-heated (OB-preH method), and (iii) the estimated apparent activation energies and pre-exponential factors for the two olefins using the MW, OB, and OB-preH methods. The crystal structure of the molybdenum tricarbonyl catalyst precursor was unveiled from single-crystal X-ray diffraction studies at 150K. The complex crystallises as a racemic twin in the monoclinic P2(1) space group. (c) 2010 Elsevier B.V. All rights reserved.

palavras-chave

CAMBRIDGE STRUCTURAL DATABASE; MAIN-GROUP ELEMENTS; HYDROGEN-PEROXIDE; ORGANIC-SYNTHESIS; IONIC LIQUIDS; TRICARBONYL COMPLEX; CARBONYL-COMPLEXES; CRYSTAL-STRUCTURES; TRANSITION-METALS; INDENYL LIGANDS

categoria

Chemistry

autores

Abrantes, M; Neves, P; Antunes, MM; Gago, S; Paz, FAA; Rodrigues, AE; Pillinger, M; Goncalves, IS; Silva, CM; Valente, AA

nossos autores

agradecimentos

We are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT, Portugal), POCI 2010, OE and FEDER for funding through the projects PTDC/QUI/65427/2006 and PTDC/QUI/71198/2006, and for financial support towards the purchase of the single-crystal diffractometer.

Partilhe este projeto

Publicações similares

Usamos cookies para atividades de marketing e para lhe oferecer uma melhor experiência de navegação. Ao clicar em “Aceitar Cookies” você concorda com nossa política de cookies. Leia sobre como usamos cookies clicando em "Política de Privacidade e Cookies".