resumo
The organotin-oxomolybdate coordination polymers [(R3Sn)(2)MoO4]-nH(2)O (R=methyl, n-butyl, cyclohexyl, phenyl, benzyl) were tested as catalysts for the liquid-phase epoxidation of cyclooctene with 30% aqueous hydrogen peroxide at 35 degrees C and atmospheric pressure. Water, acetonitrile and dichloromethane were examined as additional co-solvents for the reaction. The catalytic results vary considerably with the nature of the tin-bound R group and the co-solvent. For all systems, cyclooctene oxide was the only observed reaction product. Apart from the trimethyltin derivative, the best results were obtained without additional co-solvent or with CH2Cl2, While addition of water or CH3CN had a detrimental effect on catalytic performance. The highest turnover frequency (46 mol mol(Mo)(-1) h(-1)) was obtained for the system containing the tri-n-butyltin derivative as catalyst and CH2Cl2 as solvent. Complete conversion of the substrate was achieved for this system within 4 h. Using water instead of CH2Cl2 with the n-butyl catalyst reduced the catalytic activity considerably at the beginning of the reaction, although 91% conversion was achieved after 24 h. The behavior of the trimethyltin derivative was atypical in that conversion of cyclooctene was only possible when CH3CN was used as the co-solvent. Experiments were also carried out using a urea/hydrogen peroxide adduct as a water-free source of H2O2. However, the catalytic activities observed were significantly lower than those obtained using aqueous H2O2. (c) 2004 Elsevier B.V. All rights reserved.
palavras-chave
UREA-HYDROGEN-PEROXIDE; SELECTIVE EPOXIDATION; OXIDATION; SULFOXIDATION; MECHANISM; KINETICS; ALKENES; SOLVENT; ADDUCT
categoria
Chemistry
autores
Abrantes, M; Valente, AA; Goncalves, IS; Pillinger, M; Romao, CC
nossos autores
Anabela Tavares Aguiar Valente
Investigador Principal
Isabel Maria de Sousa Gonçalves
Professor associado