Estereo e sitio seletividade da epoxidação de diferentes terpenos com AI2O3 obtida via sol-gel / Stereo and site selectivity in the epoxidation of terpenes with alumina obtained the sol-gel process

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

Alumina was synthesized from aluminum tri(sec-butoxide) hydrolysis and condensation in an acid environment using the sol-gel process. The resulting material was characterized by TGA, CHN, and RXD, which indicated the acquisition of boehmite structure after the slow drying process of the solvent and g-alumina structure after 9 h of calcination at up to 400 °C. The catalytic activity of this material was tested in the epoxidation of terpenes using anhydrous or aqueous hydrogen peroxide as oxidants. Selectivity of 98% and conversions of up to 40% were obtained for the (S)-limonene epoxides, producing 9 g of epoxides per gram of alumina. For citronellal, 60% conversion and 65% of selectivity for epoxides was obtained under anhydrous conditions. Citral epoxidation occurred with 41% conversion, generating the monoepoxide with the oxygen bound to carbons 2 and 3, with 60% selectivity. Under anhydrous conditions, the reaction with linalool generated, with 71% conversion, the 6,7-monoepoxide with 67% selectivity. (1S)-(a)-pinene oxidation formed the epoxide with around 60% selectivity and 30% conversion. Citronellol epoxidation resulted in 47% conversion and 73% selectivity for the epoxide. Recycling experiments showed that, although the presence of water reduces the activity of the catalyst, it guarantees that the activity loss between the cycles, resulting from the absorption of molecules at the solid s surface, is smaller as a result of the beneficial effect of water in the reactivation of the catalytic sites. The products obtained in the reactions, analyzed by GC-FID, GC-MS and Eletrospray, indicate that the interactions occur preferably between the terpene´s HOMO and the peroxide s LUMO in the formation of the epoxidation products.

ASSUNTO(S)

alumina epoxidação terpenos terpenes sol-gel sol-gel epoxidation

ACESSO AO ARTIGO

Documentos Relacionados