Heterogenization of alkene epoxidation catalysts

Abstract

Este trabalho descreve nosso esforço em heterogeneizar catalisadores para epoxidação. Tanto o molibdênio ancorado quanto o engaiolado pelo método de sol-gel mostraram grande seletividade, mas possuem suas atividades fortemente reduzidas. Por outro lado, silicatos de molibdênio foram muito ativos e estáveis até a formação de diols na mistura reacional. Catalisadores heterogeneizados de rênio foram menos ativos, mas permitiram o uso do peróxido de hidrogênio anidro como oxidante. Contudo, o alto custo e a dificuldade de regeneração impedem a aplicação industrial destes catalisadores. Durante estas investigações, descobrimos que a alumina sozinha é ativa para epoxidação com peróxido de hidrogênio anidro, fornecendo boas conversões para epóxidos com alta seletividade. Mais pesquisa é necessária para esclarecer a natureza dos grupos hidroxilas responsáveis pela atividade catalítica, para produzir materiais que permitem a obtenção de epóxidos com alta seletividade em condições industriais.This account describes our efforts to heterogenize epoxidation catalysts. Anchored and sol-gel entrapped molybdenum were shown to be very selective, but had a strongly reduced activity. On the other hand, molybdenum silicates were very active and stable as long as no diols were present in the reaction mixture. Heterogenized rhenium catalysts were less active but allowed the use of anhydrous hydrogen peroxide as oxidant. However, the high cost and difficult regeneration prevents the industrial use of these catalysts. During these investigations, we found that alumina alone is active in the epoxidation with anhydrous hydrogen peroxide, giving good conversions to epoxides with high selectivity. More research is needed in order to clarify the nature of the hydroxyl groups responsible for its catalytic activity and thus to produce an appropriate material which would allow the obtention of epoxides with high selectivity under industrial conditions.

Methyltrioxorhenium and its applications in olefin oxidation, metathesis and aldehyde olefination

“…Alternative strategies to improve MTO-catalyzed oxidations have made use of host-guest inclusion chemistry [74][75][76][77][78][79][80][81]. It was found that an urea/hydrogen peroxide (UHP) complex is a very effective oxidant in heterogeneous olefin epoxidations and silane oxidations catalyzed by MTO [74].…”

Green Synthesis of Carvenone by Montmorillonite-Catalyzed Isomerization of 1,2-Limonene Oxide

“…dihydrocarvone [3,4] and 1,2-limonene oxide. Because the latter compound is easily prepared from naturally available limonene [5], the interest for direct syntheses of carvenone from 1,2-limonene oxide has been increasing [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. However, most of the related reports showed that the selectivity towards carvenone was not good as expected.…”

In situ grafting of cyclopentadienyl-molybdenum complexes on mesoporous materials: The reaction of [η5-CpMo(CO)3]−Na+ with surface fixed iodo-benzyl siloxane

“…Nevertheless, in the latter case problems are described to have occurred during the catalytic reactions, such as swelling or leaching of the active species in the organic solution phase. Another strategy for the confinement of metal centres in mesoporous silicates is the covalent attachment of organometallic or coordination compounds to form hybrid materials [39][40][41][42][43]. Recently, modified MCM-41 and MCM-48 materials were synthesized by grafting MoO 2 X 2 (X = Cl, Br) and CpMo-(CO) 3 Cl, the latter being quite efficient homogeneous epoxidation catalysts [23][24][25][26]43].…”

“…Recently, modified MCM-41 and MCM-48 materials were synthesized by grafting MoO 2 X 2 (X = Cl, Br) and CpMo-(CO) 3 Cl, the latter being quite efficient homogeneous epoxidation catalysts [23][24][25][26]43]. Additionally, surfacefixed bidentate Lewis bases have been used to bind Mo(VI) complexes as described by Gonçalves et al [44][45][46][47][48] and, independently, by Thiel et al [49][50][51] Silylation using Me 3 SiCl to remove residual Si-OH groups, which was considered to be favourable for the catalytic reaction on the surface of the mesoporous material [39][40][41][42], reduced the catalyst leaching significantly [49][50][51].…”