Gold-catalyzed oxidation of substituted phenols by hydrogen peroxide

Cheneviere, Yohan Caps, Valerie Tuel, AlainGold nanoparticles deposited on inorganic supports are efficient catalysts for the oxidation of various substituted phenols (2,6-di-tert-butyl phenol and 2,3,6-trimethyl phenol) with aqueous hydrogen peroxide. By contrast to more conventional catalysts such as Ti-containing mesoporous silicas, which convert phenols to the corresponding benzoquinones, gold nanoparticles are very selective to Wary! compounds (3,3',5,5'-tetra-tert-butyl diphenoqui none and 2,2',3,3',5,5'-hexamethy1-4,4'-biphenol, respectively). Products yields and selectivities depend on the solvent used, the best results being obtained in methanol with yields >98%. Au offers the possibility to completely change the selectivity in the oxidation of substituted phenols and opens interesting perspectives in the clean synthesis of biaryl compounds for pharmaceutical applications. (C) 2010 Elsevier B.V. All rights reserved

Synthesis and catalytic properties of TS-1 with mesoporous/microporous hierarchical structures obtained in the presence of amphiphilic organosilanes

Cheneviere, Yohan Chieux, Frederic Caps, Valerie Tuel, AlainTitanosilicates TS-1 with mesoporous/microporous hierarchical structures have been synthesized in the presence of an organosilane surfactant. Highly porous crystals, with regular pores of ca. 2.5-3.5 nm diameter, are obtained under hydrothermal conditions similar to those used for the preparation of conventional catalysts. The organosilane has a great influence on the textural properties of TS-1, but does not significantly affect the amount and coordination of Ti species in the framework. Mesoporous TS-1 have been used as catalysts in various oxidation reactions with an aqueous H2O2 and their activity has been compared with those of a conventional TS-1 and a mesoporous amorphous TiMCM-41. Data show that mesoporous TS-1 does not possess the expected properties for hierarchical catalysts, i.e. the properties of the conventional catalysts with advantages of mesoporous solids. In particular, the gain in diffusion due to intracrystalline mesopores is totally inhibited by the increase of the hydrophilic character of the zeolite, resulting from very high silanol group populations on the external surface. (c) 2009 Elsevier Inc. All rights reserved