Oxidação aeróbica de olefinas alil aromáticas catalisada por paládio e do álcool benzílico catalisada por nanopartículas de ouro

Abstract

Palladium-catalyzed aerobic oxidation of naturally occurring allyl benzenes, i.e., eugenol, methyleugenol, safrole, and estragole, in dimethylacetamide/water solutions under mild conditions (510 atm, 2560 oC) has been developed, in which palladium(II) chloride isused in the absence of co-catalysts or special stabilizing ligands as the sole and recyclable catalyst. Corresponding methyl ketones have been obtained in good to excellent yields with low catalyst loadings (12 mol%) and high average turnover frequencies (up to 20 h-1). The minor products of these reactions are corresponding aldehydes, i.e., vanillin, methylvanillin, piperonal, and p-anisaldehyde, which are also useful compounds important for flavor and/or pharmaceutical industries. This simple catalytic method represents ecologically benign and economically attractive route to valuable fragrance compounds starting from renewablesubstrates easily available from essential oils. In addition, several new materials, consisting of gold nanoparticles supported on pure hexagonal mesoporous silica (HMS) or HMS modified by metals (iron, titanium and cerium), have been tested as catalysts in the oxidation of benzyl alcohol with molecular oxygen. This reaction gives only two major products, benzaldehyde and methyl benzoate, with a virtually quantitative combined yield and turnover numbers of up to 4300 (moles of the products permole of gold). The doping metal has a remarkable effect on the stability of the supported gold catatalysts. The materials containing cerium and titanium in the structure are the most stable ones. This work is very relevant both from scientific and industrial point of view, because theinterest to catalytic reactions promoted by gold nanoparticles grows up exponentially in the last years due to the advancement of Green Chemistry.