Oxidação aeróbica de olefinas catalisada por metais de transição

Abstract

[Alfa]-Ionone and [beta]-ionone, bio-renewable substrates available from various essential oils and also produced synthetically in large scale, were selectively oxidized by molecular oxygen using the chloride-free Pd(OAc)2/p-benzoquinone catalytic system. 13-lonone was converted in one major product, whereas -ionone gave three isomeric products, all resulting from the allylic oxidation of their sterically encumbered endocyclic double bonds. In both substrates only one of two olefinic bonds was involved in the reaction. The process operates with an efficient dioxygen coupled catalytic turnover under 5-10 atm of oxygen pressure, in the absence of conventionally used metal redox-active co-catalysts. Alternatively, the reactions can be efficiently conducted under atmospheric pressure in the presence of Cu(OAc)2 to assist at the regeneration of p-benzoquinone by molecular oxygen. Highly functionalized terpenoid allylic acetates obtained in the present work are useful as ingredients of synthetic perfumes, cosmetics and pharmaceuticals due to their pleasant scents and therapeutic potential. In a second moment, silica matrices sol-gel (SG) and MCM-41 were incorpored with the transition metals Cr, Ce and Co and used as heterogeneous catalysts in the liquid phase oxidation of 13-ionone. The Cr/SG and Co/SG catalysts were prepared by the sol-gel method incorporating the metal during the preparation and thermally treated at 900 °C. The Ce/MCM-41, Cr/MCM-41 and Co/MCM-41 catalysts were also designed with the incorporation of metal in the mesoporous silica structure MCM-41. In the present work, two main products of the oxidation of I3-ionone, as a result of the epoxidation and allyl oxidation of the endocyclic olefinic bond, were obtained in a combined yield of up to 90%.