Organic transformations catalyzed by gold nanoaparticles supported on functionalized silica

Recently, we presented the preparation, without any need of additional reducing and/or stabilizing agents, of a variety of stable silica-supported gold nanoparticles (AuNPs) by using as the only reactants an aqueous solution of chloroauric acid (HAuCl4) and different functionalized-silica supports. We started using commercial polyethyleneimine-functionalized silica bead and we went on preparing silica nanoparticles with alkynyl carbamate moieties. We now present the results of our recent work with supported AuNPs, which has been focused on the synthesis of a material with the right features for the application as catalyst in a continuous flow system. Indeed, flow chemistry is recognized by the Green Chemistry Institute (GCI) as a key area for research activities in the aim of developing sustainable manufacturing. The silica-supported AuNPs have been prepared by the simple grafting of commercial available silica with the alkyne terminated organosilane [3-(2-propynylcarbamate)propyl]triethoxysilane (PPTEOS), followed by the addition of HAuCl4 to obtain the in situ formation of the target AuNPsanchored systems. The resulting material (Au/SiO2@Yne) has been characterized with various techniques, such as atomic absorption spectroscopy (AAS), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Afterwards, Au/SiO2@Yne has been employed as heterogeneous catalyst in the oxidation of alcohols to their corresponding carbonyl compounds. The reaction conditions have been chosen with particular attention to the green aspect, therefore the oxidation have been carried out using a mixture of tert-butanol and water as solvent and hydrogen peroxide as the oxidant agent.