Molybdenum heteropolyadids with Keggin structure, doped with bismuth and vanadium, as acid and redox catalyst

P.G. VÁZQUEZ; V. PALERMO; A.G. SATHICQ; H.J. THOMAS; G.P. ROMANELLI

San Juan

Congreso; 43rd World Chemistry Congress IUPAC 2011; 2011

Keggin heteropolyacids (HPAs) are known as bifunctional catalysts in which redox and acid properties can be tuned by variation of addenda transition metal atoms. We report the synthesis of H4PMo11VO40, H6PMo11BiO40, and H5PMo11V0.5Bi0.5O40 by hydrothermal treatment using a stoichiometric mixture of MoO3, H3PO4, and the corresponding metal oxide suspended inwater. These solids were characterized by thermal analysis, potentiometric titration, 31P-NMR, UV-visible, and FT-IR spectra.Furthermore, the catalytic performance of synthesized HPAs were tested in two kind of reaction: solvent-free multicomponent synthesis of dihydropyrimidinones by the Biginelli method (acid catalysis), and selective oxidation of sulfides to sulfoxides and/or sulfones, using ethanol as solvent and hydrogen peroxide as oxidant (redox catalysis). The incorporation of V, Bi, and Bi-V into the primary structure of PMo increases the catalytic activity in both reactions. The two catalysts containing vanadium were found to be the most active, and they were supported on aminopropyl-functionalized silica, in order to turn them into heterogeneous catalysts. Thereby, the two new catalysts resulted being efficient, ecofriendly, and recyclable for the selective oxidation of diphenylsulfide to the corresponding sulfoxide/sulfone. For the Biginelli synthesis, a correlation between the yields of the dihydropyrimidinones and the acidic site amount of the catalysts was observed, and again the vanadium HPAs showed the best performance. All catalysts can be recycled without loss of the catalytic activity.