Trivalent Metal Cation Exchanged-Phosphotungstic Acid Salts: Efficient Catalysts for the Oxidation of Geraniol with Hydrogen Peroxide

Abstract In this work, we have assessed the activity of various trivalent metal cations exchanged-phosphotungstic acid salts in oxidation reactions of geraniol using a green oxidant (i.e., hydrogen peroxide). A series of metal salts with general formulae MPW 12 O 40 (M 3+ = Ga, Al, In, Fe, Al, and In) was synthesized and evaluated as catalysts in the hydrogen peroxide oxidation of terpene alcohols, having geraniol as a model molecule. To understand how the nature of the metal cation impacts its activity, the main reaction parameters were assessed in reactions catalyzed by different heteropoly salts. Among the metal salts assessed, the most active and selective catalyst was the iron phosphotungstate. All the metal phosphotungstates were characterized by FT-IR, TG/DSC, BET, XRD, SEM-EDS, and potentiometric titration analyses. Besides geraniol, nerol, linalool, and β-citronellol were also successfully oxidized. Special attention was devoted to correlating the properties of catalysts with their activity. Iron(III) phosphotungstate was an efficient and recyclable catalyst, achieving high conversion (> 90%) and selectivity to epoxide (> 90%) in the oxidation of geraniol with a green oxidant (hydrogen peroxide). Graphical Abstract