One-pot synthesis of alkyl levulinates from biomass derivative carbohydrates in tin(II) exchanged silicotungstates-catalyzed reactions

Biomass is an attractive source of carbohydrates that can be converted to fuels and fine chemicals. Acid-catalyzed alcoholysis of biomass derivatives provides alkyl levulinates, which are fuel bioadditives, intermediates in the synthesis of drugs and agrochemicals. In this work, we developed a one-pot route to obtain alkyl levulinates using Sn(II) exchanged Keggin heteropolyacids (i.e., H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, and H₄SiW₁₂O₄₀) as catalysts, in alcoholysis reactions of various carbohydrates. All the catalysts were characterized by FT-IR, XRD, EDS/SEM, TG/DSC, and BET analysis. The tin(II) silicotungstate was the most active and selective catalyst. After 2 h of reaction carried out at 423 K, an almost complete conversion was achieved on the ethanolysis of the fructose, sucrose and inulin, which gave high yields of ethyl levulinate (ca. 78, 71 and 61 mol%, respectively). In all reactions, 5-ethoxymethylfurfural was always the secondary product. Maltose, galactose, and glucose were almost unreactive. The effects of main parameters of reaction, such as temperature, catalyst load, and type of alcohols were assessed. The Sn₂SiW₁₂O₄₀ catalyst was easily recovered and successfully reused for 7 cycles, without loss activity.