Acetalization of aldehydes and ketones over H4[SiW12O40] and H4[SiW12O40]/SiO2

Abstract

H₄[SiW₁₂O₄₀] (H-SiW₁₂) is demonstrated to be able to efficiently catalyze the acetalization of aldehydes and ketones with ethylene glycol and 1,3-propanediol. Nevertheless, the possible leaching and the recycling of H-SiW₁₂ are two major disadvantages that largely restrict its further application in industry. Moreover, H₄[SiW₁₂O₄₀] tends to deactivate strong proton sites due to the small surface area of 10 m² g⁻¹. Due to interactions with surface silanol groups, the proton sites of polyoxometalates (POMs) on SiO₂ are less susceptible to deactivation. As such, immobilization of H₄[SiW₁₂O₄₀] onto SiO₂ leads to the heterogeneous catalyst H₄[SiW₁₂O₄₀]/SiO₂ (H-SiW₁₂/SiO₂), which can catalyze the acetalization of aldehydes and ketones with ethylene glycol and 1,3-propanediol selectively and efficiently without the need of a drying agent. The acetalization process can proceed smoothly at a relatively low temperature under solvent-free conditions. The catalyst of H₄[SiW₁₂O₄₀]/SiO₂ can be recycled at least ten times without an obvious decrease in its catalytic activity. As far as we know, the TONs of the H-SiW₁₂/SiO₂-catalyzed acetalization of cyclohexanone with ethylene glycol, and benzaldehyde with 1,3-propanediol are the highest reported so far.