Effective acetalization of furfural catalyzed by Fe‐ and Co‐oxalates: impact of alcohols structure on products composition

Abstract Fe‐, Co‐, and FeCo‐oxalates supported on silica gel (5 wt% metal load) were synthesized, characterized, and tested for the first time in solvent‐free furfural (FF) acetalization with C1–C8 alcohols at 70–170 °C under both conventional and microwave (MW)‐assisted conditions. The interaction of FF with linear C1–C4 alcohols yielded pincer‐shaped furfuryl diacetals, whereas reactions with linear C5–C8 alcohols produced only hemiacetals. This behavior was attributed to steric hindrance from the longer carbon chains of the C5–C8 alcohols. Overall, process performance slightly depended on the alcohol chain length, decreasing progressively with increasing carbon number; nevertheless, FF conversion (65–75%) and selectivity (80–85%) remained consistent across all alcohols. In reactions with sterically hindered alcohols such as 2‐propanol, cyclohexanol, and i‐butanol, FF conversion dropped dramatically, highlighting the strong influence of stereochemistry on catalytic performance. All catalysts exhibited both Brønsted and Lewis acidic sites in roughly equal proportions, and their activities were comparable, indicating a significant role of the metal cations in governing the reaction. Calcination of the supported metal oxalates – particularly Fe‐based catalysts – in oxygen‐containing atmospheres at temperatures ≥150 °C led to a marked decrease in activity, attributed to decomposition of the oxalate component under these conditions. Notably, MW irradiation significantly shortened the acetalization reaction time by 3–4 times without compromising FF conversion or selectivity, demonstrating the potential of this approach for more efficient and sustainable catalytic processes.