Iron Oxide Encapsulated by Ruthenium Hydroxyapatite as Heterogeneous Catalyst for the Synthesis of 2,5‐Diformylfuran

Abstract Magnetic γ‐Fe 2 O 3 nanocrystallites encapsulated by hydroxyapatite (HAP), HAP @ γ‐Fe 2 O 3 , were prepared followed by cation exchange of Ca 2+ on the external HAP surface with Ru 3+ to give the γ‐Fe 2 O 3 @ HAP‐Ru catalyst. The structure of the as‐prepared catalyst was characterized, and its catalytic activity was studied in the aerobic oxidation of 5‐hydroxymethylfurfural (HMF). γ‐Fe 2 O 3 @ HAP‐Ru showed a high catalytic activity for the aerobic oxidation of HMF into 2,5‐diformylfuran (DFF). A high DFF yield of 89.1 % with an HMF conversion of 100 % was obtained after 4 h at 90 °C. Importantly, the synthesis of DFF from fructose was realized by two consecutive steps. The dehydration of fructose in the presence of a magnetic acid catalyst (Fe 3 O 4 @SiO 2 SO 3 H) produced HMF in a yield of 90.1 %. Then the Fe 3 O 4 @SiO 2 SO 3 H catalyst was removed from the reaction solution with a permanent magnet, and HMF in the resulting solution was further oxidized to DFF with a yield of 79.1 % based on fructose. The synthesis of DFF from fructose by two steps avoids the tedious separation of the intermediate HMF, which saves time and energy.