A Facile One-Pot Transformation of Aromatic Aldehydes/Ketones to Amides: Fe2O3@SiO2 as an Environmentally Benign Core-Shell Catalyst

摘要

A one-pot conversion of aldehydes and ketones to amides via atom-efficient Beckmann rearrangement over modified Fe2O3 (hematite) has been investigated. A series of core-shell catalysts were prepared having Fe2O3 core and SiO2 shell by encapsulation of Fe2O3 with varying amounts of silica and characterized. Transmission electron microscopy (TEM) of catalysts showed that silica shell thickness increased from 10 nm to 39 nm, while inductively coupled plasma atomic emission spectroscopy (ICPAES) determined that percent composition of Fe2O3 correspondingly decreased from ~83% to 59%. Due to silica encapsulation, leaching of the catalytic species was minimized from ~20% for Fe-0 (100% Fe2O3) down to ~10% for Fe-4 (59% Fe2O3, 41% SiO2). Among the catalysts, Fe-2 (71.3% Fe2O3, 28.7% SiO2) showed the best catalytic response for amide formation under optimized reaction conditions. The Brunauer Emmett Teller (BET) surface area of Fe-2 increased to 50 m2/g as compared to 34 m~2/g of Fe-0. Differential scanning calorimetry and thermogravimetric analysis (DSC-TGA) found catalyst Fe-2 to be stable till 600 ℃. The catalyst Fe-2 could be reused five times with good yield of the amide and no loss in catalytic activity. Using optimized conditions, the one-pot transformation of aldehydes to primary amides and ketones to secondary amides was efficiently carried out by the catalyst Fe-2. Thus an inexpensive, reusable and environmentally benign solid acid core-shell catalyst Fe2O3@SiO2 is proposed.