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

Publisher： John Wiley & Sons Inc

E-ISSN： 2365-6549|3|7|1967-1975

ISSN： 2365-6549

Source： ChemistrySelect, Vol.3, Iss.7, 2018-02, pp. : 1967-1975

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Abstract

AbstractA 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 (ICP‐AES) 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 m²/g of Fe‐0. Differential scanning calorimetry and thermogravimetric analysis (DSC‐TGA) found catalyst Fe‐2 to be stable till 600°C. 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.