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 (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.
The reactions of ammonium salts of dialkyldithiophosphate ligands, (RO) 2 PS 2 y NH 4 q (RsMe/Et), with Ru III Cl 3 P3H 2 O in methanol solvent and under N 2 atmosphere result in one-electron paramagnetic tris complexes {(RO) 2 PS 2 } 3 Ru III (1) in the solid state. The molecular structures of both complexes were determined by single-crystal X-ray diffraction. This shows the expected pseudo-octahedral geometry with reasonable strain due to the presence of a four-membered chelate ring. The reflectance spectra of the solid complexes display two bands in the range 596-476 nm and in the solid state the complexes exhibit one isotropic EPR signal at 77 K. Although the complexes 1 are stable in the solid state, in solution the complexes are transformed selectively into the diamagnetic and electrically non-conducting sulfur-bridged dimetallic species [{(RO) 2 PS 2 } 2 Ru IV (m-S) 2 Ru IV {S 2 P(OR) 2 } 2 ]. The formation of dimeric species in the solution state is authenticated by the electrospray mass spectrum of one representative complex where RsEt (1b). In dichloromethane solution the complexes show two moderately strong sulfur to ruthenium charge-transfer transitions in the range 514-419 nm, and two strong ligand based transitions in the UV region. The complexes exhibit two successive reversible reductions in the ranges 1.01™0.91 V and y0.44™y0.49 V versus SCE corresponding to Ru IV -Ru IV /Ru III -Ru III and Ru III -Ru III /Ru II -Ru II couples respectively. Electrochemically or chemically generated first step reduced complexes [{(RO) 2 PS 2 } 2 Ru III (m-S) 2 Ru III {S 2 P(OR) 2 } 2 ] 2y display two ligand to metal charge-transfer transitions in the visible region and in the complexes the two one-electron paramagnetic metal centers (low-spin Ru III , ,Ss1/2)are antiferromagnetically coupled.
t 2gThe second step reduced species [{(RO) 2 PS 2 } 2 Ru II (m-S) 2 Ru II {S 2 P(OR) 2 } 2 ] 4y are observed to be very unstable.
Leaching of active species is one of the major causes of catalyst deactivation. The accumulation of this leached species as chemical waste can be detrimental to the environment. In this study, a series of environmentally benign core-shell catalysts of type Bi 2 O 3 @mSiO 2 were synthesized to address these issues. The catalysts, varying in silica content and shell thickness, were characterized and evaluated for Friedel-Crafts benzoylation. Amongst them, Bi-4 (containing 71.8 % Bi 2 O 3 ), having shell thickness of ∼ 42 nm, showed the best response under optimized conditions. Textural analysis of Bi-4 confirmed the mesoporous nature of shell, with average pore diameter of ∼ 40 Å and surface area of 62 m 2 /g. During the reaction, the Bi 2 O 3 core was converted to BiOCl, which was easily recycled back to its original form. No leaching or any loss in catalytic activity was observed for the recycled catalyst during reuse. Thus, an inexpensive, reusable and environmentally benign catalyst is proposed.
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