Insight into the active sites for the Beckmann rearrangement on porous solids by in situ infrared spectroscopy

Accessibility and Interaction of Surface OH Groups in Microporous and Mesoporous Catalysts Applied for Vapor-Phase Beckmann Rearrangement of Oximes

“…Environmentally benign new processes base on the vaporphase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam on solid catalysts [4,5]. For the vaporphase Beckmann rearrangement reaction, various zeolites, such as silicalite-1 [6], [B]ZSM-5 [7], ZSM-5 [8], MCM-22 [9], Beta [10], and [B]Beta [11], and mesoporous materials, like siliceous, aluminum-containing, and niobium incorporated MCM-41 [12,13] as well as SBA-15 [14] and cross-linked TS-1 [15] have been investigated as solid acid catalysts.…”

“…A number of recent in situ spectroscopic investigations focused on the mechanism of the vapor-phase Beckmann rearrangement of oximes [12,[16][17][18][19][20]. In these studies, surface hydroxyl groups with different chemical properties and local structures, such as isolated SiOH groups and SiOH nests at the outer surface or pore mouth of zeolite particles or located in mesopores as well as SiOH groups in the neighbourhood of framework boron atoms and bridging OH groups (SiOHAl) in aluminum-containing materials, were discussed as catalytically active sites.…”

Imidazolium and pyridinium salts – solvents influencing the rate and direction of the Fries, Beckmann, and Claisen rearrangements

“…The tetrabutylammonium bromide was obtained from the Aldrich company and the 3-ethyl-1-methylimidazolium methanesulfonate (1j) from Solvent-Innovation. The aryl acetates 3a-c, ketoximes 4a-c, and allyl aryl ethers 5a-c were prepared by methods [20,21]. Compound 1c (0.75 g, 4.38 mmol) was added to the mixture and the product was held for 3 h at 120ºC.…”

Chemical diversity of zeolite catalytic sites

“…In practice, because this siloxy group is part of a network of chemically equivalent groups, the negative charge is effectively delocalized between several oxygen atoms in the defect site (Fernandez et al, 2006). 19 The stability gained by this delocalization is essential for catalytic activity as high-surface area silicas with isolated silanol groups, and less organized groups of hydrogen-bonded Si-OH groups do not catalyze this reaction. Acid aluminosilicate and borosilicate zeolites do catalyze this reaction, but with much lower selectivity (Marthala et al, 2006).…”