Rare-earth (Ce 3+, La 3+, Sm 3+, and RE 3+) exchanged Na-Y zeolites and K-10 clay as solid acid catalysts for the synthesis of benzoxazole via Beckmann rearrangement of salicylaldoxime

Abstract

Rare-earth exchanged (Ce 3+, La 3+, Sm 3+, and RE 3+) Na-Y zeolites, K-10 montmorillonite clay and amorphous silica–alumina have been employed as solid acid catalysts for the vapor phase Beckmann rearrangement of salicylaldoxime to benzoxazole. Rare-earth exchanged Na-Y zeolites were prepared by simple ion-exchange methods. These systems were characterized by energy dispersed X-ray analysis, 27Al and 29Si MAS NMR, FTIR spectroscopy, temperature programmed desorption and surface area and pore volume measurements. The catalysts show both Brönsted and Lewis acidity. Definite correlation between Brönsted acid sites amount obtained from thermodesorption of 2,6-dimethylpyridine and benzoxazole formation in the reaction were observed. Hydrolysis of salicylaldoxime to salicylaldehyde is correlated with Lewis acidity as obtained from hydrocracking of cumene.