Clean synthesis of amides over bifunctional catalysts of rhodium-loaded titanosilicates

Rhodium-loaded titanosilicates were prepared and employed as efficient bifunctional catalysts in the one-pot synthesis of benzamide from benzaldehyde, hydrogen peroxide, and ammonia, which took place through a tandem reaction including ammoximation of benzaldehyde to benzaldehydeoxime and a sequential dehydration-rehydration reaction to benzamide. Various parameters that influenced the activity and product selectivity were investigated, such as crystalline topologies of the titanosilicate supports, types of transition metals, rhodium content, reaction temperature, time, solvent, and NH₃/benzaldehyde molar ratio. Ti-MWW was proved to be a suitable support for loading the Rh(OH)_x species. Rh(OH)_x/Ti-MWWgave 84.9% of benzaldehyde conversion and 86.9% of benzamide selectivity, and it was also catalytically active for the transformation of a variety of aldehydes to the corresponding amides. The reusability of the bifunctional catalyst was also investigated. The insitu FTIR technique confirmed that the one-pot reaction included Ti-catalyzed ammoximation of benzaldehyde to the benzaldehyde oxime intermediate and sequential rhodium hydroxide related dehydration-rehydration reaction of oximes to amides.