A New Series of Tungstophosphoric Acid-Polymeric Matrix Catalysts: Application in the Green Synthesis of 2-Benzazepines and Analogous Rings

AGUILERA PALACIOS, EDNA X.; PALERMO, VALERIA; SATHICQ, ANGEL G.; PIZZIO, LUIS R.; ROMNELLI, GUSTAVO P.

Catalysts

MDPI

Año: 2022 vol. 12

A new series of composite materials (PLMTPA) based on tungstophosphoric acid (TPA)included in a polymeric matrix of polyacrylamide (PLM), with a TPA:PLM ratio of 20/80, 40/60,and 60/40, were synthesized and well characterized by FT-IR, XRD, 31P MAS-NMR, TGA-DSC,and SEM-EDAX. Their acidic and textural properties were determined by potentiometric titrationand nitrogen adsorption–desorption isotherms, respectively. Considering 31P MAS-NMR and FTIR analyses, the main species present in the samples is the [PW12O40]3− anion that, accordingto XRD results, is highly dispersed in the polymeric matrix or appears as a noncrystalline phase.The thermogravimetric analysis revealed that PLMTPA materials did not undergo any remarkablechemical changes up to 200 ◦C. Additionally, the PLMTPA materials showed strong acid siteswhose number increased with the increment of their TPA content. Finally, PLMTPA materialswere used as efficient and recyclable noncorrosive catalysts for the synthesis of 2-benzazepines andrelated compounds. Good yields (55–88%) and high purity were achieved by a Pictet-Spenglervariant reaction between N-aralkylsulfonamides and s-trioxane in soft reaction conditions: lowtoluene volume, at 70 ◦C, for 3 h. The described protocol results in a useful and environmentallyfriendly alternative with operative simplicity. The best catalyst in the optimized reaction conditions,PLMTPA60/40100, was reused six times without appreciable loss of activity.