Heterogeneous acid catalysts prepared by immobilization of H3PW12O40 on silica through impregnation and inclusion, applied to the synthesis of 3H-1, 5-benzodiazepines

MARÍA DOLORES MORALES; ANTONIA INFANTES-MOLINA; JUAN MANUEL LÁZARO MARTÍNEZ; GUSTAVO P. ROMANELLI; LUIS R. PIZZIO; ENRIQUE RODRÍGUEZ CASTELLÓN

Molecular Catalysis

Elsevier

Lugar: Amsterdam; Año: 2020

2468-8231

Solid acid catalysts were successfully prepared using mesoporous silica (MESOSI) as support and tungstophosphoric acid (KTPA) as active phase, which was incorporated by impregnation (MESOSI#KTPA) and inclusion(MESOSI@KTPA). TEM (transmission electron microscopy) images of MESOSI samples revealed the presence ofmesopores (worm-like structured) and well-defined pore channels. XRD patterns of MESOSI#KTPA samplesshowed small crystals of H3PW12O40·6H2O that were not present in the MESOSI@KTPA materials. The specificsurface area of the MESOSI modified with KTPA decreases with the increment of the heteropolyacid content. 31PNMR and FT-IR characterizations confirmed the existence of undegraded [H3-XPW12O40]X− and [PW12O40]3−anions interacting with the ^SieOH2+ groups of MESOSI. Potentiometric titration results showed that both acidstrength and number of acid sites increased with the KTPA loading in MESOSI@KTPA and MESOSI@KTPAsamples. Moreover, the acidic properties of MESOSI#KTPA materials were remarkably higher than those ofMESOSI@KTPA. The catalysts prepared were highly active, selective and reusable in the solvent-free synthesis of3H-1,5-benzodiazepine from 1,2-phenylenediamine and 1,3-diphenyl-1,3-propanedione