New vanadium Keggin heteropolyacids encapsulated in a silica framework: recyclable catalysts for the synthesis of highly substituted hexahydropyrimidines under suitable conditions

PALERMO, V.; A.G. SATHICQ; T. CONSTANTIEUX; J. RODRIGUEZ; P.G. VÁZQUEZ; G.P. ROMANELLI

CATALYSIS LETTERS

SPRINGER

Lugar: Berlin; Año: 2015 vol. 145 p. 1022 - 1032

1011-372X

Solid acid catalysts based on the direct incorporation of the vanadium Keggin heteropolyacid (PMo11V) structure during the synthesis of silica by the sol-gel technique, in acidic media using tetraethyl orthosilicate (PMo11VSiO21, PMo11VSiO22,  PMo11VSiO23, and PMo11VSiO24), were prepared and characterized by 31P-NMR, FT-IR, XRD, and textural properties (SBET). The acidic characteristics of the catalysts were determined by potentiometric titration with n-butylamine. A series of highly substituted hexahydropyrimidines were synthesized using these new materials, encapsulated in a silica framework, as catalyst in solvent-free conditions. This methodology requires short reaction time (1.5 h), a temperature of 80 ºC in solvent free-conditions to obtain good to excellent yields of trifluoromethyl-hexahydropyrimidine derivatives. The Keggin catalyst embedded in the silica matrix is insoluble in a polar media, which allows easy removal of the reaction products without affecting their catalytic activity.