Tungstophosphoric acid/zirconia composites prepared by the sol–gel method: An efficient and recyclable green catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes

Abstract

Samples of zirconia modified with different contents of tungstophosphoric acid (TPA) were synthesized from zirconium propoxide via sol–gel reactions using polyethylene glycol as template and were characterized by different physicochemical techniques (BET, XRD, FT-IR, and 31P MAS-NMR). The SBET of the solids decreases and the microporosity increases with the increase of the TPA content. According to FT-IR and 31P MAS-NMR studies, the main species present in the samples is [PW12O40]3− anion, which was partially transformed into [P2W21O71]6− and [PW11O39]7− anions during the synthesis and drying steps. The XRD patterns of the modified samples exhibit neither the characteristic peaks of TPA nor those attributed to its decomposition products.Aryl-14H-dibenzo[a,j]xanthenes have been synthesized by a one-pot condensation of 2-naphthol and aryl aldehydes, catalyzed by tungstophosphoric acid/zirconia composites in a solvent-free medium using conventional heating. The present approach offers the advantages of clean reaction, simple methodology, short reaction time, and high yield. The reaction work-up is very simple and the catalyst can be easily separated from the reaction mixture and reused several times in subsequent reactions without appreciable loss of the catalytic activity.