Abstract

SOSA, Alexis Alberto; ROMANELLI, Gustavo Pablo  and  PIZZIO, Luis René. Silica nanostructures, with variable diameter and mesopore size distribution, modified with tungstophosphoric acid as catalyst in the synthesis of quinoxalines. Rev.Colomb.Quim. [online]. 2020, vol.49, n.2, pp.37-43. ISSN 0120-2804.  https://doi.org/10.15446/rev.colomb.quim.v49n2.84249.

Tungstophosphoric acid supported on silica nanostructures (SNX#WPA) with variable diameter and mesopore size distribution were synthetized. Silica nanostructures (SNX) were prepared in octane/aqueous media using polystyrene and CTAB as organic templates. The materials were characterized by XRD, SEM, TEM and dinitrogen adsorption/ desorption isotherm analysis. The octane/ water ratio influenced the morphology and size of SNX prepared, as well as its pore size distribution. The SNX samples obtained using OCT/H2O ratios in the range 0.07-0.35 (SN4, SN5, and SN6 samples). present small (5-6 nm) and large (28-34 nm) mesopores (mainly generated by polystyrene). Large mesopores and their volume contribution were clearly higher than in the SN1, SN2, and SN3 samples. The structure and morphology of SNX#WPA samples were similar to those of the SNX. Furthermore, the characterization of all the SNX#WPA materials by FT-IR and 31P NMR indicated the presence of undegraded [PW12O40]3- and [H3-XPW12O40](3-X)-species. According to the potentiometric titration results, the solids presented very strong acid sites. The performance of SNX#WPA materials as catalysts in the synthesis of quinoxalines was evaluated. The yields achieved were high, without formation of by-products resulting from competitive reactions or decomposition products, so the prepared materials are highly selective and reusable catalysts.

Keywords : Catalysis; heteropolyacids; heterocycles; nanoparticles.

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