This study reports a simple, reusable, and recoverable niobium-based heterogeneous catalysts for Biginelli multicomponent reactions. Different methods of catalysts preparation were investigated. For this purpose, HY-340 (Nb 2 O 5 • nH 2 O) and Nb 2 O 5 were chemically and/or thermally treated and investigated as catalysts for dihydropyrimidinones (DHPMs) production. The catalysts were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, temperature-programmed desorption of NH 3 , adsorption/desorption of N 2 at −196 °C, and thermogravimetric and differential thermal analysis. The characterization results showed that niobium oxides have the potential to be used as catalysts because of high crystallinity and large surface area. Among the tested catalysts, Nb 2 O 5 chemically treated (Nb 2 O 5 /T) showed the best catalytic performance. In the absence of solvents, 94% yield of DHPMs was achieved. Also, Nb 2 O 5 /T can be reused three times without a significant yield decrease. Additionally, a feasible reaction pathway was suggested based on the Knoevenagel mechanism for DHPM synthesis using niobium-based catalysts.

The Biginelli reaction is a one-pot acid-catalyzed cyclocondensation of an aromatic aldehyde, urea, and ethyl acetoacetate to synthesize dihydropyrimidinones (DHPMs). DHPMs are extremely important due to their wide-ranging pharmacological activities,...

Neste artigo, através da análise da peça Dura lex sed lex, no cabelo só Gumex, o objetivo é refletir sobre o lugar do riso na produção dramatúrgica de Vianninha. Assim, observamos, através do uso de mecanismos do teatro de revista presentes na peça, um dos argumentos estético do autor como forma de coadunar crítica social e uma linguagem que pudesse ser considerada como ''popular''.