Novel MgO–SnO2 Solid Superbase as a High-Efficiency Catalyst for One-Pot Solvent-Free Synthesis of Polyfunctionalized 4H-pyran Derivatives

Abstract

We report for the first time the hydrothermal synthesis of MgO–SnO2 solid superbase using P123 as template. The basicity of the materials was determined by two approaches of Hammett indicators method and temperature-programmed desorption using CO2 as adsorbate (CO2-TPD). It was found that Mg/Sn molar ratio has an effect on MgO–SnO2 basicity, and superbasicity was observed only at Mg/Sn molar ratio of 1. With variation of Mg/Sn molar ratio, superbase strength (H -) was in the 26.5–33.0 range, showing superbasic value up to 0.939 mmol/g. The structure and texture of the as-prepared materials were studied by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 physio-adsorption methods. We detected particles of spherical morphology having diameter of ca. 150 nm. N2 adsorption–desorption results suggested that the materials are of mesoporous structure, having specific surface area of 115.2 m2/g and average pore diameter of 6 nm. The superbase was found to exhibit excellent catalytic activity towards the one-pot synthesis of polyfunctionalized 4H-pyrans through the condensation of aldehydes, malononitrile, and an active methylene compound. Its excellent catalytic efficiency is related to its superbasicity of the MgO–SnO2. The results provide a new route for the design and preparation of composite oxide superbases. Furthermore, the solid superbases will facilitate a strategy for high-efficiency synthesis of polyfunctionalized 4H-pyrans. Novel MgO–SnO2 solid superbase was prepared using P123 as template. Its superbase strength was in the 26.5–33.0 range, showing superbasic sites up to 0.939 mmol/g. The material is of mesoporous structure,(having specific surface area of 115.2 m2/g and average pore diameter of 6 nm. It was found to exhibit excellent catalytic activity towards the one-pot solvent-free synthesis of polyfunctionalized 4H-pyrans through the condensation of aldehydes, malononitrile, and an active methylene compound. The results provide a new route for the design and preparation of composite oxide superbases.