PI.155 Ecosustainable quinoxaline synthesis promoted by silica-supported MoO3 nanoparticles

Resumo

This work investigates the performance of a series of silica-supported MoO_x catalysts (Mo loadings of 0.5, 1.0, and 3.0 wt.%, labeled as SiMo0.5, SiMo1, and SiMo3, respectively) in the ecosustainable synthesis of 2-phenylquinoxaline from o-phenylenediamine and α-hydroxyacetophenone. The specific surface area of the catalysts decreased with Mo loading: 331, 262, and 238 m²/g for SiMo0.5, SiMo1, and SiMo3, respectively. The XRD patterns reveal diffraction peaks associated with the hexagonal crystalline MoO₃ phase (crystallite size of ~26 nm) only for SiMo3, indicating that MoO_x are either completely dispersed or amorphous at Mo loadings lower than 3 wt.%. All catalysts display two LMCT bands at 240 and 320 nm in the UV-vis spectra that correspond to octahedral polymeric molybdate species. SiMo3 also exhibits a LMCT band at 260 nm related to the MoO₃ crystallites. All catalysts show high activity in the selective synthesis of 2-phenylquinoxaline, with SiMo3 displaying the highest conversion (95% after 180 min of reaction at 80 ºC), even when different substituted o-phenylenediamines were employed. Furthermore, SiMo3 maintained its high activity after three consecutive runs.