Color-Coordinated Photocatalysis of the One-Pot Synthesis of Schiff Bases from Benzyl Alcohol and Nitro Compounds Using a Hybrid Magnetic Catalyst

Abstract

The versatility and significance of imines (Schiff bases) make them highly attractive for many industrial applications. This study investigates photocatalytic routes for the one-pot synthesis of Schiff bases using alcohol and an aromatic nitro compound as reagents, rather than the more conventional amine and aldehyde or ketone. Utilizing photoirradiation at 370 nm with TiO2 loaded with various metals, we demonstrate the exceptional efficiency of the one-pot synthesis of Schiff bases under an inert atmosphere. Notably, the Fe3O4@TiO2 magnetic catalyst offers an excellent option for synthesizing the corresponding imine, achieving a remarkable production rate of 6.8 mmol h−1 during the first 6 h of irradiation with UVA light and reaching over 99% yield after 20 h. This success is attributed to a series of reactions involving the photocatalytic oxidation of benzyl alcohol to benzaldehyde and the simultaneous in situ reduction of nitrobenzene to aniline. The subsequent catalytic condensation of these products, facilitated by the active sites at the TiO2-metal interface, ultimately yields the desired imine. Additionally, while irradiation in the UVA region alone can photocatalyze the process, incorporating blue light (450 nm) accelerates it significantly. Dual-wavelength irradiation increased the production of the benzaldehyde to 77.9 mmol and more than doubled the Schiff base yield, from 7.5 mmol (with UVA light) to 17 mmol in 3 h of irradiation. Additionally, the reusability of the catalyst under simultaneous 450 nm and 370 nm light exposure significantly enhanced Schiff base production, which rose from 16.9 mmol to 48.9 mmol after adding fresh 0.1 M nitrobenzene for the second use. This highlights the effectiveness of color-coordinated catalysis in advancing sustainable chemistry through two-color photochemistry. The magnetic catalytic system not only demonstrates remarkable performance but also shows excellent reusability, representing a promising alternative for sustainable and efficient chemical transformations.