Highly Selective Oxidation of Toluene to Benzaldehyde in Alkaline Systems

For the selective oxidation of toluene to benzaldehyde, the biggest challenge is to prevent the further oxidation of benzaldehyde as toluene conversion increases. Using benzyl benzoate as the solvent and adding benzoate to adjust the alkalinity of the system, the formation of the benzoyl radical can be well inhibited, but the oxidation of toluene is weakened. The decomposition of benzyl benzoate to benzaldehyde can activate the reaction at the initial stage, and the negative influence of alkalinity is avoided to some extent. Therefore, by using atmospheric air as an oxidant, a high selectivity and yield of benzaldehyde can be obtained in a benzyl benzoate catalytic system with alkali as an additive. The mechanism of alkaline regulation and selective oxidation of toluene was investigated by in situ infrared (IR) spectroscopy experiments. The benzaldehyde capacity is defined to characterize the tolerance of benzaldehyde in the system. Catalysts and alkaline regulators can be easily reused with high-boiling solvents, making it a convenient process for product separation and catalyst–alkaline solvent recycling.