Phase Transfer Catalyzed Oxidation of Toluene to Benzaldehyde Using Tetrameric Quaternary Ammonium Polyoxometalates
The oxidation of toluene to benzaldehyde in industrial applications typically involves toxic reagents or the generation of various difficult-to-separate byproducts.In this study,starting materials such as ethylenediamine,epichlorohydrin,and N,N-dimethyldodecylamine were used to synthesize tetrameric quaternary ammonium chloride.Subsequently,an anion exchange reaction with Keggin-type tungstovanadophosphoric heteropolyacid was conducted to prepare tetrameric quaternary ammonium polyoxometalates.These polyoxometalate catalysts were then evaluated via the oxidation of toluene to benzaldehyde using H2O2(30%,mass fraction)in acetonitrile.The introduction of four nucleated cations not only modulated the redox properties of the heteropolyanions but also provided the catalyst with densely packed cooperative catalytic active sites.Additionally,the resulting catalyst exhibited excellent amphiphilic phase-transfer catalytic capabilities,significantly enhancing the reaction rate and enabling easy catalyst recovery for repeated use.After seven repeated uses,the catalyst's performance showed minimal decline,maintaining acceptable toluene conversion(40%)and benzaldehyde selectivity(75%).Therefore,this study has developed an environmen-tally friendly process for the catalytic oxidation of hydrocarbons relevant to industry,laying a theoretical foundation for practical industrial applications.
Toluene oxidationBenzaldehydeQuaternary ammonium saltAmphipathyPhase transfer catalystpolyoxometalate
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