四聚型季铵类多金属氧酸盐相转移催化甲苯氧化合成苯甲醛

Phase Transfer Catalyzed Oxidation of Toluene to Benzaldehyde Using Tetrameric Quaternary Ammonium Polyoxometalates

甲苯氧化制备苯甲醛在工业应用中通常涉及有毒试剂或产生多种难以分离的副产物.本文采用乙二胺、环氧氯丙烷和N,N-二甲基丁基叔胺等作为初始原料,合成了四聚型季铵盐氯化物,然后与Keggin型钨钒磷杂多酸发生阴离子交换反应,制备了一系列四聚型季胺类多金属氧酸盐;并通过在乙腈中使用H_(2)O_(2)(质量分数30%)将甲苯氧化为苯甲醛作为模型反应,评价了这些新型的多金属氧酸盐的催化性能.四核阳离子的引入不仅可以调节杂多阴离子的氧化还原性质,还可以使催化剂具有密集的协同催化活性位点.另外,优选出的催化剂具有良好的两亲性相转移催化能力,不仅显著提高了反应速率,而且实现了催化剂的简便回收和重复使用.在经过7次重复使用后,催化剂的性能几乎没有下降,并且实现了可接受的甲苯转化率(40%)和苯甲醛选择性(75%).本研究开发了一条与工业相关的碳氢化合物催化氧化的环境友好型工艺,为实际工业应用奠定了一定的理论基础.

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 H_(2)O_(2)(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.