Li Yuqing, Liu Sha, Tao Shan, Zhu Yan, Zhao Qiming
College of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou 310053, China.
Department of Chemistry, Xixi Campus, Zhejiang University, Hangzhou 310028, China.
ACS Omega. 2021 Feb 25;6(9):6466-6473. doi: 10.1021/acsomega.1c00176. eCollection 2021 Mar 9.
A novel metal-free, reusable, and green catalytic system comprising hydrothermal carbon microspheres (HCMSs) supporting -hydroxyphthalimide (NHPI) was developed and employed in the aerobic oxidation of alcohol. Hierarchically porous HCMSs with good monodispersity were produced by the hydrothermal carbonization of sucrose and designed NaOH-impregnated calcination under a static air atmosphere. The meso- and macroporous pores on HCMSs make up 71% of the total pore volume. The covalent immobilization of NHPI onto HCMSs was first accomplished by grafting hyperbranched polyquaternary amine via repetitive ring-opening reactions of diglycidyl ether and subsequent amidation with 4-carboxy-NHPI. Owing to the cocatalysis of grafted quaternary ammonium salt, a designed heterogeneous catalyst has superior performance to free NHPI in the oxidation of 2-phenylethanol. The established catalytic system achieved 42% conversion and up to 96% selectivity of acetophenone at 90 °C under 1 atm O for 20 h and presented a versatile catalytic effect for diversified alcohols. Immobilized NHPI could be facilely recycled via simple filtration and displayed good stability for six cycles without a discernible decrease of reactivity or damage of catalyst morphology in repeated oxidation test.
开发了一种新型的无金属、可重复使用的绿色催化体系，该体系由负载有N-羟基邻苯二甲酰亚胺（NHPI）的水热碳微球（HCMSs）组成，并将其用于醇的有氧氧化反应。通过蔗糖的水热碳化以及在静态空气气氛下设计的NaOH浸渍煅烧，制备出了具有良好单分散性的分级多孔HCMSs。HCMSs上的中孔和大孔占总孔体积的71%。首先通过二缩水甘油醚的重复开环反应接枝超支化聚季铵盐，随后与4-羧基-NHPI进行酰胺化反应，将NHPI共价固定在HCMSs上。由于接枝的季铵盐的共催化作用，所设计的多相催化剂在2-苯乙醇的氧化反应中表现出优于游离NHPI的性能。所建立的催化体系在90℃、1 atm O₂条件下反应20 h，实现了42%的转化率和高达96%的苯乙酮选择性，并且对多种醇类呈现出通用的催化效果。固定化的NHPI可以通过简单过滤轻松回收，并且在重复氧化试验中显示出良好的稳定性，经过六个循环后反应活性没有明显下降，催化剂形态也没有受损。
