Pd/羧基功能化离子液体选择性催化氧化苯乙烯

Selective Oxidation of Styrene Catalyzed by Pd/Carboxyl-Appended Ionic Liquids

利用羧基对咪唑型离子液体的阳离子进行功能化,得到一系列具有不同羧基数目及与不同阴离子搭配的N-羧基功能化咪唑离子液体(TSILs),进而构筑PdCl2/TSILs催化剂体系.以过氧化氢为氧化剂,将PdCl2/TSILs用于选择性催化氧化苯乙烯合成苯乙酮.研究结果表明,PdCl2/TSILs催化体系对目标反应具有理想的催化性能,羧基功能化离子液体的阳离子及其搭配的阴离子对苯乙酮的选择性和产率均有显著的影响.阳离子的羧基数目越多,阳离子的不对称性越高,PdCl2/TSILs催化剂体系的活性越好.含有相同阳离子的PdCl2/TSILs催化剂体系,其催化性能按照阴离子PF6-<H2PO4-<Cl-<BF4-的顺序递增且与其酸强度顺序相反.含有三羧基的功能化离子液体与PdCl2构筑的催化剂体系具有最佳的催化性能,在55℃下,该催化剂体系的转换频率值达到125h-1,苯乙烯可以完全转化且苯乙酮的选择性为91%.

A new catalytic system, PdCl2/TSILs, for catalytic oxidation of styrene to acetophenone with hydrogen peroxide was designed through the combination of PdCl2 and task-specific ionic liquids （TSILs） of N-carboxyl-appended imidazolium cations with various anions. The PdCl2/FSILs catalytic system displayed excellent catalytic properties for the target reaction. The yield and selectivity of acetophenone depended critically on the TSILs structure with different combinations of carboxylic groups and counter-anions. The catalytic activity of PdCl2/TSILs was enhanced with the increase in the number of the carboxylic groups and the asymmetry degree of the cations. The activity of PdCl2/TSILs with the same cation also increased with the assorted anion sequence of PF6^-〈 H2PO4^-〈 CI^- 〈 BF4 , which contrasted to their acid strengths. Amongst all of these PdCl2/TSILs, TSILs with three carboxylic groups showed the best activity with a complete conversion of styrene at 55℃. The measured turnover frequency and the selectivity for acetophenone were as high as 125 h^-1 and 91%, respectively.