Methyltrioxorhenium-catalyzed epoxidation of olefins with hydrogen peroxide as an oxidant and pyridine N-oxide ionic liquids as additives

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• 作者：Yuecheng Zhang ; Zhaozhao Li ; Xiaohui Cao ; Jiquan Zhao ; ^{zhaojq@hebut.edu.cn}
• 关键词：Methyltrioxorhenium ; Pyridine N-oxide ; Ionic liquids ; Olefins ; Epoxidation ; Hydrogen peroxide
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2013
• 出版时间：January, 2013
• 年：2013
• 卷：366
• 期：Complete
• 页码：149-155
• 全文大小：411 K

文摘

Four ionic liquids (ILs) with both a pyridine N-oxide moiety and an imidazolium moiety combined by an amide spacer were synthesized through a series of reactions including amidation, peroxidation, quaterization and anion exchange reaction. Their structures were fully characterized by ¹H NMR, FT-IR, UV-vis and HR-MS. The ionic liquids were used respectively as additives in the methyltrioxorhenium (MTO) catalyzed epoxidation of olefins with 30 % H₂O₂ as an oxidant. The catalytic results displayed that the ILs had excellent performances in suppressing epoxide ring-opening reaction, which led to the significant improvement of the selectivity of the MTO-catalyzed epoxidation with low loadings compared to other substances as additives. The coexistence of the pyridine N-oxide and imidazolium moieties in the structures of ILs is necessary in improving the MTO-catalyzed epoxidation reaction. It was also displayed that the improvement degree on the selectivity of epoxidation depended on the type of anion of the ILs, but not the position of the substituent with imidazolium moiety in the ring of pyridine N-oxide. Meanwhile, the results also showed that the introduction of the ILs caused the decrease of the epoxidation rate, but this side effect was small compared to those of other substances used as additives.