Hemicucurbit[6]uril-induced aerobic oxidation of heterocyclic compounds

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• 作者：Hang Cong ; Takehiko Yamato ; Zhu Tao
• 关键词：Cucurbituril ; Supramolecular catalysis ; Aerobic oxidation ; Heterocyclic compound ; Kinetics
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2013
• 出版时间：15 November, 2013
• 年：2013
• 卷：379
• 期：Complete
• 页码：287-293
• 全文大小：1497 K

文摘

The aerobic oxidation of furan in aqueous solution in the presence of HemiQ[6] has been investigated, and the product furan-2,5-diol is stabilized by encapsulation of HemiQ[6], which could be transformed to the dione confirmation in acidic solution and escape from the macrocyclic compound. The ¹H NMR titration experiments of the host-guest interaction at different pH values suggest protonation should improve the encapsulation, and therefore an unique property that HemiQ[6] can be protonated has been revealed. The oxidizing kinetics suggests that the procedure is a consecutive reaction with a series of constants k₁ = 2.9 ¡Á 10^?2 min^?1, k₂ = 2.7 ¡Á 10^?2 min^?1, and k₃ = 5.7 ¡Á 10^?3 min^?1, respectively. The kinetic investigation at pD = 2.0 indicates the HemiQ[6]-catalytic oxidation of furan could be accelerated by acidification. As a consequence, a plausible mechanism has been established on the above evidences. 2-Methylfuran is employed to give the product 2-methylfuran-5-ol exhibiting a satisfied activity in this aerobic oxidation with the supramolecular catalysis of HemiQ[6], but the oxidation of thiophene is very slow in either neutral or acidic condition.