咪唑修饰硅胶负载乙酰丙酮钴(Ⅱ)催化分子氧氧化单萜烯研究

Autoxidation of Monoterpenes with Oxygen Catalyzed by Co(acac)_2 Supported on Silica Functionalized Imidazole

采用3-氯丙基三甲氧基硅烷和咪唑对硅胶表面进行修饰(SiIm),通过咪唑环中π电子与钴离子空d轨道之间的纵轴配位作用制得非均相负载催化剂Co(acac)2/SiIm,用IR,UV-Vis和ICP-AES对其结构进行表征.在乙腈溶剂中,催化剂催化分子氧氧化单萜烯得到了相应的氧化产物.研究表明,负载催化剂具有良好的催化氧化性能,获得了较高的反应转化率和产物选择性,其中柠檬烯和α-蒎烯的氧化以环氧产物为主,而β-蒎烯的氧化则以烯丙位氧化产物为主.另外,对反应机理和竞争反应进行了简单的阐述.

Selective oxyfunctionalization of monoterpenes is an interesting route to utilize these inexpensive natural products for a number of applications, such as pharmaceutical, flavor and perfumery industry as well as useful synthetic intermediates. The use of solid materials in catalytic oxidations in the liquid-phase has recently been extensively investigated because of their easy recovery and the possibility of regeneration which results in a reduction of the environmental impact. In this work, a new heterogeneous catalyst Co（ acac）2/SiIm was prepared with supporting Co （acac）2 on silica gel modified with 3-chloropropyhrimethoxysilane and imidazole, and the structure of catalyst was characterized by IR, UV-Vis and ICP-AES. Oxidation reactions of limonene,α-pinene and β-pinene with dioxygen in acetonitrile solutions containing catalytic amounts of Co（acac） 2/SiIm were studied. The results show that the higher conversion and products chemoselectivities were obtained. Limonene and α-pinene gave epoxides as predominant products with chemoselectivities 62% and 79% at 58% and 72% conversion, respectively. On the other hand,β-pinene gave allylic oxides as major products with chemoselectivity 85% at a 55% conversion rate. In addition, the reaction mechanism and competition were simply discussed.