Efficient catalytic epoxidation of olefins with silylated Ti-TUD-1 catalysts
Efficient catalytic epoxidation of olefins with silylated Ti-TUD-1 catalysts
复制标题
DOI：
10.1016/j.jcat.2008.09.021
复制
发表时间：
2008-12
影响因子：
7.3
通讯作者：
M. Prasad;M. S. Hamdy;G. Mul;E. Bouwman;E. Drent
中科院分区：
文献类型：
--
作者：
M. Prasad;M. S. Hamdy;G. Mul;E. Bouwman;E. Drent
通过用六甲基二硅氮烷（HMDS）处理不同Ti负载量的Ti-TUD-1样品来合成各种甲硅烷基化的Ti-TUD-1样品。通过红外光谱、疏水性（TGA）和NH3-TPD测量证实了介孔二氧化硅上的硅烷醇（SiOH）和钛醇基团（TiOH）的硅烷化。相对不反应的烯烃，如1-辛烯和对叔丁基苯基烯丙基醚，使用甲硅烷基化和未甲硅烷基化的Ti-TUD-1样品与不同的Ti负载量在1-10重量% Ti的范围内进行环氧化。催化环氧化反应是在不添加任何其他有机溶剂的情况下，用有机氢过氧化物的商业溶液作为氧化剂进行的。过氧化物利用率的选择性取决于烯烃、氧化剂和催化剂的类型。使用未硅烷化的Ti-TUD-1，对于过氧化氢枯基（CHP）实现低的环氧化物选择性，这归因于其在反应条件下容易酸催化分解为苯酚和丙酮。然而，叔丁基过氧化氢（TBHP）和枯基过氧化氢产生高选择性的环氧化物（基于转化的氢过氧化物）与甲硅烷基化的Ti-TUD-1样品。贫电子烯烃对叔丁基苯基烯丙基醚的环氧化物选择性低于简单的1-辛烯。CHP作为氧化剂的实验被用作诊断工具，以证明用TBHP的甲硅烷基化样品的增强的环氧化活性和选择性可以归功于甲硅烷基化的两个效果。的Ti-TUD-1催化剂的质子TiOH网站的消除导致在一个显着减少的竞争酸催化分解的过氧化物，而增强的疏水性的催化剂表面增强的非极性烯烃基板的住宿。
Various silylated Ti-TUD-1 samples were synthesized by treating Ti-TUD-1 samples of differing Ti loadings with hexamethyldisilazane (HMDS). The silylation of silanol (SiOH) and titanol groups (TiOH) on the mesoporous silica was confirmed by FTIR spectroscopy, hydrophobicity (TGA), and NH3-TPD measurements. The relatively unreactive olefins, such as 1-octene and p-tert-butylphenylallyl ether, were epoxidized using both silylated and unsilylated Ti-TUD-1 samples with different Ti loadings in the range of 1–10 wt% Ti. The catalytic epoxidation reactions were performed with commercial solutions of organic hydroperoxides as oxidants without the addition of any other organic solvent. The selectivities in peroxide utilization were found to depend on the type of olefin, oxidant, and catalyst. Using unsilylated Ti-TUD-1, low selectivity to epoxide was achieved for cumyl hydroperoxide (CHP), which is attributed to its facile acid-catalyzed decomposition to phenol and acetone under the reaction conditions. However, both t-butyl hydroperoxide (TBHP) and cumyl hydroperoxide yielded high selectivity to epoxide (based on converted hydroperoxide) with silylated Ti-TUD-1 samples. The selectivity to epoxide was lower for the electron-poor olefin p-tert-butylphenylallyl ether than for simple 1-octene. The experiments with CHP as the oxidant were used as a diagnostic tool to demonstrate that the enhanced epoxidation activity and selectivity of the silylated samples with TBHP can be credited to two effects of silylation. The elimination of protic TiOH sites of the Ti-TUD-1 catalyst resulted in a significant reduction of the competing acid-catalyzed decomposition of the peroxide, whereas the enhanced hydrophobicity of the catalyst surface enhanced the accommodation of the apolar olefinic substrate.