固定床反应器中丙酮酸乙酯在Pt/γ-Al_2O_3催化剂上的不对称加氢反应

Heterogeneous Asymmetric Hydrogenation of Ethyl Pyruvate on Chirally Modified Pt/Al_2O_3 Catalyst with Fixed-bed Reactor

采用固定床反应器对辛可尼定修饰的 Pt/γ-Al2 O3 催化剂上丙酮酸乙酯的多相不对称加氢体系进行了研究 ,同时用高压釜反应器进行了对比 ,分别取得 60 %和 90 %的 e.e.值 .在两种不同的反应器中 ,溶剂对反应结果的影响不同 ,在高压釜反应器中乙酸的效果好于乙醇 ,而在固定床反应器中则相反 ,推测在固定床反应器中催化表面反应机理与所用溶剂的介电常数或其极性有关 .以 CO探针分子对辛可尼定在催化剂表面的吸附行为进行了红外光谱研究 。

The enantioselective hydrogenation of ethyl pyruvate on the cinchonidine modified Pt/Al 2O 3 catalyst was investigated using a high pressure reaction system with a fixed bed reactor for the purpose to produce the chiral product without separating the catalyst from the reaction system. The reaction was also investigated in a batch reactor for comparison. About 60% e.e. and 90% e.e. were obtained with the fixed bed reactor and the batch reactor respectively, demonstrating the possibility for the heterogeneous asymmetric hydrogenation in the fixed bed reactor. Some adsorbed chiral modifier, cinchonidine, can be slowly removed from the surface of Pt/Al 2O 3 under the continuous flow reaction, as a result, the e.e. values drops with the reaction time in the fixed bed reactor. The enantio selectivity is higher in the fixed bed reactor, but lower in the batch reactor when ethanol was used as solvent than that when acetic acid as solvent. CO was used as molecular probe to characterize the adsorption of cinchonidine on the catalyst surface by IR spectroscopy. A red shift observed in IR spectra of coadsorbed CO with cinchonidine suggests that the cinchonidine adsorption is mainly through the π interaction with platinum surface and donating electron to the platinum surface.