Enantioselective hydrogenation of α-keto esters over cinchona-Pt/ Al2O3 catalysts: New interpretation of the rate acceleration and the induction of enantio-differentiation
Enantioselective hydrogenation of α-keto esters over cinchona-Pt/ Al2O3 catalysts: New interpretation of the rate acceleration and the induction of enantio-differentiation
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DOI：
10.1016/1381-1169(95)00220-0
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发表时间：
1996-05
影响因子：
--
通讯作者：
J. Margitfalvi;M. Hegedüs
中科院分区：
文献类型：
--
作者：
J. Margitfalvi;M. Hegedüs
研究了辛可尼定-Pt/Al_2O_3催化体系在不同溶剂中丙酮酸乙酯的加氢反应。使用的实验变量如下：（i）底物和改性剂浓度，(ii)乙酸的存在，（iii）（R）-乳酸乙酯的存在，（iv）相互作用组分的引入方式。在乙醇和甲苯中观察到完全不同的动力学模式。这种差异归因于甲苯中缺乏半缩酮形成。光学产率与转化率的依赖性显示在低转化率下单调增加，即外推至零转化率的光学产率接近于零。有人建议，速率加速是由于增强反应性的基板诱导的基板-改性剂相互作用。结果表明：（1）底物或乙酸诱导修饰剂的构象变化;（2）底物-修饰剂复合物的形成;（3）修饰剂的喹啉环诱导的屏蔽效应。
The hydrogenation of ethyl pyruvate over the cinchonidine-Pt/Al2O3catalyst system has been investigated in different solvents. Experimental variables used were as follows: (i) substrate and modifier concentration.,(ii) presence of acetic acid, (iii) presence of (R)-ethyl lactate, (iv) mode of introduction of the interacting components. A completely different kinetic pattern was observed in ethanol and toluene. This difference is attributed to the lack of half-ketal formation in toluene. The optical yield vs. conversion dependencies show a monotone increase at low conversion, i.e. the optical yield extrapolated to zero conversion is close to zero. It is suggested that the rate acceleration is due to the enhanced reactivity of the substrate induced by substrate-modifier interaction. It is proposed that the induction of enantio-differentiation is attributed to the following interactions: (i) conformational changes of the modifier induced by substrate or acetic acid, (ii) formation of a substrate-modifier complex, (iii) shielding effect induced by the quinoline ring of the modifier.