Reich S, Trapp O, Schurig V
Institute of Organic Chemistry, University of Tübingen, Germany.
J Chromatogr A. 2000 Sep 15;892(1-2):487-98. doi: 10.1016/s0021-9673(99)01301-1.
Enantioselective stopped-flow multidimensional gas chromatography (stopped-flow MDGC) is a fast and simple technique to determine enantiomerization (inversion) barriers in the gas phase in a range of delta G#gas(T)=70-200 kJ mol(-1). After complete gas-chromatographic separation of the enantiomers in the first column, gas phase enantiomerization of the heart-cut fraction of one single enantiomer is performed in the second (reactor) column at increased temperature and afterwards this fraction is separated into the enantiomers in the third column. From the observed de novo enantiomeric peak areas a(j), the enantiomerization time t and the enantiomerization temperature T, the enantiomerization (inversion) barrier delta G#gas(T) is determined and from temperature-dependent experiments, the activation enthalpy delta H#gas and the activation entropy delta S#gas are obtained. Enantiomerization studies on chiral 1-chloro-2,2-dimethylaziridine by stopped-flow MDGC yielded activation parameters of nitrogen inversion in the gas phase, i.e., delta G#gas(353 K)=110.5+/-0.5 kJ mol(-1), delta H#gas=71.0+/-3.8 kJ mol(-1) and delta S#gas=-109+/-11 J mol(-1) K(-1). By the complementary method of dynamic gas chromatography (GC), the apparent enantiomerization (inversion) barrier of 1-chloro-2,2-dimethylaziridine in the gas-liquid biphase system was found delta G#app(353 K)=108 kJ mol(-1). The values obtained by stopped-flow MDGC in the gas phase were used to calculate the activation parameters of nitrogen inversion of 1-chloro-2,2-dimethylaziridine in the liquid phase in the presence of the chiral selector Chirasil-nickel(II), i.e.. deltaG#liq(353 K)=106.0+/-0.4 kJ mol(-1), delta H#liq=68.3+/-1.4 kJ mol(-1) and deltaS#liq=-106+/-3.0 J mol(-1) K(-1).
对映选择性停流多维气相色谱法（停流MDGC）是一种快速简便的技术，用于测定一系列ΔG#gas(T)=70 - 200 kJ mol(-1)范围内气相中的对映异构化（反转）势垒。在第一根色谱柱中对映体完成气相色谱分离后，在第二根（反应）色谱柱中于升高的温度下对单一一种对映体的中心切割馏分进行气相对映异构化，然后在第三根色谱柱中将该馏分分离为对映体。根据观察到的新生对映体峰面积a(j)、对映异构化时间t和对映异构化温度T，确定对映异构化（反转）势垒ΔG#gas(T)，并通过与温度相关的实验，获得活化焓ΔH#gas和活化熵ΔS#gas。通过停流MDGC对手性1-氯-2,2-二甲基氮杂环丙烷进行的对映异构化研究得出了气相中氮反转的活化参数，即ΔG#gas(353 K)=110.5±0.5 kJ mol(-1)，ΔH#gas=71.0±3.8 kJ mol(-1)和ΔS#gas=-109±11 J mol(-1) K(-1)。通过动态气相色谱法（GC）这一补充方法，发现在气液双相体系中1-氯-2,2-二甲基氮杂环丙烷的表观对映异构化（反转）势垒为ΔG#app(353 K)=108 kJ mol(-1)。在气相中通过停流MDGC获得的值用于计算在手性选择剂Chirasil-镍(II)存在下1-氯-2,2-二甲基氮杂环丙烷在液相中氮反转的活化参数，即ΔG#liq(353 K)=106.0±0.4 kJ mol(-1)，ΔH#liq=68.3±1.4 kJ mol(-1)和ΔS#liq=-106±3.0 J mol(-) K(-1)。
