Bain Ryan M, Pulliam Christopher J, Cooks R Graham
Department of Chemistry , Purdue University , West Lafayette , IN 47907 , USA . Email:
Center for Analytical Instrumentation Development , Purdue University , West Lafayette , IN 47909 , USA.
Chem Sci. 2015 Jan 1;6(1):397-401. doi: 10.1039/c4sc02436b. Epub 2014 Sep 9.
Complex chemical reactions can occur in electrosprayed droplets on the millisecond time scale. The Hantzsch synthesis of 1,4-dihydropyridines was studied in this way using on-line mass spectral analysis to optimize conditions and characterize the product mixture. Changing the distance between the nanospray source and the MS inlet allowed exploration of reaction progress as a function of droplet time-of-flight. Desolvation of the charged microdroplets is associated with transformation from starting material to intermediates and eventually to product as the distance is increased. Results of the on-line experiments require a termination step that discontinuously completes the desolvation process and allows the generated gaseous ions to be used to characterize the state of the system at a particular time. The intermediates seen correspond to those known to occur in the bulk solution-phase reaction. Off-line collection of the sprayed reaction mixture allowed the recovery of 250 mg h of desired reaction product from a single sprayer, permitting characterization by NMR and other standard methods. A thin film version of the accelerated reaction is described and it could be controlled through the temperature of the collection surface.
复杂的化学反应可在毫秒时间尺度上发生于电喷雾液滴中。通过这种方式，利用在线质谱分析研究了1,4 - 二氢吡啶的汉茨希合成反应，以优化条件并表征产物混合物。改变纳米喷雾源与质谱仪进样口之间的距离，可以探究反应进程与液滴飞行时间的关系。随着距离增加，带电微滴的去溶剂化过程伴随着原料向中间体进而最终向产物的转化。在线实验结果需要一个终止步骤，该步骤能不连续地完成去溶剂化过程，并使生成的气态离子用于表征特定时刻系统的状态。所观察到的中间体与已知在本体溶液相反应中出现的中间体一致。对喷雾反应混合物进行离线收集，可从单个喷雾器中每小时回收250毫克所需反应产物，从而能够通过核磁共振及其他标准方法进行表征。文中描述了加速反应的薄膜版本，并且可以通过收集表面的温度对其进行控制。
