Chemistry Department, Purdue University, West Lafayette, IN 47907, USA.
J Am Soc Mass Spectrom. 2012 May;23(5):842-9. doi: 10.1007/s13361-012-0337-7.
Solvent-free ion/surface chemistry is studied at atmospheric pressure, specifically pyrylium cations, are reacted at ambient surfaces with organic amines to generate pyridinium ions. The dry reagent ions were generated by electrospraying a solution of the organic salt and passing the resulting electrosprayed droplets pneumatically through a heated metal drying tube. The dry ions were then passed through an electric field in air to separate the cations from anions and direct the cations onto a gold substrate coated with an amine. This nontraditional way of manipulating polyatomic ions has provided new chemical insights, for example, the surface reaction involving dry isolated 2,4,6-triphenylpyrylium cations and condensed solid-phase ethanolamine was found to produce the expected N-substituted pyridinium product ion via a pseudobase intermediate in a regiospecific fashion. In solution however, ethanolamine was observed to react through its N-centered and O-centered nucleophilic groups to generate two isomeric products via 2H-pyran intermediates. The O-centered nucleophile reacted less rapidly to give the minor product. The surface reaction product was characterized in situ by surface enhanced Raman spectroscopy, and ex situ using mass spectrometry and H/D exchange, and found to be chemically the same as the major pyridinium solution-phase reaction product.
在常压下研究无溶剂离子/表面化学，特别是吡喃鎓阳离子在环境表面与有机胺反应生成吡啶鎓离子。干燥试剂离子是通过将有机盐溶液电喷雾，并将得到的电喷雾液滴气动地通过加热的金属干燥管来产生的。然后将干燥的离子通过空气中的电场分离阳离子和阴离子，并将阳离子引导到涂有胺的金基底上。这种操纵多原子离子的非传统方法提供了新的化学见解，例如，涉及干燥分离的 2,4,6-三苯基吡喃鎓阳离子和冷凝固相乙醇胺的表面反应被发现以通过假碱基中间体以区域特异性方式产生预期的 N-取代吡啶鎓产物离子。然而，在溶液中，观察到乙醇胺通过其 N 中心和 O 中心亲核基团反应，通过 2H-吡喃中间体生成两种非对映异构体产物。O 中心亲核试剂反应速度较慢，生成较少的产物。表面反应产物通过原位表面增强拉曼光谱进行了表征，并通过质谱和 H/D 交换进行了非原位表征，发现与主要的吡啶溶液相反应产物在化学上相同。
