Yan Xin, Augusti Rodinei, Li Xin, Cooks R Graham
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084 (USA), Fax: (+1) 765-494-9421.
Department of Chemistry, Federal University of Minas Gerais, Av. Antônio Carlos, 6627, Pampulh, Belo Horizonte, Minas Gerais 31270-901 (Brazil).
Chempluschem. 2013 Sep;78(9):1142-1148. doi: 10.1002/cplu.201300172. Epub 2013 Aug 5.
Paper spray ionization can be used to study organic reactions in solution under ambient conditions by utilizing the rate acceleration that occurs in reactions in small volumes of solution. In this novel approach to performing reactions, reagents are transferred onto a triangular paper surface by drop-casting and charged droplets of the reaction product mixture are released by field evaporation and examined online by mass spectrometry. The increase in the rate of product formation is attributed to solvent evaporation, which increases reagent concentrations, changes the pH, and enhances intermolecular interactions. As a proof of principle, the Katritzky reaction between a pyrylium salt and mono- or diamines, including substituted anilines, was investigated. The influence of electronic and steric effects was evaluated straightforwardly. The carbon chain length of α,ω-diamines was found to control the formation of mono- versus disubstituted products, thus reflecting the strong destabilizing coulombic effects in the shorter carbon-chain systems. Information on the mechanism was provided by the observation of 2H-pyran intermediates and mixed pyridinium-2H-pyran ions. The rates of product formation in the base-assisted Katritzky reaction increase linearly from 0.1 to 10 equivalents of triethylamine. The reactive paper spray technique, owing to its speed and information content, has potential pedagogical value and provides a tool to explore organic reactions and correlate experimental results with current mechanistic understanding.
纸喷雾电离可用于在环境条件下研究溶液中的有机反应，利用小体积溶液中反应发生的速率加速现象。在这种进行反应的新方法中，试剂通过滴铸转移到三角形纸表面，反应产物混合物的带电液滴通过场蒸发释放，并通过质谱在线检测。产物形成速率的增加归因于溶剂蒸发，这会增加试剂浓度、改变pH值并增强分子间相互作用。作为原理验证，研究了吡喃鎓盐与单胺或二胺（包括取代苯胺）之间的卡特里茨基反应。直接评估了电子效应和空间效应的影响。发现α,ω-二胺的碳链长度控制单取代产物与双取代产物的形成，从而反映了较短碳链体系中强烈的去稳定库仑效应。通过观察2H-吡喃中间体和混合吡啶鎓-2H-吡喃离子提供了有关机理的信息。在碱辅助的卡特里茨基反应中，产物形成速率从0.1到10当量的三乙胺呈线性增加。反应性纸喷雾技术因其速度和信息含量，具有潜在的教学价值，并提供了一种探索有机反应并将实验结果与当前机理理解相关联的工具。
