To disentangle the factors controlling the rates of accelerated reactions in droplets, we used mass spectrometry to study the Katritzky transamination in levitated Leidenfrost droplets of different yet constant volumes over a range of concentrations while holding concentration constant by adding back the evaporated solvent. The set of concentration and droplet volume data indicates that the reaction rate in the surface region is much higher than that in the interior. These same effects of concentration and volume were also seen in bulk solutions. Three pyrylium reagents with different surface activity showed differences in transamination reactivity. The conclusion is drawn that reactions with surface‐active reactants are subject to greater acceleration, as seen particularly at lower concentrations in systems of higher surface‐to‐volume ratios. These results highlight the key role that air‐solution interfaces play in Katritzky reaction acceleration. They are also consistent with the view that reaction‐increased rate constant is at least in part due to limited solvation of reagents at the interface.

中文翻译：

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溶液界面的反应加速：Katritzky转氨反应的各向异性速率常数

为了弄清控制液滴中加速反应速率的因素，我们使用质谱研究了浓度范围不同但体积恒定的悬浮莱顿弗罗斯特液滴中的Katritzky转氨作用，同时通过添加蒸发后的溶剂使浓度保持恒定。一组浓度和液滴体积数据表明，表面区域的反应速率远高于内部区域的反应速率。在本体溶液中也观察到浓度和体积的这些相同影响。三种具有不同表面活性的吡啶鎓试剂在转氨反应性上显示出差异。得出的结论是，与表面活性反应物的反应具有更大的加速作用，特别是在较高的表面体积比的系统中，在较低的浓度下尤其如此。这些结果凸显了空气界面在Katritzky反应加速中的关键作用。它们也与以下观点一致：反应速度增加的速率常数至少部分是由于界面处试剂的溶剂化作用有限。