Chemical reactions in micrometer-sized droplets can be accelerated by up to six orders of magnitude. However, this acceleration factor (ratio of rate constants relative to bulk) drops to less than 10 for millimeter-sized droplets due to the reduction in surface/volume ratio. To enhance the acceleration in millimeter-sized droplets, we use a new synthesis platform that directly doses reagent vapor onto the reaction droplet surface from a second levitated droplet. Using Katritzky transamination as a model reaction, we made quantitative measurements on size-controlled vapor-dosed droplets, revealing a 31-fold increase in reaction rate constants when examining the entire droplet contents. This enhancement is attributed to a greater reaction rate constant in the droplet surface region (estimated as 100,000 times greater than that for the bulk). The capability for substantial reaction acceleration in large droplets highlights the potential for rapid synthesis of important chemicals at useful scales. For example, we successfully prepared 23 pyridinium salts within minutes. This efficiency positions droplets as an exceptional platform for rapid, in-situ synthesis. This is illustrated by the preparation of pyridinium salts as photocatalysts and their subsequent use in mediation of amine oxidation within the same droplet.

中文翻译：

---

通过来自伙伴液滴的蒸汽计量在悬浮液滴表面的反应加速


微米级液滴中的化学反应可加速多达六个数量级。然而，对于毫米级液滴，由于表面/体积比的减小，该加速因子（速率常数相对于体积的比率）下降至小于 10。为了增强毫米级液滴的加速，我们使用了一种新的合成平台，该平台可以将第二个悬浮液滴中的试剂蒸汽直接喷射到反应液滴表面上。使用 Katritzky 转氨作用作为模型反应，我们对尺寸控制的蒸汽剂量液滴进行了定量测量，结果表明，在检查整个液滴含量时，反应速率常数增加了 31 倍。这种增强归因于液滴表面区域更大的反应速率常数（估计比本体大 100,000 倍）。大液滴中显着加速反应的能力凸显了在有用规模上快速合成重要化学品的潜力。例如，我们在几分钟内成功制备了 23 种吡啶鎓盐。这种效率使液滴成为快速原位合成的特殊平台。这通过吡啶鎓盐作为光催化剂的制备及其随后用于介导同一液滴内的胺氧化来说明。