Qiu Lingqi, Psimos Michael D, Cooks R Graham
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
J Am Soc Mass Spectrom. 2022 Aug 3;33(8):1362-1367. doi: 10.1021/jasms.2c00029. Epub 2022 Mar 21.
Reactions in microdroplets can be accelerated and can present unique chemistry compared to reactions in bulk solution. Here, we report the accelerated oxidation of aromatic sulfones to sulfonic acids in microdroplets under ambient conditions without the addition of acid, base, or catalyst. The experimental data suggest that the water radical cation, (HO), derived from traces of water in the solvent, is the oxidant. The substrate scope of the reaction indicates the need for a strong electron-donating group (e.g., -hydroxyl) in the aromatic ring. An analogous oxidation is observed in an aromatic ketone with benzoic acid production. The shared mechanism is suggested to involve field-assisted ionization of water at the droplet/air interface, its reaction with the sulfone (M) to form the radical cation adduct, (M + HO), followed by 1,2-aryl migration and C-O cleavage. A remarkably high reaction rate acceleration (∼10) and regioselectivity (∼100-fold) characterize the reaction.
与本体溶液中的反应相比，微滴中的反应可以加速，并且可以呈现独特的化学性质。在此，我们报道了在环境条件下，在不添加酸、碱或催化剂的情况下，微滴中芳基砜加速氧化为磺酸的反应。实验数据表明，溶剂中痕量水衍生的水自由基阳离子(HO)是氧化剂。反应的底物范围表明芳环中需要有强供电子基团(如-羟基)。在一种芳香酮中观察到类似的氧化反应，并生成苯甲酸。推测其共同的反应机理包括在液滴/空气界面处水的场辅助电离，其与砜(M)反应形成自由基阳离子加合物(M + HO)，随后进行1,2-芳基迁移和C-O键断裂。该反应具有显著高的反应速率加速(约10倍)和区域选择性(约100倍)。
