Nandy Abhijit, Kumar Anubhav, Mondal Supratim, Koner Debasish, Banerjee Shibdas
Department of Chemistry, Indian Institute of Science Education and Research Tirupati, Tirupati 517507, India.
Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi 502284, India.
J Am Chem Soc. 2023 Jul 26;145(29):15674-15679. doi: 10.1021/jacs.3c04662. Epub 2023 Jul 12.
Although phenol is stable in bulk water, we report an exceptional phenomenon in which phenol is spontaneously transformed into a phenyl carbocation (Ph) in water microdroplets. The high electric field at the air-water interface is proposed to break the phenolic Csp-OH bond, forming Ph, which remains in equilibrium with phenol as deciphered by mass spectrometry. We detected up to 70% conversion of phenol to Ph in aqueous microdroplets, although catalyst-free activation of the phenolic Csp-OH bond is challenging. This transformation is well tolerated by a wide range of electron-donating and -withdrawing substituents in phenolic compounds. The Ph in water microdroplets could be reacted with various nucleophiles (amine, pyridine, azide, thiol, carboxylic acid, alcohol, and O-water), yielding the -substitution products of phenol through an aromatic S1 mechanism. Despite the fleeting life of Ph in the bulk, this study demonstrates its unusual stability at the aqueous microdroplet surface, enabling its detection and transformation.
尽管苯酚在大量水中是稳定的，但我们报告了一种特殊现象，即苯酚在水微滴中会自发地转化为苯基碳正离子（Ph）。据推测，气-水界面处的高电场会打破酚类Csp-OH键，形成Ph，通过质谱分析可知，Ph与苯酚保持平衡。尽管酚类Csp-OH键的无催化剂活化具有挑战性，但我们在水微滴中检测到高达70%的苯酚转化为Ph。酚类化合物中广泛的供电子和吸电子取代基对这种转化具有良好的耐受性。水微滴中的Ph可以与各种亲核试剂（胺、吡啶、叠氮化物、硫醇、羧酸、醇和O-水）反应，通过芳香族S1机制生成苯酚的α-取代产物。尽管Ph在大量水中的寿命短暂，但本研究证明了其在水微滴表面具有不同寻常的稳定性，从而能够对其进行检测和转化。
