Spontaneous Oxidation of Aromatic Sulfones to Sulfonic Acids in Microdroplets

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, (H2O)(center dot+), 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., p-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 + H2O)(+center dot) , followed by 1,2-aryl migration and C-O cleavage. A remarkably high reaction rate acceleration (similar to 103) and regioselectivity (& SIM;100-fold) characterize the reaction.

Automated summary

This study reports the accelerated oxidation of aromatic sulfones in microdroplets, which shows a high reaction rate and regioselectivity. Experimental data suggest that the water radical cation derived from traces of water in the solvent acts as the oxidant.