Epoxidation Selectivity of Cyclohexene Catalyzed by Electric Field at the Interface of Microdroplets without Catalyst

The interface of aqueous microdroplets has been proven to have a large number of unique properties, which can initiate reactions that cannot occur in bulk solution. In this work, we found that cyclohexene spontaneously oxidized at the gas-liquid interface of the microdroplets under mild conditions. Notably, tetrabutylammonium bromide as an electrolyte added to the reaction system can promote the directional epoxidation of cyclohexene. The control variable experiment proved that oxygen was the main oxygen source of the epoxidation reaction, and the product of cyclohexene oxide was detected by gas chromatography-mass spectrometry and nuclear magnetic resonance hydrogen spectrum. Additionally, density functional theory calculation results show that the energy barrier of the cyclohexene oxidation reaction at the interface in the presence of an electric field is reduced by 89.37 kJ/mol. The observed 89 kJ/mol reduction in activation energy represents the maximum achievable effect under optimal field-reaction axis alignment. The possible reasons for the increase in interfacial selectivity were analyzed from the electrochemistry. So far, there are a few reports on the effect of microdroplet interface on reaction selectivity; the impact of interfacial electric field may have broader applications in the electrochemistry field.