Chlorine-Mediated Electrooxidation of Cyclohexene at High Current Density in a Liquid Diffusion Electrode Reactor

Electrocatalysis is a promising alternative to many essential but unsustainable chemical production processes. One category of such processes is olefin epoxidations, which are necessary to produce important chemicals, including ethylene oxide, propylene oxide, and cyclohexene oxide. Herein, we demonstrate the use of a liquid diffusion electrode (LDE) reactor for the chlorine-mediated epoxidation of cyclohexene at high current densities. The LDE reactor geometry minimizes mass transport limitations that are often present in organic phase electrocatalysis, which must facilitate reactions of immiscible phases. Oxidation via a halide intermediate allows for >90% selectivity toward chlorocyclohexanol with subsequent conversion to cyclohexene oxide through contact with strong base. We report the performance of this reactor configuration as a function of pH, with low pH significantly enhancing Faradaic efficiency toward chlorocyclohexanol, and provide evidence via dynamic electrochemical mass spectroscopy to suggest that Cl2 is the active chlorine species responsible for oxidation. We then explore the effect of chloride concentration on the product profile as well as the effect of current density on product distribution and Faradaic efficiency. At 50 mA/cm2, the LDE reactor reaches a peak of ∼80% Faradaic efficiency and ∼93% selectivity toward chlorocyclohexanol. At the highest operating current tested, 100 mA/cm2, the reactor maintains a Faradaic efficiency of ∼65% and selectivity of ∼90%.