Highly efficient electro-epoxidation of olefins coupled with bromine recycling†

Organic electrosynthesis powered by renewable electricity has gained attention as a sustainable and economically advantageous method for diverse chemical transformations. Olefin epoxidation is a key reaction for producing multiple epoxides used as value-added fine chemicals and crucial industrial intermediates. The halohydrin-based method was previously utilized in large-scale productions. However, its reliance on corrosive reagents and substantial energy demands have led to a gradual transition towards more environmentally friendly methodologies, with electrosynthesis emerging as a significant alternative. In this study, we developed a Br₂/Br⁻-mediated electro-epoxidation strategy for olefins using a one-pot electrochemical cell. This method achieved an impressive yield of styrene oxide (97.5%) and Faraday efficiency (84.7%) at a high substrate concentration of 100 mM and exhibited high compatibility with an industrial-relevant current density (100 mA cm⁻²). Additionally, we developed a novel method to realize the electrolyte recyclability in a one-pot cell, ensuring ion regeneration and demonstrating strong feasibility for practical applications. Moreover, the current system exhibited exceptional stability for 23 cycles and demonstrated a broad scope for substrates. To further capitalize on these advantages, we successfully scaled up the production of styrene and cyclohexene into value-added products. These results underscore the methodological universality, economic viability, and sustainability of the developed system, highlighting its potential for industrial adoption.