Multi-step oxidative carboxylation of olefins with carbon dioxide by combining electrochemical and 3D-printed flow reactors

The selective oxidation of alkenes to form epoxides followed by the cycloaddition of CO2 is a sustainable and cost-efficient method to generate functional cyclic carbonates. The use of a continuous-flow process allows seamless integration of both reactions sequentially under tailored and optimised conditions for each of the transformations to produce the cyclic carbonates. Here, we successfully demonstrate olefin electrooxidation, followed by the cycloaddition of CO2 to produce cyclic carbonates employing 3D printed (3DP) reactors in continuous flow and without the need for intermediate purification steps. This approach is highly convenient since the electrolyte (ammonium salt) from the electrochemical reaction acts also as a catalyst in the cycloaddition reaction. Different parameters in the electrochemical oxidation were evaluated (e.g. solvent, electrode, electrolyte, concentrations and current intensity). Complete conversion and high selectivity (>80%) towards the formation of epoxide were observed. The electrolyte served as a catalyst for the cycloaddition reaction. The digital design of the 3DP reactor played a crucial role in efficient performance of the cycloaddition reaction, showing increased productivity (a space-time yield of 4.38 gprod h(-1) L-1) compared to that of a coil and a packed bed reactor. Consecutive CO(2 )cycloaddition reactions were also evaluated and a global yield of 83% of cyclic carbonates was observed for styrene. The system exhibited stability and stable activity for at least 20 h.