Continuous-flow electroreduction of nitroaromatics to anilines: Mechanistic insights and process intensification

The scalable electrochemical reduction of nitroaromatics to anilines remains challenging for industrial implementation. This work addresses this limitation through the design and optimization of three continuous-flow microreactors: sink-type, one-channel, and multi-channel series flow cells. Employing a CuSn7Pb15 cathode and acidic methanol/water electrolyte, the multi-channel series flow cell achieved exceptional performance under optimized conditions (200 mM substrate, 30 mA cm −2 , 25 mL min −1 flow rate), attaining 97 % yield, 85 % Faradaic efficiency (FE), and a remarkable space-time yield (STY) of 146 g·L −3 ·h −1 —30-fold higher than a batch reactor. Kinetic studies revealed a diffusion-controlled, two-step first-order mechanism at high current density, but a two-step zero-order mechanism at low current density. Computational fluid dynamics (CFD) and residence time distribution (RTD) analyses confirmed superior flow uniformity and thinner boundary layers in this design. Hammett studies demonstrated accelerated kinetics for electron-deficient nitroaromatics. Scalability was proven via a decagram-scale synthesis of 3-(trifluoromethyl)aniline (95 % yield, 72 % FE). This work establishes flow electroreduction as a safe, efficient, and industrially viable route to anilines.