Scalable Electrochemical Preparation of Spermidine and Spermine

We present a simple and sustainable electrochemical hydrogenation method for the preparation of two commercially relevant polyamines from their corresponding nitrile precursors at nickel foam cathodes. The hydrogenation proceeds under mild constant-current electrolysis conditions in an aqueous sulfuric acid electrolyte. After reaction parameters were established in batch-type cells, the hydrogenation process was readily transferred in flow and optimized in a flow-type electrolyzer with a 48 cm2 geometric cathode surface area. The optimal reaction parameters for either high yield or high productivity were found by a combination of DoE optimization and monitoring the reaction kinetics. To showcase the practical relevance and scalability of this approach, we demonstrated the synthesis of two technically relevant polyamines, spermidine and spermine, on a hectogram scale at a high geometric current density of 100 mA/cm2, obtaining excellent isolated yields of 85% and 84%, respectively. Importantly, the products were purified by simple and easily scalable precipitation-based procedures, avoiding energy-intensive distillation and chromatographic steps. The developed electrochemical approach eliminates the need for high-pressure hydrogen gas, minimizes byproduct formation, and enables efficient synthesis in water, offering an attractive safe, scalable, and environmentally friendly alternative route to valuable polyamines.