Enabling Al sacrificial anodes in tetrahydrofuran electrolytes for reductive electrosynthesis

Abstract

Al⁰ is widely used as a sacrificial anode in organic electrosynthesis. However, there remains a notable knowledge gap in the understanding of Al anode interface chemistry under electrolysis conditions. We hypothesize that Al interfacial chemistry plays a pivotal role in the discernible bias observed in solvent selections for reductive electrosynthesis. The majority of existing methodologies that employ an Al sacrificial anode use N,N-dimethylformamide (DMF) as the preferred solvent, with only isolated examples of ethereal solvents such as tetrahydrofuran (THF). Given the crucial role of the solvent in determining the efficiency and selectivity of an organic reaction, limitations on solvent choice could significantly hinder substrate reactivity and impede the desired transformations. In this study, we aim to understand the Al metal interfaces and manipulate them to improve the performance of an Al sacrificial anode in THF-based electrolytes. We have discovered that the presence of halide ions (Cl⁻, Br⁻, I⁻) in the electrolyte is crucial for efficient Al stripping. By incorporating halide additive, we achieve bulk Al stripping in THF-based electrolytes and successfully improve the cell potentials of electrochemically driven reductive methodologies. This study will encourage the use of ethereal solvents in systems using Al sacrificial anodes and guide future endeavors in optimizing electrolytes for reductive electrosynthesis.