Plasma Electrochemistry in Non-Aqueous Solvents and Application to Organic Synthesis

Low-temperature, atmospheric-pressure plasmas in contact with liquids have attracted interest for various chemical applications including the synthesis of colloidal nanoparticles, degradation of organic pollutants, and conversion of abundant feedstocks. Compared to other chemical approaches, plasma-liquid electrochemical processes do not require a catalyst material, are electrified, and produce unique reactive species such as solvated electrons, one of the strongest chemical reducing species. Here, we present a study of plasma-liquid electrochemistry in non-aqueous solvents and apply such a system to organic synthesis. The majority of studies to date of plasma-liquid electrochemistry have focused on water. For some applications, including organic synthesis, non-aqueous solvents are required. However, the compatibility of plasmas with these solvents and the chemistry has not been thoroughly investigated. We focused on methanol and the well-known pinacol coupling reaction. 1 Parametric studies were performed on methyl-4-formylbenzoate (MFB) as the substrate. The solvent had important effects including the generation of side products through parasitic radical formation. By adding water, the selectivity to the desired pinacol product could be improved. A reaction-diffusion model and thermodynamic calculations at the composite correlated G3(MP2)B3 molecular orbital theory level to support experimental measurements will also be discussed, as well as the potential application of this approach to other organic reactions. 1 J. Wang et al., J. Am. Chem. Soc. 2023, 14, 19, 10470-10474.