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 applications including the synthesis of colloidal nanoparticles, degradation of organic pollutants, and chemical transformation of abundant feedstocks. Compared to thermo-, photo-, and electrochemical 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.

In this talk, I will share our efforts to expand the scope of plasma-liquid electrochemistry to 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 resulting chemistry has not been thoroughly investigated. We initially focused on the well-known pinacol coupling reaction (Wang et al., J. Am. Chem. Soc. 2023). Parametric studies were performed on methyl-4-formylbenzoate (MFB) as the substrate and methanol as the solvent. The solvent had important effects including the generation of side products through parasitic radical formation. By controlling the substrate concentration and introducing water, the selectivity to the desired pinacol product could be improved. A reaction-diffusion model and thermodynamic calculations to support experimental measurements will also be discussed, as well as the potential application of this approach to other solvents and organic reactions.