Activation of molecules by non-thermal plasma in gas-liquid systems. Application to organic synthesis.

Abstract

Non-thermal plasma generates highly reactive species, such as electrons, ions, photons, neutrals at different excited states, and radicals, at ambient temperature and pressure using only electromagnetic fields. This enables the activation of chemical transformations without catalysts or additives, offering a promising route toward new and more sustainable syntheses. In organic synthesis, non-thermal plasma activation typically occurs in biphasic gas-liquid environments, where the plasma is generated in the gas phase while the liquid serves both as a source of reactants and a collector of products. This review provides a comprehensive and chemistry-centered perspective on plasma activation in biphasic gas-liquid systems, covering the literature from 1970 to 2025. Fundamental principles of plasma generation and reactivity relevant to organic synthesis are discussed by treating the plasma-induced reactivity as primarily governed by radical kinetics. Special emphasis is placed on the composition of gas and liquid phases, along with reactor design that controls gas-liquid interfaces, to tune reaction pathways and selectivity in plasma-assisted processes. Reported applications in organic synthesis are then discussed, including reduction, oxidation, C–C and C–N bond formation, together with the associated mechanistic understanding. These studies demonstrate that non-thermal plasma activation offers potential for substrate functionalization using species derived directly from a gas or solvent, an approach that seems especially attractive for volatile saturated hydrocarbons. Finally, the current challenges are outlined, such as transfer of short-lived species, competing reaction pathways, reactor scale-up, and lack of standardized methodology hindering systematic comparison. By consolidating fundamental principles and applied strategies, this review aims to serve as a reference for chemists seeking to harness plasma activation for organic synthesis.