Cooxidants

Cooxidants are substances that participate in oxidation reactions in tandem with a primary oxidant, often serving to regenerate the active oxidant or to generate reactive intermediates that propagate oxidation. They are central in catalytic oxidation where the oxidation state of the catalyst is cycled; the cooxidant supplies the oxidizing equivalents that allow the catalyst to return to its active form after a substrate is oxidized. In this sense, a cooxidant is not the main oxidant driving the substrate oxidation by itself, but rather supports the catalytic turnover.

Mechanisms include redox mediation, where the cooxidant shuttles electrons between substrate and catalyst; formation of radical species that initiate or propagate oxidation; or activation of molecular oxygen in aerobic systems to generate reactive species at the catalyst site.

Applications span synthetic chemistry, environmental chemistry, and materials science. In heterogeneous and homogeneous catalysis, cooxidants enable aerobic oxidations using O2 or air, avoiding stoichiometric oxidants. In photocatalysis and electrocatalysis, cooxidants supplement a primary oxidant to improve efficiency, selectivity, or substrate scope. In water treatment, cooxidants may help generate oxidizing radicals that degrade contaminants.

Because the term cooxidant is used in different ways, definitions vary by field. The common thread is a secondary oxidant that works with another oxidant to enable or enhance oxidation, often through catalyst regeneration or radical mediation.