On-Demand Photochemical Synthesis of Hydrogen Peroxide from Alkylated Anthraquinones

Direct illumination of anthraquinones with light, in air, to produce H2O2 reliably and robustly has been developed for aqueous, electrolyte-free, highly pure H2O2 production. Effects of chromophore, solvent, air saturation, and light source have been investigated to understand the mechanism of this transformation. Upon photosensitization of an air-saturated, biphasic solution consisting of an organic solvent and water, H2O2 can be quickly and linearly produced with the oxidized solvent remaining in the organic phase. The mechanism of this transformation has been probed using computational methods, suggesting that proton-coupled electron transfer from an organic solvent to an anthraquinone catalyst is the most likely mechanistic pathway. Commercially relevant H2O2 concentrations, as high as 2.34% (w/w), have been produced in 3 h, among the fastest photochemical H2O2 production reaction reported.