Photochemical reactions between 1,4-benzoquinone and O₂^•

The superoxide anion radical (O₂^•-) is one of the most predominant reactive oxygen species (ROS), which is also involved in diverse chemical and biological processes. In this study, O₂^•- was generated by irradiating riboflavin in an O₂-saturated solution using an ultraviolet lamp (λ_em = 365 nm) as the light source. The photochemical reduction of 1,4-benzoquinone (p-BQ) by O₂^•- was explored by 355-nm laser flash photolysis (LFP) and 365-nm UV light steady irradiation. The results showed that the photodecomposition efficiency of p-BQ was influenced by the riboflavin concentration, p-BQ initial concentration, and pH values. The superoxide anion radical originating from riboflavin photolysis served as a reductant to react with p-BQ, forming reduced BQ radicals (BQ^•-) with a second-order rate constant of 1.1 × 10⁹ L mol^-1 s^-1. The main product of the photochemical reaction between p-BQ and O₂^•- was hydroquinone (H₂Q). The present work suggests that the reaction with O₂^•- is a potential transformation pathway of 1, 4-benzoquinone in atmospheric aqueous environments.