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

The superoxide anion radical (O 2 •− ) is one of the most predominant reactive oxygen species (ROS), which is also involved in diverse chemical and biological processes. In this study, O 2 •− was generated by irradiating riboflavin in an O 2 -saturated solution using an ultraviolet lamp ( λ em = 365 nm) as the light source. The photochemical reduction of 1,4-benzoquinone ( p -BQ) by O 2 •− 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 × 10 9 L mol −1 s −1 . The main product of the photochemical reaction between p -BQ and O 2 •− was hydroquinone (H 2 Q). The present work suggests that the reaction with O 2 •− is a potential transformation pathway of 1, 4-benzoquinone in atmospheric aqueous environments.