Highly selective aerobic oxidation of polystyrene to benzoic acid catalyzed by nitrogen dioxide

The inherent stability and durability of polystyrene (PS) make it a valuable material but also complicate its chemical recycling. Oxidative degradation via hydrogen atom transfer (HAT) is a promising route for PS recovery, yet existing methods suffer from insufficient selectivity toward target products. Herein, we demonstrate an efficient approach to selectively convert PS into benzoic acid (BA) with an impressive yield of 90%. The process uses nitrogen dioxide (NO₂), generated in situ from sodium nitrite and acetic acid, as the primary catalyst, with commercially available cobalt chloride (CoCl₂) as a cocatalyst under mild conditions (180 °C, 2 bar (1 bar = 101 kPa) O₂). Mechanistic studies revealed that NO₂ simultaneously interacts with the C_α-H and C_β-H bonds of the benzyl group via a HAT mechanism to form a dioxetane intermediate. This intermediate undergoes a ring-opening process, facilitating C-C bond cleavage and subsequent oxidation to BA. Furthermore, the demonstrated applicability of real-world PS waste underscores the potential of this process to advance PS recycling technologies, ultimately helping mitigate the environmental impact of plastic waste.