Organocatalytic Aerobic Oxidative Degradation of Polystyrene to Aromatic Acids

Abstract

Polystyrenes are among the most prevalent commercial plastics produced worldwide, but their end-of-life treatment remains highly suboptimal today. Although currently only in their infancy, chemical upcycling of polystyrenes into functional chemicals have emerged as a potential solution to the growing waste plastic problem. Herein, we describe the first thermal organocatalytic method to oxidatively degrade commercial waste polystyrenes to benzoic acid and 4-nitrobenzoic acid, both of which are important chemicals in demand across multiple industries. Using N-hydroxyl catalysts such as N,N′,N″-trihydroxyisocyanuric acid and N-hydroxyphthalimide derivatives, our operationally simple method affords substantial yields of these aromatic acids in the presence of a suitable nitrate source in air at atmospheric pressure. Furthermore, our method can degrade commercial polystyrene products containing additives such as dyes on gram-scales as well as different polystyrene derivatives (e.g., polystyrene sulfonic acid) into other industrially relevant aromatic acids. Our findings not only redefine the currently overlooked potential of organocatalysis in chemical upcycling of recalcitrant plastics containing inert, non-cleavable polymer backbone structures but also complement other emerging catalytic methods for chemical degradation of plastic waste.