Organocatalytic Aerobic Oxidative Degradation of Polystyrene to Aromatic Acids

We report an organocatalytic approachfor the chemical upcyclingof waste polystyrene into benzoic acids using N-hydroxylcatalysts, oxygen, and nitrates. Polystyrenes are among the most prevalent commercialplastics producedworldwide, but their end-of-life treatment remains highly suboptimaltoday. Although currently only in their infancy, chemical upcyclingof polystyrenes into functional chemicals have emerged as a potentialsolution to the growing waste plastic problem. Herein, we describethe first thermal organocatalytic method to oxidatively degrade commercialwaste polystyrenes to benzoic acid and 4-nitrobenzoic acid, both ofwhich are important chemicals in demand across multiple industries.Using N-hydroxyl catalysts such as N,N & PRIME;,N & DPRIME;-trihydroxyisocyanuricacid and N-hydroxyphthalimide derivatives, our operationallysimple method affords substantial yields of these aromatic acids inthe presence of a suitable nitrate source in air at atmospheric pressure.Furthermore, our method can degrade commercial polystyrene productscontaining additives such as dyes on gram-scales as well as differentpolystyrene derivatives (e.g., polystyrene sulfonic acid) into otherindustrially relevant aromatic acids. Our findings not only redefinethe currently overlooked potential of organocatalysis in chemicalupcycling of recalcitrant plastics containing inert, non-cleavablepolymer backbone structures but also complement other emerging catalyticmethods for chemical degradation of plastic waste.