Catalytic Poly(ethylene terephthalate) Aromatic C–H Hydroxylation for Upcycling to Specialty Chemicals and Multivariate Metal–Organic Frameworks

Poly(ethylene terephthalate) (PET), the most produced and recovered aromatic polyester worldwide, offers numerous opportunities for upcycling into functional materials and chemicals. The aromatic terephthalate segment makes up the bulk of the total PET mass and offers opportunities to access valuable highly substituted oxygenated aromatics that are important precursors to a host of specialty chemicals and functional materials. However, chemical modification of the terephthalate segment has thus far achieved limited success due to the aromatic ring’s electron deficiency, which deactivates it toward electrophilic attack. Herein, we demonstrate the usage of transition-metal-catalyzed C–H activation as a viable strategy for direct functionalization of PET’s aromatic C–H bonds in this proof-of-concept study. Ruthenium-catalyzed C–H hydroxylation afforded the useful, yet synthetically challenging, highly substituted oxygenated aromatic compound 2-hydroxyterephthalic acid in high selectivity and synthetically useful conversions directly from PET. Notably, this procedure was tolerant to a range of PET plastic wastes, including dye-containing textiles and other non-PET plastic contaminants, and was also amenable to gram-scale aromatic functionalization of used real-life PET beverage bottles. The resulting 2-hydroxyterephthalic acid product can be further upcycled into multivariate hydroxylated MOFs with high porosity and crystallinity, which have proven to be useful for many known applications. With our aromatic C–H activation strategies, we expand the diversity and possibilities of value-added materials and chemicals accessible from PET.