Upcycling Poly(ε-caprolactone) into Azepane via Reductive Ammonolysis over a Titanium Oxide-supported Platinum Catalyst

Abstract

Upcycling aliphatic polyesters into nitrogen-containing heterocycles offers an emerging route to valuable chemicals from plastic waste. Herein, we report the first demonstration of direct transformation of poly(ε-caprolactone) (PCL) into azepane (AZP), a bioactive seven-membered N-heterocycle relevant to pharmaceutical synthesis. A titanium oxide-supported platinum catalyst (Pt/TiO₂) efficiently promotes the transformation, affording AZP in 75% yield, and exhibits robust reusability. Spectroscopic analyses and control experiments reveal that TiO₂ facilitates the initial depolymerization of PCL via vacancy-associated Lewis acid sites, while electron-rich Pt nanoparticles (NPs) promote H₂ dissociation. The synergistic interplay between Pt and TiO₂ enables the sequential depolymerization and hydrogenation of PCL, leading to highly selective formation of AZP. This catalytic platform provides a practical and reusable route for plastic valorization, enabling sustainable access to bioactive nitrogen heterocycles from polymeric feedstocks.