Ionic Liquid‐Mediated Oxidative Degradation of Polycaprolactone into Adipic Acids over Pt/TiO2 in Water

Upgrading polyester waste into high value-added chemicals can achieve carbon recycling, which is of great significance for sustainable development. Herein, we report a one-pot protocol to oxidatively degrade polycaprolactone (PCL) with air into adipic acid (AA) mediated by ionic liquid (IL, e.g., 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [BMIm][NTf2]) in water. In this protocol, IL catalyzes the hydrolysis of PCL into 6-hydroxyhexanoic acid (6-HHA) and further mediates the oxidation of 6-HHA into AA over TiO2-supported Pt nanocatalysts, reaching the highest AA yield of 85.6% under relatively mild conditions (140 °C, 1.5 MPa). Mechanism investigation indicates that both O2 •- and •OH derived from oxygen and water are involved in the oxidation of 6-HHA to form 6-oxohexanoic acid via two pathways, which further convert into AA. The IL inhibits the overoxidation of AA, thus leading to a high selectivity toward AA. This protocol provides a green and feasible way to degrade PCL and also to access AA.