Abstract:The widespread application of plastics results in the production of large amounts of waste annually, posing a significant environmental challenge due to ineffective treatment and resulting pollution. Therefore, developing green and efficient recycling methods is crucial. Hydrolysis offers a novel strategy for the degradation and recycling of polyester plastics, producing monomers or high-value-added chemicals. Polycaprolactone (PCL), a biodegradable alkyl polyester synthesized via ring-opening polymerization of ε-caprolactone monomer, possesses desirable mechanical properties and biocompatibility, yet its recovery rate remains low. This work demonstrates the efficient hydrolysis of PCL under solvent-free conditions using a cost-effective cobalt phosphine complex and a metal trifluoromethanesulfonate as catalysts. Gas chromatography and nuclear magnetic resonance hydrogen spectroscopy were used to analyze the reaction products. We investigated the effects of hydrogen pressure and temperature, optimizing reaction conditions: 160 ℃, 6 MPa hydrogen pressure, 10% Co(OAc)2-triphos (1,1,1-tris (diphenylphosphinomethyl) ethane), and 10% Sc(OTf)3 (scandium trifluoromethanesulfonate) for 12 h. Under these conditions, 1,6-hexanediol was produced with 99% conversion and 99% yield. Even at reduced pressure (2 MPa) and catalyst loading (1% each), 99% conversion and 97% yield were achieved. 1,6-hexanediol is a valuable fine chemical and important intermediate. Catalyst recovery studies revealed poor recyclability. Mechanistically, the strong Lewis acidity of metal trifluoromethanesulfonates catalyzes rearrangement; weaker Lewis acids only weaken the carbonyl group′s influence. The Co(OAc)2-triphos system catalyzes carbonyl hydrogenation (unlike the Ni(OAc)2-triphos system, which only hydrogenates C=C double bonds). Therefore, the Co(OAc)2-triphos/Sc(OTf)3 catalyst system first promotes PCL hydrogenation to form a hemiacetal, followed by intramolecular 1,3-hydrogen transfer, depolymerizing PCL to 6-hydroxyhexanal, which is then hydrogenated to produce 1,6-hexanediol. This work provides a feasible strategy for enhancing the recycling of discarded PCL plastics, contributing to addressing the environmental challenges posed by plastic waste. Close-