Kinetically guided high-yield and rapid production of ε-caprolactone in a microreactor system

Industrial production of epsilon-caprolactone, the monomer of biodegradable polycaprolactone, consists of acetic acid peroxidation and the Baeyer-Villiger oxidation of cyclo-hexanone in semi-batch reactors. The strong exothermic feature of the latter and ease of epsilon-caprolactone hydrolysis significantly affects the production efficiency. Here, collective effects of kinetic studies and density functional theory (DFT) calculations reveal activation energy of the Baeyer-Villiger oxidation is higher than that of epsilon-caprolactone hydrolysis and the hydrolysis barrier is controlled by hydrogen bond energy of the reaction medium. Then, we developed a microreactor system to intensify heat transfer thereby allowing safe and efficient production of epsilon-caprolactone. A yield of 99.6% was achieved within minutes via consecutive two-step reactions of peroxidation and the Baeyer-Villiger oxidation, as compared with state-of-the-art yield of 96% in hours of industrial operation. The high selectivity is attributed to high reaction temperature allowed by the microreactor and DFT-guided choice of solvent to mitigate the hydrolysis.