Organocatalyzed Beckmann Rearrangement of Cyclohexanone Oxime in a Microreactor: Kinetic Model and Product Inhibition

ε-Caprolactam (CPL) is the monomer for nylon-6 with wide applications in textiles, automobiles, electronics, and mechanicals. Here, we present the kinetics study of Beckmann rearrangement of cyclohexanone oxime (COX) catalyzed by trifluoroacetic acid (TFA) and acetonitrile in microreactors. The effect of temperature, ratio of TFA to acetonitrile, and concentration of COX were investigated. The inhibition effect of CPL in this reaction system was firstly reported. Based on the results, a comprehensive mathematic kinetic model considering the product inhibition effect of CPL has been developed in the temperature range of 368 K to 391 K, which is in good agreement with experimental results across a broad experimental parameter space. In addition, kinetic study indicates that the esterification reaction of COX and the transposition reaction of the intermediate are both supposed to be the rate-determining steps, and in the catalyst system, the ratio of TFA and acetonitrile mainly influences the reaction rate and the activation energy of the transposition step. The developed model could provide much reliable knowledge for industrial application.