Beckmann Rearrangement of Cyclohexanone Oxime in a Microreactor Setup with Internal Recirculation

Abstract

Beckmann rearrangement of cyclohexanone oxime dissolved in cyclooctane with oleum to ϵ‐caprolactam was demonstrated in a microreactor setup with internal recirculation operated in continuous mode. The core of the setup comprised a 316 stainless‐steel micromixer consisting of 17 split‐and‐recombine units connected to a delay loop, a 316 stainless‐steel microchannel reactor with an internal diameter of 0.250 mm and a length of 0.50 m. At 100 °C, the conversion of cyclohexanone oxime was complete and the selectivity towards ϵ‐caprolactam was approximately 99 %. The solvent cyclooctane reduces the observed purity of the produced oleum/ϵ‐caprolactam. This reduction in purity might be a severe hurdle for usage of a solvent on the industrial scale in the Beckmann rearrangement of cyclohexanone oxime in oleum to ϵ‐caprolactam.

Reusable Deep Eutectic Solvents for Clean ε-Caprolactam Synthesis under Mild Conditions

“…The effects of reaction temperatures on the conversion of CHO are shown in Figure S6, and the effects of temperatures on the yield of CPL are shown in Figure a. It is found that the reaction rate significantly increases with the rise of the reaction temperature, which may be due to its high activation energy. − Other relevant details are in the Supporting Information. Figure b shows the Arrhenius plot of ln k against 1/ T , and E a is calculated as 39.82 kJ mol –1 , which is lower than those reported in the literature, ,, supporting the advantages of DES [ChCl]­[TfOH] 3 , and then accelerating the reaction by stabilizing the transition states and decreasing the energy barriers.…”

Comprehensive updates on Beckmann Rearrangement

“…When a solvent is used in the industrial conversion of cyclohexanone oxime to caprolactam in the oleum, the created oleum/caprolactam was destroyed by the cyclooctane solvent, which could result in problems. [126] A multiphase microchemical system was used by Zhang et al [127] to illustrate the cyclohexanone oxime's mechanism. Beckmann rearrangement in oleum was developed a protonated caprolactam hydrogen sulfate equilibrium relationship which was investigated, and equilibrium constants for 70, 80, and 90 °C were found based on these results and earlier mechanism studies.…”

The Effective Catalyst (Cobalt Salt/Lewis Acid) for Beckmann Rearrangement of Cycloalkanone Oximes to Lactams under Mild Conditions

“…The Beckmann rearrangement is commonly used in organic chemistry to transform ketoximes into amides [1]- [9]. The reaction generally requires high reaction temperatures and strongly acids.…”