ε‐Caprolactamium Hydrogen Sulfate: An Ionic Liquid Used for Decades in the Large‐Scale Production of ε‐Caprolactam

Abstract

An iconic liquid: Investigation of the mechanism of the Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam (1) in sulfuric acid or oleum has led to the conclusion that the manufacturing process for ε-caprolactam is in fact the largest-scale industrial technology that has been using an ionic liquid, caprolactamium hydrogen sulfate (2), as the reaction medium for decades.