On the mechanism of the organocatalyzed Beckmann rearrangement of cyclohexanone oxime by trifluoroacetic acid in aprotic solvent

The Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam in high yield catalyzed by trifluoroacetic acid in aprotic solvents is described. The influence of the concentration of reagents, intermediates, solvents on reaction rate and selectivity in ɛ-caprolactam is studied. The identification of the key intermediate and its role in the catalysis are reported together with the influence of the acid on the reaction rate. In addition, the study of the hydrolysis reactions of reagent and intermediates highlights what are the parameters that influence the selectivity to ɛ-caprolactam. On the basis of these results a likely catalytic cycle based only on the experimentally verified intermediates is also given.