Homogeneous liquid-phase Beckmann rearrangement of oxime catalyzed by phosphorous pentaoxide and accelerated by fluorine-containing strong acid

Abstract

Phosphorous pentaoxide (P 2O 5) effectively catalyzed homogeneous liquid-phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam in N, N-dimethylformamide (DMF). The turn-over number (TON) of P 2O 5 was 20. The catalytic activity was greatly increased by addition of a co-catalyst, trifluoromethane sulfonic acid, and the TON was increased to 100. The catalyst system was successfully applied to other ketoximes such as acetone oxime, acetophenone oxime, and cyclopentanone oxime. A strongly polarized pseudo-iminium cation was proposed as an active species.