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

Phosphorous pentaoxide (P2O5) effectively catalyzed homogeneous liquid-phase Beckmann rearrangement of cyclohexanone oxime to epsilon-caprolactam in N,N-dimethylformamide (DMF). The turn-over number (TON) of P2O5 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. (C) 1999 Elsevier Science B.V. All rights reserved.