Beckmann rearrangement of cyclohexanone oxime on zeolites

The Beckmann rearrangement of cyclohexanone oxime (1) was carried out in the liquid phase in the presence of a series of acid zeolites (HY-20, HY-50, HY-100, HYD, and HZSM-5) at different reaction temperatures. Together with ε-caprolactam (2), 5-cyano-1-pentene (3), and cyclohexanone (4) were present in the reaction mixtures. From the selectivity curves of 2 and 3, it can be concluded that a Ritter equilibrium between 2 and 3 occurs under our experimental conditions, the direction of the process depending strongly on the hydrophobicity of the catalyst. The influence of the level of Na+ exchange and of the framework Si/Al ratio on the total conversion and the selectivity of 2 reveals that medium and strong acid sites (pK a < 0) catalyze the reaction. Finally, no appreciable variations in the specific activity of the catalyst were observed when changing from a tridirectional large pore size sample (Y) to a medium pore size (ZSM-5).