Chemical transformations on a weakly acidic catalyst studied by N-15 NMR: butanone oxime on silicalite-1

The chemical species formed upon adsorption and subsequent heat treatment o f 2-butanone [N-15]oxime (1) on the dried molecular sieve silicalite-1 were examined by N-15 NMR spectroscopy. The weak acidity of silicalite-l, which provided weakly adsorbed organic species, facilitated detection without so lid-state methods. Based on chemical shifts, the predominant species at 25 degrees C was a physisorbed oxime (-48 ppm). An H-bonded oxime (-71 ppm) fo rm was detected at -25 degrees C. A sealed sample of 1 was heated off-line to attempt catalytic conversion to an amide (Beckmann rearrangement). At 20 0 degrees C, 1 was hydrolyzed to an amine (-364 ppm). Higher temperatures ( 400-500 degrees C) caused fragmentation of 1 to a nitrile (-135 ppm). No am ides were detected. The large chemical shift range of N-15 provides a power ful means for investigating chemical reactions in heterogeneous systems. Co pyright (C) 1999 John Wiley & Sons, Ltd.