Ammoximation of cyclic ketones on TS-1 and amorphous SiO2-TiO2

Ammoximation of cyclic ketones on TS-1 and amorphous SiO2-TiO2 with H2O2 and NH3 was studied. The reactivity of cyclic ketones over TS-1 and amorphous SiO2-TiO2 showed the following order: cycloheptanone > cyclopentanone > cyclohexanone > cyclooctanone. Shape-selective poisoning studies revealed that the active sites of TS-1 for ammoximation of cycloheptanone are mostly inside the molecular sieve. The reactivity of cyclohexanone and methylcyclohexanones over TS-1 followed the order cyclohexanone > 2-methylcyclohexanone is approximately equal to 3-methylcyclohexanone > 2,6-dimethylcyclohexanone, reflecting the difference in the diffusivity among the reactants or products inside TS-1. Besides the diffusivity the reactivity seemed to be affected by the difficulty in access of the carbonyl group to the Ti active site inside the zeolite; from the comparison of reactivity of dimethycyclohexanone isomers, the steric hindrance of the substituent methyl group to the access of carbonyl group was considered to decrease in the following order: beta-equatorial> alpha-equatorial> beta-axial > alpha-axial. Diffusion of cyclohexanone or its oxime has been found to play an important role in the ammoximation when the TS-1 crystals larger than 1.5 mu m were employed as a catalyst. For the TS-1 crystals smaller than 0.3 mu m, the ammoximation activity was independent of the diffusivity factor and was determined by the number of active Ti sites present in the zeolite framework. (C) 1996 Academic Press. Inc.