Ammoximation of cyclohexanone over nanoporous TS-1 using UHP as an oxidant

Ammoximation of cyclohexanone to cyclohexanone oxime has been carried out using ammonia and urea hydrogen peroxide adducts as the oximation reagents. Effect of catalyst concentration, temperature, and molar ratio of reactants and effect of doping TS-1 with Fe has been studied to obtain the optimum conversion of cyclohexanone (CH) and selectivity to cyclohexanone oxime. The catalyst has been characterized employing the techniques of XRD, FT-IR, EDAX, SEM, AAS and Mössbauer spectroscopy with a view to confirm phase purity, stoichiometry, particle size distribution and oxidation state of Fe. The BET surface area of TS-1 catalyst was found to be 680 m2/g. A maximum conversion of about 70% of cyclohexanone with cyclohexanone oxime selectivity of 99.72% was obtained over TS-1 doped with Fe at a temperature of 40 °C and cyclohexanone to UHP molar ratio of 1:1. Reaction seems to proceed through a redox mechanism and follow hydroxylamine as well as imine routes. According to hydroxylamine route ammonia and UHP react within the TS-1 pores and produce hydroxylamine. The hydroxylamine thus formed reacts with cyclohexanone outside the pores to produce cyclohexanone oxime. In the imine route cyclohexanone and ammonia react to produce cyclohexanone imine, which is oxidized to cyclohexanone oxime. A tentative mechanism for the process has been proposed.