IR Observation of Selective Oxidation of Cyclohexene with H2O2 over Mesoporous Nb2O5

Liquid-phase catalytic oxidation of cyclohexene by H2O2 (35 wt %) over mesoporous Nb2O5 showed considerable conversion and high selectivity for both cis- and trans-1,2-cyclohexanediols in acetonitrile solvent. The mesoporous structure of the catalyst, in addition to its high surface area, was considered to be advantageous for the reaction due to more frequent interaction of molecules with active sites inside pores. Gradual formation of 1,2-cyclohexanediol from the reaction of adsorbed cyclohexene with diluted (10 wt %) H2O2 was observed at room temperature by in in situ infrared (IR) method. The absence of observation of an IR spectrum of 1,2-epoxycyclohexane confirmed that the hydrolysis of the oxidation product occurred immediately. In addition to the conventional stepwise oxidation and hydrolysis to produce 1,2-cyclohexanediol, a direct hydroxylation of cyclohexene was proposed: the production of cis-1,2-cyclohexanediol with about a half amount of trans-1,2-cyclohexanediol Suggests the activation of H2O2 on the acidic OH groups of mesoporous Nb2O5 to directly produce both cis- and trans-1,2-cyclohexanediols from cyclohexene without forming 1,2-epoxycyclohexane. The hydrolysis of adsorbed cyclohexene to cyclohexanol was observed when more diluted (2.5 wt %) H2O2 was used. This indicates that H2O2 can be also activated for hydrolysis of olefin, but that the preferential activation of H2O2 over H2O2 occurs during the liquid-phase reaction with 35 wt % H2O2 on mesoporous Nb2O5.