Direct FT-IR observation of oxidation of 1-hexene and cyclohexene with H2O2 over TS-1

The conventional IR method was improved for the in situ observation of oxidation of alkenes with an aqueous solution of H2O2 over heterogeneous catalysts. The reactions of 1-hexene and cyclohexene with H2O2 over TS-1 were successfully observed. In the case of 1-hexene, gradual formation of 1,2-epoxyhexane was observed. On the other hand, 1,2-epoxycyclohexane was not detected but production of 1,2-cyclohexanediol was observed in the case of cyclohexene. This is due to the rapid hydrolysis of 1,2-epoxycyclohexane, which conflicts with the highest selectivity for 1,2-epoxycyclohexane in the liquid phase reaction over TS-1. The controversy is discussed in the text. In addition, the rate of the hydrolysis of 1,2-epoxyhexane with H2O was far lower than that with H2O2, indicating that protons, which are formed by the reaction of H2O2 on Ti sites of TS-1, are responsible for the hydrolysis of epoxides.