Ring-Opening Hydration of Epoxides into Diols with a Low Water-Epoxide Ratio Catalyzed by a Fe-Incorporated Octahedra-Based Molecular Sieve

1,2-Diols are important organic intermediates in the production of a variety of organic chemicals, and their eco-friendly production has attracted much attention, especially from epoxide hydration using solid-acid catalysts. Herein, Fe-3(+)-incorporated PKU-1 molecular sieve (Fe-PKU-1), an open-framework and octahedra-based aluminoborate with 18-membered-ring channels, was successfully synthesized and behaved as a solid Lewis acid to catalyze the ring-opening hydration of epoxides. The as-synthesized Fe-PKU-1 catalyst has a high catalytic efficiency at a low water-epoxide ratio and better structural stability. The comparative tests indicated that some other Fe-containing catalysts only had a very low catalytic activity, which confirmed the structure-sensitive role of Fe3+ doped in the PKU-1 framework. Reaction kinetics analyses showed that the hydration reaction is a firstorder reaction and has a lower apparent activation energy (similar to 30 kJ.mol(-1)). Further investigations discovered that trans-1,2-cyclohexanediol was exclusively formed through a nucleophilic addition when using cyclohexene oxide as substrate molecule, and the adsorption experiment indicated an extremely high amount of epoxide was accumulated in the solid/liquid interface of Fe- PKU-1, which is nearly 100 times higher than that of Fe-free PKU-1. On the basis of the above results, a plausible catalytic mechanism was proposed to elucidate the epoxide hydration process.

Automated summary

In this study, a solid Fe-3(+)-incorporated molecular sieve catalyst Fe-PKU-1 was successfully synthesized, exhibiting high catalytic efficiency and structural stability in the hydration reaction of epoxides. Compared to other Fe-containing catalysts, Fe-PKU-1 showed significantly higher catalytic activity, confirming the structure-sensitive role of Fe3+ in the PKU-1 framework. The proposed catalytic mechanism sheds light on the epoxide hydration process.