Ring-Opening Hydration of Epoxides into Diols with a Low Water–Epoxide Ratio Catalyzed by a Fe-Incorporated Octahedra-Based Molecular Sieve
Duo Wang, Yao Yang, Fenhua Zhang, Pengfei Jiang, Wenliang Gao, Rihong Cong, Tao Yang
Abstract
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, Fe3+-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 first-order reaction and has a lower apparent activation energy (∼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.