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Abstract:
The development of environmentally benign catalysts for highly regioselective hydroxylation of phenol remains an unsolved challenge in both industry and academia because the electrophilic substitution of phenol simultaneously occurs on both ortho- and para-positions. Herein, we report a designed atomically dispersed iron-based heterogeneous catalyst, in which the iron species is coordinated by a functionalized ionic liquid monolayer on carbon nanotubes. The catalyst exhibits an unprecedented level of regioselectivity (>99%) towards the hydroxylation of phenol and displays a much better activity (TOF towards catechol productivity, 1.79 s(-1)) compared to the homogeneous free ion system (TOF towards catechol productivity, 0.44 s(-1)). Both experimental and theoretical investigations confirm that the catalytic oxidation with hydroperoxide undergoes a non-radical addition process and substitutes only the ortho-positions of phenol. This finding provides not only a quite active and selective catalyst for industrially very important reactions, but also a promising methodology of designing biomimetic iron-based heterogeneous catalysts at the atomic level.
