Liquid phase hydroxylation of benzene to phenol with hydrogen peroxide catalyzed by Fe(III)/TiO2 catalysts at room temperature

Liquid phase hydroxylation of benzene to phenol with hydrogen peroxide on Fe(III)/TiO2 catalysts was examined at room temperature. The catalytic performances of various TiO2 supports were tested. The TiO2 (JRC-TIO-1, anatase) having the highest surface area and pore volume appeared to be the most suitable support because it offered the highest activity and selectivity. The effects of the Fe(Ill) precursor and Fe(Ill) loading were investigated. The catalyst prepared from iron(III) acetylacetonate with 5 wt% Fe(III) loading was selected as a suitable catalyst. From tests of seven solvents, it was found that acetone gave the highest conversion and yield; however, acetonitrile may also be attractive because it offered high selectivity. Biphasic operation, introduced by adding more amount of solvent, did not show a potential improvement because the dilution effect seemed to play an important role in the reaction system. Finally, it was revealed that increasing the amount of ascorbic acid helped increase the conversion by enhancing the decomposition of H2O2 to hydroxyl radicals. However, it suppressed the formation of Fe(III), which resulted in a decrease in the degree of phenol formation. In addition, phenol can be further reacted with excess hydroxyl radicals to yield hydroquinone, benzoquinone, and catechol, resulting in a decreased selectivity.