Catalyst-free one-step oxidation of benzene to phenol using nanobubbles

Abstract

The direct hydroxylation of benzene to phenol is an extremely challenging work in organic chemistry due to the stable structure of benzene. Herein, the one-step formation of phenol from benzene in the absence of a catalyst is realized using nanobubbles in water for the first time. We generate nanobubbles in an aqueous solution through ultrasound irradiation, which then collapse to produce OH radicals at the gas–water interface that react with benzene molecules to form phenol. The effects of key reaction parameters, including ultrasound power and ultrasound time, on phenol yield are systematically investigated in order to determine the optimal reaction strategy. Furthermore, the illumination of a laser is employed to promote the collapse of nanobubbles in water, which significantly enhanced the yield of phenol and reduced the reaction time. Results show that this one-step method attained efficient conversion of benzene to phenol at room temperature with high selectivity. We prove that benzene molecules in aqueous solution are more likely to attach to the surface of nanobubbles than phenol molecules, thus facilitating their reaction with OH radicals generated from bubble collapse to form phenol, while phenol does not undergo further oxidation by OH radicals.