Contact-electro-catalyzed direct hydroxylation of aromatic C–H bonds under ambient conditions

The selective activation of inert aromatic C–H bonds for the synthesis of high-value phenols is of considerable scientific and industrial significance. Conventional free radical-based hydroxylation methods typically require ultraviolet irradiation or large amounts of sacrificial agents, which significantly limit their applicability. Here, we present a contact-electro-catalysis (CEC) approach that enables aromatic hydroxylation through hydroxyl radicals (·OH) and strong interfacial electric fields generated at the polytetrafluoroethylene (PTFE)–H2O interface via contact electrification. Using benzene as a model substrate, phenol was obtained via ·OH-mediated oxidation, and a variety of substrates with diverse electronic properties underwent efficient hydroxylation. For example, the transformation of 4-hydroxybenzoic acid yielded hydroquinone and 3,4-dihydroxybenzoic acid with maximum yields of 72.45 and 210.90 μmol·gcat−1 h−1, respectively. Electron paramagnetic resonance (EPR) confirmed the presence of ·OH, whereas nuclear magnetic resonance (NMR) and liquid chromatography-mass spectrometry (LC-MS) analyses identified the products, thereby supporting mechanistic investigations. This work extends the application of contact-electro-catalysis to organic synthesis, providing a sustainable alternative despite existing challenges in selectivity and scalability. Activation of C-H bonds is desirable, but selectivity is challenging. Here, the authors report a contact-electro-catalysis method for aromatic hydroxylation by production of hydroxyl radicals, formed by strong interfacial electric fields.