Sulfate radical-mediated methane conversion to C–C and C–S products in water

Abstract

The direct conversion of CH₄ into transportable liquid chemicals under ambient conditions is a fundamental goal for sustainable chemistry. However, existing approaches to valuable derivatives like methanesulfonic acid (CH₃SO₃H) and methyl bisulfate (CH₃SO₄H) typically rely on corrosive acids and complex metal catalysts. Here, we report a catalyst-free, photochemical strategy for CH₄ conversion in a purely aqueous phase under ambient conditions, yielding C–S products (CH₃SO₃H and CH₃SO₄H), alongside valuable C–C coupled products (CH₃COOH and CH₃COCH₃). Using potassium peroxydisulfate as a simple precursor, photochemically generated sulfate radicals (SO₄˙⁻) serve a dual role of mediating C–H bond activation via secondary ˙OH species from water oxidation, and acting as the sulfur source. A liquid product selectivity of 90% was achieved, and CH₄ conversion of 3.5% was demonstrated in a photochemical flow reactor at ambient pressure. Mechanistic studies reveal that CH₃SO₄H is a key intermediate, whose subsequent reaction with a ˙CH₃ radical not only forms the C–S product but also generates a methoxy radical to initiate C–C coupling. By harnessing sulfate radical reactivity in water, this work provides a simple and effective route for methane valorization under exceptionally mild conditions.