Methane Sulfonation via a Free-Radical Mechanism by Trifluoroacetylsulfuric Acid

Using trifluoroacetyl sulfuric acid (TFAOSO(3)H), we discovered a new methane activation method and revealed its radical pathway under mild conditions. Upon the addition of a radical initiator with methane, the crude solution of TFAOSO(3)H developed the methyltrifluoroacetylsulfate radical ((TFAO)CH3S-(OH)O-2 center dot). The resulting (TFAO)CH3S(OH)O-2 center dot behaved as a critical radical propagator for carbon-hydrogen bond activation, culminating in successful methane sulfonation. With 9.5 mol % of K2S2O8, TFAOSO(3)H and methane were selectively converted to methanesulfonic acid in 94 and 86% conversion yields, respectively.