Photo-Driven Aerobic Methane Nitration

Abstract

Conversion of methane to liquid oxygenates is challenging but of great value. Here, we report the oxidation of methane (CH4) to methanol (CH3OH) assisted by nitrogen dioxide (NO2) as a photo-mediator and using molecular oxygen (O2) as the terminal oxidant. Similar photoreactions are widely studied in atmospheric chemistry but were not previously used in preparative methane conversion. We used visible light to excite NO2 generated by heating aluminum nitrate Al­(NO3)3 and drove its reaction with methane and O2 to produce methyl nitrate (CH3ONO2), which is then hydrolyzed to CH3OH. Nitric acid (HNO3) and nitrate (NO3 –) were produced and recycled back to Al­(NO3)3, completing a chemical loop. HCl can catalyze this photochemical process via relay hydrogen atom-transfer reactions, with up to 17% methane conversion and 78% CH3ONO2 selectivity. This simple photochemical system provides new opportunities in selective methane transformation.

High conversion of methane to methyl ester at 298 K

“…Using the chlorine radical to give CH 3 –OO· species, Ohkubo and co-workers obtained a high yield of methane oxides, mainly as formic acid. 34,35 However, there are few reports which disclose how to convert CH 3 –OO· species to methanol or a methyl ester exclusively, 36,37 to prevent over-oxidations of methanol or methyl ester happening in the liquid-phase and to devise a chlorine catalytic system for the aerobic oxidation of methane under radical reaction conditions.…”