Photo-Driven Aerobic Methane Nitration

Aphoto-driven method has been developed to selectivelyconvert methane to methyl nitrates (CH3ONO2)using visible light, via the chlorine radical hydrogen atom-transfercycle and nitration. The NO2 was recyclable through hydrolysis,and CH3OH can be obtained. Conversionof methane to liquid oxygenates is challenging but ofgreat 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 (O-2) as the terminal oxidant. Similar photoreactions are widely studiedin atmospheric chemistry but were not previously used in preparativemethane conversion. We used visible light to excite NO2 generated by heating aluminum nitrate Al(NO3)(3) and drove its reaction with methane and O-2 to producemethyl nitrate (CH3ONO2), which is then hydrolyzedto CH3OH. Nitric acid (HNO3) and nitrate (NO3 (-)) were produced and recycled back to Al(NO3)(3), completing a chemical loop. HCl can catalyzethis photochemical process via relay hydrogen atom-transfer reactions,with up to 17% methane conversion and 78% CH3ONO2 selectivity. This simple photochemical system provides new opportunitiesin selective methane transformation.