High conversion of methane to methyl ester at 298 K

To establish an aerobic oxidation of methane to produce methanol in high yield under ambient conditions is one of dreams to researchers in both academia and industry. However, although many progresses have been made on methane functionalization for several decades, it is still a grand challenge to break through the selectivity-conversion limit in the aerobic oxidation of methane to methanol or methyl ester especially at room temperature. Herein we report a simple visible-light driven reaction of CH4/O2 with CF3CO2H (TFA) to CH3-O-COCF3 (MTFA) at 298 K, just using catalytic NaNO2 in aqueous HCl/TFA solution. In a batch reaction of CH4/O2 (1:5, 0.4 MPa), the yield of MTFA is over 90%. In a 7-day continuous experiment of CH4/O2 (2:1, 0.1 MPa), both the MTFA selectivity and the methane conversion are over 90% based on the input methane. The turnover frequency (TOF) is 2.5 mol_MTFA mol_(NaNO_2 )-1 h-1, and the turnover number (TON) is over 400. A reasonable reaction mechanism is suggested and partial confirmed by experiments, involving NOCl as a crucial species in the two-phase aerobic oxidation of methane to methyl ester. Methanol could be obtained by a common hydrolysis of MTFA at 298 K. Neither metal catalysts nor special reagents are necessary in this two-step conversion of methane to methanol.