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 a lot of progress has 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.