Selective monooxidation of light alkanes using chloride and iodate

Article abstract of DOI:10.1021/ja502657g

We describe an efficient system for the direct partial oxidation of methane, ethane, and propane using iodate salts with catalytic amounts of chloride in protic solvents. In HTFA (TFA = trifluoroacetate), >20% methane conversion with >85% selectivity for MeTFA have been achieved. The addition of substoichiometric amounts of chloride is essential, and for methane the conversion increases from <1% in the absence of chloride to >20%. The reaction also proceeds in aqueous HTFA as well as acetic acid to afford methyl acetate. ¹³C labeling experiments showed that less than 2% of methane is overoxidized to ¹³CO₂ at 15% conversion of ¹³CH₄. The system is selective for higher alkanes: 30% ethane conversion with 98% selectivity for EtTFA and 19% propane conversion that is selective for mixtures of the mono- and difunctionalized TFA esters. Studies of methane conversion using a series of iodine-based reagents [I₂, ICl, ICl₃, I(TFA)₃, I₂O₄, I ₂O₅, (IO₂)₂S₂O ₇, (IO)₂SO₄] indicated that the chloride enhancement is not limited to iodate.