DFT Mechanistic Study of Methane Mono-Esterification by Hypervalent Iodine Alkane Oxidation Process

Recent experiments report high yield (up to 40%) and selectivity (generally > 85%) for the direct partial oxidation of methane to methyl trifluoroacetate in trifluoroacetic acid solvent using hypervalent iodine as the oxidant and in the presence of substoichiometric amounts of chloride anion. We develop here the reaction mechanism for these results based on density functional theory calculations (at the M06-2X/6-311G**++/aug-pVTZ-PP level) of plausible intermediates and transition states. We find a mechanistic process that explains both reactivity as well as selectivity of the system. In this oxy-esterification (OxE) system, IO_2Cl_2– and/or IOCl_4– act as key transient intermediates, leading to the generation of the high-energy radicals IO2• and Cl• that mediate methane C–H bond cleavage. These studies suggest new experiments to validate the OxE mechanism.