Reaction Paths and Chemical Activation Reactions of 2-Methyl-5-Furanyl Radical with 3O2.

Interest in high-energy substituted furans has been increasing due to their occurrence in biofuel production and their versatility in conversion to other useful products. Methylfurans are the simplest substituted furans and understanding their reaction pathways, thermochemical properties, including intermediate species stability, and chemical kinetics would aid in the study of larger furans. Furan ring C-H bonds have been shown to be extremely strong, approximately 120 kcal mol-1, due in part to the placement of the oxygen atom and aromatic-like resonance, both within the ring. The thermochemistry and kinetics of the oxidation of 2-methyfuran radical at position 5 of the furan ring, 2-methyl-5-furanyl radical (2MF5j), is analyzed. The resulting chemically activated species, 2MF5OOj radical, has a well depth of 51 kcal mol-1 below the 2MF5j + O2 reactants; this is 4-5 kcal mol-1 deeper than that of phenyl and vinyl radical plus O2, with both of these reactions known to undergo chain branching. Important, low-energy reaction pathways include chain branching dissociations, intramolecular abstractions, group transfers, and radical oxygen additions. Enthalpies of formation, entropies, and heat capacities for the stable molecules, radicals, and transition-state species are analyzed using computational methods. Calculated ΔH°f 298 values were determined using an isodesmic work reaction from the CBS-QB3 composite method. Elementary rate parameters are from saddle point transition-state structures and compared to variational transition-state analysis for the barrierless reactions. Temperature- and pressure-dependent rate constants which are calculated using QRRK and master equation analysis is used for falloff and stabilization.