Chemical activation reactions of cyclic alkanes and ethers and tricyclodecane ring-opened diradicals with O2: Thermochemistry, reaction paths, kinetics, and modeling

The initial unimolecular dissociation reactions of tricyclodecane (TCD, C10H16) and other cyclic alkanes and ethers in combustion systems are ring opening to form a dialkyl radical. These diradicals can undergo reassociation, further reaction with the alkyl fragments, or bimolecular reactions. Either of the two radical sites on this dialkyl radical can react with 3O2 to form a peroxy radical. This peroxy radical can further react with the alkyl fragment or undergo association to form a chemically activated peroxide. This energized peroxide has near 25 kcal mol-1 energy above that needed to cleave the weak RO?OR bond, and cleavage of this peroxide bond to form a dialkoxy radical is found to be rapid under combustion conditions. The dialkoxy radicals formed can undergo beta scission reactions to form strong carbonyl bonds or undergo intra- and intermolecular abstraction reactions with the alkyl fragment or parent cyclic molecules. The exothermicity of the overall reaction to formation of carbonyls or new radical plus alcohols can serve to accelerate the overall combustion process. To our knowledge, these reactions are not considered in present combustion mechanisms. In this study, we evaluate the thermochemistry and kinetics of these reactions and use elementary reaction modeling to evaluate their importance to the TDC and C3 to C5 ring systems. Needed thermochemistry and kinetics of the three- to five-member cyclic alkanes and ethers are developed and also used for increased accuracy in work reactions for thermochemistry of the larger TCD system. (C) 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 232256, 2012