Reaction paths, kinetics, and thermochemical properties on the thioformyl radical (S=C·H) with O_2 reaction

摘要

CH_2=S and corresponding larger hydrocarbon thials (thiol aldehydes) are important products in hydrocarbon sulfide and thiol thermal and oxidative reaction paths, as C—H bonds on the carbon adjacent to the sulfur moiety are easily abstracted and the olefin formation is rapid. The reaction(s) of S= C·H (and corresponding larger hydrocarbon radicals, which result from loss of a hydrogen atom from CH_2=S and RCH=S) with O_2 form chemically activated, stable peroxy radicals, which often control the oxidation paths of these thienes. Enthalpies of formation of S=C·H and the adduct, S=CH(OO·), and other intermediates are computed by isodesmic work reactions at the CBS-QB3, G3MP2, and G2 levels. Density functional B3LYP/6-311G(d,p) frequencies are utilized to estimate S°_(298) and Cp(T) and the intramolecular rotation potentials are calculated and used to determine the contributions to entropy and heat capacities. Results show that the well depth of this peroxy formation is 32.6 kcal/mol, significantly more exothermic than results in a previous publication (PCCP, 2005, 7, 3711). Important reaction paths involve intramolecular hydrogen atom transfer to the peroxy radical, peroxy radical addition to the sulfur or carbon, dissociation and further isomerizations. Kinetics parameters are evaluated using chemical activation analysis and unimolecular dissociation of the stabilized adducts.