A Shock Tube and Modeling Study about Anisole Pyrolysis Using Time‐Resolved CO Absorption Measurements

The pyrolysis of anisole (C6H5OCH3) was studied behind reflected shock waves via highly sensitive absorption measurements of CO concentration using a rotational transition in the fundamental vibrational band near 4.7 µm. Time-resolved CO mole fractions were monitored in shock-heated C6H5OCH3/Ar mixtures between 1000 and 1270 K at 1.3–1.6 bar. The decomposition of C6H5OCH3 proceeds exclusively via homolytic dissociation, with reaction rate k1, forming methyl (CH3) and phenoxy (C6H5O) radicals. The subsequent decomposition of C6H5O by ring rearrangement and bond dissociation yields CO. To determine the rate constant k2 of C6H5O decomposition avoiding secondary reactions, allyl phenyl ether (C6H5OC3H5) was used as an alternative source for C6H5O. Its decomposition was studied between 970 and 1170 K at ∼1.4 bar. The potential-energy surface of C6H5O dissociation has been reevaluated at the G4 level of theory. Rate constants determined from unimolecular rate theory are in good agreement with the present experiments. However, the obtained rates k2 = 9.1 × 1013 exp(−220.3 kJ mol−1/RT)s−1 are significantly higher than those reported before (factor 6, 2, and 1.5 faster than those data reported by Lin and Lin, J. Phys. Chem. 1986, 90, 425–431; Frank et al., 1994; Carstensen and Dean, 2012, respectively). Good agreement was found between the measured CO concentration profiles and simulations based on the mechanism of Nowakowska et al. after substituting k2 by the value obtained from experiments on C6H5OC3H5 in this work. The bimolecular reaction of C6H5O and CH3 toward cresol was identified as the most important reaction influencing the CO concentration at longer reaction time.