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 k ₁, 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 k ₂ 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 k ₂ = 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 k ₂ 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.