A shock tube and theoretical study on the pyrolysis of 1,4-dioxane

The dissociation of 1, 2 and 4% 1,4-dioxane dilute in krypton was studied in a shock tube using laser schlieren densitometry, LS, for 1550-2100 K with 56 ± 4 and 123 ± 3 Torr. Products were identified by time-of-flight mass spectrometry, TOF-MS. 1,4-dioxane was found to initially dissociate via C-O bond fission followed by nearly equal contributions from pathways involving 2,6 H-atom transfers to either the O or C atom at the scission site. The 'linear' species thus formed (ethylene glycol vinyl ether and 2-ethoxyacetaldehyde) then dissociate by central fission at rates too fast to resolve. The radicals produced in this fission break down further to generate H, CH₃ and OH, driving a chain decomposition and subsequent exothermic recombination. High-level ab initio calculations were used to develop a potential energy surface for the dissociation. These results were incorporated into an 83 reaction mechanism used to simulate the LS profiles with excellent agreement. Simulations of the TOF-MS experiments were also performed with good agreement for consumption of 1,4-dioxane. Rate coefficients for the overall initial dissociation yielded k_123Torr = (1.58 ± 0.50) × 10 ⁵⁹ × T^-13.63 × exp(-43970/T) s^-1 and k_58Torr = (3.16 ± 1.10) × 10⁷⁹ × T^-19.13 × exp(-51326/T) s^-1 for 1600 < T < 2100 K.