Formation of D Atoms in the Pyrolysis of Toluene-d8 behind Shock Waves. Kinetics of the Reaction C7D8 + H -> C7D7H + D

Article abstract of DOI:10.1021/j150663a035

Dilute mixtures (5-20 ppm) of toluene-d8 in argon were pyrolyzed behind reflected shock waves at temperatures of 1410-1730 K and total pressures of 3 atm.In a second group of experiments, mixtures of 20 ppm toluene-d8 and 5 ppm neopentane (which acted as a source of H atoms) were similarly pyrolyzed at 1200-1460 K.Progress of the reaction was followed by analysis for H and D atoms by using resonance absorption spectroscopy.For the reaction C6D5CD3 -> C6D5CD2 + D under the experimental conditions, k_1D = 1.1 x 1E14 exp(-82000 cal/RT) s^-1.After allowance for isotope effects and unimolecular falloff, the high-pressure rate constant for the reaction C6H5CH3 -> C6H5CH2 + H is calculated to be k_{1, infinite} = 2.7 x 1E14 exp(-83000 cal/RT) s^-1 over the range 1000-1800 K.Estimated uncertainties are a factor of 1.5 in k_1D and 2 in k_{1, infinite}.For the reaction D + C6D5CD3 -> C6D5CD2 + D2, k_2D2 = 2.1 x 1E15 exp(-15000 cal/RT) mol^-1 cm³ s^-1 over the range 1300-1800 K, with an uncertainty of a factor of 1.5, while after correction for isotope effects the rate constant for H + C6H5CH3 -> C6H5CH2 + H2 over the range 600-1800 K can be expressed by the non-Arrhenius equation k₂ = 7.6 x 1E-5T^5.5 exp(-340 cal/RT) mol^-1 cm³ s^-1, with an uncertainty of a factor of 2.Data were also obtained on the exchange reaction by which H atoms add to the ring of C6D5CD3, and D atoms are eliminated.For this reaction k_4D = 3.5 x 1E13 exp(-3700 cal/RT) mol^-1 cm³ s^-1 in the range 1200-1500 K, with an estimated uncertainty of a factor of 1.5.