Pressure Dependence and Branching Ratios in the Decomposition of 1-Pentyl Radicals: Shock Tube Experiments and Master Equation Modeling
- 13 March 2012
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Physical Chemistry A
- Vol. 116 (11), 2895-2910
- https://doi.org/10.1021/jp2115302
Abstract
The decomposition and intramolecular H-transfer isomerization reactions of the 1-pentyl radical have been studied at temperatures of 880 to 1055 K and pressures of 80 to 680 kPa using the single pulse shock tube technique and additionally investigated with quantum chemical methods. The 1-pentyl radical was generated by shock heating dilute mixtures of 1-iodopentane and the stable products of its decomposition have been observed by postshock gas chromatographic analysis. Ethene and propene are the main olefin products and account for >97% of the carbon balance from 1-pentyl. Also produced are very small amounts of (E)-2-pentene, (Z)-2-pentene, and 1-butene. The ethene/propene product ratio is pressure dependent and varies from about 3 to 5 over the range of temperatures and pressures studied. Formation of ethene and propene can be related to the concentrations of 1-pentyl and 2-pentyl radicals in the system and the relative rates of five-center intramolecular H-transfer reactions and β C–C bond scissions. The 3-pentyl radical, formed via a four-center intramolecular H transfer, leads to 1-butene and plays only a very minor role in the system. The observed (E/Z)-2-pentenes can arise from a small amount of beta C–H bond scission in the 2-pentyl radical. The current experimental and computational results are considered in conjunction with relevant literature data from lower temperatures to develop a consistent kinetics model that reproduces the observed branching ratios and pressure effects. The present experimental results provide the first available data on the pressure dependence of the olefin product branching ratio for alkyl radical decomposition at high temperatures and require a value of ⟨ΔEdown(1000 K)⟩ = (675 ± 100) cm–1 for the average energy transferred in deactivating collisions in an argon bath gas when an exponential-down model is employed. High pressure rate expressions for the relevant H-transfer reactions and β bond scissions are derived and a Rice Ramsberger Kassel Marcus/Master Equation (RRKM/ME) analysis has been performed and used to extrapolate the data to temperatures between 700 and 1900 K and pressures of 10 to 1 × 105 kPa.Keywords
This publication has 46 references indexed in Scilit:
- Isomerization of Neopentyl Chloride and Neopentyl Bromide by a 1,2-Interchange of a Halogen Atom and a Methyl GroupThe Journal of Physical Chemistry A, 2010
- Chemically and Thermally Activated Decomposition of Secondary Butyl RadicalThe Journal of Physical Chemistry A, 2000
- Single-pulse shock-tube study on the decomposition of 1-pentyl radicalsSymposium (International) on Combustion, 1998
- Unimolecular Decomposition of n-C4H9 and iso-C4H9 RadicalsThe Journal of Physical Chemistry, 1996
- Average collisional vibrational energy transfer quantities. The exponential modelThe Journal of Physical Chemistry, 1986
- Enthalpies of hydration of alkenes. 2. The n-heptenes and n-pentenesThe Journal of Physical Chemistry, 1984
- The enthalpies of combustion of the isomeric pentenes in the liquid state. A warning to combustion calorimetrists about sample dryingThe Journal of Chemical Thermodynamics, 1979
- Isomerization of 1-hexyl radicals in the gas phaseThe Journal of Physical Chemistry, 1973
- The enthalpies of combustion and formation of n-octane and 2,2,3,3-tetramethylbutaneThe Journal of Chemical Thermodynamics, 1972
- Cyclization and decomposition of 4-penten-1-yl radicals in the gas phaseThe Journal of Physical Chemistry, 1972