Kinetics of phenyl radical reactions with ethane and neopentane: Reactivity of C6H5 toward the primary C‐H bond of alkanes

Abstract

The kinetics of C6H5 reactions with C2H6 (1) and neo-C5H12 (2) have been studied by the pulsed laser photolysis/mass spectrometric method using C6H5COCH3 as the phenyl precursor at temperatures between 565 and 1000 K. The rate constants were determined by kinetic modeling of the absolute yields of C6H6 at each temperature. Another major product, C6H5CH3, formed by the recombination of C6H5 and CH3, could also be quantitatively modeled using the known rate constant for the reaction. A weighted least-squares analysis of the two sets of data gave k1 = 1011.32±0.05 exp[−(2236 ± 91)/T] cm3 mol−1 s−1 and k2 = 1011.37±0.03 exp[−(1925 ± 48)/T] cm3 mol−1 s−1 for the temperature range studied. The result of our sensitivity analysis clearly supports that the yields of C6H6 and C6H5CH3 depend primarily on the abstraction reactions and C6H5 + CH3, respectively. From the absolute rate constants for the two reactions we obtained the value for the H-abstraction from a primary C-H bond, k-CH = 1010.40±0.06 exp(−1790 ± 102/T) cm3 mol−1 s−1. This result is utilized for analysis of other kinetic data measured for C6H5 reactions with alkanes in solution as well as in the gas phase. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 64–69, 2001