Kinetics of phenyl radical reactions with propane, n‐butane, n‐hexane, and n‐octane: Reactivity of C6H5 toward the secondary CH bond of alkanes

Abstract

AbstractThe kinetics of C6H5 reactions with n‐CnH2n+2 (n = 3, 4, 6, 8) have been studied by the pulsed laser photolysis/mass spectrometric method using C6H5COCH3 as the phenyl precursor at temperatures between 494 and 1051 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 four sets of data gave k (C3H8) = (1.96 ± 0.15) × 1011 exp[−(1938 ± 56)/T], and k (n‐C4H10) = (2.65 ± 0.23) × 1011 exp[−(1950 ± 55)/T] k (n‐C6H14) = (4.56 ± 0.21) × 1011 exp[−(1735 ± 55)/T], and k (n−C8H18) = (4.31 ± 0.39) × 1011 exp[−(1415 ± 65)T] cm3 mol−1 s−1 for the temperature range studied. For the butane and hexane reactions, we have also applied the CRDS technique to extend our temperature range down to 297 K; the results obtained by the decay of C6H5 with CRDS agree fully with those determined by absolute product yield measurements with PLP/MS. Weighted least‐squares analyses of these two sets of data gave rise to k (n−C4H10) = (2.70 ± 0.15) × 1011 exp[−(1880 ± 127)/T] and k (n−C6H14) = (4.81 ± 0.30) × 1011 exp[−(1780 ± 133)/T] cm3 mol−1 s−1 for the temperature range 297‐‐1046 K. From the absolute rate constants for the two larger molecular reactions (C6H5 + n‐C6H14 and n‐C8H18), we derived the rate constant for H‐abstraction from a secondary CH bond, ks−CH = (4.19 ± 0.24) × 1010 exp[−(1770 ± 48)/T] cm3 mol−1 s−1. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 49–56, 2004