Single-pulse shock-tube study on the decomposition of 1-pentyl radicals

Abstract

1-Pentyl radicals have been decomposed in single-pulse shock-tube experiments. The precursor is n-pentyl iodide, and the reaction conditions are 850–1000 K and 1.5–5 bar pressure. With 1-pentyl radicals being released with the rate expression k(n-C5H11I=1-C5H11+I)=4×1014 exp(−25,820/T)s−1 we find the branching ratios for the decomposition to form olefin products to be k(1-C5H11=2C2H4+CH3)/k(1-C5H11)=2.3 exp(−2018/T) k(1-C5H11=C3H6+C2H5)/k(1-C5H11)=0.27 exp(803/T) k(1-C5H11=1-C4H8+CH3)/k(1-C5H11)=0.068 exp(310/T) where k(1-C5H11) is the total rate constant for 1-pentyl radical decomposition. The results from the last two channels are interpreted in terms of radical isomerization through 1,4- and 1,3-hydrogen migration to form 2-pentyl and 3-pentyl radicals. From kinetic modeling, we find k(1-C5H11→2-C5H11)=1×1012 exp(−11,330/T)s−1 k(1-C5H11→3-C5H11)=3×1011 exp(−12,100/T)s−1 Under the present conditions, pentyl radicals are not being equilibrated. Some of the problems in the interpretation and extrapolation of experimental results on the decomposition of complex radicals are considered. It appears that the isomerization of secondary pentyl radicals will not be competitive with β C-C bond fission. The molecular elimination of HI from n-pentyl iodide is characterized by the rate expression (n-C5H11I=1-C5H10+HI)=1.05×1013 exp(−25,730/T)s−1 and is relatively unimportant in the present context.