A shock tube study of the decomposition of cyclohexane and 1-hexene

The decomposition of cyclohexane (c-C6H12) was studied in 131 experiments using a shock tube and the laser-schlieren technique over 1400-2000 K and from 25 to 200 Torr using mixtures of 2, 4, 10, and 20% cyclohexane in Kr. The reaction is shown to be an initial isomerization to 1-hexene 1 c-C6H12→1-C 6H121-hexene DH298Ko=19.19 kcal/gmol followed by rapid dissociation of 1-hexene to allyl and n-propyl radicals 2 1-C6H12→C 3H5allyl+ C3H7n-propyl DH298Ko=71.82 kcal/gmol which further decompose initiating a complex chain reaction. To facilitate analysis, the decomposition of 1-hexene is also examined over 1200-1700 K for 50 Torr and 200 Torr using 2 and 3% 1-hexene in Kr.;Fall-off rate constants were obtained for (1) and (2) by simulating experimental data using cyclohexane and 1-hexene dissociation mechanisms. High-pressure limit rate constants were obtained by extrapolating the fall-off rates using RRKM theory. The extrapolated high-pressure rates are in good agreement with much of the literature data.;At low pressures and/or at high temperatures, cyclohexane may directly dissociate via a 'one-step' process to C3H5 and C3H7 radicals through chemically activated 1- hexene. 1a c-C6H12 →C3H5+3H7;This 'one-step' process is hinted at by our low pressure experiments but still cannot be clearly distinguished from the 'two-step' process (reaction (1) followed by (2)). The presence of the 'one-step' process was ultimately found to have little effect on the rate of cyclohexane dissociation.