Very low‐pressure pyrolysis (VLPP) of alkanes: n‐butane, 2,3‐dimethylbutane, 2,2′,3,3′ ‐tetramethylbutane, and isobutane

Abstract

The four species in the title were decomposed under VLPP conditions at temperatures in the vicinity of 1100°K. Three model transition states were constructed that fit the low‐pressure data thus obtained and that also yield (1) E298 = ΔE298; (2) E1100 = ΔE1100; (3) log A1100 = 16.4 per C–C bond broken. The predictions of these models as to values of the high‐pressure rate constants for bond scission and the reverse rate constants (radical combination) are compared with existing data.

An absolute measurement of the rate constant for t‐butyl radical combination

“…The pressure dependence can be shown to be negligible because of the large number of oscillators in the tert-butyl group. Now we have four experimental results which should be correlated via appropriate transition state models and/or the thermochemistry of the species involved: (a) Tsang's shock-tube study for the decomposition of 2,2,3,3-tetramethylbutane at 1100°K [9], log kl (sec-l) = 16.4 -67.8/8; (b) VLPP experiments [14] on the decomposition of TMB which confirm Tsang's parameters; (c) MGB [7a] and HB's [7b] study of the relative rate constant by using "known" thermochemistry of tert-butyl radicals around 400"K, log k, (M-',sec-') = -5-6; and (d) our present study at 700"K, log k, (M-'.sec-') c x 8.8 0.3. (Since the solvent effect on radical recombination is not known accurately, we did not include the electron spin resonance kinetic study [ 101.)…”

Evidence for strongly temperature‐dependent A factors in alkane decomposition and high heats of formation for alkyl radicals

“…Another serious problem posed by these results is the proper interpretation of the nonequilibrium experiments in the literature. These involve chemical activation and very-low-pressure pyrolysis studies [19,20]. All have used essentially vibrator models.…”

Thermal dissociation of alkyl nitrites and recombination of alkyl radicals

“…The model development for iso-butyl nitrite pyrolysis was carried out similarly to the previously discussed nitrites and reaction 1 produces i-butoxy and NO. The experimental k 1,i-C4H9ONO are shown in [28,34,[43][44][45]40,46]. The shaded area represents the uncertainty in the Klippenstein et al [23] rate of 30%.…”