ISSN:
0538-8066
Schlagwort(e):
Chemistry
;
Physical Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The high temperature pyrolysi of 1,3-butadiene has been investigated in the shock tube with two time-resolved diagnostic techniques: laser schlieren measurements of density gradient with 1, 2, 4, and 5% C4H6 in Ar or Kr, 0.26 〈 P2 〈 0.66 atm, over 1550-2200 K, and time-of-flight mass spectra for 3% C4H6-Ne, P5 ∼ 0.4 atm, 1400-2000 K. When combined with a recent single-pulse shock tube product analysis covering 1050-2050 K, these measurements permit a complete modeling of major species in C4H6 pyrolysis. Extrapolated density gradients and product analyses show initiation is dominated by C4H6 → 2C2H3., significant falloff and Arrhenius curvature being seen in the derived rates. A restricted rotor, Gorin model RRKM fit to these rates with reasonable parameters generates \documentclass{article}\pagestyle{empty}\begin{document}$$ k_\infty = 4.1 \times 10^{16} {\rm exp(} - 47000/{\rm T)s}^{ - 1},{\rm 1600} - 1900{\rm K}{\rm .} $$\end{document} The derived barrier, ΔH0º = 99 ± 4 kcal/mol, translates to ΔHfº,298 = 63.4 ± 2 kcal/mol for the heat of formation of vinyl radical. A mechanism for the formation of all products detected in the above experiments is given, together with a successful but semiquantitative kinetic model for major products. The measurements require the rate of vinyl radical dissociation, C2H3 + M → C2H2 + H + M, to be extremely low, k 〈 109 cm3/mol s for 1600 K, so that the dominant chain carrier in C4H6 pyrolysis is vinyl radical.
Zusätzliches Material:
10 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/kin.550170208
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