A kinetic study of the reaction of OH with xylenes using the relative rate/discharge flow/mass spectrometry technique.
A kinetics study for the reaction of OH with o-, m-, and p-xylene has been conducted at 1-10 Torr and 240-340 K using the relative rate/discharge flow/mass spectrometry technique with 1,4-dioxane as the reference compound. At 298 K, the rate constants for the reaction of OH with all three isomers of xylene exhibited prominent positive pressure dependence up to 5 Torr, and the reactions reached a high-pressure limit at 8 Torr, with a high pressure limit rate constant of k(o-xylene) = (1.19 +/- 0.07) x 10(-11) cm(3) molecule(-1) s(-1), k(m-xylene) = (2.14 +/- 0.14) x 10(-11) cm(3) molecule(-1) s(-1), and k(p-xylene) = (1.19 +/- 0.07) x 10(-11) cm(3) molecule(-1) s(-1), respectively, which are in good agreement with literature values. The results of the temperature-dependence study indicated that, in all three reactions, there is negative temperature dependence at temperatures greater than 298 K. The reaction of OH with xylene may proceed with addition of the OH radical to the benzene ring at room temperature and below, with an equilibrium established between the reactants and the xylene-OH adduct. At 298-340 K, the equilibrium is shifted toward the reactants, giving rise to a negative temperature dependence of the rate constant, and this may also associate with a transition of the reaction from the addition mechanism to the abstraction mechanism. On the basis of our kinetic results at 277 K, the atmospheric lifetimes of o-, m-, and p-xylene are estimated to be about 29, 14, and 31 h, respectively.
Mehta
Deepali
D
Department of Chemistry and Biochemistry, California State University-Fullerton, Fullerton, California 92834, USA.
Nguyen
Andrew
A
Montenegro
Anthony
A
Li
Zhuangjie
Z