Kinetics and mechanisms of the gas‐phase reactions of the NO₃ radical with aromatic compounds

Abstract

The kinetics and nitrated products of the gas-phase reactions of the NO3 radical with methoxybenzene, 1,2-, 1,3-, and 1,4-dimethoxybenzene, dibenzofuran and dibenzo-p-dioxin have been investigated at 297 ? 2 K and in the presence of one atmosphere of air. A relative rate method was used for the kinetic measurements. No reactions of methoxybenzene or dibenzofuran with the NO3 radical were observed. The dimethoxybenzenes were observed to react by H-atom abstraction and NO3 radical addition to the aromatic ring, while dibenzo-p-dioxin reacted by NO3 radical addition to the aromatic rings. For these compounds, the NO3 radical addition pathways were observed to be reversible. At the NO2 concentrations employed, the NO3-aromatic adducts reacted with NO2 and the observed rate constants increased with increasing NO2 concentration. However, for dibenzo-p-dioxin the observed rate constant became independent of the NO2 concentration for concentrations 24.8 X 1013 molecule ~m -~, and under these conditions the rate constant of 6.8 X cm3 molecule-' s-' was taken to be that for addition of the NO3 radical to the aromatic rings. The proposed NO3 radical reaction mechanisms are discussed.

Kinetics of the gas-phase reactions of indan, indene, fluorene, and 9,10-dihydroanthracene with OH radicals, NO3 radicals, and O3

“…In particular, our data show no evidence for an NO 2 -dependent rate constant [8,10] for any of the aromatic compounds studied here, indicating that initial NO 3 radical addition to the aromatic ring(s) followed by reaction of the NO 3 -aromatic adducts with NO 2 in competition with decomposition back to reactants was not important under our experimental conditions [2]. The formation of 1-indanone from indan and 9-fluorenone from fluorene are consistent with these expectations.…”

“…NO 2 was added to the reactant mixtures to scavenge any OH radicals formed in the reactions and to investigate the reaction mechanisms [8,10]. 1-Butene was used as the reference compound for indan and fluorene, trans-2-butene for 9,10-dihydroanthracene, and 2-methyl-2-butene for indene.…”

Reactions of Gas-Phase Phenanthrene under Simulated Atmospheric Conditions

“…However, Figure 3 shows that the plot of k,bs/k2 against NO2 concentration has an intercept significantly different from zero. This non-zero intercept was verified by conducting an experiment with no initially present NOz, which exhibited a positive initial slope of the plot of eq I (Figure 2), in contrast to the behavior observed for the NO3 radical reactions with naphthalene (22,30), %methylnaphthalene (22), and dibenzo-p-dioxin (21) for which the initial slopes of plots of eq I were essentially zero in the absence of initially added NOz. This observation shows that the NO3 radical reaction with phenanthrene must also involve a reaction channel that is independent of the NO2 concentration.…”

“…NO3 radicals were generated by the thermal decomposition of Nz05, and NO2 or ethane was added to the reactant mixture to investigate the reaction mechanism and to scavenge any OH radicals formed (21)(22)(23). 1-Butene was used as the reference compound, and the initial reactant concentrations (in molecule ~m -~ units) were as follows: phenanthrene, (1.3-2.8) X loll; 1-butene, 4.8 X 1013; NO2 (when added), (4.8-24) X or ethane, 2.4 X Three to five additions of Nz05 [at initial concentrations in the chamber of (4.9-9.6) X 1Q12 molecule ~m -~l were made to the chamber during the experiments.…”

Reactions of NO3‐naphthalene adducts with O2 and NO2

“…A weighted average of the rate constant ratios k d / K , given in Table I leads to at 600 torr of 02, each with estimated overall uncertainties of a factor of 2. for the corresponding reactions of 0 2 and NO2 with the NOa-dibenzo-p-dioxin adduct derived from a study of the NO3 radical reaction with dibenzo-p-dioxin [16]. These upper limits to the rate constant ratios for the 0 2 and NO2 reactions with N03-naphthalene and Nos-dibenzo-p-dioxin adducts are an order of magnitude lower than the reported rate constant ratios of (6-17) X for the reactions of 0 2 and NO2 with the hydroxycyclohexadienyl and methylhydroxycyclohexadienyl radicals formed from the OH radical reactions with benzene and toluene [51.…”