Kinetics and mechanisms of the gas‐phase reactions of the NO 3 radical with aromatic compounds

The kinetics and nitrated products of the gas‐phase reactions of the NO 3 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 NO 3 radical were observed. The dimethoxybenzenes were observed to react by H‐atom abstraction and NO 3 radical addition to the aromatic ring, while dibenzo‐ p ‐dioxin reacted by NO 3 radical addition to the aromatic rings. For these compounds, the NO 3 radical addition pathways were observed to be reversible. At the NO 2 concentrations employed, the NO 3 ‐aromatic adducts reacted with NO 2 and the observed rate constants increased with increasing NO 2 concentration. However, for dibenzo‐ p ‐dioxin the observed rate constant became independent of the NO 2 concentration for concentrations ≥ 4.8 × 10 13 molecule cm −3 , and under these conditions the rate constant of 6.8 × 10 −14 cm 3 molecule −1 s −1 was taken to be that for addition of the NO 3 radical to the aromatic rings. The proposed NO 3 radical reaction mechanisms are discussed. © 1994 John Wiley & Sons, Inc.