Kinetic study of the gas-phase reactions of chlorine atoms with 2-chlorophenol, 2-nitrophenol, and four methyl-2-nitrophenol isomers.

Abstract

Anthropogenic activities are the main source of nitrophenols and chlorophenols in the atmosphere. Nitro and chlorophenols have a high potential to form ozone and secondary organic aerosol, thus investigations on the major photo oxidation pathways of these compounds are important to assess their contribution to urban air pollution and human health. Presented here are rate coefficients determined at atmospheric pressure and (298 ± 2) K using a relative kinetic method for the reactions of chlorine atoms with 2-chlorophenol (2ClP), 2-nitrophenol (2NP) and four methyl-2-nitrophenol (2-nitrocresol, nM2NP (n = 3,4,5,6)) isomers. The following rate coefficients (in units of cm(3) molecule(-1) s(-1)) have been obtained: (5.9 ± 1.5) × 10(-12) for 2ClP, (6.8 ± 2.3) × 10(-12) for 2NP, and (14.0 ± 4.9) × 10(-11), (4.3 ± 1.5) × 10(-11), (1.94 ± 0.67) × 10(-11) and (2.68 ± 0.75) × 10(-11) for the four methyl-2-nitrophenol isomers 3M2NP, 4M2NP, 5M2NP, and 6M2NP, respectively. This study represents the first kinetic investigation for the reaction of chlorine atoms with all the nitrophenols. In addition, to assist in the interpretation of the results, rate coefficients for the reactions of Cl atoms with the cresol ortho, meta, and para isomers have been determined for the first time. The rate coefficient for the reaction with 2ClP is in good agreement with previous data and the relative reactivity of 2NP, 4M2NP, 5M2NP, and 6M2NP can be rationalized based on known substituent effects. The rate coefficient for 3M2NP is anomalously large; the observation of significant NO2 production in only this reaction suggests that an ipso substitution mechanism is the cause of the enhanced reactivity.