Web Release Date: June 4,
Reactions of Chlorine Atoms with a Series of Aromatic Hydrocarbons
and
Air Pollution Research Center, University of California, Riverside, California 92521
Received for review December 28, 2004
Revised manuscript received April 3, 2005
Accepted May 5, 2005
Abstract:
Aromatic hydrocarbons, including polycyclic aromatic
hydrocarbons (PAHs), are present in urban and rural
atmospheres. Reactions of PAHs with Cl atoms may occur
in the marine boundary layer and in coastal regions. To
assess the importance of these reactions and to investigate
whether any unique chlorine-containing products are
formed from these reactions, we have measured the rate
constants for the gas-phase reactions of Cl atoms with
toluene-d8, 1,3,5-trimethylbenzene (1,3,5-TMB), naphthalene,
1-methylnaphthalene-d10 (1-MN-d10), 1- and 2-methylnaphthalene (1- and 2-MN), 1- and 2-ethylnaphthalene (1- and
2-EN), and the dimethylnaphthalenes (DMNs) at 296 ±
2 K. A relative rate technique was used, and, using our
measured rate constant for the reaction of Cl atoms with 1,3,5-TMB of 2.42 × 10-10 cm3 molecule-1 s-1, the rate constants
(in units of 10-10 cm3 molecule-1 s-1) are as follows:
naphthalene, 
0.0091 ± 0.0003; 1-MN, 1.21 ± 0.16; 2-MN,
1.05 ± 0.13; 1-EN, 2.12 ± 0.35; 2-EN, 1.38 ± 0.27; 1,2-DMN, 3.61 ± 0.68; 1,3-DMN, 2.90 ± 0.22; 1,4-DMN, 2.93 ±
0.30; 1,5-DMN, 2.31 ± 0.19; 1,6-DMN, 2.15 ± 0.20; 1,7-DMN, 3.05 ± 0.34; 1,8-DMN, 3.07 ± 0.44; 2,3-DMN, 2.93 ±
0.49; 2,6-DMN, 2.34 ± 0.18; and 2,7-DMN, 2.00 ± 0.22,
where the indicated errors are two standard deviations
and do not include the uncertainty in the rate constant for
1,3,5-TMB. The measured deuterium isotope effects for
the toluene-d8 and 1-MN-d10 reactions indicate that the
reactions proceed by initial H- (or D-) atom abstraction. The
products identified and quantified from the toluene and
1-MN reactions using gas chromatography and in situ direct
air sampling atmospheric pressure ionization tandem
mass spectrometry were benzaldehyde (84% ± 7% yield)
and benzyl alcohol (11% ± 2% yield) from toluene and
1-naphthaldehyde (~36%, lower limit to yield) and 1-naphthyl
alcohol (~12%, lower limit to yield) from 1-MN. These
products confirm that H-atom abstraction is the dominant,
if not sole, reaction pathway for the alkylbenzenes and
alkylnaphthalenes, consistent with the 100-fold lower rate
constant measured for naphthalene compared to the
alkylnaphthalenes and with the measured deuterium isotope
effects.
Download the full text: PDF | HTML
