Relative rate constants for the reactions of chlorine atoms with chloroethers at 298 K

PABLO R. DALMASSO, RAÚL A. TACCONE, JORGE D. NIETO, MARIANO A. TERUEL, SILVIA I. LANE.

La Plata. Buenos Aires. Argentina

Congreso; 8th Latinamerican Meeting on Photochemistry and Photobiology (ELAFOT); 2004

The gas-phase reaction of Cl atoms with organic species represents an important loss process for Cl atoms and organic compounds in the atmosphere. Despite the growing kinetic data base for the reaction of Cl atoms with organic compounds there have been relatively few studies of the reaction of Cl atoms with oxygenated organic species.

Oxygenated compounds are finding increased use as fuels, solvents, CFC and HCFC substituents and fuel additives and are thus expected to be released in increasing amounts to the atmosphere. As part of an ongoing program in our laboratory to study the atmospheric chemistry of oxygenated species, we have used the relative rate technique to investigate the kinetics of the reaction of Cl atoms with CHCl₂OCH₃ and CH₂ClCH₂OCH₃ haloethers at room temperature and at atmospheric pressure, using N₂ as the bath gas.

All the experiments were carried out in a 80 L collapsible chamber at 298 K. A gas chromatograph equipped with a flame ionisation detector(GC-FID) was used for the quantitative analysis of the reactants. Chlorine atoms were genarated by the UV photolysis of molecular chlorine. Two reference hydrocarbons (ethane and 1,2-dichloroethane) were employed. Good agreement has been found between the rate coefficients determined using the different reference compounds.

In order to check the performance of our system in obtainig reliable results, we also measured the overall rate constant for the reaction of n-pentane with Cl atoms, obtaining a value of k_{298 K} = (2.75 ± 0.50)x10^-10 cm³ molecule^-1 s^-1, which is in good agreement with the literature evaluation value of   (2.52 ± 0.30)x10^-10 cm³ molecule^-1 s^-1.

As far as we know, this kinetic study constitutes the first experimental determination of the rate coefficient for the reaction of Cl atoms with CHCl₂OCH₃.

The obtained data will be presented and discussed in terms of their reactivity compared to other compounds of similar structure, and used to estimate the day half-life of these ethers in the troposphere.