Rate Constants for the Reactions of Chlorine Atoms with Haloethers at 298 K and Atmospheric Pressure.

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

Leeds, Reino Unido.

Congreso; Faraday Discussion 130, Atmospheric Chemistry.; 2005

Recognition of the importance of  the reactions of Cl atoms with organic species has led to a number of kinetic studies of the reaction of Cl atoms with hydrocarbons, chloroalkanes and aromatic species. However, despite the growing kinetic data base for the reaction of Cl atoms with  volatile organic compounds (VOCs), few studies on the reaction of Cl atoms with oxygenated organic species have been carried out¹.

Ethers represent an important class de oxygenated organic compounds, which are increasingly used 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 determine the rate coefficient of the reaction of Cl atoms with CHCl₂OCH₃, CH₂ClCH₂OCH₃, CHFClCF₂OCH₃ and CHFClCF₂OCF₂H  haloethers at room temperature and at atmospheric pressure, using N₂ as the bath gas.

The experiments were carried out in an 80 L collapsible Tedlar bag surrounded by 6 fluorescent blacklamps which provided UV radiation to produce atomic chlorine by photolysis of molecular chlorine.

The decay rates of the organic species were measured relative to those of a reference compound (methane, dichloromethane, ethane and 1,2-dichloroethane). Good agreement was found between the rate coefficients determined using the different reference compounds.

The concentrations of the test and reference were determined by periodically sampling from the bag using calibrated gas syringes and analysing on a gas chromatograph equipped with a flame ionisation detector.

In order to check the performance of our system in obtaining reliable results, we also measured the overall rate constant for the reaction of n-pentane with Cl atoms, obtaining a  good agreement with the literature value².

The obtained data will be presented and discussed in terms of the reactivity of the haloethers compared to other compounds of similar structure.

As the reactions of Cl atoms are important processes in the chemistry of the natural and polluted atmosphere, the possible atmospheric significance of haloethers is, thus, considered in terms of their reactions with Cl atoms.

¹. B. Finlayson- Pitts and J. Pitts, Jr, Chemistry of the Upper and Lower Atmosphere-Theory,

   Experiments and Applications, Academic Press ( 2000).

². NIST Chemistry WebBook, NIST Standard Reference Database Number 68–March 2003.