A kinetic study of chlorine radical reactions with ketones by laser photolysis technique

Abstract

Rate coefficients for reactions between Cl radicals and four ketones were determined at 294 ± 1 K with a relative rate method using a laser photolysis technique. The experiments were conducted in synthetic air in a flow system at atmospheric pressure. A mixture of Cl2/ClONO2 was photolyzed and the formation of NO3 through the reaction Cl + ClONO2 → Cl2 + NO3 was measured with and without ketones in the reaction mixture. The NO3 radical concentration was measured by optical absorption using a diode laser as the light source. The rate coefficients for the Cl-ketone reactions could then be evaluated. The following rate coefficients were obtained (in units of cm3 molecule−1 s−1): cyclohexanone (7.00 ± 1.15) × 10−11; cyclopentanone (4.76 ± 0.33) × 10−11; acetone (1.69 ± 0.32) × 10−12; and 2,3-butanedione (7.62 ± 1.66) × 10−13. The accuracy of the method employed was tested by using the well-studied reaction between Cl and methane and a rate coefficient of (9.37 ± 1.04) × 10−14 cm3 molecule−1 s−1 was obtained, which is in good agreement with previous work. The errors are at the 95% confidence level. The results in this work indicate that a carbonyl group in a ketone lowers the reactivity towards α-hydrogen abstraction by Cl radicals, compared to the corresponding Cl-alkane reactions. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 195–201, 1997.