Kinetic investigation of the OH radical and Cl atom initiated degradation of unsaturated ketones at atmospheric pressure and 298 K

Abstract

Rate coefficients for the reactions of hydroxyl radicals and chlorine atoms with 4-hexen-3-one, 5-hexen-2-one, and 3-penten-2-one have been determined at 298 ± 2 K and atmospheric pressure of air. Rate coefficients for the compounds were determined using a relative kinetic technique with different reference compounds. The experiments were performed in a large photoreactor (480 L) using in situ FTIR spectroscopy to monitor the decay of reactants. From the different measurements the following rate coefficients (in units of cm 3 molecule -1 s -1) have been determined: k 1(OH + 4-hexen-3-one) = (9.04 ± 2.12) × 10 -11, k 2(OH + 5-hexen-2-one) = (5.18 ± 1.27) × 10 -11, k 3(OH + 3-penten-2-one) = (7.22 ± 1.74) × 10 -11, k 4(Cl + 4-hexen-3-one) = (3.00 ± 0.58) × 10 -10, k 5(Cl + 5-hexen-2-one) = (3.15 ± 0.50) × 10 -10 and k 6(Cl + 3-penten-2-one) = (2.53 ± 0.54) × 10 -10. The reactivity of the double bond in alkenes and unsaturated ketones at 298 K toward addition of OH radicals and Cl atoms are compared and discussed. In addition, a correlation between the reactivity of the unsaturated ketones toward OH radicals and the HOMO of the compounds is presented. On the basis of the kinetic measurements, the tropospheric lifetimes of 4-hexen-3-one, 5-hexen-2-one, and 3-penten-2-one with respect to their reaction with hydroxyl radicals are estimated to be between 2 and 3 h. © 2012 American Chemical Society.