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

摘要

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.