Atmospheric photo-oxidation of acetic anhydride: Kinetic study and reaction mechanism. Products distribution and fate of CH3C(O)OC(O)CH2O· radical

Abstract

The rate coefficient for the gas-phase reaction of acetic anhydride (Ac2O) with chlorine atoms at 298 K andatmospheric pressure was experimentally determined (kAc2O+Cl = (1.3 ± 0.4) × 10-12 cm3 molec− 1 s− 1), whilethe rate coefficient for the reaction with the hydroxyl radical was estimated (kAc2O+OH=1.9 x 10-13cm3 molec− 1 s− 1). For the Structure-Activity Relationship method, a value of 0.02 was determined for the − C(O)OC(O) group. The mechanism of photo-oxidation of acetic anhydride initiated by chlorine atoms was determinedand CO, CO2, CH3C(O)OH (32 %), CH3C(O)OC(O)C(O)H, and 3-hydroxy-1,4-dioxane-2,6-dione (20 %) wereidentified as products by infrared spectroscopy. Here we determined for the first time the relative energies of theprimary reaction pathways for the CH3C(O)OC(O)CH2O⋅ radical using computational methods, which confirmedour experimental data. Finally, the environmental implications of acetic anhydride emissions were calculated,showing an atmospheric lifetime between 31 and 220 days for the reaction with atmospheric radicals, while itswet deposition lifetime is 1.5 years.