Kinetic and mechanistic studies of the atmospheric degradation of organic anhydrides

Abstract

Anhydrides are widely used in industrial processes. Propionic anhydride (PA) and butyric anhydride (BA) are considered to be high production volume chemicals, with a total production in the order of thousands of tonnes.This study presents the rate coefficients for PA and BA with chlorine atoms for the first time: (3.8 ± 0.8) × 10-12 and (11 ± 2) × 10-12 cm3 molecule-1 s-1, respectively. The rate coefficients for the reactions of PA and BA with ?OH radicals were estimated using Linear-Free-Energy-Relationships (LFER): 3.5 × 10- 13 cm3 molecule-1 s-1 and 7.9 × 10-13 cm3 molecule-1 s-1, respectively. From here, the calculated atmospheric lifetimes (33 and 15 days, for PA and BA, respectively) indicate that, once emitted, they could be transported by air masses having a regional impact.Moreover, the main photooxidation products, both in the presence and absence of NO2 were identified by infrared spectroscopy: CH3CH2C(O)OH, CH3CH2C(O)OC(O)C(O)CH3, CH3CH2C(O)OC(O)CH2C(O)H, CH3C(O)C(O)OONO2, CH3C(O)OONO2 and CO2 for PA; and CH3CH2CH2C(O)OH, CH3CH2CH2C(O)OC(O)CH2CH2C(O)H, CH3CH2CH2C(O)OC(O)CH2C(O)H, CH3CH2C(O)OONO2, CH3CH2C(O)C(O)OONO2 and CO2 for BA. Computational studies were used to support the experimental identification of the products.Atmospheric degradation of PA and BA produces carboxylic acids that can partition into the aqueous phase of clouds and fog, affecting atmospheric processes having environmental impacts. In addition, the degradation of PA and BA in regions polluted with nitrogen dioxide leads to the formation of peroxyacyl nitrates, which can be transported long distances from their source of production, polluting remote areas.