Atmospheric oxidation chemistry of 1–methoxy 2–propyl acetate initiated by OH radicals: kinetics and mechanisms

Abstract

Kinetics and mechanism of the gas-phase reaction of CH3C(O)OCH(CH3)CH2OCH3 (MPA) with OH radicals in the presence of O2 and NO have been investigated theoretically by performing a high and reliable level of theory, viz., CCSD(T)/6-311 + G(d,p)//BH&HLYP/6-311++G(d,p) + 0.9335×ZPE. The calculations predict that the H-abstraction from the −CH2−O− position of MPA is the most facile channel, which leads to the formation of the corresponding alkoxy radicals CH3C(O)OCH(CH3)C(O •)HOCH3 under atmospheric conditions. This activated radicals CH3C(O)OCH(CH3)C(O •)HOCH3 will undergo further rearrangement, fragmentation and oxidative reactions and predominantly leads to the formation of various products (methyl formate HC(O)OCH3 and acetic anhydride CH3C(O)OC(O)CH3). In the presence of water, acetic anhydride can convert into acetic acid CH3C(O)OH via the hydrolysis reaction. The calculated total rate constants over the temperature range 263–372 K are used to derive a negative activation energy (E a= −5.88 kJ/mol) and an pre-exponential factor (A = 1.78×10−12 cm3 molecule−1 s−1). The obtained Arrhenius parameters presented here are in strong agreement with the experimental values. Moreover, the temperature dependence of the total rate constant over a temperature range of 263−1000 K can be described by k = 5.60 × 10−14×(T/298 K)3.4×exp(1725.7 K/T) cm3 molecule−1 s−1.