Atmospheric oxidation of tertiary amyl methyl and ethyl ethers. A quantum chemistry study

Abstract

In this work, a systematic investigation on the mechanism and kinetics of the reactions of t-amyl methyl ether (TAME) and t-amyl ethyl ether (TAEE) with OH radicals in the gas phase has been performed within the Density Functional Theory (DFT) framework. The potential energy surfaces were obtained at the M06-2X/6-311++G(d,p) level. Kinetic data for the initial step in the oxidative degradation of TAME and TAEE were obtained, as well as branching ratios between the possible reaction channels. The calculated total rate constants are 3.9 × 10−11 cm3 molecules−1 s−1 and 1.3 × 10−12 cm3 molecules−1 s−1, for TAME and TAEE, respectively. Contrary to what occurs in the case of the MTBE and ETBE oxidation initiated by OH radicals, for TAME and TAEE the H-abstraction from α methoxy or ethoxy groups is not favored. For both molecules, the contribution of the reaction channels involving H-abstraction from the t-amyl group amounts to about 70% of the total rate coefficients. Using our calculated rate constants and a chosen OH tropospheric concentration of 1 × 106 molecule cm−3, lifetimes of ∼43 and ∼128 min were obtained for TAME and TAEE, respectively.