Tropospheric degradation of ethylene glycol monovinyl and divinyl ethers: A mechanistic and kinetic study

摘要

In this work, we have performed a theoretical study on the mechanisms and kinetics of the ~?OH initiated oxidation of selected ethylene glycol vinyl ethers, using quantum chemistry and computational kinetics methods. We have found that the main reaction path is the ~?OH-addition to vinyl double bonds, and especially to the vinyl terminal carbon atom. Branching ratios for addition at C_1 are larger than 94%. Although divinyl ethers could be expected to react approximately twice as fast as monovinyl ethers, it was found that, in fact, ~?OH rate constants of monovinyl and divinyl ethers are very similar, in agreement with experimental results. This effect is attributed to the sharing of the oxygen lone pairs effect, when the molecule contains two vinyl groups. Thus, in EGMVE, the vinyl group is more reactive than the one in divinyl ethers. The energy of its highest occupied molecular orbital (HOMO) is closer to that of the OH radical, thus favoring the interaction with the single occupied molecular orbital (SOMO) of the radical. Negative activation enthalpies are obtained for the three molecules studied, implying that the rate constant decreases as temperature increases. This anti-Arrhenius behavior is commonly observed in ~?OH addition to alkenes. An excellent correlation is observed between experimental and calculated rate constants.