Kinetic study of the atmospheric oxidation of a series of epoxy compounds by OH radicals

Abstract

In this work, we study the kinetics of the gas-phase reactions of hydroxyl radicals with cyclohexene oxide (CHO), 1,2-epoxyhexane (EHX), 1,2-epoxybutane (12EB), trans-2,3-epoxybutane (tEB) and cis-2,3-epoxybutane (cEB) using the relative rate technique. The experiments were conducted at (298 ± 3) K and (760 ± 10) Torr ((1.01 ± 0.01) × 105 Pa) total pressure of synthetic air using different reference compounds in a 1080 L Quartz Reactor (QUAREC) and a 480 L Duran glass chamber. The following room temperature rate coefficients (cm3 molecule−1 s−1) were obtained: k1(OH+CHO)=(5.93±1.13)×10-12, k2(OH+EHX)=(5.77±0.83)×10-12, k3(OH+12EB)=(1.98±0.29)×10-12, k4(OH+cEB)=(1.50±0.28)×10-12 and k5(OH+tEB)=(1.81±0.33)×10-12. Except for previous studies on 1,2-epoxybutane and cyclohexene oxide, this is, to the best of our knowledge, the first kinetic study of the reaction of these compounds with OH radicals. We discuss the discrepancies found between the values obtained from the present study with values estimated from the structure–activity relationship method (SAR). Our findings indicate that pseudo-ethylenic character in the epoxy ring is an important factor to be included in the improvement of the SAR estimation method. Atmospheric lifetimes, reactivity trends and atmospheric implications are discussed considering the epoxy compound rate coefficients obtained in the present study.