The atmospheric oxidation of diethyl ether: chemistry of the C2H5–O–CH(O˙)CH3 radical between 218 and 335 K

Abstract

The products of the Cl atom initiated oxidation of diethyl ether (DEE) were investigated at atmospheric pressure over a range of temperatures (218–335 K) and O₂ partial pressures (50–700 Torr), both in the presence and absence of NO_x. The major products observed at 298 K and below were ethyl formate and ethyl acetate, which accounted for ≈60–80% of the reacted diethyl ether. In general, the yield of ethyl formate increased with increasing temperature, with decreasing O₂ partial pressure, and upon addition of NO to the reaction mixtures. The product yield data show that thermal decomposition reaction (3), CH₃CH₂–O–CH(O˙)CH₃ → CH₃CH₂–O–CHO + CH₃, and reaction (6) with O₂, CH₃CH₂–O–CH(O˙)CH₃ + O₂ → CH₃CH₂–O–C(O)CH₃ + HO₂ are competing fates of the CH₃CH₂–O–CH(O˙)CH₃ radical, with a best estimate of k₃/k₆ ≈ 6.9 × 10²⁴ exp(–3130/T). Thermal decomposition via C–H or C–O bond cleavage are at most minor contributors to the CH₃CH₂–O–CH(O˙)CH₃ chemistry. The data also show that the CH₃CH₂–O–CH(O˙)CH₃ radical is subject to a chemical activation effect. When produced from the exothermic reaction of the CH₃CH₂–O–CH(OO˙)CH₃ radical with NO, prompt decomposition via both CH₃- and probably H-elimination occur, with yields of about 40% and ≤15%, respectively. Finally, at temperatures slightly above ambient, evidence for a change in mechanism in the absence of NO_x, possibly due to chemistry involving the peroxy radical CH₃CH₂–O–CH(OO˙)CH₃, is presented.