OH Radical Initiated Photooxidation of  2-Ethoxyethanol under Laboratory Conditions Related to the Troposphere:  Product Studies and Proposed Mechanism

Abstract

The products formed by the hydroxyl radical-initiated oxidation of 2-ethoxyethanol (CH 3 CH 2 OCH 2 CH 2 OH) have been investigated by irradiating synthetic air mixtures containing the substrate, methyl nitrite, and nitric oxide at ppm levels in a Teflon bag reactor at room temperature. The decay of reactants and the formation of products were monitored by gas chromatography and mass spectrometry. The major products ethyl formate [HC(O)OCH 2 CH 3 ], ethylene glycol monoformate [HC(O)OCH 2 CH 2 OH], ethylene glycol monoacetate [CH 3 C(O)OCH 2 CH 2 OH], and ethoxyacetaldehyde [CH 3 CH 2 OCH 2 C(O)H] give a quantitative mass balance with the decay of the substrate molecule.The yields of these products were 34 ( 10%, 36 ( 7%, 7.8 ( 2.4%, and 24 ( 13%, respectively, in terms of percent of 2-ethoxyethanol removed by the OH radical. The product distribution is explained by a mechanism involving initial OH attack at the three CH 2 groups in 2-ethoxyethanol followed by the subsequent reactions of the resulting alkyl and alkoxy radicals. The decomposition reactions of the alkoxy radicals from 2-ethoxyethanol, which can take place either by C-C or C-O bond breaking, involve preferential C-C cleavage rather than C-O cleavage. Rate coefficients at room temperature for the reactions of OH radicals with ethoxyacetaldehyde and 2-methyl-1,3-dioxolane (CH 3 CHOCH 2 CH 2 O, a minor product) have been determined to be 16.6 × 10 -12 and 9.4 × 10 -12 cm 3 molecule -1 s -1 , respectively.

The hydroxyl radical reaction rate constant and atmospheric transformation products of 2-propoxyethanol

“…PF observation is consistent with previous studies of the hydroxyl reaction products of 2-ethoxyethyl acetate and ethyl 3-ethoxypropionate: the methylenes next to the ether oxygen are activated [4,5,10,11,21]. The PF product yield is larger than the trend expected using the data for 2-ethoxyethanol and 2-butoxyethanol that was reported by Stemmler et al [1,4]. A 43% ethyl formate yield was reported for 2-ethoxyethanol; a 35% butyl formate yield was reported for 2-butoxyethanol; while a 47% propyl formate yield was measured for 2-propoxyethanol [1,4].…”

“…From the mechanism proposed, PF is a product of hydrogen abstraction from methylene IV in the following structure: Using structure reactivity [12], a 39% propyl formate yield is expected. PF observation is consistent with previous studies of the hydroxyl reaction products of 2-ethoxyethyl acetate and ethyl 3-ethoxypropionate: the methylenes next to the ether oxygen are activated [4,5,10,11,21]. The PF product yield is larger than the trend expected using the data for 2-ethoxyethanol and 2-butoxyethanol that was reported by Stemmler et al [1,4].…”

“…The PF product yield is larger than the trend expected using the data for 2-ethoxyethanol and 2-butoxyethanol that was reported by Stemmler et al [1,4]. A 43% ethyl formate yield was reported for 2-ethoxyethanol; a 35% butyl formate yield was reported for 2-butoxyethanol; while a 47% propyl formate yield was measured for 2-propoxyethanol [1,4]. The 2-ethyl-1,3-dioxolane (5.4 Ϯ 0.4%) product was observed using the GC/MS system and is formed from abstraction of methylene III.…”

“…The rate equations for reactions (4) and (5) are combined and integrated resulting in the following equation: in the 100 L Teflon ᭨ chamber were 1 -2 ppm 2PEOH, 1 -2 ppm reference, 10 ppm CH 3 ONO, and 2.3 ppm NO in air. These mixtures were allowed to stand for 30 -60 minutes before background chamber samples were collected.…”

Products of the gas-phase photooxidation reactions of 1-propanol with OH radicals

“…For the reactions of 2-butanol, the products observed were methyl ethyl ketone and acetaldehyde. Methyl [23] with the OH radical, also suggested that the reaction of the ␣-hydroxy alkyl radical with O 2 proceeds via hydrogen abstraction rather than O 2 addition. Consequently, the ␣-hydroxy radicals produced in the reactions of 1-propanol with H are expected to react with oxygen in a similar manner.…”