Products of the Gas-Phase Reactions of the OH Radical with 1-Methoxy-2-propanol and 2-Butoxyethanol

Abstract

Glycol ethers are used as solvents and are hence liable to be released to the atmosphere, where they react and contribute to the formation of photochemical air pollution. In this work, products of the gas-phase reactions of the OH radical with 1-methoxy-2-propanol and 2-butoxyethanol in the presence of NO have been investigated at 298 ( 2 K and 740 Torr total pressure of air by gas chromatography, in situ Fourier transform infrared spectroscopy, and in situ atmospheric pressure ionization tandem mass spectrometry. The products observed from 1-methoxy-2propanol were methyl formate, methoxyacetone, and acetaldehyde with molar formation yields of 0.59 ( 0.05, 0.39 ( 0.04, and 0.56 ( 0.07, respectively. The products observed and quantified from 2-butoxyethanol were n-butyl formate, 2-hydroxyethyl formate, propanal, 3-hydroxybutyl formate, and an organic nitrate (attributed to CH 3 CH 2 CH 2 -CH 2 OCH(ONO 2 )CH 2 OH and its isomers), with molar formation yields of 0.57 ( 0.05, 0.22 ( 0.05, 0.21 ( 0.02, 0.07 ( 0.03, and 0.10 ( 0.03, respectively. An additional product of molecular weight 132, attributed to one or more hydroxycarbonyl products, was also observed from the 2-butoxyethanol reaction by atmospheric pressure ionization mass spectrometry. For both glycol ethers, the majority of the reaction products and reaction pathways are accounted for, and detailed reaction mechanisms are presented which account for the observed products.

The production of organic nitrates from atmospheric oxidation of ethers and glycol ethers

“…The magnitude of the correction factors was 1.05 for 1M3N2P, 1.01 for 1M1N2P, and 1.07 for 1NM2P. This total yield is consistent with the Tuazon et al upper limit of 2% for organic nitrates [12], and is only 14% of that for n-butane [14,16], and half of that reported above for methoxy propane. Thus it is clear that the OH substituent has had a significant effect on the organic nitrate yield, as observed previously [15].…”

“…4. H atom abstraction from the CH 2 (OH)-group will lead to formation of methoxy acetone [6,12]. We have identified three chromatographic peaks as being organic nitrates.…”

“…Using the method of Kwok and Atkinson [29], Tuazon et al [12] calculated that the relative hydrogen atom abstraction frequencies via OH reaction with 1-methoxy-2-propanol are 1%, 43%, 50%, and 6%, starting from the methyl end of the propyl group. However, according to their experimental data, 59(±5)% of the H abstractions occur at carbon #3, counting from the propyl group.…”

“…From Kwok and Atkinson [29], we know that abstraction from the methoxy group will occur ∼six times faster than from the methyl group on the propanol side. Therefore, using the Tuazon et al experimental values [12] and calculating accordingly for the two methylene groups, we obtain the following relative H abstraction rates for 1-methoxy-2-propanol: 0.8(±0.6) %, 35(±4)%, 59(±5)%, and 4.9(±2)%, starting from the methyl end in the propyl group. The uncertainties in the α values calculated on the basis of the Tuazon et al study are so large for the methyl groups that these numbers are not useful in any quantitative kinetic sense.…”

“…The OH reaction kinetics and reaction products of some of these ethers and glycol ethers have been studied previously [11,12]. As indicated in reaction (3b), formation of organic nitrates is a termination step, which consumes peroxy radicals and NO x .…”