Kinetic and product studies of the reactions of selected glycol ethers with OH radicals.

Abstract

Glycol ethers are widely used as solvents and are hence liable to be released into the atmosphere where they may contribute to the formation of photochemical air pollution in urban and regional areas. The dominant reaction of glycol ethers in the atmosphere has been previously shown to be with OH radicals. Using a relative rate method, rate constants have been measured at 296+/-2 K for the gas-phase reactions of the OH radical with 1-butoxy-2-propanol [CH3CH2CH2CH2OCH2CH(OH)CH3], diethylene glycol ethyl ether [CH3CH2OCH2CH2OCH2CH2OH], and diethylene glycol n-butyl ether [CH3CH2CH2CH2OCH2CH2OCH2-CH2OH] of (in units of 10(-11) cm3 molecule(-1) s(-1)) 3.76+/-0.54, 5.72+/-0.85, and 7.44+/-0.94, respectively, where the error limits include the estimated overall uncertainties in the rate constants for the reference compounds. Products of the OH radical-initiated reactions of these glycol ethers have been investigated using gas chromatography with flame ionization detection (GC-FID), combined gas chromatography-mass spectrometry (GC-MS), in situ Fourier transform infrared (FT-IR) spectroscopy, and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS). The products identified and quantified account for 102+/-11% of the reaction products from 1-butoxy-2-propanol, 87+/-9% of those from diethylene glycol ethyl ether, and 83+/-12% of those from diethylene glycol n-butyl ether. An empirical estimation method for calculating reaction rates of alkoxy radicals under atmospheric conditions appears to fairly well predict the products formed and their yields. Detailed reaction schemes after the initial OH radical reactions are formulated for each of these glycol ethers, with the majority of the reactions involving H-atom abstraction from the CH2 groups adjacent to the ether linkage.