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Published August 12, 2010 | Supplemental Material
Journal Article Open

Kinetics and Products of the Acid-Catalyzed Ring-Opening of Atmospherically Relevant Butyl Epoxy Alcohols

Abstract

Epoxydiols are produced in the gas phase from the photo-oxidation of isoprene in the absence of significant mixing ratios of nitrogen oxides (NOₓ). The reactive uptake of these compounds onto acidic aerosols has been shown to produce secondary organic aerosol (SOA). To better characterize the fate of isoprene epoxydiols in the aerosol phase, the kinetics and products of the acid-catalyzed ring-opening reactions of four hydroxy-substituted epoxides were studied by nuclear magnetic resonance (NMR) techniques. Polyols and sulfate esters are observed from the ring-opening of the epoxides in solutions of H₂SO₄/Na₂SO₄. Likewise, polyols and nitrate esters are produced in solutions of HNO₃/NaNO₃. In sulfuric acid, the rate of acid-catalyzed ring-opening is dependent on hydronium ion activity, sulfate ion, and bisulfate. The rates are much slower than the nonhydroxylated equivalent epoxides; however, the hydroxyl groups make them much more water-soluble. A model was constructed with the major channels for epoxydiol loss (i.e., aerosol-phase ring-opening, gas-phase oxidation, and deposition). In the atmosphere, SOA formation from epoxydiols will depend on a number of variables (e.g., pH and aerosol water content) with the yield of ring-opening products varying from less than 1% to greater than 50%.

Additional Information

© 2010 American Chemical Society. Received: April 29, 2010; Revised Manuscript Received: June 22, 2010. Publication Date (Web): July 21, 2010. N. C. E. was supported by the Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry. We also thank ManNin Chan, Fabien Paulot, Havala Pye, and Jason Surratt for helpful discussions.

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