Heterogeneous Reactions of Epoxides in Acidic Media

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• 作者：Vinita Lal ; Alexei F. Khalizov ; Yun Lin ; Maria D. Galvan ; Brian T. Connell ; Renyi Zhang
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：June 21, 2012
• 年：2012
• 卷：116
• 期：24
• 页码：6078-6090
• 全文大小：595K
• 年卷期：v.116,no.24(June 21, 2012)
• ISSN：1520-5215

文摘

Epoxides have recently been identified as important intermediates in the gas phase oxidation of hydrocarbons, and their hydrolysis products have been observed in ambient aerosols. To evaluate the role of epoxides in the formation of secondary organic aerosols (SOA), the kinetics and mechanism of heterogeneous reactions of two model epoxides, isoprene oxide and 伪-pinene oxide, with sulfuric acid, ammonium bisulfate, and ammonium sulfate have been investigated using complementary experimental techniques. Kinetic experiments using a fast flow reactor coupled to an ion drift-chemical ionization mass spectrometer (ID-CIMS) show a fast irreversible loss of the epoxides with the uptake coefficients (纬) of (1.7 卤 0.1) 脳 10^鈥? and (4.6 卤 0.3) 脳 10^鈥? for isoprene oxide and 伪-pinene oxide, respectively, for 90 wt % H₂SO₄ and at room temperature. Experiments using attenuated total reflection鈥擣ourier transform infrared spectroscopy (ATR-FTIR) reveal that diols are the major products in ammonium bisulfate and dilute H₂SO₄ (<25 wt %) solutions for both epoxides. In concentrated H₂SO₄ (>65 wt %), acetals are formed from isoprene oxide, whereas organosulfates are produced from 伪-pinene oxide. The reaction of the epoxides with ammonium sulfate is slow and no products are observed. The epoxide reactions using bulk samples and Nuclear Magnetic Resonance (NMR) spectroscopy reveal the presence of diols as the major products for isoprene oxide, accompanied by aldehyde formation. For 伪-pinene oxide, organosulfate formation is observed with a yield increasing with the acidity. Large yields of organosulfates in all NMR experiments with 伪-pinene oxide are attributed to the kinetic isotope effect (KIE) from the use of deuterated sulfuric acid and water. Our results suggest that acid-catalyzed hydrolysis of epoxides results in the formation of a wide range of products, and some of the products have low volatility and contribute to SOA growth under ambient conditions prevailing in the urban atmosphere.