Atmospheric Chemistry of Ethyl Propionate

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• 作者：Vibeke F. Andersen ; Kristian B. 脴rns酶 ; Solvejg J酶rgensen ; Ole John Nielsen ; Matthew S. Johnson
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：May 31, 2012
• 年：2012
• 卷：116
• 期：21
• 页码：5164-5179
• 全文大小：780K
• 年卷期：v.116,no.21(May 31, 2012)
• ISSN：1520-5215

文摘

Ethyl propionate is a model for fatty acid ethyl esters used as first-generation biodiesel. The atmospheric chemistry of ethyl propionate was investigated at 980 mbar total pressure. Relative rate measurements in 980 mbar N₂ at 293 卤 0.5 K were used to determine rate constants of k(C₂H₅C(O)OC₂H₅ + Cl) = (3.11 卤 0.35) 脳 10^鈥?1, k(CH₃CHClC(O)OC₂H₅ + Cl) = (7.43 卤 0.83) 脳 10^鈥?2, and k(C₂H₅C(O)OC₂H₅ + OH) = (2.14 卤 0.21) 脳 10^鈥?2 cm³ molecule^鈥? s^鈥?. At 273鈥?13 K, a negative Arrhenius activation energy of 鈭? kJ mol^鈥? is observed.. The chlorine atom-initiated oxidation of ethyl propionate in 980 mbar N₂ gave the following products (stoichiometric yields): ClCH₂CH₂C(O)OC₂H₅ (0.204 卤 0.031), CH₃CHClC(O)OC₂H₅ (0.251 卤 0.040), and C₂H₅C(O)OCHClCH₃ (0.481 卤 0.088). The chlorine atom-initiated oxidation of ethyl propionate in 980 mbar of N₂/O₂ (with and without NO_x) gave the following products: ethyl pyruvate (CH₃C(O)C(O)OC₂H₅), propionic acid (C₂H₅C(O)OH), formaldehyde (HCHO), and, in the presence of NO_x, PAN (CH₃C(O)OONO₂). The lack of acetaldehyde as a product suggests that the CH₃CH(O)C(O)OC₂H₅ radical favors isomerization over decomposition. From the observed product yields, we conclude that H-abstraction by chlorine atoms from ethyl propionate occurs 20.4 卤 3.1%, 25.1 卤 4.0%, and 48.1 卤 8.8% from the CH₃鈥? 鈭扖H₂鈥? and 鈭扥CH₂鈥?groups, respectively. The rate constant and branching ratios for the reaction between ethyl propionate and the OH radical were investigated theoretically using quantum mechanical calculations and transition state theory. The stationary points along the reaction path were optimized using the CCSD(T)-F12/VDZ-F12//BH&HLYP/aug-cc-pVTZ level of theory; this model showed that OH radicals abstract hydrogen atoms primarily from the 鈭扥CH₂鈥?group (80%).