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 NOx) gave the following products: ethyl pyruvate (CH3C(O)C(O)OC2H5), propionic acid (C2H5C(O)OH), formaldehyde (HCHO), and, in the presence of NOx, 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%).