Atmospheric chemistry of ethyl propionate

TY - JOUR

T1 - Atmospheric chemistry of ethyl propionate

AU - Andersen, Vibeke Friis

AU - Ørnsø, Kristian

AU - Jørgensen, Solvejg

AU - Nielsen, Ole John

AU - Johnson, Matthew Stanley

PY - 2012/5/31

Y1 - 2012/5/31

N2 - 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 N 2 at 293 ± 0.5 K were used to determine rate constants of k(C 2H 5C(O)OC 2H 5 + Cl) = (3.11 ± 0.35) × 10 -11, k(CH 3CHClC(O)OC 2H 5 + Cl) = (7.43 ± 0.83) × 10 -12, and k(C 2H 5C(O)OC 2H 5 + OH) = (2.14 ± 0.21) × 10 -12 cm 3 molecule -1 s -1. At 273-313 K, a negative Arrhenius activation energy of -3 kJ mol -1 is observed. The chlorine atom-initiated oxidation of ethyl propionate in 980 mbar N 2 gave the following products (stoichiometric yields): ClCH 2CH 2C(O)OC 2H 5 (0.204 ± 0.031), CH 3CHClC(O)OC 2H 5 (0.251 ± 0.040), and C 2H 5C(O)OCHClCH 3 (0.481 ± 0.088). The chlorine atom-initiated oxidation of ethyl propionate in 980 mbar of N 2/O 2 (with and without NO x) gave the following products: ethyl pyruvate (CH 3C(O)C(O)OC 2H 5), propionic acid (C 2H 5C(O)OH), formaldehyde (HCHO), and, in the presence of NO x, PAN (CH 3C(O)OONO 2). The lack of acetaldehyde as a product suggests that the CH 3CH(O)C(O)OC 2H 5 radical favors isomerization over decomposition. From the observed product yields, we conclude that H-abstraction by chlorine atoms from ethyl propionate occurs 20.4 ± 3.1%, 25.1 ± 4.0%, and 48.1 ± 8.8% from the CH 3-, -CH 2-, and -OCH 2- 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 -OCH 2- group (80%).

AB - 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 N 2 at 293 ± 0.5 K were used to determine rate constants of k(C 2H 5C(O)OC 2H 5 + Cl) = (3.11 ± 0.35) × 10 -11, k(CH 3CHClC(O)OC 2H 5 + Cl) = (7.43 ± 0.83) × 10 -12, and k(C 2H 5C(O)OC 2H 5 + OH) = (2.14 ± 0.21) × 10 -12 cm 3 molecule -1 s -1. At 273-313 K, a negative Arrhenius activation energy of -3 kJ mol -1 is observed. The chlorine atom-initiated oxidation of ethyl propionate in 980 mbar N 2 gave the following products (stoichiometric yields): ClCH 2CH 2C(O)OC 2H 5 (0.204 ± 0.031), CH 3CHClC(O)OC 2H 5 (0.251 ± 0.040), and C 2H 5C(O)OCHClCH 3 (0.481 ± 0.088). The chlorine atom-initiated oxidation of ethyl propionate in 980 mbar of N 2/O 2 (with and without NO x) gave the following products: ethyl pyruvate (CH 3C(O)C(O)OC 2H 5), propionic acid (C 2H 5C(O)OH), formaldehyde (HCHO), and, in the presence of NO x, PAN (CH 3C(O)OONO 2). The lack of acetaldehyde as a product suggests that the CH 3CH(O)C(O)OC 2H 5 radical favors isomerization over decomposition. From the observed product yields, we conclude that H-abstraction by chlorine atoms from ethyl propionate occurs 20.4 ± 3.1%, 25.1 ± 4.0%, and 48.1 ± 8.8% from the CH 3-, -CH 2-, and -OCH 2- 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 -OCH 2- group (80%).

U2 - 10.1021/jp300897t

DO - 10.1021/jp300897t

M3 - Journal article

C2 - 22524192

SN - 1089-5639

VL - 116

SP - 5164

EP - 5179

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

IS - 21

ER -