Kinetic Studies of OH Reactions with a Series of Acetates

Abstract

Absolute rate constants have been measured for the gas phase reactions of hydroxyl radicals with a series of aliphatic acetates: methyl acetate (k 1), ethyl acetate (k 2), n-propyl acetate (k 3), n-butyl acetate (k 4), and n-pentyl acetate (k 5). Experiments were carried out using the pulsed laser photolysislaser induced fluorescence technique over the temperature range 243−372 K. The obtained kinetic data were used to derive the Arrhenius expressions, and since the Arrhenius plots were slightly curved they were fitted, using a three-parameter expression. The Arrhenius expressions obtained are: k 1 = (0.53 ± 0.09) × 10-12 exp[−(128 ± 102)/T] ; k 2 = (0.48 ± 0.09) × 10-12 exp[(397 ± 103)/T]; k 3 = (1.03 ± 0.12) × 10-12 exp[(370 ± 69)/T] ; k 4 = (2.10 ± 0.28) × 10-12 exp[(299 ± 81)/T], and k 5 = (2.75 ± 0.46) × 10-12 exp[(302 ± 102)/T] (in units of cm3 molecule-1 s-1). At room temperature, the rate constants obtained (in units of 10-12 cm3 molecule-1 s-1) were as follows: methyl acetate, 0.32 ± 0.03; ethyl acetate, 1.67 ± 0.22; n-propyl acetate, 3.42 ± 0.26 ; n-butyl acetate, 5.52 ± 0.51; n-pentyl acetate, 7.34 ± 0.91. Our results are compared with the previous determinations and discussed in terms of structure−activity relationships.

Rate Coefficients for Reactions of OH and Cl with Esters

“…Such near-zero or negative dependences have been also observed for the reaction of OH radicals with a series of saturated esters in the same temperature range as herein. [14][15][16][17]21] This temperature dependence of the reactions of OH with other oxygenated organic compounds could be partly attributed to the occurrence of an alternative channel in parallel to the direct H-atom abstraction occurring through formation of an adduct which decomposes to the products.…”

Electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy and ab initio calculations of ethyl acetate

“…Rate constants for gas-phase reactions of OH, Cl, NO 3 radicals with ethyl acetate have been extensively studied [35][36][37][38][39][40][41][42] and rate constants for reactions at room temperature of (1.67 ± 0. 22 [2] on ethyl acetate in aqueous phase that is of importance for acid rain chemistry.…”

The atmospheric oxidation of ethyl formate and ethyl acetate over a range of temperatures and oxygen partial pressures

“…The alkoxy radical product of reaction (5biii), 3 , may then undergo any of three possible competing reaction pathways, the α-ester rearrangement (9), reaction with O 2 (10), or decomposition via C-C bond scission (11):…”

“…Thus, the atmospheric oxidation of these species has the potential to contribute to air quality on regional and global scales. Although the esters are reasonably unreactive (lifetimes against reaction with OH range from a few days to a couple of months for C 3 C 5 formates and acetates [e.g., [2][3][4]8,10,19,26,27]) and are not likely major sources of ozone in urban regions [28], their main oxidation products are often soluble organic acids and acid anhydrides [5][6][7][8][9][10][11][12][13][14][15]25,29], which may contribute to the atmospheric buildup of condensed-phase organic mass.…”

“…In this paper, we describe an environmental chamber study of the oxidation of ethyl formate and ethyl acetate, the major products of the atmospheric oxidation of diethyl ether [16,18,20,31]. These studies were carried out over a range of temperatures (249-325 K) and O 2 partial pressures (50-700 Torr) to examine competition, under conditions relevant to the lower atmosphere, between the α-ester rearrangement and the reaction with O 2 for HC(O)OCH(O • )CH 3 and CH 3 C(O)OCH(O • )CH 3 derived from ethyl formate and ethyl acetate. The data allow activation barriers to the α-ester rearrangement to be determined, and these values are compared with previous estimates [13][14][15] for related species.…”