Reaction Rate Coefficients of OH Radicals and Cl Atoms with Ethyl Propanoate,n-Propyl Propanoate, Methyl 2-Methylpropanoate, and Ethyln-Butanoate

Abstract

Kinetics of the reactions of OH radicals and Cl atoms with four saturated esters have been investigated. Rate coefficients for the gas-phase reactions of OH radicals with ethyl propanoate (k(1)), n-propyl propanoate (k(2)), methyl 2-methylpropanoate (k(3)), and ethyl n-butanoate (k(4)) were measured using a conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. At (296 +/- 2) K, the rate coefficients obtained by the two methods were in good agreement. Significant curvatures in the Arrhenius plots have been observed in the temperature range 243-372 K for k(1), k(3), and k(4). The rate coefficients for the reactions of the four esters with Cl atoms were determined using the relative rate method at (296 +/- 2) K and atmospheric pressure. The values obtained are presented, compared with the literature values when they exist, and discussed. Reactivity trends and atmospheric implications for these esters are also presented.

Rate Coefficients for Reactions of OH and Cl with Esters

“…Comparison of the room-temperature rate coefficients shows an increase in reactivity from methyl butyrate (k = 0.86) [24] through ethyl butyrate (k = 1.0) [21] and n-propyl butyrate (k = 1.4, this work) to n-butyl butyrate (k = 1.7, this work). This reactivity trend may indicate that longer alkoxyl groups (!…”

“…Examination of the reactivity of the studied esters towards Cl atoms shows (units of 10 À10 cm 3 molecule À1 s À1 for the following values of k) that n-butyl butyrate (k 6 = 1.7) is about 20 % more reactive than n-propyl butyrate (k 3 = 1.4). Comparison of the room-temperature rate coefficients shows an increase in reactivity from methyl butyrate (k = 0.86) [24] through ethyl butyrate (k = 1.0) [21] and n-propyl butyrate (k = 1.4, this work) to n-butyl butyrate (k = 1.7, this work). This reactivity trend may indicate that longer alkoxyl groups (!…”

“…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.…”

“…Moreover, in continental regions where large amounts of reactive chlorine compounds were found in the lowest part of the atmosphere, [12,13] reaction with Cl atoms may be a more important removal pathway than previously thought. To date, relatively few studies [14][15][16][17][18][19][20][21] have been carried out on the temperature dependence of the reaction of OH with esters.…”

Reactions of OH and Cl with isopropyl formate, isobutyl formate, n-propyl isobutyrate and isopropyl isobutyrate

“…Comparison of the room temperature rate coefficients shows an increase of the OH reactivity with the increase of the chain length in the linear esters: formates (methyl formate (0.179), ethyl formate (0.87), n-propyl formate (1.85) and n-butyl formate (3.68)); acetates (methyl acetate (0.346), ethyl acetate (1.67), npropyl acetate (3.45), n-butyl acetate (5.66) and n-pentyl acetate (7.39)); propionates (methyl propionate (0.873), ethyl propionate (2.1) and n-propyl propionate (4.2)) and butyrates (methyl butyrate (3.36), ethyl butyrate (4.5), n-propyl butyrate (4.71) and n-butyl butyrate (10.6) (in 10 À12 cm 3 molecule À1 s À1 ) [2,11,12]. The observed increase in the reactivity is due to the contribution of the alkoxy side of the ester (-C(O)OR) as the reaction coefficient value increases with the increase of the number of -CH 2 -groups, consistent with hydrogen atom abstraction by OH from the -OR group.…”