Rate Coefficients for Reactions of OH and Cl with Esters

Abstract

Rate coefficients for the gas-phase reactions of OH radicals with n-propyl butyrate (k(1)), n-butyl propionate (k(2)) and n-butyl butyrate (k(3)) are measured by both absolute and relative methods. The kinetics data obtained over the temperature range 273-372 K are used to derive the Arrhenius expressions (in units of cm(3) molecule(-1) s(-1)): k(1)=(1.92±0.50)×10(-12) exp[(400±80)/T], k(2)=(2.98±1.32)×10(-12) exp[(209±139)/T] and k(3)=(5.35±3.34)×10(-12) exp[(180±194)/T]. In addition, the rate coefficients for reactions of the three esters with Cl atoms are determined by the relative-rate method at room temperature and atmospheric pressure. The rate coefficients measured are (in units of 10(-10) cm(3) molecule(-1) s(-1)) as follows: n-propyl butyrate (1.4±0.1), n-butyl propionate (1.6±0.1), and n-butyl butyrate (1.7±0.1). The values obtained are presented, compared with previous determinations and discussed. Reactivity trends and atmospheric implications resulting from this work are also presented.

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

“…Comparison was made with the data obtained using the SAR of Kwok and Atkinson [13] Negative temperature dependence of the rate coefficient of OH reaction with esters observed in this Letter has been reported previously [2,12]. It is presumed that this near-zero or negative temperature dependence of the rate coefficients for reactions of OH could be partly attributed to an alternative channel in parallel to the direct H-atom abstraction occurring through formation of an adduct which decomposes to products.…”

“…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.…”

Temperature-Dependent Kinetics of the Reactions of Methyl-2-methyl Propionate and Methyl-2-methyl Butanoate with Cl Atoms under Tropospheric Conditions

“…Overall, the rate of the reaction showed a significant decrease with an increase in the temperature because of the existence of PRC1 along the MEP of TS1. It is evident from Table 3 and Figure 2b that the calculated rate coefficient (k, in units of cm 3 molecule −1 s −1 ) at 298 K was observed to be in accordance with the measured one (k M2MB+Cl 298K = (9.44 ± 1.90) × 10 −11 ) and the previously reported data (k M2MB+Cl 298K = (9.41 ± 1.39) × 10 −10 ), 11 within the uncertainty limits.…”

“…Hence, to evaluate the influence of these organics on the global climatic conditions, a thorough understanding of their kinetics with atmospheric agents is needed. There are a few databases available on the gas-phase reactions of saturated and unsaturated MAEs with OH radicals and Cl atoms. − However, to date, the rate coefficients of the title reactions were reported only at 298 K. For the first time, Cometto et al . investigated the reaction of methyl-2-methyl propionate (M2MP) with Cl atoms using the relative rate (RR) technique with methanol (CH 3 OH) and ethane (C 2 H 6 ) as reference compounds.…”

Cl Atoms and OH Radicals Initiated Kinetic and Mechanistic Study on the Degradation of Propyl Butanoate under Tropospheric Conditions

“…On the contrary, the reactivity of PB toward OH radicals at 298 K was computed to be k PB + OH = 8.0 × 10 –12 cm 3 molecule –1 s –1 . The theoretically predicted rate coefficient value was found to be lower by 17% and higher by 5% when compared to the rate coefficients obtained by Melluoki et al . using both RR and absolute methods.…”