Kinetic and reactivity of gas-phase reaction of acyclic dienes with hydroxyl radical in the 273–318 K temperature range†
Abstract
As dienes contain two C![[double bond, length as m-dash]](https://www.rsc.org/images/entities/char_e001.gif)
C bonds, theoretically, they are much more chemically reactive with hydroxyl radical (˙OH) than alkenes and alkanes, and the reaction with ˙OH is one of the main atmospheric degradation routes of dienes during the daytime. In our work, rate coefficients of three types of acyclic dienes: conjugated as 3-methyl-1,3-pentadiene (3M13PD), isolated as 1,4-hexadiene (14HD), and cumulated as 1,2-pentadiene (12PD) reaction with ˙OH were measured in the temperature range of 273–318 K and 1 atm using the relative rate method. At 298 ± 3 K, the rate coefficients for those reactions were determined to be k3M13PD+OH = (15.09 ± 0.72) × 10−11, k14HD+OH = (9.13 ± 0.62) × 10−11, k12PD+OH = (3.34 ± 0.40) × 10−11 (as units of cm3 per molecule per s), in the excellent agreement with values of previously reported. The first measured temperature dependence for 3M13PD, 14HD and 12PD reaction with ˙OH can be expressed by the following Arrhenius expressions in units of cm3 per molecule per s: k3M13PD+OH = (8.10 ± 2.23) × 10−11 exp[(173 ± 71)/T]; k14HD+OH = (9.82 ± 5.10) × 10−12 exp[(666 ± 123)/T]; k12PD+OH = (1.13 ± 0.87) × 10−12 exp[(1038 ± 167)/T] (as units of cm3 per molecule per s). The kinetic discussion revealed that the relative position between these two CC could significantly affect the reactivity of acyclic dienes toward ˙OH. A simple structure–activity relationship (SAR) method was proposed to estimate the reaction rate coefficients of acyclic dienes with ˙OH.
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